Surface treatment and protection method for cadmium zinc telluride crystals
View Patent ↗A method for treatment of the surface of a CdZnTe (CZT) crystal that provides a native dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals. A two step process is disclosed, etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and after attachment of electrical contacts, passivating the CZT crystal surface with a solution of 10 w/o NH 4 F and 10 w/o H 2 O 2 in water.
1. A method for forming a detector sensitive to ionizing radiation, comprising the steps of:
a) etching a surface of a CdZnTe crystal with a solution of bromine in methanol;
b) growing a dielectric layer on said etched surface forming thereby a passivated surface;
c) applying a photoresist layer onto said dielectric layer;
d) exposing a portion of said photoresist using electromagnetic radiation and a lithography means;
e) developing and removing said exposed portion thereby creating an image pattern in said photoresist and exposing a corresponding portion of said passivated surface;
f) removing said corresponding portion of said passivating surface and thereby replicating said image onto said CdZnTe crystal surface;
g) depositing a metal conductor onto said surface image thereby forming an electrode on said exposed CdZnTe crystal surface; and
h) removing the remaining photoresist layer.
2. The method of claim 1 , wherein the step of etching comprises etching in a solution of 5 vol. % bromine in methanol.
3. The method of claim 1 , wherein said step of growing a dielectric layer comprises treating the surface of the CdZnTe crystal with a solution of about 10 wt. % ammonium fluoride and about 10 wt. % hydrogen peroxide in water.
4. The method of claim 1 , wherein said lithography means comprises radiation from wavelengths of about 1 nm to about 750 nm.
5. The method of claim 1 , wherein said lithography means comprises either a positive or a negative mask, said mask used in one of either a contact, a projection, or a reflection mode.
6. The method of claim 1 , wherein the step of etching includes utilizing an etching process selected from the list consisting of an acid etch, etching by an oxygen or argon plasma, and etching by a reactive ion plasma.
7. The method of claim 3 , wherein both ammonium fluoride and hydrogen peroxide are present in equal amounts.
8. The method of claim 7 , wherein the electrodes are selected from the group of elements on the Periodic Table of elements in groups 8A through 1B.
9. The method of claim 8 , wherein the metal is gold.
10. The method of claim 1 , wherein the CdZnTe crystal has the composition of Cd 1−x Zn x Te, and where x is less than or equal to 0.5.
11. The method of claim 10 , wherein the CdZnTe crystal has the composition Cd 0.9 Zn 0.1 Te.
12. The method of claim 1 , wherein the step of passivating includes the step of encapsulating said CdZnTe crystal to provide a barrier between said dielectric layer and gases present in ambient air.
13. The method of claim 12 , wherein said step of encapsulating includes forming a polymer layer on said dielectric layer.
14. The method of claim 13 , wherein said polymer layer comprises an acrylic conformal coating.
15. The method of claim 12 , wherein said step of encapsulating includes depositing a reactively sputtered hard-coat nitride layer on said dielectric layer.
16. The method of claim 15 , wherein the hard-coat nitride layer is selected from the group consisting essentially of silicon nitride, boron nitride, germanium nitride, aluminum nitride, or gallium nitride.