SEPARATION OF DOPING DENSITY AND MINORITY CARRIER LIFETIME IN PHOTOLUMINESCENCE MEASUREMENTS ON SEMICONDUCTOR MATERIALS

• US 20140224965A1
• Filed: 04/18/2014
• Published: 08/14/2014
• Est. Priority Date: 07/20/2009
• Status: Active Grant

• Current Assignee: BT Imaging Pty., Ltd. (Aurora Solar Technologies, Inc.)
• Original Assignee: BT Imaging Pty., Ltd. (Aurora Solar Technologies, Inc.)
• Inventors: TRUPKE, Thorsten
• Granted Patent: US 9,157,863 B2
• Time in Patent Office: Days
• US Class Current: 250/208.1
• CPC Class Codes: G01N 21/6489 Photoluminescence of semiconductors
• CPC Class Codes: G01N 2201/06113 Coherent sources; lasers
• CPC Class Codes: G01N 2201/10 Scanning
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14

Abstract

Methods are presented for separating the effects of background doping density and effective minority carrier lifetime on photoluminescence (PL) generated from semiconductor materials. In one embodiment the background doping density is measured by another technique, enabling PL measurements to be analysed in terms of effective minority carrier lifetime. In another embodiment the effective lifetime is measured by another technique, enabling PL measurements to be analysed in terms of background doping density. In another embodiment, the effect of background doping density is removed by calculating intensity ratios of two PL measurements obtained in different spectral regions, or generated by different excitation wavelengths. The methods are particularly useful for bulk samples such as bricks or ingots of silicon, where information can be obtained over a much wider range of bulk lifetime values than is possible with thin, surface-limited samples such as silicon wafers. The methods may find application in solar cell manufacturing.

Claims

1. A method of conducting an analysis of a silicon ingot or brick, said method including the steps of:

(a) exciting at least one side facet of said silicon ingot or brick to produce photoluminescence;

(b) obtaining at least one image of the photoluminescence emitted from said at least one side facet; and

(c) interpreting said at least one image to identify variations in effective and/or bulk minority carrier lifetime in said ingot or brick.

2. A method according to claim 1, wherein the step of interpreting said at least one image comprises normalising the photoluminescence intensity within said at least one image with regard to variations in the background doping density of said ingot or brick, to identify variations in effective minority carrier lifetime in said ingot or brick.

3. A method according to claim 2, wherein the normalised photoluminescence intensity is converted to bulk minority carrier lifetime data using a predetermined theoretical relationship.

4. A method according to claim 3, wherein the photoluminescence emitted from said at least one side facet is long-pass filtered to strengthen the dependence of the normalised photoluminescence intensity on bulk minority carrier lifetime.

5. A method according to claim 4, further comprising the step of correcting said at least one image for the angular dependence of the transmission of a filter used for the long-pass filtering.

6. A method according to claim 3, wherein two or more images are obtained of photoluminescence produced with different illumination intensities, and said interpreting step comprises calculating the injection level dependence of the bulk minority carrier lifetime.

7. A method according to claim 2, wherein the normalised photoluminescence intensity is converted to bulk minority carrier lifetime data using a predetermined empirical relationship.

8. A method according to claim 7, wherein the photoluminescence emitted from said at least one side facet is long-pass filtered to strengthen the dependence of the normalised photoluminescence intensity on bulk minority carrier lifetime.

9. A method according to claim 8, further comprising the step of correcting said at least one image for the angular dependence of the transmission of a filter used for the long-pass filtering.

10. A method according to claim 7, wherein two or more images are obtained of photoluminescence produced with different illumination intensities, and said interpreting step comprises calculating the injection level dependence of the bulk minority carrier lifetime.

11. A method according to claim 1, wherein steps (a) and (b) are performed when scanning said ingot or brick and an illumination/detection system relative to each other.

12. A method according to claim 1, wherein the at least one photoluminescence image is used as a cutting guide in wafer production.

13. A method according to claim 1, wherein the information obtained from said method is used in the manufacturing of silicon bricks or ingots.

14. A method according to claim 1, wherein the information obtained from said method is used to determine the price of wafers derived from said ingot or brick.

15. A method according to claim 1, wherein the at least one photoluminescence image is used as a guide in wafer production to sort wafers into quality bins.

16. A method according to claim 1, wherein the information obtained from said method is used to obtain feedback on feedstock quality in the production of silicon wafers.

23. A system when used to implement the method according to claim 1.

17. A system for conducting an analysis of a silicon ingot or brick, said system including:

a photodetection unit for obtaining at least one image or line scan of photoluminescence generated from at least one side facet of said silicon ingot or brick; and

a processor for interpreting said at least one photoluminescence image or line scan to identify variations in effective and/or bulk minority carrier lifetime in said ingot or brick.

18. A system according to claim 17, further comprising a long-pass filter for filtering the photoluminescence generated from said at least one side facet of said silicon ingot or brick.

19. A system according to claim 17, further comprising a mechanism for scanning said photodetection unit and said ingot or brick relative to each other.

20. A system according to claim 17, further comprising:

an optical source emitting light with wavelength longer than the band-gap of silicon; and

a detector for measuring the transmission of said light through said silicon ingot or brick.

21. A system according to claim 17, wherein said photodetection unit comprises an InGaAs camera.

22. A system according to claim 17, wherein said photodetection unit comprises a silicon camera.