JPH05259010A - Method for discrimination of semiconductor wafer - Google Patents

Abstract

PURPOSE:To measure the distance between linear patterns of a plurality of markings in each wafer using an optical means by providing for each identifiable wafer and at different intervals, the markings of the linear patterns which are in parallel with each other in the prescribed ranges distributed on the wafer surface, and the wafers are discriminated automatically. CONSTITUTION:The pattern of markings 20 is printed on an accurate position while the position of a reticle 30 is being ascertained by an attached laser length-measuring device. A wafer is discriminated by the mutual distance D of the marking 20. In order to discriminate the wafer 1 on which the markings 20 are provided, the reflected light coming from the markings 20 is detected by a photo-sensor while the spot of laser beam scans the wafer 1, the wafer is discriminated by correctly computing the time difference, generated by two detected pulses, corresponding to the two markings 20, by a high frequency clock pulse. The laser beam spot can be scanned at a fixed high speed using the means such as reflection and the like of a rotary mirror, and the mutual distance D of the markings 20 can be measured with a high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for identifying wafers individually or by lot for process control in a wafer process for handling a large number of wafers such as semiconductor silicon.

[0002]

2. Description of the Related Art At a wafer processing site for manufacturing semiconductor devices, a large number of wafers are flowing in a clean room, and the number of processes to be performed for each wafer is large. Damage may occur.

The reason for this is that all wafers have almost the same shape and size, and it is not possible to easily identify what they are for or what process has been completed by visual inspection. Therefore, it is desirable to display the product type, model number, lot number, wafer number, etc. in order to prevent the confusion of wafers. A rule using a hard pen such as diamond on the back side where the wafer is not processed for a long time. The means of writing characters and codes has been taken by the writing work. Also,
Since this scoring work requires a great deal of work, display using the laser engraving method has been widely performed. As a simpler means, it is common to move several steps in a state where several tens of wafers are accommodated in a carrier and the display is often performed on this carrier.

[0004]

However, it is necessary for a human to read or visually confirm the above-mentioned display by characters or codes, and an error of the operator may occur at this time, so that the wafer is actually printed. Confusion cannot be completely prevented. The cause of such human error is that the probability that the wafers are confused is originally low and the confirmation result is good in most cases, so it is easy for the operator to be alert and the oversight occurs when it is important. Thought to be
To eradicate this problem, it is important to reduce the daily burden on workers as much as possible.

In addition, since the wafer is dug into shallowly by both the marking method of the display and the laser engraving method, fine particles of silicon or fine powder are generated at that time, and the clean environment in the clean room is contaminated. Don't be afraid. In addition, it is not possible to prevent the risk of confusing or confusing the wafers between the carriers simply by providing the labels on the wafer carriers.

On the basis of the present situation, an object of the present invention is to make it possible to automatically identify a wafer by a reliable means without requiring special labor when marking each wafer.

[0007]

SUMMARY OF THE INVENTION According to the present invention, an object of the present invention is to identify mutually parallel linear pattern markers within a plurality of predetermined areas distributed on the wafer surface during the initial steps of the wafer process. This is accomplished by providing different wafer-to-wafer distances from each other, and by using optical means to measure the distances between the linear patterns of a plurality of markers in each wafer to distinguish the wafers from each other.

The mark is preferably formed by a film attached to the surface of the wafer by a wafer process, for example, a so-called initial oxide film. A dedicated reticle with a linear pattern is used for patterning as a marker, and the distance between the patterning patterns of a plurality of markers should be mutually distinguished by shifting the patterning position with this reticle. By making them different from each other, the marker can be provided during the initial step of the wafer process without adding steps.

In order to optically measure the mutual distance between a plurality of marks, it is most advantageous to detect the reflected light from the marks while scanning the surface of the wafer with a sbot of a laser beam. As the process progresses, the reflected light from parts other than the mark on the wafer increases and it becomes difficult to distinguish it from the reflected light from the mark.Therefore, the range within which the index on the wafer is provided when measuring the distance between the marks It is advantageous to remove the extra reflected light by applying a mask having a window pattern corresponding to, so that the reflected light from the sign can be easily detected. As the mask, of course, an optical mask as well as an electronic mask for the reflected light detection circuit can be used.

The width of the linear pattern of the marker used in the method of the present invention is preferably set to be slightly larger than the size of the light spot used for the optical detection, and the spot of the laser light is usually 1 to 2 μm. Therefore, it is advantageous to set the linear pattern width to about 2 μm. Further, it is advantageous to set the distance between the markers to be different for each wafer to the same extent as the linear pattern width.

When the width of the linear pattern of the mark is several μm or less and the width of the range where each mark is provided is about several mm, the number of wafers that can be identified by the method of the present invention is 1000 or more in the case of two marks. However, it is advantageous to increase the number of wafers that can be identified by the combination of their mutual distances by increasing the number of markers. For example, it is possible to identify over one million wafers using only three or two pairs of labels.

[0012]

In the method of the present invention, as described in the constitution in the preceding paragraph, the identification mark is arranged on the front surface side of the wafer contrary to the conventional method, so that the wafer can be easily manufactured by utilizing the wafer process. By providing this mark during the initial step of the wafer process, the wafer can be identified through the subsequent wafer processes, and by providing the marks in a plurality of predetermined ranges of the wafer in a linear pattern parallel to each other, It is possible to increase the number of identifiable wafers by measuring the distance optically easily so that the wafers can be identified with certainty, and by making the pattern of markers that should be provided at different distances for each wafer into a thin line. This is to solve the above-mentioned problems.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wafer identification method according to the present invention will be described below with reference to the drawings. Figure 1 shows the procedure for providing a marker on a wafer, and Figure 2 shows the procedure for detecting this marker.
Some examples of markings on the wafer are shown in FIG.

The wafer 1 shown in FIG. 1 is for an integrated circuit device manufactured according to a rule of, for example, 2 μm or less, and the rectangular regions 2 arranged in the vertical and horizontal directions on the surface thereof are enlarged to the lower left side of the figure during the photo process. The area where the pattern is printed using the reticle 40 shown in FIG. As is well known, the reticle 40 is a kind of photomask having a pattern of one or a plurality of, in the illustrated example, nine integrated circuits 3.
The pattern is sequentially shifted using equipment commonly referred to as a stepper, and the area inside the wafer 1 is normally printed on each region 2 of about 10 mm square while being reduced in size.

In this embodiment, two areas 10 to be provided with marks are set on the left and right peripheral portions of the wafer 1, and when the above stepper is used, the size is set to be the same as the area 2. Is convenient. The pattern of the mark 20 to be provided within this range 10 is printed by the reticle 30 shown in an enlarged manner in the lower right part of the drawing. The reticle 30 has, for example, a vertically long outer shape as shown in the drawing, and has a linear pattern for the marker 20 therein. The linear pattern has a width W of 2 μm when the marker 20 is printed in the range 10 from the reticle 30,
The height H is set to about 10 mm.

The mark 20 is provided on the wafer 1 in the initial step of the wafer process, for example, the step of applying an initial oxide film, and the stepper equipment is sequentially printing the pattern of the reticle 40 for this initial step in the region 2. When the turn comes to the marking range 10, the reticle 40 is switched to the reticle 30 and the pattern of the marking 20 is printed. In addition, the position of the reticle 30 at the time of printing is shown in the range 10 in the figure.
The deviation S with respect to each wafer is specified to differ by about 2 μm for each wafer.

For this purpose, the position at which the reticle 40 is switched to the reticle 30 and the designated value of the deviation S within the range 10 of the reticle 30 for each wafer may be programmed in advance for the stepper equipment. While confirming the position of the reticle 30 with the attached laser length measuring device based on the designated value of this deviation S, the pattern of the marker 20 is usually printed at an accurate position within an error range of about 0.3 μm. In the example of FIG. 1, the number of the markers 20 is two, and in the present invention, the wafer is identified by the mutual distance D between the two, so in practice, for example, the marker 20 on the left side of the drawing is always provided in the center of the range 10 and the right side. It suffices to change only the position of the marker 20 in accordance with the specified value of the above-mentioned deviation S.

After the pattern is baked, the initial oxide film having a film thickness of, for example, about 1 μm is patterned by etching to form the marker 20 within the range 10. 15mm in this example
Since the markers 20 are provided laterally offset by 2 μm within the angular range 10, this allows a maximum of 7500 wafers to be identified.

FIG. 2 shows how to identify the wafer 1 provided with the mark 20 as shown in FIG. For this identification, while the wafer 1 is scanned by the spot of the laser light L as shown in the figure, the reflected light from the mark 20 is detected by the optical sensor and two detection pulses corresponding to the two marks 20 are generated. For example, the time difference is accurately counted by a clock pulse having a high frequency. The spot of the laser beam L can be scanned at a constant high speed by means such as reflection by a rotating mirror as in the case of a bar code reader, and the time difference is accurately measured by counting clock pulses.
The mutual distance D can be measured with high accuracy.

However, as the wafer process progresses, a large number of small irregularities are formed in the surface of the wafer 1, and the reflection of the laser light due to the small irregularities becomes confusing with the reflection from the mark 20, so that the embodiment shown in FIG. This problem is solved by overlaying a black optical mask 50 on the wafer 1 to reduce extra reflections, and exposing each of the areas 10 within the pair of windows 51 provided with the indicia 20. In this embodiment, the mask is an optical mask for easy understanding. However, in practice, an electronic mask or window is used in the output detection circuit of the optical sensor for receiving the reflected light of the laser light L. It is advantageous to obtain the same effect as.

If the scanning direction of the laser beam L deviates from the direction perpendicular to the linear pattern of the marker 20, an error will occur in the measurement result of the mutual distance D, so that the wafer 1 always has the cutout 1a as shown in the figure. Therefore, it is desirable to adjust the scanning direction to the optical mask 50, and to adjust the optical mask 50 accordingly. Further, it is desirable that the scanning of the laser beam L is performed a plurality of times as shown in the figure, and that the measured mutual distance D is matched each time the scanning is performed to ensure the certainty of the measurement.

Some different embodiments of the method of the invention will now be described with reference to FIG. In these embodiments, only the wafer 1 corresponding to FIG. 1 is shown, and for the sake of convenience of illustration, only the main part thereof is shown.

In the embodiment shown in FIG. 3A, the measurement result of the mutual distance D of the markers 20 is not influenced by the spot scanning direction of the laser light. In this embodiment, the wafer 1
The four ranges 10 arranged as shown in the figure are set, the markers 20 are provided at the same positions in the two ranges 10 arranged in the vertical direction, and the laser light L forms an angle θ with each other. Scanning from two directions is performed to measure the trapezoidal mutual distances a and b between each two markers 20. This angle θ can be set to a constant value by, for example, two reflecting surfaces of the rotary mirror for scanning the laser light L. As can be easily understood, the mutual distance D to be obtained is the perpendicular length from the apex of a triangle having two sides a and b to the opposite side sandwiching the angle θ, so if the length of the opposite side is c, then D = (Ab / c) sin θ, and the length c can be easily calculated by a computer based on a simple trigonometric formula. This embodiment has the advantage that the measurement result is not affected by the scanning direction itself, as long as the angle θ between the two scanning directions of the laser light L is kept constant.

The embodiment of FIG. 3B is for increasing the number of identifiable wafers. Also in this embodiment, four marks 20 are used, and two marks 20 on the left side are provided at the same position.
The two right-hand units are provided at positions independent of each other, and one pair of left and right markers 20 are used as a pair to measure the mutual distances D1 and D2 as shown in the figure. Since the wafers can be identified by using the distance between these two, the number of identifiable wafers increases dramatically. In this embodiment, the range 11 for the two signs 20 on the left side, which are always provided at the same position, is the range 10 on the right side.
It is set smaller.

In the embodiment shown in FIG. 3 (c), the left and right marking areas 12 are set wide, and the markings 21 provided therein have a plurality of linear patterns arranged at equal intervals.
Since the reflected light when the marker 21 is scanned with the laser light L is repeatedly generated at a constant time interval by the number of linear patterns, the marker 21 can be accurately specified from the generation time and number of detection pulses by the optical sensor. .. Therefore, this embodiment has an advantage that the detection accuracy of the label 21 can be enhanced as compared with the previous embodiment.
The distance D between the two markers 21 may be determined by the distance between the last linear patterns as shown in the figure.

In the embodiment of FIG. 3 (d), the distance D between the signs is set smaller than ever. Therefore, as shown in the figure, 2
The individual marking areas 10 are set in contact with each other on the upper edge of the wafer 1 in this example. Of course, since the markers 20 are provided in the respective ranges 10, the mutual distance D becomes much shorter than before, but this does not hinder the identification of the wafer, and rather the relative accuracy in measuring the mutual distance D can be improved. ..
Further, there is an advantage that the range 10 can be set in the peripheral portion of the wafer 1 where the utility value is low. As can be seen from these embodiments of FIG. 3, the present invention is not limited to the embodiments described above and can be implemented in various modes.

[0027]

As described above, in the wafer identification method according to the present invention, wafers for which parallel linear markers are to be mutually identified within a plurality of predetermined ranges distributed on the wafer surface during the initial step of the wafer process. Different distances are provided for each wafer, and the following effects can be obtained by mutually distinguishing the wafers from the result of measuring the distance between the linear patterns of a plurality of markers in each wafer by optical means. it can.

(A) By providing the mark on the front surface side of the wafer, it is possible to easily make the mark by using the steps in the wafer process for making the semiconductor device in the wafer without any particular trouble. it can.

(B) Since the markers are formed in a linear pattern and are arranged in parallel with each other in a plurality of predetermined areas of the wafer, the distance between the markers can be optically easily measured when the wafers are identified. And this measurement can be easily automated.

(C) Since the marking pattern is a thin linear shape, the mutual distance between the markings can be made different for each wafer by slightly shifting the positions where the markings are provided. The wafers can be accurately identified, and the number of identifiable wafers can be greatly increased by slightly increasing the number of labels.

(D) Since the wafers are identified by the mutual distance between the marks, and therefore the marks cannot be visually read, it is necessary to identify them by a dedicated device, so that there is no room for human error to intervene and the wafer process is eliminated. The management level of can be improved.

As described above, the method of the present invention has an advantage that a marker can be provided on a wafer without particular trouble and the wafer can be identified accurately and automatically while eliminating the intervention of human error. It can make a significant contribution to improving the control level of the manufacturing process and preventing the reduction of the manufacturing yield due to an error.

[Brief description of drawings]

FIG. 1 is a top view of a wafer showing an embodiment of a marker for identifying a wafer according to the method of the present invention and a procedure for providing the marker on the wafer.

FIG. 2 is a top view of a wafer and an optical mask overlaid on the wafer, showing how to identify the wafer by the mark of FIG.

FIG. 3 shows different embodiments of the present invention from FIG.
FIG. 3D is a top view of the essential part of the wafer shown in FIG.

[Explanation of symbols]

 1 Wafer 10 Marking range 11 Marking range 12 Marking range 20 Marking 21 Marking 30 Marking patterning reticle 50 Optical mask D Distance between markers D1 Distance between markers D2 Distance between markers H Marking Height of linear pattern S Deviation of marker position W Width of marker linear pattern

Claims (3)

[Claims] 1. In a plurality of predetermined ranges distributed on the surface of a wafer during an initial step of a wafer process, linear markers parallel to each other are provided at different distances for each wafer to be distinguished from each other. A method for identifying semiconductor wafers, wherein the wafers can be identified from each other by measuring the distance between a plurality of linear patterns of markers in each wafer by optical means. 2. The method according to claim 1, wherein a dedicated reticle having a linear pattern is used for patterning the markers on the wafer, and the plurality of markers are moved by shifting the patterning position by the reticle. A method for identifying a semiconductor wafer, wherein the distance between the linear patterns is made different for each wafer to be identified. 3. The method according to claim 1, wherein an index in the wafer is provided when the distance between the linear patterns of a plurality of markers in each wafer is measured by optical means. A method of identifying a semiconductor wafer, characterized in that a liner pattern of a marker can be identified from other patterns in a wafer by applying a mask having a window pattern.