Fabrication And Characterization Of Small Pixel InSb Infrared Focal Plane Array

InSb infrared focal plane array(IRFPA)as a typical photovoltaic detector working in the medium infrared band(1?5.5?m),has been applied in the fields of infrared guidance,staring imaging,space exploration,astronomical detection and so on,due to its high sensitivity(comparing to Pt Si)and high maturity process in mass production(comparing to Hg Cd Te).The small pixel IRFPA detectors have always been a research hotspot at both home and abroad.In order to improve the spatial resolution,large scale focal plane arrays have been developed,but this brings the issues of power consumption and cost increase of system.In order to reduce the power consumption and overall cost of system,small size focal plane arrays have been developed.As the pixel size of the focal plane array is reduced,the uniformity of the mesa etching is reduced.The defects within the resulting indium bump are increased,and the effective fill factor is reduced.Therefore,it is necessary to explore the mesa etching technology,indium bump preparation technology and silicon diffraction microlens array technology for InSb IRFPA.That will accelerate the fabrication of small pixel InSb IRFPA detector and improve the quality stability of detector.It is conducive to shortening the gap between home and abroad.In this thesis,the mesa etching,indium bump preparation and silicon diffraction microlens arrays techniques,which adopted in small pixel InSb IRFPA fabrication,were studied systematically.The method of mesa etching with high uniformity and low etching damage was discussed.The cause mechanism of defects was studied.The fabrication of high precision and diffraction efficiency silicon microlens array was discussed.The investigations on defect and crosstalk for small pixel InSb IRFPA were developed.Based on the above preparation and detection techniques,640×512 InSb IRFPA detectors with the size of 25?m×25?m,and 15?m×15?m,respectively,were designed and developed.The performance of detectors was evaluated.The etching process of small pixel IRFPA detector has been studied by both the inductively coupled plasma(ICP)dry etching technique and the damage layer wet etching removal technique.The results suggested that the etch rate and surface roughness increased with the increase of ICP power.The etch rate increased with the increase of RF power was in the range of 100 W-200 W.However,in the range of 200W-300 W,the surface roughness sharply increased with the increase of RF power.The etching rate increased with the increase of the pressure in the reaction chamber.The surface roughness decreased with the increase of the pressure in the reaction chamber.But the anisotropy of etching weakened.An 80 degree angle and good I-V curve of the InSb array chip were obtained by using the etching and damage layer removal optimization process mentioned above.The I-V curve showed that the short-circuit current was reduced by 19.2%.The indium bump fabrication technology of small pixel InSb IRFPA has been studied.In order to study the causes of indium bump defects in IRFPA,during the fabrication of InSb IRFPAs,indium bumps of different pixel sizes were studied using positive photoresist.The surface morphology of the chip,and the connectivity of the detector of the 50?m×50?m pixel size sample was better than other chips.Due to the small pixel size,the surface topography of the chip was connected or missing to the defective indium bump.The connected defects were due to the surface of the indium bump with connecting caused by the indium remnants during lithography and stripping.The missing defects were due to the lack of elemental indium bumps caused by positive photoresist residual during photolithography.Fabrication process such as photolithography,eroding and lift-off was optimized to reduce defective elements.The Si diffraction microlens array applied in the small pixel InSb IRFPA detector has been studied.The fabrication errors of Si diffraction microlens array by the conventional multiphotolithography technology were analyzed.The high-precision Si diffraction microlens array was fabricated by the sacrificial layer technology.In the sacrificial layer technology,the alignment accuracy of the multiple engraving layers was determined by the precision of the first mask lithography.In the subsequent etching,the etched region was protected by the sacrificial layer and the mask layer.The unprotected region was engraved.The non-etched areas were effectively blocked,thus the desired etched areas were achieved.The high-precision silicon diffraction microlens arrays could be obtained by the sacrificial layer technology.The diffraction efficiency could reach 92.6%.The detectivity of InSb IRFPA integrated with Si diffraction microlens array was increased by 10%.The characteristics of defects in small pixel InSb IRFPA have been studied by the high power optical microscope and the FPA test-bench.The response voltage of missing defective elements was zero,and the response voltage of the nearest neighbor elements comparing to normal element was increased by about 25%.So it was easy to identify missing defective elements.It is difficult to identify connected defective elements by FPA test-bench because the response voltage of connected defective elements is basically the same as that of normal elements.A novel method which realized the identification and orientation of connected defective elements by measuring the response voltage of detectors was proposed.Results suggested that the response voltage of detector can be divided into two sections by using the proposed method.The response voltage of connected defective elements was average of corresponding response voltage of the two sections units.The test data was analyzed by MATLAB software.The particular information of connected defective elements such as number,shape and location was shown.The connected defective elements were identified and orientated markedly by the technique.A novel eyelet point method which to realize the crosstalk of small pixel IRFPA was proposed.The transmittance of the eyelet point in the substrate was 100%,while the transmittance of the other component in the substrate was 0.The substrate with the eyelet pattern was fixed at the front of InSb IRFPA.25 detection units were selected as the eye-hole patterns,which were formed by closely repeating the eye-hole unit pattern.The crosstalk of InSb IRFPA with the pixel size of 25?m×25?m was 3.86%.The 640×512 InSb IRFPA detectors with pixel sizes of 25?m×25?m,and 15?m×15?m,respectively,were designed and fabricated by the technologies mentioned above.The performance of small pixel InSb IRFPA detectors was characterized by the proposed detection techniques associated with the defect and crosstalk.The results suggested that the average blackbody responsivity of 640×512 InSb IRFPA with the pixel size of 25?m×25?m is 1.2×10⁹ V/W.The responsivity nonuniformity was 9.5%.The average blackbody detectivety was 2×10¹¹ cm·Hz^1/2·W^-1.The rate of defective elements was 1.2%.The crosstalk was 3.86%.The results in the infrared system imaging had high contrast images,clean edges,rich lays,and few defects.The main performance of the 640×512 InSb IRFPA with the pixel size of 15?m×15?m encapsulated into the test Dewar was as follows:the average blackbody responsivity of7.79×10⁹ V/W,the nonuniformity of responsivity of 12.1%,and the average blackbody detectivety of 1.08×10¹⁰ cm·Hz^1/2·W^-1.