Method and apparatus to scribe thin film layers of cadmium telluride solar cells

• US 8,890,025 B2
• Filed: 04/01/2011
• Issued: 11/18/2014
• Est. Priority Date: 09/24/2009
• Status: Expired due to Fees

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: ESI-Pyrophotonics Lasers, Inc. (MKS Instruments Incorporated)
• Inventors: Panarello, Tullio, Rekow, Mathew, Murison, Richard
• Primary Examiner(s): Evans, Geoffrey S
• Application Number:
  US13/078,787
• Publication Number:
  US 20110240614A1
• Time in Patent Office: 1,327 Days
• Field of Search: 219/121.69, 219/121.72, 219/121.61, 219/121.62, 438/463, 438/940
• US Class Current: 219/121.69
• CPC Class Codes: B23K 2103/172 wherein at least one of the layers is non-metallic
• CPC Class Codes: B23K 26/0624 using ultrashort pulses, i.e. pulses of 1ns or less
• CPC Class Codes: B23K 26/361 for deburring or mechanical trimming B23K26/351 takes precedence
• CPC Class Codes: B23K 26/364 for making a groove or trench, e.g. for scribing a break initiation groove
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved

Abstract

A method of laser scribing a CdTe solar cell structure includes providing a laser operable to produce an optical pulse. The optical pulse is characterized by a temporal profile having a first power level during a first portion of the optical pulse and a second power level less than the first power level during a second portion of the optical pulse. The method also includes directing the optical pulse to impinge on the CdTe solar cell structure. The CdTe solar cell structure includes a substrate, a transmission spectrum control layer adjacent the substrate; a barrier layer adjacent the transmission spectrum control layer, and a conductive layer adjacent the barrier layer. The method further includes initiating a removal process for the conductive layer and terminating the removal process prior to removing the barrier layer.

Claims

1. A method of removing at least a portion of a thin film structure, the thin film structure including at least a first layer and a second layer in contact with the first layer, the method comprising:

providing a laser pulse characterized by a temporal pulse shape having a first peak power level during a first portion and a subsequent second peak power level during a second portion;

directing the laser pulse to impinge on the thin film structure;

initiating a removal process in the first layer by initiating a dissociation reaction in the first layer during the first portion;

maintaining the dissociation reaction in the first layer during the second portion; and

terminating the removal process at the end of the second portion.

2. The method of claim 1 wherein a fall time between the first portion and the second portion is less than 5% of a duration of the temporal pulse shape.

3. The method of claim 2 wherein the fall time is less than 2%.

4. The method of claim 1 wherein the thin film structure comprises a conductive film overlying an insulating film.

5. The method of claim 4 wherein the insulating film comprises at least one of an oxide-based or nitride-based dielectric.

6. The method of claim 5 wherein the oxide or nitride based dielectric comprises SiO₂.

7. The method of claim 4 wherein the conductive film comprises a transparent conductive oxide.

8. The method of claim 7 wherein the transparent conductive oxide comprises SnO₂:

F.

9. A method of removing at least a portion of a thin film structure, the thin film structure including at least a first layer and a second layer in contact with the first layer, the method comprising:

providing a laser pulse, with an infrared wavelength, characterized by a temporal pulse shape having a first peak power level during a first portion and a subsequent second peak power level during a second portion;

directing the laser pulse to impinge on the thin film structure;

initiating a removal process in the first layer by initiating a dissociation reaction in the first layer during the first portion;

maintaining the dissociation reaction in the first layer during the second portion; and

terminating the removal process at the end of the second portion;

wherein the peak power in the first portion is at least twice the peak power in the second portion.

10. The method of claim 9 wherein the peak power in the first portion is at least twenty times the peak power in the second portion.

11. A method of removing at least a portion of a thin film structure, the thin film structure including at least a first layer and a second layer in contact with the first layer, the method comprising:

providing a laser pulse, with an infrared wavelength, characterized by a temporal pulse shape having a first peak power level during a first portion and a subsequent second peak power level during a second portion;

directing the laser pulse to impinge on the thin film structure;

initiating a removal process in the first layer by initiating a dissociation reaction in the first layer during the first portion;

maintaining the dissociation reaction in the first layer during the second portion; and

terminating the removal process at the end of the second portion;

wherein maintaining the dissociation reaction during the second portion comprises maintaining a temperature of the first layer at a substantially constant temperature during the second portion.

12. A method of laser scribing a CdTe solar cell structure, the method comprising:

providing a laser operable to produce an optical pulse, with an infrared wavelength, being characterized by a temporal profile having a first power level during a first portion of the optical pulse and a second power level less than the first power level during a second portion of the optical pulse;

directing the optical pulse to impinge on the CdTe solar cell structure, wherein the CdTe solar cell structure comprises a substrate, a conductive layer, and a barrier layer between the conductive layer and substrate;

initiating a removal process for the conductive layer by initiating a dissociation reaction;

and terminating the removal process prior to removing the barrier layer.

13. The method of claim 12 wherein the temporal profile comprises a pulse length between about 1 ns and 600 ns.

14. The method of claim 12 wherein the substrate comprises soda lime glass.

15. The method of claim 12 including an additional layer between the barrier layer and the substrate, the additional layer comprising at least one of SnO₂ and another material to color balance light transmitted through or reflected from structure.

16. The method of claim 12 wherein the barrier layer comprises at least one of SiO₂ or Si₃N₄.

17. The method of claim 12 wherein initiating the removal process for the conductive layer comprises maintaining a temperature of the conductive layer at a constant temperature during the second portion.

18. The method of claim 12 wherein the optical pulse is characterized by a non-Gaussian, shaped spatial profile.

19. The method of claim 12 wherein the conductive layer comprises a transparent conductive oxide.

20. The method of claim 19 wherein the conductive oxide comprises at least one of SnO₂:

F, In₂O₃, ZnO, or CdSnO_x.