JP2017072723A - Line width correction method and correction device for photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing variation in line widths caused inside a plane of a photomask, and improving uniformity of line widths inside the plane of the photomask, and a device therefor.SOLUTION: A line width correction method for a light-shielding film of a photomask includes the steps of: locally depositing a film for correction, so as to include a lateral face of a light-shielding film pattern, in an area with a thin line width requiring correction; and etching the area so that the film for correction remains only at a lateral wall of the light-shielding film pattern. The material of the light-shielding film pattern and the material of the film for correction are the same. A line width correction device is provided for the method.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for correcting a pattern line width in manufacturing a photomask used in the photolithography technique, and more particularly, to a method for correcting a pattern having a small line width in a photomask plane, and a correction apparatus therefor.

  In recent years, further miniaturization and higher integration of semiconductor elements are required. A slight variation in the width of the pattern line produced on the photomask greatly affects the wafer transfer accuracy. For this reason, in order to reduce a line width error such as a mask error enhancement factor (MEEF), a photomask which is an original necessary for wafer transfer is also required to produce a fine and accurate pattern. Yes.

  Such variations in line width occur at the stage of development, etching, etc., which are photomask manufacturing processes, but it is difficult to accurately adjust the line width in these processes. A correction technique for adjusting the line width is required.

  In the variation in the pattern line width, for example, an in-plane tendency in only one direction (x direction) as shown in FIG. 1 is observed, but a more complicated in-plane tendency occurs depending on a drawn pattern or a manufacturing apparatus.

  In a conventional line width correction method, for example, Patent Document 1 discloses a technique for adjusting the line width after wafer transfer by changing the transmittance of a light shielding film using a laser. However, in this method, there is a possibility that optical parameters such as a phase difference fluctuate.

  Further, if LER (Line Edge Roughness), which is an index of roughness of the pattern side wall of the photomask, is large, there is a problem that the roughness is traced to the pattern formed at the time of wafer transfer. In addition, fine irregularities formed on the pattern side wall may be detected as defects during inspection of the photomask.

  When correcting the LER, a method of physically cutting with a cantilever or the like used for measurement by an atomic force microscope (AFM) or a method of cutting with a focused ion beam (FIB) can be considered. It takes an enormous amount of time to correct one pattern at a time for many patterns scattered in the mask surface.

JP 2009-153103 A

  The present invention has been made in order to solve the above-described problems, and reduces variations in line width generated in the photomask surface, thereby improving line width uniformity (CDU: Critical Dimension Uniformity) in the photomask surface. It is an object to provide an improved method and an apparatus therefor.

In order to solve the above-mentioned problem, the invention described in claim 1 is a method for correcting a line width of a light shielding film pattern of a photomask, wherein a side surface of the light shielding film pattern is provided in an area having a narrow line width that needs to be corrected. Including a step of locally forming a correction film, and a step of performing etching so that the correction film remains only on a side wall of the light shielding film pattern with respect to the region. This is a mask line width correction method.

  The invention according to claim 2 is the photomask line width correcting method according to claim 1, wherein the material of the light shielding film pattern and the material of the film for correction are the same. is there.

  The invention according to claim 3 is an apparatus for correcting a line width of a light-shielding film pattern of a photomask, which includes a film forming mechanism and an etching mechanism, and is commonly used for the film forming mechanism and the etching mechanism. The film forming mechanism is configured to include a shielding object, and the film forming mechanism is a mechanism for locally forming a film for correction in an area having a narrow line width that needs to be corrected, and the etching mechanism is a light shielding film that needs to be corrected. It is a mechanism for etching so that the correction film remains on the sidewall of the pattern, and the shield forms an opening having the same shape as that of the region having a narrow line width that needs to be corrected or a part thereof, and The photomask line width correcting apparatus is characterized in that the opening can be moved to a position overlapping the area or a position included in the area.

  According to a fourth aspect of the present invention, the film formation mechanism is a mechanism capable of performing film formation by at least one method of sputtering, CVD, or atomic layer deposition. This is a mask line width correcting device.

  The invention according to claim 5 is characterized in that the etching mechanism can perform etching by at least one method of reactive ion etching or etching capable of setting a bias output applied to an object to be etched. A line width correcting device for a photomask according to claim 3 or 4.

  According to a sixth aspect of the present invention, in the photomask according to any one of the third to fifth aspects, the shield is made of a material resistant to the etching of the correction film. This is a line width correcting device.

  The photomask line width correction method of the present invention not only eliminates in-plane line width variations, but can simultaneously reduce LER.

  Since the photomask line width correction method of the present invention is corrected using a film made of the same material as the light shielding film, it can be corrected without changing the optical characteristics.

It is a schematic diagram which shows an example of the photomask which has two area | regions where line | wire widths differ. It is a cross-sectional schematic diagram of the photomask of FIG. It is a cross-sectional schematic diagram which shows the process of correcting the line | wire width of the photomask of FIG. 2 with the method of this invention. It is a schematic diagram which shows the example of the method of forming an opening part with four movable shields.

  In this embodiment, there are two regions 2a and 2b having different line widths of the light shielding film pattern on the photomask as shown in FIG. 1, and the second region 2a is lighter than the light shielding film pattern 3a in the first region 2a as shown in FIG. The case where the line width of the light shielding film pattern 3b in the region 2b is narrow will be described as an example.

The main steps of the correction method of the light shielding film pattern 3b that needs to be corrected are as shown in FIG. First, as shown in FIG. 3A, the light shielding film particles 5 on the first region 2a that do not require correction are shielded by the shielding material 4 so that the light shielding film is not formed.

  In the step of FIG. 3A, a correction film is locally formed on the second region 2b including the light shielding film pattern 3b that needs to be corrected, including the side surface of the light shielding film pattern 3b. At this time, by using a film forming method with high step coverage, the film is formed on the side wall of the light shielding film pattern 3b with good uniformity.

  Examples of a film formation method having high step coverage include an ALD (ALD: Atomic Layer Deposition) method, a sputtering method, and a CVD (Chemical Vapor Deposition) method.

  ALD is a film forming technique that can form a film at a single atom level and has a very high step coverage. When sputtering is used, it is preferable to use a gas pressure condition higher than that of normal film formation because sputtered particles collide with the residual gas and the mean free path is shortened. CVD is a reaction on the surface, and a thin film grows on the surface regardless of the unevenness, so that the step coverage is good. Among the CVDs, plasma CVD capable of forming a film at a low temperature is preferable for this purpose.

  The material of the light-shielding film pattern and the material of the film for correction are preferably the same, but if there is no effect on the photomask characteristics, another material is used because it is advantageous in terms of film formation ease. May be.

  When film formation on the upper surface and side surfaces of the transparent substrate 1 and the light shielding film pattern 3b is completed, a film is locally formed only in the second region 2b as shown in FIG.

  Next, only the correction film attached to the upper surface of the transparent substrate 1 and the upper surface of the light shielding film is etched by using a highly perpendicular etching method while covering the first region 2a with the shield 4. Since the film for correction on the side surface of the light shielding film is removed and remains without being removed, the line width of the modified light shielding film pattern 7 (FIG. 3C) is larger than that in the original state 3b.

  As a highly vertical etching method, dry etching is preferably performed so that a bias applied to an object to be etched is large. More specifically, in RIE (Reactive Ion Etching), self-bias is applied. Etching under low pressure, high power conditions, or ICP (Inductively Coupled Plasma) capable of setting a bias output is preferable.

  As an example of a method of forming an arbitrary correction region using the shield 4, there is a method shown in FIG. 4. This can be applied to a correction region by forming an arbitrary rectangular opening 8 by combining four movable rectangular shields 4 as shown in FIG.

  If the area that requires line width correction is as simple as a square and the line width errors are almost uniform, the opening made from the combination of the shielding objects has the same shape as the correction area and moves to a position that overlaps the correction area. The line width can be corrected by performing film formation and etching.

  On the other hand, when the variation in the pattern line width has a more complicated in-plane tendency, local correction film formation and etching are performed in multiple steps. Specifically, the correction area is divided into a plurality of small areas having a close line width error, an opening having the same shape as each small area is formed, the opening is moved to the position of the small area, and the correction is performed. The target line width correction can be performed by repeating a series of operations for film formation and etching. Needless to say, the small area forms a part of the entire correction area and is included in the entire correction area.

  The shield is sufficiently thicker than the thin film material, but is preferably made of a material resistant to the etching of the correction film in order to avoid the influence on the line width correction.

  In order to produce a photomask using the line width correcting method of the present invention, first, a resist was applied to a photomask blank in a normal process, a pattern was drawn by an electronic drawing apparatus, and a light-shielding film pattern was formed by dry etching. . The light-shielding film was a MoSi-based halftone film, and was prepared so that the phase difference was 185 ° with respect to the exposure wavelength of 193 nm.

  When the line width in the photomask plane was measured using a scanning electron microscope for length measurement, the line width of the light shielding film in the first region was an average of 100 nm. A region of 500 μm × 300 μm was selected as the second region requiring a large correction for the line width error, and the average line width of the light shielding film in the second region was 96 nm.

  Next, using four SUS metal masks as a shield, a square opening of 500 μm × 300 μm was formed and moved to a predetermined position requiring correction.

  The method for forming the light-shielding film for correction in the second region is to use sputtering, and the same halftone material as that of the present example obtained in advance by a preliminary experiment is perpendicular to the step. Sputtering conditions were used such that the film thickness was set to 3: 2.

  In order to adjust the line width of the light-shielding film in the second region to 100 nm, the same halftone material as that of the light-shielding film was used, and a film having a thickness of 3 nm was formed in the vertical direction under the sputtering conditions described above. At this time, the film should be formed with a film thickness of 2 nm on one side.

  Etching was continued with the positions of the four metal masks fixed. In order to etch 3 nm on the upper surface of the light shielding film and the upper surface of the transparent substrate in the vertical direction, an etching process with high verticality is performed using an ICP type dry etching apparatus with a source output of 300 W and a bias output of 50 W. For 2 seconds.

  When the line width of the light-shielding film pattern in the second region after correction was measured using a scanning electron microscope, it was within the target value at 99.5 nm, and it was confirmed that the line width was corrected. Further, when 3σ, which is an index indicating the line width variation of the entire photomask, was measured before and after the correction, it was 2.07 nm before the correction, but became 0.47 nm after the correction, which is an effect of improving the line width variation. Was confirmed.

  Further, when the phase difference was measured with respect to the light-shielding film (in this embodiment, the halftone film) before and after the correction was performed, the phase difference before the correction was 184.11 ° and after the correction was 183.95 °. As a result, there was almost no change in optical characteristics.

  Moreover, since the LER of the pattern before correction was an average of 3.6 nm, the LER after the correction was an average of 3.1 nm, it was confirmed that the LER was improved.

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2a 1st area | region 2b 2nd area | region 3a 1st area light shielding film pattern 3b 2nd area light shielding film pattern 4 Shielding object 5 Shielding film particle 6 Shielding film 7 Modified light shielding film pattern 8 4 Square opening formed by a single movable shield

Claims (6)

A method for correcting a line width of a light shielding film pattern of a photomask,
A step of locally forming a correction film including a side surface of the light-shielding film pattern in an area where the line width that needs correction is narrow;
Etching so that the correction film remains only on the sidewall of the light shielding film pattern with respect to the region;
A method for correcting a line width of a photomask, comprising:   2. The photomask line width correcting method according to claim 1, wherein a material of the light shielding film pattern and a material of the correcting film are the same. A device for correcting a line width of a light-shielding film pattern of a photomask, comprising a film-forming mechanism and an etching mechanism, and comprising a shielding object commonly used for these film-forming mechanism and etching mechanism,
The film forming mechanism is a mechanism for locally forming a film for correction in an area where the line width that needs to be corrected is thin,
The etching mechanism is a mechanism for etching so that the correction film remains on the side wall of the light shielding film pattern that needs to be corrected,
The shield forms an opening having the same shape as the area or a part of the area having a narrow line width that needs to be corrected, and moves the opening to a position overlapping or included in the area. A device for correcting a line width of a photomask, wherein   4. The line width correcting apparatus for a photomask according to claim 3, wherein the film forming mechanism is a mechanism capable of forming a film by at least one of sputtering, CVD, or atomic layer deposition.   5. The photo according to claim 3, wherein the etching mechanism is a mechanism capable of performing etching by at least one of reactive ion etching or etching capable of setting a bias output applied to an object to be etched. Mask line width correction device.   6. The line width correcting device for a photomask according to claim 3, wherein the shield is made of a material resistant to etching of the correction film.