JPH0690142B2 - Mask inspection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for automatically inspecting defects on a mask used in an exposure apparatus.

2. Description of the Related Art As semiconductor elements are miniaturized and the minimum dimension thereof is set to 1 μm or other submicrons as a reference, an exposure apparatus used in a linography process is a step-and-repeat type reduction projection exposure apparatus, a so-called stepper. Is becoming mainstream. In the stepper, a mask is used to transfer the pattern onto the patterned semiconductor substrate, but if the mask has pattern defects or contamination (dust, scratches, etc.), these are also transferred at the same time. The transfer of such pattern defects and contamination (hereinafter abbreviated as defects) causes defects in the semiconductor element. Further, since such defect transfer occurs in all shots, the yield is remarkably reduced. In order to prevent such defects, the mask pattern is inspected. In particular, in order to prevent defects caused by dust adhering to the mask, a semiconductor substrate coated with a photoresist, which is different from the semiconductor substrate on which elements are to be formed, is used with the mask in a state in which it is ready to be exposed by the stepper. Test exposure is performed thereon, a mask pattern to be inspected is formed from photoresist, and it is inspected. In most cases, this inspection is done visually by a person using a microscope.
When a plurality of equivalent semiconductor element patterns are drawn on one mask, it is also possible to use an apparatus that performs an automatic inspection by chip comparison. However, in the case where one semiconductor element or a plurality of semiconductor elements that are not equivalent to each other are drawn on one mask, there is no other method than visually inspecting.

Problems to be Solved by the Invention According to the conventional inspection method, when one semiconductor element or a plurality of semiconductor elements that are not equivalent to each other are drawn on one mask, a person must inspect visually.

The present invention solves the above-mentioned problems, and it is not possible with an automatic inspection apparatus that performs an inspection by comparing chips with one mask
This enables inspection when individual semiconductor elements or a plurality of semiconductor elements that are not equivalent are drawn.

Means for Solving the Problems In the present invention, the first pattern is formed in a partial region of the substrate, and the second pattern is formed in another region. Next, the first pattern and the second pattern are inspected by chip comparison using an automatic inspection device, and the data or mask used for forming the first pattern and the mask used for forming the second pattern are compared and inspected. .

Operation According to this inspection method, in the case where one semiconductor element or a plurality of unequal semiconductor elements are drawn on one mask, which is conventionally impossible with an automatic inspection apparatus for inspecting by chip comparison, Inspection can be enabled. Therefore, the inspection accuracy is improved as compared with the case where a person visually inspects, and thus the yield can be significantly improved.

Embodiments Five embodiments of the inspection method according to the present invention will be described in detail with reference to the drawings.

First, the first embodiment will be described with reference to FIG.
An aluminum film of about 650 Å is formed by sputtering on the surface of a quartz substrate 1 having a thickness of about 650 μm, and a negative type electron beam resist is spin-coated on the surface of the aluminum film about 5000 Å. Mask data of a mask to be inspected in a predetermined area 2 of the quartz substrate 1 is directly drawn by an electron beam exposure apparatus and developed (FIG. 1a). At this time, alignment marks necessary for exposure of the stepper are also formed. Further, the resist is left in the region 3 where the pattern is to be formed using the mask. Next, using the desired resist pattern as a mask, the aluminum film 650Å
Is dry-etched, and then the resist is removed by ashing. Next, about 2 μm of a positive type photoresist is spin-coated on the surface of the quartz substrate 1, exposed by a stepper using a mask to be inspected, and developed. It is the region 3 shown in FIG. 1b that is exposed at this time. The resist is left in the area 2. Next, the aluminum film 650Å is dry-etched by using this photoresist pattern as a mask, and then the photoresist is removed. Next, the quartz substrate 1 on which the pattern has been formed is inspected by an automatic inspection device which inspects the pattern by comparing the chips. The automatic inspection device used at this time is of a type that performs inspection by detecting transmitted light. By this inspection, it is possible to determine whether or not the etching pattern formed by exposure with the stepper using the mask is equivalent to the etching pattern obtained by the direct drawing method from the mask data.

An example of the comparison judgment is shown in FIG. The automatic inspection apparatus compares the chip pattern 4 directly drawn from the data with the chip pattern 5 formed using the mask. The display of the part that has a difference in comparison is operated as shown in FIG. 2 (c), for example.
Done on the CRT. If the pattern defect 8 is found in the portion 7 as shown in FIG.
Since the chip pattern 5 is formed by repeated exposure in steps, the same position 9 of other chips in the region 3 is formed.
Further, if the same defect 10 is found, the mask used for forming the pattern of the chip pattern 5 has a defect. Alternatively, it can be seen that there is a factor that causes a defect in the exposure system used to form the pattern of the chip pattern 5. If the portion 9 is the same as the portion 6, the defect 8 is considered to be caused by contamination on the wafer. If the displayed portion 7 of the inspection device is the same as the portion 6 or if there is no problem in pattern formation, it is ignored as a pseudo defect.

If the chip patterns 4 and 5 are exactly the same, the inspection apparatus cannot find any difference and determines that the defect is 0.
In this case, it can be determined that the mask used for pattern formation is equivalent to the data, that is, there is no defect. At the same time, it can be determined that there is no problem in the exposure system using the mask.

Furthermore, when the pattern formed using the mask is subjected to the comparison inspection with the data, only the defects transferred by the used exposure apparatus are subject to the determination. When the mask is directly inspected, it is extremely difficult to judge whether the found defect causes a problem in pattern formation. Particularly in the case of a fine defect, it is necessary to actually perform a pattern formation test with an exposure apparatus which is scheduled to use the mask. This is because the resolution limit differs depending on the exposure apparatus, and the size of the problematic defect also differs depending on the device and the process using the mask. Therefore, if a mask defect inspection is performed on a pattern formed using a mask, all these judgments can be performed simultaneously, which is very advantageous.

In this way, the comparison inspection with the data of the mask pattern can be performed by using the automatic inspection device by the chip comparison using the transmitted light.

In the above embodiment, a quartz substrate having a thickness of 650 μm was used, but this has a visible light transmittance within an allowable range of the inspection apparatus, and may be thinner or thicker if it can withstand the pattern forming process. Can also be used. Also, an aluminum film 650Å was used to form the etching pattern, but this can be formed on a quartz substrate, and the visible light transmittance and the contrast with the quartz substrate's transmittance can be recognized by an automatic inspection device. Any conductive thin film can be used. Although a negative type was used as the electron beam resist and a positive type was used as the photoresist, either positive type negative type may be used in any case, and resist components, additives such as dyes, and the resist film thickness can also be patterned. If it is, it will not be particularly limited. As a matter of course, the resist process may be performed using a method advantageous in pattern formation, such as a multilayer resist method.

Next, a second embodiment of the present invention will be described. In this embodiment, a P-type semiconductor substrate is used instead of the quartz substrate used in the first embodiment, and an automatic inspection device of a type that detects reflected light is used.

A thermal oxide film of about 1000Å is formed on the surface of the P-type semiconductor substrate,
About 5000 Å of negative electron beam resist is spun on it. As shown in FIG. 1A, by using mask data of a mask to be inspected in a predetermined area 2 of the semiconductor substrate, an electron beam exposure apparatus directly draws and develops. At this time, alignment marks necessary for exposure of the stepper are also formed. At the same time, the mask is used to leave the resist in the region 3 where the pattern is to be formed.

Next, the oxide film is formed using the desired resist pattern as a mask.
Dry etch 1000Å, then remove the resist by ashing. Next, about 1 μm of a positive photoresist is spin-coated on the surface of the semiconductor substrate, exposed by a stepper using a mask to be inspected, and developed. At this time, the area 3 to be exposed is shown in FIG. Next, the oxide film of about 1000 Å is dry-etched using the photoresist pattern as a mask, and then the photoresist is removed by ashing. Next, as shown in FIG. 1B, the semiconductor substrate 1 having a desired pattern formed in each region is inspected by an automatic inspection device that detects reflected light and compares chips to inspect the pattern. To do. By this inspection, it is possible to determine whether or not the etching pattern formed by exposure with the stepper using the mask is equivalent to the etching pattern obtained by the direct drawing method from the mask data.
The determination method is the same as in the first embodiment.

In this way, the comparison with the data of the mask pattern can be performed by using the automatic inspection device by the chip comparison.

Although the P-type semiconductor substrate is used in the above embodiment, it may be N-type. Although a thermal oxide film of about 1000 Å was used to form the etching pattern, it can be formed on a semiconductor substrate and any film can be used as long as the etching pattern can be detected by an automatic inspection device.

Further, there are no particular restrictions on the electron beam resist / photoresist / resist process as in the first embodiment.

Next, a third embodiment of the present invention will be described. First
The positive type photoresist of about 2 μm was spin-coated on the quartz substrate 1 having the aluminum film of about 650 Å similar to that used in the above Example, and the first mask was used to form the area 2 shown in FIG. 1 (a). Exposure is performed with a stepper. At this time, an alignment mark necessary when performing exposure using the second mask is also formed. Further, the resist is made to remain in the region 3 where the pattern is to be formed using the second mask.

Aluminum film approximately 650Å using this resist pattern as a mask
Are etched and then the resist is removed by ashing.

Next, about 2 μm of positive photoresist is again spin-coated on the surface of the quartz substrate, the second mask is used to align with the previously formed alignment mark, and the stepper exposes and develops. At this time, the area to be exposed is the area 3 shown in FIG. Further, the resist is left in the region 2 where the pattern is formed using the first mask. Next, using this photoresist pattern as a mask, the aluminum film of about 650 Å is etched, and then the resist is removed. Thereafter, as in the first embodiment, the patterned quartz substrate 1 is automatically inspected.

By this inspection, it is possible to determine whether or not the etching pattern formed using the first mask and the etching pattern formed using the second mask are equivalent. If they are exactly the same, then either mask has no defects at all, or both masks have exactly the same defects. In this case, it is extremely unlikely that defects having exactly the same shape will occur in exactly the same case on the mask, and since it is almost unlikely, it can be determined that both masks have no defects. If they are not equal, it is determined which mask is used to form the abnormal pattern. It can be seen that the mask used to form the abnormal pattern has a defect.

Although one stepper used for exposure is used in this embodiment, separate steppers may be used.

Next, a fourth embodiment of the present invention will be described. Second
The surface of a P-type semiconductor substrate with a thermal oxide film of about 1000 Å similar to that used in Example 1 was spin-coated with about 1 μm of a positive photoresist, and a first mask was used to show the same in FIG. 1 (a). The area 2 is exposed with a stepper and developed. At this time the second
The mask is used to leave the resist in the region 3 where the pattern is to be formed. Using this resist pattern as a mask, the thermal oxide film of about 1000Å is etched and then the resist is removed. Next, a positive photoresist of about 1 μm is spin-coated on the surface of the semiconductor substrate 1 again, a second mask that is exactly the same as the first mask is used to align with the previously formed alignment marks, and exposure is performed. develop. At this time, the area to be exposed is the area 3 shown in FIG. Further, the resist is left in the region 2 where the pattern is formed using the first mask. Next, using this photoresist pattern as a mask,
Etch 1000Å, then remove resist. Then, similarly to the second embodiment, the reflected light is detected, the chips are compared, and the pattern is inspected by an automatic inspection device. The method of comparison and determination is the same as in the third embodiment.

Next, a fifth embodiment of the present invention will be described.

About 1 μm of a positive resist is spin-coated on the surface of the semiconductor substrate 1 on which the etching pattern of the alignment mark necessary for overlaying the mask pattern at the time of stepper exposure is formed, and only one integrated circuit is provided in the area 2 shown in FIG. Exposure is performed with a stepper using the first mask in which is drawn. At this time, the pattern of the mask is aligned with the alignment mark formed on the surface of the semiconductor substrate 1. Then, the semiconductor substrate 1 is replaced with a second mask which is identical to the first mask mounted on the stepper instead of the first mask.
The region 3 on the surface of is exposed. At this time, as in the case of the first mask, the mask pattern is aligned with the alignment mark formed on the surface of the semiconductor substrate 1. After that, development is performed to obtain a semiconductor substrate to be inspected in which a photoresist pattern formed using the first mask in the region 2 and a photoresist pattern formed using the second mask in the region 3 exist.

Next, the resist pattern formed using the first mask and the resist pattern formed using the second mask are compared and inspected by an automatic inspection device that detects reflected light and inspects the pattern by chip comparison. .

The method of comparison and determination is the same as in the third and fourth embodiments. According to the method shown in this embodiment, it is not necessary to apply an oxide film to the surface of the substrate in advance, so that the preparation of the base is easy. Further, in the first to fourth embodiments, since the etching pattern is formed one by one, a process such as etching and subsequent resist removal is necessary. However, in the fifth embodiment, only the etching pattern of the alignment mark is formed. The photoresist pattern may be directly formed on the surface of the formed semiconductor substrate 1. As described above, according to the fifth embodiment, as compared with the methods shown in the first to fourth embodiments, the number of process steps is small, so that the time required for the inspection confirmation is as short as about 20 minutes and the cost is reduced. Very cheap.

The circuit pattern in which the masks used in the above five embodiments are drawn does not matter at all.

EFFECTS OF THE INVENTION According to the method of the present invention, one semiconductor integrated circuit or a plurality of unequal semiconductor integrated circuits are drawn on one mask, which is conventionally impossible with an automatic inspection apparatus for inspecting by chip comparison. If it is, enable automatic inspection. Further, in such a case, the inspection accuracy is much improved as compared with the case where a person visually inspects, which greatly contributes to the improvement of the mask quality and the improvement of the yield.

[Brief description of drawings]

1 (a) and 1 (b) are diagrams for explaining an embodiment of the present invention, and FIGS. 2 (a) to 2 (d) are diagrams for explaining an example of inspection confirmation. 1 ... Substrate, 2 ... First pattern forming region, 3 ... Second pattern forming region, 4 ...
Pattern of chip formed in area 2, 5 ... Pattern of chip formed in area 3, 5 '... Pattern of chip formed in area 3, 6 ... Partial pattern of chip pattern 4, 7 ... Chip Part of the pattern 5, a pattern corresponding to the pattern 6, 8 ... Defects in the pattern 7, 9 ...
... A part of the chip pattern 5'corresponding to the patterns 6 and 7, 10 ... a defect in the pattern 9.

Claims (5)

[Claims] 1. A step of forming a visible light opaque thin film on a substrate which transmits visible light, and a visible light opaque to a partial area on the substrate by using a direct drawing method from mask data of a mask to be inspected. Forming a first etching pattern of a thin film, forming a second etching pattern of a visible light opaque thin film in a region on the substrate other than a region where the first etching pattern is formed using a mask to be inspected And a step of comparing and inspecting the first etching pattern and the second etching pattern on the substrate using an automatic inspection device that detects transmitted light and inspects the pattern by etching comparison. A mask inspection method characterized by the above. 2. A step of forming an oxide film on a semiconductor substrate that does not transmit visible light, a first etching pattern is formed on a partial region of the semiconductor substrate by using a direct drawing method from mask data of a mask to be inspected. Forming a second etching pattern in a region on the semiconductor substrate other than a region where the first etching pattern is formed using a mask to be inspected, the first etching pattern on the semiconductor substrate
And the second etching pattern are compared and inspected by using an automatic inspection device that detects reflected light and inspects the pattern by chip comparison. 3. A step of forming a visible light impermeable thin film on a substrate that transmits visible light, a step of forming a first etching pattern using a first mask in a partial region on the substrate, Forming a second etching pattern on a region of the substrate where the first etching pattern does not exist using a second mask that is exactly the same as the first mask; the first etching pattern and the second etching pattern; A mask inspection method comprising a step of comparing and inspecting an etching pattern with an automatic inspection device that inspects the pattern by detecting transmitted light and comparing chips. 4. A step of forming an oxide film on a semiconductor substrate which does not transmit visible light, wherein a first region is formed on a part of the semiconductor substrate.
Forming a first etching pattern using the first mask, and using a second mask that is exactly the same as the first mask, a second mask is formed on a region of the semiconductor substrate where the first etching pattern does not exist. Forming an etching pattern, the first etching pattern and the second
And an etching pattern of the above-mentioned etching pattern are compared and inspected by an automatic inspection device for inspecting the pattern by chip comparison to detect reflected light. 5. A step of forming a first pattern using a first mask in a partial region of a surface of a semiconductor substrate that does not transmit visible light, and a second mask which is exactly the same as the first mask. Forming a second pattern in a region on the semiconductor substrate other than the region in which the first pattern is formed by using the method of forming the first pattern and the second pattern,
And a step of performing a comparative inspection using an inspection device that detects reflected light and inspects a pattern by chip comparison.