JPS639670B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a high-power, high-voltage semiconductor device having stable blocking characteristics.

A thyristor is a semiconductor device that has three or more pn junctions and can be switched from a current blocking state to a conducting state by electrical or optical triggering means, and vice versa by electrical means. .

A typical example will be explained with reference to the drawings.

A thyristor with a pnpn structure in which the conductivity type of the semiconductor wafer as a starting material is n-type will be explained based on a general manufacturing method.

In FIG. 1, a semiconductor substrate 10 has p-type emitter layers 1 and 1 exposed on one main surface ₁₀₁ thereof.
n-type base n _B layer 2, n adjacent to type emitter layer 1
n adjacent to type base layer 2 and exposed on the other main surface 102 of semiconductor substrate 10 together with p-type base layer ₃
It consists of a type emitter n _E layer 4. Between the p-type emitter layer 1 and the n-type base layer 2, between the n-type base layer 2 and the p-type base layer 3, and the p-type base layer 3
and the n-type emitter layer 4, there is a p-n junction, respectively.
J ₁ , J ₂ , and J ₃ are formed, with J ₁ and J ₂ terminating at the side surface 103 of the semiconductor body 10 and J ₃ terminating at the other main surface 102 . One main surface 10 of semiconductor substrate 10
An anode electrode 5, a cathode electrode 6, and a control electrode 7, which are main electrodes, are formed on exposed portions of the p-type base layer 3 on the upper and other main surfaces 102, respectively. The anode electrode 5 also serves to protect the fragile semiconductor wafer. Furthermore, the n emitter layer 4
The p-n junction J ₃ between the p-base layer 3 and the p-base layer 3 is partially short-circuited by the cathode electrode 6 in a region 41 to have a short-emitter structure, and the outermost periphery of the cathode electrode 6 is connected to the p-base layer 3. A peripheral short-circuit structure is provided in the region 42 so as to be short-circuited. The end region 400 of the semiconductor body 10 is therefore
It has a pnp structure.

Short-emitter structures and peripheral short-circuit structures are both known techniques for improving the blocking characteristics of thyristors. Here, the blocking characteristic of a thyristor means that when a voltage is applied between the anode electrode 5 and the cathode electrode 6, the J ₁ or J ₂ junction becomes a reverse bias state (this is called a blocking state). The ability to block a voltage as high as possible with as little leakage current as possible. Semiconductor substrate 10
Even if it is possible to block high voltages inside, the blocking ability at the surface is usually inferior to that inside.
This is because the electric field strength at the surface is higher than that inside, which causes avalanche destruction. In order to eliminate this, it is necessary to lower the surface electric field strength compared to the inside. Lowering the surface electric field strength can be achieved by increasing the spread of the depletion layer at the surface.

For this reason, conventionally, the end side surface 103 of the semiconductor substrate 10 has been processed into various shapes, such as a two-step bevel shape and a Σ-shape. However, since the J ₁ and J ₂ junctions are exposed on the end side surface 103, a surface stabilizing film 200 (hereinafter referred to as a passivation material) is used to prevent contamination from the outside and adhesion of impurity ions. It had to be painted. However, conventional thyristors have the following problems.

When a high blocking voltage is applied to a thyristor and this state is maintained for a long time, leakage current increases abnormally, the blocking characteristics deteriorate significantly, and in the worst case scenario, thermal runaway occurs and the thyristor is destroyed.

Conventionally, it has been generally accepted that such a problem is not a phenomenon inside the semiconductor substrate, but is a problem caused by the side surface of the end portion of the semiconductor 10 in connection with the passivation material. For this reason, studies have been made on the material itself of the passivation material and on chemical treatment methods for the end and side surfaces, and some of the results have been proposed.

However, a detailed model of the causes of deterioration and a proposed solution have not yet been submitted after detailed investigation using a structure similar to the actual device illustrated in Figure 1. Until now, there has been no semiconductor device that has solved the above problems apart from the structure.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and specifically, to provide a semiconductor device that has a highly reliable blocking ability without increasing leakage current even when a blocking voltage is applied for a long period of time. It is to provide.

The semiconductor device of the present invention that achieves the above object is characterized in that at least one pn junction is exposed on the side surface of the semiconductor substrate, and the first main electrode is connected to one main surface of the semiconductor substrate with low resistance. and a second main electrode is in low resistance contact with the other main surface of the semiconductor substrate, the first main electrode protruding from the periphery of this main surface on the one main surface side of the semiconductor substrate. A first current collecting electrode electrically connected to the main electrode is provided on the other main surface side of the semiconductor substrate, protruding from the periphery of this main surface and electrically connected to the second main electrode. second
A current collecting electrode is provided, and a passivation material is provided so as to cover the side surface from the first current collecting electrode to the second current collecting electrode.

By providing the first and second current collecting electrodes, when a blocking voltage is applied, impurity ions in the passivation material are absorbed by the electric field acting in the passivation material to the first and second current collecting electrodes. By having a new structure and effect that prevents impurity ions from drifting to the electrode or the first and second main electrodes and accumulating on the surface of the semiconductor substrate, and collecting these impurity ions to the current collecting electrode, the semiconductor layer surface The abnormal increase in leakage current due to depletion or n-type inversion is eliminated, and a semiconductor device having stable and reliable blocking characteristics can be realized.

The present invention will be explained in more detail below.

As described above, an object of the present invention is to realize a semiconductor device having stable blocking characteristics without fluctuations in leakage current in the blocking state. As a first step toward achieving this objective, the present inventors conducted a detailed study on the phenomenon of deterioration of blocking characteristics of a thyristor having a conventional structure as illustrated in FIG. As a result, the deterioration phenomenon is not a problem inside the semiconductor substrate,
It was found that this was caused by impurity ions scattered in the passivation material applied to the side surface of the end. In other words, trace amounts of impurity ions, such as water, sodium ions, and ions dissociated and produced by electrolysis, are scattered in the passivation material, and can never be removed. When a blocking voltage is applied, an electric field is created within the passivation material. The impurity ions are moved by this electric field and are accumulated in large quantities in the region where the electric field, that is, the lines of electric force terminate.

Here, we will specifically discuss the phenomena observed in actual thyristors.

FIG. 2 is an enlarged view of only the peripheral portion of the conventional device shown in FIG. 1 in order to explain the above phenomenon in more detail. However, the same parts as in FIG. 1 are indicated by the same symbols. Further, the thyristor is shown in a forward blocking state, that is, a state in which a voltage is applied between the main electrodes 5 and 6 with the anode electrode 5 being positive and the cathode electrode 6 being negative.

The dotted lines shown in the passivation material 200 in the figure are lines of electric force 30, and impurity ions move along these lines of electric force. Regarding these lines of electric force, since this thyristor is not provided with the current collecting electrode of the present invention, most of the lines of electric force are on the side surface of the end where the p-type base layer 3 is exposed and the semiconductor layer on the surface thereof. terminate. As a result, a large number of positively charged impurity ions are accumulated on this surface. It is known that when positive charges are segregated on the surface of a p-type semiconductor layer, the hole concentration on the surface decreases, resulting in depletion and further inversion to n-type.

When the blocking voltage applied to the thyristor acts for a long time, the amount of positive charges accumulated on the surface of the p-type base layer 3 gradually increases, and depletion of the surface of the p-type base layer 3 or n-type inversion progresses. Eventually, the leakage current reaches the cathode electrode 6, which is the second main electrode provided on the n-type emitter layer 4, and an abnormally large leakage current flows through this region. The dashed-dotted lines shown in the n-type base layer 2 and p-type base layer 3 in the figure indicate the depletion layer region.
It is shown that depletion has already progressed on the surface of the mold base layer 3 and has reached the cathode electrode 6.

As is clear from the above explanation, the deterioration of the blocking characteristics that occurs in conventional thyristors is caused by impurity ions in the passivation material being moved by the electric field and accumulated on the surface of the p-type base layer 3, causing the surface to become depleted or n-type. We proposed a new way of thinking that this phenomenon is caused by reversal.

According to this concept, it is understood that it is essential to reduce the amount of impurity ions that collect on the surface of the p-type base layer 3 as a means to solve the problem of poor deterioration.
As a means of achieving this point, there is a method of lowering the content of impurity ions by improving or creating a new passivation material that has been used in the past, but the present invention proposes a different solution. In other words, in the past, most of the electric lines of force during passivation terminated at the p-type base layer 3, and most of the impurity ions were accumulated there; By providing a current collecting electrode, the impurity ions accumulated on the surface of the p-type base layer 3 are accumulated in a new current-collecting electrode, and the amount of accumulated charge on the surface of the p-type base layer 3 is substantially lowered, thereby preventing leakage. Current is significantly reduced.

Further, the background of the present invention is the analysis of experimental results shown below.

Figures 3a and 3b show the shapes of experimental samples, and Figure 4 shows the results.

Main electrodes 5 and 6 are provided on a pair of opposing surfaces of a semiconductor substrate 10 having a pnp structure. In (a), the main electrode 6 is formed from a W plate and is connected to the adjacent p-type semiconductor layer.
It is provided with a 1.5mm protruding structure. In (b), both main electrodes 5 and 6 are formed by vapor-depositing aluminum. And, contrary to (a), the main electrode 6 is
It is regressed by 1.5 mm from the adjacent p-type semiconductor layer.

FIG. 4 shows the change over time in the leakage current that flows when a DC voltage of 3000 V is applied with the polarity shown in FIG. 3. Curve A shows the measurement results in Figure 3(a), and curve B
shows the measurement results in Figure 3(b). It can be seen that curve A has a smaller increase in leakage current than curve B.

By examining the experimental results in detail, we found that (a)
In the sample shown in (b), the W plate 6, which is the main electrode, essentially also functions as the current collecting electrode of the present invention, whereas the main electrode 6 in the sample shown in (b) does not have this function, and is simply an electrode. It will be understood that it is nothing more than

FIG. 5 shows an embodiment of the present invention.

Using an n-type silicon single crystal with a resistivity of 200 to 300 Ω-cm and a thickness of about 1 mm as a starting material, a p-type impurity such as gallium or aluminum is diffused using a known diffusion technique to form a p-type diffusion layer. The surface of one diffusion layer is uniformly etched in the depth direction by chemical etching.
Remove about 50μm and adjust the thickness. The p-type layer thinned by etching removal becomes the p-type base layer 3, and the thick p-type layer adjacent to the other main surface 101 on the opposite side becomes the p-type emitter layer 1, sandwiched between them. The removed n-type layer is an n-type base layer 2. Next, an n-type emitter layer 4 adjacent to the p-type base layer 3 is formed using, for example, a phosphorus diffusion technique and a chemical etching technique using PoCl ₃ as a diffusion source.
However, in a partial region inside the n-type emitter layer 4, the p-type base layer 3 is exposed to the surface 102. Adjacent to the opposing main surfaces 101 and 102, the p-type emitter layer 1 has an anode electrode 5, the n-type emitter layer 4 has a cathode electrode 6, and a part of the p-type base layer 3 exposed on the main surface 102. A control electrode 7 is formed in each of the regions, and the cathode electrode 6 partially connects the p-type base layer 3 and the n-type emitter layer 4 to 4 in the figure.
This is a so-called short emitter structure in which the region indicated by 1 is short-circuited.

In this example, the anode electrode 5, cathode electrode 6, and control electrode 7 were formed by vapor-depositing aluminum, which is commonly used. Both main surfaces 101 and 102 of the semiconductor substrate 10 on which the electrodes are formed are sliding surfaces, and both surfaces are electrically and thermally contacted by mechanical pressure welding, and assembled by being sealed in a flat package. It will be done. p-n junction J ₁ and J ₂
The end side surface 103 where is exposed is processed into a Σ-shape in which both pn junctions have positive bevels.
Further, in an end region 300 on the main surface 101 of the semiconductor substrate 10, the p-type emitter layer 1 is exposed on the surface, and in an end region 400 on the main surface 102 of the semiconductor substrate 10, the p-type base layer 3 is exposed on the surface. Each of them has a pnp structure. The current collecting electrode 8 of the present invention is adjacent to the end region 300.
, and a current collecting electrode 9 is provided adjacent to the end region 400 . The current collecting electrodes 8 and 9 were ring-shaped which protruded from both main surfaces and covered the entire circumference, and were made of tungsten. However, it is not necessary to limit it to tungsten, and it is important that it is a good electrical conductor that does not chemically react with the passivation material 200 described below and does not corrode.
Note that the current collecting electrodes 8 and 9 were made to protrude from the peripheral edges of the main surfaces 101 and 102 of the semiconductor substrate 10 by 1.0 mm or more.

Furthermore, ohmic contact is obtained so that the current collecting electrodes 8 and 9 have approximately the same potential as the anode electrode 5 and the cathode electrode 6, respectively.

The present inventors have discovered that the current collecting electrode 8 and the anode electrode 5 are
It has been confirmed that the effect can be sufficiently achieved even with a simple structure in which the current collecting electrode 9 and the cathode electrode 6 are in contact with each other.

For the purpose of protecting the surface of the side surface of the end portion, a passivation material 200 is thickly applied to surround the periphery thereof. In this embodiment, the current collecting electrodes 8 and 9 are installed almost completely buried in the above-mentioned passivation material, but the installation condition is such that at least a part of each of the current collecting electrodes 8 and 9 is buried. It is sufficient. Further, as the passivation material 200, a silicone/rubber-based organic material, which is generally put into practical use in power thyristors, is used.

FIG. 6 is a diagram for explaining the function of the current collecting electrodes 8 and 9, and the end portion of the semiconductor substrate 10 shown in FIG. 5 is shown in an enlarged manner for easier understanding. However, since the pair of current collecting electrodes 8 and 9 provided at the end regions of both surfaces of the semiconductor substrate each have the same effect,
The current collecting electrode 9 provided on the cathode side will be explained. There is no essential difference in the operation and effect of the current collecting electrode 8 on the anode side except that the polarity of the voltage applied to the semiconductor substrate is opposite. Passivation material 200
The dotted lines inside indicate the lines of electric force 30.

When a voltage is applied with the polarity shown in the figure, the electric lines of force extending through the passivation material are concentrated on the surface of the p-type base layer 3 and terminate in the conventional structure shown in FIG. In the thyristor, fewer lines of electric force are gathered to the p-type base layer 3, and new lines of electric force are generated that terminate at the current collecting electrode 9. In such a situation, most of the impurity ions scattered in the passivation material 200 receive a force directed toward the current collecting electrode 9, and are accumulated on the current collecting electrode 9 as indicated by marks in the figure. Note that the dashed-dotted lines in the figure indicate the depletion layers on both sides of the pn junction _J2 .

In addition, in the conventional thyristor shown in FIG. 1, a metal member such as tungsten or molybdenum plate is bonded to the semiconductor substrate 10 as the anode electrode 5, and therefore, due to the difference in thermal expansion coefficient between the two, there may be problems during bonding. A curve will occur. This curvature makes it difficult to make thermal and electrical contact, increases thermal resistance, and forward voltage drop (FVD).
This has the undesirable effect of increasing the However, in this embodiment shown in FIG. 5, the anode electrode 5 is not provided by adhering a metal member such as a tungsten plate, but instead is provided on the main surface 10 of the semiconductor substrate 10 in the same way as the cathode electrode 6.
Since the structure is formed by simply vapor depositing aluminum on the surface of the surface of the surface, there is no problem of curvature due to differences in thermal expansion coefficients, and it is easy to make electrical and thermal contact on the sliding surface.

FIG. 7 shows another embodiment of the invention.

While the embodiment shown in FIG. 5 has a Σ-shape in which both J ₁ and J ₂ junctions have positive bevels, this embodiment is a convex-shaped thyristor in which both pn junctions have negative bevels. This is an example. In FIG. 7, the same reference numerals as in FIG. 5 indicate the same or equivalent parts. Furthermore, the end shape to which the present invention can be applied is Σ
There is no need to limit it to a letter-shaped or convex shape.
It can be applied to any shape.

Furthermore, the invention can be applied not only to the thyristors shown in both embodiments, but also to semiconductor devices of various types, such as diodes, transistors, reverse conduction thyristors, and bidirectional thyristors.

In addition, not only organic materials but also inorganic materials such as glass can be used as the passivation material.

According to the present invention, even if a state in which a high voltage such as 3KV to 6KV is blocked for a long time,
The amount of impurity ions accumulated on the surface of the semiconductor layer is small, so there is no increase in leakage current, and a novel semiconductor device with a current collecting electrode having extremely stable blocking characteristics can be obtained.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a conventional thyristor, Figure 2 is a sectional view showing a conventional thyristor.
The figure is an enlarged partial sectional view of the peripheral part of the thyristor shown in Figure 1, Figures 3 and 4 are diagrams showing samples and results of experiments studied in the process of obtaining the present invention, and Figure 5 is a diagram showing the invention of the present invention. A cross-sectional view of a thyristor showing one embodiment, FIG. 6 is a partial cross-sectional view enlarging the peripheral part of the thyristor shown in FIG. 5 for explaining the action of the current collecting electrode, and FIG. FIG. 2 is an enlarged partial cross-sectional view of a peripheral portion of a thyristor showing an example. 1... p-type emitter layer, 2... n-type base layer,
3...p-type base layer, 4...n-type emitter layer, 5
... Anode electrode, 6 ... Cathode electrode, 7 ...
Control electrode, 8, 9... Current collecting electrode, 10... Semiconductor substrate, 200... Passivation material, 300,
400... End region, 30... Lines of electric force.

Claims (1)

[Claims] 1 At least one pn junction is exposed on the side surface of the semiconductor substrate, a first main electrode is in low resistance contact with one main surface of the semiconductor substrate, and a second main electrode is in low resistance contact with the other main surface of the semiconductor substrate. in which the main electrodes of the semiconductor substrate are in low-resistance contact, the first main electrode protruding from the periphery of the main surface and electrically connected to the first main electrode on one main surface side of the semiconductor substrate.
A second current collecting electrode is provided on the other main surface side of the semiconductor substrate, protruding from the periphery of this main surface and electrically connected to the second main electrode, A semiconductor device characterized in that a passivation material is provided so as to cover the side surface from the first current collecting electrode to the second current collecting electrode.