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Apparatus and method for flow of process gas in an ultra-clean environment Number:6,949,202 from the United States Patent and Trademark Office (PTO) owispatent

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Title: Apparatus and method for flow of process gas in an ultra-clean environment

Abstract: Processes for the addition or removal of a layer or region from a workpiece material by contact with a process gas in the manufacture of a microstructure are enhanced by the use of recirculation of the process gas. Recirculation is effected by a pump that has no sliding or abrading parts that contact the process gas, nor any wet (such as oil) seals or purge gas in the pump. Improved processing can be achieved by a process chamber that contains a baffle, a perforated plate, or both, appropriately situated in the chamber to deflect the incoming process gas and distribute it over the workpiece surface. In certain embodiments, a diluent gas is added to the recirculation loop and continuously circulated therein, followed by the bleeding of the process gas (such as an etchant gas) into the recirculation loop. Also, cooling of the process gas, etching chamber and/or sample platen can aid the etching process. The method is particularly useful for adding to or removing material from a sample of microscopic dimensions.

Patent Number: 6,949,202 Issued on 09/27/2005 to Patel,   et al.

Inventors: Patel; Satyadev R. (Elk Grove, CA); Schaadt; Gregory P. (Santa Clara, CA); MacDonald; Douglas B. (Los Gatos, CA); MacDonald; Niles K. (San Jose, CA)
Assignee: Reflectivity, INC (Sunnyvale, CA)
Appl. No.: 649569
Filed: August 28, 2000

Current U.S. Class: 216/58; 156/345.29; 156/345.33; 156/345.37; 216/63; 216/64; 216/67; 216/78; 252/79.1
Intern'l Class: C23F 001/08; C23F 001/12
Field of Search: 156/34529,345.33,345.41,345.43,345.48,345.5,345,37 216/58,63,64,67,73 252/791

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Other References

Streller et al., "Selectivity in Dry Etching of Si(100) and XeF2 and VUV Light", Elsevier Science B.V., Applied Surface Science, (1996), 106: pp. 341-346.
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Primary Examiner: Olsen; Allan
Attorney, Agent or Firm: Muir; Gregory R.
Parent Case Text


CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of commonly owned, U.S. patent application Ser. No. 09/427,841, inventors Patel et al., filed Oct. 26, 1999 now U.S. Pat. No. 6,290,864, the contents of which are incorporated herein by reference.
Claims


1. Apparatus for etching a simple, said apparatus comprsing:

(a) a source of etchant gas selected from a noble gas halide and a halogen halide;

(b) an etching chamber in communication with said source of etchant gas;

(c) a recirculation loop passing through said etching chamber;

(d) a valve connecting the source to the recirculation loop such that the etchant gas can be introduced into the recirculation loop when the valve is turned on, and the source can be disconnected from the recirculation loop when the valve is shut off; and

(e) a pump disposed within said recirculation loop for recirculating etchant gas along said recirculation loop so as to recirculate the etchant gas in the recirculation loop while the source is disconnected from the recirculation loops.

2. Apparatus in accordance with claim 1 in which said gas flow spreading means is a baffle.

3. Apparatus in accordance with claim 1 in which said gas flow spreading means is a perforated plate.

4. Apparatus in accordance with claim 1, further comprising an energy source and/or electric field source at the etching chamber for forming a plasma therein.

5. Apparatus in accordance with claim 1 further comprising a filter disposed within said recirculation loop, said filter being one that removes a member selected from the group consisting of byproducts or effucent from gases flowing through said recirculation loop, or particulates.

6. Apparatus in accordance with claim 1 in which said pump is a dry pump.

7. Apparatus in accordance with claim 6 in which said dry pump has not wet seals and adds no gas to said recirculation loop.

8. Apparatus in accordance with claim 7 in which said dry pump is a bellows pump.

9. Apparatus in accordance with claim 8 in which said bellows pump comprises a housing with bellows-type wall sections enclosing a hollow interior, and at least one partition disposed to divide said hollow interior into a plurality of sections.

10. Apparatus in accordance with claim 1 in which said pump is constructed to circulate etchant gas substantially continuously within said recirculation loop.

11. Apparatus in accordance with claim 1, wherein the source of etchant gas is a source of xenon difluoride crystals.

12. Apparatus in accordance with claim 1, wherein the source of etchant gas is a source of bromine trifluoride liquid.

13. The apparatus of claim 1, wherein the etchant gas is not condensed.

14. Apparatus in accordance with claim 1 in which said source of etchant gas comprises a source chamber.

15. Apparatus in accordance with claim 14 further comprising gas flow spreading means in said etching chamber for diverting incoming gas.

16. Apparatus in accordance with claim 14 in which said source of etchant gas further comprises fluoride crystals retained within said source chamber.

17. Apparatus in accordance with claim 16 in which said fluoride crystals are xenon difluoride crystals.

18. Apparatus in accordance with claim 14 further comprising an expansion chamber communicating with said source chamber and with a gas source for a gas other than said etchant gas, said expansion chamber arranged for mixing gas from said source chamber with gas from said gas source.

19. Apparatus in accordance with claim 18 in which said expansion chamber is in communication with said recirculation loop.

20. Apparatus in accordance with claim 18 in which said gas source for a gas other than said etchant gas comprises a plurality of gas sources, the gases from which, when mixed, yield a gaseous mixture with molar averaged molecular weight less than or equal to that of N2.

21. Apparatus in accordance with claim 20 in which said plurality of gas sources are sources of two or more members selected from the group consisting of Ar, Ne, He and N2.

22. Apparatus in accordance with claim 18 in which said pump is defined as a first pump and said apparatus further comprises a second pump arranged to draw gases from a member selected from the group consisting of said expansion chamber, said source chamber, and said recirculation loop.

23. Apparatus in accordance with claim 18 in which said gas source for a gas other than said etchant gas comprises a source of a gas with molar averaged molecular weight less than or equal to that of N2.

24. Apparatus in accordance with claim 23 in which said gas other than said etchant gas is a member selected from the group consisting of Ar, Ne, He and N2.

25. A method for etching a sample, said method comprising:

(a) placing said sample in an etching chamber disposed within a gas recirculation loop, said etching chamber in communication with a source of etchant gas selected from a noble gas halide and a halogen halide, and said gas recirculation loop having a pump disposed therein;

(b) passing etchant gas from said source of etchant gas into said etching chamber to expose said sample to said etchant gas; and

(c) disconnecting the recirculation loop from the source; and

(d) recirculating said etchant gas through said recirculation loop by way of said pump.

26. A method in accordance with claim 25 further comprising passing said etchant gas through an expansion chamber prior to step (b) and, while said etchant gas is in said expansion chamber, forming a mixture of said etchant gas with non-etchant gases, and step (b) comprises passing said etchant gas as part of said mixture into said etching chamber.

27. A method in accordance with claim 25 in which said pump is a continuous recirculation pump and step (c) comprises continuously recirculating said etchant gas through said recirculation loop.

28. A method in accordance with claim 25 further comprising bleeding etchant gas into said recirculation loop during step (c).

29. A method in accordance with claim 25, wherein the source of etchant gas comprises xenon difluoride.

30. A method in accordance with claim 25, wherein the source of etchant gas comprises bromine trifluoride.

31. The method of claim 25, wherein the step of recirculating said etchant gas through said recirculation loop further comprises:

shutting off a valve that connecting said source to said recirculation loop; and

recirculating the etchant gas in said recirculation loop by way of said pump.

32. A method comprising:

providing an apparatus according to claim 1;

providing a solid or liquid etchant selected from a noble gas halide and a halogen halide at said etchant source at a temperature and pressure sufficient to cause said etchant to vaporize;

providing a sample to be etched within the etching chamber;

passing the vaporized etchant through the etching chamber; and

recirculating the etchant multiple times through the etching chamber with said pump.

33. A method in accordance with claim 32, wherein the etchant gas is passed through the pump without additional gas being added thereto.

34. A method in accordance with claim 32, wherein the source of etchant gas comprises two chambers, wherein the temperature and/or pressure of one chamber is different from the pressure and/or temperature of the other so that predominantly liquid or solid etchant remains in one chamber and predominantly gas etchant is in the other, prior to passing into the recirculation path and etching chamber.

35. A method in accordance with claim 32 comprising heating the process gas so as to at least avoid condensation, and cooling the etching chamber and/or sample to improve selectivity between the silicon and non-silicon portions of the sample.

36. A method in accordance with claim 32 in which said sample comprises a silicon portion existing in at least one layer and one or more non-silicon portion existing in at least one layer, said silicon etchant is a fluoride gas selected from the group consisting of noble gas fluorides and halogen fluorides, and said gas is a gas mixture which further comprises a non-etchant gas additive at a partial pressure and a molar ratio relative to said fluoride gas such that said gas mixture achieves substantially greater etching selectivity toward said silicon portion than would be achieved with said fluoride gas alone.

37. A method in accordance with claim 36 in which said non-etchant gas additive is a member selected from the group consisting of nitrogen, argon, helium, neon, and mixtures thereof.

38. A method in accordance with claim 36 in which said non-etchant gas additive is a member selected from the group consisting of helium, a mixture of helium and nitrogen, and a mixture of helium and argon.

39. A method in accordance with claim 36 in which said fluoride is a xenon fluoride and said non-etchant gas additive is helium.

40. A method in accordance with claim 36 in which said non-silicon portion is a member selected from the group consisting of titanium, gold, tungsten, and compounds thereof.

41. A method in accordance with claim 36 in which said silicon portion is a silicon layer deposited over a substrate and said non-silicon portion is a layer of a member selected from the group consisting of silicon nitride, silicon carbide, and silicon oxide, deposited over said silicon layer, said non-silicon layer being patterned to leave vias therein for access of said gas to said silicon layer, the exposure of said sample to said gas being of sufficient duration to laterally etch away substantially all of said silicon layer by access through said vias.

42. A method in accordance with claim 32 in which said sample is a substrate for a member selected from the group consisting of a semiconductor and/or a MEMS device.

43. A method in accordance with claim 32 in which said sample is a substrate for a MEMS device.

44. A method in accordance with claim 32, wherein the etchant gas is passed through a baffle and a perforated plate within the etching chamber.

45. A method in accordance with claim 32, wherein the solid or liquid etchant comprises xenon difluoride crystals.

46. A method in accordance with claim 32, wherein the solid or liquid etchant comprises xenon difluoride crystals.

47. Apparatus for adding or removing a layer of material from a sample by contacting said sample with a process gas, said layer having at least one dimension less than 1 mm, said apparatus comprising:

(a) a source of said process gas selected from a noble gas halide and a halogen halide;

(b) a fabrication chamber in communication with said source of process gas;

(c) a recirculation loop passing through said fabrication chamber,

(d) a valve connecting the source to the recirculation loop such that the etchant gas can be introduced into the recirculation loop when the valve is turned on, and the source is disconnected from the recirculation loop when the valve is shut off; and

(e) a pump disposed within said recirculation loop for recirculating process gas along said recirculation loop so as to recirculate the etchant gas in the recirculation loop when the source is disconnected from the recirculation loop.

48. Apparatus in accordance with claim 47 in which said process gas corrodes metal in the presence of moisture.

49. Apparatus in accordance with claim 48 in which said moisture is water moisture.

50. Apparatus in accordance with claim 47 further comprising a filter disposed within said recirculation loop, said filter being one that removes a member selected from the group consisting of byproducts, particulates or effluents from gases flowing through said recirculation loop.

51. Apparatus in accordance with claim 47 in which said source of process gas is comprised of a member selected from the group consisting of (i) chamber retaining a said process gas and a condensed liquid phase of said process gas in equilibrium with said process gas, (ii) a pressurized chamber of said process gas, and (iii) a chamber retaining a solid condensed phase of said process gas.

52. Apparatus in accordance with claim 51 further comprising a source of pressurized diluent gas and an expansion chamber positioned to receive diluent gas from said source of diluent gas and process gas from said source of process gas and to mix said diluent gas and said process gas thus received.

53. Apparatus in accordance with claim 47 in which said source of process gas is comprised of first and second chambers, said first chamber retaining primarily a liquid or solid condensed form of said process gas, and said second chamber retaining said process gas evaporated or sublimed from said condensed form, said first and second chambers being maintained at different temperatures.

54. Apparatus in accordance with claim 47 in which said layer has at least one dimension less than 500 μm.

55. Apparatus in accordance with claim 47 in which said layer has at least one dimension less than 100 μm.

56. Apparatus in accordance with claim 47, wherein the source of etchant gas comprises a source of xenon difluoride crystals.

57. Apparatus in accordance with claim 47, wherein the source etchant gas comprises a source of bromine trifluoride liquid.

58. Apparatus for exposing a silicon-containing sample to a gas comprising a gaseous fluoride etchant selected from a noble gas fluoride and a halogen fluoride for etching silicon, said apparatus comprising:

a flow-through etching chamber comprising:

a sample support,

entry and exit ports for said gas;

a source chamber comprising a noble gas fluoride or halogen fluoride etchant in solid or liquid form, the source chamber and the etching chamber capable of being in fluid communication with each other;

a recirculation loop and recirculation pump within the loop, the recirculation loop constructed to connect to the etching chamber at two locations to allow etching gas to flow into and out of the etching chamber, and the recirculation pump in communication with the etching chamber and adapted to pump etching gas repeatedly through the etching chamber;

a valve connecting the source to the recirculation loop such that the etchant gas can be introduced into the recirculation loop when the valve is turned on, and the source is disconnected from the recirculation loop when the valve is shut off; and

a pump disposed within said recirculation loop for recirculating etchant gas along said recirculation loop so as to recirculate the etchant gas in the recirculation loop when the source is disconnected from the recirculation loop.

59. Apparatus in accordance with claim 58, wherein the etchant is provided from xenon difluoride crystals in the source chamber.

60. Apparatus in accordance with claim 58, wherein the etchant is provided from bromine trifluoride in the source chamber.

61. Apparatus in accordance with claim 58 further comprising a baffle and perforated plates comprising parallel circular plates arranged coaxially within said flow-through chamber.

62. Apparatus in accordance with claim 61 in which said perforations in said perforated plate are of decreasing from the center of said perforated plate outward.

63. Apparatus in accordance with claim 62, further comprising a plasma generator at said etching chamber.

64. Apparatus for etching silicon from a sample by exposing said sample to a gas comprising a silicon etchant selected from a noble gas halide and a halogen halide, said apparatus comprising:

a source of etchant gas selected from a noble gas halide and a halogen halide;

a flow-through chamber having:

a sample support,

entry and exit ports for said etchant gas,

a perforated plate between said entry port and said sample support, and

a baffle between said entry port and said perforated plate, said baffle positioned to deflect said etchant gas from said etchant port radially toward the periphery of said perforated plate, and said perforated plate containing an array of perforations arranged to distribute said deflected etchant gas over all exposed surfaces of said sample; and

a reciprocating pump driving said gas toward said entry port, said reciprocating pump comprising:

an enclosed housing comprising bellows-type wall sections and a partition arranged to divide the interior of said housing into first and second chambers, said partition being movable in a reciprocating manner to cause collapse and extensions of said bellows-type wall sections whereby one chamber contracts while the other expands and vice versa;

inlet and outlet ports for each chamber with controllable shutoff valves at each port; and

a partition driver for moving said partition in a reciprocating manner and opening and closing said shutoff valves in a coordinating sequence, causing said chambers to draw fluid in through alternating inlet ports while discharging fluid through alternating outlet ports and thus together to produce a continuous outlet flow.

65. Apparatus in accordance with claim 64 in which said reciprocating pump draws gas from said exit port.

66. Apparatus in accordance with claim 64, wherein the source of etchant gas comprises a source chamber comprising xenon difluoride crystals.

67. Apparatus in accordance with claim 64, wherein the source of etchant gas comprises a source chamber bromine trifluoride liquid.

68. Apparatus for etching a sample by contacting the sample with a vapor fluoride etchant gas selected from a noble gas fluoride and a halogen fluoride:

(a) a source of said fluoride etchant gas, said source of etchant gas being comprised of first and second chambers, said first chamber retaining primarily a liquid or solid condensed form of said fluoride etchant gas, and said second chamber retaining said fluoride etchant gas volatilized from said condensed form, said source comprising a temperature regulator for maintaining the first and second chambers at different temperatures;

(b) an etching chamber in communication with said source of fluoride etchant gas for holding the sample to be etched by the fluoride etchant gas;

(c) a recirculation loop passing through said etching chamber;

(d) a valve connecting the source to the recirculation loop such that the etchant gas can be introduced into the recirculation loop when the valve is turned on, and the source if disconnected from the recirculation loop when the valve is shut off; and

(e) a pump disposed within said recirculation loop for recirculating etchant gas along said recirculation loop so as to recirculate the etchant gas in the recirculation loop when the source is disconnected from the recirculation loop.

69. Apparatus in accordance with claim 68, wherein the cooling unit is adapted to cool the process gas, one or more of the aforementioned chambers and/or sample below room temperature.

70. Apparatus in accordance with claim 68, wherein the cooling unit is adapted to cool in the range of from about 1 to 15 degrees C.

71. Apparatus in accordance with claim 68, wherein the dielectric is a silicon nitride or silicon oxide layer.

72. Apparatus in accordance with claim 68, wherein the source of said fluoride etchant gas comprises xenon difluoride crystals.

73. Apparatus in accordance with claim 68, wherein the source of said fluoride etchant gas comprises bromine trifluoride liquid.

74. Apparatus in accordance with claim 68, in the absence of a source of energy for energizing the etchant gas once in gas form.

75. Apparatus in accordance with claim 74, wherein the first source chamber comprises primarily liquid or crystals of a halogen or noble gas fluoride.

76. Apparatus in accordance with claim 74, further comprising a cooling unit for cooling the process gas, one or more of the aforementioned chambers and/or the sample being etched.

77. Apparatus in accordance with claim 74, wherein the sample comprises silicon and one or both of a dielectric and a metal, and the silicon is etched relative to the dielectric and/or metal.

78. Apparatus in accordance with claim 74, wherein the first source chamber is held at a temperature less than the second source chamber.

79. Apparatus in accordance with claim 78, further comprising a recirculation path for recirculating the fluoride etchant gas repeatedly through the etching chamber.

80. Apparatus in accordance with claim 78, wherein the two source chambers are maintained at more than 3 degrees C difference.

81. Apparatus in accordance with claim 80, wherein both source chambers are maintained at temperatures under 40 degrees C.

82. Apparatus for etching a sample comprising a silicon material and a dielectric material, comprising:

a source of a noble gas halide and/or halogen halide etchant gas;

an etching chamber in communication with the source of the etchant gas;

a surface within the etching chamber for holding the sample to be etched;

a cooling unit for cooling the surface, etching chamber and/or etching gas within the etching chamber below room temperature.

83. Apparatus according to claim 82, wherein the source comprises a source chamber having therein a liquid or solid noble gas halide or halogen halide.

84. Apparatus according to claim 83, further comprising a sample held by a holder, the sample comprising a sacrificial silicon portion and a dielectric portion.

85. Apparatus according to claim 82, wherein the source chamber comprises xenon difluoride crystals and/or bromine trifluoride liquid.

86. Apparatus according to claim 82, comprising a second source chamber connected to said source chamber and maintained at a temperature higher than the temperature of said source chamber.

87. Apparatus in accordance with claim 82, wherein the source of etchant gas comprises xenon difluoride crystals.

88. Apparatus in accordance with claim 82, wherein the source of etchant gas comprises bromine trifluoride liquid.

89. An apparatus for use in etching a sample, comprising:

a source of an etchant gas selected from a noble gas halide and a halogen halide;

an etching chamber having the sample and in communication with the source; and

a recirculation loop passing through the etching chamber;

a reciprocating pump disposed within said recirculation loop for recirculating the etchant gas along said recirculation loop.

90. The apparatus of claim 89, wherein the source is connected to the recirculation loop via a valve such that:

(a) an amount of etchant gas can be introduced into the loop during etching; and

(b) said amount of etchant flows within the recirculation for etching the sample when the source is disconnected from the recirculation loop by shutting off said valve.

91. An etching system for etching a sample, comprising:

first means for containing an etchant gas selected from a noble gas halide and a halogen halide;

second means in communication with the first means for holding the sample and providing an apace in which the sample can be etched with the etchant gas;

a recirculation loop passing through said second means;

third means for connecting the first means to the recirculation loop such that the etchant gas can be introduced into the recirculation loop when said third means is turned on, and the first means is disconnected from the recirculation loop when the third means is shut off; and

fourth means disposed within said recirculation loop for recirculating the etchant gas along said recirculation loop so as to continuously recirculating the etchant gas in the recirculation loop when the first means is disconnected from the recirculation loop.

92. The etching system of claim 91, wherein the fourth means is a reciprocate pump.

93. The etching system of claim 91, further comprising:

third means for maintaining the etchant gas within the etching system at a pressure such that the etchant gas has substantially no condensation.

94. A method for etching a sample, comprising:

placing said sample in an etching chamber disposed within a gas recirculation loop, said etching chamber in communication with a source of etchant gas selected from a noble gas halide and a halogen halide, and said gas recirculation loop having a pump disposed therein;

passing etchant gas from said source of etchant gas into said etching chamber to expose said sample to said etchant gas; and

maintaining the etchant gas in the recirculation loop at a temperature so as to keep the etchant gas in vapor form.

95. The method of claim 94, wherein the step of recirculating the etchant gas further comprises:

recirculating the etchant gas without introducing another etchant gas.

96. The method of claim 94, wherein the step of maintaining the etchant gas in the recirculation loop at a temperature so as to keep the etchant gas in vapor form further comprises:

maintaining the etchant gas in the recirculation loop at a temperature so as to avoid condensation of the etchant gas.

97. The method of claim 94, wherein the step of maintaining the etchant gas in the recirculation loop further comprises:

maintaining the etchant gas in the recirculation loop at a temperature so as to avoid the condensation of the etchant gas.

98. An apparatus for use in etching a sample, comprising:

a source of an etchant gas selected from a noble gas halide and a halogen halide;

an etching chamber having the sample and in communication with the source; and

a recirculation loop passing through the etching chamber;

a bellows pump disposed within said recirculation loop for recirculating the etchant gas along said recirculation loop.

99. A method for etching a sample, said method comprising:

(a) placing said sample in an etching chamber disposed within a gas recirculation loop, said etching chamber in communication with a source of etchant gas selected from a noble gas halide and a halogen halide, and said gas recirculation loop having a reciprocating pump disposed therein;

(b) passing etchant gas from said source of etchant gas into said etching chamber to expose said sample to said etchant gas; and

(c) recirculating said etchant gas through said recirculation loop by way of said reciprocating pump.

100. A method comprising:

providing an apparatus according to claim 1;

providing a solid or liquid etchant selected from a noble halide and a halogen halide at said etchant source at a temperature and pressure sufficient to cause said etchant to vaporize;

providing a sample to be etched within the etching chamber;

passing the vaporized etchant through the etching chamber; and

recirculating the etchant multiple times through the etching chamber with said reciprocating pump.

101. Apparatus for exposing a silicon-containing sample to a gas comprising a gaseous fluoride etchant selected from a noble gas fluoride and a halogen fluoride for etching silicon, said apparatus comprising:

a flow-through etching chamber comprising:

a sample support,

entry and exit ports for said gas;

a source chamber comprising a noble gas fluoride or halogen fluoride etchant in solid or liquid form, the source chamber and the etching chamber capable of being in fluid communication with each other;

a recirculation loop and reciprocating pump with the loop, the recirculation loop constructed to connect to the etching chamber at two locations to allow etching gas to flow into and out of the etching chamber, and the reciprocating pump in communication with the etching chamber and adapted to pump etching gas repeatedly through the etching chamber.

102. Apparatus for etching a sample by contacting the sample with a vapor fluoride etchant gas selected from a noble gas fluoride and a halogen fluoride;

(a) a source of said fluoride etchant gas, said source of etchant gas being comprised of first and second chambers, said first chamber retaining primarily a liquid or solid condensed form of said fluoride etchant gas, and said second chamber retaining said fluoride etchant gas volatilized from said condensed form, said source comprising a temperature regulator for maintaining the first and second chambers at different temperatures;

(b) an etching chamber in communication with said source of fluoride etchant gas for holding the sample to be etched by the fluoride etchant gas; and

(c) a reciprocating pump in connection with the etching chamber and the source so as to recirculate the etchant gas through the etching chamber.

103. A method comprising:

providing an apparatus according to claim 1;

providing a solid or liquid etchant selected from a noble gas halide and a halogen halide at said etchant source at a temperature and pressure sufficient to cause and etchant to vaporize;

providing a sample to be etched within the etching chamber;

passing the vaporized etchant through the etching chamber;

recirculating the etchant multiple times through the etching chamber with said pump; and

maintaining the etchant in the recirculation loop at a temperature so as to keep the etchant gas in vapor form.

104. The method of claim 103, wherein the step of maintaining the etchant gas in the recirculation loop further comprises:

maintaining the etchant gas in the recirculation loop at a temperature so as to avoid the condensation of the etchant gas.
Description


BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention lies in the technology of the manufacture of microstructures, which include such devices as microelectromechanical structures, micro opto-electromechanical structures, and semiconductor devices. In particular, this invention addresses gas-phase etching and deposition procedures, with particular emphasis on those involving the etching of silicon. This invention further addresses apparatus that is especially useful in meeting the needs of gas-phase etching and deposition.

2. Description of the Prior Art

The use of selective etchants to remove sacrificial layers or regions in a multilayer structure without removal of an adjacent layer or region is a necessary and common step in the manufacture of semiconductor devices, microelectromechanical structures (MEMS), and micro opto-electromechanical structures (MOEMS). MEMS and MOEMS have found applications in inertial measurement, pressure sensing, thermal measurement, micro-fluidics, optics, and radio-frequency communications, and the range of possibilities for these structures continues to grow. One example of such a structure is a reflective spatial light modulator, which is a device consisting of a planar array of electrostatically deflectable mirrors, each microscopic in size. The device is used as a microdisplay system for high-resolution, large-screen projection. In such a device, the sacrificial layer temporarily supports the mirror structure during the fabrication process. Once the mirror structure is formed, the sacrificial layer is removed to leave gaps below the mirrors and a microhinge along one edge of each mirror to join the mirror to the remainder of the structure. The gap and the microhinge provide the mirror with the freedom of movement needed for its deflection. Devices of this type are described in U.S. Pat. No. 5,835,256 (issued Nov. 10, 1998, to Andrew Huibers, assignor to Reflectivity, Inc., Santa Clara, Calif.). The contents of U.S. Pat. No. 5,835,256 are incorporated herein by reference.

The success of an etch step in the manufacture of microstructures depends on a number of factors, prominent among which are the completeness and uniformity of the etch among the areas to be etched, both across and throughout the microstructure surface. For deflectable mirror structures, the integrity of the microhinges (the structure undergoing mechanical deformation) is important to achieving uniform microstructure properties and a high yield of defect-free product. For other MEMS and for semiconductor devices, completeness and uniformity of the etch are likewise critical to insure that features on all areas of the structure function fully and property when in use. These factors are important in both isotropic and anisotropic etching. Isotropic etching is of particular interest, in structures where the purpose of the etch is to remove a sacrificial layer that is intervening between functional layers or between a functional layer and a substrate. The bulk of the sacrificial layer in these structures is accessible to the etchant only through vias in the functional layer and etchant must proceed laterally outward from the vias. The structures described in U.S. Pat. No. 5,835,256 above preferably employ isotropic etchant for this reason. The "vias" in these structures are the narrow gaps between the facing edges of adjacent mirror elements or between a mirror edge and an adjacent feature. Likewise, in the manufacture of any MEMS or semiconductor, all features on the structure surface must be fully defined and all materials that are not functional in the finished product must be fully removed.

Of potential relevance to certain embodiments of this invention is the prior art relating to particular etchant gases. Prominent among the etchants that are used for the removal of sacrificial layers or regions in both isotropic and anisotropic etching procedures are noble gas fluorides and halogen fluorides. These materials, used in the gas phase, selectively etch silicon relative to other materials such as silicon-containing compounds, non-silicon elements, and compounds of non-silicon elements. Descriptions of how these materials are used in etching procedures appear in co-pending U.S. patent application Ser. No. 09/427,841 and in portions of the present specification that follow. The invention claimed in application Ser. No. 09/427,841 offers an improvement in the selectivity of the silicon etch. Further means of improving the etch process particularly the uniformity and thoroughness of the etch, continue to be sought, since improvements in these features of the process significantly benefit the cost and reliability of the products manufactured.

The method of the present invention is useful for producing deflectable elements (deflectable by electrostatic or other means) which, if coated (before or after gas phase processing) with a reflective layer, can act as an actuatable micromirror. Arrays of such micromirrors can be provided for direct view or projection display systems (e.g. projection television or computer monitors). Also, if the micromirrors are provided alone or in an array and of a size of 100 micrometers or more (preferably 500 micrometers or more), the mirror is useful for steering light beams, such as in an optical switch. The present invention is also adaptable to processing (e.g. etching) semiconductor devices, and is not limited to MEMS devices.

SUMMARY OF THE INVENTION

The present invention provides improvements in the apparatus and methods used for the etching of layers or areas, or for the addition or deposition of layers or elements, in or on a microstructure. In one such improvement, a recirculating and/or cooling system is introduced into the etch or deposition process to thereby provide a controlled reaction environment while improving the effectiveness of the process gas and the efficiency of the process. Recirculation has not been done in the prior art due to the risk of introducing foreign bodies or substances into the ultra-clean reaction environment and contaminating the sample, a risk that is associated with the use of recirculation pumps. One embodiment of this invention thus resides in the discovery that recirculation can indeed be performed without such risk. Another improvement provided by this invention is the use of an etching or deposition chamber that contains internal structural features that help distribute the incoming process gas over the sample surface. This distribution serves to reduce, minimize, or even eliminate the occurrence of localized areas of high concentration of the process gas and any resulting "hot spots" on the sample surface. Still another improvement is the design and use of a reciprocating pump for recirculating the process gas. The pump fully seals the process gas from the environment without the use of lubricants or of any materials that may contaminate the environment or are susceptible to corrosion by the process gas. The pump nevertheless provides process gas at a highly controllable flow rate to the chamber in which the reaction occurs. Use of the pump thus leads to the reduction of the effluents and an increase in product uniformity. Each of these improvements results in an increase in the efficiency of the process, and to the yield and quality of the product, and each can be used either alone or in combination with one or more of the others.

The internal structural features of the reaction chamber that contribute to the distribution of the incoming process gas are a baffle that deflects the incoming gas stream to prevent the stream from striking the sample surface directly, a perforated plate that distributes the gas stream over a broad spatial area, or a combination of such a baffle and perforated plate. When both the baffle and perforated plate are present, the plate is preferably positioned between the baffle and the sample. Whether the plate is used alone or in combination with a baffle, the plate is arranged such that the process gas flow must pass through the perforations in the plate before reaching the sample, and the perforations are sized and spatially arranged in the plate to promote the distribution of the process gas stream across the perforation array. With these features, the process can be performed with greater control over the quantity, flow rate, and flow pattern of the process gas. The benefits that this offers include a uniform reaction over the sample area and an improved chemical efficiency resulting in greater uniformity, a higher yield of defect-free product, and improved reproducibility. When the process is a selective etching process, selectivity of the etch toward silicon or any other materials sought to be etched is also improved as a result of greater control over the reaction conditions.

While the recirculation described above can be effected by use of any of a variety of pumps of varying construction and operation, one such pump, which is described in detail below, is a reciprocating pump constructed of a housing with bellows-type wall sections and one or more movable internal partitions that divide the pump interior into individual chambers. Each partition engages the bellows-type wall sections such that movement of the partition in one direction causes a first chamber to expand while a second chamber contracts, followed by movement of the partition in the opposite direction causing the first to contract while the second expands. Continuous cycles of back and forth movement of the partition, synchronized with the opening and closing of separate inlet and outlet valves for each chamber cause the chambers to alternate between drawing the gas in and discharging the gas. The result is a relatively continuous and steady discharge of gas during both strokes of the pump cycle. A pump of this design allows the operator to modify the flow rate of process gas with a high degree of efficiency and control by simply adjusting the partition speed and cycle period. These benefits are achieved without danger of corrosion of the pump or of contamination of the process gas with pump lubricant or any other liquid or particulate matter from the pump.

This is one example of a dry pump, which term is used herein to denote a pump that contains no liquid components such as those that might otherwise be used as seals or lubricants, that come into contact with the process gas stream. Other dry pumps may also be used. This particular dry pump however offers the further advantage of avoiding any introduction of a purge gas into the flow stream.

Also disclosed are cooling systems and methods for cooling the process gas, whether recirculated or not. The cooling can be directly to the sample being processed, to the processing/etching chamber, or to the process/etching gas prior to arrival in the process chamber. Such cooling is particularly suitable for etching silicon, and particularly with non-plasma phase halides (and preferably with vapor phase fluorides that do not have external electric fields or electromagnetic energy added thereto).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of an example of a process for etching silicon using the methods and apparatus of this invention.

FIG. 2 is a plan view of one example of a perforated plate that can be used in the practice of this invention.

FIG. 3 is a plan view of a second example of a perforated plate that can be used in the practice of this invention.

FIG. 4a is a side elevation view of one example of a reciprocating pump in accordance with this invention.

FIG. 4b is a pump flow diagram of the reciprocating pump of FIG. 4a together with associated flow lines and shutoff valves.

FIG. 5 is a process flow diagram showing a further embodiment of the invention.

FIG. 6 is a process flow diagram showing a still further embodiment of the invention.

FIG. 7 is a cross section of a sample after being subjected to different processes in accordance with the present invention, as an illustration of different effects that can be achieved by the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIME


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