JPS62232165A - Bonding-surface machining method for semiconductor element - Google Patents

Abstract

PURPOSE:To reduce breaking of a layer, in which a bevel groove is formed, and deformation of the groove, to provide a specified bevel angle and to improve the withstanding voltage of an element, by etching and removing a part to be dug in forming the bevel groove, and making the depth of the bevel digging depth small. CONSTITUTION:A bevel groove 5, which reaches a P1 layer from the surface of a P2 layer around a power thyristor, is dug by a sand blasting method. At this time, a position to be dug in the P2 layer is etched away to a depth h1, which does not reach an N1 layer, before the groove is dug. Thereafter, a bevel groove 5 is formed by the sand blasting method from the surface of the P2 layer at the removed part (region shown by broken lines). In this machining method, the digging depth of the bevel groove 5 becomes shallow by the depth h1 of the removed part at the previous process. Breakdowns and deformations at the deepest part and the starting point of the digging in the groove 5 are made less or can be completely avoided. The desired angles can be obtained at the surfaces of the p1N1 junction and the N1P2 junction.

Description

DETAILED DESCRIPTION OF THE INVENTION A. FIELD OF INDUSTRIAL FLI APPLICATIONS The present invention relates to a method for processing a bonding surface of a power semiconductor device.

B1 Summary of the Invention The present invention provides a method for processing bevel grooves on the bonding surface of a power semiconductor element having a PN junction, by removing the excavated surface of the groove to a predetermined depth and then performing the groove processing. This allows for reliable 114 machining.

C Conventional technology Power semiconductor devices such as thyristors and transistors are required to have improved breakdown voltage as one of their performance characteristics, and have traditionally been
It is known that a bevel groove is formed on the joining surface with a certain angle of inclination.

FIG. 4 does not show the cross-sectional structure of a conventional power thyristor. P
A tungsten plate (anode electrode) 2 is formed on the surface of the P1 layer using a brazing material 1 mainly made of aluminum on the silicon with a 4-layer 3-junction structure made of N, P, ,N.
An aluminum electrode (cathode electrode) 3 is bonded to the surface of the N7 layer, and an aluminum electrode (gate electrode) 4 is bonded to the surface of the Pt layer. In such a cyrisk structure, in order to have a voltage applied between the electrodes 2.3, the so-called blocking voltage, of 100 OV or more, N is removed from the surface of the P7 layer around the element to increase the forward and reverse breakdown voltage, that is, the reverse breakdown voltage of the N+P+, N1Pt junction. , P, dig a bevel groove 5 deep enough to reach the joint surface, and make the turning angle of this groove 5 N, Pt,
By obtaining the cut plane angle θ1 (usually 45°) of the N, P, and N, P junctions, the reverse withstand voltage is increased in the N, P, N, and Pl junctions. Note that the bevel groove 5 is formed by digging by sandblasting. Fill i'I\ with silicone varnish.

03 Problems to be Solved by the Invention In the conventional machining method, sand grains are sprayed in the digging direction by forming the beveled groove 5, but at this time the depth of the groove 5 increases, as shown in an enlarged view in Fig. 5. As shown, the i74 shape at the deepest part (shaded area A) is deformed differently from the original shape, and P
, N, the groove angle θ1 of the bonding surface may not be obtained.

In addition, the deformation of the deepest part can be prevented by the subsequent application of silicone varnish.
Air bubbles were generated during filling, and etching and cleaning were insufficient, causing leakage in the grooves.

In addition, as shown in Fig. 5, when the bevel groove 5 is deep, the 21st layer or the like may be chipped at the excavation opening, and the N1Pt junction may be damaged, making it impossible to obtain the desired withstand voltage and reducing the yield. Something happened.

E1 Means for Solving Problems The present invention has been made in view of the above-mentioned problems, and involves removing the excavated surface of the bevel groove by etching to a predetermined depth in advance, and then removing the etched surface of the bevel groove from the removed element surface. The processing method involves digging, and the depth of digging by sandblasting is reduced to obtain processing that eliminates chipping and groove deformation on the layer surface.

F. Embodiment FIG. 1 is an enlarged view of essential parts showing an embodiment of the method of the present invention. In digging a bevel groove 5 reaching P and FJ from the peripheral Pt layer surface of the power SIRISK by sandblasting method,
Before digging the trench, remove the 27th layer by etching to a depth hl that does not reach the N1 layer. Thereafter, a bevel groove 5 is dug from the layer surface of the removed portion (dashed line area) by sandblasting.

With this processing method, the digging depth of the bevel groove 5 is reduced by the depth hl of the removed portion in the previous process, and the iM 5
It is possible to reduce or completely eliminate chipping and deformation both at the deepest part of the tunnel and at the excavation entrance. As a result, P, N, junction and N,
It is possible to obtain the desired angle for both P and joint surfaces.

In addition, in the conventional method, when forming the bevel groove 5, there was a risk that sand grains would scatter on the element surface during the initial sandblasting and damage the NtPt bonding surface, etc. However, in this embodiment, the etching removal part is removed by the sandblasting. By acting as a mouth, it reduces the scattering of sand grains. in this regard,
In the conventional method, in order to protect the NyPt joint from sand grains,
Although a protective material is applied to the peripheral surface of the element, this step can be omitted or simplified in this embodiment.

Note that when the bevel groove depth becomes large even when removing by etching, the etching depth is increased to a value reaching the N1 layer as shown in FIG.
Make sure to also cut the joining surface. This makes the depth of the Beher groove even shallower.

Both N, P and joints can have a Hevel angle.

In addition, in the example, when the silicon substrate becomes thick due to the high withstand voltage of SiRisk, when a structure with P, N, and junction angles of 0 (for example, 45°) is created, the element peripheral surface as shown in FIG. A two-stage bell structure having an inclination θ may also be used. At this time, the order of the elements (N1Pt junction) and the reverse (PI
N, junction) while improving the withstand voltage of both +7+〒
Easy to form and even cut the circumferential surface.

Note that although the embodiment is shown in the case where the present invention is applied to a power thyristor, it can be applied to a GTO thyristor, a power transistor, a diode, etc. to obtain the same effect.

G Effect of the invention As described above, according to the method of the present invention, Heher'tl+1
When digging in step 1, remove the digging opening by etching,
By using a processing method that reduces the depth of bevel iM Ia, it is possible to obtain the desired bevel angle by reducing layer chipping and groove deformation in the bevel 11η digging, making it easier to improve the element withstand voltage. It has the effect of being able to manufacture products with good yields.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of main parts showing an embodiment of the method of the present invention;
Figures 2 and 3 are cross-sectional structural diagrams of the main parts without showing other embodiments of the present invention, Figure 4 is a diagram of the structure of a power silisk with bevel grooves, and Figure 5 is a diagram of the conventional bevel groove structure. be. 2... Anode electrode, 3... Cathode electrode, 4...
- Gate electrode, 5... bevel groove. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] When processing a bevel groove on a PN junction surface of a power semiconductor element, the surface into which the bevel groove is to be processed is removed by etching to a predetermined depth in advance, and the bevel groove is dug from the removed element surface. A method for processing a bonding surface of a semiconductor device, characterized by: