JPS6246505B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a printing glass paste for use in surface stabilization of semiconductor devices. In the glass passivation method, which covers the pn junction of a semiconductor device with a glass film, there are various methods for attaching glass powder to the pn junction.
Generally, electrophoresis is often used. The method for attaching glass by electrophoresis is to remove the oxide film only at the pn junction where the glass powder is to be attached and expose the silicon surface, and then add NH ₃ gas as an electrolyte to isopropyl alcohol in which the glass powder is dispersed. This is a simple method that allows glass powder to be attached to the pn junction by applying a DC voltage with the silicon wafer on the negative side and the counter electrode on the positive side in the blown electrophoresis liquid, making it relatively suitable for mass production. The disadvantage of the conventional method mentioned above is that the glass powder commercially available for passivation is passed through a 325-mesh sieve, and the glass powder used in electrophoresis is approximately 15 μm in size. The effective amount of glass powder used is as low as about 20%. Furthermore, since a large amount of an organic solvent such as isopropyl alcohol is used as a dispersion medium, there is a lot of waste, and since a relatively high voltage is applied in the organic solvent, there is a risk of ignition due to discharge. Furthermore, because it is difficult to adjust the NH ₃ concentration and glass concentration in the dispersion medium, the amount of glass adhered to the semiconductor wafer varies, and the thickness of the glass film obtained by baking this wafer has poor reproducibility. There were problems of poor characteristics and poor yield. Screen printing methods and doctor blading methods can be cited as methods for avoiding the drawbacks of the conventional methods described above. These methods, along with electrophoresis, centrifugal sedimentation, and the like, have been studied for a long time. Currently, in the field of hybrid ICs, it is common to use screen printing to construct circuits such as conductive films, resistive films, dielectric films, etc., and glass paste for printing is also commercially available. However, the organic medium in commonly used printing glass pastes is mainly a combination of diethylene glycol monobutyl ether and celluloses or terepinol and celluloses.
Among these, ethyl cellulose, terepinol, etc. contain a large amount of alkali. In the past, attempts have been made to screen print the pn junction of a semiconductor device using a printing paste using the organic medium described above for passivation. No favorable results have been obtained in terms of reliability. Therefore, there is a demand for the development of a printing paste for use in screen printing as a method of adhering glass powder that overcomes the drawbacks of the electrophoresis method described above. The present invention eliminates the above-mentioned drawbacks and provides a semiconductor device.
The purpose of the present invention is to provide a printing glass paste suitable for glass pn junction. The organic medium used in the printing glass paste of the present invention is a generally commercially available isobutyl methacrylate ester dissolved in diethylene glycol dibutyl ether. It has been found that printing glass pastes obtained using these organic media exhibit printing characteristics comparable to those obtained using commonly used cellulose-based organic media. Therefore, as a result of analyzing the Na content of these organic media, it was found to be 600 ppm for cellulose.
In contrast, the amount contained in methacrylic acid isobutyl ester is 10 to 17 ppm, and diethylene glycol dibutyl ether is 1 to 3 ppm, which is about 1/2 lower than the 40 ppm contained in generally commercially available passivation glass. I found out. Figure 1 shows the glass paste for printing according to the present invention.
That is, the relationship between the blending ratio of glass powder and isobutyl methacrylate and the molecular weight of isobutyl methacrylate is shown. Since isobutyl methacrylate is in powder form at room temperature, a solution dissolved in diethylene glycol dibutyl ether, an organic medium, was used as the organic solvent. Adjustment of the viscosity of the glass paste for printing to the viscosity generally used in screen printing methods is determined by the amount of glass powder or the amount of organic medium. Further, the viscosity of the glass paste for printing varies depending on the particle size of the glass powder and the molecular weight of the organic medium, in addition to the amount of glass powder and the concentration of the organic medium described above. A and B in the figure each have a molecular weight of
The case where different methacrylic acid isobutyl esters of 50,000 to 60,000 and 80,000 to 90,000 are used are shown. In addition, regarding the particle size of glass powder, the purpose is the passivation of semiconductor devices, and the general particle size of glass powder for passivation that meets this purpose is approximately 40 μm or less. The amount, concentration or molecular weight of the organic medium are considered to be the most important factors. In addition to viscosity, the printing paste must have fluidity against the sliding action of a squeegee, and must have the property that the printing paste will not flow out and lose the shape of the pattern after being printed on the substrate. The printing glass paste of the present invention uses an organic medium in which methacrylic acid isobutyl ester is dissolved in diethylene glycol dibutyl ether. Naturally, the amount of methacrylic acid isobutyl ester has a great influence on printability. For example, a printing paste using less than 2% by weight of isobutyl methacrylate in an organic medium may lack fluidity, and the glass powder may not pass through the screen mask, or only the organic medium may pass through the mask. It is difficult to form a desired pattern. Organic solvents of methacrylic acid isobutyl ester (e.g. xylene and toluene)
The proportion dissolved in other substances is approximately 50 to 60% by weight. Even with diethylene glycol dibutyl ether used in the present invention, the limit is about 70% by weight. However, even if glass powder is added to this relatively high concentration of isobutyl methacrylate to create a printing paste and patterned by screen printing, the glass powder is not uniformly dispersed. The baked glass film is not suitable for printing glass paste for semiconductors because the film thickness is not uniform and there are parts where the glass film is not formed. The upper limit of the concentration of isobutyl methacrylate that can form a glass film without the above-mentioned drawbacks is 50% by weight or less.
Therefore, as the organic medium for printing glass paste suitable for the purpose of the present invention, 2 to 50% by weight of isobutyl methacrylate may be used, and glass powder may be added to this to adjust the viscosity to 15,000 to 50,000 cp. If the viscosity of the printing glass paste is lower than 15000 cp, the printed pattern will flow and a clear pattern cannot be obtained. Furthermore, in the case of 50,000 cp or more, there are parts where the printing glass paste does not pass through the screen mask, which also causes pattern defects. Next, the molecular weight of methacrylic acid isobutyl ester used in the present invention will be explained. Since the printing glass paste of the present invention is intended for use in the passivation of semiconductor devices, it is undesirable for carbon to remain in the glass film after baking into the pn junction of the semiconductor device. Therefore, before baking the glass onto the pn junction surface of a semiconductor device, it is necessary to ash or scatter the organic medium in the printing glass paste in an electric furnace. In this case, it is desirable that the organic medium ash or scatter at a temperature below the softening temperature of the glass powder mixed in the printing glass paste. In other words, if the temperature at which the organic medium ashes or scatters is higher than the softening temperature of the glass powder, the softening of the glass and the ashing or scattering of the organic medium occur simultaneously, resulting in carbon being trapped in the glass coating or Bubbles or pores may be formed in the glass coating, deteriorating the electrical characteristics of the semiconductor. The organic medium methacrylic acid isobutyl ester used in the present invention has a different molecular weight depending on its manufacturing method. As mentioned above, curve A in FIG. 1 is for a molecular weight of 50,000 to 60,000, and curve B is for a molecular weight of 80,000 to 90,000. FIG. 2 shows the thermal decomposition curves of the above-mentioned isobutyl methacrylate, where curve A is an example when the molecular weight is 57,000 and curve B is an example when the molecular weight is 85,000. In both cases, the temperature at which thermal decomposition begins is approximately 200℃.
However, the weight decreases due to ashing or scattering,
The temperature at which the value becomes almost zero varies depending on the molecular weight, and the larger the molecular weight, the higher the temperature. Therefore, it is not preferable to use an organic medium with too large a molecular weight because the temperature at which ashing or scattering is completed will be close to the softening temperature of the glass powder. Glasses made of three components, ZnO, B ₂ O ₃ and SiO ₂ , are often used as passivation glasses in view of the electrical characteristics and reliability of semiconductor devices. Generally speaking, the softening temperature of glass for passivation which is mainly composed of the above three components is approximately within the range of 600 to 670°C. Therefore, it will be appreciated that the temperature at which the organic medium is incinerated or scattered is preferably lower than this temperature. Next, the range of components of the glass powder in the glass paste for printing according to the present invention will be explained in Table 1.

[Table] The coefficient of thermal expansion of the glass film to be passivated to the pn junction of a semiconductor device is preferably as close to that of silicon as possible. Regardless of whether the coefficient of thermal expansion of glass is larger or smaller than that of silicon, if it is baked onto a silicon wafer, the silicon wafer will curve, causing problems in the subsequent photolithography process, which is not the case for conventional passivation. The same is true for glass. ZnO-based glass for patches is
Unlike PbO glass, the coefficient of thermal expansion decreases due to crystallization, but even in this case, the coefficient of thermal expansion varies depending on the composition ratio. these are,
Although the coefficient of thermal expansion can be lowered by processing at a higher temperature, the temperature is high, which is undesirable for use in passivation of semiconductor devices. As for the glass composition, ZnO is 63.3 to 69.2wt%,
Nos. 1 to 6 in Table 1 are preferred, with B ₂ O ₃ in the range of 19.5 to 30.2 wt% and SiO ₂ in the range of 5.4 to 14.0 wt %. ZnO
69.2wt% or more and B ₂ O ₃ is 19.5wt% or less, or
In a composition range in which SiO ₂ is 14 wt% or more and ZnO is 63.3 wt% or less, surface crystals, surface devitrification, phase separation, etc. are observed, and this is not preferable as a glass for passivation. Furthermore, in a composition range in which B ₂ O ₃ is 30.2 wt% or more and SiO ₂ is 5.4 wt % or less, the coefficient of thermal expansion of the glass is large, which is also unfavorable from the electrical characteristics of the semiconductor device. It is not suitable as a glass for packaging. Furthermore, the glass film that directly insulates the pn junction surface of a semiconductor device must further have the following electrical properties. In other words, a glass film (Isolation) baked on a silicon wafer (Silicon)
The surface charge density (N _FB ) obtained from the CV characteristic curve of a MIS element with a structure in which electrodes (Metal) such as aluminum are formed on the surface of the MIS element must be within the range of -3.0 to +3.0×10 ¹¹ cm ^-2. is required. The glass in the printing glass paste of the present invention is as described above.
63.3-69.2 wt% ZnO and 19.5-30.2 wt%
It is composed of B ₂ O ₃ and the remainder is SiO ₂ , and if it is within this range, N _FB satisfies the above value. For example, when N _FB takes a value of +3.0×10 ¹¹ cm ^-2 or more, the depletion layer at the junction end is compressed by the charges induced by the charges on the glass, and more The blocking voltage is lowered to induce a higher voltage and make avalanche breakdown more likely. Also, N _FB is −3.0
If it is larger than ×10 ¹¹ cm ^-2 , the electric field strength at the edge of the junction decreases, and the blocking voltage increases, but there is a drawback that leakage current increases. Therefore, exceeding the above-mentioned glass composition range may cause problems in semiconductor devices.
It is not preferred as a glass for insulating the pn junction. Figure 3 shows the influence of Na content in the organic medium. When the Na content exceeds 40 ppm, the leakage current Ir after the high temperature voltage application test increases rapidly, indicating that the element has deteriorated. That is, it is thought that Na in the organic medium remains in the glass even after the glass is fired, and that this Na moves during the high-temperature voltage application test, increasing the leakage current. Therefore, the Na content in the organic medium used for printing glass paste is 40ppm.
Must be kept below. Next, an example in which the printing glass paste of the present invention is applied to a semiconductor device as shown in FIG. 4 will be described. In the figure, 31 is a p layer, 32 is an n layer
33 is an n ⁺ layer, 34 is a groove, and 35 is a glass layer. That is, in this example, the semiconductor device is a ppm ⁺ type diode, but it will be easily understood that the printing glass paste of the present invention can also be used in other semiconductor devices such as thyristors and transistors. As shown in the figure, the glass paste for printing according to the present invention is screen printed on the groove portion 34 of a mesa type or moat type diode in which a groove 34 extending beyond the p layer 31 and reaching a part of the n layer 32 is created. This is treated at a temperature below the softening temperature of glass to incinerate or scatter the organic medium in the paste.
Next, the glass layer 35 is obtained by baking the glass at a temperature equal to or higher than the softening temperature of the glass. When the blocking voltage of the diode obtained by the above method was measured, a breakdown voltage distribution as shown in FIG. 5 was obtained. FIG. 6 shows the results of testing the reliability of the diode described above. The exam is 135
This study investigated the change in reverse leakage current when a DC voltage of 500V was reverse biased for 1000 hours in a constant temperature bath at ℃. From these figures, it can be seen that the printing glass paste of the present invention exhibits good characteristics. As explained above, the printing glass paste of the present invention is suitable for passivation of semiconductor devices, and by using this printing glass paste, the utilization rate of glass powder can be improved compared to the conventional electrophoresis method. , reduction in the amount of organic matter used, and elimination of the need for waste treatment.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between glass powder and isobutyl methacrylate concentration in the printing glass paste of the present invention, Figure 2 is a thermal decomposition curve diagram of isobutyl methacrylate, and Figure 3 is a diagram showing the relationship between glass powder and isobutyl methacrylate concentration in the printing glass paste of the present invention. Figure 4 shows the relationship between the Na content in the organic medium and the leakage current Ir when the semiconductor surface is subjected to glass percussion. FIG. 6 is a diagram showing the frequency of blocking voltage and the change over time of leakage current when passivation is performed using the printing glass paste of the present invention. 31...p layer, 32...n layer, 33...n ⁺ layer, 34
...Groove, 35...Glass layer.

Claims (1)

[Claims] 1. A printing glass paste for forming a glass film on the surface of a semiconductor device, comprising: 63.3 to 69.2 wt.
% ZnO and 19.5~ _30.2wt % _B2O3 .
It consists of a glass powder consisting of 86 wt% and the rest being SiO ₂ , 2 to 50 wt% of isobutyl methacrylate, and 50 to 98 wt% of diethylene glycol dibutyl ether, and the Na content is 40 ppm or less and the softening point of the glass is below. contains an organic medium that evaporates or ashes, has a viscosity of 15,000 to 50,000 cp, and has a surface charge density of -3 to +3×10 ¹¹ cm of the formed glass film.
Printing glass paste characterized by being in the range ^-2 .