Semiconductor substrate minority carrier lifetime measurements

• US 5,049,816 A
• Filed: 05/31/1990
• Issued: 09/17/1991
• Est. Priority Date: 05/31/1990
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Moslehi, Mehrdad M.
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/532,284
• Time in Patent Office: 474 Days
• Field of Search: 324/158 D, 324/158 R, 324/158 T
• US Class Current: 324/762.02
• CPC Class Codes: G01R 31/2656 using non-ionising electromagnetic radiation, e.g. optical radiation

Abstract

A sensor system (50) for measurements of semiconductor wafer minority carrier lifetime. The sensor (50) includes a microwave source (78) for generating a plurality of microwave signals and a waveguide (52) for emitting the microwave signals in the direction of the semiconductor wafer (20) in a processsing chamber (18). A collector waveguide (84) detects the reflected microwave signals from the semiconductor wafer (20) and directs the microwave signals to and from the emitter waveguide (52) so as to generate a plurality of electrical signals relating to semiconductor wafer (20) physical properties. A photon energy source (102) intermittently emits photon energy in the direction of the semiconductor wafer (20). Based on the differing microwave reflectance measurements following the injection and removal of photon energy, process control computer (76) calculates semiconductor substrate physical characteristics. These physical characteristics include semiconductor minority-carrier lifetime, electrical conductivity, doping level, and temperature.

Claims

1. An apparatus for semiconductor substrate minority carrier lifetime measurements of a wafer, comprising:

a signal source for generating electromagnetic waves;

a microwave emitter spaced a selected distance from said substrate for emitting said electromagnetic waves toward said substrate and a microwave detector spaced from said substrate for detecting a portion of said electromagnetic waves that reflect from said substrate;

a generator for generating a first set of signals in response to said emitted electromagnetic waves and for generating a second set of signals proportional to said detected electromagnetic waves;

an energy source for emitting photon energy toward the substrate; and

measuring circuitry for measuring said first and second sets of signals into substrate characteristics measurements and for measuring the associated substrate response to said phonton energy.

2. The apparatus of claim 1, wherein said electromagnetic waves have a frequency range bounded by a lower frequency and an upper frequency, said lower frequency producing a signal wavelength that is small relative to the dimensions of the wafer and said upper frequency providing for optimal measurement sensitivity to electromagnetic wave interaction with the wafer substrate.

3. The apparatus of claim 1, wherein said signal source comprises a low frequency source capable of frequency scanning.

4. The apparatus of claim 1, further comprising a microwave signal chopper within said signal source for chopping said electromagnetic waves to improve signal-to-noise ratios for said detected electromagnetic waves.

5. The apparatus of claim 1, wherein said microwave detector comprises a separate collector waveguide for collecting a portion of said electromagnetic waves.

6. The apparatus of claim 1, further comprising circuitry for microwave signal amplitude modulation to improve signal-to-noise ratios and minimize signal drift for said detected electromagnetic waves.

40. The apparatus of claim 1 wherein said selected distance is about 30 mm.

41. The apparatus of claim 1 wherein said electromagnetic waves have a frequency range of between about 10 and 30 GHz.

7. An apparatus for semiconductor substrate carrier lifetime measurements, comprising:

an electromagnetic signal source for generating electromagnetic waves;

at least one waveguide terminating a selected distance from said substrate in communication with said electromagnetic signal source for emitting said electromagnetic waves toward the wafer and for detecting a portion of electromagnetic waves returning from the wafer,

at least one coupler in communication with said at least one waveguide for generating a plurality of signals, said plurality of signals comprising an emitted set of signals proportional to the power of said electromagnetic waves and for generating a set of signals proportional to the power of said portion of said electromagnetic waves reflected from said substrate;

a photon energy source for intermittently emitting phonton energy in the direction of the said substrate; and

measuring circuitry in communication with said coupler for receiving said plurality of signals and converting said signals into wafer electromagnetic wave reflectance measurements and in communication with said photon energy source for relating said intermittent photon energy to said electromagnetic wave reflectance measurements.

8. The apparatus of claim 7, wherein said electromagnetic waves have a frequency range bounded by a lower frequency and an upper frequency, said lower frequency producing a signal wavelength that is small relative to the dimensions of the wafer and said upper frequency providing for optimal measurement sensitivity to electromagnetic wave interaction with the wafer.

9. The apparatus of claim 7, wherein said electromagnetic signal source comprises a low frequency source capable of frequency scanning.

10. The apparatus of claim 7, further comprising a microwave signal chopper within said electromagnetic signal source for chopping said electromagnetic waves to improve signal-to-noise ratios for said reflected electromagnetic waves.

11. The apparatus of claim 7, wherein said emitter waveguide further comprises a microwave transmitter for transmitting said electromagnetic waves and a microwave detector for detecting said reflected electromagnetic waves.

12. The apparatus of claim 7, further comprising circuitry for microwave signal amplitude modulation to improve signal-to-noise ratios and minimize signal drift for said detected electromagnetic waves.

13. The apparatus of claim 8, further comprising, a collector waveguide for collecting a portion of said reflected electromagnetic waves.

14. The apparatus of claim 13, wherein said at least one coupler comprises a gallium arsenide amplifier for communicating among said electromagnetic wave source, said collector waveguide, and said measuring circuitry.

15. The apparatus of claim 7, wherein said at least one coupler comprises a dual directional coupler for communicating among said electromagnetic wave source, said emitter waveguide, and said measuring circuitry.

16. The apparatus of claim 7, further comprising a plurality of detectors for measuring a predetermined aspect of said portion of electromagnetic waves.

17. The apparatus of claim 7, wherein said photon energy source comprises a light source capable of dispersing a photon energy at least equal in level to the band gap energy of the wafer substrate.

18. The apparatus of claim 7, wherein said photon energy source comprises a light source capable of dispersing a photon energy having a wavelength not greater than one micron.

19. The apparatus of claim 7, wherein said measuring circuitry comprises a process control computer for calculating wafer electromagnetic wave reflectance measurements as a function of said emitted and reflected electromagnetic waves.

20. The apparatus of claim 19, wherein said process control computer includes necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements.

21. The apparatus of claim 20, wherein said process control computer includes necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements and for relating said intermittent photon energy signals and said substrate conductivity measurements to substrate carrier lifetime measurements.

22. The apparatus of claim 21, wherein said process control computer further controls said photon energy source intermittent operation and said data and instructions further comprise controls that de-energize said photon energy source for period sufficiently to permit said electromagnetic wave reflectance measurements to return to thermal equilibrium levels following deenergizing said photon energy source.

23. The apparatus of claim 22, wherein said process control computer further controls said photon energy source energy level and said data and instructions further comprise calculate proper photon energy source levels to ensure a linear relationships between electromagnetic wave reflectance measurements and substrate conductivity as said electromagnetic wave reflectance measurements return to thermal equilibrium levels following de-energizing said photon energy source.

24. The apparatus of claim 21, wherein said process control computer includes necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements and for relating said intermittent photon energy signals and said substrate conductivity measurements to substrate carrier lifetime measurements.

25. The apparatus of claim 24, further comprising a plurality of look-up tables for converting said electromagnetic wave reflectance measurements into substrate purity levels.

26. The apparatus of claim 25, further comprising a plurality of look-up tables for converting said electromagnetic wave reflectance measurements into substrate dopant levels.

27. The apparatus of claim 26, wherein said electromagnetic signal source comprises a low frequency source capable of frequency scanning and said process control computer further comprises necessary data and instructions to perform substrate doping profile measurements.

28. The apparatus of claim 21, further comprising a plurality of look-up tables for converting said electromagnetic wave reflectance measurements into wafer temperature measurements.

29. The apparatus of claim 7, wherein said apparatus is configured within a cleaning reactor for removing contaminants from the wafer substrate and wherein said measuring circuitry comprises a process control computer, said process control computer comprising necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements and for relating said intermittent photon energy signals and said substrate conductivity measurements to substrate carrier lifetime measurements.

30. The apparatus of claim 7, wherein said apparatus is configured within a cleaning reactor load lock for removing contaminants from the wafer substrate and wherein said measuring circuitry comprises a process control computer, said process control computer comprising necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements and for relating said intermittent photon energy signals and said substrate conductivity measurements to substrate carrier lifetime measurements.

31. The apparatus of claim 7, wherein said apparatus is configured within a metrology chamber for performing associated processes with the wafer and wherein said measuring circuitry comprises a process control computer, said process control computer comprising necessary data and instructions for converting electromagnetic wave reflectance measurements into substrate conductivity measurements and for relating said intermittent photon energy signals and said substrate conductivity measurements to substrate carrier lifetime measurements.

38. The method of claim 24, further comprising the step of converting said plurality of signals to substrate dopant levels.

42. The apparatus of claim 7 wherein said selected distance is about 30 mm.

43. The apparatus of claim 7 wherein said electromagnetic waves have a frequency range of between about 10 and 30 GHz.

32. An apparatus for wafer substrate carrier lifetime measurements, comprising:

an electromagnetic wave source for generating electromagnetic waves and comprising a low-power microwave signal source capable of frequency scanning and a microwave signal chopper for chopping said electromagnetic waves;

a waveguide in communication with said electromagnetic wave source and terminating a selected distance from the substrate, said waveguide comprising a microwave transmitter for transmitting said electromagnetic waves toward the wafer and a microwave detector for detecting a predetermined aspect of said electromagnetic waves reflected from the wafer, said electromagnetic waves having a frequency range bounded by a lower frequency and an upper frequency, said lower frequency bounded by a lower frequency and an upper frequency, said lower frequency producing a signal wavelength that is small relative to the dimensions of the wafer and said upper frequency providing for optimal measurement sensitivity to electromagnetic wafer interaction with the substrate;

a dual directional coupler for communicating among said electromagnetic wave source and said electromagnetic wave source and said emitter waveguide, said dual directional coupler comprising measuring circuitry for generating a plurality of signals, said plurality of signals comprising an emitted set of signals proportional to the power of said electromagnetic waves and a reflected set of signals proportional to the power of said portion of said reflected electromagnetic waves, said plurality of signals from said at least one coupler being directly related to measurements of the wafer substrate;

a photon energy source for intermittently emitting photon energy in the direction of the wafer, said photon energy source comprising a light source capable of dispersing a photon energy level at least equal in level to the band gap energy of the wafer substrate and having a wavelength not greater than one micron;

a process control computer in communication with said dual directional coupler and said photon energy source for calculating said electromagnetic wave reflectance measurements as a function of said emitted and reflected electromagnetic waves in conjunction with said photon energy level dispersing; and

a plurality of look-up tables set within said process control computer for converting wafer electromagnetic wave reflectance measurements into substrate conductivity measurements.

33. The apparatus of claim 32, wherein said plurality of look-up tables comprises a set of look-up tables for converting said reflectance measurements into substrate dopant level measurements.

44. The apparatus of claim 32 wherein said selected distance is about 30 mm.

45. The apparatus of claim 32 wherein said electromagnetic waves have a frequency range of between about 10 and 30 GHz.

34. A method for performing substrate carrier lifetime measurements, comprising:

spacing a source of electromagnetic waves and a substrate to be measured at a selected distance from each other;

emitting said electromagnetic waves toward said substrate;

intermittently emitting photon energy toward said substrate;

detecting a portion of said electromagnetic waves reflected from said substrate within a deposition chamber;

generating a plurality of signals to form an emitter set of signals proportional to said electromagnetic waves and a reflected set of signals proportional to said portion of said reflected electromagnetic waves, said plurality of signals being directly related to the wafer conductive layer measurements; and

converting said plurality of signals into wafer conductive layer measurements.

35. The method of claim 34, further comprising the step of chopping said electromagnetic waves.

36. The method of claim 34, wherein said step of generating a plurality of signals further comprises the step of producing DC voltages proportional to said emitted set of signals and said reflected set of signals.

37. The method of claim 34, wherein said detecting step further comprises the step of detecting said portion of reflected electromagnetic waves at different deposition process temperatures.

39. The method of claim 34, wherein said converting step further comprises the step of converting said plurality of signals into wafer temperature measurements.

46. The method of claim 34 wherein said source and said substrate are spaced apart by about 30 mm.

47. The method of claim 34 wherein said electromagnetic waves are emitted at a frequency between about 10 and 30 mm.