KR101971280B1 - Method for fabricating photomask - Google Patents

Abstract

There is disclosed a method of manufacturing a photomask capable of measuring various factors that can guarantee the quality of a mask without using a separate device according to the wavelength of a light source, thereby reducing manufacturing cost. A method of manufacturing a photomask of the present invention is a method of measuring an aerial image of a photomask for a light source having a second wavelength longer than the first wavelength by using an aerial image measuring instrument using a light source of a first wavelength .

Description

[0001] The present invention relates to a method for fabricating photomask,

The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method for measuring an aerial image of a photomask to verify the effect of defects on the photomask.

As the pattern size of a semiconductor memory device becomes smaller, the ability to implement mask manufacturing and measuring instruments is also continuously improved. Technological advances have been made, such as increasing the precision of mask manufacturing equipment, while reducing the error rate of the equipment. As the technology of the mask manufacturing equipment develops, the cost of the equipment also exponentially increases, thereby contributing to increase the average manufacturing cost of the mask. In order to guarantee the quality and the quality of the mask, it is necessary to purchase measurement equipment capable of measuring the respective characteristics, and the cost of maintaining the equipment and the cost of each equipment is increased.

On the other hand, as the line width of the memory semiconductor device is drastically reduced, critical layers lacking a margin in a photolithography process are used as an ArF light source having a shorter wavelength than a KrF light source in order to enhance resolution, Phase inversion mask (PSM). Also, metal wiring lines, contact plugs, etc., which are semi-critical or non-critical layers that have been exposed in conventional i-line light sources, are converted into KrF light sources and exposed.

In this way, a light source of a scanner is switched from a KrF (248 nm) light source to an ArF (193 nm) light source, and an ariel image, in which a defect of a mask can be predicted in advance, There has also been a great shift in measurement equipment. Basically, by calculating the intensity of light obtained by passing a laser of the same wavelength as the scanner through a photomask, an aerial image measurement As the operation of the equipment becomes simpler, the workability of the workers is improved and the throughput of the equipment is also improved. Therefore, in the mask manufacturing process, defects of the mask using the ArF light source can easily control the defects of the mask while improving the workability between the repair and the defect detection process (the aerial image measurement process), but the KrF light source The aerial image measurement equipment of the mask used is still not used smoothly due to the complexity of the operation and the need for raising the defect verification process of the mask for the KrF light source to the same level as that of the ArF is increased .

Several features must be verified to ensure the quality of the mask. The first is CD data that can confirm whether the pattern size designed in the database and the line width of the mask pattern are implemented in the same manner. The second is the registration data which can confirm the direction in which each pattern of the mask is rotated from the X / Y axis. The third is the transmittance of the molybdenum silicon nitride (MoSiN) layer, which is an important characteristic of the halftone phase reversal mask, and the phase shift of light between the quartz (Qz) substrate and the MoSiN layer after the pattern is formed. And the last four are aerial image data to confirm that defects on the mask are formed on the wafer. At this time, the aerial image data should be measured using a light source of the same wavelength as the scanner, and since the measurement method of the aerial image measuring device of the ArF light source is simplified, productivity is increased and it is universally accepted and used in the mask making field, .

To verify these basic mask characteristics, each measurement instrument is required, such as a CD measurement instrument (SEM), a registration measurement instrument, a transmittance measurement instrument, a phase shift measurement instrument, and an aerial image measurement instrument. However, as the size of the mask pattern decreases, the equipment technology for measuring the characteristics of the mask also improves, and the difficulty of the equipment manufacturing technique increases, so that the unit cost of the equipment increases exponentially, resulting in an increase in the manufacturing cost of the mask . This may cause an increase in manufacturing cost of the semiconductor device.

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a photomask capable of measuring various factors that can guarantee the quality of a mask without using a separate device according to the wavelength of a light source, .

According to an aspect of the present invention, there is provided a method of manufacturing a photomask, the method comprising the steps of: measuring an aerial image of a light source photomask having a second wavelength longer than the first wavelength using an aerial image measuring instrument using a light source of a first wavelength; And the image is measured.

In one example, the light source of the first wavelength is an ArF light source, and the light source of the second wavelength may be any one of a KrF and an I-line light source.

In one example, the light source of the first wavelength may be a KrF light source, and the light source of the second wavelength may be an I-line light source.

The aerial image measuring apparatus includes a diaphragm capable of adjusting a numerical aperture (NA), and when measuring an aerial image of a light source photomask of the second wavelength, a numerical aperture (NA) of the diaphragm is adjusted .

When measuring the aerial image of the photomask for the light source of the second wavelength by using the aerial measuring instrument of the first wavelength, light whose light from the light source is reduced by the ratio of the first wavelength and the second wavelength is irradiated It is preferable to adjust the numerical aperture (NA) of the diaphragm.

When measuring an aerial image of a KrF light source photomask using an aerial image measuring instrument of an ArF light source, it is desirable to adjust the numerical aperture (NA) of the aperture so that 70% of the light emitted from the light source is transmitted.

When the photomask is a phase inversion mask, it is preferable that the numerical aperture (NA) of the aperture stop is further reduced in consideration of the transmittance of the phase reversal film of the mask.

According to another aspect of the present invention, there is provided a method of manufacturing a photomask for verifying an influence of a defect on a photomask by measuring an aerial image formed based on light passed through a photomask from at least one light source The method comprising the steps of: preparing an aerial image measuring instrument including a diaphragm capable of adjusting a numerical aperture (NA) using a light source of a first wavelength; The method comprising the steps of: disposing a photomask for a light source having a second wavelength longer than the first wavelength on a first side; measuring an aerial image of transmitted light transmitted through the photomask from the light source; And verifying the influence of the defect in the mask.

In one example, the light source of the first wavelength is an ArF light source, and the light source of the second wavelength may be any one of a KrF and an I-line light source.

In one example, the light source of the first wavelength may be a KrF light source, and the light source of the second wavelength may be an I-line light source.

In the step of measuring the aerial image of the photomask for the light source of the second wavelength, the numerical aperture (NA) of the diaphragm can be adjusted.

(NA) of the aperture so that light having reduced light from the light source is irradiated on the photomask at a ratio of the first wavelength to the second wavelength in the measurement of the aerial image of the light source photomask of the second wavelength, Can be adjusted.

When measuring an aerial image of a KrF light source photomask using an aerial image measuring device of an ArF light source, the numerical aperture (NA) of the aperture can be adjusted so that 70% of the light emitted from the light source is transmitted.

When the photomask is a phase inversion mask, it is preferable that the numerical aperture (NA) of the aperture stop is further reduced in consideration of the transmittance of the phase reversal film of the mask.

According to the method of manufacturing a photomask of the present invention, it is possible to measure an aerial image of a photomask of two or more wavelengths (ArF, KrF, I-Line) with one wavelength (ArF) equipment. Thus, the efficiency of the equipment is improved, and the number of functions is included in one equipment, thereby reducing the necessity of other equipment, reducing the manufacturing cost of the mask, and facilitating the management of the equipment. In addition, since the throuput of the equipment of a generation ahead is faster, the production time of the KrF mask can be reduced, and the productivity can be improved.

1 is a view briefly showing a mask exposure process.
FIGS. 2A and 2B are views showing the results of a resolution simulation of ArF and KrF light sources of the same mask. FIG.
3 is a diagram showing a method of adjusting the NA size of the ArF light source to the NA size of the KrF light source.
FIGS. 4A and 4B are diagrams comparing light transmittances according to wavelengths in an attenuated PSM. FIG.
FIG. 5 is a diagram showing an image of a defect in the scanner exposure of the KrF light source by comparing the aerial image of the ArF light source.

Hereinafter, embodiments of a method of manufacturing a photomask according to an aspect of the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description with reference to the accompanying drawings, the same or corresponding components are denoted by the same reference numerals, and a duplicate description thereof will be omitted.

The process of manufacturing a photomask and pre-verifying how weak points or defect points of the mask will appear during wafer exposure before shipment is becoming common. Furthermore, the masks exposed by the scanner of the ArF light source have been verified with weakened points in the aerial image measurement equipment with the advanced specification, and the aerial image measurement equipment used at this time uses the laser of the same wavelength as the scanner to which the mask is exposed . For example, if the mask is exposed in a scanner of an ArF light source, it is verified in an aerial image measuring instrument of the same wavelength as the ArF light source, and when the mask is exposed in a scanner of a KrF light source, it is verified in an aerial image measuring instrument of the same wavelength as the KrF light source . This is basically because the aerial image measurement equipment is a reduced model of the scanner and follows the exposure conditions of the scanner.

The present invention proposes a method for allowing masks exposed in a scanner of a KrF light source or an I-line light source to be verified in an aerial image measuring device of a preceding generation, i.e., a short wavelength ArF light source, out of this basic rule .

First, the present invention is based on the fact that an aerial image measurement device measures an aerial image using conditions similar to those of a scanner device that exposes a mask to a wafer. Basically, resolution (R) in an exposure process using a mask is defined by the following formula called Rayleigh equation.

Where k1 is a process parameter determined by a mask type, a photoresist, an illumination type, etc., lambda is a wavelength of a light source used for exposure, NA is a numerical aperture, that is, ) The size of the lens. Only the point where the ArF and KrF light sources are used to improve the resolution R. The scanner of the KrF light source and the scanner of the ArF light source satisfy the conditions such as numerical aperture (NA), illumination method, inner / outer sigma Is the same. This means that the same resolution can be obtained by adjusting the numerical aperture (NA) or k1 irrespective of the light source used. Therefore, in order to obtain images of an aerial image of a KrF light source in an aerial image measuring apparatus of an ArF light source, it is necessary to make the same resolution (R) condition. The numerical aperture (NA) is reduced by measuring the ratio of the ArF light source to the KrF light source (at a level of about 70%) among the measurement conditions of the KrF light source, thereby obtaining a desired aerial image. At this time, the attenuated PSM of the KrF light source has the same effect as the binary mask because the ArF light source can not transmit the phase reversal film (MoSi). However, this can be solved by applying an energy offset equal to the difference between the binary mask and the attenuated PSM.

In Equation (1), the wavelength 248 nm of the KrF light source and the wavelength 193 nm of the ArF light source are respectively substituted and the resolving power R of the two light sources is equalized as follows.

The above equations are formulas showing how to change the numerical aperture (NA) to realize the same resolution as the KrF light source in the ArF light source. From these equations, it can be seen that the resolution of the KrF light source is similar to that of the KrF light source when the NA value is reduced from the ArF light source to the wavelength of the KrF light source, ie, about 70%.

In order to confirm this, the results of a resolution simulation of the ArF and KrF light sources of the same mask are shown in FIGS. 2A and 2B. FIG. 1 briefly shows the mask exposure process.

First, referring to FIG. 1, a mask 100, a lens unit 200 for focusing light of a light source, and a wafer 300 are sequentially arranged from a light source. Light passing through the mask 10 starting from the light source is diffracted by ± 1, 3, and 5-order light. Light that is transferred to the wafer 30 through the lens unit (NA) 20 forms a pattern. At this time, the ratio of the primary light passing through the lens unit 20 was simulated by using the same illumination system in the wavelength condition of the KrF and ArF light sources, but with different NA conditions.

2A and 2B, the ratio of the primary light is 74.4% in the 0.8 NA annular 0.85 / 0.55 sigma condition of the KrF light source, and 0.625 NA annular 0.85 / 0.55 of the ArF light source Under the sigma condition, the primary light ratio is 74.5%, and the resolution of the two light sources is very similar. In other words, by modifying only the NA condition, the aerial image measuring apparatus of the ArF light source can measure the aerial image of the mask using the KrF light source, and as a result, it is confirmed that the defect of the mask can be verified. At this time, an example of a method of changing the NA condition in the KrF light source to the NA condition of the ArF light source is shown in FIG.

3 is a diagram for explaining a method of adjusting the NA size of the ArF light source to the NA size of the KrF light source.

Reference numeral 200 denotes a lens portion of an aerial image measuring instrument using an ArF light source. Reference numeral 210 denotes a lens of a full size at the ArF wavelength, reference numeral 220 denotes a primary blade that opens only a 70% area of the entire lens size and covers the remaining area of the lens, and reference numeral 230 denotes a KrF A secondary blade capable of adjusting the open area of the lens according to an exposure condition such as PSM, and 240 denotes an aerial image measurement device of an actual ArF light source, when measuring an aerial image of a KrF mask Respectively.

Referring to FIG. 3, a primary blade 220 serving as a light shielding film that opens only 70% of the lens of the ArF light source is installed in the lens unit. Secondary blade 230, which can set the area of the lens like second measurement condition of KrF wavelength, is inserted. At this time, the NA adjustment method of the secondary blade 230 may be performed such that the area opened in the primary blade 220 is recognized as 100%, and then the area is reduced from the range.

The light of the ArF light source whose wavelength is shorter than that of KrF is the phase reversal film MoSi because the mask is designed so that the transmittance of the phase reversal film MoSi in the KrF wavelength is 6% The difference between the binary mask and the attenuated PSM can not be recognized in the ArF light source. On the contrary, MoSi having a transmittance of 6% in an ArF light source exhibits a transmittance of about 20% in a KrF light source having a longer wavelength than ArF.

FIGS. 4A and 4B are diagrams comparing light transmittances according to wavelengths in an attenuated PSM. FIG.

4A, a KrF light source photomask 100a having a phase reversal film pattern 110 formed on its surface with a transmittance of 6% with respect to transmitted light is irradiated with light of a KrF light source and light of an ArF light source The transmittance of light at the time of exposure. As shown in the figure, the transmittance of the KrF light source was 6% in the phase reversal film pattern 110, but the transmittance of 0% in the case of the light source of the ArF wavelength.

Referring to FIG. 4B, a mask 100b for an ArF light source having a phase reversal film pattern 120 formed on its surface so as to have a transmittance of 6% with respect to transmitted light is irradiated with light of a KrF light source and light of an ArF light source The transmittance of the ArF light source was 6% in the phase reversal film pattern 120, but the transmittance of the KrF wavelength light was 20%.

However, such a part can compensate the significant difference according to the mask type by applying different energy to the analysis even after the measurement of the aerial image, as the wafer exposure energy varies depending on the mask type in the same pattern size. A comparison of the results obtained by measuring the defects of the actual KrF light source photomask in the aerial image measuring device of the ArF light source and the exposure of the actual KrF light source by the scanner shows that there is no significant difference, .

FIG. 5 is a diagram showing an image of a defect in the scanner exposure of the KrF light source by comparing the aerial image of the ArF light source.

In the figure, the first column from the left shows the serial number of the photomask for the KrF light source, the second column shows the aerial image of the KrF photomask measured using the aerial image measuring device of the ArF light source, The second column shows the image of the pattern implemented on the wafer using the photomask and scanner of the KrF light source, and the third column shows the AIMS simulation results.

As shown, it can be seen that defects have occurred on the wafer in approximately the same pattern as in the aerial image. Thus, even without using the aerial image measuring device of the KrF light source, it is possible to verify the defect of the mask for KrF in advance by using the aerial image measuring device of the ArF light source. This not only improves the productivity of KrF photomask fabrication, but also improves the quality of the mask.

According to the photomask manufacturing method of the present invention described above, it is possible to measure an aerial image of a photomask of two or more wavelengths (ArF, KrF, I-Line) with one wavelength (ArF) equipment. Thus, the efficiency of the equipment is enhanced. In addition, since a single device includes various functions, the necessity of other equipment is reduced, which not only reduces the manufacturing cost of the mask but also provides an advantage of easy management of the equipment. In addition, since the throuput of the equipment of a generation ahead is faster, the production time of the KrF mask can be reduced, and the productivity can be improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

100, 100a, 100b ... Mask 110, 120 ... phase halftone pattern
200 ... lenses 220, 230 ... blades
300 ... wafer 400 ...

Claims (14)

Measuring an aerial image of a photomask for a light source of a second wavelength longer than the first wavelength by using an aerial image measuring instrument using a light source of a first wavelength,
When measuring the aerial image of the photomask for the light source of the second wavelength by using the aerial measuring instrument of the first wavelength, light whose light from the light source is reduced by the ratio of the first wavelength and the second wavelength is irradiated Wherein the numerical aperture (NA) of the diaphragm is controlled so that the numerical aperture (NA) of the diaphragm is adjusted. ◈ Claim 2 is abandoned due to payment of registration fee. The method according to claim 1,
The light source of the first wavelength is an ArF light source,
Wherein the light source of the second wavelength is any one of a KrF and an I-line light source. ◈ Claim 3 is abandoned due to the registration fee. The method according to claim 1,
The light source of the first wavelength is a KrF light source,
And the light source of the second wavelength is an I-line light source. ◈ Claim 4 is abandoned due to the registration fee. The method according to claim 1,
The aerial image measuring equipment includes a diaphragm capable of adjusting a numerical aperture (NA)
Wherein a numerical aperture (NA) of the diaphragm is adjusted when an aerial image of the light source photomask of the second wavelength is measured. delete ◈ Claim 6 is abandoned due to the registration fee. The method according to claim 1,
When measuring an aerial image of a KrF light source photomask using an aerial image measuring instrument of an ArF light source,
(NA) of the diaphragm is controlled such that 70% of the light emitted from the light source is transmitted. ◈ Claim 7 is abandoned due to registration fee. The method according to claim 1,
When the photomask is a phase inversion mask,
Wherein the numerical aperture (NA) of the aperture stop is further reduced in consideration of the transmittance of the phase reversal film of the mask. A method of manufacturing a photomask for verifying an influence of a defect on a photomask by measuring an aerial image formed based on light passed through a photomask from at least one light source,
Preparing an aerial image measuring instrument using a light source of a first wavelength and including a diaphragm capable of adjusting a numerical aperture (NA);
Disposing a photomask for a light source of a second wavelength longer than the first wavelength on one side of the measuring equipment so that the light emitted from the light source is irradiated with light passing through the iris;
(NA) of the diaphragm is adjusted so that light having reduced light from the light source is irradiated to the photomask at a ratio of the first wavelength to the second wavelength, while measuring an aerial image of the transmitted light transmitted through the photomask from the light source ; And
And inspecting the aerial image to verify the effect of the defect in the photomask. ◈ Claim 9 is abandoned upon payment of registration fee. 9. The method of claim 8,
The light source of the first wavelength is an ArF light source,
Wherein the light source of the second wavelength is any one of a KrF and an I-line light source. ◈ Claim 10 is abandoned due to the registration fee. 9. The method of claim 8,
The light source of the first wavelength is a KrF light source,
And the light source of the second wavelength is an I-line light source. delete delete ◈ Claim 13 is abandoned due to registration fee. 9. The method of claim 8,
When measuring an aerial image of a KrF light source photomask using an aerial image measuring instrument of an ArF light source,
Wherein the numerical aperture (NA) of the diaphragm is adjusted so that 70% of the light irradiated from the light source is transmitted. ◈ Claim 14 is abandoned due to registration fee. 9. The method of claim 8,
When the photomask is a phase inversion mask,
Wherein the numerical aperture (NA) of the aperture stop is further reduced in consideration of the transmittance of the phase reversal film of the mask.

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