JPS6255686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for writing an identification code on the surface of a semiconductor wafer, and more specifically to a method for forming a place on a semiconductor wafer for writing an identification number such as a lot number.

In the manufacturing process of semiconductor devices, wafers are manufactured in lots, and each lot typically includes tens to hundreds of wafers. These wafers are required to be numbered by lot for management and identification.

In the prior art, identification numbers were written on wafers using a pen with a diamond nib or a laser. At that time, protrusions are formed around the written numbers, letters, symbols, etc., and such protrusions cause uneven positioning when the wafer is placed in equipment for subsequent processes. For example, problems such as exposure deviation occurred. Since this type of obstruction is a serious drawback in the semiconductor device manufacturing process, it is required to eliminate the above-mentioned protrusions.

In addition to the above-mentioned problems, the wafer is ground to a predetermined thickness in the last step of the semiconductor device manufacturing process. If you do so, the numbers you originally entered will disappear and you will have to enter the same numbers again.

The present invention solves the above-described problems in the prior art, and involves forming a recess in a part of a wafer that serves as a substrate for semiconductor devices, and inserting numbers, letters, and symbols such as manufacturing lot numbers into the recess. be able to fill in the information. Hereinafter, the method of the present invention will be explained using the accompanying drawings as an example.

As already explained, in the semiconductor device manufacturing process, each lot of wafers must be marked with a lot identification code, which means marking the wafers with numbers, letters, symbols, etc. using a pen with a diamond tip or a laser. Fill in using . (The act of writing such a recognition code is generally called numbering.) For example, when the back side of a wafer is numbered as described above, the area around the written code can be marked with a pen like the one described above. But even when using a laser, protrusions are formed. FIG. 1 shows a cross section of a wafer 1 supported on a wafer support plate 2. When numbering is done on the back side of the wafer, protrusions 3 are raised around the numbers. It is made like this. An exposure mask 4 is placed on top of the wafer 1, and light is irradiated in the direction of the arrow, but because of the protrusion 3, the right side of the wafer 1 is higher in the figure, and the exposure mask 4 and wafer 1
parallelism is not maintained, causing erroneous irradiation during exposure. Moreover, in the later process, the shaded ground portion 5 on the back side of the wafer is ground by etching or mechanical grinding so that the wafer has a predetermined thickness, so it is not necessary to number the wafer and provide identification codes. It will be deleted without any error. Therefore, the operator must re-enter the recognition code based on his or her memory or notes.

Further, numbering on the surface of the wafer has been proposed, but since a pattern must be formed on the surface of the wafer, numbering is strongly restricted by location. In addition, even if the surface of the wafer is marked, protrusions such as those described above will necessarily be formed, and since the exposure mask is placed on the wafer, the imbalance between the exposure mask and the wafer surface will be reduced. This causes erroneous irradiation during exposure. In other words, there is the same problem as when an identification code is written on the back side of a wafer.

The semiconductor wafer numbering location forming method according to the present invention solves the problems described above. Referring to FIG. 2, a top view and a cross-sectional view of wafer 11 are shown. This wafer 11 is used to fabricate, for example, about several hundred MOS type memory chips on one wafer, and its thickness is several hundred μm.
When the shaded grinding portion 15 is ground, the thickness of the wafer becomes the dimensions of the finished wafer. According to the method of the present invention, recesses for numbering are formed at or near the periphery of the back surface of the wafer 11. In the example shown in FIG. The recess 16 is formed by cutting deeper, for example, by about 100 μ beyond the ground portion 15. Formation of the recess by such a notch can be performed using a known grinding device or etching. Even if such recesses are numbered, there will be no adverse effect of the protrusions caused by marking the recognition code as shown in FIG. Even after the part 15 has been ground, the recognition mark on the recess 16 is not affected in any way.

In the example shown in FIG. 3, the recess 16' is cut out like a depression near the periphery. Recess 1
The depth of the notch 6' is the same as the depth of the recess 16.

As explained above, according to the method of the present invention, the periphery of the back surface of the wafer or near the periphery can be etched to a depth slightly deeper than the ground portion of the back surface of the wafer by grinding or etching, without using any special equipment. The numbering locations are formed by notching, thereby not only eliminating the cause of erroneous exposure during exposure experienced in the prior art, but also eliminating the trouble of renumbering in the prior art. In the above example, if the yield rate of the wafer process is 50%, according to the conventional technology, there was a risk that 10% of the chips would be adversely affected by the presence of protrusions, but according to the present invention, this is possible. This danger is to be avoided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a semiconductor wafer with an identification code written on its back surface supported on a support plate according to the prior art, and FIGS. 2 and 3 show a semiconductor wafer with a recess formed on its back surface according to the method of the invention FIG. 2 is a diagram showing a plan view and a cross-sectional view of a semiconductor wafer, respectively. In the figure, 1, 11, 11' are semiconductor wafers, 2 is a support plate for the wafer, 3 is a protrusion created by writing a recognition code, 4 is an exposure mask, 5,
15, 15' are the grinding parts on the back side of the wafer, 1
6 and 16' indicate recessed portions, respectively.

Claims (1)

[Claims] 1. In a method of writing a desired recognition code on a wafer, a recess is formed in a peripheral portion of the back surface of the element forming surface of the wafer to a depth deeper than a predetermined thickness at which the back surface is polished away in a later step, and the recess is A method for writing a recognition code on a wafer surface, the method comprising the step of writing the desired recognition code on a wafer surface.