RU2285976C1 - Method for producing high-power microwave transistors - Google Patents

Abstract

FIELD: electronic engineering; high-power microwave transistors and small-scale integrated circuits built around them.

SUBSTANCE: proposed method for producing high-power microwave transistors includes formation of transistor-layout semiconductor wafer on face side, evaporation of metals, application and etching of insulators, electrolytic deposition of gold, formation of grooves on wafer face side beyond transistor layout for specifying transistor chip dimensions, thinning of semiconductor wafer, formation of grooves on wafer underside just under those on face side, formation of through holes for grounding transistor leads, formation of integrated heat sinks for transistor chips around integrated heat sink followed by dividing semiconductor wafer into transistor chips by chemical etching using integrated heat sinks of transistor chips as mask.

EFFECT: enhanced power output due to reduced thermal resistance, enhanced yield, and facilitated manufacture.

2 cl, 1 dwg, 1 tbl

Description

The invention relates to electronic equipment, and in particular to methods of manufacturing powerful microwave transistors and MIS based on them.

A known method of manufacturing a powerful field-effect transistors (PTSH) microwave, including the following operations:

- the formation of a PTS topology on a semiconductor wafer — the epitaxial structure of gallium arsenide — using electron and photolithography, metal sputtering, deposition and etching of dielectrics, and galvanic deposition of gold;

- thinning of the semiconductor wafer up to 60-80 microns;

- the formation of through holes for grounding the sources of transistors;

- galvanic deposition of gold with a thickness of 2 μm from the back of the semiconductor wafer;

- separation of the semiconductor wafer into transistor crystals by sharp diamond disks (1).

The disadvantages of this method are the low power of the field effect transistor due to the high thermal resistance due to the large thickness of about 60-80 μm gallium arsenide semiconductor wafer, low yield due to mechanical damage, chips and cracks in the operation of semiconductor wafer separation by cutting diamond disks.

A known method of manufacturing powerful microwave field-effect transistors and MIS based on them is a prototype that includes the following basic operations:

- the formation of a PTS topology on a semiconductor wafer — the epitaxial structure of gallium arsenide — using electron and photolithography, metal sputtering, deposition and etching of dielectrics, and galvanic deposition of gold;

- thinning of the semiconductor wafer of gallium arsenide to a thickness of the order of 25-30 microns;

- galvanic deposition of an integral heat sink from gold with a thickness of about 30 μm from the back of the semiconductor wafer of gallium arsenide;

- separation of the gallium arsenide semiconductor wafer into transistor crystals by sharp diamond disks (2).

Thinning of the semiconductor wafer of gallium arsenide to a thickness of 25-30 μm made it possible to reduce the thermal resistance of PTSh and, therefore, increase its power compared to the previous method.

However, on the other hand, when dividing the semiconductor wafer into transistor crystals, in order to ensure its strength, it is necessary to stick a thin semiconductor wafer on a flexible carrier, which complicates the method.

And the separation of the semiconductor wafer into transistor crystals by sharp diamond disks, as in the previous method, causes mechanical damage, chips and cracks, which also determines a low yield.

In addition, during the separation of the wafer into crystals, including the cutting of an integral heat sink from gold with a thickness of about 30 μm, a quick “salting” of the cutting tool and the formation of a gold “bead” around the transistor's crystal occur. This causes difficulties during the subsequent installation of the transistor crystal in the microwave circuit, which can negatively affect both the output of the suitable microwave circuits and their electrical characteristics.

The technical result of the invention is to increase power by reducing thermal resistance, increasing yield and simplifying the method of manufacturing powerful microwave transistors.

The technical result is achieved by the fact that in the known method of manufacturing high-power microwave transistors, which includes forming the topology of transistors on the front side of a semiconductor wafer using electronic and photolithography, metal sputtering, deposition and etching of dielectrics, galvanic deposition of gold, thinning of the semiconductor wafer to a thickness of less than 30 microns, etching in a semiconductor wafer of grounding holes for transistor leads, galvanic deposition on the back of the semiconductor single plate integrated heat sink of gold with a thickness of more than 30 μm, the separation of the semiconductor wafer into transistor crystals, grooves 5-10 μm deep and 70-100 μm wide are formed on the front side of the transistor topology before thinning the semiconductor wafer to thin the semiconductor wafer to specify the size of the transistor crystals, and after the thinning of the semiconductor wafer form grooves on its reverse side with a depth of 5-10 μm directly under the grooves on the front side, while the ratio of their width is 3-2, and form a channel Using photolithography and etching, after the formation of an integral heat sink, the integral heat sinks of transistor crystals are formed by photolithography by an integrated heat sink followed by etching in the locations of the grooves on the back of the semiconductor wafer, and the semiconductor wafer is divided into transistor crystals by chemical etching, while the integral heat sinks of the crystals transistors serve as a mask.

As a semiconductor wafer, for example, a gallium arsenide wafer is used.

The formation of grooves on the front and back of the semiconductor wafer opposite each other and with the given dimensions in conjunction with a different sequence of operations allowed:

- firstly, to separate the semiconductor wafer into transistor crystals, if it is possible to use integrated heat sinks of transistor crystals as a mask, by chemical etching and thereby eliminate mechanical damage, chips and cracks if diamond cutting is used during separation and, as a result, increase the yield ,

- secondly, to increase the reproducibility of the size of the crystals, which allows to reduce the tolerances when mounting the transistor crystal in the microwave circuit and thereby reduce losses in the supply circuits, and therefore, increase power,

- thirdly, to improve the quality of installation due to a decrease in the thickness of the solder or glue used when mounting the transistor crystal in the microwave circuit, which was made possible by eliminating the gold "bead" around the transistor crystal that occurs when cutting a semiconductor wafer with diamond disks, and thereby reduce thermal resistance and, as a consequence, in addition to the above, increase the power,

fourthly, to ensure reproducibility of the size of the transistor crystals due to the specified size of the grooves on the front and back of the semiconductor wafer and the elimination of the gold "collar", and therefore, to further increase the yield,

fifthly, to simplify the manufacturing method by separating the semiconductor wafers by chemical etching and eliminating diamond cutting.

The formation of a groove both on the front side of the semiconductor wafer and on the reverse side of it with a depth of less than 5 μm is not sufficient for the subsequent determination of the crystal size, and more than 10 μm is undesirable due to possible destruction of the plate in subsequent technological operations.

The formation of a groove on the front side of a semiconductor wafer with a width of less than 70 μm is unacceptable, because with the specified ratio of their width, the width of the groove on the back is so small that the subsequent operations — the formation of integral heat sinks of transistor crystals and the separation of the semiconductor wafer into transistor crystals — becomes difficult, and more than 100 microns is impractical due to the unjustified consumption of semiconductor material.

The ratio of the width of the grooves on the front and back of the semiconductor wafer is determined by its residual thickness under the grooves and the ratio of the etching rate in the lateral and vertical directions.

Based on the foregoing, for a specified thickness of the semiconductor wafer less than 30 microns, this ratio is 3-2.

The invention is illustrated in the drawing,

where the stage of separation of a semiconductor wafer fragment into transistor crystals is given, where

- semiconductor wafer - 1,

- transistor topology - 2,

- groove on the front side of the semiconductor wafer - 3,

- groove on the back of the semiconductor wafer - 4,

- grounding hole of the terminals of the transistor - 5,

- integral heat sink of the crystal of the transistor - 6,

- crystal power microwave transistor - 7

An example of a specific implementation:

- on the front side of the semiconductor wafer 1, for example gallium arsenide, with a thickness of 520 μm, the topology of transistor 2 is formed by known methods: electron and photolithography, metal sputtering, deposition and etching of dielectrics, galvanic deposition of gold,

- further on the front side of the semiconductor wafer 1, outside the topology of the transistor 2, grooves 3 are formed with a depth of 8 μm and a width of 85 μm to set the crystal size of the transistor using also known photolithography and etching methods,

- further, the semiconductor wafer 1 is thinned, for which it is glued onto a carrier, for example, glass with a plane parallelism of less than 1 μm, and its thickness is adjusted to 120 μm by mechanical grinding, then the semiconductor wafer is glued onto a sapphire carrier and thinned by chemical-dynamic polishing to a thickness 25-30 microns,

- form grooves 4 with a depth of 8 μm and a width of 56 on the reverse side of the semiconductor wafer also known methods of photolithography and etching,

- form through grounding holes 5 for the transistor leads also by photolithography and chemical etching,

- form an integral heat sink by galvanic deposition of gold with a thickness of 25-30 microns,

- form the integral heat sink of the crystal of the transistor 6 by photolithography along the integral heat sink with subsequent etching at the location of the grooves 4 on the back of the semiconductor wafer 1,

- divide the semiconductor wafer 1 into the crystals of the transistors 7, for which using the integrated heat sink of the crystal of the transistor 6 as a mask, etch the semiconductor wafer of gallium arsenide 1 at the locations of the grooves 4 on its reverse side.

Thus, we have separated crystals of high-power microwave transistors on a sapphire carrier, which are removed from the carrier in organic solvents.

Examples 2-3.

Analogously to example 1, high-power microwave transistors were made, but with grooves on the front and back sides with a depth of 5 and 10 μm and a width on the front side of 70 and 100 μm and the reverse side of 46 and 66, respectively.

Examples 4-5.

Analogously to example 1, high-power microwave transistors were made, but with grooves on the front and back sides with a depth of less than 5 and more than 10 microns and a width on the front side of less than 70 and more than 100 microns and a width on the reverse side of 40 and 74, respectively.

On the manufactured samples of high-power microwave transistors, a visual analysis was conducted under a LEICA INM 100 microscope for mechanical damage, chips, cracks, reproducibility of transistor crystal sizes.

On manufactured samples of high-power microwave transistors, power was measured.

The data are tabulated.

As can be seen from the table, the microwave transistors made by the proposed method (examples 1-3) have a power exceeding the power of the microwave transistor - prototype of about 10 percent and the reproducibility of transistor crystal sizes of about 90 percent compared to 70 percent in the prototype.

When forming grooves on the front and back side of a semiconductor wafer with a depth that goes beyond the limits specified in the claims, it is observed:

either low reproducibility (example 4) and, as a result, reduced power and yield,

or destruction of the plate (example 5).

Thus, the proposed method of manufacturing high-power microwave transistors allows, in comparison with the prototype:

- firstly, to reduce thermal resistance and thereby increase the power of the microwave transistor of about ten percent,

- secondly, to increase the yield due to the exclusion of mechanical damage, chips, cracks and increase the reproducibility of crystal sizes.

- thirdly, to simplify the manufacturing method by eliminating diamond cutting.

The proposed method for manufacturing high-power microwave transistors can be used in the manufacture of MIS microwave based on them.

INFORMATION SOURCES

1. Ivashchuk A.V., Bosy V.I., Kovalchuk V.N. Microwave field-effect transistors of medium power of the millimeter wavelength range. Technology and design in electronic equipment. No. 6, 2003, pp. 27-31.

2. Handbook of Microwave and Optical Component Vol 2, 1990, Fabrication processes, p. 518-523.

No. p / p The depth of the groove on the front side of the semiconductor substrate, microns The depth of the groove on the back of the semiconductor substrate, microns The width of the grooves on the front side of the semiconductor substrate, microns The width of the grooves on the back side, microns with a ratio of their width 3-2 Transistor power Yield one 8 8 85 56 Power increase of about 10% The reproducibility of crystal sizes is about 90%. No mechanical damage, chips, cracks 2 5 5 70 46 Power increase of about 10% Same 3 10 10 one hundred 66 Power increase of about 10% Same four 3 3 60 40 Power reduction Decrease in percent of an exit about 10% 5 12 12 110 74 Plate destruction 6 prototype one hundred% The reproducibility of crystal sizes does not exceed 70%. There are mechanical damage, chips, cracks

Claims (2)

1. A method of manufacturing high-power microwave transistors, including the formation of the topology of the transistors on the front side of the semiconductor wafer using electronic and photolithography, metal sputtering, deposition and etching of dielectrics, gold plating, thinning of the semiconductor wafer to a thickness of less than 30 microns, etching in the semiconductor wafer of grounding openings for transistor leads, galvanic deposition on the reverse side of a semiconductor wafer integrated gold heat sink and a thickness of more than 30 μm, the separation of the semiconductor wafer into transistor crystals, characterized in that before thinning the semiconductor wafer, grooves of 5-10 μm deep and 70-100 μm wide are formed on the front side of the transistor topology outside the topology of the transistors to specify the size of the transistor crystals, and after thinning semiconductor wafers form grooves on its reverse side with a depth of 5-10 μm directly under the grooves on the front side, while the ratio of their width is 3-2, and form grooves using photolithography and t After forming an integral heat sink, integral heat sinks of transistor crystals are formed by photolithography along an integrated heat sink followed by etching at the locations of the grooves on the back of the semiconductor wafer, and semiconductor wafers are separated into transistor crystals by chemical etching, while the integral heat sinks of transistor crystals serve as a mask. 2. A method of manufacturing high-power microwave transistors according to claim 1, characterized in that, for example, a gallium arsenide plate is used as a semiconductor wafer.