JPH048780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a method for inspecting a mask, and more particularly to a method for detecting defects on a patterned surface of a photomask or a wafer chip.

(b) Background of the technology In recent years, as semiconductor devices and semiconductor integrated circuits have become more sophisticated and highly integrated, patterns have become increasingly dense, and the masks and wafer chips used in these devices also need to further improve their precision. be done.

Particularly in the case of semiconductor devices, photolithography technology, in which patterning is performed using light, is used in many manufacturing steps, and there are many types of photomasks used for this.

If for some reason there is a black figure outside the black positive pattern figure on the pattern figure side of this photomask, the defective part of the photomask will appear directly on the patterned semiconductor wafer surface. Therefore, photomasks must be inspected particularly carefully.

However, due to the higher performance and higher integration of semiconductor integrated circuits, the patterns patterned on photomasks have become more precise, and inspection using conventional microscopes alone requires a great deal of time and care. However, there is a need for an automatic inspection method that does not rely on a microscope, since defects in pattern figures may be overlooked.

(c) Prior art and problems The conventional photomask inspection method inspects a reticle mask, and the size of this reticle mask is larger than the photomask actually used. If the original plate is about 10 times the size and the reticle is perfect and free of defects, it will be reduced and a practical photomask will be produced.

There are mainly two types of inspection methods for defects on the patterned surface of the reticle.The first method uses the fact that the pattern on the reticle surface is patterned repeatedly.
This is a method of inspecting patterned figures by superimposing and comparing a plurality of identical patterned retakes.

In this case, the surface of the reticle is scanned with a magnifying glass, the image is converted into an electrical signal by an image sensor, and the signal is input to an imaging device to create a graphic.The inspection is performed by visually observing the patterning of this graphic surface. be exposed.

The second method is to compare the data pattern input to a computer, but in this method, the reticle mask to be inspected is scanned with a video camera, the video signal is converted to a digital signal, and then input to a magnetic tape MT. This is a method of testing by comparing this data with the MT at the time of design.

However, both of these methods have drawbacks, and in the first comparison method that utilizes the repeatability of patterning, when a common defect exists on the pattern surfaces of multiple overlapping reticle masks, It is impossible to extract the defects, and the method of comparing with the second data pattern has the drawbacks of the complexity of creating the data pattern and the difficulty of creating data that is exactly the same as the actual pattern surface. be.

(d) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention provides a method for detecting defects in the pattern surface of a photomask used for semiconductor devices, etc. by scanning a pattern surface patterned on a reticle mask at a predetermined scanning pitch. It is an object of the present invention to provide a method for automatically inspecting a pattern figure by scanning the width linearly and in parallel and counting the number of scanning pulses.

(e) Structure of the Invention According to the present invention, when inspecting a positive pattern figure on a mask surface having a pattern figure by scanning linearly and in parallel with a predetermined scanning pitch width, the positive pattern The number of pulses that scanned the figure is counted, the counted number of pulses is compared with a predetermined plurality of adjacent scanning lines, and the difference in the compared number of pulses is the number of pulses that scan the smallest minute area that constitutes the positive pattern figure. This can be achieved by providing a method for inspecting a mask that detects positive pattern features that are smaller and larger than the number of pulses corresponding to the pattern creation tolerance.

Since semiconductor integrated circuit masks are manufactured in an environment with extreme protection against dust, the minimum area constituting the positive pattern to be manufactured (usually the area of the so-called contact hole, 0.9 μm x The possibility of a defect larger than approximately 0.9 μm (accordingly, several times to ten times this size on a reticle mask) occurring is extremely small. Therefore, if a pattern larger than this minimum area is detected, it can be assumed that it is not a defect but another regular pattern.

The present invention utilizes the above regularity in pattern creation to detect defects that deviate from this rule. Of course, the drawing tolerance when configuring the pattern (0.1μm x minimum area for the above)
0.1 μm) is not considered a defect.

Pattern figure 5 on mask substrate 1 shown in FIG.
is the minimum minute area figure required for pattern creation 5-
1, 5-2, and 5-3, the size of the defect can be determined by comparing the protruding portion 3 or the interrupting portion 4 caused by the defect with the figure 5-3 without the defect. is detected, and if it is larger than the figure 5-3, it is not considered a defect from the above-mentioned viewpoint, and if it is smaller than this and larger than a separately defined tolerance error in pattern creation, it is considered to be a defect.

Since area comparison can be replaced by comparing the number of pulses of the same width, it is relatively easy to scan the pattern drawing with a width that divides the above minute area into smaller areas, measure the length with the number of pulses, and perform comparative detection. Defects can be detected by means.

(f) Embodiments of the Invention The gist of the present invention will be specifically explained below with reference to illustrated embodiments.

That is, for example, pattern 5 in FIG. 1 is a set of minimum area pattern figures 5-1, 5-2, and 5-3.

FIG. 2 is a block diagram of an inspection apparatus according to the present invention, in which 11 is a reticle mask for an object to be inspected, 12 is an illumination system for illuminating the object to be inspected;
3 is an optical system which is set to read the pattern figure of the mask, and 14 is a light receiving system which is converted into a light signal by an image sensor or the like.

This optical signal is received by a light receiving signal device 15 and 16
The waveform is shaped by the A-D converter, converted to 17 bit memories, and input to 18 image processing devices. Since the digital signal is input as a signal from the image signal device 19, these two signals are compared and the comparison result is displayed on the detection device 20.

FIG. 3 is a block diagram of a detection method in the image processing apparatus, and FIG. 4 shows pulse waveforms at various parts in FIG. 21 is a scanning signal that scans the reticle mask with a plurality of scanning lines, A is its output, and 22
is a constant pulse wave reference signal B, and 23
The 21 scanning signals are converted into pulses by the AND circuit.

24 is a counter which counts the number of scanned pulses for each scanning line and stores it in the first memory 25.
At the same time, pulses D at the start of scanning and at the end of scanning are input to this memory by a trigger from the scanning signal.

26 is a register in which a pattern figure of a predetermined minute area that is initially set is digitized, and the corresponding signal E is digitized into a predetermined number of scans and a number of pulses.

27 is a second memory circuit, in which only the initial value is written from the counter 24, and 28 is a comparison circuit, in which only the initial value is written from the counter 24.
5, the second memory circuit 27, and the figure register 26 corresponding to a predetermined minute area are compared and output to the abnormal value detection device 29, but at the same time, the position information 30 of the X-Y stage and the XY overlap coordinates are compared. information 31 is input via an AND circuit 32.

Also, in this case, it is necessary to have a certain margin in order to judge it as an abnormal value, so 3.
The margin setting signal No. 3 is input, and the test result with the margin added is detected as an output.

In FIG. 5, it is assumed that the reticle mask 35 has a black figure 37, which is a protruding part outside the regular pattern figure 36, and a recessed part 38, and when this figure is smaller than a predetermined minute area. A specific scanning example is shown.

In scanning, the reticle mask is divided into multiple areas as shown in the figure, and each area is scanned. For example, the scanning area is divided into a, b, c, d, e, f, g, and h. Then, the scanning signal becomes as shown in FIG. 52, and this length can be counted as the number of pulses.

The signals are labeled with symbols corresponding to the scanning areas of FIG. 51.

The scanning signals of a, b, d, f, g, and h are continuous in the length direction of the reticle mask because they are regular patterns. Since there is an extra black figure whose number is smaller than the number of pulses and an extra white figure corresponding to the retracted part, the scanning length is expanded or contracted by the length of the extra figure.

In this case, the difference between the number of pulses of the scanning signal c and the number of pulses of the scanning signal b is the number of pulses for scanning the smallest minute area (in this case, the number of pulses corresponding to the scanning signal ab)
It is considered abnormal because it is smaller. The scanning signal d of the retracted portion is also determined to be abnormal by the same comparative detection.

The reference signal is shown in FIG. 6, and by ANDing it with the waveform shown in FIG. 5, the signal can be made into a pulse.

(g) Effects of the invention As explained in detail above, by adopting the reticle mask inspection device of the present invention, there is a great effect that it can be used as a method for easily and reliably detecting defects in pattern figures. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a partial pattern for explaining the principle of the present invention. FIG. 2 is a block diagram of the inspection device of the present invention. FIG. 3 is a block diagram of a detection method for image processing. FIG. 4 is a waveform diagram of the above embodiment. FIG. 5 is a waveform signal diagram. FIG. 6 is a reference signal diagram. In the figure, 11 is a reticle mask, 12 is an illumination, 13 is an optical system, 14 is a light receiving system, 15 is a light receiving signal, 16 is an A-D converter, 17 is a bit memory, 18 is an image processing device, and 19 is an image signal device. ,
20 is a detection device, 21 is a scanning signal, 22 is a reference signal, 23 is an AND circuit, 24 is a counter, 25
is a first memory circuit, 26 is a predetermined minute pattern figure register, 27 is a second memory circuit,
28 is a comparison circuit, 29 is a detection device, 30 is X-Y
Stage position information, 31 is XY overlapping coordinate information, 32 is an AND circuit, 33 is a margin setting device, 35 is a reticle mask, 36 is a pattern, 3
7 is a protruding portion, and 38 is a recessed portion.

Claims (1)

[Claims] 1. When inspecting a positive pattern figure on the mask surface while scanning linearly and in parallel with a predetermined scanning pitch width, the number of pulses scanning the positive pattern figure is counted, and the counted number of pulses is divided into adjacent scanning lines. The pattern figure is characterized in that the difference between the compared numbers of pulses is smaller than the number of pulses for scanning the smallest area constituting the pattern figure, and larger than the number of pulses corresponding to the tolerance for pattern creation, as a defect. Method for inspecting masks.