JP4563101B2 - Mask pattern data correction method - Google Patents

Description

  The present invention relates to a photomask drawing data correction method, and more particularly to a mask pattern drawing data correction method that takes into account variations in mask dimensions during photomask manufacturing.

Conventionally, in order to form a circuit pattern on a semiconductor wafer, a method of transferring the pattern mainly by light reduction projection exposure is used. In recent years, with the miniaturization of device patterns, the pattern dimensions on the wafer are becoming smaller and approaching the optical resolution limit.
In device fabrication, it is necessary to transfer a fine pattern as designed on a wafer with high accuracy. However, along with the miniaturization of device patterns, even if a mask pattern formed according to the design pattern is used, the line width may deviate from the mask pattern due to various factors when the mask pattern is transferred onto the wafer. .

For example, with the miniaturization of the pattern dimension, exposure light diffraction becomes remarkable, and a mask pattern 51 having a right angle 52 on the photomask as shown in FIG. 5A is formed on the semiconductor wafer as shown in FIG. As shown in FIG. 5B, there arises a problem of the optical proximity effect that can be transferred only as a resist pattern image 54 having arcuate corners 53. Also, the optical proximity effect is that when adjacent patterns approach each other, the light passing through the mask pattern interferes with each other, the light intensity between the patterns changes, and the line width of the formed resist pattern deviates from the design value. This is a problem as semiconductor devices are highly integrated and miniaturized.
Therefore, in the transfer process using a mask, in order to reduce the above-described optical proximity effect and improve the rectangularity of the pattern, as shown in FIG. 6, a desired pattern formed on the mask pattern 61 of the photomask. A technique called optical proximity correction (OPC) is used in which an auxiliary pattern 62 that is finer than a desired pattern and has a predetermined shape is formed together with the desired pattern at a desired position such as a corner or a side. (See, for example, Patent Document 1, Patent Document 2, and Patent Document 3.)
However, the optical proximity effect correction techniques described in Patent Documents 1 to 3 are all transferred when the mask pattern is transferred to the photoresist of the wafer when the mask pattern is transferred onto the semiconductor wafer by light exposure. This is a technique related to mask pattern correction related to image enhancement, and the above-described mask pattern correction technique is based on the premise that the mask pattern is accurately formed.

However, in photomask manufacturing, as the mask pattern becomes finer and more highly integrated, there is a problem that the mask pattern cannot be formed according to the design pattern due to various factors. For example, in an electron beam lithography apparatus used in photomask manufacturing, there is a problem that an electron beam resist is not resolved as designed due to the proximity effect due to scattering of electron beams, and a desired resist pattern cannot be obtained. For example, in a rectangular pattern that is often used as a device pattern, with the miniaturization of the pattern, there is a problem that the rectangularity as designed is not obtained, and the corner portion of the mask pattern becomes an arc instead of the original right angle. ing.
In view of this, there has been a proposal to obtain an accurate mask pattern by changing or correcting drawing conditions during drawing with a charged beam such as an electron beam (see, for example, Patent Document 4 and Patent Document 5). .
Japanese Patent Laid-Open No. 58-200288 JP-A-8-248614 JP-A-8-32450 JP-A-9-45600 JP 9-63930 A

  However, the drawing method described in Patent Document 4 aims at forming an auxiliary pattern for correcting the proximity effect of a photomask used in an optical exposure apparatus, and a dose ratio of an energy beam such as an electron beam between a desired mask pattern and the auxiliary pattern This is a drawing method in which the image is appropriately changed and is not intended to improve the rectangularity of the photomask itself. The pattern data correction method described in Patent Document 5 is intended to correct the proximity effect at the time of drawing with a charged beam such as an electron beam. However, the presence or absence of another pattern is determined around the desired pattern, and the presence or absence is determined. This is a method of correcting the subdivided pattern by assigning the exposure amount at the time of each drawing, and has a problem that complicated processing is required.

  The present invention has been made in view of the above-described problems, and assists as drawing data in order to improve the rectangularity of a mask pattern in manufacturing a photomask using a drawing apparatus using a charged beam such as an electron beam. An object of the present invention is to provide a versatile and practical mask pattern drawing data correction method by determining a pattern correction amount.

  The present inventor has found that in the photomask manufacturing process, the major factor that reduces the rectangularity of the mask pattern of the photomask is more dominant in the dry etching process of the light shielding film than in the process of developing a resist such as an electron beam resist. The present invention has been completed with a focus on clarifying a correction amount determination method at the time of heading and light-shielding film dry etching.

The mask pattern data correction method according to claim 1 of the present invention is a mask pattern data correction method comprising an auxiliary pattern for correcting variations in mask pattern dimensions when manufacturing a photomask. A resist film is formed on the provided photomask blank, and using the drawing data before the auxiliary pattern is inserted, the resist film is patterned with a charged beam, and the resist film on which the pattern is drawn is developed to form a resist pattern. Forming and measuring a dimension of the resist pattern; dry etching a photomask blank provided with the resist pattern; removing the resist pattern to form a light shielding film pattern; and measuring the dimension of the light shielding film pattern The resist pattern dimension and the light shielding film pattern Possess calculating a difference between the law, and creating drawing data has been inserted an auxiliary pattern to a side dimension of the 1/2 of the difference between the calculated pattern size, and the mask pattern is rectangular the shape, the drawing data inserting the auxiliary pattern and is characterized that you have a rectangular auxiliary patterns are provided at the corners of the four corners of the mask pattern.

The mask pattern data correction method according to claim 2 of the present invention is characterized in that the rectangular auxiliary pattern is in contact with corners and vertices of four corners of the mask pattern.

The mask pattern data correction method according to claim 3 of the present invention is characterized in that the mask pattern is a contact hole.

According to the present invention, by measuring the pattern dimensions after resist development and after light-shielding film dry etching, the auxiliary pattern correction amount on the drawing data can be easily improved to improve the mask pattern rectangularity in photomask manufacturing. It becomes possible to decide.
Further, the auxiliary pattern correction amount of the present invention is determined by the shift amount of the pattern dimension after resist development and after the light shielding film dry etching, and does not depend on the size of the mask pattern, thereby facilitating pattern correction. A high-precision mask can be manufactured at low cost.
Furthermore, since the mask pattern data correction method of the present invention is defined by the shift amount of the pattern dimension CD, it can be applied without depending on the blank material.

Hereinafter, the mask pattern data correction method of the present invention will be described with reference to the drawings in the case where a representative electron beam is used as a charged beam.
FIG. 1 is a flowchart showing the steps of the mask pattern data correction method of the present invention.

As shown in step S1 of FIG. 1, using a drawing data before inserting an auxiliary pattern, a resist film coated and formed on a mask blank provided with a light shielding film on a transparent substrate is drawn with an appropriate exposure amount. As the drawing apparatus, an electron beam drawing apparatus generally used in photomask manufacturing is suitable, and the appropriate exposure amount is determined by the above drawing apparatus with an exposure amount suitable for a resist such as an electron beam resist to be used and after development. This means the exposure amount at which an optimum resist pattern can be obtained.
As the transparent substrate, optically polished low expansion glass, synthetic quartz glass, or the like is used. As the light shielding film, chromium, a two-layer structure film of chromium and low reflection chromium, other light shielding film materials, or the like is used. In the invention, a mask blank usually used for mask manufacturing can be applied.

Next, the patterned resist film is developed, and the pattern dimension of the resist pattern after development (hereinafter referred to as resist CD: CD: Critical Dimension) is measured (step S2 in FIG. 1).
FIG. 2A is a top view showing a state in which a resist CD (resist CDx; resist Cdy) in the X and Y directions of a rectangular resist pattern is measured, and a case where the inside of the rectangle is an opening. Illustrated.
As the resist, a negative-type or positive-type electron beam resist having resistance to dry etching, which is generally used for manufacturing a photomask, can be applied. For CD measurement, a micro-dimension measuring device for a photomask is used.

Next, the light shielding film of the mask blank is dry-etched, and after the resist pattern is removed, the pattern dimension of the light shielding film pattern (hereinafter referred to as the light shielding film CD) is measured (step S3 in FIG. 1). In the fine pattern targeted by the present invention, wet etching is not a preferable method because the amount of side etching increases, and dry etching is generally used.
FIG. 2B is a top view showing a state in which the light shielding film CD (light shielding film CDx; light shielding film Cdy) in the X and Y directions of the rectangular light shielding film pattern is measured, and the inside of the rectangle is an opening. Indicates the case.

Next, a difference in pattern dimension (ΔCD) between the resist CD after development and the light-shielding film CD after dry etching is calculated (step S4 in FIG. 1). That is,
ΔCD = light shielding film CD−resist CD
Ask for. Since side etching is usually performed during etching, the light shielding film CD has a larger value than the resist CD.
FIG. 2C is a top view showing a state in which a rectangular resist pattern and a light shielding film pattern are overlaid, and the dimensional difference between the two patterns is ΔCD.

  Next, the shape and dimensions of the auxiliary pattern are set. Since the pattern of the semiconductor device is often rectangular, the auxiliary pattern according to the correction method of the present invention is also preferably rectangular, and the dimension of one side is set to ΔCD / 2 at the corners of the four corners of the rectangular mask pattern. Drawing data provided with a rectangular auxiliary pattern is created.

FIG. 3 is an explanatory diagram of drawing data in which an auxiliary pattern 32 is provided on the mask pattern 31. As drawing data, a rectangular auxiliary pattern having sides of ΔCD / 2 provided at the four corners of the mask pattern is represented by a mask. It shows a state in contact with the pattern at each vertex.
When the mask pattern is a square pattern such as a contact hole, the X direction and the Y direction are targets, and the dimensional shift amount during dry etching is generally the same in the X direction and the Y direction. The same numerical value can be used.
As described above, the mask pattern data correction including the auxiliary pattern according to the present invention is performed by creating the drawing data in which the rectangular auxiliary pattern having a side dimension of ΔCD / 2 is inserted (step S5 in FIG. 1). ).

  In the present invention, it is possible to overlap the mask pattern and the auxiliary pattern around the corners of the drawing data as drawing data. For example, the auxiliary pattern can be overlapped by several tens of percent. However, the overlapping process complicates the processing of the drawing data, which may cause a problem that the pattern accuracy at the time of drawing is lowered. Therefore, in the present invention, in the drawing data, it is more preferable that the rectangular auxiliary patterns provided at the four corners of the mask pattern are in contact with the mask pattern at each vertex.

A mask with excellent rectangularity is obtained by drawing a photomask blank on which a resist film has been formed with a predetermined exposure amount using the corrected drawing data and performing a subsequent dry etching step and resist stripping step. A photomask having a pattern can be obtained.
Since the present invention corrects the mask pattern data side, no trace of the auxiliary pattern is recognized in the obtained photomask, and a mask pattern with good rectangularity can be obtained.

As described above, in the present invention, the difference in pattern dimensions after development of the resist and after dry etching of the light shielding film is measured, and drawing data having an auxiliary pattern with one half of the auxiliary pattern as one side is created. Thus, it is possible to easily determine the auxiliary pattern correction amount on the drawing data for improving the rectangularity of the mask pattern in photomask manufacturing.
Further, the auxiliary pattern correction amount of the present invention is determined by the shift amount of the pattern dimension CD, and does not depend on the desired mask pattern size, which facilitates pattern correction and manufactures a high-precision mask at a low cost. It becomes possible to do.

Although the above description has been given of the case where electron beam lithography is performed using an electron beam resist, the present invention can also be applied to the case where other charged beam lithography such as an ion beam is used.
The mask pattern data correction method of the present invention can also be applied to a phase shift mask.

  A photomask blank in which a two-layer chromium light-shielding film of an 80 nm thick chromium thin film and a 40 nm thick low-reflection chromium thin film is formed on an optically polished 6-inch square high-purity synthetic quartz glass substrate is prepared. A chemically amplified resist (FEP-171 manufactured by Fuji Film Arch Co., Ltd.) was applied as an electron beam resist by a spin coating method to prepare a blank having a resist film formed thereon.

Next, using a contact hole as a mask pattern, using the drawing data before insertion of the auxiliary pattern on the substrate, drawing was performed with an electron beam drawing apparatus (JBX-3030MV, manufactured by JEOL Ltd.) at an acceleration voltage of 50 kV. The contact holes used in this example were formed with several types of contact holes having different side dimensions.
Next, post-exposure baking was performed, followed by development with a resist-dedicated developer and rinsing with pure water to form a contact hole resist pattern.
Next, when the CD (resist CD; CDx, CDy) of the resist pattern was measured by a mask micro-dimension measuring apparatus (HULON: EMU-220), both Cdx and CDy were 400 nm.

  Next, the chromium light-shielding film exposed from the opening of the resist pattern is dry-etched with an etching gas containing chlorine gas as a main component by a dry etching apparatus (manufactured by UNAXIS: VLR-700), and then remains. The resist film was removed by ashing with oxygen plasma to form a light shielding film pattern of contact holes. Next, the CD (light-shielding film CD; CDx, CDy) of this light-shielding film pattern was measured using the same mask micro-dimension measuring apparatus as described above, and both CDx and CDy were 432 nm.

  Next, when a difference (ΔCD) between the light shielding film CD and the resist CD was obtained, a value of ΔCD = 32 nm was obtained in both the x direction and the y direction.

  Next, drawing data was created by inserting a square auxiliary pattern having a side of ΔCD / 2 (16 nm) at the four corners of the mask pattern so as to be in contact with the mask pattern at each vertex.

  Next, using the drawing data after inserting the auxiliary pattern, a photomask blank coated with an electron beam resist is drawn with an electron beam under the same conditions as described above, developed, and the light shielding film is etched with a dry etching apparatus. The pattern was removed to obtain a photomask with improved rectangularity at the corners of the mask pattern.

(Comparative example)
As a comparative example, an ordinary photomask was manufactured by the same process as described above using drawing data without data correction in which no auxiliary pattern was inserted.

In this embodiment, in order to compare and evaluate the rectangularity between the photomask produced by using the drawing data obtained by correcting the mask pattern data of the present invention and the normal mask using drawing data without data correction, Several types of contact holes with different dimensions were prepared, and the contact hole area ratios were compared. Conventionally, for the evaluation of rectangularity, there is a method of comparing by the radius of the inscribed circle of the rectangular pattern, but since the measurement error is large, in this embodiment, the comparison was made by the method of obtaining the “area ratio” below.
Area ratio = contact hole area / CDx × CDy
In both of the examples and the comparative examples, CDx was equal to CDy.

  FIG. 4 shows a comparison of the area ratio (Ratio) with respect to the target CD (Target CD: unit nm) of the contact hole of the mask according to the present invention and the normal mask with data correction. When the target CD is 700 nm or less, the area ratio (solid line) of the mask of the present invention is always higher than the area ratio (dotted line) of the normal mask, and the mask pattern correction method of the present invention improves the rectangularity of the mask pattern. It was shown that there is a sufficient effect. Further, as described above, it is shown that the mask pattern correction method of the present invention can easily manufacture a high-precision photomask without handling complicated calculations and a large amount of data and without depending on the pattern size. It was done.

It is a flowchart which shows the step of the mask pattern data correction method of this invention. It is a figure explaining the method of determining the correction value of the mask pattern data correction method of this invention. It is explanatory drawing of the correction method which provided auxiliary pattern data in the rectangular mask pattern data for drawing of this invention. It is the figure which compared the area ratio of the contact hole of the mask by the mask pattern data correction method of this invention shown in an Example, and a normal mask. It is a figure explaining an optical proximity effect. It is an upper surface schematic diagram of the conventional photomask which carried out optical proximity effect correction.

Explanation of symbols

31 Mask pattern 32 as drawing data 32 Auxiliary pattern 51 as drawing data Mask pattern 52 Right-angle corner 53 Arc-shaped corner 54 Resist pattern image 61 on semiconductor wafer Mask pattern 62 Auxiliary pattern

Claims (3)

In a mask pattern data correction method provided with an auxiliary pattern for correcting variations in mask pattern dimensions during photomask manufacturing,
Forming a resist film on a photomask blank provided with a light-shielding film on a transparent substrate, and using the drawing data before inserting an auxiliary pattern, patterning the resist film with a charged beam; and
Developing the patterned resist film to form a resist pattern, and measuring the dimensions of the resist pattern;
Dry etching the photomask blank provided with the resist pattern, removing the resist pattern to form a light shielding film pattern, and measuring the dimensions of the light shielding film pattern;
Calculating a difference between the resist pattern dimension and the light-shielding film pattern dimension;
Creating drawing data in which an auxiliary pattern having one side dimension of a value of 1/2 of the calculated pattern dimension difference is inserted;
I have a,
The mask pattern is rectangular, the drawing data inserting the auxiliary pattern, the mask pattern data correcting method rectangular auxiliary pattern is characterized that you have provided at the corners of the four corners of the mask pattern. The mask pattern data correction method according to claim 1 , wherein the rectangular auxiliary pattern is in contact with corners and vertices of four corners of the mask pattern. 3. The mask pattern data correction method according to claim 1, wherein the mask pattern is a contact hole.

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