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

• US 6,949,202 B1
• Filed: 08/28/2000
• Issued: 09/27/2005
• Est. Priority Date: 10/26/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: MacDonald, Niles K., Patel, Satyadev R., Schaadt, Gregory P., MacDonald, Douglas B.
• Primary Examiner(s): OLSEN, ALLAN W
• Application Number:
  US09/649,569
• Time in Patent Office: 1,856 Days
• Field of Search: 156/345.29, 156/345.33, 156/345.41, 156/345.43, 156/345.48, 156/345.5, 156/345, 156/37, 216/58, 216/63, 216/64, 216/67, 216/73, 252/79.1
• US Class Current: 216/58
• CPC Class Codes: B81C 1/00587 Processes for avoiding or controlling over-etching not provided for in B81C1/00571 - B81C1/00579
• CPC Class Codes: B81C 2201/0138 Monitoring physical parameters in the etching chamber, e.g. pressure, temperature or gas composition
• CPC Class Codes: B81C 99/0025 Apparatus specially adapted for the manufacture or treatment of microstructural devices or systems not provided for in B81C99/001 - B81C99/002
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C03C 15/00 Surface treatment of glass, not in the form of fibres or filaments, by etching etching or surface-brightening compositions, in general C09K13/00
• CPC Class Codes: C03C 2218/33 by etching
• CPC Class Codes: C23F 1/08 Apparatus, e.g. for photomechanical printing surfaces photo- mechanical reproduction G03F
• CPC Class Codes: H01L 21/67017 Apparatus for fluid treatment H01L21/67126, H01L21/6715 take precedence
• CPC Class Codes: H01L 21/67063 for etching

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.

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.

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.

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.

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.

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.

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 μ

m.

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

m.

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.

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.