RU2515960C1 - METHOD FOR MANUFACTURE OF PbS-BASED PHOTORECEIVING MODULE - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: PbS-based photoreceiving module represents a hybrid microassembly consisting of a photosensitive cell as a PbS-based line and a LSI chip (multiplexor) interconnected as a flip-chip assembly. Indium plugs are applied on lamellar bond areas of the photosensitive cell, which, besides Cr, Pd and Au layers, contain Cr and In sublayers and join indium plugs applied to the LSI chip thus forming electrical and mechanical bonds. The method for manufacture of the photoreceiving cell allows significant reduction in labour intensity of the assembly and increase in manufacturing efficiency using the method of grouped cold welding.

EFFECT: possible design of the photoreceiving cell as a hybrid microassembly and location of LSI chips at the photosensitive cell, reduction of dimensions and improvement of reliability.

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Description

The inventive method relates to the manufacture of semiconductor devices that are designed to register infrared radiation and use in optoelectronic equipment where the detection of infrared radiation is required. Such equipment includes thermal imaging devices and heat direction finders used in various fields of technology.

The PbS-based photodetector module is a hybrid microassembly consisting of a PbS-based photosensitive element made in the form of a multi-element line with a contact raster made using advanced chalcogenide technology on a matted quartz substrate and an LSI chip (multiplexer) made using p -channel technology interconnected by inverted mounting method (flip-chip).

An analogue is a method of manufacturing a 256 element LMA-15S sensor, [Cal Sensors brochure, published December 1, 2008], which contains a photosensitive structure based on lead chalcogenide and a signal pick-up and signal processing circuit connected by wire links.

The closest analogue (prototype) of the proposed method is a method of performing a two-color photoconductive linear detector [US patent No. 5,525,801 from 06/11/1996]. This device incorporates a photodetector module located on a heat-conducting substrate, similar to the proposed one. The photosensitive element is made in the form of a ruler based on PbS, on a quartz plate and connected by electrical conductors using microwelding with a multiplexer, which provides the collection and processing of signals from photosensitive elements.

The disadvantage of the selected analogues are: the high complexity of the installation and low reliability at the junction of the contact pads of the photosensitive element with signal readout circuits.

Until recently, as a method of joining photosensitive structures based on lead chalcogenides and LSI readout, the thin wire contact welding method was used, as was realized in the analogue and prototype of the photodetector module [US Patent No. 5,525,801 of June 11, 1996]. In connection with a significant increase in the number of photosensitive elements and a corresponding decrease in their size, this process becomes laborious. In addition to the time required for installation, the photodetector modules boiled with gold have large weight and size characteristics and low reliability in the places of welding. Against the background of the above disadvantages, it becomes preferable to use flip-chip technology using indium microcontacts, which provide electrical and mechanical connection of the photosensitive element with LSI readout, significantly reducing the complexity of installation and increasing the efficiency of manufacturing the photodetector module. This allows you to make a photodetector module in the form of a hybrid assembly and place LSI readouts on a photosensitive element, reduce overall dimensions and increase reliability.

The objective of the method of manufacturing a photodetector module is to reduce the overall dimensions of the structure, increase reliability and reduce the time and complexity of manufacturing.

The technical result is achieved in that the photodetector module containing a PbS-based photosensitive element, made in the form of a multi-element array, and LSI readout, is made in the form of a hybrid assembly using the Flip-chip method. where indium columns formed on the contact pads of the lamellas of the photosensitive element, which are joined with the indium columns of the BIS-reading, made by p-channel technology, form an electrical and mechanical connection.

The reduction in overall dimensions, compared with the design of the boiled thin wire, is achieved by installing an LSI readout on a photosensitive element with the formation of electrical and mechanical coupling, therefore, additional fixation of the readout circuit relative to the photosensitive element is not required.

The increase in reliability, compared with the use of thin wire, is achieved by increasing the area of the contacting surfaces and protecting the joints from external influences by the LSI-reading housing.

Reducing the time and complexity of manufacturing is achieved by applying the method of group cold welding, where the docking of the contacts is carried out simultaneously, in one operation using a special installation. Welding of contacts with wire is carried out sequentially and takes much longer.

The proposed solutions are illustrated by the following illustrations:

figure 1 - photodetector module PbS;

figure 2 is a fragment of a photosensitive element;

figure 3 is a photograph of a photodetector module PbS.

The photomodule includes:

1 - a photosensitive element based on PbS;

2 - photosensitive elements located in the form of a ruler;

3 - lamellas;

4 - LSI reading;

5 - substrate;

6 - indium columns.

The technology of assembly of the photodetector module provides separate production and control of photosensitive elements, autonomous production and control of multiplexers with the subsequent assembly of the photomodule, which ensures a satisfactory yield.

Microcontacts made in the form of indium columns are applied to the contact pads of the photosensitive element and the LSI readout, then the contact pads of the photosensitive element and the LSI readout are precisely joined. At room temperature, under pressure on the LSI chip, the indium microcontacts diffuse into each other with the formation of an electrical and mechanical connection between the photosensitive element and the LSI chip.

Indium contact posts provide mechanical and electrical connection of functional units of semiconductor devices assembled by group cold welding (flip-chip), stringent requirements are imposed on the strength of their connection.

The strength of the joint is determined by the pressure applied during assembly, which, in turn, is due to the size of the surfaces to be joined to form a contact, as well as their purity, in particular, the presence and thickness of natural oxide, since the highest quality welding is achieved by sticking together pure indium.

The photosensitive element is made on a substrate, which is traditionally used on a matted quartz substrate for a PbS layer of size 25.0 × 25.0 mm ² with a line of photosensitive areas of 256 elements each.

Photosensitive elements have dimensions of 40 × 60 μm, the gap between adjacent elements in the same row of 10 μm.

The substrate with photosensitive elements is divided into two zones: the photosensitive element itself with a number of photosensitive sites and a contact raster with lamellas, 60 μm wide and 80 μm pitch, onto which, after manufacturing the photosensitive element and raster, ~ 5 μm high indium contacts are applied, which are necessary for electrical and mechanical docking with LSI readout. The qualitative implementation of this process is difficult due to the significant thickness of the sprayed layer of indium, the granular structure of the film, low mechanical strength and low melting point.

The substrate coating consists of three components - chromium (Cr), palladium (Pd), gold (Au) with a total thickness of about 0.2 microns. The ohmic contact gold - lead sulfide is provided by a gold film, which is deposited in a vacuum process using the reverse photolithography process. At this stage, photosensitive lines and a common electrode are formed. Photosensitive sites and a contact raster are formed by ion-plasma etching through a photoresist mask.

To stabilize the parameters of the photosensitive pads and protect the contact raster from mechanical influences, the entire photosensitive element, with the exception of weld lamellas, is covered with a protective film; for a photosensitive element based on PbS - chalcogenide glass (arsenic trisulfide).

It is not possible to dock the LSI reading with the photosensitive element directly through the indium columns using the classical technology, where the contact raster of the photosensitive element is a sublayer of three Cr-Pd-Au metals, since the Au sublayer undergoes degradation upon contact with indium, worsening electrical and mechanical parameters.

New operations are additionally introduced into the standard manufacturing technology of photosensitive elements, such as applying chromium and indium sublayers onto the pads over the main sublayer, which made it possible to obtain photosensitive elements ready for docking with LSI readout.

The combination of the described manufacturing features made it possible to create a compact, technologically advanced photodetector module.

In this method of manufacturing a photodetector module, we can designate the first-used operation of docking photosensitive elements based on lead chalcogenides directly from an LSI-reader made using p-channel technology with switching rasters made on optical quartz glass, where the raster tracks and contact pads are made using classical chalcogenide technologies.

Claims (1)

A method of manufacturing a photodetector module, which consists in the fact that a photosensitive element based on PbS is performed on the substrate, LSI readouts are separately manufactured, characterized in that the hybrid assembly of the photosensitive element and LSI readings is carried out using the flip-chip method: indium the columns are applied to the contact pads of the photosensitive element lamellas, which, in addition to the Cr, Pd, Au layers, contain a Cr and In sublayer and are joined with indium columns deposited on the LSI readings, forming an electric and mechanical connection.

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