RU2796482C1 - Method for diffusion welding of single-crystal silicon and glass - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: production of sensitive elements used in the manufacture of micromechanical accelerometers, microgyroscopes, integral pressure sensors. The method for diffusion welding of single-crystal silicon and glass includes heating the package, isothermal exposure, and supplying a constant voltage to the package. This isothermal exposure is carried out for two hours, and after the voltage is applied, the current passing through the package being welded is monitored until it stops. Then, additional isothermal exposure of the welded package is carried out for two hours, after which controlled cooling is carried out at a rate of 1 to 4 deg/min.

EFFECT: reduction of residual internal stresses arising in a package of glass and single-crystal silicon, causing an increase in the accuracy characteristics of manufactured micromechanical sensors.

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Description

The invention relates to the field of instrumentation and can be used in the manufacture of sensitive elements used in the manufacture of micromechanical accelerometers, microgyroscopes, integral pressure sensors.

A known method of assembling sensitive elements, which consists in combining a glass lining and a crystal of single-crystal silicon, installing and clamping in a special fixture, heating to a temperature of 400 ° C, holding at this temperature for 1 hour and applying a voltage of 700 V to the glass lining and silicon crystal [1].

The disadvantage of this method is that the anodic connection is carried out at a high voltage of 700 V. Although the connection is carried out, such a voltage leads to high internal stresses of the glass-lined package and the single-crystal silicon die after the assembly processes are completed. This is due to the fact that the exposure time is short - 1 hour at a temperature of 400 ° C and for welding it is necessary to apply a higher voltage, namely at least 700 V.

There is a method in which the parts to be welded made of semiconductor and glass are heated to the welding temperature, a constant voltage is applied to them to create an ion diffusion current between the surfaces to be joined, and they are squeezed cyclically [2].

The disadvantage of this method is the stresses that occur in the materials, which reduce the accuracy of the sensitive elements of integrated sensors. The occurrence of stresses is associated with different coefficients of linear expansion of the semiconductor and glass, and elastic deformation from the elimination of the initial non-flatness of the contact surfaces in the package by mechanical normalized clamping.

A known method of assembling a sensitive element of a micromechanical sensor, which consists in combining a glass lining and a single-crystal silicon crystal, installing and clamping in a special device, heating, holding at a given temperature and applying voltage, simultaneously combines two glass linings and a single-crystal silicon crystal located between them , and apply a voltage of at least 160 V to both plates for at least two minutes, turn off the voltage, reverse the voltage polarity, apply voltage again, repeat the polarity reversal cycle at least three times [3].

The disadvantage of this method is the ultra-low welding voltage, which requires a high temperature of the welding process and, accordingly, the manifestation of high residual stresses.

Although the process of supplying a reverse polarity current somewhat reduces the residual stresses and naturally the mutual deflection of the resulting package, however, the absence of a slow or controlled voltage during the assembly process significantly increases the residual stresses and, accordingly, as a result, significantly reduces the accuracy of the sensors.

Closest to the claimed invention is a method for diffusion welding of a package of glass and single-crystal silicon, including its compression with a normalized force, heating, isothermal exposure and supply of constant voltage to the compressed package, characterized in that the isothermal exposure of the compressed multilayer package is carried out at a temperature above the temperature welding, and the voltage is applied after the compressed package is cooled to a temperature below the welding temperature [4].

The disadvantage of this method is the stresses arising in the materials, which appear as a result of its compression with force and further isothermal exposure and subsequent diffusion welding. The welded crystal remains in a stressed state after welding. This leads to a high zero offset and significant hysteresis during sensor operation. Another disadvantage is that the package of glass and monosilicon is heated to temperatures above 450°C, which is unacceptable if aluminum conductors or displacement sensor plates with various metallized sublayers are formed on the sensitive element. Such high temperatures lead during further operation to the delamination of the conductors from the silicon or glass substrate. Another disadvantage of the method is that the method does not indicate that heating, isothermal exposure, welding, cooling should be carried out in a closed space in air or in a vacuum. So only the closed space contributes to the gradual cooling throughout the entire volume of the assembled package structure. Otherwise, we will get a package with large residual internal stresses inside the glass and silicon, which reduce the accuracy of the sensors, namely, lead to a significant hysteresis and a large zero shift in the operating temperature range. Another disadvantage is the uncontrolled cooling process of the resulting assembly. This also leads to high residual stresses after the end of the process and, accordingly, to a significant increase in the zero offset.

The task to be solved by the claimed invention is to reduce the residual internal stresses that occur in a package of glass and single-crystal silicon and, consequently, improve the accuracy of micromechanical sensors.

The problem is solved due to the fact that in the method of diffusion welding of single-crystal silicon and glass, including its heating, isothermal exposure and applying a constant voltage to the package, according to the invention, the said isothermal exposure is carried out for two hours, and after the voltage is applied, the control passing through welded current package and after its termination, an additional isothermal exposure of the welded package is carried out for two hours, after which controlled cooling is carried out at a rate of 1 deg/min to 4 deg/min.

Distinctive features of the claimed invention is that the said isothermal exposure is carried out for two hours, and after the voltage is applied, the current passing through the package to be welded is monitored, and after its termination, an additional isothermal exposure of the welded package is carried out for two hours, after which controlled cooling is carried out at a rate from 1 deg/min to 4 deg/min.

Temperature and charge distribution over the surface

should be even. Therefore, after the welding process, the processes in the package do not immediately stop. It is necessary to hold the welded package at a constant temperature and without voltage. As a result of the connection, residual stresses are formed. The stresses arising due to the difference between the TCLE of glass and silicon are called coefficient stresses. Also, mechanical stresses resulting from the difference in the TCLE of the materials being joined after they are cooled are called thermal. Before heating, the glass and silicon parts have the same dimensions; when heated, the parts expand. After, connecting the part, cooling down to the working

temperature, mutually deform. That is precisely why the package after welding must be kept at that temperature. Also, the uneven distribution of the composition over the area of the plate due to the use of both point and flat electrodes.

it is proposed to reduce the resulting deflection of the plates by controlled cooling of no more than 1 deg/min.

An example of the implementation of the claimed method.

Produced diffusion welding sensitive elements of the accelerometers, which is a package of glass single-crystal silicon KEF-4.5 - glass LK5. Package size 9×6×2.9 mm (length-width-height). The package was heated to a temperature of 390°C, then an isothermal exposure was made for two hours, after which a voltage of 420 V was applied to the package, followed by control of the current through the package being welded until it stopped. Then spent the exposure for two hours. Next, controlled cooling was carried out at 1 deg/min.

Produced diffusion welding sensitive elements of the accelerometers, which is a package of glass - single-crystal silicon KEF-4.5 - glass "pyrex 7740". Package size 9×6×2.9 mm (length-width-height). The package was heated to a temperature of 410°C, then an isothermal exposure was made for two hours, after which a voltage of 390 V was applied to the package, followed by control of the current through the package being welded until it stopped. Then spent the exposure for two hours. Next, controlled cooling was carried out at 3 deg/min.

Produced diffusion welding sensitive elements of accelerometers, which is a package of glass - single-crystal silicon KEF-4.5 - glass "Borofloat 33". Package size 9×6×2.9 mm (length-width-height). The package was heated to a temperature of 410°C, then an isothermal exposure was made for two hours, after which a voltage of 420 V was applied to the package, followed by control of the current through the package being welded until it stopped. Then spent the exposure for two hours. Next, controlled cooling was carried out at 4 deg/min.

As a result of the application of the proposed method, the residual stresses arising during diffusion welding in glass and single-crystal silicon have decreased. Residual stresses were checked using a PKS-250 polariscope-polarimeter.

In FIG. Figures 1-4 show samples of sensitive elements of micromechanical accelerometers in linearly polarized light on the table of the PKS-250 setup. Glow in the samples indicates the presence of residual stress. As can be seen on different samples, the size and brightness of the glow is different. This indicates that the samples were welded under different conditions. Thus, it is confirmed that how the welding modes affect the magnitude of residual stresses in the sensitive elements of accelerometers, and, consequently, the accuracy of the sensors.

Breadboard tests of sensors showed that the temperature shift of accelerometers decreased, on average, by 50-75%, due to which the accuracy characteristics of micromechanical accelerometers increased.

Information sources:

1. US patent No. 6537938.

2. Author's certificate of the USSR No. 1454612.

3. RF patent No. 2525715

4. RF patent No. 2491158 - prototype.

Claims (1)

A method for diffusion welding of single-crystal silicon and glass, including heating the package to be welded, isothermal holding and supplying a constant voltage to the package, characterized in that said isothermal exposure is carried out for two hours, and after the voltage is applied, the current passing through the package to be welded is monitored and after it stops an additional isothermal exposure of the welded package is carried out for two hours, after which it is subjected to controlled cooling at a rate of 1 to 4 deg/min.

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