Measuring Bulk Lifetime

• US 20120286806A1
• Filed: 11/09/2011
• Published: 11/15/2012
• Est. Priority Date: 01/14/2010
• Status: Abandoned Application

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: MKS Instruments Incorporated
• Inventors: Machuca, Francisco, Chiarello, Ronald, Miller, G. Lorimer, Foster, Joseph W., Tigwell, David C., Cornwell, David
• Application Number:
  US13/292,850
• Publication Number:
  US 20120286806A1
• Time in Patent Office: Days
• US Class Current: 324/655
• CPC Class Codes: G01R 31/2648 Characterising semiconductor materials testing of materials or semi-finished products G01R31/2831; testing during manufacture H01L22/00
• CPC Class Codes: G01R 31/2656 using non-ionising electromagnetic radiation, e.g. optical radiation
• CPC Class Codes: G01R 31/318511 Wafer Test
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

A substrate is electromagnetically coupled into an inductance-capacitance resonant circuit formed from (i) a member comprising a ferromagnetic material, (ii) an inductor and (iii) the substrate. The substrate is illuminated for a first time period X to cause photoconduction in the substrate. Decay in conductivity of the substrate is monitored for a second time period Y. The ratio of X to Y is greater than 1:10. Bulk lifetime of the substrate is determined from the decay.

Claims

1. A method comprising:

electromagnetically coupling a substrate into an inductance-capacitance resonant circuit formed from (i) a member comprising a ferromagnetic material, (ii) an inductor and (iii) the substrate;

illuminating the substrate for a first time period X to cause photoconduction in the substrate;

measuring decay in conductivity of the substrate for a second time period Y, wherein a ratio of X to Y is greater than 1;

10; and

determining bulk lifetime of the substrate from the decay.

2. The method of claim 1 further comprising measuring a drive current of the inductance-capacitance resonant circuit between illumination and monitoring to determine the decay.

3. The method of claim 1 further comprising illuminating the substrate with at least one light emitting diode.

4. The method of claim 1 further illuminating the substrate with a square pulse.

5. The method of claim 1 wherein the ratio of X to Y is about 1:

1.

6. The method of claim 1 wherein the ratio of X to Y is greater than 1:

2.

7. The method of claim 1 wherein the duration of illumination is about 0.5 millisecond to 50 milliseconds.

8. The method of claim 1 wherein the duration of illumination is about 5 milliseconds to 32 milliseconds.

9. The method of claim 1 further comprising utilizing an analog to digital converter having a conversion speed less than 1 Mega sample per second.

10. An apparatus comprising:

a member comprising a ferromagnetic material, the member including a post disposed at its center and a surface extending to an outer wall, the member defining a gap between the post and the outer wall;

an inductance-capacitance resonant circuit configured to resonate at a measurement frequency, the circuit including an inductor disposed relative to the post;

a substrate disposed relative to the member, the substrate electromagnetically coupled to the inductor;

at least one radiation source configured to illuminate the substrate; and

a controller configured to (i) illuminate the substrate with the at least on radiation source for a first time period X to cause photoconduction in the substrate, (i) monitor decay in conductivity of the substrate for a second time period Y, wherein a ratio of X to Y is greater than 1;

10, and (iii) determine bulk lifetime of the substrate from the decay.

11. The apparatus of claim 10 further comprising a plurality of radiation sources disposed radially outward from and circumferentially around the post of the member.

12. The apparatus of claim 10 wherein the controller is further configured to measure a drive current of the inductance-capacitance resonant circuit between illumination and monitoring to determine the decay.

13. The apparatus of claim 10 wherein the controller is further configured to cause the at least one radiation source to illuminate the substrate with a square pulse.

14. The apparatus of claim 10 wherein the ratio of X to Y is about 1:

1.

15. The apparatus of claim 10 wherein the ratio of X to Y is greater than 1:

2.

16. The apparatus of claim 10 wherein the duration of illumination is about 0.5 millisecond to 50 milliseconds.

17. The apparatus of claim 10 wherein the duration of illumination is about 5 milliseconds to 32 milliseconds.

18. The apparatus of claim 10 wherein the controller is further configured to utilize an analog to digital converter having a conversion speed less than 1 Mega sample per second.

19. The apparatus of claim 10 further comprising:

a second member comprising the ferromagnetic material, the second member including a second post disposed at its center and a second surface extending to a second outer wall, the second member defining a second gap between the second post and the second outer wall, the substrate disposed between the member and the second member; and

a plurality of radiation sources disposed radially outward from and circumferentially around the second post of the second member, the plurality of radiation sources having a first wavelength that is different than a second wavelength of the second plurality of radiation sources.

20. An apparatus comprising:

means for electromagnetically coupling a substrate into an inductance-capacitance resonant circuit formed from (i) a member comprising a ferromagnetic material, (ii) an inductor and (iii) the substrate;

means for illuminating the substrate for a first time period X to cause photoconduction in the substrate;

means for measuring decay in conductivity of the substrate for a second time period Y, wherein a ratio of X to Y is greater than 1;

10; and

means for determining bulk lifetime of the substrate from the decay.