JPS6035517A - Inspection device - Google Patents

Abstract

PURPOSE:To improve the reliability of inspection by a method wherein the gain of the detection signal level of an image-pickup element is brought into a changeable state in accordance with the change in speed of the scanning table of an automatic appearance inspecting device such as a photomask, a wafer and the like. CONSTITUTION:A pattern detecting system 5, with which the pattern appearance of the sample 1 which moves horizontally together with a scanning table 2 will be inspected, has an image-pickup element 7, an amplifier 8 and a comparator 9, a detection signal is compared with master table data 10, a defective or non-defective judgement is given, and it is indicated on a display 11. The scanning speed detecting device 12, provided with a length measuring device 13 with which the distance between the table 2 and the sample 1 will be measured using a laser beam, is connected to a gain control device 17 with which the gain of the amplifier 8 will be controlled. Even when the output level of the image-pickup element 7, on which the photosignal on the same level will be received, is increased or decreased by the speed of the scanning table 2, the amplification factor of the amplifier 8 changes to the reverse direction, and the output of the amplifier 8 is turned into the same level, thereby enabling to prevent the generation of an erroneous inspection caused by the non-uniformity of speed of the scanning table.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an inspection device suitable for use in automatic visual inspection of photomasks, wafers, etc. in semiconductor technology.

[Background technology]

2. Description of the Related Art One of the manufacturing processes for semiconductor devices is a so-called appearance inspection process in which a pattern on a photomask or wafer formed by photolithography is inspected for defects. This visual inspection process is now almost automated, and while the sample to be inspected, such as a photomask or wafer, is placed on a scanning table and moved, a pattern detection system using laser light, etc. It is conceivable to detect the pattern of the sample by relatively scanning the sample by moving the sample, and to compare the detected pattern information with M/T (master tape) data to inspect the pattern (appearance).

By the way, this type of device uses the above-mentioned pattern detection type image pickup device, and converts the optical signal received by the image pickup device into an electric signal to detect it (g and extract it as 2. It has been found that the detection signal level of an image sensor has a positive correlation with the light accumulation time of the element, and the longer the light accumulation time, the higher the detection signal level of the same C signal.

It has also been found that this light accumulation time has an inverse correlation with the scanning speed of the element, and the culm accumulation time becomes shorter when the speed is high.

Therefore, when detecting the same optical signal, the detection signal level will be different if the scanning speed of the imaging device with respect to the sample is different. For this reason, if there are speed irregularities on the scanning table, the speed will increase.

The detection signal level varies depending on the L-threshold.For example, even with the same optical signal, the signal level varies above and below the l-threshold, resulting in completely different pattern detection. The inventors have found that this reduces the reliability of visual inspection and reduces the yield of products.

To prevent this, it is possible to use a scanning tape A with uniform speed, but such a scanning table is expensive, and the reality is that it is almost impossible to completely eliminate the speed fluctuation.

[Purpose of the invention]

The object of the present invention is to provide an inspection device that can always obtain a constant detection signal level from a constant optical signal regardless of speed variations in the scanning table, and that can improve the reliability of inspection. It's about doing.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

In other words, by detecting the speed of the scanning table 2 and changing the gain of the detection signal level of the image sensor in accordance with changes in this speed, a constant optical signal is always detected regardless of changes in the speed of the scanning table. A detection signal of a certain level can be obtained, which improves the reliability of the test.

〔Example〕

The figure shows one embodiment of the present invention, and 1 is a sample exemplified as a photomask as an object to be inspected. This sample 1 is XY
A scanning motor 3. placed on a scanning table 2 consisting of a table and a feeding motor 3. It is moved in the horizontal X and Y directions together with the scanning table 2 which is driven by a drive mechanism such as a beam shaft 4. A pattern detection system 5 for inspecting the pattern or appearance of the sample 1 includes an L-shaped objective lens 6 and an image sensor 7 arranged above the scanning table 2, and an amplifier 8 connected to the image sensor 7. It has a comparator 9. The amplifier 8 amplifies the detection signal of the image sensor 7, and the comparator 9 compares this detection signal with the M/T take 10 to determine the quality of the detection pattern. II is a display for displaying the results.

On the other hand, a scanning speed detecting means 12 for detecting the scanning speed, or in other words, the table movement speed, is arranged close to the scanning table 2. This scanning speed detection means 12 includes a length measuring device 13 that projects a laser beam toward the table 2 and measures the distance to the table 2 using the reflected light, and a length measuring device 13 that measures the number of pulses output from the length measuring device 13. Counter 14 to count fl
and Zangling 1, which controls the operation of this count 14.
The scanning speed detecting means 12 has a lag of 16 and ytme which temporarily holds the number of pulses. A rate control means 17 for varying and controlling the amplification factor, that is, the gain, of the amplifier 8 is connected.

This gain control means 17 has, for example, a D/A converter 18, which proportionally converts the pulse information held in the lug '16 into an analog signal, and automatically changes the gain using this analog signal (AGC). It is configured as.

According to the above configuration, when the scanning daple 2 is moved by the drive mechanism and the sample 1 is scanned with respect to the image sensor 7, the image sensor 7 images the sample pattern l:lri times and The detected M number is output. At this time, if there are speed irregularities in the scanning table 2, the light accumulation time will be adjusted accordingly, and the detection level will vary slightly. The detection signal is amplified by an amplifier 8 and then compared with M/T data 10 as a reference signal by a comparator 9, and the quality of the pattern is determined and displayed on a display 11.

However, at this time, the speed of the scanning table 2 is detected from time to time by the scanning speed detection means 12, so if a speed unevenness occurs in which the table speed is larger or smaller than the predetermined speed (reference speed) K, this speed will be The gain control means 17 changes the amplification factor of the amplifier 8 according to the fluctuation. Specifically, if the speed decreases, the amplification factor is lowered, and if the speed increases, the amplification factor is increased.

Therefore, even if the image sensor 7 receives an optical signal of the same 17 bells and its output level is increased or decreased depending on the speed of the scanning table 2, the amplification factor of the amplifier 8 is changed in the opposite direction accordingly. The output from amplifier 8 will be at the same level. This prevents erroneous inspections caused by uneven speed of the scanning table 2, and enables accurate inspections.d.

Note that the pattern detection system 5 may have a configuration in which the detection signal is digitized by an A/D converter and compared with the M/T data; in this case, the scanning speed detection means J
The output of the second latte 16 is directly input to the A'/D converter to control the reference value (threshold value) of the CA/D converter, thereby controlling the relative gain corresponding to the scanning speed. Good too.

〔effect〕

(1) It has a scanning speed detection means and a gain control means responsive to the scanning speed detection means, and is configured so that the gain of the output signal of the C pattern detection system can be changed according to the scanning speed. With the B-C signal, an output at a constant level can always be obtained regardless of the difference in the speed of the scanning table, and a comparison with a reference signal can be performed accurately to perform highly accurate pattern accumulation.

(Since the scanning speed is determined from the moving speed of the scanning table, an existing length measuring device can be used as is, and a so-called AGC circuit can be used as the gain control means, so there is an advantage that it can be configured easily.

(3) Since the Hals detection thread can have any configuration including analog processing or digital processing of the detection signal, it can be configured appropriately in relation to peripheral equipment.

Although the invention made by the present inventor has been specifically explained above based on examples, the present invention is not limited to the above-mentioned examples (although it is possible to make changes without departing from the gist of the invention). For example, the scanning speed detection means may be configured so that it can detect the speed of the scanning table not only in one direction of the X or Y direction, but also in both the X and Y directions, and in some cases, in the θ direction. , and its configuration can be varied in various ways.Furthermore, an apparatus having a structure in which the sample is fixed and the detection system is moved and scanned can be similarly constructed by simply changing the structure of the scanning speed detection means.

[Application field]

In the above explanation, we have explained the case where the invention made by the present inventor is applied to a photomask inspection device, which is the background field of application. It can also be applied to inspections and other techniques for inspecting the appearance of articles.

[Brief explanation of the drawing]

The figure is an overall diagram of a device that is one of the embodiments of the present invention. l...sample, 2...scanning table, 5...pattern detection system, 7...imaging element, 8...amplifier, 9...
・Comparator, 10...M/T data, 12...
Scanning speed detection means, 13... Length measuring device, 17... Gain control means.

Claims (1)

[Scope of Claims] 1. A scanning table on which a sample such as a photomask or a wafer as an object to be inspected is placed, and an image sensor placed opposite to the scanning table scans the sample surface to detect an optical signal. This is compared with a reference signal to inspect the pattern of the sample. A pattern detection system, means for detecting the relative scanning speed of the sample and the image sensor, and detecting the pattern according to the output of the scanning speed detection means. 1. A test device characterized by comprising: gain control means for changing the signal gain of the system. 2. The inspection apparatus according to claim 1, wherein the scanning speed detection means is capable of detecting the speed of the scanning table moved relative to the pattern detection system. 3. The test device according to claim 1 or 2, wherein the gain control means comprises an AGO (automatic gain control) circuit.