KR20060124886A - Method for inspecting defects of photomask having plurality of dies with different transmittance - Google Patents

Abstract

A method for inspecting defects of a photomask having plural dies of different transmittance is provided to detect the defects of the transmittance-corrected photomask by lowering a clear level value. A determination process is performed to determine a dark level of transmittance and a clear level less than 100 percent by performing an optical calibration process for a photomask(100). An irradiation process is performed to irradiate light onto the photomask. A detection process is performed to detect optical signals transmitting a plurality of dies(110,120) and having values between the dark level and the clear level. A decision process is performed to compare the optical signals with each other in order to decide a defect of at least one of the dies.

Description

Method for inspecting defects of photomask having multiple of dies with different transmittance}

1 is a photograph showing the results of a conventional defect inspection method for a photomask having dies having different transmittances;

2 is a flowchart showing a defect inspection method of a photomask according to an embodiment of the present invention;

3 is a flowchart showing a defect inspection method of a photomask according to another embodiment of the present invention;

4 is a schematic diagram showing a photomask having a pair of dies and a key pattern;

5 is a schematic diagram showing transmittance correction of the key pattern of FIG. 4; And

6 is a graph showing whether or not an error of the defect inspection according to the optical signal.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measurement method for a semiconductor device, and more particularly, to a defect inspection method of a photomask including dies having different transmittances.

As the degree of integration of semiconductor devices increases, design rules become increasingly strict. Such design rules require more sophisticated fine pattern formation techniques in the manufacture of semiconductor devices. Therefore, in the manufacture of semiconductor devices, management of a photo-lithography process for forming fine patterns has become an important issue. In particular, shot uniformity of the semiconductor substrate in the photolithography process has a great influence on the yield of the semiconductor device.

As one of methods for improving shot uniformity of a semiconductor substrate, a method of fabricating different transmittances of regions inside a photomask used in photolithography for each region has been used. The photomask may have nonuniformity of the photomask itself due to nonuniformity in the manufacturing process. Therefore, in order to correct such a non-uniformity of the photomask itself, a process test is performed on the fabricated photomask, and then transmittance correction is performed to correct the non-uniformity.

For example, a phase grating pattern may be formed on the backside of the photomask, or a shading element may be formed inside the photomask using a laser. Transmittance correction may be performed in a die unit, and in this case, a transmittance correction map for each die may be used. The photomask in which the transmittance is corrected for each region is called a customized photomask.

However, there is a problem in inspecting defects of such custom photomasks. This is because a method of comparing light transmittance between dies of a photomask is widely used in inspecting such defects. For example, the presence or absence of a defect can be detected by reading the difference in transmittance between a defective die and a non-defective die. For example, defects in pattern shape, particles, and the like may be defects. As such a defect inspection apparatus, reference may be made to, for example, "AUTOMATED PHOTOMASK INSPECTION APPARATUS" of US Pat. No. 6,363,166 to Mark Joseph Wihl et al.

Referring to FIG. 1, it can be seen whether an error occurs when inspecting a defect due to a difference in transmittance of the photomask 50. The transmittances of the dies 10b, 20b, 30b, and 40b in the right column are not corrected, and the transmittances of the dies 10a, 20a, 30a, and 40a in the left column are corrected differently. For example, the left first die 10a has a 3% lower transmittance than the right first die 10b, and the left second die 20a has a 6% lower transmittance than the right second die 20b. The left third die 30a has a 9% lower transmittance than the right third die 30b, and the left fourth die 40a has a 12% lower transmittance than the right fourth die 40b. Dies 10a, 20a, 30a and 40a in the left column and dies 10b, 20b, 30b and 40b in the right column are formed with the same pattern or dies in the same row, for example dies 10a and 10b. It may be formed in the same pattern with each other.

The dies 10a and 20a with 0-6% transmittance have been inspected once (indicated by ○) when the inspection sensitivity is lowered (marked with ○), but the die 40a with 12% transmittance correction has not been inspected at all. There was no progress. However, even in the case of the dies 10a and 20a which have been inspected, a large number of errors that incorrectly indicate defects have occurred due to the difference in transmittance between the inspection die 10a and the reference die 10b. This can be interpreted as occurring because the inspection apparatus cannot distinguish between the difference in transmittance between dies due to a defect and the difference in transmittance due to the correction of the die itself.

Therefore, even in the absence of defects, reliability of defect inspection for photomasks having dies having different transmittances, for example, custom photomasks, is lowered. In addition, inspection time is increased due to the fact that the defects are actually checked through optical or electron microscopy.

An object of the present invention is to provide an economical and reliable defect inspection method for photomasks having dies having different transmittances.

According to an aspect of the present invention for achieving the above technical problem, there is provided a method for defect inspection of a photomask having at least a pair of dies having different transmittances comprising the following steps. Light calibration is performed on the photomask to determine the dark and clear levels of the transmittance. Clear level is less than 100%. Light is irradiated to the photomask. Each of the optical signals passing through the dies has a value between the dark level and the clear level. The optical signals are compared with each other to determine whether there is a defect in at least one of the dies.

According to an aspect of the aspect of the present invention, the photomask includes a key pattern having a clear pattern for determining the clear level and a dark pattern for determining the dark level, wherein the optical calibration is to be performed in the key pattern Can be.

According to another aspect of the aspect of the present invention, the method may further include correcting the transmittance of the key pattern before the optical calibration. The transmittance correction of the key pattern may be performed by forming a phase grating on the back of the transparent substrate of the clear pattern or by forming a shading layer on the transparent substrate of the clear pattern.

According to another aspect of the aspect of the present invention, the clear level can be obtained by correcting the calibration result in consideration of the transmittance of the dies.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the components are exaggerated in size for convenience of description.

Referring to FIG. 4, a photomask 100 including dies 110 and 120 having different transmittances will be described. The photomask 100 may further include a plurality of dies in addition to the illustrated dies 110 and 120. Respective pixels 112 and 120 may be defined within the dies 110 and 120. For example, a plurality of pixels 112 may be defined in a matrix in the first die 110, and a plurality of pixels 122 may be defined in the second die 120, corresponding to the first die 110. have. These pixels 112 and 122 may be reference units in the defect inspection apparatus.

The dies 110 and 120 may have their respective transmittances corrected based on a preliminary inspection result. Transmittance correction may be performed using a value of a transmittance correction map (not shown). For example, the transmittance of the first die 110 may be corrected according to the first transmittance correction map, and the transmittance of the second die 120 may be corrected according to the second transmittance correction map. The transmittance correction maps may be expressed as contour maps of transmittance values of the dies 110 and 120. Accordingly, the transmittances for the dies 110 and 120 may be values obtained by averaging the values of the transmittance correction maps. In addition, the transmittance of each of the pixels 112 and 122 may be an average value of the pixels in each transmittance correction map. As such, the photomask 100 whose transmittance is corrected using the transmittance correction maps is called a custom photomask.

The key pattern 150 is formed in an area outside the dies 110 and 120. However, the key pattern 150 may be formed in the region of the dies 110 and 120. The key pattern 150 is provided to provide a reference for transmittance for the various photomasks 100. The key pattern 150 may include a dark pattern 135 and a clear pattern 140.

Referring to Fig. 5A, the transmittance of the key pattern 150 is described. Ideally, the dark pattern 135 may have a transmittance of 0%, and the clear pattern 140 may have a transmittance of 100%. In practice, however, the dark pattern 135 will have a transmittance close to 0% and the clear pattern 140 will have a transmittance close to 100%. For example, the dark pattern 135 may be formed of a chromium layer, and the clear pattern 140 may be formed of a transparent substrate.

Referring to Figure 2, a defect inspection method of the photomask 100 according to an embodiment of the present invention will be described. First, the transmittance of the key pattern 150 of the photomask 100 is corrected (step 210). For example, the transmittance correction can be performed by forming a phase grating on the back surface of the transparent substrate (not shown) of the clear pattern 135. As the grating, that is, the step is formed on the transparent substrate, the phase and intensity of light passing through the step may vary.

As another example, the transmittance correction may be performed by forming a shading layer (not shown) on the transparent substrate of the clear pattern 135. In more detail, the light shielding layer may be formed by ion implanting gallium (Ga) into the transparent substrate. The transparent substrate portion in which the light shielding layer is formed will exhibit lower transmittance than the transparent substrate portion without the light shielding layer. Therefore, by selectively forming the light shielding layer only on the clear pattern 135, the transmittance of the light shielding layer can be corrected.

Referring to FIG. 5, the change in transmittance of the clear pattern 140 ′ due to the correction is illustrated. After correction, the transmittance of the clear pattern 140 ′ may be greater than 80% and less than 100%. More specifically, the transmittance of the clear pattern 140 ′ may be an average value of the transmittances of the dies 110 and 120. This is because, if the transmittance of the clear pattern 140 'is too low, the range of detectable defects can be reduced. As an example, the case where the transmittance of the clear pattern 140 'is 97% is illustrated.

More specifically, the case where the first die 110 is used as the inspection die and the second die 120 is used as the reference die can be considered. For example, the transmittance of the first die 110 is corrected to 91%, and the transmittance of the second die 120 is 100%. The transmittance of the dies 110 and 120 can be obtained from the transmittance correction maps used in the transmittance correction.

Subsequently, a light calibration is performed on the key pattern 150 to determine a clear level and a dark level (step 220). For example, the clear level may be a value for determining the upper limit of the transmittance based on the transparent pattern, and the dark level may be a value for determining the lower limit of the transmittance based on the light shielding pattern. More specifically, for example, the clear level may be a transmittance value obtained in the clear pattern 140 ′, and the dark level may be a transmittance value obtained in the dark pattern 135.

That is, the light calibration may be a task of determining a lower limit of transmittance, such as a dark level and an upper limit, such as a clear level, so that sensitivity may be set for various types of photomasks 100. Then, by appropriately dividing the dark level and the clear level, a sensitivity for detecting a defect can be set.

Subsequently, light is irradiated to the photomask 100 (step 230). For example, light may be irradiated to each of the dies 110 and 120 of the photomask 100 in a batch. For another example, light may be irradiated to each of the pixels 112 and 122. In the latter case, the inspection may be performed by irradiating light on the entire dies 110 and 120 by repeatedly irradiating light in units of the pixels 112 and 122. Light can be supplied, for example, from a laser source.

Then, optical signals are transmitted through the dies 110 and 120, respectively, having a value between the dark level and the clear level (step 240). The optical signals passing through the dies 110, 120 depend on the corrected transmittance of the dies 110, 120 and the defects of the dies 110, 120. For example, poor pattern formation of the dies 110 and 120 or particles on the dies 110 and 120 may change the intensity of the transmitted optical signal. In particular, the inspection in units of the pixels 112 and 122 may examine the pattern formation defect or the existence of particles more precisely.

The optical signals are then compared to determine if there is a defect for at least one of the dies 110, 120 (step 250). For example, the dies 110 and 120 have no defects. When the optical calibration is performed using the key pattern 150, the optical signal of the first die 110 will be 91%, and the optical signal of the second die 120 will be 100%, which is a clear level. However, when the optical calibration is performed using the key pattern 150 'after correction, the optical signal of the first die 110 is 91%, but the optical signal of the second die 120 is 97%, which is a clear level. Will be.

Therefore, the optical signal difference between the dies 110 and 120 after the optical calibration using the key pattern 150 is 9%, but the optical signal between the dies 110 and 120 after the optical calibration using the key pattern 150 '. The difference can be reduced to 6%. The reduction of the difference in the optical signal may be adjusted by differently correcting the transmittance of the key pattern 150 '. That is, the transmittance of the clear pattern 140 ′ may affect the clear level, and the clear level may affect the optical signal.

Referring to FIG. 6, it can be seen that the difference between the optical signals of the dies 110 and 120 affects the defect determination. When the key pattern 150 is used, since the difference Δ of the optical signals is larger than the sensitivity, the first die 110 may be erroneously determined in this case. However, when the key pattern 150 'is used, since the difference (o) of the optical signals is smaller than the sensitivity, in this case, the first die 110 can be correctly determined to be free of defects.

That is, according to the exemplary embodiment of the present invention, the defect may be detected with higher reliability even for the photomask 100 having a corrected transmittance, for example, a customized photomask. Thereby, since the defect determination reliability of a test | inspection apparatus becomes high, the time which examines the substance of the defect using an optical or an electron microscope can be shortened. This increases the economics of defect inspection.

Meanwhile, when the dies 110 and 120 are inspected in units of the pixels 112 and 122, the above-described steps 210 to 240 are repeatedly performed in units of the pixels 112 and 122. Accordingly, inspecting the entire pixels 112 and 122 completes the inspection of the dies 110 and 120. When the inspection is performed in units of the pixels 112 and 122, the defect map in units of pixels may be obtained in the dies 110 and 120.

Referring to Figure 3, a defect inspection method of the photomask 100 according to another embodiment of the present invention will be described. Other embodiments may be modified from the above-described embodiment and may refer to the description of the above-described embodiment. Hereinafter, another embodiment will be described based on the difference.

First, a light calibration is performed to determine a clear level and a dark level (step 310). Determination of the clear level and the dark level may refer to step 220 of the above embodiment. The clear level is then corrected (step 320). As described in the above embodiment, in the case of the customized photomask 100, it is preferable to lower the clear level according to the transmittance of the dies 110 and 120.

If it is a mechanical method to lower the clear level by using the key pattern 150 'whose transmittance is corrected in the above embodiment, the present embodiment lowers the clear level in software. For example, the corrected clear level may be at least 80% and less than 100%. More specifically, for example, the corrected clear level may be an average value of the transmittance of the dies 110 and 120. The transmittance of the dies 110 and 120 can be obtained using the respective transmittance correction maps.

Subsequently, the photomask 100 is irradiated with light (step 330), and optical signals passing through the dies are detected (step 340). The optical signals are then compared to determine if there is a defect for at least one of the dies 110, 120 (step 350). The steps (steps 330 to 350) may refer to steps (steps 230 to 250) of an embodiment, respectively. Accordingly, according to another exemplary embodiment of the present invention, defects can be economically detected with higher reliability even for the photomask 100 having a corrected transmittance, for example, a customized photomask.

The foregoing description of specific embodiments of the invention has been presented for purposes of illustration and description. Therefore, the present invention is not limited to the above embodiments, and various modifications and changes are possible in the technical spirit of the present invention by combining the above embodiments by those skilled in the art. It is obvious.

According to the present invention, by lowering a clear level value, defects can be detected by compensating for a difference in transmittance of a photomask whose transmittance is corrected, for example, a custom photomask.

For example, the clear level can be lowered by correcting the transmittance of the clear pattern of the key pattern. Alternatively, after the optical calibration, the clear level value may be lowered in software.

Accordingly, it is possible to reduce the difference between the optical signals passing through the dies 110 and 120 having different transmittances, thereby lowering the possibility of misjudgment of a defect determination. That is, the reliability of defect determination with respect to the photomask can be improved. Moreover, since the defect determination reliability of an inspection apparatus becomes high, the time which examines the substance of the defect using an optical or an electron microscope can be shortened. This increases the economics of defect inspection.

Claims (12)

A method of detecting defects in a photomask having at least a pair of dies having different transmittances, Performing light calibration on the photomask to determine a dark level for transmittance and a clear level of less than 100%; Irradiating light onto the photomask; Detecting light signals passing through the dies, each having a value between the dark level and the clear level; And Comparing the optical signals with each other to determine whether there is a defect for at least one of the dies; and a plurality of dies having different transmittances. The transmittance of claim 1, wherein the photomask includes a key pattern having a clear pattern for determining the clear level and a dark pattern for determining the dark level, and the optical calibration is performed on the key pattern. A defect inspection method of a photomask having a plurality of different dies. The method of claim 2, further comprising correcting the transmittance of the key pattern before the optical calibration. The method of claim 3, wherein the transmittance of the clear pattern is 80% or more and less than 100%. 4. The method of claim 3, wherein the transmittance of the clear pattern is an average value of the transmittances of the dies. 6. The plurality of photomasks of claim 5, wherein each of the dies is a custom photomask in which transmittance is corrected using transmittance correction maps, and transmittances of the dies are obtained from the transmittance correction maps. A defect inspection method of a photomask having dies of. 4. The method of claim 3, wherein the correction of the transmittance of the key pattern forms a phase grating on a back surface of the transparent substrate of the clear pattern. 4. The method of claim 3, wherein the correction of the transmittance of the key pattern forms a shading layer on the transparent substrate of the clear pattern. 10. The method of claim 8, wherein the light shielding layer is formed by doping gallium to the transparent substrate. The method of claim 1, wherein the clear level is obtained by correcting the calibration result in consideration of the transmittances of the dies. The method of claim 10, wherein the corrected clear level is an average value of transmittances of the dies. 11. The method of claim 10, wherein the corrected clear level is at least 80% and less than 100%.

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