JPS6235568A - Semiconductor device - Google Patents

Abstract

PURPOSE:To form a preferable and effective positive bevel shape by forming a protective film for protecting the outer periphery of a semiconductor substrate against a blowing collision of polishing material powder on the outer periphery. CONSTITUTION:This is of the case adapted for an inverted conduction thyristor by outer peripheral gate type, and a protective film 7 is formed by means such as depositing, sputtering or plating through an oxide film 6 on the entire outer periphery of the second main surface of a semiconductor substrate 1 to coat the entire outer periphery separated from a gate electrode 4. The material of the film 7 needs to form directly on a silicon or through the film 6 at suffi ciently slow grinding speed as compared with the silicon of the substrate 1 in case of sand-blasting with polishing material powder, is preferably metal and particularly soft metal such as gold, silver, aluminum or copper to sufficient ly perform the purpose, and the thickness is suitably approx. 5-30mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor device, and particularly to an improved structure around an element in a semiconductor device that requires high breakdown voltage in one direction.

[Conventional technology]

As a conventional semiconductor device of this type,
The cross-sectional structure of the device configuration described in Japanese Patent No. 21867, in this case a reverse conduction thyristor, is shown in FIGS. 5 and 6.

In each of these figures, reference numeral 1 indicates a semiconductor substrate, 2 indicates an anode electrode plate (supporting electrode plate) brazed with a solder material 5 on the first main surface of the semiconductor substrate 1, and 3 and 4 indicate the same second electrode plate. They are a cathode electrode and a gate electrode formed on the main surface, and n is an n-nimifta region, PB is a p base region, and rlB
is an n base region, and PE is a p emitter region.

In this type of semiconductor device, generally, in order to obtain a high breakdown voltage, a bevel structure is introduced with an inclined angle between the pn junction surface and the wafer end surface. In the case of a positive bevel, the angle θ between the pn junction surface and the wafer end surface of the high resistivity layer adjacent thereto is:
It is said that tens of degrees is optimal, and in the case of negative bevel, several degrees is said to be optimal.

In each of these cases, for positive bevel, the depletion layer when voltage is applied is on the 18 side (high resistivity side), and for negative bevel, the depletion layer when voltage is applied is on the PB side (low resistivity side), respectively. The negative In case of bevel,
Compared to the case of a positive bevel, since the angle 0 is extremely small, the area around the urinary ridge that must be reserved for the bevel structure inevitably becomes larger, which is disadvantageous in terms of effective utilization of the wafer. In addition, in the case of a negative bevel, the bevel angle θ must be further reduced as the withstand voltage becomes higher, which is disadvantageous when compared to the case of a positive bevel in terms of control of the same angle θ. Therefore, in order to increase the voltage resistance and improve the effective utilization rate of the wafer, conventionally, even if there is only one J2 junction, the positive hevel shown in Figs. 5 and 6 has been conventionally used. Many structures are used.

[Problem that the invention seeks to solve]

In addition, normally, a mesa-shaped structure using a circular chip is adopted for large-capacity, high-voltage semiconductor devices, and in order to obtain the positive bevel shape, the chip must be rotated and The target area was ground by spraying abrasive powder on it. So-called sandblasting is commonly used, and the shape of silicon ground by this sandblasting largely depends on the density distribution of the abrasive powder ejected from the blast nozzle.

FIG. 7 is a partially enlarged view of the chip end shape during sandblasting in the semiconductor device manufacturing process in this conventional example, where 8 indicates the blast nozzle, arrows indicate streamlines of the abrasive powder being ejected, and FIG. FIG. 7 shows the density distribution of the abrasive powder in one line.

In other words, during silicon grinding, the abrasive powder is
Because the blasting depends on the density distribution shown in Figure 8 and the streamlines shown in Figure 7, the shape of the end face of the chip as the processed part does not become the expected positive bevel shape.
As seen in the figure, the outer periphery edge part has a rounded shape, so the bevel angle 0 between the J2 junction and the wafer edge is not as acute as expected, but is instead a right angle or There is an inconvenience that the end face ends up at an obtuse angle, and the shape of the end face to be machined depends largely on the density distribution and streamlines of the abrasive powder at the time of blasting, as described above, so the angle of the ejection direction of the blasting nozzle 8 is It has problems such as poor reproducibility due to the influence of settings, and extremely difficult processing control of the end face shape.

For these reasons, in this type of semiconductor device, the withstand voltage characteristics tend to become unstable and leakage current tends to increase. Incidentally, the curved line in FIG. 9 shows the off-state characteristics of such a conventional semiconductor element.

This invention was made in order to improve these conventional problems, and its purpose is to: - provide a good and efficient grinding process in an apparatus configuration that performs grinding by spraying abrasive powder onto the end face of a wafer; An object of the present invention is to provide a semiconductor device capable of forming an effective positive heel shape.

[Means for Solving the Problems] A semiconductor device according to the present invention has a protective film formed on the outer periphery of a semiconductor substrate to protect the outer periphery from being bombarded with abrasive powder.

[For production]

Therefore, in this invention, since a protective film is formed on the outer periphery of the semiconductor substrate, the silicon under the protective film is not damaged during sandplasting, and the abrasive powder that is sprayed has a substantial density distribution. It is possible to ideally create a sharply rising edge from the edge of the end face to be machined, thereby making it possible to perform sharp grinding and improve the reproducibility of the machined shape.

〔Example〕

Hereinafter, the first embodiment of the semiconductor device according to the present invention will be described.
This will be explained in detail with reference to the drawings to FIG.

1 and 2 are schematic cross-sectional views showing the general structure of a semiconductor device to which the first and second embodiments of the present invention are applied. The same reference numerals as in the figures indicate the same or corresponding parts.

First, the first embodiment shown in FIG. 1 is applied to a peripheral gate type reverse conduction thyristor. In this case, the oxide film 6 is formed by, for example, deposition or sputtering, so as to cover the entire outer peripheral surface separated from the gate electrode 4.

A protective layer 7 is formed by a method such as a coating.

This is the above-mentioned Ho XCf Ii! ,! As for the material of 7,
When performing sandblast grinding using abrasive powder, the grinding speed must be sufficiently slow compared to the silicon on one side of the semiconductor substrate, and it must be possible to form the abrasive directly on the silicon or through the oxide film 6. Particularly suitable are soft metals such as gold (Au), silver (Ag), aluminum (
Al), M (G:u), etc. can fully achieve the purpose, and the thickness is 5IL to 30
It has been found that approximately 3 g is appropriate, and that less than 3 l has almost no effect.

Further, the second embodiment shown in FIG. 2 is applied to a center gate type reverse conduction thyristor, and in the case of this second embodiment structure, the protective film 7 may be connected to the cathode electrode 3. It is possible.

In order to obtain the structure of each of these embodiments.

Sand Plus I using abrasive powder in the manufacturing process
The mode of the grinding process is shown in FIG. 3, and the density distribution of the abrasive powder at the line 2-rv is shown in FIG. 4.

As is clear from these figures, in this example, the outer periphery of the chip, which is included in the sandblasting and grinding range, is covered and blocked by the protective film 7. The density distribution of the abrasive powder that can grind silicon during sandblasting is the one that excludes the area blocked by the protective film 7, that is, the area B in FIG. The density distribution of the material powder has a sharp rise, which makes it possible to perform very sharp grinding using the edge of the chip as a boundary.At the same time, due to the protection provided by the protective film 7, during sandblasting, There is no risk of damaging the outer periphery of the chip.

The shape of the end face of the chip processed and formed in this manner exhibits an extremely good acute angle shape as shown in Fig. 3, and also because the edges of the density distribution of the abrasive powder are sharpened as described above. , on the other hand, it is possible to control the hevel angle θ,
Moreover, it is easy to form the end face with high precision. Incidentally, curve C in FIG. 9 shows the off-state characteristics of the semiconductor device according to this embodiment, and compared to the conventional example using curve C, it is possible to obtain better off-state characteristics with less leakage current. be.

In the above embodiments, the case where the present invention is applied to a reverse conduction thyristor has been described, but it is also applicable to general high-voltage semiconductor devices such as thyristors whose J2 junction has a positive bevel structure, gate turn-off thyristors, and transistors. Of course, it can be applied to

〔Effect of the invention〕

As detailed above, according to the present invention, in order to form a protective film on the outer periphery of a semiconductor substrate, during sandblasting with abrasive powder for forming a bevel structure, the silicon under the protective film is There is no risk of damage, and the actual density distribution of the sprayed abrasive powder can be made ideal, rising sharply from the edge of the edge of the chip to be processed, making it possible to grind sharp edges. It has excellent features such as being able to perform the process with high precision and good controllability, improving the reproducibility of the machined shape, and being structurally simple and easy to implement.

[Brief explanation of the drawing]

1 and 2 are schematic cross-sectional views showing the general structure of a semiconductor device to which the first and second embodiments of the present invention are applied, and FIG. 3 is a mode of sandblasting grinding using abrasive powder in the manufacturing process of the same. Partially enlarged view showing 4th
The figure is an explanatory diagram showing the density distribution of the abrasive powder at the TV-■ line section in Figure 3, and Figures 5 and 6 are cross-sectional schematic diagrams showing the general structure of a conventional semiconductor device. Figure 7 is a partially enlarged view showing the mode of sandblasting grinding using abrasive powder in the same manufacturing process;
FIG. 8 is an explanatory diagram showing the density distribution of the abrasive powder in the section 1--2 in FIG. 1... Semiconductor substrate, 2... Anode electrode plate, 3
...Cathode electrode, 4...Gate electrode, 8...
... Oxide film, 7... Protective film. Agent Masu Oiwa Yuusaku * Kiyoshi - Figure 5 Figure 6 Figure 7 Figure 8 A/p +

Claims (5)

[Claims] (1) A semiconductor substrate having at least one pn junction and two main surfaces, a support electrode plate brazed on the first main surface, and an electrode formed on the second main surface; In a semiconductor device whose cross-sectional area gradually increases from the side of the first main surface to the side of the second main surface, the outer periphery of the second main surface of the semiconductor substrate is prevented from being bombarded with abrasive powder. A semiconductor device characterized by forming a protective film for protection. (2) Claim 1, wherein the material of the protective film is a soft metal such as gold, silver, aluminum, or copper.
1. Semiconductor device described in Section 1. (3) The semiconductor device according to claim 1 or 2, wherein the protective film has a thickness of 5 μ to 30 μ. (4) A protective film is formed on the outer periphery of the second main surface via an oxide film. Semiconductor equipment. (5) Claims 1, 2 and 2, characterized in that a protective film is formed on the outer periphery of the second main surface, separate from the electrodes on the same main surface. The semiconductor device according to any one of Item 3 and Item 4.