CH661933A5 - Process for the preparation of a coating composition for the surface of a semiconductor component, this composition, and the use thereof for preventing surface breakdown - Google Patents

Description

The invention relates to a method for producing a composition for the coating of surfaces of semiconductor components for the purpose of preventing a surface breakthrough, the product of this method and its use.

Methods for forming a coating on at least preselected, exposed or exposed surface areas of semiconductor components using electrically insulating oxide materials are known. These coatings are thin layers which are in fact not resistant to mechanical abrasion and which require a relatively expensive processing device for their formation. In almost all cases, a second, thicker coating of a protective coating material is provided to protect the initially formed, electrically insulating material. It has been found that silicone greases, lacquers, rubbers or rubbers and resins, which are used as coatings of protective material, lack desired physical properties.

US Pat. No. 3,615,913 discloses the use of a coating made of a cured, protective coating material selected from polyimides and polyamide polyimides, which coating is arranged on exposed or exposed end sections of at least one PN junction, the coating being used for passivating these End sections serves. Although these materials showed good abrasion resistance properties, they still need improvement because of the passivation requirements of the semiconductor device.

From US Pat. No. 3,615,913 the use of silicon oxide, glass fibers, boron nitride, aluminum oxide, quartz, mica, magnesium oxide and reactivated polytetrafluoroethylene etc. is also known for regulating the consistency of the polymeric material to be applied to the selected surface areas. To support a specific surface cleaning treatment for semiconductor materials, alizarin is also mixed into various coating materials.

At present, oxide / glass layers are widely used for the passivation and encapsulation or encapsulation of semiconductor components, in which the stability and long life or durability are important considerations. However, if the glass-like layer has to be applied with aluminum after metallization, which is required to a large extent, the selection of suitable glass systems is narrowed to a large extent by allowing a maximum of ~ 577 ° C for the temperature used during application. This limitation is imposed by the aluminum-silicon eutectic and must be carefully observed in all processing steps that follow the aluminization of the silicon.

Various methods of coating with glass are currently used. Examples of this are chemical deposition from the steam or. Gas phase (CVD), the application of glass frits or sintering together of glass and the spinning or spin-on of glass-forming alcoholates. The latter method allows only very thin layers with a thickness of the order of 200 nm to be formed, these layers being composed of glasses which tend to be more reactive than desired, which is why they are used for packaging or packing are of limited use. Glass frits are widely used for packaging or packaging, but generally not for passivating surfaces, due to the fact that it is difficult to formulate glasses that are sufficiently compatible with silicon in terms of their expansion or expansion coefficient and at the same time suitable passivation agents and are chemically stable. CVD processes allow a wide selection of the composition and the achievement of a sufficient thickness and a suitable coefficient of expansion etc., however, difficulties regarding the regulation or prevention of the contamination with sodium in CVD reaction vessels have the achievement of satisfactory passivation layers by direct ones Deposition based on silicon made difficult. This process is therefore generally limited to the formation of coatings on SiO 2 and layers produced by metallization.

It is assumed that none of these methods in their current state of development can provide a reliable method for passivation and / or encapsulation or encapsulation for large thyristors and other conductive semiconductor components.

In recent times, a passivation coating material for the coating of electronic components has been developed. The material is a copolymer, which is a reaction product of a silicon-free, organic diamine, an organic tetracarboxylic acid dianhydride and a polysiloxane. This material represents a significant improvement over known materials; it shows better adhesion and 30 corona resistance than available polyimide and polyamide-imide coatings. In view of the useful surface properties of such a material, the use of this material for coating high-voltage semiconductor components is desirable. 35 With such semiconductor devices, it is desirable that the surface coating lowers the high electric fields that occur on the surface of the silicon, which are sufficiently low so that there is no surface flashover or corona in the surrounding area the air and no significant surface leakage current. It is difficult to do this with very thin layers of polymeric materials. Applying trouble-free coatings in thick layers is time-consuming and expensive.

The object of the invention is to provide a production method for a coating material for passivating semiconductor components and such a coating material, into which selective filler materials are mixed in order to improve its physical and electrical properties, whereby the marking by means of a laser is improved.

The inventive method for producing a composition for the coating of surfaces of semiconductor components in order to prevent a surface breakdown is specified in claim 1, the product of the method in claim 6 and a use of this product in claim 7. Advantageous further developments result from the dependent claims.

On a semiconductor component of the type given in claim 7 to 60, the polyimide layer converted from the coating material for the surface area which is coated with it represents a passivation coating and, if appropriate, a means for encapsulation or inclusion.

65 The coating composition from which the polyimide layer used for passivation of the semiconductor component is converted contains, on the one hand, the structural units (I) and optionally (II), for example

661 933

4th

in a total number of 10 to 10,000 or more structural units, optionally in the proportions specified in claim 1, on the other hand at least one admixed filler material selected from rutile, barium titanate and lead zirconate. The filler material serves to improve the physical and electrical properties of the polyimide coating material formed, in particular its dielectric constant is set to a high value by the filler material.

1 and 2 are side elevations of cross sections of semiconductor components in which the polymeric materials according to the invention are contained.

The invention is explained in more detail below.

1 shows a semiconductor component 10 in which a body 12 made of a semiconductor material is contained. The body 12 is made by suitable methods, e.g. by polishing and lapping the semiconductor material until two opposite surfaces 14 and 16 are parallel. The body 12 is made of a suitable semiconductor material such as e.g. Silicon, silicon carbide, germanium, compounds of elements of group II and group VI compounds of elements of group III and group V.

In order to explain the invention in more detail, the body 12 is described below by way of example as a body which consists of a silicon semiconductor material with five conductivity regions and four P-N junctions. An element 10 constructed in this way can act as a thyristor. The body 12 accordingly has regions 18 and 20 with a conductivity of the P type, regions 19 with a conductivity of the P + type and regions 22, 24 and 26 with a conductivity of the N type. P-N junctions 28, 30, 32 and 34 are formed by the adjacent surfaces of the corresponding pairs of regions 18 and 22, 22 and 20, 20 and 24 and 20 and 26 of opposite conductivity type.

One means of regulating the surface electric field on such a thyristor is that the side surface 36, after the partially machined body 12 is fastened to a large-area contact or carrier electrode 38 by means of a layer 40 of an electrical solder with a suitable ohmic resistance, profiled. Electrical contacts 42 and 44 are attached to respective regions 24 and 26. As shown, the profiling of the surface 36 leads to the known surface with “double gate”.

FIG. 2 shows a semiconductor component 50 in which a double positive gate is formed to regulate the electrical surface field. All objects that are designated by the same reference numerals as the objects in the semiconductor component 10 of FIG. 1, correspond to the corresponding objects of the semiconductor component 10 and act in the same way. The semiconductor component 50 acts in the construction shown as a thyristor.

Regardless of which surface electrical field regulation method is used, selected end portions of at least some of the P-N-junctions are exposed on surface areas of body 12, which is why it is necessary to apply a suitable material to protect the exposed end portions of the P-N junctions.

On at least the surface 36 and the exposed 15 or exposed end section of at least the P-N junctions 28 and 30, a layer 46 of a coating material serving for encapsulation or confinement or for protection is arranged. Desirably, the material of the layer 46 adheres to both the top surface 36 and the material of the layer 44 and to the contact or carrier electrode 38. The material of the layer 46 must have suitable or appropriate dielectric properties and must also be able to withstand the elevated temperatures which occur during the processing of the semiconductor component 10. In addition, the material of layer 46 must be capable of providing an adhesive bond to the selected surface of semiconductor device 10 when cured, and the material of layer 46 should have good abrasion resistance 30 and also resistance to the chemicals that be used at the completion of the manufacture of the semiconductor device 10.

Layer 46 can be formed by applying a solution of the carboxyl group-containing polyamide precursor of 35 polyimide containing the filler in an organic solvent.

Upon heating, the solvent is evaporated and the material of layer 46 is 4oimidized in situ on surface 36 and on the end portion of at least one P-N junction. The material is applied by suitable methods, e.g. by spraying or dusting, spinning or spinning or brushing, etc. The body 12 with the applied, protective coating material is then heated to convert the resinous, soluble, polymeric intermediate into a cured, solid, and selectively insoluble material.

Examples of the diaminosiloxanes of the formula III which can be used in the practice of the invention are compounds having the formulas given below:

H2N_ (CH2) r

CH "

-Si_

CH.

h2n- <ch2) 4

CH_

CH "

Ji o— li

<ch2) 4-

-NH,

CH_

CH_

661 933

C6H5 C6H5

I I. H2N (CH2) 3 — si —o — Si— (ch2> 3 NH2

C6H5 C6H5

CH "

CH.

CH- CH

I I

Si — 0 —Si

NH,

CH "CH.

/ <

CH_ 1 CH.

H2N— (CH2) 3 - li— 0 J_Ji (CH ^

NH,

CH.

I.

H2N— (CH2) ^ Si

CH.

> i (CH2) -

-NH

2:

C6H5

C6H5

CH ^ —CH ^ —CH3 CH2 — CH —CH3

h2n —ch2ch (ch3)

Si

CH.

-sì — ch (ch3) ch2 nh2

CH.

The diamines with the formula IV specified in claim 1 are known and for the most part commercially available materials. Typical examples of such diamines from which the prepolymer can be prepared are: M-phenylenediamine;

p-phenylenediamine;

4,4'-diaminodiphenylpropane;

4,4'-diaminodiphenylmethane;

4,4'-methylenedianiline;

Benzidine;

4,4'-diaminodiphenyl sulfide;

4,4'-diaminodiphenyl sulfone;

4,4'-diaminodiphenyl ether;

1,5-diaminonaphthalene;

3,3'-dimethylbenzidine;

3,3'-dimethoxybenzidine;

2,4-bis (β-amino-t-butyl) toluene;

Bis (p-β-amino-t-butylphenyl) ether;

Bis (p-β-methyl-o-aminopentyl) benzene;

1,3-diamino-4-isopropylbenzene;

1,2-bis (3-aminopropoxy) ether;

m-xylylenediamine;

p-xylylenediamine; Bis (4-aminocyclohexyl) methane; 50 decamethylene diamine; 3-methylheptamethylene diamine;

4,4-dimethylheptamethylene diamine;

2.11-dodecanediamine; 2,2-dimethylpropylenediamine;

55 octamethylenediamine; 3-methoxyhexamethylene diamine;

2,5-dimethylhexamethylene diamine; 2,5-dimethylheptamethylene diamine; 3-methylheptamethylene diamine;

60 5-methylnonamethylene diamine; 1,4-cyclohexanediamine;

1.12-octadecanediamine; Bis (3-aminopropyl) sulfide; N-methyl-bis (3-aminopropyl) amine;

65 hexamethylenediamine; Heptamethylene diamine; Nonamethylenediamine and mixtures thereof.

661933

6

In the tetracarboxylic acid dianhydrides of the formula V, R "is a group which is derived from or contains an aromatic group which contains at least 6 carbon atoms and is characterized by benzoid unsaturation, or contains such an aromatic group, each of the four carbonyl groups of the dianhydride having a separate carbon atom in depends on the tetravalent group and where the

Carbonyl groups are arranged in pairs so that the carbonyl groups of a pair each hang on adjacent or at most one carbon atom from the group R ", so that a 5-5 or 6-membered ring is formed with the following structure:

0 0 0

II II ^ I!

C 0 C or C

_t i_ J

Examples of dianhydrides which are suitable for use in the context of the invention (short names in brackets) are:

Pyromellitic dianhydride (PMDA);

2,3,6,7-naphthalenetetracarboxylic acid dianhydride;

3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride;

1,2,5,6-naphthalenetetracarboxylic acid dianhydride;

2,2'3,3'-biphenyltetracarboxylic acid dianhydride;

Bis (3,4-dicarboxyphenyl) sulfone dianhydride;

2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propanedianhydride;

(BPA dianhydride);

2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propanedianhydride; Benzophenonetetracarboxylic acid dianhydride (BPDA); Perylene-l, 2,7,8-tetracarboxylic dianhydride; Bis (3,4-dicarboxyphenyl) ether dianhydride and bis (3,4-dicarboxyphenyl) methane dianhydride.

The admixture of other anhydrides such as trimellitic acid anhydride for the production of amide-imide-siloxane polymers is not excluded.

The coating material also contains an admixed filler material, which is selected from rutile, lead zirconate and barium titanate. The filler material improves the electrical properties of the polymer mass used for confinement or passivation by supporting the regulation of the dielectric constant of the polymeric material.

The solution of the precursor to form coating 46 consists of the carboxyl group-containing polyamide in a suitable solvent (e.g., N-methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, etc.), the solvent alone or together with not Solvents are used and the solution contains 10 to 40 wt .-% solids and preferably 20 to 40% solids. The coating material is applied to the surface 36 in an amount sufficient to

that a layer 46 with a thickness of 1 to 100 (xm) is formed.

The applied carboxyl group-containing polyamide precursor solution, which also contains the filler, is dried in an initial heating step for a sufficient time at temperatures of about 75 to 125 ° C, often under vacuum, to remove the solvent. The polyamide with carboxyl groups in the solution of the polymer precursor is then converted into the corresponding polyimide siloxane by heating it to about 150 to 300 ° C. for a sufficient period of time to achieve the desired conversion into the polyimide structure.

A preferred conversion cycle is shown below:

(a) 15 to 30 min at 135 ° C to 150 ° C in dry

N2.

0

c — c i%

(b) 15 to 60 min at about 185 ° C ± 10 ° C in dry

N2.

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

20 On the other hand, it has been found that it is possible to use layer 46 in other atmospheres, e.g. in air, to facilitate the commercial or industrial application of the invention.

A suitable solution of a polymer precursor is formed by reacting benzophenonetetracarboxylic acid dianhydride with methylene dianiline and bis (Y-aminopropyl) tetramethyldi-siloxane. The latter two diamine materials are in a molar ratio of 85:15 to 55:45. Preferably, the range of the desirable molar ratio of the two diamine materials is between 75:25 and 65:35, and even more preferred is a molar ratio of 70:30. The reaction of the chemical components is to favor a high molecular weight polymer at a temperature carried out below 50 ° C using appropriately cleaned and dried materials.

The fillers must be added to this solution.

The polymer obtained after the conversion has a dielectric constant of the order of about 3.7. The intensity of the electric field in the polymeric material not provided with a filling material is. when the polymeric material is applied to selected surface areas of silicon that has a dielectric constant of 45, 12, approximately 3 times the intensity of the field in the silicon, the intensity of the field in the silicon at breakdown being 1 x 105 can reach up to 2 x 105 V / cm. The polyimide must therefore be able to withstand maximum electrical fields in the order of magnitude of approximately 6 x 105V / cm (3 x 2 x 105V / cm). If the dielectric constant of a film of a polyimide-silicone copolymer material is increased by introducing a selected filler material into the copolymer material, the electrical field that the material must withstand is reduced. E.g. leads a material provided with rutile (dielectric constant = 90) as filler material, which has an average value of the dielectric constant of approximately 12, to the fact that the hardened film of the coating material has an electric field of approximately 2 x 105 V / cm, if the filler is present in an amount of 10% by volume based on the volume of the cured mixture.

In the polymer provided with a filler and obtained by conversion, the maximum filler material content has a value in the order of about 50% by volume, so a maximum dielectric constant of ~ 47 can be achieved when using rutile as filler material.

0 0

1 'II

-O Cr or C

/

The maximum weight ratio in which the filler material is added to or mixed into the solutions of the polymer precursor depends both on the particle size and the shape of the filler material and on the density and solids content of the solution of the polymer. Assuming a spherical shape of the particles of the rutile configured in a cubic configuration after curing and a void-free composite, the maximum weight of solids that can be effectively added to the polymer precursor solution is:

W

W

ps

3.21 WF, '?

VII,

max where

Ws the weight of the solid filling material,

Wps the weight of the solution of the polymer (polymer precursor) and

WFp is the weight fraction of the polymers in the solution of the polymer precursor.

The following table shows e.g. some typical values for solutions of polymer precursors, in which rutile is contained as filler material:

WF

(% By weight)

10 25 40 50

(^)

v (% r max.

IT 80 128 161

At higher values of (Ws / Wps) no void-free composites are obtained after curing.

The surface charge at the interface between the hardened film of the coating material and a silicon element is, in certain cases, an effect of the electrical charge distributed in the coating material

In such cases, a higher dielectric constant has the additional advantage that the value of the effective surface charge is reduced. This is desirable in the semiconductor PN junctions where both the n-5 and p regions are sparingly doped where the surface charge factors are minimized to a maximum breakdown voltage and a minimum reverse leakage current leads.

According to the invention, it was found that rutile, which is a tetragonal and the most stable form of titanium dioxide, is a dielectric material that is an excellent filler material. Rutile has the extremely desirable property of a high dielectric constant in the order of 90. This value 15 for the dielectric constant is very favorable in comparison with the dielectric constant 12 for silicon, 8.6 for “3 51 glass” (a glass composition from the General Electric Company) and 3.8 for silicon dioxide.

Leakage current and avalanche multiplication in two-dielectric materials generally depend on the intensity of the electric field. The intensity of the electric field is inversely proportional to the dielectric constant of the material. A higher dielectric constant results in a 2s reduction in the field in the dielectric for a given applied voltage. The coating material according to the invention, in which added rutile is contained, can therefore withstand higher applied voltages in comparison with coating materials without filler material.

30 Other suitable fillers are barium titanate and lead zirconate, which act in the same way as rutile. The range of amounts in which these fillers are added to the resinous solids in a solution of the polymer precursor differs somewhat from the values given in the table due to different densities, but this range can be calculated in the same way.

The addition of the filling materials also improves the possibility of marking or marking silicon wafers or wafers coated with the 40 polymeric materials described above by means of a laser, which represents a second advantage of using the desired filling materials.

45

50

55

60

65

c

1 sheet of drawings

Claims (8)

661933 PATENT CLAIMS 1. Method for producing a composition for the coating of semiconductor components in order to prevent a surface breakthrough, characterized in that this coating composition (a) is a solution of (AO a polyamic acid, which is a polymeric reaction product of a diprimeric organic diamine of the formula N - Q - N (IV), exists, is convertible, or of (a2) a polyamic acid which is a copolymeric reaction product of a diamine mixture which comprises 85 to 55 mol% of a diprimary organic diamine of the type defined under (ai hievor s) and the remaining 15 to 45 mol% of a diprimary siloxane diamine of the formula H io \ N / H - R ( - Si 0 - R 'I Si i ' - R H ( (HI), H whose divalent organic radical Q is silicon-free, and an organic tetracarboxylic acid dianhydride of the formula <!> ti 0 > where R "is a tetravalent organic radical, and that in polyimide, which consists essentially of units of the formula 15 where R is a divalent hydrocarbon radical, R 'is a monovalent hydrocarbon radical and x is an integer from 1 to 8, and an organic tetracarboxylic acid dianhydride of the type defined under (a ^ above) and which is in copolymeric polyimide, essentially from units of the formula (V), 25 II c. -NO' H 30 o 0 / SN N: ' H 0 N - Q (I) - N Î 8 N - Q - « 0 • p / c \ / c \ - N R "N 8th " - R - (I) 35 and units of the formula R1 I Si - 0 i '' 45 1 R 'I Si I R1 - R - (II) in a molar ratio corresponding to the molar ratio of the diamines in the aforementioned diamine mixture, is convertible into (a3) an organic solvent and (b) at least one filler material selected from rutile, barium titanate and lead zirconate with a high dielectric constant, and that for their preparation the filler material defined under (b) above is mixed with the solution defined under (a) above and is completely distributed in it. 2. The method according to claim 1, characterized in that the filling material is barium titanate. 3. The method according to claim 1, characterized in that the filling material is lead zirconate. 4. The method according to claim 1, characterized in that the filling material is rutile. 5. The method according to claim 4, characterized in that the amount by weight of the rutile is not greater than 3.21 times the amount by weight of the polymer in the solution defined in claim 1 under (a). 6. Product of the method according to claim 1. 7. Use of the product according to claim 6 for coating a body made of a semiconductor material A semiconductor device having at least a pair of regions of opposite conductivity type, a PN junction between each pair of regions of opposite conductivity type formed by the adjacent surfaces of the regions of which the pair is made, and one has a surface of the body exposed end portion of at least one PN junction, for the purpose of preventing a surface breakthrough, characterized in that at least that surface on which the end portion is exposed by at least one PN junction is coated with the product according to claim 6 and then converts the polyamic acid in the coating into the corresponding polyimide. 65 8. Use according to claim 7, characterized in that the semiconductor material is silicon. 3rd 661 933