Title: Fiducial alignment marks on microelectronic spring contacts
Abstract: Microelectronic spring contacts with fiducial alignment marks for use on a semiconductor wafer contactor or similar apparatus, and methods for making such marks, are disclosed. Each alignment mark is placed on a pad adjacent to a contact tip. The alignment mark is positioned on the pad so that it will not contact the terminal or any other part of a wafer under test. The alignment mark and the contact tip are preferably positioned on the pad in the same lithographic step. Then, the pad and like pads, selected ones of which also have similar alignment marks, are attached to the ends of an array of resilient contact elements. A plurality of alignment marks in accurate registration with a plurality of contact tips on a contactor is thus disclosed. Configurations for ensuring that the alignment marks remain free of debris and easily located for essentially the entire life of the contactor are disclosed, as are various different exemplary shapes of alignment marks.
Patent Number: 6,933,738 Issued on 08/23/2005 to Martin, et al.
| Inventors:
|
Martin; Robert C. (San Francisco, CA);
Watje; Eric T. (Santa Clara, CA)
|
| Assignee:
|
FormFactor, Inc. (Livermore, CA)
|
| Appl. No.:
|
906999 |
| Filed:
|
July 16, 2001 |
| Current U.S. Class: |
324/758; 324/755 |
| Intern'l Class: |
G01R 031/02 |
| Field of Search: |
324/754,755,757,758,765,158.1,762
|
References Cited [Referenced By]
U.S. Patent Documents
| 5686318 | Nov., 1997 | Farnworth et al.
| |
| 6239590 | May., 2001 | Krivy et al.
| |
| 6285203 | Sep., 2001 | Akram et al.
| |
| Foreign Patent Documents |
| 61154044 | Jul., 1986 | JP.
| |
| 02065150 | Mar., 1990 | JP.
| |
| 06209033 | Jul., 1994 | JP.
| |
| 10160793 | Jun., 1998 | JP.
| |
Primary Examiner: Nguyen; Vinh
Assistant Examiner: Kobert; Russell M.
Attorney, Agent or Firm: O'Melveny & Myers, Burraston; N. Kenneth
Claims
1. A tip structure for a contact element for contacting a semiconductor device, comprising
a contact tip disposed on a surface of a pad and having a distal end protruding
above the surface of the pad;
an alignment mark fixed relative to the pad and spaced apart from the contact
tip,
wherein the alignment mark is disposed on the pad entirely substantially below
the distal end of the contact tip.
2. The tip structure according to claim 1, wherein the alignment mark is recessed
below the surface of the pad.
3. The tip structure according to claim 1, wherein the alignment mark protrudes
above the surface of the pad.
4. The tip structure according to claim 1, wherein the alignment mark comprises
a shape selected from a pyramid, an elongated pyramid, a cross, a circle, a square,
a triangle, and parallel lines.
5. A contactor for contacting a semiconductor device, the contactor comprising:
a plurality of contact structures disposed above the upper surface of a substrate
and presenting a plurality of contact tips each for contacting a terminal of the
semiconductor device;
means for aligning each of the plurality of contact tips with a terminal of the
semiconductor device,
wherein the means for aligning comprises a plurality of alignment marks on at
least selected ones of the plurality of contact structures and spaced apart from
the plurality of contact tips.
6. A contactor for contacting a semiconductor device in wafer form, the contactor comprising;
a plurality of contacts disposed on a substrate to present a plurality of contact
tips having their distal tips in a plane substantially parallel to the substantially
planar surface; and
a plurality of alignment marks disposed on the contactor substantially below
the plane wherein the distal tips of the contact tips are disposed.
7. The contactor according to claim 6, wherein at least selected ones of the
plurality of contacts further comprises a tip structure, the tip structure comprising
a pad, a contact tip attached to the pad, and at least one of the plurality of
alignment marks attached to the pad.
8. The contactor according to claim 7, wherein the at least one of the plurality
of alignment marks is recessed below a surface of the pad.
9. The contactor according to claim 7, wherein the at least one of the plurality
of alignment marks is raised above the surface of the pad.
10. The contactor according to claim 6, wherein at least selected ones of the
plurality of contacts further comprise a tip structure, the tip structure comprising
a first pad, and a contact tip attached to the first pad, and a second pad in substantially
the same plane as the first pad, the second pad comprising at least one of the
plurality of alignment marks.
11. The contactor according to claim 6, further comprising a plurality of raised
platforms disposed on the surface of the substrate, each of the plurality of raised
platforms comprising at least one of the plurality of alignment marks attached thereto.
12. The contactor according to claim 11, wherein each of the plurality of raised
platforms further comprises a pad attached thereto, and wherein the at least one
of the plurality of alignment marks is recessed below a surface of the pad.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to components for testing of semiconductor devices,
and more particularly to fiducial alignment marks on microelectronic contacts for
use on probe cards, contactors, and similar components.
2. Description of Related Art
Testing of semiconductor devices, particularly wafer-level testing done prior
to singulation of semiconductor devices from a wafer, is frequently performed using
a component, such as a contactor assembly having a plurality of microelectronic
contacts, each of which contacts a terminal pad, solder ball, or other such terminal
on the wafer. Because of the very fine pitch at which the terminals on the wafer
are disposed, and the correspondingly small scale of the microelectronic contact
structures, alignment of contacts and the terminals on the wafer is accomplished
with the help of special alignment machines and methods.
According to one prior art alignment method, at least three alignment marks
(sometimes called "fiducial" alignment marks) are placed on the wafer at an earlier
device manufacturing stage. The position of these marks is known with a high degree
of accuracy relative to the terminals or contact pads on the wafer. On the contactor,
comparably accurate alignment marks are not present. This has limited the accuracy
with which certain types of contactors, such as those with tungsten wire contact
elements, can be placed. Tungsten wire contacts cannot be placed on the contactor
with a high degree of accuracy, and hence cannot be maintained in registration
with marks on the contactor. However, certain other types of contactors, such as
contactors with composite contacts having lithographically placed contact tip structures
as disclosed, for example, in U.S. Pat. No. 5,864,946 (Eldridge et al.), may be
provided with a plurality of very accurately positioned spring contact tips.
Generally, to be useful as an alignment mark, a mark must be positioned
with an accuracy that is at least one-half the finest pitch (spacing) between adjacent
terminals on the wafer. That is, the position of the alignment mark must be known
with certainty to be within a sphere having a diameter no greater than one-half
of the pitch of the terminals on the semiconductor device. For memory devices,
many of which have a pitch of about 80 micrometers (3.2 mil), an accuracy of at
least about 40 micrometers (1.6 mil) is accordingly required. Because they are
formed during the same lithographic steps used to create electronic features on
the wafer, wafer alignment marks can be disposed on the wafer with the required
accuracy. Lithographically placed contact tips on some types of contactors are
also capable of being disposed on the contactor with comparable accuracy.
According to the prior art alignment method, three or more of these lithographically
placed contact tips are selected to serve the function of alignment marks during
a subsequent positioning step. Typically, a relatively small flat area on the distal
end of the contact tips is used as a visual target. These flat areas are relatively
easy to see and distinguish using commonly used vision systems. Using the alignment
marks on the wafer and the selected contact tips on the contactor as reference
points, the wafer and contactor are then positioned relative to one another so
that each of the contact tips on the contactor can make contact with a corresponding
terminal on the wafer. Using this method, it is possible to make contact with an
array of terminals disposed at a very fine pitch.
Although the foregoing alignment method represents advancement over older
methods in that it permits alignment with terminals disposed at pitches down to
about 40 micrometers, it suffers from certain limitations. One limitation is related
to the use of spring contact tips for alignment of the contactor. During repeated
applications of the contactor, such contact tips can become contaminated with debris
(such as metal oxides or organic residue) from terminals on the wafers under test.
Such debris normally does not interfere with the electrical operation of the contactor,
but can make it difficult to locate the selected contact tips with the requisite
degree of accuracy. The target areas on the contact tips may become obscured or
difficult to see. As even finer pitches for terminals on semiconductors are tested,
and the size of contact tips shrinks accordingly, this limitation of the prior
art method becomes increasingly apparent and costly to overcome. It is desired,
therefore, to provide an apparatus and method that overcomes the limitations of
the prior art method and yet is compatible with the installed base of vision and
positioning systems.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for providing fiducial
alignment marks on a contactor, that overcomes the limitations of prior art methods.
According to an embodiment of the invention, an alignment mark is placed on a region
or pad adjacent to the contact tip. The alignment mark is positioned on the pad
so that it does not contact the terminal or any other part of the wafer under test,
preferably so that it remains free of debris from the contact tip after repeated
use of the contactor. The alignment mark and the contact tip are preferably positioned
on the pad in the same lithographic step. Then, the pad and like pads, selected
ones of which also have similar alignment marks, are attached with the assembled
alignment marks and contact tips to the ends of an array of resilient contact elements.
A plurality of alignment marks in accurate registration with a plurality of contact
tips on a contactor may thus be provided. The alignment marks may readily be located
to within an accuracy of at least about 3-5 μm (about 0.1 to 0.2 mil), and
so may be used in connection with wafers having terminals disposed at a pitch as
fine as about 20-30 μm (about 0.8 to 1.2 mil). Higher accuracies, such as
positioning the alignment marks with an accuracy of about 1.5 micrometers (0.06
mil), are also believed to be attainable. Furthermore, the alignment marks, including
any targets thereon, may be positioned so as to remain free of debris and, therefore,
easily located for essentially the entire life of the contactor. The alignment
marks may be provided in various different shapes, exemplary ones of which are
disclosed herein.
A more complete understanding of the fiducial alignment marks will be afforded
to those skilled in the art, as well as a realization of additional advantages
and objects thereof, by a consideration of the following detailed description of
the preferred embodiment. Reference will be made to the appended sheets of drawings
which will first be described briefly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view at very high magnification of a cantilever-type
microelectronic spring contact having a tip structure according to the invention
with a co-located contact tip and alignment mark.
FIG. 2A is a side elevation view of the spring contact shown in FIG. 1.
FIG. 2B is a side elevation view of the tip structure for the spring contact
shown in FIG. 1.
FIGS. 3A-3C are plan views of exemplary alternative tip structures having co-located
contact tips and alignment marks for use with a spring contact.
FIGS. 4A-4B are side elevation and plan views, respectively, of a tip portion
of a spring contact, showing a circular-pad type of alignment mark and an adjacent
contact tip.
FIG. 5A is a plan view of an exemplary contactor having a plurality of microelectronic
spring contacts, selected ones of which have tip structures with alignment marks
according to the invention.
FIGS. 5C-5D are plan views, at successively higher levels of magnification,
of the spring contacts and tip structures with alignment marks on the exemplary
contactor shown in FIG. 5A.
FIG. 5E is a plan view of a tip structure similar to that shown in FIG. 5D,
having an alternative shape of alignment mark.
FIG. 6 is a perspective view of a sacrificial substrate at an exemplary step
of a process for making a plurality of tip structures like those shown in FIGS. 5A-5D.
FIG. 7A is a cross-sectional view of a portion of the sacrificial substrate
shown in FIG. 6, showing etched features for forming a co-located contact tip and
alignment mark in an exemplary step of a process for forming a spring contact with
an alignment mark according to the invention.
FIGS. 7B-7D are cross-sectional views of a sacrificial substrate and materials
layered thereon during exemplary steps of a process for forming a spring contact
with an alignment mark according to the invention.
FIG. 7E is a cross-sectional view showing a spring contact and tip structure
with an alignment mark during an exemplary attachment step.
FIG. 8A is a plan view showing an alternative structure with an alignment mark
according to the invention and adjacent spring contacts having relatively small
"microtip" contact tips on a contactor substrate.
FIG. 8B is a cross-sectional view of the substrate and alternative structure
shown in FIG. 8A.
FIGS. 9A-9D are cross-sectional views of a sacrificial substrate and materials
layered thereon during exemplary steps of a process for forming recessed alignment
marks and adjacent contact tips such as shown in FIG. 8B.
FIGS. 10A-10C are plan views of an exemplary tip structure during steps of
a process for forming an alignment mark using a tool for marking the tip structure
after attachment of the contact tip.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides a method and apparatus for providing precise fiducial
alignment marks on microelectronic contacts and on contactors carrying a plurality
of microelectronic contacts. In the detailed description that follows, like element
numerals are used to describe like elements shown in one or more of the figures.
Referring to FIG. 1, in an embodiment of the invention, an alignment mark
116 is provided on microelectronic spring structure
100. Spring structure
100 may be configured in various ways as known in the art. In the embodiment
shown in FIG. 1, spring structure
100 is configured as disclosed in the
commonly-owned, co-pending application Ser. No. 09/746716, filed Dec. 22, 2000,
which is incorporated herein by reference, in its entirety. That is, microelectronic
spring structure
100 comprises a group of column elements or posts
104,
a cantilevered beam
102 secured transverse to the group of column elements,
and a contact tip
114 on a portion of the cantilevered beam distal from
the column elements. In an alternative embodiment, a lithographically deposited
post component is used instead of the column elements
104, as disclosed,
for example, in the commonly-owned, co-pending application Ser. No. 09/023,859,
filed Feb. 13, 1998. Additional examples of suitable microelectronic spring contacts
for use with the present invention, and methods for making such contacts, are provided,
e.g., by commonly-owned, co-pending applications Ser. No. 09/023,859, filed Feb.
13, 1998, Ser. No. 09/364,788, filed Jul. 30, 1999, and Ser. No. 09/710,539, filed
Nov. 9, 2000, all of which applications are incorporated herein, in their entirety,
by reference.
Each of the foregoing applications discloses methods, and the resulting spring
structures, for making a microelectronic spring structure by depositing (such as
by electroplating) a resilient material on or in a sacrificial layer over a substrate,
and then removing the sacrificial layer. The sacrificial layer may be shaped to
have a sloped or contoured region extending above and away from the substrate,
such as by impressing a moldable (plastic) layer using a specially shaped forming
tool to form a mold. In the alternative, or in addition, the sacrificial layer
is patterned to provide openings revealing the substrate below it. A seed layer
is deposited over the sacrificial layer and/or exposed region of the substrate,
and patterned in the plan shape of the desired spring structure or component. The
resilient layer is then plated onto the seed layer. The sacrificial layer is removed,
leaving beam, tip and/or post components that are subsequently assembled to provide
structures like structure
100. In some embodiments, no assembly is required
because the deposition/patterning steps provide a spring structure having a base
portion attached to the substrate and a contoured and/or sloped beam extending
therefrom. However, each of the foregoing structures may include a contact tip
that is precisely formed using a pattern-masking/etching process and assembled
to the spring contact structure. Accordingly, the invention may be readily adapted
for use with each of the foregoing structures and methods, and to any other structure
that provides a similar opportunity for precise formation of a contact tip to a
microelectronic contact structure.
As shown in FIG. 1, microelectronic contact structure
100 comprises a
beam
102 having an upper surface
108 that serves as a datum surface for
attachment of a tip structure
110. To achieve precise planarity of surface
108, beam
102 is preferably formed by a lithographic process, for
example, by deposition of a resilient material on a sacrificial layer or substrate
as described, e.g., in Ser. No. 09/023,859 referenced above. As used herein, "sacrificial
layer" refers to a material, such as a photoresist, that is deposited on a substrate
during formation of a desired component or structure, such as a microelectronic
spring contact component, and later removed from the substrate. "Sacrificial substrate"
refers to a substrate that is attached to a desired component or structure, such
as a microelectronic spring component, during its formation, and later removed
from the component or structure. So long as structure
100 provides a datum
surface
108 for attachment of a contact tip
114 and/or a tip structure
110, the remaining details of structure
100 may be configured in
various different ways. For the purpose of illustrating an exemplary application
of the present invention, other details of structure
100 are described below,
but it should be appreciated that the invention is not limited thereby.
The beam
102 of structure
100 is secured to substrate
106
by column elements
104. Substrate
106 comprises a contactor for a
semiconductor device, such as a semiconductor wafer. Such contactors often comprise
specially shaped slabs of ceramic materials having terminals on opposing major
surfaces and internal electrical traces connecting each terminal on a first surface
with a corresponding terminal on a second surface. In the alternative, substrate
106 may comprise some other electronic component, such as, for example,
a probe card, or other printed circuit board; a semiconductor device, such as a
silicon chip or wafer; a ceramic material, or an electrical connector. Column elements
104 are typically attached to a terminal (not shown) of substrate
106,
which is in turn connected to a circuit element of an electronic component, such
as, for example, an interconnect or interposer substrate, a semiconductor wafer
or die, a production or test interconnect socket; a ceramic or plastic semiconductor
package, or chip carrier.
Contact tip
114 is attached to surface
108 of beam
102.
In an embodiment of the invention, contact tip
114 is attached to pad (stand-off)
112, which is in turn mounted to surface
108. Together, contact tip
114 and pad
112 comprise tip structure
110. Tip structure
110 further comprises an alignment mark
116. Pad
112 is used
to elevate contact tip
114 above the upper surface
108 of beam
102,
so that the contact tip contacts a face of a mating electronic component before
any other part of structure
100. In an alternative embodiment, such as when
beam
102 is sloped away from column elements
104 and substrate
106,
pad
112 may be omitted, and contact tip
114 and alignment mark
116
may be attached directly to surface
108. In both cases, the contact tip
114 and alignment mark
116 may be formed on a sacrificial substrate
and attached together to beam
102, thereby providing precise positioning
of the alignment mark with respect to the contact tip as necessary to provide alignment
that is at least about as accurate as aligning to the contact tip itself.
A side view of structure
100 is shown in FIG.
2A. Contact tip
114
is preferably located on pad
112 towards columns
104 (i.e., towards
the secured base of beam
102), relative to alignment mark
116, which
is located towards the free end of beam
102. This relative positioning helps
to avoid accumulation of debris on the alignment mark, because debris tends to
be pushed towards the fixed end (base) of beam
102 when tip
114 is
pressed against a mating terminal. Also, positioning the alignment mark towards
the free end of the beam helps to avoid inadvertent contact between the alignment
mark and a mating substrate, because the free end of the beam tends to be depressed
further away from the mating substrate than portions closer to its fixed base.
Contact with the mating substrate may damage the mark or cause it to be occluded
with debris, and thus is usually not desirable. However, for some applications,
there may not be sufficient available space to allow for locating the alignment
mark towards the free (distal) end of beam
102. In other cases, the beam
may be configured differently so that a location closer to the distal end is disadvantageous
for other reasons. For such applications, the alignment mark
116 may be
positioned closer to the fixed base of beam
102, such as shown in plan view
in FIG.
3C.
FIG. 2B shows an enlarged side view of the tip structure
110, showing
exemplary relative sizes and positions of a contact tip
114 and alignment
mark
116 on a pad
112. Contact tip
114 may be a truncated
pyramid shape, having a height "h
1" and a flat surface
118 at
its apex. In other embodiments of the invention, the contact tip may be pyramidal
without a truncated apex, or may be prism-shaped, with or without a truncated tip;
or any other suitable shape such as a hemisphere. Pyramids and prisms are commonly
used because they are tapered shapes capable of providing a well-supported raised
tip, and are readily formed by etching silicon anisotropically along its crystal
planes to provide pyramidal or prism-shaped pits, and then using the silicon pits
as an electroplating mold. However, the invention is not limited to particular
shapes of contact tips.
Similarly, alignment mark
116 may also be prism or pyramidal shaped,
because it is advantageous to form the mark
116 on the same sacrificial
substrate as the contact tip
114 using the same silicon etching and plating
technique. To avoid inadvertent contact with a mating component, mark
116
preferably has a height "h
2" that is substantially less than "h
1,"
such as, for example, between about one-fourth to three-quarters of "h
1."
The degree of difference between "h
1" and "h
2" may vary depending
on the requirements of the application and the geometry of the spring contact.
For example, an alignment mark that is placed "inboard" of the contact tip, that
is, closer to the fixed end of beam
102, as shown in FIG. 3C, must be relatively
short to prevent inadvertent contact with the mating component and build-up of
debris on the alignment mark. In comparison, an alignment mark "outboard" of the
contact tip, that is, towards the free end of the beam relative to the contact
tip, as shown in FIGS. 2A and 2B, may be somewhat longer relative to the contact
tip. Of course, whatever the relative lengths of the contact tip and alignment
mark, it is generally preferable that the alignment mark be positioned so as to
not contact the mating component, and this will usually mean that the alignment
mark be made substantially shorter than the contact tip.
Consequently, as shown in FIG. 2B, the width "w" of the alignment mark
will generally be less than the width of the contact tip, especially when pyramidal
or prism-shaped features are used. At the same time, the width of the mark must
be at least great enough to be visible on the vision system that will be used to
align the contactor that the mark is on. Accordingly, it may be advantageous to
increase at least one dimension of the alignment mark, for example, its length,
to provide a more readily resolvable feature, while maintaining the height of the
mark less than the corresponding contact tips.
The prism-shaped alignment mark
116 shown in plan view in FIG. 3A exemplifies
such an approach. Mark
116 may be compared with pyramidal alignment mark
120 shown in plan view in FIG.
3B. Marks
120 and
116
have the same width "w" and the same height "h
1," but mark
120
is square in plan view while mark
116 is elongated rectangular in plan view
and extends for substantially the width of pad
120. In a vision system having
a minimum resolvable feature size about equal to the plan area of mark
120,
the mark will appear as a single pixel or small cluster of pixels. As such, it
may be difficult to distinguish from the surrounding environment that may contain
irregularities, such as accumulated debris or oxidation. Such irregularities may
appear as single pixels or irregular clusters of pixels, creating a mottled background
from which it may be difficult to discern the alignment mark. By comparison, mark
116 will appear as a line of pixels that is much more likely to stand in
visual contrast to the surrounding environment. As shown in FIG. 3C, in an embodiment
of the invention, alignment mark
116 has a length 'I1' that is less than
the width length 'I2' of pad
112 so that an open region exists at each end
of alignment mark
116. A point of the line, such as an endpoint or midpoint,
may be selected for use as a reference point.
In other embodiments of the invention, a slab-shaped alignment feature, such
as
a pad, is provided on a contact structure, optionally separate from the pad of
the contact tip. An exemplary circular slab-shaped alignment pad
126 is
shown in FIGS. 4A-4B. Pad
126 is essentially a form of alignment mark produced
at a different step of a process for forming microelectronic contacts. FIG. 4A
shows a side view of the mark
126 and an adjacent tip structure
110
on a tip portion of a spring contact beam
102. FIG. 4B shows the same structure
in plan view. Such slab-shaped pads shaped and positioned for alignment purposes
may be particularly useful for certain applications, for example, when there is
very limited available height for an alignment mark, when the contact tip
114
is formed by some process other than an etch/plating process, or when a relatively
large alignment structure is desired. Alignment pad
126 is preferably formed
and attached to beam
102 in the same process steps with contact tip pad
112, thereby achieving accurate registration with respect to contact tip
114. Alignment pad
126 is preferably separate and spaced apart from
pad
112, to avoid contamination with debris from tip
114 and for
greater visibility. Alignment pad
126 also preferably has a distinct shape
for greater visibility. A circular shape is particularly preferred because the
center of the circle is readily determined for use as a reference point, while
the relatively large circle is readily visible. However, any other suitable shape
may be used.
FIGS. 5A-5E illustrate application of the foregoing structures to an exemplary
contactor. Contactor
130 comprises a generally slab-shaped substrate
132,
typically a ceramic material. As used herein, "contactor" includes specialized
devices for making electrical contact with semiconductor devices in wafer form
during the electrical testing of semiconductor devices. In addition, "contactor"
may include any other device having a plurality of contact elements, for example,
but not limited to, microelectronic spring contacts, for making contact with any
type of mating component, wherein the contacts on the contactor are aligned with
the mating component using a vision system.
As shown in FIG. 5A, a typical contactor may comprise a plurality of spring contacts
136, that may in turn be arrayed in a plurality of groups
138. In
an embodiment of the invention, most of the plurality of spring contacts
136
will not have an alignment mark. A selected few of the spring contacts, for example,
the four spring contacts
134, are provided with an alignment mark. The marked
contacts
134 are located so that the position of all of the contacts
136
may be accurately determined from the position of the marked contacts. For many
applications, at least three or four alignment marks are needed to align the contactor.
However, additional marked contacts
134 may be provided for purposes of
redundancy; for example, a marked contact may be provided in each group
138
(not shown). It should be appreciated that contactor
130 and contacts
136
are not drawn to scale. Furthermore, for illustrative clarity, contacts
136
are drawn somewhat larger relative to contactor
130 than may be typical
for semiconductor wafer applications. Details of contactor
130, contacts
136, and methods of making these components, may be as known in the art
or as otherwise disclosed in the incorporated references.
FIG. 5B shows an enlarged view of a group of spring contacts
138 on contactor
130. A typical interleaved arrangement of the spring contacts
136
is apparent, as are individual beams
102 and contact tips
114 of
each spring contact
142. The post or column elements are hidden behind the
beam
102 of each spring contact. Also apparent is a distinctive-shaped pad
140. A relatively large pad, such as pad
140, may additionally provide
space for a larger alignment mark; or may itself serve as an alignment mark. The
distinctive shape of pad
140 facilitates locating the marked contactor
134.
The pad
140 may be located using a vision system at low magnification, because
of its relatively large size and distinctive shape. Then, magnification of the
vision system may be increased to locate the alignment mark on the contactor
134.
FIG. 5C shows the marked contact
134 and adjacent unmarked contacts
142.
The components of unmarked contacts
142 and marked contact
134 are
more readily apparent in this enlarged view. Pad
112, contact tip
114,
and beam
102 of each contact
142 are apparent. Tip
114, pad
140, beam
102, and alignment mark
116 of contact
134
are also apparent. The free end
146 and fixed end
148 of the contacts
142,
134 are also indicated respectively. In an embodiment of the
invention, unmarked contacts
142 and marked contacts
134 are provided
with the same type of beams
102 and contact tips
114. However, in
alternative embodiments, the marked contact
134 may use a beam configuration
and/or contact tip configuration that is different from unmarked contacts
142.
For example, in an embodiment of the invention, structure
134 serves only
as a support for an alignment mark, and has no contact tip.
FIG. 5D shows an enlarged view of pad
140 at the free end
146
of beam
102. A prism-shape alignment mark
116 is provided on pad
140, as previously described with respect to FIGS. 2A-2B. Alternatively,
the circular portion of pad
140 may be used as the aligning feature, and
mark
116 may be omitted. Or, more than one alignment mark may be provided
on the same pad
140, for example, two parallel alignment marks like mark
116 may be provided. A cross-shaped mark
144, as shown in FIG. 5E,
comprised of two crossed prisms, may be particularly helpful for indicating a reference
point at the intersection of the cross. Each of the foregoing marks may be made
using a lithographic mask/etch process as described below.
FIG. 6 shows a perspective view of a sacrificial substrate
150 covered
by a resist layer
152 during an exemplary step of a method for making an
alignment mark according to the invention. Substrate
150 is typically a
silicon substrate and has a planar face extending for a region preferably at least
as large as the face of the contactor to be provided with spring contacts. Other
substrate materials may be used if sufficiently uniform and capable of providing
a planar surface that may be uniformly and predictably etched under a patterned
resist layer. Resist layer
152 may be any suitable photo-resist material,
as known in the art. Layer
152 is patterned to provide square openings
154
(four of many shown) in the positions where contact tips are desired and rectangular
openings
156 (one of many shown) where alignment marks are desired. As should
be apparent, a square hole will yield a pyramidal pit when the underlying substrate
is etched, and a rectangular hole will yield a prism-shaped pit. Other shapes,
e.g., crosses, cones, truncated cones, etc., may be provided by a suitable combination
of substrate and opening shape.
FIG. 7A shows a cross-section through exemplary ones of the square openings
154 and rectangular openings
156 after etching of substrate
152.
In an embodiment of the invention, the etching is halted at a point before the
pyramidal pit is fully etched. At this point, prism-shaped pit
160, although
over-etched, is shallower than pit
158. That is, the depth of pit
158
is controlled primarily by the time of exposure to the etch solution while the
depth of pit
160 is controlled primarily by the relative size of opening
156. After pit
160 is etched to the edge of opening
156, further
etching ("over-etching"), should proceed more slowly than etching of adjacent pit
158. Production of adjacent pits of different and controllable depth is
thereby achieved.
FIG. 7B shows the same portion of substrate after further processing, as follows.
After the desired pit depths are achieved, etching is halted and resist layer
152
is removed as known in the art. Typically, a conductive seed and/or release layer
164 is applied over the surface of the substrate to facilitate subsequent
electroplating and release of the tip structure from substrate
150. Suitable
materials for seed and/or release layer
164 are known in the art, or are
described in the incorporated references. A second resist layer is applied as known
in the art and patterned to reveal a pad-shaped opening
166 for electroplating
a tip structure and support pad for an alignment mark. FIG. 7B shows a single opening
disposed over both pits
158 and
156. However, two separate openings
(one disposed over each pit
156,
158) may be provided for forming
separate pads, if desired. Furthermore, for embodiments where no raised alignment
mark is to be formed, e.g., where the alignment mark is pad-shaped, pit
156
may be omitted.
The pad shaped opening
166 is then filled with one or more metallic layers
168,
170, such as by electroplating, to provide a filled opening
as shown in FIG.
7C. The composition of layers
168,
170 is
as known in the art. Any number or composition of layers may be used, and the invention
is not limited thereby. The exposed surface
172 of the topmost layer
170
may then be planarized, such as by chemical-mechanical polishing, and the second
resist layer
162 is removed to reveal a tip structure
110, comprised
of a pad
112, a contact tip
114, and an alignment mark
116,
as shown in FIG.
7D and as previously described. It should be apparent that
a plurality of similar tip structures, for example, some with alignment marks like
mark
116, others with only one of a contact tip or alignment mark, and perhaps
others with no contact tip or alignment mark at all, will be present on substrate
150, having their exposed surfaces in substantially the same plane. Such
tip structures are then ready for joining to an array of spring contacts like,
for example, those shown in FIGS. 5A-5C. It should be appreciated that tip structures
110 may take a variety of shapes and are not limited to the pyramidal shape
discussed in the preceding paragraphs.
FIG. 7E shows a cross-section of an exemplary contact structure
134 during
a step for joining beam
102 to tip structure
110. A joining material
178, such as a solder paste, is accurately dispensed on surface
172,
as known in the art. Substrate
150 is placed in a suitable holding fixture
and substrate
106, with a plurality of contact structures in place on its
surface, is lowered in parallel relationship to substrate
150 and aligned
so that each contact structure, e.g., contact structure
134, is aligned
with a corresponding tip structure, e.g., structure
110. The substrates
are moved together until the joining material contacts both tip structure
110
and beam
102. The joining material is then activated, e.g., by heating,
which then pulls the tip structure and beam together by surface tension to a relatively
uniform position in which the material is hardened (such as by cooling). Careful
control over the surface properties of the material to be joined, the amount of
joining material applied per unit area, the alignment of substrates
106
and
150, and curing conditions (such as temperature), will generally yield
a uniform thickness of bond over the large plurality of tip structures across a
contactor substrate. The bond thickness affects the accuracy with which the z-position
(direction perpendicular to substrate
106) of the contact tips and alignment
marks are known. The x- and y-positions (positions in a plane parallel to substrate
106) are fixed by the sacrificial substrate and pattern masking steps. Hence,
the position of adjacent tip structures and alignment marks can be determined with
the required accuracy in three dimensions across the substrate. The positional
accuracy can be confirmed by comparing measured versus expected positions of selected
contact tips across a substrate, relative to the principal alignment marks. If
variances exceed the specified tolerance (e.g., ½ the semiconductor device
terminal pitch), the substrate should be repaired or discarded.
Alignment marks need not be placed on contact structures exactly like the
structures which carry contact tips. The alignment function of the marks may also
be realized by placing them on elevated platforms that are constructed to provide
a mounting surface substantially co-planar with the surfaces to which the contact
tips are mounted. The elevated platform may be resilient, or supported to be substantially
rigid (i.e., substantially non-resilient). A plan view of a substantially rigid
elevated platform
180 adjacent to spring contacts
184 on a substrate
106 is shown in FIG.
8A. The configuration shown in FIG. 8A may be
desirable in applications which use contact "microtips"
182 on tip structures
194, and correspondingly small contact structures
184. Structures
184 may be too small to support alignment marks
188,
192.
Therefore, an elevated platform
180 with a relatively large beam
186
may be provided for mounting the alignment marks. Alignment marks
188,
192
may thus be formed on the same sacrificial substrate as microtips
182, and
transferred together with the microtips to structures
180,
184 on
substrate
106. Registration between the alignment marks and the microtips
is achieved in the same way as previously described.
A side cross-section of platform
180 is shown in FIG. 8B, with portions
of contact structures
184, and especially, tip structures
194, visible
behind the platform. Pad-type alignment mark
192 has a smooth surface without
raised or recessed structures. Recessed alignment marks
188 are provided
in an upper surface of pad
190. Beam
186 is supported along its length
by four columns
104, and is accordingly substantially rigid relative to
cantilevered beams of spring contacts
184.
When the alignment marks are large relative to the contact tips, if may be preferable
to use pad-type marks like mark
192 or recessed marks like marks
188.
Raised alignment marks may be less preferred for such applications, because of
the small clearance provided by the contact tips. Furthermore, contact tips like
microtips
182 may not provide sufficient vertical clearance even when the
alignment marks are not raised, e.g., pad-type mark
192 and/or marks
188
below the surface of pad
190. Therefore, it may be further desirable to
recess the pad-type mark and pads for alignment marks below the base of the microtips,
as shown in FIG.
8B. At the same time, however, the alignment marks and/or
their pads are preferably formed on the same sacrificial substrate as the microtips,
for the purpose of maintaining accurate registration between the marks and the
tips. To achieve the desired structure on the same sacrificial substrate, a different
sequence of manufacturing steps than previously described is used.
FIGS. 9A-9F show cross-sectional views of a substrate and materials layered
thereon during steps of an exemplary sequence for making relatively large alignment
marks adjacent to microtips. The sacrificial substrate
200 may be silicon
or other etchable material as previously described. A first resist layer
202
is deposited and patterned to reveal most of the substrate
200 except for
directly over where any recessed alignment marks are to be formed. The substrate
200 is then etched to provide protrusions under the remaining areas of resist
202. The shape of the protrusions will depend on the etching properties
of the substrate
200, the etching method employed, and the shape of the
resist areas
202. For example, under-etching a rectangular resist area on
a crystalline silicon substrate will provide a truncated prism-shaped protrusion.
An exemplary cross-section of two such protrusions
204 is shown in FIG.
9A.
The first resist layer
206 is then stripped and a second resist layer
206 is applied and patterned to reveal pad-shaped openings like opening
208 where tip structures are to be formed. The substrate is again etched
to provide a plurality of pad-shaped recesses like recess
209 shown in FIG.
9B.
The second resist layer is then stripped, and a third resist layer
210
is applied and patterned to provide a plurality of small openings like opening
212 where contact tips are to be formed. The substrate
200 is again
etched to form a plurality of pyramidal pits like pit
214 shown in FIG.
9C.
The third resist layer is then stripped and a seed/release layer (not shown)
is applied. A fourth resist layer (not shown) is applied to substrate
200
and patterned to provide pad-shaped openings over protrusions
204 and pits
214, similarly to as previously described in connection with FIG.
7B.
The substrate is then plated with one or more layers of metal to substantially
fill the openings, and the exposed plated areas are planarized, similarly to as
previously described in connection with FIG.
7C. The fourth resist layer
is removed to reveal a plurality of tip structures
194 and recessed alignment
marks
188 in pads
190, like those shown in FIG.
9D. The tip
structures and pads have planarized mounting surfaces
216 suitable for joining
to a plurality of contact structures, similarly to as previously described in connection
with FIG.
7E. Structures like those shown in FIGS. 8A-8B may thereby be produced.
It should also be appreciated that the alignment mark may be added to the tip
structure after producing the tip structure, for example, by further selective
etching or laser marking. Although it is generally preferable to form the alignment
marks in the same lithographic step as the contact tips, this may not always be
possible. For example, it some cases it may be desirable to add alignment marks
to a contactor that was manufactured without them. The following example exemplifies
a method for adding alignment marks in a later step.
Referring to FIG. 10A, the pad
300 of tip structure
312 includes
a contact tip
314, which may be produced, for example, by one of the processes
described above. Tip structure
312 may optionally be mounted to a beam
302
of a spring structure. Marking area
304 is provided in which the alignment
mark is to be placed. In FIG. 10B, a laser marking system
324 can be aligned
by targeting a low power beam
326 on the contact tip
314, and then
offset a defined distance to a marking location
320. The laser
324
may then be fired to emit a higher power beam
328 of sufficient power to
create a precise mark
316 (shown in FIG.
10C). The marking location
316 (target of the laser beam) is offset a predetermined spatial distance,
for example, an offset in x, and y and directions is shown. The offset may additionally
include an offset in a z-direction (not shown). As shown in FIG. 10C, the mark
316 is defined at the center of the target of the laser beam. Alignment
of a contactor using a subsequently formed mark, such as mark
316, as a
reference point is possible. By way of further example, direct deposition of mark
316 can be accomplished using a gas phase organo-metallic precursor and
ion beam direct write. The contact tip
314 is targeted and then the ion
beam assisted metal deposition is used to create the features of mark
316
a defined offset away from the contact tip.
In some embodiments of the invention, the relative position(s) of the contact
tips may be measured and recorded in a data file or database. This data may be
obtained from the design process, or measured directly after fabrication by optical
or other measurement methods. Such data may be particularly useful for contactors
having a plurality of contacts and alignment marks, where the amount of offset
between the contact tips of the contacts and the alignments marks varies somewhat
from contact to contact across the contactor. Such variations may be more likely
to occur when the alignment marks are not formed in the same lithographic step
as the contact tips, such as, for example, when the alignment marks are formed
by laser. To obtain such data, a single point, such as the tip of a contact tip
on the contactor, is preferably selected as a reference point. It can sometimes
be assumed that all of the contact tips are in substantially fixed relation to
the reference point, but for precise positioning, it may be desirable to measure
the positions of the contact tips as well. The position of each alignment mark
relative to one or more adjacent contact tips (i.e., the offset) may then be measured.
From the measured offsets the coordinates of the alignment mark with respect to
the fixed reference point may be determined, irrespective of any variations in
offset distances. The coordinate data may then be input into the test system used
to align and place the contact tips for the testing operation, and thus an optimal
alignment between the contactor and the device or wafer to be tested can be obtained.
A method for aligning and contacting corresponding arrays of microelectronic
contact
elements using alignment marks is exemplified as follows. The arrays comprise a
first array and a second array, and the object is to achieve contact between corresponding
contact elements of the first array and of the second array. The contact elements
of the first array comprise a plurality of contact tips in a substantially fixed
relationship to the first array, and a plurality of alignment features. Selected
ones of the contact elements of the first array each further comprises an alignment
feature spaced apart from a contact tip, as described above. The first array may
comprise contact elements of a probe card, and the second array may comprise contact
elements of a wafer, but the invention is not limited thereby.
The method comprises, as an initial step, determining coordinates of the plurality
of alignment features relative to selected ones of the plurality of contact tips
of the first array. This can be accomplished by direct measurement, or based on
a known relationship between elements formed using a pattern-masking/etch process.
The second array is maintained in a known position, such as by being held in a
wafer chuck mounted to the frame of a testing system. The first array is also mounted
in a corresponding movable test head of the testing system. When the arrays are
mounted in a suitable testing system, a position of the first array relative to
the second array is determined by transforming measured positions of the plurality
of alignment features relative to the second array using the coordinates. That
is, the position of the contact tips of the first array is determined by measuring
the position of the alignment features and applying a suitable correction based
on the coordinate data. The first array is then positioned relative to the second
array based on its determined position until contact is achieved between corresponding
contact elements of the first array and of the second array. The position of the
contact tips may be repeatedly determined as often as desired during the positioning
process. Using the method, the contact tips can be positioned with accuracy to
contact corresponding pads or other contact elements of the second array, without
any need to find or measure the location of the contact tips themselves during
the testing process.
Having thus described a preferred embodiment of fiducial alignment marks on
microelectronic contacts, it should be apparent to those skilled in the art that
certain advantages of the within system have been achieved. It should also be appreciated
that various modifications, adaptations, and alternative embodiments thereof may
be made within the scope and spirit of the present invention. For example, a fiducial
alignment mark on or adjacent to a pad with a contact tip has been illustrated,
but it should be apparent that the inventive concepts described above would be
equally applicable to any fiducial mark that is attached to (or formed on) an array
of contacts in the same manufacturing step as the contact tips of the array. Furthermore,
the inventive concepts would also be applicable to alignment marks that are placed
on other types of microelectronic contacts than shown herein, in registration with,
or in measured relation to co-located contact tips. For example, alignment marks
may be placed on membrane probe cards or on contact elements that are not primarily
resilient, such as on buckling-type probes. Similarly, the method of aligning arrays
of contact elements using alignment marks on contact elements of at least one of
the arrays is not limited to use with a particular type of contactor or device.
Rather, the method may be used with any array of contact elements upon which it
is possible to place alignment marks or features in registration or measured relation
with the contact tips or points of such contact elements. The invention is further
defined by the following claims.
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