Method for vapor phase etching of silicon

• US 7,041,224 B2
• Filed: 03/22/2002
• Issued: 05/09/2006
• Est. Priority Date: 10/26/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Patel, Satyadev R., Huibers, Andrew G., Schaadt, Gregory P., MacDonald, Douglas B., Heureux, Peter, Shi, Hongqin
• Primary Examiner(s): OLSEN, ALLAN W
• Application Number:
  US10/104,109
• Publication Number:
  US 20020195423A1
• Time in Patent Office: 1,509 Days
• Field of Search: 216/2, 216/51, 216/60, 216 72- 74, 216/79, 216/24, 252/79.1
• US Class Current: 216/2
• CPC Class Codes: B81B 2201/045 Optical switches
• CPC Class Codes: B81C 1/00 Manufacture or treatment of devices or systems in or on a substrate B81C3/00 takes precedence
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence
• CPC Class Codes: B81C 1/00531 Dry etching
• CPC Class Codes: B81C 1/00595 Control etch selectivity
• 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: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/3081 characterised by their composition, e.g. multilayer masks, materials
• CPC Class Codes: H01L 21/32135 by vapour etching only

Abstract

The etching of a material in a vapor phase etchant is disclosed where a vapor phase etchant is provided to an etching chamber at a total gas pressure of 10 Torr or more, preferably 20 Torr or even 200 Torr or more. The vapor phase etchant can be gaseous acid etchant, a noble gas halide or an interhalogen. The sample/workpiece that is etched can be, for example, a semiconductor device or MEMS device, etc. The material that is etched/removed by the vapor phase etchant is preferably silicon and the vapor phase etchant is preferably provided along with one or more diluents. Another feature of the etching system includes the ability to accurately determine the end point of the etch step, such as by creating an impedance at the exit of the etching chamber (or downstream thereof) so that when the vapor phase etchant passes from the etching chamber, a gaseous product of the etching reaction is monitored, and the end point of the removal process can be determined. The vapor phase etching process can be flow through, a combination of flow through and pulse, or recirculated back to the etching chamber. A first plasma or wet chemical etch (or both) can be performed prior to the vapor phase etch.

Claims

1. A method for making a micromechanical device, comprising:

depositing a silicon material and one or more functional layers on a substrate;

removing the silicon material by providing a vapor phase etchant to the silicon material and removing the silicon material that is intervening between functional layers and/or between a functional layer and the substrate where a total gas pressure proximate to the silicon material is greater than 10 Torr, and wherein the vapor phase etchant is a non-plasma etchant and comprises a noble gas halide; and

wherein a micromechanical device is formed after removing the silicon material.

2. The method of claim 1, wherein the silicon is PECVD amorphous silicon deposited in a glow discharge.

3. The method of claim 1, wherein the selectivity toward a material other than silicon is 2000:

1 or more.

4. The method of claim 1, wherein the silicon has a long range order of 100 nm or less.

5. The method of claim 1, wherein a micromirror array is formed.

6. The method of claim 1, wherein the silicon is polysilicon.

7. The method of claim 1, wherein the silicon is doped during or after deposition.

8. The method of claim 1, wherein the silicon is etched at a pressure greater than 20 Torr.

9. The method of claim 8, wherein the selectivity toward a material other than silicon is 10000:

1 or more.

10. The method of claim 8, wherein the silicon is etched at a pressure greater than 50 Torr.

11. The method of claim 1, wherein the silicon is amorphous silicon having a hydrogen concentration of 25 at % or less.

12. The method of claim 11, wherein the silicon is PECVD, LPCVD or sputtered silicon.

13. The method of claim 1, wherein prior to etching the silicon material:

depositing the silicon material on a substrate; and

depositing a layer other than silicon on the silicon material.

14. The method of claim 13, wherein the layer other than silicon is a silicon compound.

15. The method of claim 13, wherein the layer other than silicon is a metal or metal alloy.

16. The method of claim 13, wherein a plurality of layers other than silicon are deposited on the silicon material.

17. The method of claim 1, wherein the etching of the silicon material is at a pressure of from 100 to 760 Torr.

18. The method of claim 17, wherein the etching of the silicon material is at a pressure of from 200 to 600 Torr.

19. The method of claim 17, wherein the silicon comprises a dopant is selected from PH3, P2H5, B2H5 and BCl3.

20. The method of claim 17, wherein the silicon comprises a dopant is added during deposition of the silicon.

21. The method of claim 17, wherein the silicon comprises a dopant is added by ion implantation of the silicon.

22. The method of claim 21, wherein the ion implantation is performed at a 5 to 10 degree tilt angle of the substrate having the silicon thereon relative to the direction of the beams of ions.

23. The method of claim 1, wherein the silicon is preferentially etched relative to a material other than silicon.

24. The method of claim 23, wherein the material other than silicon is a silicon compound.

25. The method of claim 24, wherein the silicon compound is silicon nitride or silicon dioxide.

26. The method of claim 24, wherein the material other than silicon is a ceramic material.

27. The method of claim 26, wherein the ceramic material is a nitride or oxide of a transition metal.

28. The method of claim 1, wherein the vapor phase etchant is provided to a chamber in which the sample comprising silicon is disposed, and wherein the vapor phase etchant is capable of etching the sample in a non-energized state, and further comprising:

monitoring the gas in or from the etching chamber; and

determining the end point of the etch based on the monitoring of the gas from the etching chamber.

29. The method of claim 28, wherein an end point is determined based on a value of an etching product passing below a threshold.

30. The method of claim 28, wherein an end point is determined when a partial pressure of a gas component decreases for a predetermined period of time.

31. The method of claim 28, wherein curve smoothing is performed prior to determining an end point of the etch.

32. The method of claim 28, wherein a derivative is taken of partial pressure values of an etching product.

33. The method of claim 32, wherein an end point is determined when a derivative value is negative.

34. The method of claim 28, wherein the material is silicon and the etchant is a plurality of gas phase etchants.

35. The method of claim 34, wherein the etch product that is monitored is a silicon fluoride compound.

36. The method of claim 35, wherein the etch product that is monitored is SiF, SiF2, SiF3 and/or SiF4.

37. The method of claim 34, wherein the gas phase etchants are xenon difluoride and chlorine trifluoride.

38. The method of claim 37, wherein the doping is achieved by implantation at 10¹⁰ to 10¹⁴ ions/cm³.

39. The method of claim 38, wherein the doping is performed at an energy of 10 to 70 keV.

40. A method for making a micromechanical device, comprising:

depositing a silicon material on a substrate;

depositing a layer other than silicon on the silicon material so as to form a sample to be etched;

providing the sample to be etched to an etching chamber;

providing a non-plasma vapor phase etchant to the silicon material in the etching chamber; and

etching the silicon material from between the layer other than silicon and the substrate with an etchant comprising a noble gas halide, wherein the total gas pressure in the etching chamber proximate to the silicon material during the etch is 10 Torr or greater; and

wherein a micromechanical device is feinted alter etching the silicon.

41. The method of claim 40, wherein the etching of the silicon material is at a pressure of from 50 to 600 Torr.

42. The method of claim 40, wherein the selectivity toward a material other than silicon is 2000:

1 or more.

43. The method of claim 40, wherein the silicon has a long range order of 100 nm or less.

44. The method of claim 40, wherein a micromirror array is formed.

45. The method of claim 40, wherein the layer other than silicon is a silicon compound.

46. The method of claim 40, wherein the layer other than silicon is a metal or metal alloy.

47. The method of claim 40, wherein a plurality of layers other than silicon are deposited on the silicon material.

48. The method of claim 40, wherein the silicon is polysilicon.

49. The method of claim 40, wherein the silicon is etched at a rate of 15 um/hr or less.

50. The method of claim 40, wherein the providing of the vapor phase etchant to the silicon material is after a plasma etch of the silicon.

51. The method of claim 40, wherein the providing of the vapor phase etchant to the silicon material is after a wet chemical etch of the silicon.

52. The method of claim 40, wherein the silicon is a-Si.

53. The method of claim 52, wherein the silicon is PECVD a-Si.

54. The method of claim 52, wherein the silicon is PECVD, LPCVD or sputtered silicon.

55. The method of claim 40, wherein the vapor phase etchant is a noble gas fluoride or interhalogen.

56. The method of claim 55, wherein the vapor phase etchant is xenon difluoride.

57. The method of claim 40, wherein the silicon material is etched at a rate of 25 um/hr or less.

58. The method of claim 57, wherein the silicon material is etched at a rate of 20 um/hr or less.

59. The method of claim 57, wherein the silicon material is etched at a rate of 7.2 um/hr or less.

60. The method of claim 57, wherein the silicon material is etched at a rate of 3 um/hr or less.

61. The method of claim 40, wherein the etching of the silicon material is at a pressure of from 100 to 500 Torr.

62. The method of claim 61, wherein the silicon comprises a dopant is selected from PH3, P2H5, B2H5 and BCl3.

63. The method of claim 61, wherein the silicon comprises a dopant is added during deposition of the silicon.

64. The method of claim 61, wherein the silicon comprises a dopant is added by ion implantation of the silicon.

65. The method of claim 64, wherein the ion implantation is performed at a 5 to 10 degree tilt angle of the substrate having the silicon thereon relative to the direction of the beams of ions.

66. The method of claim 40, wherein a partial pressure of the vapor phase etchant is 10 Torr or below.

67. The method of claim 66, wherein a partial pressure of the vapor phase etchant is 5 Torr or below.

68. The method of claim 67, wherein a partial pressure of the vapor phase etchant is 1 Torr or below.

69. The method of claim 67, wherein a partial pressure of the vapor phase etchant is 5 Torr or below.

70. The method of claim 40, the silicon material is part of a silicon portion that is etched relative to a non-silicon portion of the sample, said non-silicon portion consisting of a member selected from the group consisting of a non-silicon metal, a compound of a non-silicon metal, and a silicon-containing compound in which silicon is bonded to a non-silicon element, by exposing both said silicon portion and said non-silicon portion to an etchant gas selected from the group consisting of noble gas fluorides and halogen fluorides, wherein said etchant gas is utilized in the form of a gas mixture in which said etchant gas is mixed with a non-etchant gaseous additive, the partial pressure of said etchant gas in said gas mixture being at least about 0.1 mbar, and the molar ratio of said non-etchant gaseous additive to said etchant gas being from about 1:

1 to about 500;

1, such that said gas mixture achieves substantially greater etching selectivity toward said silicon portion than would be achieved with said etchant gas alone.

71. The method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged formula weight of less than about 25.

72. A method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged formula weight of from about 4 to about 25.

73. A method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged formula weight of from about 4 to about 20.

74. A method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged formula weight of from about 4 to about 10.

75. A method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged thermal conductivity at 300 K and atmospheric pressure of from about 10 mW/(m K) to about 200 mW/(m K).

76. A method in accordance with claim 70 in which said non-etchant gaseous additive has a molar-averaged thermal conductivity at 300 K and atmospheric pressure of from about 140 mW/(m K) to about 190 mW/(m K).

77. A method in accordance with claim 70 in which said molar ratio is from about 10:

1 to about 200;

1.

78. A method in accordance with claim 70 in which said molar ratio is from about 20:

1 to about 150;

1.

79. A method in accordance with claim 70 in which said non-etchant gaseous additive is a member selected from the group consisting of nitrogen, argon, helium, neon, and mixtures thereof.

80. A method in accordance with claim 70 in which said non-etchant gaseous additive is a member selected from the group consisting of helium, neon, mixtures of helium and neon, and mixtures of one or both of helium and neon with one or both of nitrogen and argon.

81. A method in accordance with claim 70 in which said non-etchant gaseous additive is a member selected from the group consisting of helium, a mixture of helium and nitrogen, and a mixture of helium and argon.

82. A method in accordance with claim 70 in which said non-etchant gaseous additive is a member selected from the group consisting of helium and a mixture of helium and nitrogen.

83. A method in accordance with claim 70 in which said non-etchant gaseous additive is helium.

84. A method in accordance with claim 70 in which the partial pressure of said etchant gas is from about 0.3 mbar to about 30 mbar.

85. A method in accordance with claim 70 in which the partial pressure of said etchant gas is from about 1 mbar to about 15 mbar.

86. A method in accordance with claim 70 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 mixture to said silicon layer, the exposure to said gas mixture being of sufficient duration to laterally etch away substantially all of said silicon layer by access through said vias.

87. A method in accordance with claim 70 in which said etchant gas is a noble gas fluoride.

88. A method in accordance with claim 87 in which said noble gas fluoride is a member selected from the group consisting of krypton difluoride and the xenon fluorides.

89. A method in accordance with claim 87 in which said noble gas fluoride is a member selected from the group consisting of xenon difluoride, xenon tetrafluoride, and xenon hexafluoride.

90. A method in accordance with claim 87 in which said noble gas fluoride is xenon difluoride.

91. A method in accordance with claim 87 in which said noble gas fluoride is xenon difluoride and said non-etchant gaseous additive is a member selected from the group consisting of helium, neon, and mixtures one or more or helium and neon with one or more of nitrogen and argon.

92. A method in accordance with claim 87 in which said noble gas fluoride is xenon difluoride and said non-etchant gaseous additive is a member selected from the group consisting of helium and a mixture of nitrogen and helium.

93. A method in accordance with claim 70 in which said etchant gas is a halogen fluoride.

94. A method in accordance with claim 93 in which said halogen fluoride is a member selected from the group consisting of chlorine trifluoride, bromine trifluoride, and iodine pentafluoride.

95. A method in accordance with claim 93 in which said halogen fluoride is a member selected from the group consisting of chlorine trifluoride and bromine trifluoride.

96. A method in accordance with claim 93 in which said halogen fluoride is bromine trifluoride.

97. A method in accordance with claim 70 in which the partial pressure of said etchant gas is from about 1 mbar to about 15 mbar, and the mole ratio of said non-etchant gaseous additive to said etchant gas is from about 10:

1 to about 200;

1.

98. A method in accordance with claim 97 in which the partial pressure of said etchant gas is from about 1 mbar to about 15 mbar, and the mole ratio of said non-etchant gaseous additive to said etchant gas is from about 20:

1 to about 150;

1.

99. A method in accordance with claim 70, in which said non-silicon portion is a member selected form the group consisting of non-silicon metals and metal compounds.

100. A method in accordance with claim 99 in which said non-silicon portion is a member selected from the group consisting of titanium, gold, tungsten, and compounds thereof.

101. A method in accordance with claim 99 in which said non-silicon portion is gold.

102. A method in accordance with claim 70 in which said silicon layer is a polysilicon layer deposited over a substrate and said non-silicon portion is a layer of silicon nitride, said silicon nitride layer being patterned to leave vias therein for access of said gas mixture to said polysilicon layer, said exposure to said gas mixture being of sufficient duration to laterally etch away substantially all of said polysilicon layer by access through said vias.

103. A method in accordance with claim 102 in which said polysilicon layer is from about 200 nm to about 5000 nm in thickness.

104. A method in accordance with claim 102 in which said polysilicon layer is from about 250 nm to about 3000 nm in thickness.

105. A method in accordance with claim 102 in which said polysilicon layer is from about 300 nm to about 1000 nm in thickness.

106. A method in accordance with claim 102 in which said silicon nitride layer is from about 10 nm to about 500 nm in thickness.

107. A method in accordance with claim 102 in which said silicon nitride layer is from about 20 nm to about 200 nm in thickness.

108. The method of claim 40, wherein the silicon is etched at a pressure greater than 20 Torr.

109. The method of claim 108, wherein the selectivity toward a material other than silicon is 10000:

1 or more.

110. The method of claim 108, wherein the silicon is etched at a pressure greater than 50 Torr.

111. The method of claim 110, wherein a partial pressure of the vapor phase etchant is 50 Torr or below.

112. The method of claim 111, wherein a partial pressure of the vapor phase etchant is 25 Torr or below.

113. The method of claim 40, wherein the silicon is preferentially etched relative to a material other than silicon.

114. The method of claim 113, wherein the material other than silicon is a silicon compound.

115. The method of claim 114, wherein the silicon compound is silicon nitride or silicon dioxide.

116. The method of claim 114, wherein the material other than silicon is a ceramic material.

117. The method of claim 116, wherein the ceramic material is a nitride or oxide of a transition metal.

118. The method of claim 40, wherein the vapor phase etchant is provided to a chamber in which the sample comprising silicon is disposed, and wherein the vapor phase etchant is capable of etching the sample in a non-energized state, and further comprising:

monitoring the gas in or from the etching chamber; and

determining the end point of the etch based on the monitoring of the gas from the etching chamber.

119. The method of claim 118, wherein an end point is determined based on a value of an etching product passing below a threshold or a value of an etchant passing above a threshold.

120. The method of claim 118, wherein an end point is determined when a partial pressure of a gas component decreases for a predetermined period of time.

121. The method of claim 118, wherein curve smoothing is performed prior to determining an end point of the etch.

122. The method of claim 118, wherein the end point detection is an infrared analyzer.

123. The method of claim 118, wherein a derivative is taken of partial pressure values of an etching product.

124. The method of claim 123, wherein an end point is determined when a derivative value is negative.

125. The method of claim 118, wherein the material is silicon and the etchant is a gas fluoride etchant.

126. The method of claim 125, wherein the etch product that is monitored is a silicon fluoride compound.

127. The method of claim 126, wherein the etch product that is monitored is SiF, SiF2, SiF3 and/or SiF4.

128. The method of claim 40, wherein the etch rate of the silicon material is 25 um/hr or less.

129. The method of claim 128, wherein the etch rate of silicon material is 20 um/hr or less.

130. The method of claim 129, wherein the etch rate of the silicon material is 7.2 um/hr or less.

131. The method of claim 130, wherein the etch rate of the silicon material is 3 um/hr or less.

132. The method of claim 40, wherein a diluent is provided with the vapor phase etchant.

133. The method of claim 132, wherein the diluent comprises one or both of a diatom and a noble gas.

134. The method of claim 132, wherein the diluent is an inert gas.

135. The method of claim 134, wherein the diluent comprises helium, neon, argon and/or xenon.

136. The method of claim 132, wherein the diluent is a diatom.

137. The method of claim 136, wherein the diatom is H2, N2 and/or O2.

138. The method of claim 136, wherein the diatom is a halogen diatom.

139. The method of claim 138, wherein the halogen diatom is Cl2, F2, Br2 and/or I2.

140. The method of claim 40, wherein the silicon is doped during or after deposition.

141. The method of claim 140, wherein the silicon is doped with boron, phosphorous or arsenic.

142. The method of claim 141, wherein the doping is achieved by implantation at 10¹⁰ to 10¹⁸ ions/cm³.

143. The method of claim 142, wherein the implantation is at 10¹⁴.

144. The method of claim 142, wherein the doping is performed at an energy of 10 to 70 keV.

145. The method of claim 144, wherein the doping is performed at an energy of 20 to 40 keV.

146. A method in accordance with claim 40, wherein the silicon material is etched at a pressure greater than 75 Torr.

147. A method in accordance with claim 146, wherein the silicon material is etched at a pressure greater than 200 Torr.

148. A method in accordance with claim 147, wherein the silicon material is etched at a pressure of 200 Torr to 2 atm.

149. A method in accordance with claim 148, wherein the silicon material is etched at a pressure of 200 Torr to 1 atm.

150. A method in accordance with claim 149, wherein the silicon material is etched at a pressure of 300 to 500 Torr.

151. The method of claim 147, wherein a partial pressure of the vapor phase etchant is 200 Torr or below.

152. The method of claim 151, wherein a partial pressure of the vapor phase etchant is 100 Torr or below.

153. The method of claim 152, wherein a partial pressure of the vapor phase etchant is 50 Torr or below.

154. The method of claim 40, wherein the vapor phase etchant is more than one vapor phase etchants.

155. The method of claim 154, wherein the vapor phase etchants are xenon difluoride and chlorine trifluoride.

156. The method of claim 154, wherein a diluent is provided with the vapor phase etchants.

157. The method of claim 156, wherein the diluent is a diatom.

158. The method of claim 157, wherein the diatom is H2, N2 and/or O2.

159. The method of claim 157, wherein the diatom is a halogen diatom.

160. The method of claim 159, wherein the halogen diatom is Cl2, F2, Br2 and/or I2.