Plasma uniformity control by gas diffuser hole design

• US 20050251990A1
• Filed: 07/12/2004
• Published: 11/17/2005
• Est. Priority Date: 05/12/2004
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Anwar, Suhail, Park, Beom Soo, Kurita, Shinichi, Choi, Soo Young, Won, Tae Kyung, White, John M., Tiner, Robin L., Hou, Li, Wang, Qunhua, Kim, Ki Woon
• Granted Patent: US 8,083,853 B2
• Time in Patent Office: Days
• US Class Current: 29/558
• CPC Class Codes: C23C 16/345 Silicon nitride
• CPC Class Codes: C23C 16/455 characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
• CPC Class Codes: C23C 16/45565 Shower nozzles
• CPC Class Codes: C23C 16/5096 Flat-bed apparatus
• CPC Class Codes: H01J 2237/327 Arrangements for generating the plasma
• CPC Class Codes: H01J 2237/3321 CVD [Chemical Vapor Deposition]
• CPC Class Codes: H01J 2237/3323 uniformity
• CPC Class Codes: H01J 2237/3325 large area
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• CPC Class Codes: H01J 37/32091 the radio frequency energy being capacitively coupled to the plasma
• CPC Class Codes: H01J 37/3244 Gas supply means
• CPC Class Codes: H01J 37/32541 Shape
• CPC Class Codes: H01J 37/32596 Hollow cathodes
• CPC Class Codes: Y10T 29/49885 with coating before or during assembling
• CPC Class Codes: Y10T 29/49996 Successive distinct removal operations

Abstract

Embodiments of a gas diffuser plate for distributing gas in a processing chamber are provided. The gas distribution plate includes a diffuser plate having an upstream side and a downstream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate. The gas passages include hollow cathode cavities at the downstream side to enhance plasma ionization. The depths, the diameters, the surface area and density of hollow cathode cavities of the gas passages that extend to the downstream end can be gradually increased from the center to the edge of the diffuser plate to improve the film thickness and property uniformity across the substrate. The increasing diameters, depths and surface areas from the center to the edge of the diffuser plate can be created by bending the diffuser plate toward downstream side, followed by machining out the convex downstream side. Bending the diffuser plate can be accomplished by a thermal process or a vacuum process. The increasing diameters, depths and surface areas from the center to the edge of the diffuser plate can also be created computer numerically controlled machining. Diffuser plates with gradually increasing diameters, depths and surface areas of the hollow cathode cavities from the center to the edge of the diffuser plate have been shown to produce improved uniformities of film thickness and film properties.

Claims

1. A gas distribution plate assembly for a plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a downstream side; and

inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element and comprising hollow cathode cavities at the downstream side, wherein the hollow cathode cavity volume density of the inner gas passages is less than the hollow cathode cavity volume density of the outer gas passages.

2. The gas distribution plate assembly of claim 1, wherein the hollow cathode cavities are cone or cylinder shaped and the hollow cathode cavity volume density can be increased by increasing the diameters or the lengths or a combination of both of the hollow cathode cavities.

3. The gas distribution plate assembly of claim 2, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

4. The gas distribution plate assembly of claim 2, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch.

5. The gas distribution plate assembly of claim 2, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

6. The gas distribution plate assembly of claim 2, wherein the depths of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

7. The gas distribution plate assembly of claim 2, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

8. The gas distribution plate assembly of claim 2, wherein the flaring angles of the cones are between about 20 degrees to about 40 degrees.

9. The gas distribution plate assembly of claim 2, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

10. The gas distribution plate assembly of claim 9, wherein the flaring angles of the cones are constant.

11. The gas distribution plate assembly of claim 1, wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

12. The gas distribution plate assembly of claim 1, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

13. The gas distribution plate assembly of claim 1, wherein the diffuser plate element is rectangular.

14. The gas distribution plate assembly of claim 13, wherein the diffuser plate element size is at least 1,200,000 mm².

15. The gas distribution plate assembly of claim 2, wherein the diameter or the lengths or a combination of both of the cones or cylinders gradually increases from center to edge of the diffuser plate element.

16. A gas distribution plate assembly for a plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a downstream side; and

inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element and comprising hollow cathode cavities at the downstream side, wherein the hollow cathode cavity surface area density of the inner gas passages is less than the hollow cathode cavity surface area density of the outer gas passages.

17. The gas distribution plate assembly of claim 16, wherein the hollow cathode cavities are cone or cylinder shaped and the hollow cathode cavity surface area density can be increased by increasing the diameters or the lengths or a combination of both of the hollow cathode cavities.

18. The gas distribution plate assembly of claim 17, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

19. The gas distribution plate assembly of claim 17, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch.

20. The gas distribution plate assembly of claim 17, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

21. The gas distribution plate assembly of claim 17, wherein the depths of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

22. The gas distribution plate assembly of claim 17, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

23. The gas distribution plate assembly of claim 17, wherein the flaring angles of the cones are between about 20 degrees to about 40 degrees.

24. The gas distribution plate assembly of claim 17, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

25. The gas distribution plate assembly of claim 24, wherein the flaring angles of the cones are constant.

26. The gas distribution plate assembly of claim 16, wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

27. The gas distribution plate assembly of claim 16, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

28. The gas distribution plate assembly of claim 16, wherein the diffuser plate element is rectangular.

29. The gas distribution plate assembly of claim 28, wherein the diffuser plate element size is at least 1,200,000 mm².

30. The gas distribution plate assembly of claim 16, wherein the diameter or the lengths or a combination of both of the cones or cylinders gradually increases from center to edge of the diffuser plate element.

31. A gas distribution plate assembly for a plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a down stream side; and

a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate element wherein each gas passage has a diffuser hole intersecting the downstream side of the diffuser plate element, wherein the densities of the diffuser holes gradually increase from the center to the edge of the diffuser plate element.

32. The gas distribution plate assembly of claim 31, wherein the densities of the diffuser holes are between about 10% to about 100%.

33. The gas distribution plate assembly of claim 31, wherein the densities of the diffuser holes are between about 30% to about 100%.

34. The gas distribution plate assembly of claim 31, wherein the diffuser holes are cone or cylinder shaped.

35. The gas distribution plate assembly of claim 31, wherein the gas passages are substantially identical.

36. The gas distribution plate assembly of claim 34, wherein the diameters of the cones or cylinders at the downstream ends are between about 0.1 inch to about 1.0 inch.

37. The gas distribution plate assembly of claim 34, wherein the diameters of the cones or cylinders at the downstream ends are between about 0.1 inch to about 0.5 inch.

38. The gas distribution plate assembly of claim 34, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

39. The gas distribution plate assembly of claim 34, wherein the depths of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

40. The gas distribution plate assembly of claim 34, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

41. The gas distribution plate assembly of claim 34, wherein the flaring angles of the cones are between about 20 degrees to about 40 degrees.

42. The gas distribution plate assembly of claim 34, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

43. The gas distribution plate assembly of claim 42, wherein the flaring angles of the cones are constant.

44. The gas distribution plate assembly of claim 31, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

45. The gas distribution plate assembly of claim 31, wherein the diffuser plate element is rectangular.

46. The gas distribution plate assembly of claim 45, wherein the diffuser plate element size is at least 1,200,000 mm².

47. A plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a downstream side;

a RF power source coupled to the diffuser plate element;

inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element and comprising hollow cathode cavities at the downstream side, wherein the hollow cathode cavity volume density of the inner gas passages is less than the hollow cathode cavity volume density of the outer gas passages; and

a substrate support adjacent the downstream side of the diffuser plate element.

48. The plasma processing chamber of claim 47, wherein the hollow cathode cavities are cone or cylinder shaped and the hollow cathode cavity volume density can be increased by increasing the diameters or the lengths or a combination of both of the hollow cathode cavities.

49. The plasma processing chamber of claim 48, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

50. The plasma processing chamber of claim 48, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

51. The plasma processing chamber of claim 48, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

52. The plasma processing chamber of claim 48, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

53. The plasma processing chamber of claim 52, wherein the flaring angles of the cones are constant.

54. The plasma processing chamber of claim 47, wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

55. The plasma processing chamber of claim 47, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

56. The plasma processing chamber of claim 47, wherein the diffuser plate element is rectangular.

57. The plate plasma processing chamber of claim 56, wherein the diffuser plate element size is at least 1,200,000 mm².

58. The plasma processing chamber of claim 48, wherein the diameter or the lengths or a combination of both of the cones or cylinders gradually increases from center to edge of the diffuser plate element.

59. A plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a downstream side;

a RF power source coupled to the diffuser plate element;

inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element and comprising hollow cathode cavities at the downstream side, wherein the hollow cathode cavity surface area density of the inner gas passages is less than the hollow cathode cavity surface area density of the outer gas passages; and

a substrate support adjacent the downstream side of the diffuser plate element.

60. The plasma processing chamber of claim 59, wherein the hollow cathode cavities are cone or cylinder shaped and the hollow cathode cavity surface area density can be increased by increasing the diameters or the lengths or a combination of both of the hollow cathode cavities.

61. The plasma processing chamber of claim 60, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch.

62. The plasma processing chamber of claim 60, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

63. The plasma processing chamber of claim 60, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

64. The plasma processing chamber of claim 60, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

65. The plasma processing chamber of claim 64, wherein the flaring angles of the cones are constant.

66. The plasma processing chamber of claim 59,

wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

67. The plasma processing chamber of claim 69, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

68. The plasma processing chamber of claim 59, wherein the diffuser plate element is rectangular.

69. The plasma processing chamber of claim 68, wherein the diffuser plate element size is at least 1,200,000 mm².

70. The plasma processing chamber of claim 60, wherein the diameter or the lengths or a combination of both of the cones or cylinders gradually increases from center to edge of the diffuser plate element.

71. A plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a down stream side;

a RF power source coupled to the diffuser plate element;

a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate element, wherein surface area densities of hollow cathode cavities of the plurality of gas passages gradually increase from the center to the edge of the diffuser plate element; and

a substrate support adjacent the downstream side of the diffuser plate element.

72. The plasma processing chamber of claim 71, wherein the surface area densities of the hollow cathode cavities of the plurality of gas passages are between about 10% to about 100%.

73. The plasma processing chamber of claim 71, wherein the hollow cathode cavities of the Plurality of gas passages are cone or cylinder shaped.

74. The plasma processing chamber of claim 71, wherein the gas passages are substantially identical.

75. The plasma processing chamber of claim 73, wherein the diameters of the cones or cylinders at the downstream ends are between about 0.1 inch to about 1.0 inch.

76. The plasma processing chamber of claim 73, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

77. The plate plasma processing chamber of claim 73, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

78. The plasma processing chamber of claim 73, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

79. The plasma processing chamber of claim 78, wherein the flaring angles of the cones are constant.

80. The plasma processing chamber of claim 71, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

81. The plasma processing chamber of claim 71, wherein the diffuser plate element is rectangular.

82. The plate plasma processing chamber of claim 81, wherein the diffuser plate element size is at least 1,200,000 mm².

83. A gas distribution plate assembly for a plasma processing chamber, comprising:

a diffuser plate element having an upstream side and a down stream side and the gas diffuser plate are divided into a number of concentric zones; and

a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate element, wherein the gas passages in each zones are identical and the density, the volume, or surface area of hollow cathode cavities of gas passages in each zone gradually increase from the center to the edge of the diffuser plate element.

84. The gas distribution plate assembly of claim 83, wherein the number of concentric zones are at least two.

85. The gas distribution plate assembly of claim 83, wherein the densities of the bores are between about 10% to about 100%.

86. The gas distribution plate assembly of claim 83, wherein the densities of the bores are between about 30% to about 100%.

87. The gas distribution plate assembly of claim 83, wherein the hollow cathode cavities are cone or cylinder shaped.

88. The gas distribution plate assembly of claim 87, wherein the diameters of the cones or cylinders at the downstream ends are between about 0.1 inch to about 1.0 inch.

89. The gas distribution plate assembly of claim 87, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

90. The gas distribution plate assembly of claim 87, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

91. The gas distribution plate assembly of claim 87, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

92. The gas distribution plate assembly of claim 91, wherein the flaring angles of the cones are constant.

93. The gas distribution plate assembly of claim 83, wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

94. The gas distribution plate assembly of claim 83, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

95. The gas distribution plate assembly of claim 83, wherein the diffuser plate element is rectangular.

96. The gas distribution plate assembly of claim 95, wherein the diffuser plate element size is at least 1,200,000 mm².

97. A method of making a gas diffuser plate for a plasma processing chamber, comprising:

making a gas diffuser plate to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate;

bending the diffuser plate to make it convex smoothly toward downstream side; and

machining out the convex surface to flatten the downstream side surface.

98. The method claim 97, wherein making a diffuser plate to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate, comprising:

creating hollow cathode cavities that have same dimensions across the entire diffuser plate.

99. The method of claim 98, wherein the hollow cathode cavities are cone or cylinder shaped.

100. The method of claim 97, wherein making a diffuser plate to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate, comprising:

creating hollow cathode cavities that have gradually increasing volumes from center to edge of the diffuser plate.

101. The method claim 100, wherein the hollow cathode cavities are cone or cylinder shaped.

102. The method of claim 101, wherein the volumes of hollow cathode cavities can be increased by increasing the diameter and/or depths of the cones or cylinders.

103. The method of claim 102, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch, the depths of the cones or cylinders are between 0.1 inch to about 1.0 inch and the flaring angles of the cones are between about 10 degree to about 50 degrees.

104. The method of claim 103, wherein the flaring angles of the cones are constant.

105. The method of claim 97, wherein bending the diffusing plate to make it convex smoothly toward downstream side, comprising

placing the diffuser plate in a controlled thermal environment that supports the diffuser plate only at the edge;

treating the diffuser plate under thermal condition at a temperature that the differ plate softens; and

stopping the thermal treatment process when the curvature of the diffuser plate reaches a pre-determined value.

106. The method of claim 105, wherein the temperature is greater than 400°

C.

107. The method of claim 105, wherein the diffuser plate was treated under iso-thermal condition once the treatment temperature has been reached.

108. The method of claim 97, wherein bending the diffusing plate to make it convex smoothly toward downstream side, comprising:

placing the diffuser plate on a vacuum assembly that supports the diffuser plate only at the edge;

pulling vacuum in the volume between the diffuser plate and the bottom plate of the vacuum assembly; and

stopping vacuum pulling and restore the pressure in the volume between the diffuser plate and the bottom plate of the vacuum assembly to be equal to the surrounding environment.

109. A method of making a gas diffuser plate element for a plasma processing chamber, comprising:

machining a gas diffuser plate element to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate element, wherein densities, volumes or surface area of hollow cathode cavities of the diffuser plate element gradually increase from the center to the edge of the diffuser plate element.

110. The method of claim 109, wherein the machining is accomplished either by computer numerically controlled machining or by manually controlled machining.

111. The method of claim 109, wherein the hollow cathode cavities are cone or cylinder shaped.

112. The method of claim 111, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch, the depths of the cones or cylinders are between 0.1 inch to about 1.0 inch and the flaring angles of the cones are between about 10 degree to about 50 degrees.

113. The method of claim 112, wherein the flaring angles of the cones are constant.

114. A method of making a gas diffuser plate element for a plasma processing chamber, comprising:

machining a gas diffuser plate element to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate element, wherein the densities and volumes or densities and surface areas of hollow cathode cavities of the diffuser plate element gradually increase from the center to the edge of the diffuser plate element.

115. The method of claim 114, wherein the machining is accomplished either by computer numerically controlled machining or by manually controlled machining.

116. The method of claim 114, wherein the hollow cathode cavities are cone or cylinder shaped.

117. The method of claim 116, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch, the depths of the cones or cylinders are between 0.1 inch to about 1.0 inch and the flaring angles of the cones are between about 10 degree to about 50 degrees.

118. The method of claim 117, wherein the flaring angles of the cones are constant.

119. A method of depositing a thin film on a substrate, comprising:

placing a substrate in a process chamber with a gas diffuser plate element having an upstream side and inner and outer gas passages passing between the upstream and downstream sides of the diffuser plate element and comprising hollow cathode cavities at the downstream side, wherein either the hollow cathode cavity volume density, or the hollow cathode cavity surface area density, or the hollow cathode cavity density of the inner gas passages are less than the same parameter of the outer gas passages;

flowing process gas(es) through the diffuser plate element toward a substrate supported on a substrate support;

creating a plasma between the diffuser plate element and the substrate support; and

depositing a thin film on the substrate in the process chamber.

120. The method of claim 119, wherein the densities of the hollow cathode cavities are between about 10% to about 100%.

121. The method of claim 119, wherein the hollow cathode cavities are cone or cylinder shaped.

122. The method of claim 121, wherein the diameters of the cones or cylinders at the downstream ends are between about 0.1 inch to about 1.0 inch.

123. The method of claim 121, wherein the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch.

124. The method of claim 121, wherein the flaring angles of the cones are between about 10 degrees to about 50 degrees.

125. The method of claim 121, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 1.0 inch, the depths of the cones or cylinders are between about 0.1 inch to about 2.0 inch, and the flaring angles of the cones are between about 10 degrees to about 50 degrees.

126. The method of claim 125, wherein the flaring angles of the cones are constant.

127. The method of claim 119, wherein a spacing between the downstream ends of the hollow cathode cavities of adjacent gas passages is at most about 0.6 inch.

128. The method of claim 119, wherein the thickness of the diffuser plate element is between about 0.8 inch to about 3.0 inch.

129. The method of claim 119, wherein the diffuser plate element is rectangular.

130. The method of claim 129, wherein the diffuser plate element size is at least 1,200,000 mm².

131. The method of claim 129, wherein the process chamber is a plasma enhanced chemical vapor deposition chamber.

132. The method of claim 129, wherein the thin film is deposited on the substrate to create flat panel displays.

133. The method of claim 129, wherein the thin film thickness and property uniformity can be modified by adjusting the diameters and the depths of the hollow cathode cavities across the diffuser plate element.

134. The method of claim 129, wherein the thin film thickness and property uniformity can be modified by the surface areas of the hollow cathode cavities across the diffuser plate element.

135. The method of claim 129, wherein the thin film can be silicon dioxide (SiO₂), silicon oxynitride (SiON), silicon nitride (SiN), amorphous silicon (α

-Si) or doped amorphous silicon (doped α

-Si).

136. A diffuser plate, comprising:

a body having a top surface and a bottom surface;

a plurality of gas passages between the top surface the bottom surface; and

an outer region and an inner region wherein the body between the top and the bottom of the outer region is thicker than the body between the top and the bottom of the inner region.

137. The plate of claim 136, wherein the top surface is substantially flat and the bottom surface is concave.

138. The plate of claim 136, wherein the top surface is concave and the bottom surface is substantially flat.

139. A method of making a gas diffuser plate for a plasma processing chamber, comprising:

making a gas diffuser plate to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate; and

machining the downstream surface to make the downstream surface concave.

140. The method claim 139, wherein making a diffuser plate to have an upstream side and a down stream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate, comprising:

creating hollow cathode cavities that have same sizes across the entire diffuser plate.

141. The method of claim 140, wherein the hollow cathode cavities are cone or cylinder shaped.

142. The method of claim 139, wherein the machining is accomplished either by computer numerically controlled machining or by manually controlled machining.

143. The method of claim 141, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch, the depths of the cones or cylinders are between 0.1 inch to about 1.0 inch and the flaring angles of the cones are between about 10 degree to about 50 degrees.

144. The method of claim 143, wherein the flaring angles of the cones are constant.

145. The method of claim 139 further comprising:

bending the diffuser plate to make the downstream surface substantially flat.

146. A method of making a gas diffuser plate for a plasma processing chamber, comprising:

bending a diffuser plate that has an upstream side and a down stream side to make the downstream surface concave and the upstream surface convex;

making a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate by making hollow cathode cavities to the same depth from a fictitious flat downstream surface; and

making all gas passages to have the same-size orifice holes which are connected to the hollow cathode cavities.

147. The method claim 146, wherein the hollow cathode cavities have same sizes and shapes from the fictitious flat downstream surface across the entire diffuser plate.

148. The method of claim 147, wherein the hollow cathode cavities are cone or cylinder shaped.

149. The method of claim 148, wherein the diameters of the cones or cylinders are between about 0.1 inch to about 0.5 inch, the depths of the cones or cylinders are between 0.1 inch to about 1.0 inch and the flaring angles of the cones are between about 10 degree to about 50 degrees.

150. The method of claim 149, wherein the flaring angles of the cones are constant.

151. The method of claim 146 further comprising:

bending the diffuser plate to make the downstream surface substantially flat.