CN1632933A - Surface passivation method for nuclear detector tellurium-zinc-cadmium wafer - Google Patents

Abstract

This invention relates to a nucleus detector Te cadmium and zinc crystal pad surface passivation. The method comprises the following steps: first to polish the crystal pad, surface erosion and deposition gold electrode and surface passivation and comprises four process and is characterized by the two step method in the surface passivation, which comprises the following steps: first to get the surface near to chemical metering; then to use mixture solution of NH#-[4]F/H#-[2]O#-[2] to make oxidation layer through passivation.

Description

The method of nuclear detector tellurium-zinc-cadmium wafer surface passivation

Technical field

The present invention relates to a kind of method of nuclear detector tellurium-zinc-cadmium wafer surface passivation, is exactly the improving one's methods of last procedure passivation technology in the nuclear detector tellurium-zinc-cadmium wafer manufacture process specifically, belongs to semiconductor detecting material manufacturing technology field.

Background technology

Tellurium zinc cadmium (CZT) compound semiconductor detecting material is owing to have higher average atomic number and bigger energy gap, so the detector of being made by these materials has bigger absorption coefficient, higher counting rate, volume is little, easy to use, and can be in advantages such as working and room temperatures.This novel ray detector of tellurium zinc cadmium CZT has very high detection efficient, compares with silicon, Ge detector, and it can at room temperature be worked, and compares with traditional sodium iodide scintillator probe, and its volume is littler, has higher energy resolution.And this semiconductor detector is easy to be processed into the pel array detector, cooperates the integrated signal read circuit of silicon of bridge joint.Can make compactness, efficient, high-resolution χ ray imaging device, can be widely used in aspects such as safety check, industrial flaw detection, medical diagnosis, celestial body x-ray telescope, therefore become the current focus of research in the world.Yet, the noise limit that the leakage current of tellurium zinc cadmium device surface causes the CZT detector reach its optimum capacity resolution, must carry out passivation to the CZT device surface, to reduce the tracking current of device.Therefore the surface passivation of CZT device is the critical process of device preparation.

High performance semiconductor nuclear radiation detector need have lower leakage current.Though the chemical corrosion of CZT crystal process is the place to go mechanical damage layer effectively, can make the CZT surface stay the rich Te layer of one deck, reduce the CZT surface resistivity, thereby cause the higher leakage current in CZT surface.Must introduce passivating method for this reason and form the high resistant passivation layer or improve its non-accurate chemical constituent ratio in surface, thereby reduce the tracking current of device, improve the detector operation performance at semiconductor surface.The surface passivation method that the CZT device is commonly used has passivation of dry method physics and wet chemistry passivation at present: the physics passivation is meant by depositing suitable high resistant insulating film material at semiconductor surface, thereby realize the purpose of surface passivation, chemical change generally can not take place in the plane of crystal composition, and electrode can not be affected yet.The physics passivation comprises oxygen atom bombardment, at CZT surface sputtering Si _1-xN _xLayer and plasma sputtering etc.But physics paralysis facility complexity, and in the passivation film deposition process, need to consider the influence of depositing temperature to base material character.And the required equipment of chemical passivation is simple, easy to operate, but process conditions are very big to the influence of device passivation effect, at present the chemical passivation method that uses adopts chemical solution directly to produce chemical reaction to improve plane of crystal stoichiometric proportion or generation high resistant oxide layer with plane of crystal, and single solution is mainly adopted in traditional chemical passivation.Adopt single solwution method can improve the plane of crystal stoichiometric proportion, but be difficult to form the passivation layer that one deck is isolated from the outside, influence the long-time stability of device at plane of crystal; Perhaps, can generate the high resistant oxide layer on the CZT surface, but usually have remaining Te in oxide layer, or rich Cd layer appears in semiconductor surface under oxide layer, this can have influence on the electric property of passivation layer.

Summary of the invention

The objective of the invention is to overcome the shortcoming that the single solution of above-mentioned employing causes, a kind of two step method chemical deactivation process is provided, both can obtain the reasonable CZT of stoichiometry surface, can form the high resistant oxide layer that one deck shields on this surface again.Thereby further reduce the leakage current of plane of crystal, finally improve the performance of CZT nuclear detector.

For achieving the above object, the present invention adopts following technical scheme:

A kind of method of nuclear detector tellurium-zinc-cadmium wafer surface passivation, this method be earlier by traditional handicraft with cadmium zinc telluride crystal wafer polish, surface corrosion, deposited gold electrode and surface passivation, include four processes, it is characterized by, adopt two-step method in last surface passivation program, the concrete process of this method is as follows:

A. the polishing of tellurium-zincium-cadmium crystal: earlier cadmium zinc telluride crystal wafer is slightly thrown with diamond dust, make surfacing, after thick the throwing wafer is cleaned, put into the beaker that fills deionized water, carry out sonic oscillation, to remove the pollutant and the foreign particle of wafer surface, then wafer is carefully thrown, be minute surface until wafer surface; Subsequently, remove surface impurity with sonic oscillation once more, wafer is immersed in waits in the absolute methanol to corrode;

B. wafer surface corrosion: the wafer after the polishing adopts the BM corrosive liquid earlier, and promptly the corrosive liquid of 5%Br+ methyl alcohol composition carries out the surface chemistry corrosion, and the time is 1-2 minute; To re-use the LB corrosive liquid after the rinse in methyl alcohol through the wafer after the corrosion of BM corrosive liquid, promptly the corrosive liquid of 2%Br+20% lactic acid+ethylene glycol composition corrodes wafer, to increase the wafer surface smooth degree; Then with wafer in methyl alcohol ultrasonic cleaning to remove surperficial remaining Br and other impurity;

C. the deposition of gold electrode: will corrode good wafer and take out, at N ₂Dry up under the protective atmosphere.Adopt chemical method gold-plated, deposit circular gold electrode at the two-sided suitable position of wafer, its diameter is about 1-3mm, thickness is 200 .

D. surface passivation: will prepare the wafer of electrode, and adopt two step solwution methods that its surface is handled; Earlier carry out surface treatment with KOH-KCl solution, it is identical that the concentration of KOH and KCl solution keeps, and is controlled at 10-20wt%, and the time is 20-60 minute; Then use the NH of 10wt% again ₄F/H ₂O ₂Mixed solution carries out passivation, and the Passivation Treatment time is 10-30 minute, puts into the abundant various ions that clean with the removal remained on surface of a large amount of deionized waters with finishing passivation wafer afterwards; Obtain the cadmium zinc telluride crystal wafer of surface passivation at last.

Compare with prior art, the present invention has following remarkable advantage: adopt the corrective measure of two step method passivation technology, utilize two kinds of different solution that get.Obtain earlier accurate stoichiometry specific surface, re-use oxidizing solution and on this accurate stoichiometry surface, generate one deck high resistant oxide layer, and in this oxide layer, avoided the appearance of remaining tellurium or rich cadmium layer, improved the electric property of passivation layer.Because the rich tellurium layer of floor height conduction can appear in chemical corrosion tellurium-zincium-cadmium crystal surface, thereby cause the higher leakage current in tellurium-zincium-cadmium crystal surface, adopted the two-step method chemical deactivation process just can avoid the ubiquitous shortcoming of traditional single chemical deactivation process.

Embodiment:

Embodiment one: the technical process of present embodiment comprises following each program,

The polishing of a.CZT crystal: well cutting is of a size of 5 * 5 * 2mm ³The CZT wafer adopt earlier diamond dust slightly to throw, it is polished, make surfacing; After thick the throwing, wafer is cleaned, put into the beaker sonic oscillation 5 minutes that fills deionized water, to remove the pollutant and the foreign particle on surface, on grinder, be that the corundum powder polishing fluid of 1um, 0.5um, 0.2um is carefully thrown the CZT wafer with particle diameter successively then, be minute surface until wafer surface.After thin the throwing, remove surface impurity with sonic oscillation once more, wafer is immersed in waits in the absolute methanol to corrode.

B. wafer surface corrosion: the CZT wafer after the polishing adopts BM corrosive liquid (5%Br+ methyl alcohol) to carry out the surface chemistry corrosion earlier, and the time is 1 minute; To in methyl alcohol, re-use LB corrosive liquid (2%Br+20% lactic acid+ethylene glycol) after the rinse through the wafer after the corrosion of BM corrosive liquid the CZT wafer will be corroded, increase the wafer surface smooth degree.The ultrasonic cleaning three times in methyl alcohol of the wafer of finishing corrosion, each time is 5 minutes, to remove surperficial remaining Br and other impurity.

C. the deposition of gold electrode: will corrode good CZT wafer and take out, at N ₂Dry up under the protective atmosphere.Adopting concentration is the AuCl of 100ppm ₃The aqueous solution is at the circular Au electrode of CZT sample double-sided deposition, and the diameter of circular Au electrode is about 2mm, and thickness of electrode is 200

D. surface passivation: the CZT sample that will prepare gold electrode adopts KOH-KCl solution to carry out surface passivation earlier and handles.It is identical that the concentration of KOH and KCl solution keeps, and is controlled at 15wt%, and the time is 40 minutes; Then use the NH of 10wt% again ₄F/H ₂O ₂Mixed solution carries out passivation.The Passivation Treatment time is 30 minutes.Put into the abundant various ions that clean with the place to go remained on surface of a large amount of deionized waters with finishing passivation CZT wafer afterwards.

With the above-mentioned cadmium zinc telluride crystal wafer that makes, the tellurium-zinc-cadmium detector that is assembled, measured the I-V characteristic of passivation front and back devices with Keithley4200 type microgalvanometer, device before and after the cadmium zinc telluride crystal wafer passivation is done the comparison of I-V feature, compare two orders of magnitude that descended before the leakage current of finding the device that wafer of the present invention is made and the passivation, with independent employing KOH-KCl solution or NH ₄F/H ₂O ₂The reduction that also all has is in various degree compared in the solution passivation.Test analysis shows, the oxide layer that wafer surface has formed one deck strong adhesion, has been difficult to peel off, and the stoichiometric proportion on the CZT surface under oxide layer is improved.Above result shows that passivation effect of the present invention is better than the various chemical passivation methods of use at present, is with a wide range of applications.

Claims (1)

1. the method for a nuclear detector tellurium-zinc-cadmium wafer surface passivation, this method be earlier by traditional handicraft with cadmium zinc telluride crystal wafer polish, surface corrosion, deposited gold electrode and surface passivation, include four processes, it is characterized by, adopt two-step method in last surface passivation program, the concrete process of this method is as follows:

A. the polishing of tellurium-zincium-cadmium crystal: earlier cadmium zinc telluride crystal wafer is slightly thrown with diamond dust, make surfacing, after thick the throwing wafer is cleaned, put into the beaker that fills deionized water, carry out sonic oscillation, to remove the pollutant and the foreign particle of wafer surface, then wafer is carefully thrown, be minute surface until wafer surface; Subsequently, remove surface impurity with sonic oscillation once more, wafer is immersed in waits in the absolute methanol to corrode;

B. wafer surface corrosion: the wafer after the polishing adopts the BM corrosive liquid earlier, and promptly the corrosive liquid of 5%Br+ methyl alcohol composition carries out the surface chemistry corrosion, and the time is 1-2 minute; To re-use the LB corrosive liquid after the rinse in methyl alcohol through the wafer after the corrosion of BM corrosive liquid, promptly the corrosive liquid of 2%Br+20% lactic acid+ethylene glycol composition corrodes wafer, to increase the wafer surface smooth degree; Then with wafer in methyl alcohol ultrasonic cleaning to remove surperficial remaining Br and other impurity;

C. the deposition of gold electrode: will corrode good wafer and take out, at N ₂Dry up under the protective atmosphere.Adopt chemical method gold-plated, deposit circular gold electrode at the two-sided suitable position of wafer, its diameter is about 1-3mm, thickness is 200 .

D. surface passivation: will prepare the wafer of electrode, and adopt two step solwution methods that its surface is handled; Earlier carry out surface treatment with KOH-KCl solution, it is identical that the concentration of KOH and KCl solution keeps, and is controlled at 10-20wt%, and the time is 20-60 minute; Then use the NH of 10wt% again ₄F/H ₂O ₂Mixed solution carries out passivation, and the Passivation Treatment time is 10-30 minute, puts into the abundant various ions that clean with the removal remained on surface of a large amount of deionized waters with finishing passivation wafer afterwards; Obtain the cadmium zinc telluride crystal wafer of surface passivation at last.