RF measurement feedback control and diagnostics for a plasma immersion ion implantation reactor

• US 20060088655A1
• Filed: 10/23/2004
• Published: 04/27/2006
• Est. Priority Date: 10/23/2004
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Ramaswamy, Kartik, Hanawa, Hiroji, Collins, Kenneth S., Nguyen, Andrew, Al-Bayati, Amir, Gallo, Biagio
• Granted Patent: US 7,666,464 B2
• Time in Patent Office: Days
• US Class Current: 427/8
• CPC Class Codes: C23C 14/48 Ion implantation
• CPC Class Codes: C23C 14/54 Controlling or regulating the coating process
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32412 Plasma immersion ion implantation
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A method of measuring ion dose in a plasma immersion ion implantation reactor during ion implantation of a selected species into a workpiece includes placing the workpiece on a pedestal in the reactor and feeding into the reactor a process gas comprising a species to be implanted into the workpiece, and then coupling RF plasma source power to a plasma in the reactor. It further includes coupling RF bias power to the workpiece by an RF bias power generator that is coupled to the workpiece through a bias feedpoint of the reactor and measuring RF current at the feedpoint to generate a current-related value, and then integrating the current-related over time to produce an ion implantation dose-related value.

Claims

1. A method of measuring an ion dose-related quantity in a plasma immersion ion implantation reactor during ion implantation of a selected species into a workpiece, comprising:

placing said workpiece on a pedestal in said reactor and feeding into said reactor a process gas comprising a species to be implanted into said workpiece;

coupling RF plasma source power to a plasma in said reactor;

coupling RF bias power to said workpiece by an RF bias power generator that is coupled to said workpiece through a bias feedpoint of said reactor;

measuring RF current at a measurement point at or displaced from said feedpoint to generate a current-related quantity; and

computing the ion dose-related quantity from said current-related.

2. The method of claim 1 wherein said ion dose-related quantity is the ion dose, and wherein the step of computing the ion dose-related quantity comprises integrating said current-related quantity over time to produce the ion dose-related quantity.

3. The method of claim 1 wherein said ion dose-related quantity is ion dose rate, and wherein the step of computing the ion dose-related quantity comprises treating said current-related quantity as being proportional to the dose rate.

4. The method of claim 1 further comprising:

dividing by the area of said workpiece and by the charge of a single ion of a plasma in said reactor one of;

(a) said current-related value,

(b) said ion dose-related value.

5. The method of claim 1 further comprising multiplying, by an ion efficiency factor corresponding to the proportion of said selected species relative to the total ions implanted into said workpiece, one of:

(a) said current-related value,

(b) said dose-related value.

6. The method of claim 5 further comprising determining said ion efficiency factor by the following steps:

sensing present values of a predetermined set of process parameters;

applying said present values to corresponding inputs of a look-up table; and

obtaining from said look-up table said ion efficiency factor.

7. The method of claim 6 further comprising constructing said look-up table prior to the step of placing said workpiece in said reactor, said constructing comprising:

ion implanting plural test workpieces in said reactor under different process conditions corresponding to different values of said predetermined set of process parameters;

testing each of said test workpieces to determine an ion efficiency factor for each of said test workpieces; and

correlating in said look-up table each measured ion dose to the corresponding set of values of said set of process parameters.

8. The method of claim 7 wherein the step of testing comprises:

measuring volume density of said selected species in said workpiece as a function of depth in said workpiece and forming a density versus depth distribution; and

integrating said density versus depth distribution over depth to produce an area density of said selected species.

9. The method of claim 7 wherein:

at least some of said present values of said process parameters lie between respective ones of the sets of process parameter values contained in said look-up table; and

the step of obtaining said efficiency factor comprises interpolating between corresponding efficiency factors stored in said look-up table.

10. The method of claim 6 wherein said predetermined set of process parameters comprise at least one of:

plasma source power level, RF bias voltage on the workpiece, RF bias current on the workpiece, chamber pressure, atomic weight of the selected species, flow rate of the process gas.

11. The method of claim 1 wherein the step of integrating is preceded by transforming said RF current from said measurement point to a location at least near said workpiece by a measurement point-to-workpiece transform.

12. The method of claim 11 further comprising determining said measurement point-to-workpiece transform prior to placing said workpiece in said reactor by the following steps:

measuring a complex open circuit input impedance-related quantity at said measurement point;

measuring a complex short circuit input impedance-related quantity at said measurement point; and

computing said measurement point-to-workpiece transform from a combination of said open circuit input impedance-related quantity and said short circuit input impedance-related quantity.

13. The method of claim 12 wherein said open circuit impedance related quantity is one of:

a. open circuit impedance;

b. open circuit admittance;

c. open circuit current, open circuit voltage and open circuit phase.

14. The method of claim 12 wherein said closed circuit impedance related quantity is one of:

a. closed circuit impedance;

b. closed circuit admittance;

c. closed circuit current, open circuit voltage and open circuit phase.

15. The method of claim 12 wherein the step of transforming comprises:

obtaining a plurality of frequency components comprising the fundamental and plural harmonics of the current and a voltage measured at the measurement point;

combining said plurality of frequency components with said transform to obtain a frequency domain version of the current at the workpiece; and

transforming the frequency domain version of the current into a time domain waveform of the current at the workpiece.

16. The method of claim 1 further comprising:

coupling RF source power at a selected source power level to plasma in a process zone of said reactor over said workpiece;

comparing said current-related value with a target dose rate value and generating a dose rate error value; and

changing said selected source power level by an amount that is a function of said dose rate error value.

17. The method of claim 1 wherein:

the step of controlling the source power comprises halting the ion implantation of said workpiece when said dose-related value reaches said target dose-related value.

18. The method of claim 1 further wherein the ion dose-related quantity is dose rate, said method further comprising:

issuing an alarm at a user interface if said dose rate exceeds a dose-rate limit value.

19. The method of claim 1 wherein the step of entering the dose-related quantity into a monitoring system comprises:

comparing the dose-related quantity with a related target quantity; and

displaying the results of said comparing at a user interface.

20. The method of claim 1 further comprising:

measuring RF voltage at said measurement point.

21. The method of claim 20 further comprising measuring ion energy of said selected species from said RF voltage.

22. The method of claim 21 wherein the step of determining the ion energy comprises determining a characteristic parameter of said RF voltage.

23. The method of claim 22 wherein said characteristic parameter of said RF voltage comprises one of:

A. a time average of said RF voltage;

B. a peak value of said RF voltage;

C. a peak-to-peak value of said RF voltage;

D. an RMS value of said RF voltage.

24. The method of claim 22 further comprising multiplying said characteristic parameter by the charge of an ion of said selected species in the plasma in said reactor.

25. The method of claim 22 further comprising:

comparing said ion energy with a target ion energy value to determine an ion energy error; and

adjusting the power level of said RF bias power by an amount that is a function of said ion energy error.

26. The method of claim 22 further comprising:

comparing said ion energy with a target ion energy value to determine an ion energy error; and

rendering a display at a user interface relating to said ion energy error.

27. The method of claim 20 further comprising:

transforming said RF voltage from said measurement point to a location at least near said workpiece by a measurement point-to-workpiece transform.

28. The method of claim 27 further comprising determining said measurement point-to-workpiece transform prior to placing said workpiece in said reactor by the following steps:

measuring a complex open circuit input impedance-related quantity at said measurement point;

measuring a complex short circuit input impedance-related quantity at said measurement point; and

computing said measurement point-to-workpiece transform from a combination of said open circuit input impedance-related quantity and said short circuit input impedance-related quantity.

29. The method of claim 28 wherein said open circuit input impedance-related quantity comprises one of:

an open circuit input impedance;

an open circuit input admittance;

an open circuit current voltage and phase.

30. The method of claim 28 wherein said closed circuit input impedance-related quantity comprises one of:

a closed circuit input impedance;

a closed circuit input admittance;

a closed circuit current voltage and phase.

31. The method of claim 28 wherein the step of transforming comprises:

obtaining a plurality of frequency components comprising the fundamental and plural harmonics of the voltage and a current measured at the measurement point;

combining said plurality of frequency components with said transform to obtain a frequency domain version of the voltage at the workpiece; and

transforming the frequency domain version of the voltage into a time domain waveform of the voltage at the workpiece.

32. The method of claim 20 further comprising:

holding said workpiece on said pedestal by applying a D.C. chucking voltage to a buried electrode in said pedestal;

determining from said RF voltage a D.C. workpiece voltage; and

determining a net clamping voltage from said D.C. workpiece voltage and said D.C. chucking voltage.

33. The method of claim 32 wherein the step of determining the workpiece D.C. voltage comprises determining a time average of said RF voltage.

34. The method of claim 32 further comprising:

comparing said net clamping voltage with a target value to determine a clamping voltage error; and

adjusting said D.C. chucking voltage in accordance with said clamping voltage error.

35. The method of claim 32 further comprising:

sensing a temperature of said workpiece;

comparing said temperature with a target temperature to determine a temperature error; and

adjusting said D.C. chucking voltage by an amount tending to result in a reduction in said temperature error.

36. The method of claim 35 further comprising comparing said net clamping voltage with a clamping voltage target range and rendering a user display in accordance with the comparing of said net clamping voltage and said clamping voltage target range.

37. The method of claim 32 further comprising, prior to the step of determining the D.C. workpiece voltage:

transforming said RF voltage from said measurement point to a location at least near said workpiece by a measurement point-to-workpiece transformation.

38. The method of claim 37 further comprising determining said measurement point-to-workpiece transformation prior to placing said workpiece in said reactor by the following steps:

measuring a complex open circuit input impedance-related quantity at said measurement point;

measuring a complex short circuit input impedance-related quantity at said measurement point; and

computing said measurement point-to-workpiece transform from a combination of said open circuit input impedance-related quantity and said short circuit input impedance-related quantity.

39. The method of claim 38 wherein said open circuit input impedance-related quantity comprises one of:

an open circuit input impedance;

an open circuit input admittance;

an open circuit current voltage and phase.

40. The method of claim 38 wherein said closed circuit input impedance-related quantity comprises one of:

a closed circuit input impedance;

a closed circuit input admittance;

a closed circuit current voltage and phase.

41. The method of claim 1 wherein the step of measuring said RF current comprises sensing the current measurement output of an RF probe connected at a measurement point at or displaced from said feedpoint, said method further comprising obtaining a calibration factor for said RF current by performing the following steps prior to placing said workpiece on said pedestal:

coupling said RF probe between said RF bias power generator and a dummy resistance;

comparing the current measurement output of said RF probe with the square root of the quotient of a known power output of said RF bias power generator divided by the resistance value of said dummy resistance to determine the calibration factor of said current measurement; and

after the step of measuring the RF current, multiplying said current related value by said calibration factor.

42. The method of claim 20 wherein the step of measuring said RF voltage comprises sensing the voltage measurement output of an RF probe connected at a measurement point at or displaced from said feedpoint, said method further comprising obtaining a calibration factor for said RF voltage by performing the following steps prior to placing said workpiece on said pedestal:

coupling said RF probe between said RF bias power generator and a dummy resistance;

comparing the voltage measurement output of said RF probe with the square root of the product of a known power output of said RF bias power generator multiplied by the resistance value of said dummy resistance, to determine the calibration factor of said voltage measurement; and

after the step of measuring the RF voltage, multiplying said RF voltage by said calibration factor.

43. In a toroidal source plasma reactor wherein RF plasma source power is coupled into the interior of an external reentrant conduit of the reactor to generate a toroidal plasma current across a process region of the reactor and through the conduit, a method for measuring a quantity related to one of voltage, current or power, comprising:

measuring RF current flow through said external reentrant conduit.

44. The method of claim 43 further comprising comparing said RF current flow with a threshold value to determine an error, and governing said RF plasma source power in accordance with said error.

45. The method of claim 43 further comprising:

measuring RF voltage drop along an axis of said external reentrant conduit and determining therefrom a loop voltage of said toroidal plasma current; and

determining plasma power from said RF current flow and said RF voltage drop.

46. The method of claim 45 further comprising:

comparing said plasma power with a target power level to produce a power difference error; and

changing the level of said RF plasma source power by an amount corresponding to said power difference error.

47. The method of claim 43 wherein measuring current flow along an axis of said external reentrant conduit is followed by determining the real component of said RF current flow.

48. The method of claim 45 further comprising displaying at least one of said RF current flow, RF voltage drop and plasma power at a user interface.

49. The method of claim 43 further comprising obtaining a calibration factor for said RF current flow by performing the following steps prior to placing said workpiece on said pedestal:

coupling said RF source power generator to said conduit near one end thereof and coupling a resistive load to said conduit near an opposite end thereof;

comparing the current flow in said conduit with the square root of the quotient of a known power output of said RF source power generator divided by the resistance value of said resistive load to determine the calibration factor of said current measurement; and

after the step of measuring the RF current flow, multiplying said RF current flow by said calibration factor.

50. The method of claim 45 further comprising obtaining a calibration factor for each of said voltage probes by performing the following steps for each one of said voltage probes prior to placing said workpiece on said pedestal:

comparing the voltage measured at the one voltage probe with the square root of the product of a known power output of said RF source power generator multiplied by the resistance value of said resistive load, to determine the calibration factor of the one voltage probe; and

multiplying the output of the one voltage probe by said calibration factor.

51. A method of controlling a plasma immersion ion implantation reactor during ion implantation of a selected species into a workpiece, comprising:

placing said workpiece on a pedestal in said reactor and feeding into said reactor a process gas comprising a species to be implanted into said workpiece;

coupling RF plasma source power to a plasma in said reactor;

coupling RF bias power to said workpiece by an RF bias power generator that is coupled to said workpiece through a bias feedpoint of said reactor;

measuring RF voltage at a measurement point at or displaced from said feedpoint;

determining from said RF voltage an energy-related quantity that is related to the ion energy of said selected species; and

comparing said energy-related quantity to a target value to generate a difference, and controlling said RF bias power in accordance with said difference.

52. The method of claim 51 wherein said energy-related quantity is one of:

bias voltage;

ion energy;

ion implantation depth.

53. The method of claim 51 wherein the step of determining the energy-related quantity comprises determining a characteristic parameter of said RF voltage.

54. The method of claim 53 wherein said characteristic parameter comprises one of:

A. a time average of said RF voltage;

B. a peak value of said RF voltage;

C. a peak-to-peak value of said RF voltage;

D. an RMS value of said RF voltage.

55. The method of claim 53 further comprising multiplying said characteristic parameter by the charge of an ion of said selected species in the plasma in said reactor.

56. The method of claim 51 wherein said energy-related quantity is ion energy, said method further comprising:

comparing said ion energy with a target ion energy value to determine an ion energy error; and

rendering a display at a user interface relating to said ion energy error.

57. The method of claim 51 wherein said energy-related quantity is bias voltage, said method further comprising:

comparing said bias voltage with a target bias voltage value to determine bias voltage error; and

rendering a display at a user interface relating to said bias voltage error.

58. The method of claim 51 further comprising:

transforming said RF voltage from said measurement point to a location at least near said workpiece by a measurement point-to-workpiece transform.

59. The method of claim 58 further comprising determining said measurement point-to-workpiece transform prior to placing said workpiece in said reactor by the following steps:

measuring a complex open circuit input impedance-related quantity at said measurement point;

measuring a complex short circuit input impedance-related quantity at said measurement point; and

computing said measurement point-to-workpiece transform from a combination of said open circuit input impedance-related quantity and said short circuit input impedance-related quantity.

60. The method of claim 59 wherein said open circuit input impedance-related quantity comprises one of:

an open circuit input impedance;

an open circuit input admittance;

an open circuit current voltage and phase.

61. The method of claim 59 wherein said closed circuit input impedance-related quantity comprises one of:

a closed circuit input impedance;

a closed circuit input admittance;

a closed circuit current voltage and phase.

62. The method of claim 59 wherein the step of transforming comprises:

obtaining a plurality of frequency components comprising the fundamental and plural harmonics of the voltage and a current measured at the measurement point;

combining said plurality of frequency components with said transform to obtain a frequency domain version of the voltage at the workpiece; and

transforming the frequency domain version of the voltage into a time domain waveform of the voltage at the workpiece.

63. The method of claim 51 further comprising:

holding said workpiece on said pedestal by applying a D.C. chucking voltage to a buried electrode in said pedestal;

determining from said RF voltage a D.C. workpiece voltage; and

determining a net clamping voltage from said D.C. workpiece voltage and said D.C. chucking voltage.

64. The method of claim 63 wherein the step of determining the workpiece D.C. voltage comprises determining a time average of said RF voltage.

65. The method of claim 63 further comprising:

comparing said net clamping voltage with a target value to determine a clamping voltage error; and

adjusting said D.C. chucking voltage in accordance with said clamping voltage error.

66. The method of claim 63 further comprising:

sensing a temperature of said workpiece;

comparing said temperature with a target temperature to determine a temperature error; and

adjusting said D.C. chucking voltage by an amount tending to result in a reduction in said temperature error.

67. The method of claim 66 further comprising comparing said net clamping voltage with a clamping voltage target range and rendering a user display in accordance with the comparing of said net clamping voltage and said clamping voltage target range.

68. The method of claim 63 further comprising, prior to the step of determining the D.C. workpiece voltage:

transforming said RF voltage from said measurement point to a location at least near said workpiece by a measurement point-to-workpiece transform.

69. The method of claim 68 further comprising determining said measurement point-to-workpiece transform prior to placing said workpiece in said reactor by the following steps:

measuring a complex open circuit input impedance-related quantity at said measurement point;

measuring a complex short circuit input impedance-related quantity at said measurement point; and

computing said measurement point-to-workpiece transform from a combination of said open circuit input impedance-related quantity and said short circuit input impedance-related quantity.

70. The method of claim 69 wherein said open circuit input impedance-related quantity comprises one of:

an open circuit input impedance;

an open circuit input admittance;

an open circuit current voltage and phase.

71. The method of claim 69 wherein said closed circuit input impedance-related quantity comprises one of:

a closed circuit input impedance;

a closed circuit input admittance;

a closed circuit current voltage and phase.

72. The method of claim 69 wherein the step of transforming comprises:

obtaining a plurality of frequency components comprising the fundamental and plural harmonics of the voltage and a current measured at the measurement point;

combining said plurality of frequency components with said transform to obtain a frequency domain version of the voltage at the workpiece; and

transforming the frequency domain version of the voltage into a time domain waveform of the voltage at the workpiece.

73. The method of claim 51 wherein the step of measuring said RF voltage comprises sensing the voltage measurement output of an RF probe connected to said measurement point, said method further comprising obtaining a calibration factor for said RF voltage by performing the following steps prior to placing said workpiece on said pedestal:

coupling said RF probe between said RF bias power generator and a dummy resistance;

comparing the voltage measurement output of said RF probe with the square root of the product of a known power output of said RF bias power generator multiplied by the resistance value of said dummy resistance, to determine the calibration factor of said voltage measurement; and

after the step of measuring the RF voltage, multiplying said RF voltage by said calibration factor.