JPS5846058B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a glass passivation semiconductor device in which a pn junction of a semiconductor device is filled with glass powder using a screen printing method.

There are various methods for covering the pn junction of a semiconductor device with a glass film, but generally a method of selectively depositing glass on the pn junction using electrophoresis is often used.

The method of depositing glass by electrophoresis is to remove the oxide film only at the pn junction where the glass should be attached to expose the silicon surface, and then blow NH3 gas as an electrolyte into isopropyl alcohol in which glass powder is dispersed. This is a simple method in which glass powder can be deposited on the pn junction surface by applying a DC voltage in an electrophoresis solution with the silicon wafer on the negative side and the opposing electrode plate on the positive side.

The disadvantages of the conventional method are (1) The glass powder commercially available for passivation is passed through a sieve with a particle size of 325 mesh, whereas the particle size used in electrophoresis is about 15 mesh.
(2) There is a lot of waste, such as using a large amount of organic solvent such as isopropyl alcohol as a dispersion medium.
(3) Since a relatively high voltage is applied in an organic solvent, there are concerns about the risk of ignition due to discharge.

Furthermore, the glass concentration in the dispersion medium and NH3 as an electrolyte
Since it is difficult to adjust the gas concentration, there is a problem in that the reproducibility of the resulting glass film thickness is poor, and the characteristics of the semiconductor device are often likely to be deteriorated.

Furthermore, in order to deposit glass only at the pn junction by selective migration, a relatively high quality oxide film is required.

If there is a defect such as a pinhole in the oxide film, glass will accumulate in that area, causing problems such as poor breakdown voltage between the gate and cathode in SIRISK, and poor breakdown voltage or current amplification factor between the emitter and base in transistors. there were.

A screen printing method can be cited as a method for avoiding the drawbacks of the conventional methods described above.

A method of depositing glass on a pn junction using a screen printing method has been studied for a long time, along with electrophoresis, a doctor blade method, centrifugal sedimentation, and the like.

Furthermore, in the field of hybrid ICs, it is common to use screen printing in circuit configurations such as conductor coatings, resistors, and dielectric coatings.

At present, the organic medium in printing inks that are commercially available and commonly used are mainly diethylene glycol dibutyl etherulose, or a combination of terepinol and ethyl cellulose.

Among these, ethyl cellulose, terepinol, etc. are natural products and contain a large amount of alkali, and therefore are unsuitable for use as an insulating coating on the pn junction of a semiconductor device.

That is, the electrical characteristics of the semiconductor device, for example, the blocking voltage,
This may cause reverse leakage current or reduce reliability.

Furthermore, the crystalline glass used for passivation of semiconductor devices has poor fluidity compared to other common glasses, so pinholes and bubbles form after the organic medium passes through, which impairs the electrical properties of semiconductor devices. It is decreasing.

Therefore, it was necessary to find a printing ink suitable for passivation of semiconductor devices and a method for applying the same.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a semiconductor device using a printing method suitable for glass passivating a pn junction of a semiconductor device, while eliminating the above-mentioned drawbacks.

This will be explained below along with examples.

FIG. 1 shows a method for manufacturing a semiconductor device according to the present invention.

The following describes an example in which the present invention is applied to a diode, but it can be easily assumed that this method can also be applied to general glass passivation elements such as transistors and silices. Glass is printed on the grooves of a semiconductor wafer using a screen printing method.

In this case, since the oxide film is not necessary, it is removed in advance.

S2: Dry and fire for 30 minutes at a temperature below the softening temperature of glass in an oxygen atmosphere to incinerate or scatter the organic medium.

In this case, it can be easily inferred that the decomposition temperature differs depending on the type or molecular weight of the organic medium.

S3: The wafer in which the organic medium has been sufficiently ashed or scattered is kept at the softening temperature of glass for about 5 to 30 minutes and welded to the pn junction portion of the semiconductor wafer.

Thereafter, the temperature is raised to around the crystallization temperature of the glass to crystallize the glass.

The above is a description of each step of the method for manufacturing a semiconductor device according to the present invention, and subsequent steps such as forming electrodes are commonly performed.

In this actual case, the printing ink used in the first step S1 is adjusted in advance.

That is, 2 to 50% by weight of methacrylic acid isobutyl ester in diethylene glycol dibutyl ether.
The dissolved organic medium and the crystalline glass containing ZnO, B2O3 and 8102 as main components are mixed and kneaded.

The molecular weight of methacrylic acid isobutyl ester is approximately 100,
000 or less is good; if the molecular weight is larger than this, it becomes difficult to ash or scatter when the organic medium is burned off in the second process S2, and the amount of residual carbon increases and the electrical characteristics of the semiconductor device are impaired. result.

The maximum dissolution amount of methacrylic acid isobutyl ester in diethylene glycol dibutyl ether is 60~ by weight.
It is about 70%.

However, in order to uniformly disperse the glass powder in this organic medium and obtain a glass film free of bubbles, pinholes, etc., approximately 50% is the upper limit.

If the amount is less than 2% by weight, bleeding or deformation easily occurs, resulting in poor printing accuracy and is not suitable for passivation of semiconductor devices.

Figure 2 shows that crystalline glass containing ZnO, B2O3 and SiO2 as main components was mixed in an organic medium containing varying amounts of methacrylic acid isobutyl ester dissolved in diethylene glycol dibutyl ether.
These are the results of examining the reverse leakage current of a passivated mesa diode by printing glass in the mesa groove using printing ink adjusted to a viscosity of 0.00 cp.

The results show that as the amount of isobutyl methacrylate increases, the reverse leakage current of the diode increases little by little, and when it exceeds 40% by weight, it tends to increase rapidly.

This is thought to be due to the influence of residual carbon.

FIG. 3 shows the results of measuring the thermal decomposition curve of isobutyl methacrylate.

Curve 31 shows that when the molecular weight is 50,000, curve 32 shows that s
This is the case of o, ooo.

The temperature at which the weight decreases by 100% at the end temperature of thermal decomposition (
In other words, the temperature at which ashing and scattering occur completely) is higher as the molecular weight is larger.

From this result, it can be easily inferred that when the molecular weight of methacrylic acid isobutyl ester exceeds 100,000, the above temperature becomes even higher.

Therefore, the temperature in this case is close to the softening temperature of ZnO, B2O3, and 5102-based passivation glasses that are currently commonly used, and the amount of residual carbon increases, which deteriorates the electrical characteristics of the semiconductor device. It would be easy to imagine that this would be the case.

The molecular weight of methacrylic acid isobutyl ester used in this example was 100,000 or less.
Since the amount of carbon remaining after the organic medium is burned off at 500° C. in step 2 is 5 ppm or less, the electrical characteristics of the semiconductor device are not impaired.

Next, the advantages of the present invention will be explained.

FIG. 4 is a cross-sectional view of a wafer in which glass is deposited by ordinary electrophoresis, and FIG. 5 is a cross-sectional view of a semiconductor wafer according to the present invention.

In these figures, 41 is an oxide film, 42 is a p layer, and 43 is an oxide film.
44 is an n layer, 44 is a single layer, and 45° 54 is glass.

The difference between FIG. 5 and FIG. 4 is that no oxide film is required.

In electrophoresis, p
It is necessary to electrically insulate the area other than the n-junction, and an oxide film must be left in this area.

Then, the formation of a photoresist film for photoetching to remove the oxide film during subsequent electrode formation becomes a very important operation.

For example, if there are protrusions on the glass surface or if the glass film is thick, there will be steps on the silicon surface, creating areas where the photoresist film will not stick, and the glass will be eroded by the etching solution used to remove the oxide film, such as hydrofluoric acid, resulting in passivation. There are many cases where it becomes defective.

In comparison, as shown in FIG. 5, when a printing method is used, an oxide film is not required, so the oxide film can be removed in advance from the diode.

Furthermore, for silice and transistors, it is possible to use a material in which only the necessary portions of the oxide film are photo-etched first.

For the above reasons, an improvement in the yield of semiconductor devices can be expected.

Next, the glass firing method in the third step S3 in FIG. 1 will be explained.

Commonly commercially available ZnOt B2O3 and 8102
The e-firing method for passivation glass whose main component is different depending on the manufacturer.

Depending on the glass firing method, bubbles may be generated in the glass or on the pn junction, impairing the electrical characteristics of the semiconductor device.

This type of glass generally has a higher viscosity at high temperatures than PbO type glass and has a property of being difficult to flow.

However, it is often used as a passivation material for semiconductor devices because of its high reliability.

When used in the printing method, as described above, since a high-molecular organic medium such as isobutyl methacrylate is used, there is a drawback that the organic medium tends to form bubbles, pinholes, etc. after being incinerated or scattered.

Therefore, as a way to prevent these bubbles and pinholes,
The idea was to hold the glass at the softening temperature for 5 to 30 minutes.

As a result, no bubbles or pinholes occur at all.
Furthermore, the number of protrusions on the glass has been reduced, making subsequent processes such as photoresist coating and alignment work in the electrode formation process easier than before, and pattern accuracy has also improved.

In firing the glass, the glass may be kept at its softening temperature for a period of time, then heated to near the crystallization temperature and held for a certain period of time in order to lower the coefficient of thermal expansion of the glass.

As a result of fabricating the moat type diode shown in FIG. 5 by the method described above, the breakdown voltage distribution shown in FIG. 6 was obtained.

The horizontal axis of the figure shows the blocking voltage with a leakage current of 5 μA as the reference value, and the vertical axis shows the number of samples.

From this, it can be seen that the blocking voltage is concentrated around the design value, and a good manufacturing yield can be obtained.

Furthermore, FIG. 7 shows the results of testing the reliability of diodes using the method of the present invention.

The test was conducted at a DC voltage of 500V for 100 seconds in a constant temperature chamber at 135℃.
The change in reverse leakage current when reverse biased for 0 hours was investigated.

It can be seen from this that the reverse leakage current hardly increases.

As described above, the diode produced by the method of the present invention exhibits good characteristics.

As explained above, by applying printing ink using a low-alkali organic binder suitable for passivation of semiconductor devices and a method of forming a glass film with good uniformity without bubbles or pinholes, etc., semiconductor devices exhibiting good characteristics can be produced. I was able to get it.

By applying this method, the actual usage rate of glass powder is 10
The amount of organic matter used was less than 1150% compared to the conventional method, and other advantages were found, such as cost savings and no need to dispose of waste.

Furthermore, since the oxide film removal step for electrode formation, which was conventionally performed after the glass firing, can be performed before the glass firing, improved pattern accuracy can be expected.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the outline of the process of the present invention, Figure 2 is a diagram for explaining the required amount of methacrylic acid isobutyl ester, Figure 3 is a diagram for explaining the thermal properties of methacrylic acid, and Figure 4 is a diagram for explaining the thermal properties of methacrylic acid. 5 is a cross-sectional view of a semiconductor device to which the conventional method is applied, FIG. 5 is a cross-sectional view similar to FIG. 4 according to the present invention, and FIGS.
FIG. 3 is a diagram showing an example of electrical characteristics of the semiconductor device shown in the figure. 42...p layer, 43...n layer, 44...
...N layer, 45.54...Glass.

Claims (1)

[Claims] 1. Organic medium consisting of diethylene glycol dibutyl ether and meccrylic acid isobutyl ester and ZnO
, B203 and crystalline glass containing 5102 as main components.
A method for manufacturing a semiconductor device comprising the steps of attaching the organic medium to an exposed portion of the bond, incinerating or scattering the organic medium at a temperature below the softening temperature of the glass, and baking the remaining glass onto the semiconductor device. 2 The above mixture contains diethylene glycol dibutyl
An organic medium prepared by dissolving 2 to 50% by weight of meccrylic acid isobutyl ester in ester and ZnO. Mix crystalline glass containing B2O3 and S t 02 as main components and have a viscosity of 15,000 to 50,000.
2. The method of manufacturing a semiconductor device according to claim 1, wherein the cp-adjusted material is attached to the exposed portion of the pn junction. 3. The method for manufacturing a semiconductor device according to item 1 or 2, wherein the molecular weight of the isobutyl meccrylate is 100,000 or less.