JPS63133A - Method of testing photomask - Google Patents

Abstract

PURPOSE:To realize easy and reliable detection of defects even in an extremely fine pattern, by forming a defect detecting pattern having the same configuration as a predetermined pattern in the peripheral space of a photomask and exposing it with an amount of light lower than an appropriate exposure. CONSTITUTION:Predetermined patterns 2 are formed lengthwise and crosswise in the central portion of the principal face of a mask substrate 1 for forming a circuit functioning element. A defect detecting pattern 3 is formed in the peripheral space of the principal face of the substrate at a distance from the group of the predetermined patterns 2. The defect detecting pattern 3 is formed in the following manner: first, an original pattern formed in a reticle is exposed by the step-and-repeat technique to form the group of the predetermined patterns 2, and then the same pattern as the predetermined pattern 2 is exposed with an amount of light corresponding to about 0.8 times as large as the exposure of the predetermined pattern 2. The size of the defect detecting pattern 3 thus formed is generally decreased in comparison with that of the predetermined pattern 2, while a defective portion 13 in a bridge is formed in an enlarged and exaggerated manner. Accordingly, provision of such defect detecting pattern 3 enables any defect in the pattern to be detected reliably even with a conventional detecting apparatus.

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a method for inspecting a patterned surface of a photomask.
In particular, the present invention relates to a method for inspecting a photomask for positive resist.

(B) Prior Art Photomasks used in the manufacture of semiconductor devices are manufactured by reducing and repeatedly transferring a predetermined pattern formed on a mask called a reticle. Therefore, if there is even one defect in the reticle, which is the original plate, it will appear as a common defect in which the same defect exists in the same place in all patterns, and the wafer using that photomask will be completely destroyed, so this must be avoided at all costs.

However, even if a reticle with zero defects is prepared, if foreign matter adheres to the reticle surface during transfer or there is some abnormality in the optical system, it will still become a common defect. Photomasks also need to be carefully inspected.

Visual inspection using a microscope has traditionally been used as an inspection method for such photomasks, but this method has the drawbacks of being time-consuming and overlooking defects in pattern figures. An inspection device such as that described in Japanese Patent No. 220934 is often used. Such an apparatus scans a predetermined pattern of a photomask to be inspected with a video camera, converts the signal into a digital signal, and compares the signal with CAD data at the time of design to determine the quality of the pattern. Using this device, almost accurate inspections can be performed in a short period of time.

(c) Problems to be solved by the invention However, as miniaturization progresses, even higher detection accuracy is required of the above-mentioned devices, but currently there are still devices with high accuracy that satisfy the requirements. This has not been realized, and there has been a drawback that only incomplete inspections can be performed, especially in the case of a hole mask for positive resist, which has the smallest pattern, or a mask for electrode wiring.

For example, as shown in Fig. 4, when inspecting a photomask with a black background mostly made of chrome and a white pattern with a width of 2 to 4 μm in the area corresponding to the contact hole, a white pattern like the abnormal pattern (11) shown in the figure is detected. Defects such as parts of the punched pattern being chipped, bridges between wires in the electrode wiring pattern, etc. cannot be detected. Another possible defect may be a white pinhole on a black background, but it has been confirmed that such a defect rarely occurs if the reticle is perfect.

(=) Means for Solving the Problems The present invention has been made in view of the above-mentioned drawbacks, and a defect detection pattern (3) having the same pattern as the predetermined pattern (2) is formed in the margin around the photomask. The method is characterized in that the white pattern is reduced in size and the defective part is exaggerated for inspection by exposing it to a light amount that is less than the appropriate exposure amount.

(*) Effect According to the present invention, since the pattern for defect detection is exposed with a light amount less than the appropriate exposure amount, the white pattern is reduced and developed, and for example, the normal pattern (10
), the defect detection pattern (3) will almost completely collapse if the abnormal pattern (11) is only 60% of the opening area of the pattern (11). Therefore, if such a pattern is used, defective portions can be reliably detected even with conventional inspection equipment.

(f) Example Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a plan view of a photomask to which the present invention is applied, in which a predetermined pattern (2) for forming a circuit functional element is formed in the center of the main surface of a mask substrate (1) in a repeating manner vertically and horizontally; A defect detection pattern (3) is formed in the blank space spaced apart from the predetermined pattern (2) group. The blank space is an unnecessary area for the wafer, and there is no problem in forming the defect detection pattern (3) there. The defect detection pattern (3) is first formed by step-and-repeat exposure of the original pattern formed on the reticle using a device called a photorepeater to form a predetermined pattern (2) group, and then the exposure amount is The pattern is formed by exposing the same pattern as the predetermined pattern (2) with an amount of light about 0.8 times that of the predetermined pattern (2).

The defect detection pattern (3) thus formed is formed with a smaller overall pattern than the predetermined pattern (2) due to intentional underexposure.

This will be explained using FIGS. 2 and 3. Figure 2 is a schematic cross-sectional view when exposing a pattern using a photorepeater, (4) is a reticle, (5) is a lens, (, (6)
) is a photomask. A predetermined pattern (2) made of a chrome film (7) has been selectively formed on the surface of the reticle (4), and an unprocessed chromium film (7) and a positive pattern that is advantageous for microfabrication are formed on the surface of the photomask (6). Resist (8)
is completely stuck. When exposure light (9) such as ultra-high-pressure mercury lamp ultraviolet rays is irradiated from the top of the reticle (4), the light that has passed through the white pattern formed on the reticle (4) passes through the lens (5) to the resist ( 8) Reach the surface;
It is configured to image a predetermined pattern (2) formed on a reticle (4) on the surface of a photomask (6) at a scale of, for example, 10:1.

The exposure light (9) irradiated onto the resist (8) is accompanied by light diffraction development, so the irradiation amount (exposure amount) is plotted on the vertical axis.
When the distance from the center of the pattern is plotted on the horizontal axis, it has a distribution characteristic as shown in FIG. Therefore, the exposure amount that satisfies the film thickness remaining rate of resist (8) after development is 0% is XY as shown in the figure.
If it is set to the level of , then only the range AB shown in the figure will be opened during proper exposure, where the distribution characteristic is shown by the solid line. However, in the case of underexposure, where the distribution characteristic is shown by the broken line, the absolute amount of exposure is insufficient, so that only the range CD shown in the figure can be opened. Therefore, if the chromium film (7) is removed by etching in this state, the underexposed defect detection pattern (3) will be formed with a reduced overall pattern.

4 and 5 are plan views showing the negative part of the predetermined pattern (2) and the defect detection pattern (3), respectively, and show a contact hole mask for positive resist as an example. , most of which is a black background made of chromium film (7), and areas corresponding to contact holes are opened to form a white pattern.Then, in the negative part of the predetermined pattern (2), a normal pattern with completely opened holes is formed. (
10) and an abnormal pattern (11) having a defective part where a part of the white pattern is missing for some reason are formed, then the defect detection pattern (3) is a normal pattern due to the above-mentioned reason. The abnormal pattern (11), which is formed by reducing the size of pattern (10) to approximately half, and which appears to be half crushed from the beginning, is formed almost crushed.

Furthermore, as shown in FIG. 6, if the pattern for electrode wiring has a bridging defect (13) between the wirings (12) (12) due to residual chromium, the defect detection pattern (3) As shown in FIG. 7, the bridge defect portion (13) is completely enlarged and exaggerated.

Therefore, by using the defect detection pattern (3) formed as shown in FIGS. 5 and 7, it is possible to reliably detect defects even with conventional detection equipment. The amount of light used for exposure at this time depends on the accuracy of the inspection device. In other words, since there is a certain range in the detection accuracy of the inspection equipment, it is possible to form multiple patterns of different sizes by reducing the normal pattern (10) by changing the exposure amount, and to judge that the normal pattern (10) is normal. All you have to do is find the limit exposure amount and set the exposure amount with a little margin to that exposure amount as the exposure amount for the defect detection pattern (3).If you set it in this way, it will be more open than the normal pattern (10). Abnormal pattern with small hole size (
11) will be reliably detected.

In practice, the defect detection pattern (3) is first scanned by an inspection device, and if no defects are detected, the product is non-defective. You just have to judge whether it's good or bad. For even more perfection, a plurality of defect detection patterns (3) may be formed by scanning both the predetermined pattern (2) and the defect detection pattern (3) with an inspection device, or by varying the amount of exposure.
It is also possible to inspect the

(g) As described in detail, the present invention has the advantage that defects in patterns can be easily and reliably detected even in extremely fine patterns. Furthermore, since the defect detection pattern (3) is formed around the photomask, it has the advantage that it does not affect the actual pattern in any way.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the photomask of the present invention, FIG. 2 is a schematic cross-sectional view of the exposure device, and FIG. 3 is a distribution characteristic diagram of the exposure amount.
4 and 6 are plan views showing the negative part of the predetermined pattern (2), and FIGS. 5 and 9 are plan views showing the negative part of the defect detection pattern (3).
FIG. (1) is a mask substrate, (2) is a predetermined pattern, (3)
is the defect detection pattern, (10) is the normal pattern, (1
1,) is an abnormal pattern. Applicant Sanyo Electric Co., Ltd. and one other agent Patent attorney Takuji Nishino and one other person Fig. 1 Fig. 2 Fig. 3 Dear Commissioner of the Agency, To u1, Indication of the case 1986 Patent Application No. 14335 '92, Name of the invention Photomask inspection method 3, Person making the amendment Relationship with the case Patent applicant name (18U Sanyo Electric Co., Ltd. (1 other person) 4. Agent address: 2-18 Keihan Hondori, Moriguchi City Contact information: Nakagawa 5, stationed at Patent Center 835-1111 (Tokyo) Date of amendment order (shipment date) August 26, 1985 On Day 7, on page 10 of the statement of contents of the amendment, line 2, 'Figure 9' was amended to read 'Figure 1, Figure 7.'

Claims (1)

[Claims] (1) Forming a defect detection pattern of the same pattern as the predetermined pattern in the peripheral margin of a photomask in which a plurality of predetermined patterns are regularly arranged, and exposing this defect detection pattern with a light amount less than the appropriate exposure amount. 1. A method for inspecting a photomask, which is characterized by inspecting a defective part while exaggerating it.