Plasma immersion ion implantation reactor having an ion shower grid

• US 20060019477A1
• Filed: 07/20/2004
• Published: 01/26/2006
• Est. Priority Date: 07/20/2004
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Tanaka, Tsutomu, Ramaswamy, Kartik, Hanawa, Hiroji, Collins, Kenneth S., Nguyen, Andrew, Al-Bayati, Amir
• Granted Patent: US 7,767,561 B2
• Time in Patent Office: Days
• US Class Current: 438/514
• CPC Class Codes: C23C 14/48 Ion implantation
• CPC Class Codes: H01J 37/32357 Generation remote from the workpiece, e.g. down-stream
• CPC Class Codes: H01J 37/32412 Plasma immersion ion implantation
• CPC Class Codes: H01L 21/02164 the material being a silicon oxide, e.g. SiO2
• CPC Class Codes: H01L 21/02266 deposition by physical ablation of a target, e.g. sputtering, reactive sputtering, physical vapour deposition or pulsed laser deposition
• CPC Class Codes: H01L 21/02274 in the presence of a plasma [PECVD]
• CPC Class Codes: H01L 21/2236 from or into a plasma phase
• CPC Class Codes: H01L 21/31612 on a silicon body

Abstract

A plasma immersion ion implantation process for implanting a selected species at a desired ion implantation depth profile in a workpiece is carried out in a reactor chamber with an ion shower grid that divides the chamber into an upper ion generation region and a lower process region, the ion shower grid having plural elongate orifices oriented in a non-parallel direction relative to a surface plane of the ion shower grid. The process includes placing a workpiece in the process region, the workpiece having a workpiece surface generally facing the surface plane of the ion shower grid, and furnishing the selected species into the ion generation region in gaseous, molecular or atomic form and evacuating the process region at an evacuation rate sufficient to create a pressure drop across the ion shower grid from the ion generation region to the process region of about a factor of at least four. The process further includes applying plasma source power to generate a plasma of the selected species in the ion generation region, and applying a grid potential to the ion shower grid to create a flux of ions from the plasma through the grid and into the process region. The process also includes applying a sufficient bias voltage to at least one of: (a) the workpiece, (b) the grid, relative to at least one of: (a) the workpiece, (b) a plasma in the ion generation region, (c) a surface of the chamber, to accelerate the flux of ions to a kinetic energy distribution generally corresponding to the desired ion implantation depth profile in the workpiece.

Claims

1. A plasma immersion ion implantation process for implanting a selected species at a desired ion implantation depth profile in a workpiece, comprising:

providing a reactor chamber with an ion shower grid that divides said chamber into an upper ion generation region and a lower process region, said ion shower grid having plural elongate orifices oriented in a non-parallel direction relative to a surface plane of said ion shower grid;

placing a workpiece in said process region;

furnishing said selected species into said ion generation region;

evacuating said process region;

applying plasma source power to generate a plasma of said selected species in said ion generation region, and applying a grid potential to said ion shower grid to create a flux of ions from the plasma through said grid and into said process region; and

applying a bias voltage to said workpiece.

2. The process of claim 1 wherein the step of evacuating is carried out at an evacuation rate sufficient to maintain an ion-neutral mean collision distance in said process region in excess of a multiple of a distance between said workpiece and said ion shower grid.

3. The process of claim 1 wherein the steps of (a) applying plasma source power and (b) applying a grid potential are comprised in a single step of applying a potential between said ion shower grid and said ion generation region.

4. The process of claim 3 wherein the step of applying a grid potential between said grid and said ion generation region comprises applying a potential between said grid and a wall of said ion generation region.

5. The process of claim 4 wherein said grid potential is at least one of:

(a) a pulsed D.C. potential, (b) an RF potential, (c) a D.C. potential, (d) a pulsed RF potential.

6. The process of claim 1 further comprising controlling the temperature of said ion shower grid.

7. The process of claim 6 wherein the step of controlling the temperature of said ion shower grid comprises pumping a thermal transfer fluid through fluid flow passages thermally coupled to said ion shower grid and controlling the temperature of said thermal transfer fluid.

8. The process of claim 1 further comprising providing neutralization electrons in the vicinity of said workpiece.

9. The process of claim 8 wherein the step of providing neutralization electrons comprises establishing a magnetic field near said workpiece having sufficient magnetic flux to trap electrons near said workpiece surface.

10. The process of claim 8 wherein the of providing neutralization electrons comprises generating a flow of electrons from an electron gun toward said workpiece surface.

11. The process of claim 8 wherein the step of providing neutralization electrons comprises injecting an electron-donor gas into said process region and near said workpiece.

12. The process of claim 8 wherein the step of providing neutralization electrons comprises providing a plasma in said process region.

13. The process of claim 1 wherein the step of applying plasma source power comprises capacitively coupling plasma source power into said ion generation region and the step of applying a grid potential comprises applying a grid potential between said plasma and said ion shower grid.

14. The process of claim 13 wherein the step of capacitively coupling plasma source power comprises applying RF power from an RF generator between a ceiling of said reactor and one of (a) said grid, (b) a side wall of said reactor.

15. The process of claim 14 wherein the step of applying a grid potential between said plasma and said ion shower grid comprises applying a potential from a grid potential source between a chamber surface of said ion generation region and said ion shower grid.

16. The process of claim 15 wherein said bias voltage is such that said plasma, said grid and said workpiece have successively greater attractive potentials for ions.

17. The process of claim 13 wherein said plasma source power comprises RF power and said grid potential comprises at least one of:

(a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage (d) a pulsed RF voltage.

18. The process of claim 17 wherein said grid potential comprises a mixture of at least two of (a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

19. The process of claim 1 wherein the step of applying plasma source power comprises inductively coupling plasma source power into said ion generation region and the step of applying said grid potential comprises applying a grid potential between said plasma and said ion shower grid.

20. The process of claim 19 wherein the step of applying a grid potential between said plasma and said ion shower grid comprises applying a potential from a grid potential source between a chamber surface of said ion generation region and said ion shower grid.

21. The process of claim 19 wherein said bias voltage is such that said plasma, said grid and said workpiece have successively greater attractive potentials for ions.

22. The process of claim 19 wherein said plasma source power comprises RF power and said grid potential comprises at least one of:

(a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

23. The process of claim 16 wherein said grid potential comprises a mixture of at least two of (a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

24. The process of claim 1 wherein the step of applying plasma source power comprises coupling microwave plasma source power into said ion generation region and the step of applying said grid potential comprises applying a grid potential between said plasma and said ion shower grid.

25. The process of claim 24 wherein the step of applying a grid potential between said plasma and said ion shower grid comprises applying a potential from a grid potential source between a chamber surface of said ion generation region and said ion shower grid.

26. The process of claim 24 wherein said bias voltage is such that said plasma, said grid and said workpiece have successively greater attractive potentials for ions.

27. The process of claim 24 wherein said grid potential comprises at least one of:

(a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

28. The process of claim 27 wherein said grid potential comprises a mixture of at least two of (a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

29. The process of claim 1 wherein the step of applying plasma source power comprises generating a torroidal plasma current in said ion generation region through an external reentrant conduit coupled across said ion generation region, and the step of applying said grid potential comprises applying a grid potential between said plasma and said ion shower grid.

30. The process of claim 29 wherein the step of applying a grid potential between said plasma and said ion shower grid comprises applying a potential from a grid potential source between a chamber surface of said ion generation region and said ion shower grid.

31. The process of claim 29 wherein said bias voltage is such that said grid and said workpiece have successively greater attractive potentials for ions.

32. The process of claim 29 wherein said plasma source power comprises RF power and said grid potential comprises at least one of:

(a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

33. The process of claim 32 wherein said grid potential comprises a mixture of at least two of (a) a pulsed D.C. voltage, (b) an RF voltage, (c) a D.C. voltage, (d) a pulsed RF voltage.

following steps carried out prior to the step of placing a workpiece in said process region:

depositing a layer of a process-compatible material on reactor chamber interior surfaces.

38. The process of claim 1 wherein the step of applying bias voltage to said workpiece comprises applying an RF bias voltage, said process further comprising:

adjusting ion energy at said workpiece surface by adjusting the frequency of said RF bias voltage.

39. The process of claim 1 wherein the step of applying a grid potential comprises holding the potential of said plasma at a reference potential and applying a negative voltage to said ion shower grid relative to said reference potential.

40. The process of claim 39 wherein said reference potential is ground.

41. The process of claim 16 wherein the step of applying a grid potential and the step of applying a bias voltage comprise holding said plasma at a reference potential and applying successively greater negative voltages to said ion shower grid and to said workpiece, respectively, relative to said reference potential.

42. The process of claim 41 wherein said reference potential is ground.

43. The method of claim 1 wherein said bias voltage comprises an RF bias voltage having a bias frequency that is sufficiently low for ions in a plasma sheath near said workpiece to follow electric field oscillations across said sheath at said bias frequency and that is sufficiently high so that RF voltage drops across dielectric layers on said workpiece do not exceed a predetermined fraction of the RF bias voltage applied to said workpiece support.

44. The method of claim 1 wherein said bias voltage has a bias frequency between 10 kHz and 10 MHz.

45. The method of claim 1 wherein said bias voltage has a bias frequency between 50 kHz and 5 MHz.

46. The method of claim 1 wherein said bias power or volotage has a bias frequency between 100 kHz and 3 MHz.

47. The method of claim 1 wherein said bias voltage has a bias frequency of about 2 MHz to within about 5%.

48. The method of claim 1 wherein said workpiece comprises a semiconductor material, and said selected species is a dopant impurity that promotes one of a p-type or n-type conductivity in said semiconductor material, and wherein said desired depth profile corresponds to a desired p-n junction depth, whereby said bias voltage affects said junction depth.

49. The method of claim 48 wherein said selected species comprises a chemical combination of said dopant impurity and another element.

50. The method of claim 49 wherein said selected species comprises a fluoride of said dopant impurity.

51. The method of claim 49 wherein said selected species comprises a hydride of said dopant impurity.

52. The method of claim 49 wherein said selected species further comprises a co-implant ion bombardment element which removes from a top surface of said workpiece a material that tends to accumulate during implantation of said dopant impurity.

53. The method of claim 1 wherein said workpiece comprises a semiconductor crystal which is to be implanted with a dopant impurity element, and wherein said selected species comprises a pre-implant ion bombardment species that creates damage in said semiconductor crystal.

54. The method of claim 1 wherein said workpiece comprises a dielectric thin film, and wherein said selected species comprises a surface-enhancement species which enhances a characteristic of said dielectric thin film layer upon implantation and substitution.

55. The method of claim 54 wherein said characteristic is the electrical behavior of said dielectric thin film.

56. The method of claim 54 wherein said dielectric thin film comprises an oxide of a semiconductor element, and said selected species comprises a non-oxygen element to be substituted for oxygen atoms in said dielectric thin film.

57. The method of claim 1 wherein the step of furnishing said selected species is preceded by:

introducing a passivation gas containing a passivation layer-forming species;

generating from said passivation gas a plasma;

attracting passivation layer-forming species from said plasma to said workpiece by applying bias voltage to said workpiece support, to form a passivation layer on said workpiece.

58. The method of claim 57 wherein said passivation gas comprises one of:

(a) a hydride, (b) a fluoride, (c) an oxide of a semiconductor element.

59. The method of claim 1 wherein the step of placing said workpiece on said workpiece support is preceded by:

introducing a passivation process gas containing passivation-forming chemical species;

generating from said passivation gas a plasma;

attracting passivation layer-forming species from said plasma to interior surfaces of said reactor chamber, to form a passivation layer on said interior surfaces.

60. The method of claim 59 wherein said passivation gas comprises one of a hydride, a fluoride or an oxide of a semiconductor element.

61. The method of claim 59 wherein said passivation gas comprises a chemical species containing carbon and fluorine.

62. The method of claim 59 wherein the step of generating a plasma from said passivation gas is followed by:

removing said workpiece from said reactor chamber;

introducing a passivation layer-removing gas into said chamber;

generating a plasma from said passivation layer-removing gas, so as to remove said passivation layer from said interior surfaces of said chamber.

63. The method of claim 62 further comprising heating said interior surfaces of said reactor chamber during the removal of said passivation layer.

64. The method of claim 63 wherein said passivation layer-removing gas comprises a fluorine-containing gas.

65. The method of claim 1 wherein the step of generating a plasma is followed by:

heating said workpiece to a temperature sufficiently high to cause atoms of said selected species implanted in said workpiece to be substituted into atomic sites in a crystal lattice of said workpiece.

66. The method of claim 65 wherein said workpiece is masked by a photolithographic layer defining a pattern of ion implantation, and wherein the step of heating said surface is preceded by:

removing said photolithographic layer.

67. The method of claim 66 wherein the step of removing said photolithographic layer is carried out in a pyrolization chamber.

68. The method of claim 65 wherein the step of heating said workpiece is carried out after removing said workpiece from said reactor chamber and placing it in an anneal chamber.

69. The method of claim 52 wherein said selected species is a hydride of said dopant species and said ion bombardment element comprises one of Helium, Hydrogen, a fluoride of a semiconductor element, or SiF4.

70. The method of claim 62 wherein said passivation layer-removing gas comprises NF3.

71. The method of claim 48 wherein said semiconductor material is silicon and said dopant impurity is boron.

72. The method of claim 48 wherein said semiconductor element is silicon and said dopant impurity is phosphorus.

73. The method of claim 48 wherein said semiconductor element comprises one of silicon or germanium.

74. The method of claim 1 wherein:

said workpiece comprises plural dielectric gates formed over an underlying layer having horizontal and non-horizontal surfaces;

the step of applying bias voltage comprises selecting a level of said bias voltage promotive of a sufficiently collisional plasma sheath over said workpiece to produce a significant fraction of ions impacting said workpiece at trajectories other than orthogonal to said workpiece whereby to implant ions in said horizontal and non-horizontal surfaces of said workpiece.

75. The method of claim 48 wherein said workpiece comprises a crystal lattice and wherein the step of generating a plasma is preceded by:

introducing into said chamber an amorphizing gas comprising an ion bombardment species;

generating a plasma from said amorphizing gas;

applying bias voltage to said workpiece support to attract ions of said ion bombardment species toward said workpiece whereby said ions cause damage in said crystal lattice.

76. The method of claim 75 wherein said ion bombardment species comprises a semiconductive species.

77. The method of claim 76 wherein said ion bombardment species comprises one of silicon or germanium.

78. The method of claim 49 wherein said selected species further comprises an ion bombardment species for co-implantation with said dopant impurity in said workpiece.

79. The method of claim 78 wherein ions of said ion bombardment species are implanted in said workpiece to cause crystal lattice damage for amorphizing said workpiece during implantation of said dopant impurity in said workpiece.

80. The method of claim 79 wherein said ion bombardment species comprises a semiconductor species.

81. The method of claim 80 wherein said semiconductor species comprises one of silicon or germanium.

82. The method of claim 1 further comprising pulse modulating said bias voltage.

83. The method of claim 82 further comprising pulse modulating said source power.

84. The method of claim 83 further comprising maintaining a relation between the pulse modulating of said bias voltage and the pulse modulating of said source power that is one of:

(a) push-pull;

(b) in-synchronism;

(c) symmetrical;

(d) non-symmetrical.

85. The method of claim 1 wherein the step of applying said bias voltage comprises applying a single burst of said bias voltage to said workpiece.

86. The method of claim 85 wherein said single burst has a duration corresponding to a desired implant dosage.

87. The method of claim 1 further comprising distributing ion flux across said workpiece by translating said grid and said workpiece relative to one another in a direction parallel to the plane of said workpiece.

88. The process of claim 1 further comprising the following steps carried out after the implanting of said selected species at said desired depth:

removing said workpiece from said chamber;

cleaning the reactor chamber interior surfaces.

89. The process of claim 88 wherein the step of cleaning the reactor interior chamber surfaces comprises:

introducing a process gas comprising an etchant species into said ion generation region;

applying plasma source power into said ion generation region and applying an ion extraction potential to said grid.

90. The process of claim 88 wherein the step of cleaning the reactor interior surfaces comprises:

furnishing into at least one of said ion generation and process regions ions or radicals of an etchant species.

91. The process of claim 1 wherein the step of furnishing said selected species comprises injecting a process gas containing said selected species into said ion generation region.

92. The process of claim 1 wherein the step of furnishing said selected species comprises:

providing a sputter target of a material comprising said selected species;

sputtering said sputter target.

93. The process of claim 92 wherein said selected species is one of (a) molecular, (b) atomic.

94. The process of claim 91 wherein said process gas comprises one of:

(a) a gaseous metal compound;

(b) a metal organic compound.

95. The process of claim 92 wherein said target comprises one of:

(a) a metal;

(b) a dielectric;

(c) a semiconductor.

96. The process of claim 1 wherein the step of furnishing said selected species comprises producing a metal vapor in said ion generation region.

35. The process of claim 34 wherein the step of depositing a layer of a process-compatible material comprises:

introducing a process gas comprising a precursor of said process-compatible material into said ion generation region;

applying plasma source power into said ion generation region.

36. The process of claim 35 further comprising applying an ion extraction potential to said grid.

37. The process of claim 34 wherein the step of depositing a layer of a process-compatible material comprises furnishing into at least one of said ion generation and process regions ions or radicals of said process-compatible material from a plasma source external of said chamber.

97. A plasma immersion ion implantation process for implanting a selected species at a desired ion implantation depth profile in a workpiece, comprising:

providing a reactor chamber with an ion shower grid that divides said chamber into an upper ion generation region and a lower process region, said ion shower grid having plural elongate orifices oriented in a non-parallel direction relative to a surface plane of said ion shower grid;

placing a workpiece in said process region, said workpiece having a workpiece surface generally facing the surface plane of said ion shower grid;

furnishing a said selected species into said ion generation region in gaseous, molecular or atomic form;

evacuating said process region at an evacuation rate sufficient to create a pressure drop across said ion shower grid from said ion generation region to said process region of about a factor of at least four;

applying plasma source power to generate a plasma of said selected species in said ion generation region, and applying a grid potential to said ion shower grid relative to at least one of (a) said workpiece, (b) a plasma in said ion generation region, (c) a surface of said chamber, to create a flux of ions from the plasma through said grid and into said process region with a kinetic energy distribution generally corresponding to said desired ion implantation depth profile in said workpiece.

98. The process of claim 97 wherein said evacuation rate is sufficient to maintain an ion-neutral mean collision distance in said process region in excess of a multiple of a distance between said workpiece and said ion shower grid.