JPS58181B2 - hand taiiso - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and particularly to a protective coating structure on the surface of a semiconductor device.

Conventionally, a silicon dioxide film or an oxide film mainly composed of silicon dioxide has been used as a protective film on the surface of a semiconductor element, particularly on the surface of a semiconductor element where a pn junction is exposed.

Such a protective film needs to be formed after forming a p-n junction so as to cover the exposed surface of the semiconductor element at the junction. It is necessary to carry out the process at a low temperature without thermal transfer, and for this reason, prior art techniques such as chemical vapor deposition are used.

Therefore, if the exposed surface of the p-n junction is the top surface of the semiconductor element, it is relatively easy to form a protective film mainly made of silicon dioxide by chemical vapor deposition;
When the exposed surface of the p-n junction is a side surface of a semiconductor element, the steeper the slope of the side surface with respect to the top surface, the more difficult it is to grow a protective film mainly composed of silicon dioxide by chemical vapor deposition. Such protection is difficult, and even if it can be grown, the necessary properties such as mechanical strength, electrical insulation, etc. are very inadequate and expensive chemical vapor deposition is required. It has disadvantages such as requiring equipment.

Instead of such a protective film mainly made of silicon dioxide, proposals have been made to use polymeric resin materials such as polyamide, which can be formed sufficiently thick, can withstand mechanical wear, and has excellent electrical insulation properties. It has been found that the adhesion between polyamide and semiconductor substrates is unreliable.

In other words, when we measured the adhesive strength between a semiconductor substrate and a polyamide coating formed on it, we found that the peel strength per unit width (1 cm) was so strong that the coating itself could be cut immediately after it was formed. However, the forced humidity test (120
It was found that the adhesive strength after 60 minutes of exposure to water vapor at 2 atm and 2 atm) was almost 0, and decreased as the bond was separated without any load.

Therefore, an object of the present invention is to use a polyimide resin or the like as a protective coating, interpose a third substance between the coating and the semiconductor substrate, thereby significantly improving the adhesion between the two, and further, It is an object of the present invention to provide a semiconductor element coated with a highly reliable polyimide resin that also has improved electrical insulation properties.

In order to achieve the above objective, first of all, polyimide resin (a polymer resin obtained by reacting aromatic diamine and aromatic tetracarboxylic dianhydride) or PI resin ( A polymer resin (hereinafter referred to as PI resin) obtained by reacting an aromatic diamine, an aromatic diaminocarbonamide, and an aromatic tetracarboxylic dianhydride was used.

The thermal decomposition starting temperature of polyimide resin is about 420°, which is about 30 to 50°C higher than the thermal decomposition starting temperature of polyamide resin.
Therefore, a semiconductor element formed by coating the surface of a semiconductor substrate with this is relatively stable against heat treatment that will be applied later in the assembly process.

In addition, the thermal decomposition onset temperature of PI resin is 30 to 50 degrees Celsius higher than that of polyimide resin, so it is not only stable during the above assembly process, but also when used as a semiconductor device after assembly. It has sufficiently satisfactory characteristics in terms of reliability.

Next, as a second method for achieving the object of the present invention, a thin film made of a heat-treated aluminum chelate compound was disposed between the protective film made of the polyimide resin or PI resin and the semiconductor film.

The present invention will be explained below using FIG. 1 in order to better understand the present invention.

FIG. 1 shows a first region 3 having a first type of semiconductivity in a semiconductor body in which the major surface 1 and the other major surface 2 opposite thereto are substantially parallel to each other. and a second region 4 having a semiconductivity opposite to the first type of semiconductivity, and there is a p-n junction 5 between the first region 3 and the second region 4. A cross section of such a semiconductor device is shown.

Here, as the semiconductor substrate material, for example, a group Ⅰ element such as silicon or germanium or a group ① element and a group ① element such as silicon or germanium are used.
In this explanation, it will be referred to as a silicon semiconductor material, although it may be any compound made of a compound with a group element.

A thin film 7 obtained by heat-treating an aluminum chelate compound is formed on the surface 6 of the semiconductor substrate where the p-n junction 5 is exposed.

The aluminum chelate compound for forming the thin film 7 is dissolved in a suitable solvent such as toluene in advance, and
After applying this to the surface 6, it is heated.

The aluminum chelate compound for forming the thin film 7 has the following chemical structure.

Here, R1, R2, R3 are alkyl groups having 1 to 4 carbon atoms, and Xl, X2°X3. X4. X6. X6 is a ligand forming a coordinate bond with aluminum (in the formula, R4, R5, Ra, R7, R8, and R9 are alkyl groups having 1 to 4 carbon atoms).

A ligand selected from the group consisting of

The above aluminum chelate compound is relatively stable against humidity in the air and is dissolved in the following solvent xylene isopropyl alcohol n-butyl alcohol trichlorethylene carbon tetrachloride.

When a solution dissolved in these solvents is applied to a semiconductor surface, film forming properties are extremely good.

Organoaluminum compounds other than aluminum chelate compounds, such as aluminum triethylate aluminum-n-butylade aluminum-1so-butylade aluminum-5ec-butylade aluminum-ter-butylade aluminum-methylated aluminum tri-n-propylade aluminum Aluminum alcoholade compounds such as Mootrie 1so-propylade have a very fast hydrolysis rate and are unstable, so when they are dissolved in a solvent and applied as a solution, they immediately turn into a white powder and do not form a film.

In addition, regarding aluminum fatty acid esters such as aluminum palmitate, aluminum stearate, and aluminum acetate, when the number of carbon atoms in the fatty acid is 4 or less, hydrolysis is extremely rapid and it is difficult to form a film. is 5
If it is above, it is difficult to dissolve in the solvent and it is suspended in the solvent, so it is also difficult to form a film.

After forming the thin film 7, a coating 8 made of polyimide or PI resin is formed.

The polyimide resin provided for coating 8 has the following repeating units.

Here, n is an integer of at least 5, R1 is a tetravalent group selected from the group consisting of, and R2 is a divalent group selected from the group consisting of.

A further preferred material provided for the coating 8 is a PI resin, which has the following repeating units:

Here, n is an integer of at least 5, R1 is a trivalent group having a benzene ring, for example, selected from the group below, and R3 is a divalent group having a benzene ring, For example, selected from the group.

Further, R2 and R4 are tetravalent groups having a benzene ring, and are selected from the following group.

The PI resin and its manufacturing method are described in further detail in Japanese Patent Publication No. 48-2956.

The thermal decomposition temperature of PI resin is 30° higher than that of polyimide resin.
Because it has excellent heat resistance up to ~50°C, it has properties that satisfy the reliability even when used in the heat process that occurs during the assembly process of elements after being coated with PI resin, and when used as semiconductor devices after assembly. .

When forming the protective coating 8 made of polyimide resin or PI resin, the prepolymer of these resins is mixed with a suitable solvent such as N-methyl-2-pyrrolidone or N,N
- It is preferable to apply the resin solution as a solution dissolved in dimethylacetamide or the like and then heat it in stages.

For example, in the case of the above-mentioned resin, the stepwise heating is performed by heating a semiconductor element coated with a predetermined prepolymer solution at 100°C for 6 hours.
Heat for 0 minutes.

Next, heat to 200℃ for 60 minutes, then heat to 300℃ for 60 minutes in the case of polyimide resin, and 300℃ in the case of P resin.
Alternatively, heat to 350°C for 60 minutes.

Although a minimum heating time of 30 minutes at each temperature is possible, the above-mentioned times are recommended.

In some cases, a series of continuous heating steps may be employed, and in some cases, heating at 200° C. may be omitted.

A minimum thickness of 1 μm is sufficient for the resin film 8.

The semiconductor element functioned satisfactorily with a thickness of 1 μm for a transistor with a breakdown voltage of 1500V.

As described above, a thickness of 1 μm for the resin film 8 is sufficient for electrical insulation, but when considering mechanical strength, it is preferable that the thickness of the resin film 8 is 5 μm or more.

The adhesive strength between the polyimide resin film or PI resin film and the semiconductor substrate is as follows: when there are no inclusions between the two,
Although it has a peel strength of about 100 to 250 g per unit width (1 cm), when it is subjected to a humidity test, for example, when exposed to saturated steam at 120°C and 2 atm for 30 minutes, the peel strength is almost negligible. It became 0.

However, when a thin film made of a heat-treated aluminum chelate compound was interposed between the resin film and the semiconductor substrate, no decrease in peel strength was observed even after the humidity test was conducted for 50 hours.

After conducting a humidity test for 50 hours, we measured the thickness of the thin film 7 made of a heat-treated aluminum chelate compound necessary to maintain the peel strength at 50°A.
The exact thickness was unknown.

As an aluminum chelate compound, for example, in a solution prepared by dissolving ethyl acetoacetate aluminum isopropylate having the following structure in toluene, even if the concentration of the aluminum chelate compound in toluene was 0.01% by weight, the above humidity test still showed no peeling. No deterioration in strength was observed at all.

Further, when a 50% by weight solution was applied, the thickness of the thin film 7 was 5,000 to 10,000 Å, and the effect regarding adhesiveness was also extremely good.

As a method for forming a thin film of an aluminum chelate compound, the aluminum chelate compound has a concentration of 0.5 to 5.0
A solution of toluene, xylene, isopropyl alcohol, etc. containing % by weight is applied to the p-n junction by spin coating, spraying, brushing, or the like.

When using the above solution and performing spin coating at a rotation speed of 5000 rpm and then heat treatment, the final result is 50 to 2
A thin film of 00 Å is formed.

In the case of spin coating, the thickness of the layer formed is determined by the concentration of the coating solution and the speed of the rotating machine.

In addition to the above-mentioned aluminum chelate compounds, aluminum triacetylacetonate is also useful.

Further examples include aluminum tris (ethyl acetoacetate) and aluminum tris (malonic acid ethylate).

Example 1 This embodiment will be explained with reference to FIG.

FIG. 2 is a cross section of a silicone power transistor implementing this embodiment, showing a first region 23 having a first type of semiconductor and a semiconductor of a type opposite to that of the first region. and a third region 26 having the same type of semiconductor as the second region 24 and surrounded by the first region 23. There is a p-n junction 27 disposed between the region 23 and the second region 24, an insulating film 30 containing silicon oxide on one main surface 31 of the semiconductor substrate, and an insulating film 30 provided on the insulating film 30. A toluene solution containing 1 weight of an aluminum chelate compound represented by the following chemical formula is applied to the surface of a semiconductor element in which conductive metal electrodes 21 are provided in the openings and on almost the entire surface of the other main surface 32. After application, by keeping the temperature at 300℃ for 30 minutes,
Film 2 made of heat-treated aluminum chelate compound
form 8.

When an aluminum chelate compound is heated, its weight gradually decreases, but at a heat treatment temperature of 300° C. or higher, the weight loss becomes almost constant and stops, turning into a stable heat-treated product.

Therefore, the heat treatment temperature is preferably 300°C or higher.

The upper limit temperature of the heat treatment temperature is determined by the specific structure of the semiconductor element.

That is, in order to form the heat-treated product of the aluminum chelate compound itself, it is possible to heat the aluminum chelate compound at a temperature up to approximately 1200°C, but in order to prevent the p-n junction from moving due to the heat treatment, the heat treatment range is up to 900°C.

Further, for example, when an Al electrode is used as an electrode of a semiconductor element, the temperature is 500 to 550°C, and when solder or the like is used, the temperature is 35°C.
0°C is the upper limit temperature for heat treatment.

This thin film 28, of course, sufficiently covers one surface 26 of the semiconductor substrate where the pn junction 27 is exposed.

After that, a prepolymer solution of PI resin was applied, and 1
Heat treatment was performed at 00°C for 40 minutes, at 220°C for 40 minutes, and at 300°C for 60 minutes, resulting in a thickness of approximately 2 μm on the surface of the thin film 28.
A PI resin film 29 was formed.

To introduce an example of the humidity test results of the semiconductor device shown in Fig. 2, the reverse breakdown voltage of the p-n junction 27 is 250 to 300V.
Prepare 120 transistors such that
After conducting a severe humidity test of leaving it in 2 atmospheres of water vapor for 16 hours, we measured the reverse pressure resistance again.
It was confirmed that all 120 pieces had satisfactory reverse breakdown voltage characteristics.

In addition, in the structure shown in FIG. 2, 80 transistors were prepared in which a PI resin film 29 was directly formed on the surface of the semiconductor substrate without forming the thin film 28 made of a heat-treated aluminum chelate compound, and the above humidity test was conducted. When the test was carried out for 4 hours, only 3 pieces had a satisfactory reverse pressure resistance.

Furthermore, silicone resin is applied to the surface of the semiconductor substrate, and p
- When 80 pieces of the exposed surface of the -n junction 27 were directly coated with this resin were prepared and subjected to the above humidity test for 166 hours, only 32 pieces passed the test.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view for explaining the present invention in detail, and FIG. 2 is a schematic cross-sectional view of a semiconductor device implementing the present invention. In FIG. 1, 1, 2... Main surface of the semiconductor substrate, 3... Semiconducting region, 4... Semiconductor having conductivity opposite to 3. Sexual area, 5...3
p-n junction disposed between membrane or polyimide resin membrane, 31,3 in FIG.
2... Main plane of semiconductor substrate, 26...
・One surface of semiconductor, 27... p-n junction, 28
. . . A thin film made of a heat-treated aluminum chelate compound, 29 . . . A PI resin film or a polyimide resin film.

Claims (1)

[Claims] 1 having a first region having a first type of semiconductivity and a second region having a semiconductivity opposite to the first type of semiconductivity;
and p-n disposed between the first region and the second region.
A semiconductor body having a junction, at least one terminal end of the p-n junction exposed on the surface of the main body, and a polyimide resin or PI-resistant resin disposed to cover the terminal end of the p-n junction. A semiconductor element having a protective wave and a film formed by the above, characterized in that a thin film made of a heat-treated aluminum chelate compound is disposed between the end of the p-n junction and the protective film. element.