JPH079894B2 - Semiconductor element end face processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an end surface processing method, particularly a groove processing method, for forming an angle on a PN junction surface of a power semiconductor element.

B. SUMMARY OF THE INVENTION The present invention provides an end face processing method for obtaining a bevel structure of a mesa semiconductor element by groove processing, in which a contact reaching the inner bottom surface of the groove is provided, and the contact and the surface opposite to the processed surface are provided. By applying a voltage between the electrodes of the electrode and detecting the current change, the joining position of the element is detected from the sudden change in the current, the processing end point is clarified, and the groove shape is made constant. .

C. Conventional Technology In mesa-type power semiconductor devices such as thyristors and GTOs, the PN junction surface is angled to reduce the electric field strength on the surface. When the angle is set so that the high impurity concentration side of the PN junction occupies a large region (positive bevel), the angle is effective at about 30 ° to 60 °. As a kind of this, there are cases where grooves are processed as shown in FIG.

FIG. 3 shows an example of a thyristor structure in which a groove 3 is formed in a silicon pellet 2 (a four-layer structure of P ₁ N ₁ P ₂ N ₂ ) obtained by alloying a tungsten plate 1 also serving as an anode with aluminum or the like. Bevel structure. In this case, the central P ₂ N ₁ junction (J ₂ junction) that blocks the forward voltage is grooved so that the high-concentration P ₂ side becomes an obtuse angle, and the outer region is also left. . The reason for leaving this outside is to serve as a mechanical protection of the outer peripheral portion of the silicon pellet 2 in the step after cutting and to facilitate the application of the passivation film.

Such grooving is usually done by alloying the silicon plate 2 with the tungsten plate 1, placing it on a rotating disk, fixing it, and then using a side blasting device to sand the silicon pellet 2 with high-pressure air. It is done by spraying.

D. Problems to be Solved by the Invention However, since the grooves are formed in the semiconductor element obliquely as described above, it is difficult to visually recognize the grooves, and the end point detection is controlled by calibrating the cutting speed in advance and time. Since this cutting speed (groove processing speed) changes due to changes in diameter due to wear of the nozzle of sandblast, humidity of sand, air pressure, etc., it is difficult to maintain a constant value. As a result, excess or deficiency of processing occurs, which results in a groove shape as shown in FIGS. 4 (a) and 4 (b), which causes a reduction in withstand voltage yield of the device.

E. Means for Solving the Problems The present invention provides a semiconductor device end face processing method of forming a bevel structure on a PN junction surface of a mesa type semiconductor device by groove processing, reaching an inner bottom surface of a groove being processed. A contact was provided, and a voltage was applied between this contact and the electrode on the semiconductor element surface on the side opposite to the groove processed side, and current detection means for detecting the current was provided, and the groove reached the junction. It is characterized in that the machining end point is determined based on the sudden change in the current at the time point.

F. When the working groove reaches the joint, the current passing through the contact changes abruptly. This sudden change in the current and its value are detected by the current detecting means to determine which joint, and when the joint is at the position to be detected, the machining end point is determined based on the detection. As a result, there is no excess or deficiency in the machining amount, and the groove shape becomes constant.

G. Examples Hereinafter, the present invention will be described in detail based on illustrated examples.

FIG. 1 shows an embodiment of the present invention, in which P ₁ N ₁ P ₂ N ₂
A semiconductor element in which a tungsten plate (anode electrode) 1 is alloyed with a layered silicon pellet 2 is placed on a rotary table 11 of a groove processing apparatus, for example, a sandblasting apparatus, and the rotary table 11 is rotated in the direction of arrow a while Groove processing is performed by spraying sand 13 from the nozzle 12 onto the upper surface of the element.

In this case, the contact 14 is brought into contact with the bottom surface of the groove 3. Contact
Reference numeral 14 is a needle-shaped body of tungsten or molybdenum, and the surface excluding the tip portion and the lead wire lead portion is subjected to insulation coating with polyimide or the like, and the lead wire 15 is connected to the lead wire lead portion. This lead wire 15 is connected to one end of an AC power supply 17 having a voltage of several V via a resistor (load) 16. The other end of the power source 17 is connected to the rotary base 11, and a current detector 18 is inserted in the middle thereof.

When a voltage of several V is applied between the contact 14 and the turntable 11 during the groove processing as described above, no current flows when the depth of the groove 3 is in the P ₂ region, and when the groove 3 is in the N ₁ region, P _The current flows only when ₁ is a positive potential. Then, when it reaches the P ₁ region, current flows in both directions. The current value at this time is determined by the load 16. The state of this current change is shown in FIG. As is apparent from FIG. 2, the current changes abruptly when the bottom of the groove 3 reaches the junction. Therefore, if this current sudden change is detected by the current detector 18, the depth of the groove can be known.Therefore, set the current level, and turn off the power of the sandblasting device when the detected current exceeds this level. If the groove processing is stopped automatically, the groove processing is properly performed.

The power source may be a DC power source. If the position to be detected is the junction J ₂ , the DC current that causes P _{1 to be} positive and P _{2 to} be negative may cause a sudden increase in current.
It is J ₂ . Further, when the junction J _{3 is} to be detected, if a DC voltage is applied so that P ₁ is negative and P ₂ is positive, the position at which the current sharply increases is the junction J ₃ .

H. Effects of the Invention As described above, according to the present invention, a contactor is provided on the inner bottom surface of the groove during machining of the groove, and a voltage of several V is applied between the contactor and the turntable (anode electrode of the device). The machining end point is determined by detecting a sudden change in the current when the groove depth reaches the junction, so that the groove shape can be kept constant without excess or deficiency in the machining amount, and the device breakdown voltage yield can be improved. Can be improved. Further, since the processing end point becomes clear, the work becomes easier and the work efficiency improves. Further, there is an advantage when it is possible to automatically stop and operate a large number of vehicles.

[Brief description of drawings]

FIG. 1 is an operation principle diagram showing an embodiment of a method for processing an end face of a semiconductor device according to the present invention, FIG. 2 is a characteristic diagram showing a relationship between groove depth and current in the embodiment, and FIG. 3 is groove processing. 4 is a structural explanatory view of a semiconductor device having a bevel structure according to FIG.
(a), (b) is structure explanatory drawing which shows the shape example of a groove | channel. 1 ... Tungsten plate (anode electrode), 2 ... Silicon pellet (four-layer structure of P ₁ N ₁ P ₂ P ₂ ), 3 ... Groove, 11 ...
Turntable, 12 ... Nozzle, 13 ... Sand, 14 ... Contact, 16 ...
… Load, 17… Power supply, 18… Current detector, J ₁ , J ₂ and J ₃
…… Joined.

Claims (1)

[Claims] 1. A method for processing an end face of a semiconductor device, wherein a bevel structure is formed on a PN junction surface of a mesa type semiconductor device by processing a groove, a contact reaching an inner bottom surface of the groove being processed is provided,
A voltage is applied between the contact and the electrode on the side of the semiconductor element opposite to the side where the groove is formed, and current detection means for detecting the current is provided, and the current changes suddenly when the groove reaches the junction. A method for processing an end face of a semiconductor element, characterized in that a processing end point is determined based on the above.