RU127908U1 - PbSe-based photodetector module - Google Patents

Abstract

A photodetector module containing a PbSe-based photosensitive element, made in the form of a multi-element array, and an LSI reading, characterized in that it is made in the form of a hybrid assembly using the Flip-chip method, where indium columns are applied to the contact areas of the lamellas photosensitive element, are joined with indium columns LSI-reading, made by p-channel technology, forming an electrical and mechanical connection.

Description

The inventive utility model relates to the field of semiconductor devices, which are designed for registration of infrared radiation and use in optoelectronic equipment, which requires the detection of infrared radiation. Such equipment includes thermal imaging devices and heat direction finders used in various fields of technology.

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

An analogue of the proposed device is a sensor that includes an array of sensitive elements and a circuit for individual adaptation of sensitive elements [US patent No. 5,600,143 from 02/04/1997]. The device contains a photosensitive structure based on lead chalcogenide and a signal pick-up and signal processing circuit, connected by wire connections.

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

The disadvantage of the selected analogues is: large dimensions, the high complexity of installation, as well as low reliability at the junction of the contact pads of the photosensitive element with signal reading circuits.

Until recently, as a method of joining photosensitive structures based on lead chalcogenides and BIS readings, a thin wire contact welding method was used, as is implemented in the analogue and prototype photomodule [US patent No. 5,600,143 of February 4, 1997], [US patent No. 5,525,801 of 06/11/1996]. 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, such designs, boiled in gold, have large weight and size characteristics and low reliability in the places of welding. Against the background of the aforementioned shortcomings, it becomes preferable to use flip-chip technology using indium microcontacts, which provide electrical and mechanical connection of the photosensitive element with LSI readout, which can significantly reduce the complexity of installation and increase the efficiency of manufacturing the photomodule. This allows you to constructively execute the photomodule in the form of a hybrid assembly and place the LSI readout on the photosensitive element, reduce the size and increase the reliability of the photomodule.

For lead chalcogenide photodetectors (PbSe), this design is fundamentally new.

The objective of the utility model is to reduce the overall dimensions of the structure, increase reliability and reduce the time and complexity of manufacturing.

The technical result is achieved by the fact that a photodetector module containing a PbSe-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 are deposited on contact the slats of the photosensitive element are joined with the indium columns of the BIS-reading, made by p-channel technology, forming an electrical and mechanical connection.

The reduction in overall dimensions, compared with the design of a 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 by protecting the connections from external influences by the BIS-reading housing.

Reducing the time and complexity of manufacturing is achieved by applying the method of group cold welding, where the contacts are docked and 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 - photomodule. Photosensitive elements and lamellas in the selected area are enlarged and shown conditionally;

figure 2 is a fragment of a photosensitive element;

The photomodule includes:

1 - a photosensitive element based on PbSe;

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

3 - lamellas;

4 - LSI reading;

5 - substrate;

6 - indium columns.

The design of the photomodule allows for the separate manufacture and control of photosensitive elements, the autonomous manufacture and control of multiplexers with the subsequent assembly of the photomodule, which ensures a satisfactory yield of suitable photomodules.

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 for PbSe films with a substrate of polished photo glass measuring 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 the photosensitive element and the raster are made, indium contacts ~ 5 μm high 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 - Cr, Pd, Au with a total thickness of about 0.2 microns. The ohmic contact of lead gold-selenide is provided by a gold film, which is deposited in a vacuum process using the reverse photolithography process. At this stage, photosensitive lines 40 μm wide and a common electrode 80 μm wide 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 coated with a protective coating - a photoresist.

It is impossible to use the classical technology for docking an LSI reading with a photosensitive element directly through indium columns, 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, with deterioration of electrical and mechanical parameters. New operations, such as coating on the pads over the main sublayer of chromium and indium sublayers, were additionally introduced into the standard technology for the production of photosensitive elements, which made it possible to obtain photosensitive elements ready for docking with LSI readouts.

The combination of the described design features made it possible to create a compact, technologically advanced photomodule.

Claims (1)

A photodetector module containing a PbSe-based photosensitive element, made in the form of a multi-element array, and an LSI reading, characterized in that it is made in the form of a hybrid assembly using the Flip-chip method, where indium columns are applied to the contact areas of the lamellas photosensitive element, are joined with indium columns of the BIS-reading, made by p-channel technology, forming an electrical and mechanical connection.

Images