JPS597213B2 - Method for controlling surface state and surface charge in silicon semiconductor junctions coated with polyimide-silicon copolymer junction coatings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device and a method for controlling a surface electric field and adjusting a surface charge thereof.

Passivation or surface stabilization (passivation) and protection of PN junctions exposed on the surface of semiconductor devices is a constant concern in industry.

This is particularly important in high voltage power semiconductor devices such as thyristors, diodes and the like. In such devices, the surface electric field and surface charge distribution of the semiconductor element are extremely important. This is because this usually determines the breakdown voltage of the device. It is based on this fact that such high voltage devices tend to be surface limited. That is, surface failure occurs before internal failure or surface leakage becomes large enough to limit the usefulness of the device. In order to avoid the above-mentioned limitations, it is common to adjust the surface electric field in a convenient manner, if possible and/or by choosing the contour of the element surface. It is normal to decrease it.

An example of a conventional method is the use of proprietary glassy materials to stabilize lightly doped (DOpe) N-type silicon surfaces in power devices. The large negative charges in patent glasses tend to deplete the surface of majority carrier devices. This passivation technique expands the depletion layer near the surface, reduces the electric field at the surface, and helps suppress surface breakdown. Further increasing the volume of the depletion layer near the surface
The result is more generation and recombination centers, increasing undesirable surface leakage.

Because of the presence of this large negative charge, patent glasses are not expected to be useful in lightly doped P-type silicon.

Therefore, this solution of charge control for semiconductor devices is completely useless when used in high voltage thyristors. In the case of high voltage thyristors, a P-N junction is formed between lightly doped N-type conductive silicon and P-type conductive silicon. High surface field conditions that tend to bias one side of the PN junction will therefore promote breakdown on the other side. In this type of device, the best force method is to keep the surface electric field as small as possible. It is an object of the present invention to provide a new and improved method of surface field control of semiconductor devices.

Another object of the present invention is to coat selected surfaces and exposed portions of the P-N junction with a polyimide-silicon copolymer material and subject the coated junction to a suitable high temperature heat treatment in suitable atmospheric conditions. It is an object of the present invention to provide a new and improved method of controlling the surface electric field of a semiconductor device by subjecting the semiconductor device to a surface electric field. Other objects of the invention will be partly obvious and partly known from the text below.

In accordance with the teachings of the present invention, a method is provided for the treatment of selected surface areas of a semiconductor material body having at least two regions having opposite types of conductivity.

A P-N junction is located intermediately and is formed by the abutting surfaces of each pair of regions of opposite type conductivity. There are at least 14-8NlT and eight Tsume Tsumugi. A layer of a suitable polymeric variable permeability thin film material is applied to selected surface areas of the device.

The polymeric material cures in situ to form a film of polymeric material thereon. The element and coating are then heated to an elevated temperature range to render the coating material permeable to selected gases, such as humid nitrogen, oxygen, and hydrogen. At least one of the selected gases is diffused through the film and reaches the
and/or reacted at selected surface areas of the device. Removal of the reaction products and the excess amount of the at least one selected gas during the conditioning process is effected through the membrane to the atmosphere. The element and coating are cooled to a low polarization range to ensure the full impermeability of the polymeric material coating.
to re-establish the characteristics of The polymeric material is silicon-free (SilicOn-Free).
e) selected from the group of substances consisting of reaction products of organic diamines, organic tetracarboxylic dianhydrides, and polysiloxanes, having cyclic structural units of the structural formula and containing from 5 to 50 mole percent of the structural formula; It is desirable that it contains a co-condensed structural unit.

Here, R is a divalent hydrocarbon group, R' is a monovalent hydrocarbon group, R'' is a tetravalent organic group, and Q does not contain divalent silicon, which is the residue of an organic diamine (free silicon X is an integer having a value greater than zero, m and n are integers greater than 1 and possibly equal to each other. Preferred materials are methylene dianiline, benzophenone tetracarboxylic acid and bis(γ-aminopropyl ) is a reaction product of tetramethyldisiloxane.

Excellent effects are obtained when the molar ratio of methylene dianiline to bis(r-aminopropyl)tetramethyldisiloxane is 70:30. Regarding Figure 1,
A semiconductor device 10 is shown comprising a body 12 of semiconductor material.

The body 12 is formed in any suitable manner, for example on two opposite sides 14 and 1.
6 by parallel polishing and wrapping. Body 12 has two or more electrically conductive regions of opposite type and a P-N junction formed by the abutting surfaces of each pair of electrically conductive regions of opposite type. At least one end of the P-N junction is exposed on the surface of the body 12. Body 12 is constructed of a suitable semiconductor material, such as silicon, silicon carbide, germanium, a compound of Group and Group elements, or a compound of Group and Group V elements.
To more fully describe the invention, and for no other purpose, body 12 will be described as consisting of a silicon semiconductor having five conductive regions and four P-N junctions.

The element 10 having such a configuration works as a thyristor.
The body 12 thus includes regions 18 and 20 of P-type conductivity, regions 19 of P-type conductivity, and regions 22, 24 and 2 of N-type conductivity.
6. P-N junctions 28, 30, 32 and 34
are regions of opposite type conductivity 18 and 22, 22 and 20,
It is formed by the abutting surfaces of the respective pairs 20 and 24 and 20 and 26. One of the auxiliary means in controlling the surface field of such a controlled rectifier is to coat the partially treated body 12 with a layer 40 of a suitable ohmic electrical solder at the large area contact or support electrode 38. After attaching, the side surface 36 is molded.

Electrical contacts 42 and 44 connect regions 24 and 26, respectively.
Can be worn on. As shown, the shaping of surface 36 creates the well-known double bevel surface effect. Next, referring to FIG. 2, a semiconductor device 50 is shown which realizes a double normal slope structure for surface electric field control.

All parts labeled with the same reference numerals as element 10 in FIG. 1 are the same and function in the same manner as corresponding parts of element 10. Element 50 operates as a thyristor due to the structure described above. Depending on the method used for surface field control, at least some selected ends of the P-N junction
exposed on the surface area of body 12.

It is therefore necessary to apply a suitable material to protect the exposed end of the PN junction. A layer of protective coating material 46 covers at least the surface 36 and at least the P-N junction 2.
8 and 30 on the exposed ends.

The material of layer 46 is preferably in intimate contact with surface 36 as well as with the material of layer 44 and contact or support electrode 38. The material of layer 46 must act as a variable permeability material so that it can withstand the prolonged high temperatures required to treat selected surface areas of element 10 with the special gas. Furthermore, the material of the layer must be "permeable" at the high temperatures of gas processing. That is, it acts as a coating and allows the passage of selected gases through layer 46 towards the surface of element 10 and from the surface.
must be allowed to pass. Additionally, the material of layer 46 must be sufficiently porous at elevated temperatures to permit passage of other gaseous products through layer 46 into the atmosphere. Upon cooling to room temperature, the material of layer 46 becomes sufficiently impermeable to the atmosphere and therefore provides a sufficient hermetic seal to the surface to which it is applied.
must be formed. In other words, the operating atmosphere does not have an adverse effect on the surface charge of the coated surface.
A protective coating material, such as a polyimide-silicon copolymer, has been found to be such a desirable material when applied to at least the surface 36 and at least to the exposed ends of the P-N junctions 28 and 30.

The protective coating material is applied to the surface 36 as a PrecursOr polymer dissolved in a suitable solvent.

layer 46 by heating or by evaporation at room temperature.
The protective coating material on the surface 36 and at least 1P
- Polymerized in situ on the end of the N junction. The material of layer 46 is preferably applied to preselected surface areas of surface 36 of body 12 as a solution of an intermediate polymer.
The material may be applied to at least the surface 36 of the body 12 by suction, spinning, brushing, or any other suitable force method. The protective coating material 12 is then heated to convert the resinous soluble intermediate polymer into a hardened solid selectively insoluble material.
The protective coating material for layer 46 is preferably one that exhibits good adhesion to surface 36 when cured.

Furthermore, the material should exhibit good abrasion resistance and resistance to the chemicals used in the finishing of the manufacture of the element 10. Furthermore, the material should exhibit good heat resistance. This is because high temperatures are applied to the device 10 in order to adjust and control its surface condition and charge. Additionally, it is desirable that the material of layer 46 have the inherent property of not exhibiting outgassing during the heat treatment process. Suitable materials meeting the aforementioned requirements for forming layer 46 are reaction products of silicon-free organic diamines, organic tetracarboxylic dianhydrides, and polysiloxane diamines.

This is a polymer precursor that is soluble in a suitable organic solvent.
Upon curing, it yields a copolymer having circulating structural units of the structural formula and having from 5 to 50 mole percent co-condensed structural units of the structural formula.

Here, R is a divalent hydrocarbon group, R' is a monovalent hydrocarbon group, "R" is a tetravalent organic group, and Q does not contain divalent silicon, which is the residue of an organic diamine (silicon free) organic group, X is an integer with a value of 1 to 1,000 or more, m<l!: n is greater than 1, preferably 10
the same or different integers from 10,000 to 10,000 or more. The above-mentioned block copolymer is prepared by preparing a suitable mixture of components consisting of a diaminosiloxane having the general formula, a silicon-free diamino compound having the structural formula, and a tetracarboxylic dianhydride having the structural formula. It can be prepared as a result of a reaction in molar ratios.

where R, R', R'', Q and It will be recognized that

However, the actual precursor resulting from the reaction of diaminosiloxane, a silicon-free (silicon-free) organic diamine, and a tetracarboxylic dianhydride is initially a polyamic acid structure consisting of structural units of the structural formula It is of the model.

wherein R, R', R", Q,

and similar.

Diamines of the above-mentioned structural formulas are materials described in the prior art and for the most part commercially available.

Typical such diamines from which the PrepOlymer is prepared are as follows. and mixtures thereof.

It should be noted that these diamines are given for illustrative purposes only and are not to be considered all-inclusive. Other diamines not listed will be readily apparent to those skilled in the art. The structural formula of tetracarboxylic dianhydride is further clarified as follows. That is, R'' is a group derived from or containing a tetravalent group, such as an aromatic group containing at least 6 carbon atoms characterized by an unsaturated benzenoid, where the dianhydride Each of the four carbonyl groups is bonded to a separate carbon atom of the tetravalent group, and the carbonyl groups are in pairs, with each pair of groups bonded to adjacent carbon atoms of the R group, or up to Bonded to a carbon atom of the R group missing one carbon atom to give a 5- or 6-membered ring: C-0-C or C-0-C or C-0-C Invention Examples of dianhydrides suitable for use in (with their abbreviations in parentheses) include:

Anhydrous.

The assembly of other anhydrides, such as trimerite anhydrides, is not prevented to make amide-imido-siloxane polymers. Application of the block copolymer or mixture of polymers, alone or in combination with a non-solvent, can be carried out in a suitable solvent (e.g. N-methylpyrrolidone, N,N-dimethylacetamine, N,N-dimethylformamide, etc.). (containing) and applied to the substrate material using a conventional method, such as doping (D
ipping), suction, smearing (Paintin)
g), a conventional method such as spinning may be used.

The block copolymer or polymer blend is dried during the initial heating stage at about 75 to 150 DEG C. for a sufficient period of time, often under vacuum, to remove the solvent. Polyamic acid is then about 1
By heating at a temperature of 50° C.-300° C. for a sufficient period of time, the polyimide-siloxane is converted into the corresponding polyimide-siloxane,
This produces the desired conversion to polyimide structure and final curing effect. A suitable material is a polymer precursor in the form of polyamic acid, in a weight ratio of 250! ), N-
It is prepared as a solution in methyl-2-pyrrolidone.

This solution is applied to the surface of the body. In this case, the ends of the PN junction are applied in a suitable manner, for example by smearing or spinning. A special polymer precursor solution is formed by reacting benzophenone tetracarboxylic dianhydride with methylene dianiline and bis(r-aminopropyl)tetramethyldisiloxane. The latter two diamide materials are present in a 70:30 molar ratio. The reaction is carried out using suitably purified and dried materials at temperatures below 50° C. to facilitate the formation of high molecular weight polymers.
The preferred curing cycle for materials of the above general structure is as follows.

(a) 135°C to 15°C for 15 to 30 minutes in dry N2.

(b) 15 at approximately 185°C ± 10°C in dry N2.
or 60 minutes.

(c) 1 to 3 hours at about 225°C in vacuum.

Alternatively, it has been found that the coating material can be cured in other atmospheres, such as air, to facilitate commercial application of the invention. When a sufficient amount of material is applied to surface 36, a layer 46 from 1 micron to 100 microns thick will result.

Due to the requirement that the cured material not break down electrically at the maximum electric field present in the forward or reverse blocking state,
A minimum thickness is determined. Other suitable protective coating materials for polyimides, polyamides, polyimide-polyamides, and methods of making the same, polysiloxane implementations are all described in U.S. Pat. Nos. 3,325,450 and 3,553.
, No. 282, No. 3,598,784 and No. 3,74
No. 0,305, the disclosure of which is incorporated herein by reference. The coated element 10 is then processed into a treated body 12.
exposed to a dehumidifying or inert atmosphere to reduce the density of surface states in the surface area.

The coated element 10 is heated to about 450°C ± 25°C for about 30 minutes.
For example, heating in nitrogen, oxygen, argon, methane, hydrogen and similar atmospheres. The atmosphere may or may not contain water vapor. It is desirable to use nitrogen containing about 1 to 3 percent water vapor by volume to control active surface condition factors. The material of layer 46 has been found to effectively form a hermetic seal to device 10 in the operating atmosphere.

However, it has been found that upon heating to elevated temperatures of about 450° C., the material now becomes permeable to the gas used to adjust the density of surface states in the surface area of element 10. Atmospheric gases, including water vapor if desired, are free to migrate from the external atmosphere through the material of layer 46 to the surface of body 12. After acting on the surface of body 12, the reaction products of the gas and the material present on the surface of body 12 can pass through the hardened polyimide-silicon polymer from the surface and into the surrounding atmosphere. Some of the products that escape from the surface during processing are products generated during previous processing steps on body 12. The material of layer 46 acts as a variable permeability membrane with permeability controlled by temperature.
Upon completion of the heat treatment, the coated device is cooled to room temperature.

The material of layer 46 takes on the properties of its unique hardened state forming a virtually hermetic seal of the surface to which it is applied. The material is no longer transparent and the surface charge state is retained. This process seems to be effective.

This is because most of the surface charges present in the element 10 are probably present as interface states. A relatively small portion of the surface states are fixed charges. The material of layer 46 therefore provides an excellent surface condition control and forms an excellent passivating (surface stabilizing) coating for semiconductor devices. The present materials and processes are particularly suitable for high power semiconductor devices with high voltage-low reverse leakage requirements. Additionally, the materials and processes are also suitable for transistor and integrated circuit manufacturing operations. Embodiments of the present invention will be listed below. 1. The molar ratio of methylene dianiline to bis(r-aminopropyl)tetramethyldisiloxane is 95:5 to 5.
The force method according to claim 3, characterized in that the ratio is 0:50.

2. 5. Process according to claim 4, characterized in that the molar ratio is between 75:25 and 63:35.

3. The method according to item 1, wherein the molar ratio is about 70:30.

4. A method according to any of the claims and preceding claims, characterized in that the at least one selected gas is one selected from the group consisting of nitrogen containing water, oxygen and hydrogen.

5. The method according to each of the claims and each of the preceding claims, characterized in that the semiconductor element is made of silicon material.

6. A method according to any of the claims and preceding claims, characterized in that at least one selected gas contains about 1 to 3 percent water vapor.

7. The force method described in each of the claims and each of the preceding claims, characterized in that the second vorticity range is 450°C±100°C.

8. A method according to any of the claims and preceding claims, characterized in that the adjustment of surface charge and control of the surface electric field in selected surface areas is typically carried out for about 30 minutes.

9. The organic diamine that does not contain silicon (silicon is released) is methylene dianiline, the organic dianhydride is benzophenonetetracarboxylic acid, and the polysiloxane is bis(r-aminopropyl)tetramethyldisiloxane. The method according to claim 4, characterized in that:

10. The molar ratio of methylene dianiline to bis(r-aminopropyl)tetramethyldisiloxane is 70:3.
5. The method according to claim 4, wherein: 0.

[Brief explanation of the drawing]

1 and 2 are side elevational views, partially in cross-section, of a semiconductor device made in accordance with the teachings of the present invention. 10, 50... Semiconductor element, 12...
Main body, 14, 16... Mutually parallel surfaces, 18, 1
9, 20...P-type conductive region, 22, 24, 2
6...N-type conductive region, 28, 30, 32, 3
4...P-N junction, 36... Surface, 3
8...Support electrode, 40...Solder layer,
42, 44... Electrical contact portion.

Claims (1)

Claims: 1. The following process steps: (a) applying a suitable polymeric variable permeability material film to selected surface areas of a semiconductor device; (b) applying a film of a suitable polymeric variable permeability material to selected surface areas of a semiconductor device; c) curing the polymeric material to form a film of material that is virtually impermeable to the processing atmosphere of the device in a first temperature range; (c) permeating the polymeric material to a selected gas; (d) heating the at least one of the selected gases to a second elevated temperature range to render the semiconductor device (e) accessing and/or reacting the selected surface area with at least one of the selected gases;
a step of conditioning the surface condition at or near a selected surface area of the device; (f) at least one product of the conditioning process step from the selected surface area through the polymeric material coating; (g) re-establishing the substantially impermeable properties of the polymeric material coating. How to treat selected surface areas. 2. A method according to claim 1, characterized in that the semiconductor material consists of a silicon semiconductor material body. 3 The polymeric material contains methylene dianiline and bis(γ
2. A method according to claim 1, characterized in that it is derived from benzophenone tetracarboxylic dianhydride reacted with tetramedildine loxane (aminopropyl). 4. Polymer variable permeability membrane material is a reaction product of silicon-free organic diamine, organic tetracarboxylic dianhydride, and polysiloxane, and has a cyclic structural unit with the structural formula ▲ Numerical formula, chemical formula, table, etc. ▼ and contains 5 to 50 mole percent co-condensed structural units of the structural formula ▲There are mathematical formulas, chemical formulas, tables, etc.▼, where R is a divalent hydrocarbon group and R' is a monovalent Hydrocarbon group, R″ is a tetravalent organic group, Q is a divalent silicon-free organic group that is the residue of an organic diamine, m and n
2. A method according to claim 1, wherein are equal or different integers greater than 1.