Radiation detectors and methods of fabricating radiation detectors

• US 9,000,389 B2
• Filed: 03/14/2012
• Issued: 04/07/2015
• Est. Priority Date: 11/22/2011
• Status: Active Grant

• Current Assignee: GE Medical Systems Israel, Ltd
• Original Assignee: General Electric Company
• Inventors: Rusian, Peter, Shahar, Arie
• Primary Examiner(s): Smith, Bradley K
• Assistant Examiner(s): GOODWIN, DAVID J
• Application Number:
  US13/419,934
• Publication Number:
  US 20130126999A1
• Time in Patent Office: 1,119 Days
• Field of Search: 257/448, 257/E31.124, 438/73, 438/778, 438/958, 438/58, 250/370.01, 216/37, 216/97
• US Class Current: 250/370.13
• CPC Class Codes: G01T 1/161 Applications in the field of nuclear medicine, e.g. in vivo counting apparatus for radiation diagnosis A61B6/00
• CPC Class Codes: G01T 1/241 Electrode arrangements, e.g. continuous or parallel strips or the like constructional or manufacturing details H01L31/00
• CPC Class Codes: H01L 27/1462 Coatings
• CPC Class Codes: H01L 27/14658 X-ray, gamma-ray or corpuscular radiation imagers measuring X-, gamma- or corpuscular radiation G01T1/00
• CPC Class Codes: H01L 27/14676 X-ray, gamma-ray or corpuscular radiation imagers measuring X-, gamma- or corpuscular radiation G01T1/00
• CPC Class Codes: H01L 31/02966 including ternary compounds, e.g. HgCdTe
• CPC Class Codes: H01L 31/085 the device being sensitive to very short wavelength, e.g. X-ray, Gamma-rays

Abstract

Radiation detectors and methods of fabricating radiation detectors are provided. One method includes mechanically polishing at least a first surface of a semiconductor wafer using a polishing sequence including a plurality of polishing steps. The method also includes growing a passivation oxide layer on a top of the polished first surface and depositing patterned metal contacts on a top of the passivation oxide layer. The method further includes applying a protecting layer on the patterned deposited metal contacts, etching a second surface of the semiconductor and applying a monolithic cathode electrode on the etched second surface of the semiconductor. The method additionally includes removing the protecting layer from the patterned metal contacts on the first surface, wherein the patterned metal contacts are formed from one of (i) reactive metals and (ii) stiff-rigid metals for producing inter-band energy-levels in the passivation oxide layer.

Claims

1. A method for fabricating a radiation detector, the method comprising:

mechanically polishing at least a first surface of a semiconductor wafer using a polishing sequence including a plurality of polishing steps to form a polished first surface, wherein a last polishing step of the polishing sequence includes polishing with a slurry having a grain size smaller than about 0.1 μ

m to create the polished first surface;

growing a passivation oxide layer on a top of the polished first surface to seal and passivate the polished first surface;

depositing patterned metal contacts on a top of the passivation oxide layer having at least one pattern being (i) a pattern of pixelated anode electrodes or (ii) a pattern of pixelated anode electrodes with grid electrodes having lines of electrodes aligned along centers of gaps between the pixelated anode electrodes;

applying a protecting layer on a top of the patterned metal contacts to protect a first surface of the patterned metal contacts;

etching a second surface of the semiconductor wafer to form an etched second surface;

applying a monolithic cathode electrode on the etched second surface of the semiconductor wafer; and

removing the protecting layer from the patterned metal contacts on the first surface, wherein the patterned metal contacts are formed from one of (i) reactive metals and (ii) stiff-rigid metals for producing inter-band energy-levels in the passivation oxide layer.

2. The method of claim 1, wherein the inter-band energy-levels enhance a tunneling of charge-carriers from and to the semiconductor wafer via the passivation oxide layer for causing the patterned metal contacts to behave as electrical rectifying contacts, the inter-band energy-levels formed in the passivation oxide layer by one of (i) diffusion of at least part of the patterned metal contacts into the passivation oxide layer to create doping therein (ii) creating local damage in the passivation oxide layer by producing mechanical stress between the patterned metal contacts and the passivation oxide layer.

3. The method of claim 1, wherein the mechanical polishing forms the polished first surface having a resistivity substantially the same as a bulk resistivity of the semiconductor wafer.

4. The method of claim 1, wherein the passivation oxide layer cause the first surface to have a resistivity substantially the same as a bulk resistivity of the semiconductor wafer.

5. The method of claim 1, wherein the semiconductor wafer is one of an N-Type semiconductor and a P-Type semiconductor.

6. The method of claim 1, wherein the grid electrodes is a steering grid that is biased by a voltage potential lower than a voltage potential of the pixelated anode electrodes.

7. The method of claim 1, wherein the patterned metal contacts are one of Indium, Platinum, Aluminum or Nickel.

8. The method of claim 7, wherein the patterned metal contacts have a reactive level to at least partially penetrate into the passivation oxide layer to create therein the inter-band energy-levels.

9. The method of claim 7, wherein the patterned metal contacts are formed to have a thickness, stiffness and rigidity in amounts that create mechanical stress on the passivation oxide layer to produce, in the passivation oxide layer, the inter-band energy-levels.

10. The method of claim 1, wherein the etching of the second surface produces in the etched regions a semiconductor having an excess of one of a component of the semiconductor wafer material.

11. The method of claim 1, wherein the etching of the second surface comprises one of a chemical wet etching and an ion-etching.

12. The method of claim 1, wherein the semiconductor wafer comprises Cadmium Zinc Telluride (CZT).

13. The method of claim 1, wherein the passivation oxide layer comprises Tellurium Oxide (TeO2).

14. The method of claim 1, wherein the passivation oxide layer is grown on the semiconductor wafer using a plasma process.

15. The method of claim 14, wherein the plasma process includes ionizing of gas by microwave radiation.

16. The method of claim 15, wherein the gas is a mixture of gases including oxygen.

17. The method of claim 1, wherein the pixelated anode electrodes and the monolithic cathode electrode are formed from a metal, the metal being at least one of Indium, Gold, Platinum, Nickel or Aluminum.

18. The method of claim 1, wherein the patterned metal contacts are applied to the semiconductor wafer by a processing technique including evaporation via a shadowing mask.

19. The method of claim 1, wherein the monolithic cathode electrode produced on the semiconductor wafer is formed from electrical contacts being one of Ohmic contacts or blocking contacts.

20. The method of claim 1, wherein the first and second surfaces of the semiconductor wafer are polished simultaneously in a same fabrication step.

21. The method of claim 1, wherein the first and second surfaces of the semiconductor wafer are polished in a plurality of different fabrication steps.

22. The method of claim 1, wherein a leakage current between the pixelated anode electrodes and the grid electrodes flows along a path including a rectifying contact that is reversely biased and is in a blocking state.

23. The method of claim 1, wherein the pixelated anode electrodes and the monolithic cathode electrode are applied to the semiconductor wafer simultaneously in a same fabrication step.

24. The method of claim 1, wherein the pixelated anode electrodes and the monolithic cathode electrode are applied to the semiconductor wafer in a plurality of different fabrication steps.

25. The method claim of claim 1, wherein the last polishing step includes a slurry having grain size of about 0.05 μ

m.