JPH0375854B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for inspecting a patterned surface of a photomask, and particularly 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, 1 is applied to the reticle, which is the original plate.
If there is a defect even in one photomask, it will appear as a common defect where 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 0 defects is prepared, if foreign matter adheres to the reticle surface during transfer or some abnormality occurs in the optical system, it will still become a common defect. Photo masks also need to be carefully inspected.

Visual inspection using a microscope has traditionally been used as a method for inspecting photomasks, but this method has the drawbacks of being time-consuming and overlooking defects in the pattern.
An inspection device such as that described in Japanese Patent No. 60-220934 is often used. Such equipment scans a predetermined pattern of the photomask to be inspected with a video camera, converts the signal into a digital signal, and then scans the photomask to be inspected.
The quality of the pattern is determined by comparing it with CAD data. With this device,
Almost accurate inspection can be performed in a short time.

(c) Problems to be solved by the invention However, as miniaturization progresses, even higher detection accuracy is required of the above-mentioned devices;
Currently, a device with high precision that satisfies the requirements has not yet been realized, and in particular, contact hole masks for positive resists and masks for electrode wiring, where patterns are the smallest, can only be inspected incompletely. There was a drawback that I couldn't do it.

For example, as shown in FIG.
When inspecting a photomask with a 4μm□ white pattern, defects such as parts of the white pattern missing, as shown in abnormal pattern 11, and bridges between wires in the electrode wiring pattern cannot be detected. Can not. Another possible defect is a white pinhole on a black background.
It has been confirmed that such defects rarely occur if the reticle is perfect.

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

(e) 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 developed in a reduced size, and for example, the defective portion reduces the opening area of the normal pattern 10. If the abnormal pattern 11 is only 60% open, the defect detection pattern 3 will almost completely collapse it.
Therefore, if such a pattern is used, defective portions can be reliably detected even with conventional inspection equipment.

(f) Examples 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 repeatedly formed in the center of the main surface of a mask substrate 1 vertically and horizontally, and the margins around it are A defect detection pattern 3 is formed apart from the second group of predetermined patterns. The blank space is an unnecessary area for the wafer, and there is no problem in forming the defect detection pattern 3 there. And defect detection pattern 3 is
First, the original pattern formed on the reticle is step-and-printed using a device called a photo repeater.
By repeating exposure, a predetermined pattern 2 is created.
After forming the group, the same pattern as the predetermined pattern 2 is formed by exposing the group with a light amount that is about 0.8 times the exposure amount.

Defect detection pattern 3 formed in this way
The predetermined pattern 2 is due to intentional underexposure.
The pattern is generally reduced in size compared to .

This will be explained using FIGS. 2 and 3. FIG. 2 is a schematic cross-sectional view when a pattern is exposed by a photo repeater, in which 4 is a reticle, 5 is a lens, and 6 is a photomask. A predetermined pattern 2 of a chrome film 7 is selectively formed on the surface of the reticle 4, and an unprocessed chromium film 7 and a positive resist 8, which is advantageous for fine processing, are adhered to the surface of the photomask 6. When exposure light 9 such as ultraviolet rays from an ultra-high-pressure mercury lamp is irradiated from above the reticle 4, the light that passes through the white pattern formed on the reticle 4 reaches the surface of the resist 8 via the lens 5, and is exposed to the reticle 4. Predetermined pattern 2 formed
For example, it is configured to form an image on the surface of a photomask 6 at a scale of 10:1.

Since the exposure light 9 irradiated onto the resist 8 is accompanied by light diffraction and development, the irradiation amount (exposure amount) is plotted on the vertical axis and the distance from the center of the pattern is plotted on the horizontal axis as shown in FIG. It has similar distribution characteristics. Therefore, if the exposure time that satisfies the residual rate of film thickness after development of resist 8 is 0% is set to the level shown in the figure There will be a hole. However, at the time of underexposure, where the distribution characteristics are shown by the broken line,
Since the absolute exposure amount is insufficient, holes can only be opened in the range CD shown. Therefore, if the chromium film 7 is removed by etching in this state, the defect detection pattern 3 that has been underexposed will be formed with a reduced size overall.

4 and 5 are plan views showing a 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. Since it is for a positive resist, most of it is a black background made of the chromium film 7, and areas corresponding to contact holes are opened to form a white pattern. Then, in a part of the predetermined pattern 2,
If a normal pattern 10 with a completely opened hole and an abnormal pattern 11 having a defective part where a part of the white pattern is missing for some reason are formed, the above-mentioned reason will occur in the defect detection pattern 3. As a result, the normal pattern 10 is formed reduced to approximately half its size, and the abnormal pattern 11, which has been half collapsed from the beginning, is formed almost collapsed.

Further, as shown in FIG. 6, if the pattern for electrode wiring has a bridge defect 13 due to residual chromium between the wirings 12, 12, the defect detection pattern 3 will cause a bridge defect 13 as shown in FIG.
The bridge defect 13 is 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 devices. 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, a plurality of patterns of different sizes are formed by reducing the normal pattern 10 by changing the exposure amount, and the exposure limit is reached at which the normal pattern 10 is judged to be normal. What is necessary is to determine the exposure amount and set the exposure amount with a slight margin as the exposure amount of the defect detection pattern 3. With this setting, the abnormal pattern 11 having a smaller opening than the normal pattern 10 can 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, and if any defects are detected, the part of the predetermined pattern 2 corresponding to that part is visually inspected using a microscope, and the quality is determined again. All you have to do is judge. For even more perfection, it is conceivable to scan both the predetermined pattern 2 and the defect detection pattern 3 with an inspection device, or to inspect a plurality of defect detection patterns 3 formed with different exposure doses.

(G) Effects of the Invention As explained above, 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 on the periphery of the photomask, it has the advantage that it does not affect the actual pattern in any way.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a photomask of the present invention;
FIG. 2 is a schematic cross-sectional view of the exposure device, FIG. 3 is an exposure dose distribution characteristic diagram, FIGS. 4 and 6 are plan views showing a part of the predetermined pattern 2, and FIGS. 5 and 7 are defects. FIG. 3 is a plan view showing a part of the detection pattern 3. FIG. 1 is a mask substrate, 2 is a predetermined pattern, 3 is a defect detection pattern, 10 is a normal pattern, and 11 is an abnormal pattern.

Claims (1)

[Claims] 1. A defect detection pattern having the same pattern as the predetermined pattern is formed in the peripheral margin of a photomask in which a plurality of predetermined patterns are regularly arranged, and the defect detection pattern is exposed to a light amount less than the appropriate exposure amount to detect the defective part. A photomask inspection method characterized by exaggerating and inspecting.