Claims
- 1. A non-contact method of determining the doping concentration profile of a specimen of semiconductor material, the specimen having a surface arranged for illumination, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, said specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. illuminating a region of the surface of the specimen arranged for illumination with a beam of light of wavelength shorter than that of the energy gap of the semiconductor, the beam of light being intensity modulated at a predetermined frequency,
- d. applying a variable DC bias voltage between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- e. the intensity of the light beam and the rate at which the DC bias voltage varies being such that no inversion layer is formed at the surface of the specimen,
- f. providing a signal corresponding to the total capacitance between the two electrodes during the DC voltage sweep,
- g. providing a signal representing the ac photovoltage at the region of the specimen illuminated by the light beam,
- h. the intensity of the light beam and frequency of modulation of the light beam being such that the ac photovoltage is nearly proportional to the intensity of the light beam,
- i. providing a signal corresponding to the variable DC bias voltage, and then
- j. determining the doping concentration profile using said ac photovoltage, total capacitance and DC bias voltage information.
- 2. The method of claim 1 wherein said nonconducting medium is a gas.
- 3. The method of claim 2 wherein said gas is air.
- 4. The method of claim 2 wherein said gas is nitrogen or SF.sub.6.
- 5. The method of claim 1 wherein determining the doping concentration profile comprises:
- a. determining the value of the induced charge Q.sub.ind at a plurality of points during a segment of the DC bias voltage sweep period,
- b. determining the depletion width W.sub.d at said plurality of points, and
- c. determining the doping concentration profile N.sub.SC (Z) using Q.sub.ind and W.sub.d.
- 6. The method of claim 5 where Q.sub.ind is determined using the formula Q.sub.ind =C.sub.tot .multidot.V.sub.p
- where C.sub.tot =the total capacitance between the pair of electrodes and V.sub.p =the sensor potential.
- 7. The method of claim 6 where W.sub.d is determined using the formula:
- I.sub.ac =.vertline.e.vertline./.epsilon..sub.si .multidot.C.sub.tot .multidot.W.sub.d .multidot..phi..sub.1 ;
- where:
- W.sub.d =the depletion layer width,
- e=electron charge,
- .epsilon..sub.si =dielectric constant of Si,
- C.sub.tot =total capacitance between the pair of electrodes,
- .phi.=absorbed flux (photons/cm.sup.2 .multidot.s) where s=seconds and
- I.sub.ac =current induced in a reference electrode by the ac surface photovoltage.
- 8. A method of determining the resistivity of a specimen of semiconductor material, the specimen having a surface arranged for illumination, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, said specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. providing a signal corresponding to the total capacitance between the two electrodes,
- d. illuminating a region of the surface of the specimen arranged for illumination with a beam of light of wavelengths shorter than that of the energy gap of the semiconductor, the beam of light being intensity modulated at a predetermined frequency,
- e. applying a variable DC bias voltage (V.sub.g) between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- f. the intensity of the light beam and the rate at which the DC bias voltage varies being such that no inversion layer is formed at the surface of the specimen,
- g. providing a signal representing the ac photovoltage at the region of the specimen illuminated by the light beam,
- h. the intensity of the light beam and frequency of modulation of the light beam being such that the ac photovoltage is nearly proportional to the intensity of the light beam,
- i. providing a signal corresponding to the bias voltage (V.sub.g),
- j. determining the doping concentration (N.sub.sc) profile using said ac photovoltage, total capacitance and DC bias voltage information, and
- k. determining the resistivity using the doping concentration.
- 9. The method of claim 8 wherein determining the doping concentration profile includes determining the depletion layer width using the formula:
- I.sub.ac =.vertline.e.vertline./E.sub.si .multidot.C.sub.tot .multidot.W.sub.d .multidot..phi.,
- where:
- W.sub.d =the depletion layer width,
- e=electron charge,
- .epsilon..sub.si =dielectric constant of Si,
- C.sub.tot =total capacitance between the pair of electrodes,
- .PHI.=absorbed flux (photons/cm.sup.2 .multidot.s) where s=seconds and
- I.sub.ac =current induced in a reference electrode by the ac surface photovoltage.
- 10. The method of claim 9 wherein the doping concentration profile is determined using the formula:
- N(z)=(1/.vertline.e.vertline.A).multidot.(dQ.sub.ind /dW.sub.d);
- where,
- z=W.sub.d.
- 11. A method of determining the resistivity of a specimen of semiconductor material, the specimen having a surface arranged for illumination, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, said specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. providing a signal corresponding to the total capacitance between the two electrodes,
- d. illuminating a region of the surface of the specimen arranged for illumination with a beam of light of wavelengths shorter than that of the energy gap of the semiconductor, the beam of light being intensity modulated at a predetermined frequency,
- e. applying a variable DC bias voltage (V.sub.g) between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- f. the intensity of the light beam and the rate at which the DC bias voltage varies being such that no inversion layer is formed at the surface of the specimen,
- g. providing a signal representing the ac photocurrent at the region of the specimen illuminated by the light beam,
- h. the intensity of the light beam and frequency of modulation of the light beam being such that the ac photovoltage is nearly proportional to the intensity of the light beam,
- i. providing a signal corresponding to the bias voltage (V.sub.g),
- j. determining the doping concentration (N.sub.sc) profile using said ac photocurrent, total capacitance and DC bias voltage information, and
- k. determining the resistivity using the doping concentration.
- 12. The method of claim 11 wherein the specimen is boron-doped silicon and the resistivity .rho. is determined using the formula:
- .rho.=(6.242.times.10.sup.13 /N.sub.sc).multidot.10 .sup.t
- t=(A.sub.0 +A.sub.1 .multidot.Y+A.sub.2 .multidot.Y.sup.2 +A.sub.3 .multidot.Y.sup.3)/(1+B.sub.1 .multidot.Y+B.sub.2 .multidot.Y.sup.2 +B.sub.3 .multidot.Y.sup.3).
- 13.
- 13. A non-contact sensor assembly for making ac surface photocurrent measurements of a specimen of semiconductor material when illuminated by light comprising:
- a. a housing having a top and a bottom,
- b. a bellows assembly, said bellows assembly comprising an upper plate, a lower plate and a bellows connecting the upper plate to the lower plate, said upper plate being mounted on said bottom of said housing,
- c. an air bearing assembly mounted on said bottom plate of said bellow assembly, and
- d. a sensor tip mounted on said air bearing assembly, said sensor tip including an electrode,
- e. said housing having an inlet for receiving air from an air supply and direct said air into said air bearing through said bellows.
- 14. A non-contact capacitive pickup type sensor assembly comprising:
- a. a housing,
- b. a bellows assembly mounted on said housing, said bellows assembly including a first bellows,
- c. an air bearing assembly mounted on said bellow assembly, and
- d. a sensor tip mounted on said air bearing assembly, said sensor tip including an electrode,
- e. said housing having an inlet for receiving air from a first air supply and directing said air into said air bearing assembly through said bellows, said air passing through said bellows causing said bellows to expand.
- 15. The sensor assembly of claim 14 wherein said air bearing assembly includes a plurality of orifices and wherein said air from said first bellows exits through said orifices.
- 16. The sensor assembly of claim 15 wherein said bellows assembly includes a second bellows and wherein said housing includes an inlet for receiving air from a second air supply and directing air into said air bearing through said second bellows.
- 17. The sensor assembly of claim 16 wherein said bearing assembly includes a porous ring and said air from said second bellows exits said air bearing through said porous ring.
- 18. The sensor assembly of claim 17 and further including a light source and wherein said first bellows is an outer bellows and said second bellows is an inner bellows.
- 19. The sensor assembly of claim 18 wherein said sensor tip including a substrate having a coating serving as a reference electrode.
- 20. The sensor assembly of claim 19 wherein said sensor tip further includes a coating serving as a guard electrode.
- 21. The sensor assembly of claim 20 wherein said sensor tip further includes a soft protective layer.
- 22. The sensor assembly of claim 21 wherein said soft protective layer is a plastic.
- 23. The sensor assembly of claim 22 wherein said plastic is a polyamide or parylene.
- 24. A method of determining the doping concentration profile of a specimen of semiconductor material, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, the specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. applying a variable DC bias voltage between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- d. the rate at which the DC bias voltage varies being such that no inversion layer is formed at the surface of the specimen and the period of variation being small compared to the amount of time required to charge or discharge the surface states associated with an unknown surface,
- e. providing a signal corresponding to the DC bias voltage,
- f. providing a signal corresponding to the total capacitance between the two electrodes during the DC bias voltage sweep,
- g. providing information corresponding to the area of the electrode spaced from the specimen,
- h. determining the capacitance of the nonconductive medium using the total capacitance signal,
- i. determining the depletion width using the total capacitance, the capacitance of the nonconducting medium and the area of the electrode spaced from the specimen information, and
- j. determining the doping concentration profile using the depletion width, the total capacitance, the DC bias voltage, and the area of the electrode spaced from the specimen information.
- 25. The method of claim 24, wherein determining the capacitance of the nonconductive gaseous medium comprises measuring the total capacitance between the two electrodes when the DC bias voltage corresponds to that for accumulation for the specimen.
- 26. The method of claim 24 wherein the depletion width is determined using the formula:
- W.sub.d .epsilon..sub.s E.sub.o A[(1C.sub.tot)-(1/C.sub.nm)]
- where:
- W.sub.d =the depletion layer width,
- .epsilon..sub.s =the relative dielectric constant of the semiconductor,
- .epsilon..sub.o =the absolute dielectric constant of a vacuum,
- A=the area of the electrode spaced from the specimen,
- C.sub.tot =the total capacitance between the pair of electrodes, and
- C.sub.nm =the capacitance of the nonconducting medium.
- 27. The method of claim 26 wherein the doping concentration profile is determined using the formula:
- N(W.sub.d)=C.sup.3.sub.tot /q.epsilon..sub.s .epsilon..sub.o A.sup.2 (dC.sub.tot /dV)
- where:
- N=the doping concentration,
- W=the depletion layer width,
- C.sub.tot =the total capacitance between the pair of electrodes,
- q=the elementary charge
- .epsilon..sub.s =the relative dielectric constant of the specimen,
- .epsilon..sub.s =the absolute dielectric constant of a vacuum,
- A=the area of the electrode spaced from the specimen, and
- V=the applied DC bias voltage.
- 28. The method of claim 24, wherein the nonconductive medium is air.
- 29. The method of claim 7, wherein the doping concentration profile is determined using the formula:
- N.sub.sc (Z)=(-1/eA).multidot.(dQ.sub.ind /dW.sub.d)
- where:
- N.sub.sc (Z) the doping concentration at a depth Z,
- A=the sensor area, and
- Z=W.sub.d.
- 30. A method of determining properties of a specimen of semiconductor material, the specimen having a surface arranged for illumination, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, said specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. illuminating a region of the surface of the specimen arranged for illumination with a beam of light of wavelength shorter than that of the energy gap of the semiconductor, the beam of light being intensity modulated at a predetermined frequency,
- d. applying a variable DC bias voltage between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- e. the intensity of the light beam and the rate at which the DC bias voltage varies being such that no inversion layer is formed at the surface of the specimen,
- f. providing a signal corresponding to the total capacitance between the two electrodes during the DC voltage sweep,
- g. providing a signal representing the ac photovoltage at the region of the specimen illuminated by the light beam,
- h. the intensity of the light beam and frequency of modulation of the light beam being such that the ac photovoltage is nearly proportional to the intensity of the light beam,
- i. providing a signal corresponding to the variable DC bias voltage, and then
- j. determining properties of said specimen of semiconductor material using said ac photovoltage, total capacitance and DC bias voltage information.
- 31. A non-contact method of determining properties of a specimen of semiconductor material, the specimen having a surface arranged for illumination, the method comprising:
- a. providing a pair of electrodes,
- b. positioning the specimen between the pair of electrodes, said specimen being disposed on one of said electrodes and spaced from said other electrode by a nonconducting medium,
- c. illuminating a region of the surface of the specimen arranged for illumination with a beam of light of wavelength shorter than that of the energy gap of the semiconductor, the beam of light being intensity modulated at a predetermined frequency,
- d. applying a variable DC bias voltage between the pair of electrodes, the variable bias voltage varying between that corresponding to accumulation and that corresponding to depletion for the specimen,
- e. providing a signal corresponding to the total capacitance between the two electrodes during the DC voltage sweep,
- f. providing a signal representing the ac photovoltage at the region of the specimen illuminated by the light beam,
- g. the intensity of the light beam and frequency of modulation of the light beam being such that the ac photovoltage is nearly proportional to the intensity of the light beam,
- h. providing a signal corresponding to the variable DC bias voltage, and then
- i. determining properties of said specimen of semiconductor material using said ac photovoltage total capacitance and DC bias voltage information.
- 32. The method of claim 31 wherein said other electrode is spaced from said one electrode through an air bearing.
- 33. The method of claim 24, wherein the nonconductive medium is a gas.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No. 08/873,410 filed on Jun. 12, 1997, now U.S. Pat. No.6,034,535, and is claiming the priority of provisional application Ser. No. 60/038,003, filed on Feb. 14, 1997.
US Referenced Citations (12)
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
873410 |
Jun 1997 |
|