JPS6244366A - Grinding method for semiconductor wafer - Google Patents

Abstract

PURPOSE:To make such an element as being small in contact resistance with an envelope formable so easily in a lapping process at the time of setting a brazing material, by installing grinding grooves of more than two directions on a grinding surface when grinding a semiconductor wafer with a grinding wheel. CONSTITUTION:A semiconductor wafer 2 of about 600mum in film thickness is clamped to a fixed block 1, rotating a grinding wheel 3a in an X direction, and this fixed block 1 is moved in a Y direction, whereby the wafer 2 is ground so as to be formed into about 300mum in film thickness. Likewise, it is ground so as to become about 200mum in the film thickness by a grinding wheel 3b, and a one directional grinding groove of several mum in depth is formed. Next, a position of the wafer 2 is rotatively moved as far as 90 deg., and its surface is lightly ground by a grinding wheel 3c, whereby a reticulate grinding groove is formed on a surface of the wafer 2. In succession, the wafer 2 on which the reticulate grinding groove is formed is divided into plural elements, and each grinding surface of these elements is stuck and locked to an envelope 5 via a brazing material. Thus, the wafer surface is reticulated at a lapping process whereby it contact resistance with the envelope 5 is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to surface grinding of semiconductor wafers, and in particular to a grinder lapping method.

[Technical background of the invention and its problems]

An example of conventional grinder wrapping will be explained using a diagram.

Generally, a silicon wafer obtained by slicing a silicon single crystal has a film thickness of about 600 μm. In the grinder lapping process, this wafer is ground with a grindstone to a thickness of about 200 μm.

Conventionally, as shown in FIG.
Grinding was done by rotating the machine in one direction.

The ground wafer 2 is then divided into a plurality of elements, and each element is fixed to the envelope of the semiconductor device with a fixing brazing material.

Conventionally, as described above, the wafer 2 has been ground by rotating the grindstone 3 in only one direction, so that the grinding surface of the wafer 2 has grinding grooves oriented in one direction as shown in FIG. 3(b). Ru.

When an element having such unidirectional grinding grooves is fixed to an envelope with a brazing filler metal, the contact area with the envelope is small, so the contact resistance at this fixed portion becomes large.

However, in integrated circuits using PN isolation, leakage current due to parasitic PNPs through the semiconductor substrate cannot be completely prevented. Therefore, when the contact resistance between the element and the envelope is large as described above, the voltage drop increases due to leakage current. Then, the internal potential of the device at the portion where the leakage current occurs becomes unnecessarily high, giving an undesirable bias to the nearby active region and causing it to malfunction.

Furthermore, when an electrical signal, such as a collector current, to the element is inputted or outputted from the fixed portion of the envelope, if the contact resistance is large here, the power consumption becomes large.

As a method to solve such problems, for example, wafer 2
After the grinding is completed, it is possible to form multiple scratches on the grinding surface using a diamond cutter, but in this case, the number of steps increases and production efficiency deteriorates.

[Purpose of the invention]

The present invention solves the above-mentioned conventional problems, and provides a semiconductor wafer that can easily form elements with low contact resistance with the envelope in a lapping process when a semiconductor element is fixed to the envelope using a brazing material. The purpose of this invention is to provide a grinding method.

[Summary of the invention]

To achieve the above object, the present invention provides a method for grinding a semiconductor wafer, which comprises forming grinding grooves in at least two directions on the grinding surface of the semiconductor wafer when the semiconductor wafer is ground using a grinding wheel.

[Embodiments of the invention]

An example of grinding the back surface (joint surface with the envelope) of a semiconductor wafer using the method of the present invention will be described with reference to the drawings.

First Step As shown in FIG. 1(a), a semiconductor wafer 2 having a film thickness of 600 μm is fixed on a fixing table 1, and a first grindstone 3a is rotated in the direction indicated by an arrow x. Then, the fixed table 1 is moved in the direction indicated by the arrow Y, and the wafer 2 is ground by the first grindstone 3a to a film thickness of 300 μm. (Rough grinding process) Second process As shown in FIG. 1(b), the wafer 2 whose film thickness has become 300 μm due to the rough grinding process is further polished to a film thickness of 200 μm by the second grinding wheel 3b.
Grind it so that it becomes m. Through this step, a unidirectional grinding groove with a depth of several μm is formed on the wafer 2. (Intermediate finishing process) Third process As shown in FIG. 1(c)K, the position of the wafer 2 is rotated by 90 degrees and the surface is lightly ground with the third grindstone 3c. As a result, mesh-like grinding grooves are formed on the surface of the wafer 2 as shown in FIG. 1(d).

(Final finishing process) As described above, the wafer 2 on which the mesh-like grinding grooves have been formed is divided into a plurality of elements, and each element has its ground surface polished by the brazing material 4 as shown in FIG. Envelope 5V through
This will be glued and fixed. The contact resistance of the t-pole on the upper surface of the element 2b with the envelope 5 can be reduced by making the adhesive surface to the bonding wire 5 mesh-like in a grinder wrapping process.

The wafer 2 in which the mesh-like grinding grooves are formed in this way has a larger surface area than the wafer in which the grinding grooves are formed in one direction. Therefore, the element 2b formed by dividing the wafer 2 has a larger bonding area with the brazing material 4, and the contact resistance with the envelope 5 is reduced.

Therefore, undesired high potential due to leakage current is reduced and malfunctions are prevented. 7) Power consumption is also reduced.

Conventionally, Sn-pb, which has good conductivity, has been used as the brazing material 4.
Although the conductivity is somewhat lower than that of solder, it becomes possible to use an inexpensive adhesive such as a silver-containing resin base.

In addition, since the contact area with the brazing filler metal 4 is large, the adhesive strength of the envelope 5 is improved.

The present invention is not limited to the above embodiment; for example, the thickness of the semiconductor wafer may not be 200 μm. Further, three or more types of grindstones may be used to form finer mesh-like grinding grooves.

〔Effect of the invention〕

According to the method of the present invention, by forming mesh-like grinding grooves in a semiconductor wafer using a grinding wheel, an element having low contact resistance with an envelope can be easily formed.

[Brief explanation of the drawing]

1(a) to 1(c) are process diagrams showing a method according to an embodiment of the present invention. FIG. 1(a) is a wafer perspective view showing mesh-shaped grinding grooves on a wafer formed by this embodiment. , Fig. 12 is a side view showing a state in which an element formed by dividing a wafer ground by an embodiment method of the present invention is adhered and fixed to an envelope, and Fig. 3(a) is a side view showing a state in which an element formed by dividing a wafer ground by an embodiment method of the present invention is adhered and fixed to an envelope. Perspective view shown, same figure (
b) is a perspective view showing a wafer in which conventional unidirectional grinding grooves are formed; Time Shaku Soku Jingten 1st prisoner (a) Figure 1 (C) (d) Figure 2 3 rA

Claims (1)

[Claims] A method for grinding a semiconductor wafer, which comprises forming grinding grooves in at least two directions on a grinding surface of the semiconductor wafer using a grinding wheel.