JP2907885B2 - Thyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an electrode structure of a thyristor.

(Prior Art) In a thyristor, a P base layer and an N emitter layer are usually provided continuously on the top surface of a semiconductor substrate formed by alternately arranging at least four semiconductor layers having different conductivity types. The present invention is suitable for a planar type (Planer) type shown in FIGS. 1 and 2 or a Mesa type thyristor (Thyrister) not shown. As is apparent from the figure, a surface concentration of 10 ^{18 on} one top surface of the silicon semiconductor substrate 1 having the PNPN structure.
/ cm and about ³ of the P-type base region 2 (referred to as hereinafter gate region) is formed a surface concentration of 10 ²⁰ / cm ³ order of N-type cathode (Cathode) region 3 in succession, the The resulting PN junction ends 3 are led out in the thickness direction of the semiconductor substrate in the mesa shape, and to the top surface of the semiconductor substrate in the planar shape. The PN junction ends 3 are planar and protected by an insulator layer, for example, a thermal oxide layer 4, and covered by a mesa-shaped silicon encap material. The two regions 2, 3 exposed in the opening formed by the patterning (patterning) process using the Lithography technology are covered with the cathode and the gate electrodes 5, 5 for electrical connection. Thyristor approximately rated current 10A having such a structure, I _T 1
000A, pulse surge t _S 500 microns _S a (Puls Surge) is added at 15 second intervals. For this reason, the linear electrode terminals 6 having a large current capacity are provided in preparation for a large current to be applied to each of the regions 2 and 3, and a soldering process or a wire bonding process is known as a mounting method thereof. Have been.
FIG. 1 shows an example in which the linear electrode terminals 6, 6 are formed by a soldering process, and FIG. 2 shows a cross-sectional view of a planar thyristor formed by a wire bonding process. . Also, (1) JP-A-54-71564, (2) JP-A-54-163675, and (3)
JP-A-62-269332 discloses an electrode structure. In other words, in the publication of (1), in order to form an ohmic wiring, Ti is formed in a diffusion region having a small xj, that is, a shallow diffusion region.
(2) discloses a technique for forming an Al wiring through a metal alloy of (Titanium) and Al. In order to prevent the deterioration of a shallow junction, a metal silicide, a barrier metal such as Ti, and Al are used in an electrode window.
(3) discloses that a TiN (Titanium Ni-tri) is interposed between a phosphorus-containing silicon dioxide and an Al film.
d) to prevent the difficulties caused by the intrusion of water.
This is a method to prevent deterioration of low junction or prevent ingress of moisture.

(Problems to be Solved by the Invention) The thyristor of the solder electrode type clarified in FIG. 1 is connected to the linear electrode terminal 6 attached by the solder layer 7 provided on the entire surface of the cathode and gate regions 2 and 3 as described above. For example, I _T 10
00A, t _S even when repeatedly applying a pulse surges 500μs at about 15 second intervals, the damage to the current flowing through the solder electrodes uniformly (Damage) is small, to thyristor help heat radiation action of the upper solder layer There is a feature that the influence is small and the resistance is strong. However, in the assembling process, the electrodes 5, 5 made of a conductive metal are formed in the respective regions 2, 3, and then the linear electrode terminals 6, 6 are attached by the soldering process. On the other hand, in the simplified method of using a thin metal wire ultrasonically welded by the wire bonding process as a linear electrode terminal, the Al power 5, 5 and the Al fine wire are applied, which reduces the man-hours and can be mechanized, thus rationalizing. Can be achieved. However, this type of thyristor has a small resistance to a pulse surge of about 2000 cycles.

The reason for this is that the current flowing from the anode formed on the back surface of the semi-moving body substrate to the cathode region is applied in a short time, and contributes to conduction. As a result, a high current density occurred, and a phenomenon occurred in which heat was generated and melted at the interface between the Al electrode and the silicon semiconductor substrate in the vicinity. As a result, it is presumed that an alloy such as Al-Si is formed and grows to have a high resistance, so that the power loss (Power Loss) becomes large and eventually breaks.

The present invention has been made in view of such circumstances, and it is an object of the present invention to prevent adverse effects caused by current concentration when a pulse surge is applied.

[Configuration of the invention]

(Means for Solving the Problems) In order to solve this problem, according to the present invention, at least four semiconductor layers having different conductivity types are alternately stacked, and the end of the junction surface of the different semiconductor layers is exposed to the surface. A semiconductor substrate formed on the substrate, an insulating layer for protecting an end of the bonding surface exposed on the surface of the substrate, and a semiconductor layer of the different conductivity type exposed on the surface of the substrate laminated via a high-melting metal layer. The above problem is solved by a thyristor comprising an electrode metal layer provided and an electrode terminal crimped to the surface of the electrode metal layer by ultrasonic bonding.

(Operation) In a model such as a thyristor, which is required to withstand a surge, a linear electrode terminal having a large current capacity must be provided on a semiconductor layer having a different conductivity type, that is, an electrode adjacent to a cathode region and a gate region. . In addition, the thyristor according to the present invention employs a wire bonding method as a method of simplifying the process while avoiding complicated steps. This is because when a molybdenum (Mo-lybdenum) belonging to a high melting point metal and a double layer of a titanium layer and an Al layer are provided adjacent to a cathode region and a gate region, and a linear electrode terminal is placed thereon, Satisfies surge withstand capability. That is, when a predetermined pulse is repeatedly applied, a current flows from the cathode region and the gate region near the linear electrode terminal, and a heat generation phenomenon occurs. However, it was confirmed that the inconvenience of melting the interface between the semiconductor substrates due to the electrode layer formed of the high melting point metal layer acting as a thermal barrier could be prevented. The present invention has been completed based on this fact.

Embodiment An embodiment according to the present invention will be described with reference to FIGS. 3 to 5. FIG. Although there are some overlaps with the conventional technology section,
In order to facilitate understanding, a mask layer having selectively formed openings is provided on one surface of the semiconductor layer 10 containing about 10 ₁₅ to ₁₆ / cm ³ of N-type impurities such as phosphorus, and then boron or the like is formed. Introduce and diffuse P-type impurities to make impurity surface concentration 10 ¹⁸ / c
An about m ³ separation P layer 11 and a gate layer 12 are formed to form a thyristor silicon semiconductor substrate. P layer for separation 11
The thickness of the thyristor is set to about 250 μm so as to cover the semiconductor layer 10 in the thickness direction, and a dicing process is performed on the semiconductor layer 10 to break the individual thyristors.

By the way, the base layer 12 having a length of approximately 2.5 mm has 2
A cathode region 13 having a length of about mm is formed to a surface concentration of about 10 ²⁰ / cm ³ by introducing and diffusing an N-type impurity such as phosphorus.
A thyristor silicon semiconductor substrate 14 in which different conductivity types are alternately arranged is completed. Before and after the description, prior to a series of steps, a thermal oxide film 15 having a thickness of about 3 μm is formed by a conventional method.
To form Of course, before forming the cathode region 13, a patterning process by an anisotropic or isotropic etching method using a photo lithography technique is performed to prepare for the formation of the cathode electrode and the gate electrode.

The openings provided in the thermal oxide film 15 corresponding to the two regions 12 and 13 are provided by a vacuum evaporation method or a sputtering method.
After the pure molybdenum layer 16 is deposited by about 2000 ° by the method g), the Al layer 17 is deposited by 10 μm each by the same means to form the cathode electrode 18 and the gate electrode 19 each having a two-layer structure. This Al
The layers 17, 17 serve for ultrasonic welding with the Al fine wires 20 described later.

The Al wires 20 operate as the linear electrode terminals 20 of the thyristor, and about 500 μm is welded to the cathode electrode 18 and about 250 μm to the gate power 19 by ultrasonic bonding using an ultrasonic bonding method. That is, the perfect circular Al balls formed at the tips of the Al layers 17, 17 and the Al fine wires 20 are ultrasonically welded, and electrical conduction between the cathode electrode 18 and the gate electrode 19 and the linear electrode terminals 20 is established. can get. Of course, this ultrasonic bonding step can also be achieved by a thermocompression bonding method. The metal layer 21 is coated as an anode of the thyristor on the back surface on the front side of the silicon semiconductor substrate 14 on which the cathode electrode 18 and the gate electrode 19 are provided, that is, the exposed surface of the separation P layer 11 on the silicon semiconductor substrate 14 to form a thyristor. .

Such thyristors are made of plastic (Plas-ti
c) It is assembled in an envelope (not shown) made of the present invention, but it is not directly related to the present invention, and the description is omitted.

[Effect of the Invention] In order to streamline the assembling process by changing the conventional solder electrode type thyristor to an Al bonding type electrode, the resistance to repeated application of pulse surge is improved.

As clarified in FIG. 4, for example, I _T = 1000 A, t _S
When a pulse surge of = 500 μs is repeatedly applied at intervals of 15 seconds, current flows intensively around the bonding area, so that the linear electrode terminals 20 and silicon generate heat near the semiconductor substrate 4 interface, but the high melting point metal The formation of the electrodes 18 and 19 made of layers can prevent the phenomenon of melting, suppress the generation and growth of Si-Al alloy and the like, and prevent the thyristor from being broken. FIG. 5 is a table showing the results of a repeated application test of pulse surge under the above conditions. The vertical axis shows the number of cycles, and the horizontal axis shows the type of electrode. As is clear from this, 2000 cycles are obtained for the Al electrode where electrode breakdown occurs, whereas 5000 cycles are obtained, which is twice or more, for the electrode structure according to the present invention.

In other words, the production yield of the thyristor and hence the reliability are improved.

[Brief description of the drawings]

1 and 2 are cross-sectional views of a thyristor having a conventional electrode structure, FIG. 3 is a cross-sectional view of a thyristor according to the present invention, and FIGS. 4 and 5 show characteristics of the thyristor of the present invention. FIG. 1, 14: semiconductor substrate, 2, 12: gate region, 11: isolation P layer, 3, 13: cathode region, 6, 20: linear extraction electrode, 7: solder layer, 5: electrode, 15: thermal oxide film 16: molybdenum layer, 17: Al layer, 18: cathode electrode, 19: gate electrode, 21: anode.

Claims (1)

(57) [Claims] At least four semiconductor layers having different conductivity types are alternately stacked, and an end of a junction surface of the different semiconductor layer is exposed on a surface, and the junction is exposed on a surface of the substrate. An insulator layer for protecting a surface end portion, an electrode metal layer laminated on the semiconductor layer of different conductivity type exposed on the substrate surface via a refractory metal layer, and ultrasonic bonding to the electrode metal layer surface A thyristor comprising: an electrode terminal crimped by the method described above.