JPS59144176A - Method of producing rectifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing rectifying elements, which are used to provide metallization and contact connections in power semiconductor devices having tabs or bottles made by pressing. be.

The conventional technology for manufacturing rectifying elements is to chemically deposit metal such as nickel on two opposing surfaces of a semiconductor structure (plating), and then coat the metal with a thermal expansion coefficient close to that of silicon. It is known that a heat sink made of materials such as molybdenum, tungsten, and these materials and δ gold is bonded to one surface of a semiconductor structure in a liquid phase state by soldering or the like (Soviet Union Inventor's Certificate No. 664. (See No. 244).

However, from the outside, the metal deposited layer of the rectifying element manufactured by this method has high contact resistance, increased pores, and easy peeling when the metal layer thickness exceeds 51 tm. Pulse forward voltage
ard voltage) and thermal resistance.

Also, chemical deposition techniques are limited to a limited number of materials that can be used to metallize semiconductor structures.

Moreover, metal layers formed by chemical deposition processes are not uniform in thickness.

This method has the complication of preheating the rectifying element after performing the metal deposition operation on the conductor structure to ensure good adhesion of the deposited metal layer to the semiconductor structure.

Moreover, this method does not allow simultaneous coating of different metals on each of two opposing sides of the semiconductor structure.

As a conventional technique for manufacturing a rectifying element for a power semiconductor device, two opposing surfaces of a semiconductor structure are coated with metal by vacuum sputtering, and then a heat sink is attached to one of the metal coated surfaces of the semiconductor structure using a liquid phase process such as soldering. It is also known that they are joined in a state (U.S. Pat. No. 3,987)
, No. 217).

This method uses appropriate high-purity metals and performs the process in vacuum to reduce contact resistance, and the sputtered metal layer has fewer pores and is difficult to peel off even when the sputtered layer has a thickness of more than 5 μm. The number of metals used for sputtering is increasing, eliminating the need for heat treatment operations on sputtered layers.

However, this method does not allow simultaneous deposition of different metals on two opposing surfaces of a semiconductor structure.

Furthermore, when the thickness of the metal layer exceeds 10 μm, it becomes porous and easily peels off, leading to an increase in pulse forward voltage and thermal resistance of the rectifying element.

The increase in the surface area of the semiconductor structure affects the uniformity of the spuck layer thickness.

When bonding a heat sink to a semiconductor structure in a liquid state, it is difficult to achieve the desired homogeneous contact because it is difficult in reality to achieve complete wettability of the bonding surface.
As a result, the pulse forward voltage and thermal resistance of the rectifying element will increase.

Additionally, metallizing the semiconductor structure and bonding the heat sink thereto are performed in two consecutive operations, increasing the labor load of the production process and increasing the number of rejected rectifier elements.

The conventional method for manufacturing rectifying elements is to metallize two opposing sides of a semiconductor structure by chemical metal deposition or vacuum metal sputtering thereon, and then diffuse a heat sink onto one of the metallized sides of the semiconductor structure. There are some welded ones. Be-be-Sumberov (V, V.

Zumberov), Be-xle, Kuzmin (V,L
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Kuzumin), N.D. Khutryansky (
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D, Khutoryansky), Gehenkov (G, N, 5urzhenkov)
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Because diffusion welding provides a bond in phase, the resulting contact is characterized by a high degree of homogeneity, allowing for a reduction in pulse-forward voltage and thermal resistance of the rectifying element.

However, since the opposing surfaces of the semiconductor structure are metallized by chemical deposition or vacuum sputtering, the rectifying elements are affected by the pulse-forward voltage and thermal It also shows an increase in resistance.

Because of their porosity, metal layers formed by chemical deposition or vacuum sputtering on semiconductor structures are more resistant to deformation than metal layers of areal density materials that are diffusion welded to the opposite side of the semiconductor structure during the diffusion welding process with a heat sink. gender is small. This in turn increases residual bending of the rectifying element.

Moreover, this method involves two consecutive operations: metallizing the semiconductor structure and bonding the heat sink thereto, increasing the labor involved in the production process and increasing the number of defective rectifying elements.

The main object of the invention is to provide a method for metallizing a semiconductor structure and attaching it to a heat sink in such a way that the metal layer does not peel off at any thickness, analogous to the two opposing surfaces of the semiconductor structure. making it possible to simultaneously metallize and dissimilar gold scraps, obtaining a highly uniform thickness of the metal layer, reducing residual bending, reducing the amount of labor in the manufacturing process of rectifier elements. The main objectives are to save energy consumption, and to reduce the number of defective rectifying elements.

Considering this main objective in the method of manufacturing a rectifying element comprising a metal coating on two opposite sides of a semiconductor structure, according to the invention the metal coating is obtained by diffusion welding a metal foil onto the semiconductor structure. The welding is performed simultaneously on two sides of the semiconductor structure.

The non-uniformity of the thickness and chemical non-uniformity of the metal layer coated on rectifying elements produced in this way is determined only by the similar properties of the foil material to be welded.

The foil corresponds to a dense metal layer with better thermal conductivity and lower electrical resistance than the metal deposited on the surface of the semiconductor structure, and the rectifier elements made by the method proposed in the present invention similarly It has low thermal conductivity and pulse forward voltage.

The uniform thickness of the metal layer ensures better conditions for providing pressed contacts on the rectifying element, which further reduces the thermal resistance and the pulse forward voltage of the semiconductor device as a whole.

This method does not cause delamination of the metal layer from the semiconductor structure at any thickness and also makes it possible to provide a metallization over the semiconductor structure with a dense metal without pores or oxidized inclusions.

It is desirable to diffusion weld the metal foil to the semiconductor structure at the same time as diffusion weld the heat sink to at least one side of the semiconductor structure.

Performing the metallization of the opposite side of the semiconductor structure at the same time as the heat sink welding operation reduces the amount of labor in the production process, the number of defective rectifying elements, and reduces energy consumption.

Simultaneously with the diffusion welding of the metal foil to the semiconductor structure, a rigid connection of an electrode made of silver or a silver alloy is made to at least one metallized side of the semiconductor structure, after which the rectifying element made in this way is °C up to 01 to 15
It is desirable to cool at a rate of 0.degree. C./sec.

At the same time as metal foil is coated on the outer surface of the heat sink, electrodes made of silver or silver-gold are rigidly connected to the outer surface of the heat sink by diffusion welding, and the rectifying element thus made is heated at 250 to 230 degrees. 0.1 to 1 up to C
It is desirable to cool at a rate of 5°C/sec.

The use of diffusion welding to rigidly connect electrodes made of silver or silver alloys to the metallized surfaces of semiconductor structures or to the metallized surfaces of heat sinks is used to connect metallized semiconductor structures over the entire nominal contact area with surface atoms of the electrodes. causes the formation of metallic bonds between surface atoms. This means that heat transfer is not only by conduction (unlike in clean pressed contacts, where heat transfer occurs by convection or radiation, the most efficient atomic-molecular heat transfer mechanism in contacts is water droplets). This action ensures a reduction in thermal resistance.

Thus, this method can easily obtain close physical contact over the entire nominal area, reducing thermal resistance, substantial plastic deformation of the electrode, and its extrusion into the current path.
Diffusion welding of electrodes made of silver or silver alloys to metallized semiconductor structures or heat sinks can be done in accordance with traditional methods at the expense of performance, since it minimizes the thermal cycling and eliminates the associated thermal cycling at the same time. The quality of the manufactured rectifier can be improved. The latter property is due to the fact that the axial stresses generated during thermal cycling are absorbed not only by the electrode, as in the case of a free-positioned electrode, but also by the surface to which the electrode is firmly fixed by diffusion welding. achieved.

If aluminum is used as the metal foil, during diffusion welding a solid solution of aluminum diffused into silver is formed in the weld area. When cooling is performed after welding at a temperature of 390°C according to the phase diagram, a peritectic reaction of decomposition of a supersaturated solid solution occurs while generating an intermetallic compound Ag3Al. The formation of such intermetallic interlayers increases the thermal resistance and results in a substantial loss of the strength and plasticity of the rigid direct connection between the applied aluminum layer and the silver or silver alloy electrode. , which in turn is highly undesirable since it can lead to breakdown of the connections, especially in the cycling of temperature loads that occur during current cycling.

A certain rate of post-weld cooling prevents the formation of undesirable layers. This means that cooling starts from the welding temperature at 250°C.
0.1 within the temperature range down to temperatures between 230°C and 230°C.
This is achieved when carried out at a rate of between 15°C and 15°C/sec. This provides hardening, ie, establishment of an unbalanced state of supersaturated aluminum solid solution in the chain. 250 to 2
At temperatures below 30° C., the diffusion process becomes so slow that the formation of an intermetallic interlayer becomes impossible. When cooling is carried out in the above temperature range at a rate of less than 0.1° C./sec, a 6-intermetallic compound Ag3Al is formed in the weld area.

If the cooling rate is greater than 15° C./sec, there is a risk of cracking of the semiconductor structure due to insufficient time for thermal shock and stress relaxation.

The ratio of the thickness of the metal foil inserted between the semiconductor structure and the heat sink to the thickness of the metal foil on the opposite side of the semiconductor structure is 02.
It is desirable to set it in the range of 5 to 0.5.

When designing a rectifier, the materials and geometrical dimensions of the semiconductor structure and heat sink are selected based on a set of requirements for the electrical and physical properties of the device, making it the only controllable component of the rectifier. The design variables are semiconductor 47
The ratio between the plating thickness of the 4-layer plate and the thickness of the gold FA foil used for bonding the heat sink thereto.

When the structure of the rectifying element is combined with a heat sink that has high machinability (and therefore reduces residual bending strain), the thickness of the metal foil inserted between the semiconductor structure and the heat sink and the metal on the opposing surface of the semiconductor structure It is desirable to choose a ratio of foil thickness close to 5. Such a ratio maintains a high degree of flatness of the device and makes it possible to use a thin metal foil for plating the surface opposite the surface adjacent to the heat sink of the semiconductor structure. The use of thin foils is more desirable as it allows for highly accurate and high quality photoetching of the foil if photolithography is used in subsequent operations during rectifier manufacturing.

When the rectifying element has low rigidity to remove residual bending strain, the ratio of the thickness of the metal foil inserted between the semiconductor structure and the heat sink to the thickness of the metal foil on the opposite side of the semiconductor structure is o, 25. It is desirable to get it close to . However, if the ratio between these colors is less than 0.25, the sign of the residual bending of the semiconductor structure will be negative with respect to the bending of the heat sink, and the pressure applied during the process of mounting the rectifier on the housing will be resulting in defects.

Features of the invention are further explained by the detailed description illustrated in the drawings.

The proposed method works as follows.

A stack comprising a semiconductor structure 1 with metal foil disks 2, 3 arranged on opposite sides is heated, compressed and held in vacuum for a predetermined time. These operations simultaneously provide a welded joint along the plane indicated by horizontal lines a" and 1b" in FIG.

When manufacturing the rectifying element shown in FIG. 2, a stack is assembled comprising a semiconductor structure 1 with metal foil disks 2.3 arranged on opposite sides and a heat sink 4. The ratio between disk 3 and disk 2 should be selected in the range of 0.25 or constant 5. The assembled stack is heated, compressed,
These operations are carried out by being kept in a vacuum for a predetermined period of time, as indicated by the horizontal line "a" in FIG.

Welded joints along the planes designated 1b" and 1C" are simultaneously provided.

When manufacturing the rectifying element shown in FIG. 3, a stack comprising a semiconductor structure 1 with metal foil disks arranged on opposite sides and a heat sink 4, 5 is assembled. Disc 3
and 2 should be selected in the range 015 to 10. The assembled stack is heated, compressed, and held in vacuum for a predetermined period of time, these operations being indicated by the horizontal line "a"%b" in FIG.

At the same time, a welded joint along the plane indicated by 'C' is provided.

When manufacturing the rectifying element shown in FIG. 4, a semiconductor structure 1 with metal foil discs arranged on opposite sides, a heat sink 4, a metal foil disc 6, electrodes 7, 8 made of silver or its alloys are used. A stack containing is assembled. The assembled stack is heated, compressed, and held in vacuum for a predetermined period of time, and these operations are indicated by horizontal lines "a" and "a" in FIG.
ゝb", 1C".

At the same time, a welded joint is provided along the planes indicated by %e, %e, and 1g.

Immediately thereafter, the rectifying element is cooled at a rate of 0.1 to 15°C/sec to a temperature of 250 to 230°C.

A special application of the proposed method is given below.

(Example 1) A dynamic thyristor rectifier element having a rating of 630 A current and 2 to 3 KV repetition voltage was made. The diameters of the silicon semiconductor structure, tungsten heat sink, and aluminum foil disk were each 50 ml.

The thickness of the 7 recon structure was 0.6 vrx and the thickness of the heat sink was 3 vrx. The thickness of the aluminum foil inserted between the heat sink and the semiconductor structure is 0.12+
+i and the thickness of the foil for metallizing the opposite side of the silicon structure was 0.0131 g, and the ratio between these foil thicknesses was equal to 9.

Diffusion welding of the assembled stack is 6'6.5 MP
It was carried out for 300 seconds at a unit compressive pressure of 15 MPa and a temperature of 550° C. in a vacuum chamber of a.

After the parts are diffusion welded together, the residual bending flexion is 0.0
It was on the 08th.

(Example 2) A diode rectifier element for a welding device having a current rating of 2.00 OA and a repetition voltage of 400 μm was manufactured.

The silicon structure, molybdenum heat sink, and aluminum foil disk each had a diameter of 40 mm.

The thickness of the silicon structure was 0.251 m and the thickness of the molybdenum heat sink was 0.5 mm. The thickness of the aluminum foil inserted between the heat sink and the semiconductor structure is 0.05 nm, and the thickness of the foil for metallizing the opposite side of the semiconductor structure is 0.28 mm. The gap ratio was equal to 0.18.

Diffusion welding of the assembled stack was carried out in a 66.5 MPa vacuum chamber at a unit compression pressure of 15 MPa, 5
It was carried out for 300 seconds at a temperature of 50°C.

After the parts are diffusion welded together, the residual bending flexion is 0.0
It was 1 mm.

(Example 3) Current 80 to 100A, (repetition voltage 0.7 to 1
．． A rectifier element was made for a reverse polarity connected diode with a rating of 5KV. The diameter of the silicon structure and tungsten heat sink was between 18 mm. The aluminum foil disk inserted between the heat sink and the semiconductor structure and the disk for metallizing the opposite side of the semiconductor structure have the same diameter and a thickness of 0.05 mm and 0.12 mm respectively, i.e. The ratio between these thicknesses was equal to 4.2. The thickness of the silicon structure was 0.3 mm and the thickness of the tungsten heat sink was 1.5 mm.

Diffusion welding of the assembled stack was carried out at a unit compression pressure of 15 MPa in a vacuum chamber of 66.5 MPa, 550
It was carried out for 300 seconds at a temperature of °C.

After the aforementioned parts were diffusion welded together, the residual bending flex was 0.01.

Example 4 A frequency reverse connected diode rectifier with a rating of 1000 A was manufactured, with the diameter of all parts to be welded being 32 mm. Silver disk 0.15 mm thick, aluminum disk 01 mm thick, silicon structure, aluminum disk 0.1 mm thick, 0.15 t thick
A stack with tm silver discs was assembled. Diffusion welding was carried out under the conditions described in Example 1, with a welding temperature of 550°C.
Cooling from to 250°C was performed at a rate of 0.15°C/sec.

Metallographic and X-ray spectroscopic examination of the weld after welding clearly showed that the weld was free of intermetallic AgaAl layer. Additionally, diode testing showed high electrical, temperature and operating characteristics.

(Example 5) The diameters of all parts to be welded are in order of 32, and 320
An industrial Sirisk rectifier having a rating of A was manufactured. 0.05 t given all welds of the rectifier
At the same time, a silver disk-shaped electrode with a thickness of nn was rigidly fixed.

A stack was assembled with a silver disk, a 0.02 mrtr thick aluminum disk, a silicon structure, a 0.1 mm thick aluminum disk, a tungsten, heat sink, a Q,05 mm thick aluminum disk, and a silver disk. Diffusion welding was carried out under the conditions given in Example 1, with cooling from 550°C to 230°C at a rate of 14°C/sec.

Metallographic examination of the five rectifying elements showed that the welds were free of intermetallic interlayers and the semiconductor structure was crack-free.

Testing of the rectifying elements in the device showed that the proposed method is efficient and advantageous with regard to electrical, pneumatic and thermal elements.

(Example 6) A frequency diode rectifier element with a diameter of 18 pots was manufactured. The silver electrode is rigidly fixed at the same time as the remaining contacts in the rectifying element are provided by diffusion welding.

002 thick aluminum disk, silicon structure, 01m
m thick aluminum disk, 1.57+m thick tungsten disk, 0.05 mm thick aluminum disk,
A stack with 0.05 mm thick silver discs was assembled. Diffusion welding of the stack was performed at a temperature of 550° for 300 seconds and in a vacuum of 66.5 MPa at 15 MPa.
This was done with unit compression. Cooling to 230°C after welding was performed at a rate of 45°C/sec. Metallographic examination showed the absence of aluminum and silver intermetallic compounds in the weld, and testing of the welded rectifying elements within the device showed high electrical, temperature and operating characteristics.

The advantages of the manufacturing method of a rectifying element according to the present invention, compared to the prior art, are that a rectifying element with low thermal resistance and low pulse forward voltage can be manufactured, and the operating load carrying capacity of the rectifying element as a whole can be increased; The consumption of high-purity metals can be reduced, and silver can be saved by reducing the thickness of the electrodes made of silver or silver alloys, and at the same time forming all the contacts of the rectifying elements. The rigid direct connection of electrodes made of silver or silver alloy can be provided, which can reduce the labor concentration and power consumption of the process of manufacturing rectifying elements, and can reduce the number of defective rectifying elements. The advantage is that the number and cost of equipment used and the area required to house them can be reduced.

Although specific embodiments of the invention have been shown and described, various variations thereof will be apparent to those skilled in the art, and the invention therefore includes a description of the proposed method of rectifying elements as discussed above;
limited to these details

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a rectifying element manufactured by an embodiment of the rectifying element manufacturing method according to the present invention, and FIG. 2 is a sectional view showing a rectifying element manufactured by another embodiment of the present invention.
FIG. 3 is a sectional view showing a rectifying element manufactured according to still another embodiment of the present invention, and FIG. 4 is a sectional view showing a rectifying element manufactured according to still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor structure, 2, 3... Metal foil, 4... Heat sink, 6... Metal foil, 7.8... Silver or silver alloy electrode. Applicant's agent Kiyoshi Inomata Fl, 2 F Hiro 3 Chi Karpov Soviet Union Tallinn Uritsa Velikie Hoki 22 Kave 104 0 Inventor Oleg Mikhailovich Korolkov Soviet Union Tallinn Uritsa Feduns Koho 56 Kabe 98 0 Inventor Viktor Leonidovich Kuzmin Soviet Union Tallinn Ismyya Kochi 114 Kabe 20 0 Inventor Gennady Nikolaevich Sluzhenkov Soviet Union Tallinn Filtli Chi 8 Kabe 14 Transfer inventor Gunnar Karlowicz Thomsor Soviet Union Tallinn Tamsare Kyi 121 Kabe 27 0 Inventor Efim Davidovich Khutruyanskiy Soviet Union Tallinn Ulitsa Kreizbarda 4A Rikichibe-24

Claims (1)

[Claims] 1. A method for manufacturing a rectifying element including metal coating two opposing surfaces of a semiconductor structure (1), wherein the metal coating includes metal foil (2°3) on the semiconductor structure (1). A method for manufacturing a rectifier element, characterized in that it is provided by diffusion welding, said welding being carried out simultaneously on both sides of the semiconductor structure. 2. diffusion welding a heat sink (4) to at least one side of the semiconductor structure (1), said metal foil (2,
Diffusion welding to the semiconductor structure in step 3) is performed using the heat sink (4).
2. The method for manufacturing a rectifying element according to claim 1, wherein said method is carried out simultaneously with diffusion welding. 3. The ratio of the thickness of the metal foil (3) inserted into the semiconductor structure (1) and the heat sink (4) and the thickness of the metal foil placed on the opposite side of the semiconductor structure (1) is 0.15. 3. The method of manufacturing a rectifying element according to claim 2, wherein the rectifying element is in a range from 10 to 10. 4. An electrode made of silver or a silver alloy is fixed to at least one metallized surface of the semiconductor structure (1), and this fixation is done by diffusion welding at the same time as diffusion welding the metal foil (2) to the semiconductor structure (1). Furthermore, the rectifying element made in this way is given by 01 to 15°
2. The method of manufacturing a rectifying element according to claim 1, wherein the rectifying element is cooled to 250 to 230° C. at a rate of C/sec. 5. An electrode made of silver or silver alloy is fixed to the outer surface of the heat sink (4), and this electrode is fixed by diffusion welding at the same time as coating the outer surface of the heat sink (4) with metal foil (6). Furthermore, the rectifying element made in this way has a power of 0.1 to 1
3. The method of manufacturing a rectifying element according to claim 2, wherein the rectifying element is cooled to 250 to 230° C. at a rate of 5° C./sec.