JP2010015000A - Multilevel gradation photomask and method for correcting the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilevel gradation photomask, wherein normal transfer can be performed by preventing abnormality in film thickness, followed by abnormality in transmittance, from occurring when forming a corrected semi-translucent film in a process for correcting the multilevel gradation photomask. <P>SOLUTION: The multilevel gradation photomask includes, on a translucent substrate: a translucent portion; a light-shielding portion; and a semi-translucent portion. In a light-shielding portion, a pattern is formed with a pattern 2a of the light-shielding film; and in a semi-translucent portion, a pattern is formed with a pattern 4a of the semi-translucent film. The pattern 4a of the semi-translucent film has a gradation portion G configured such that the closer to a boundary of the translucent portion the pattern comes, the higher the transmittance becomes in at least part of a boundary region with the translucent portion. Accordingly, the abnormality will not be caused in a correction step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multi-tone photomask and a correction method therefor, and more particularly to avoiding abnormalities at the end of a correction film caused by a conventional correction process.

  The “multi-tone photomask” generally exposes a semi-transparent part that transmits an amount of light corresponding to the transmittance of the semi-transparent film, a light-shielding part that does not transmit light at all by the light-shielding film, and a transparent substrate. It is comprised with a translucent part.

  If a defect such as an abnormal pattern or pattern defect is found in the semi-transparent part in the multi-tone photomask inspection process, a part of the transparent substrate is partially removed by partially removing the region including the defect in the semi-transparent part. The area is exposed, a correction semi-transparent film is formed in a part of the exposed area, and unnecessary correction semi-translucent film is removed, and “defect correction” is performed. Hereinafter, in this specification, the semi-transparent film formed in the photomask forming process is referred to as an “initial semi-transparent film” and a part of the initial semi-transparent film is removed in order to correct a defect. The semi-transparent film is called a “modified semi-translucent film”, and the two are distinguished as necessary.

  6 (a) to 6 (b) and FIGS. 7 (c) to 7 (d) are schematic views for explaining a conventional multi-tone photomask correction process. FIG. 6A shows a part of the pattern of the conventional multi-tone photomask 100. As shown in this figure, the multi-tone photomask 100 includes a translucent portion 101, a light shielding film pattern 102a, and a semi-transparent film pattern 103a (initial semi-transparent film). Here, the defect D exists in the pattern 103a of the initial semi-transparent film of the multi-tone photomask 100.

  FIG. 6B is an enlarged view of the multi-tone photomask pattern showing a state where a part of the semi-translucent portion including the defect D is removed. That is, in order to remove the defect D, the correction region R1 including the defect D (inside the broken line portion in the drawing) is partially removed from the state of FIG. 6A (FIG. 6B). By this step, the defect D is removed and a part of the transparent substrate is exposed.

  Next, as shown in FIG. 7C, the modified semi-transparent film 104 is formed so as to include the removed part, and further, the modified semi-transparent film 104 is unnecessary by irradiating laser light. By removing the portion, a modified translucent film pattern 104a is formed (FIG. 7D). A method of selectively removing the modified semi-transparent film by irradiating laser light is referred to as laser zapping method. The irradiation region of the laser beam is usually rectangular, and it is normal to move the laser beam sequentially while irradiating the laser beam with pulses, but it is not limited to such a method.

  FIG. 7D shows a state where the formation of the modified semi-transparent film pattern 104a is completed. As shown in this figure, the defect D in the semi-translucent portion is completely removed.

  By the way, with the miniaturization of the pattern, in recent years, the uniformity of the transmittance in the semi-translucent portion has become more important. This is because, in the case of a multi-tone photomask, a slight difference in transmittance directly affects the resist film thickness after pattern formation, as compared with a conventional photomask having only a light shielding portion and a light transmitting portion. .

For this reason, conventionally, most attention has been paid to adjusting the transmittance of the initial semi-transparent film and the modified semi-transparent film with respect to the exposure light equally (see, for example, Patent Documents 1 and 2). In other words, it was thought that other problems would not occur if the transmittance could be adjusted and adjusted equally.
JP 2008-058943 A JP 2007-233350 A

  However, in some multi-tone photomasks, although the initial translucent film and the modified semi-transparent film are correctly corrected to have the same transmittance, the corrected multi-tone photomask is used. When gradation exposure was performed and developed, a phenomenon that a defective resist pattern was generated was confirmed. This defective resist pattern has a concern that some patterns may cause a short circuit if left untreated.

  In order to investigate this problem in detail, an analysis of the cross-sectional structure of a modified multi-tone photomask (see FIG. 7D) obtained by a conventional correction method (FIGS. 6 and 7) was performed.

  FIG. 5A is a cross-sectional view taken along line X1-X1 of the modified multi-tone photomask (see FIG. 7D) obtained by the conventional correction method, and FIG. A cross-sectional view of a resist pattern 111a obtained after the exposure and development processes using the multi-tone photomask of a) is shown. As shown in FIG. 5A, it can be seen that the film thickness of the modified translucent film at the pattern edge portion 104b is thicker than the surrounding area.

  The reason why such an abnormal thickness portion is formed in the pattern edge portion 104b of the modified semi-transparent film is not clear, but when the modified semi-transparent film is removed by laser zapping, the edge of the modified semi-transparent film is obtained. This is because the part is heated by the energy of the laser beam and turned up. Such a trace due to laser zapping is referred to as a “laser zapping trace” for convenience in this specification. FIGS. 5A, 7C, and 7D show that laser zapping marks are formed along the locus of laser zapping. Note that zapping marks are a problem when the light-transmitting portion and the semi-light-transmitting portion are adjacent to each other, for example, on the light-transmitting portion such as a source electrode and a drain electrode of a thin film transistor. It is the pattern of the semi-transparent film | membrane of the part performed. Even if a laser zapping mark is formed at the boundary between the semi-transparent part and the light-shielding part, exposure light is literally shielded by the light-shielding part. Therefore, even if a thick film part due to the laser zapping mark is formed in the vicinity, exposure is performed. This is because the influence on the pattern is small.

  FIG. 5B shows a resist pattern obtained by performing exposure and development using this multi-tone photomask. In the example of the resist pattern of FIG. 5B, the resist film thickness is the thickest at the portion corresponding to the light-shielding film pattern 102a having the lowest transmittance, and the film thickness at the portion corresponding to the modified semi-transparent film pattern 104a. Is thinner than the light-shielding film, and the resist is removed from the film thickness in the part corresponding to the transparent part 101 having the highest transmittance, but the resist pattern edge part 114b corresponding to the pattern edge part of the modified semi-transparent film. It can be seen that the film thickness is locally thick. In this portion, the transmittance becomes an “abnormal portion of transmittance” which is smaller than the surrounding transmittance, and thus such a pattern is determined as a defective resist pattern.

  Note that even if laser zapping marks are formed on the light shielding film, the shape of the resist pattern is not affected. That is, it is considered that the influence of the laser zapping mark appears when a local thick film part called a laser zapping mark is formed in the boundary region between the light transmitting part and the semi-light transmitting part.

  The present invention has been made on the basis of such knowledge, and in a correction process of a multi-tone photomask, a necessary range of occurrence of an abnormal portion of transmittance that may newly occur when a corrected semi-transparent film is formed. This is a technical issue.

  In the multi-tone photomask according to the present invention, a translucent part, a light-shielding part, and a semi-translucent part are provided on a transparent substrate, and the semi-translucent part is formed by a pattern of a semi-translucent film, The optical film includes a gradation portion configured to have a higher transmittance as it is closer to the boundary with the light transmitting portion in at least a part of a boundary region with the light transmitting portion.

  With this configuration, the transmittance changes stepwise in the gradation portion, so the photoresist film after pattern transfer is formed thinner as the resist film thickness is closer to the boundary with the light-transmitting portion. The change in transmittance over time becomes moderate. For this reason, it is possible to avoid the transmittance abnormality caused at the periphery of the effective area of the modified semi-transparent film, which is caused when the modified semi-transparent film is formed, and to avoid the abnormal resist film thickness during the transfer exposure. can do.

  The semi-transparent film in the semi-transparent portion includes a first semi-transparent film and a second semi-transparent film formed by a different film formation method from the first semi-transparent film. In addition, it is preferable that the second semi-transparent film is adjusted to be substantially equal to the transmittance of the first semi-transparent film in a region other than the gradation portion.

  Thus, even if the multi-tone photomask according to the present invention is a case where the semi-transparent film is formed by different film forming methods, the transmittance of both is adjusted to the same level, and the pattern edge portion By providing the gradation portion, the transmissivity of the semi-translucent portion becomes substantially uniform in portions other than the pattern edge portion, and formation of an abnormal portion of the transmissivity can be prevented.

  In this case, it is preferable that the film thickness of the semi-translucent film in the gradation portion is made thinner toward the end portion. One of the most effective methods for adjusting the transmittance is to adjust the film thickness. The relationship between the film thickness and the transmittance is expressed by the equations (1) and (2). Qualitatively, the thinner the film thickness, the higher the transmittance, and the thicker the film thickness, the lower the transmittance. .

The transmittance at the unit film thickness L ₀ is T ₀ , the density at the transmittance T ₀ is D ₀ , and the density at the film thickness L is D,
D ₀ = −log T ₀ (1)
D = (L / L ₀ ) · D ₀ (2)

  In the multi-tone photomask according to the present invention, the second semi-transparent film is locally included so as to include a removed region after a part of the first semi-transparent film is removed. It is preferable that the film is formed. In this configuration, the first semi-transmissive film means the initial semi-transmissive film, and the second semi-transmissive film means the modified semi-transmissive film.

  In the multi-tone photomask according to the present invention, the second semi-transparent film is preferably a film formed by a vapor deposition method. Further, the gradation portion can be configured to be obtained by changing the deposition range of the vapor phase growth stepwise.

  As the vapor phase growth method, various methods such as a chemical vapor deposition method and a physical vapor deposition method can be considered. In the case of the chemical vapor deposition method, a film forming method capable of locally depositing in a specific region, such as a photo CVD (chemical vapor deposition) method, is preferable. In an optical CVD apparatus, it is easy to change conditions such as the number of times of light irradiation (pulse frequency) and light irradiation intensity, as compared with other film forming methods. This is because there is an advantage that the modified semi-transparent film can be formed in a stepped shape or a tapered shape by changing the range.

  The multi-tone photomask correction method according to the present invention is a multi-tone photomask correction method in which a transparent portion, a light shielding portion, and a semi-transparent portion are provided on a transparent substrate, A step of exposing a partial region of the transparent substrate by removing a region including a defect in the portion, a modified semi-transparent film is formed so as to include the exposed partial region, and then the modified half-transparent film is formed. Forming a light-transmitting film while shifting an end portion.

  By the above method, it is possible to prevent an abnormal pattern of the semi-translucent portion from being formed at the boundary between the semi-translucent portion and the translucent portion.

  If necessary, a step of selectively removing a part of the modified translucent film by a method such as laser zapping may be further included. This is because when the modified semi-transparent film is removed by laser zapping or the like, the film thickness of the pattern edge portion increases, but the occurrence of a defective resist pattern is avoided by providing the gradation portion. In this sense, it is possible to include a step of selectively removing a part of the modified translucent film within a range where a defective resist pattern is not formed.

  Moreover, it is preferable that the edge part of the said modified semi-transparent film is an edge part of the pattern of the modified semi-transparent film isolated on the source electrode and drain electrode formation area of the thin film transistor which has a source and a drain, and other translucent parts. .

  According to the multi-tone photomask and the defect correcting method according to the present invention, an abnormal pattern causing a defective resist pattern is not formed at the pattern edge portion of the corrected translucent film. Can be prevented.

(Embodiment)
FIGS. 1A to 1B and FIGS. 2C to 2D are schematic views for explaining a correction process for a multi-tone photomask according to an embodiment of the present invention. FIG. 1A shows a part of the pattern of the multi-tone photomask 10 according to the embodiment of the present invention. As shown in this figure, the multi-tone photomask 10 includes a light transmitting portion 1, a light shielding film pattern 2a, and an initial semi-light transmitting film pattern 3a. Here, the defect D exists in the pattern 3a of the initial semi-transparent film of the multi-tone photomask 10.

  Note that this defect D is opposite to a defect in which a semi-transparent film is not formed in a portion where a semi-transparent film is originally to be formed or a film thickness is locally thin (this is a “white defect”). The defect is roughly classified into a defect having a locally high transmittance (this is referred to as a “black defect”). In the correction method according to the present invention, a region including the defect is removed to newly form a film. Since it does, the kind of defect does not ask | require.

  FIG. 1B is an enlarged view of the multi-tone photomask pattern showing a state in which a part of the semi-transparent portion including the defect D (a part of the initial semi-transparent film) is removed. That is, in order to remove the defect D, the correction region R2 (inside the broken line portion in the drawing) including the defect D is partially removed from the state of FIG. 1A (FIG. 1B). By this step, the defect D is removed and a part of the transparent substrate is exposed.

  Next, the modified semi-transparent film 4 is formed so as to include the removed portion. Before that, the modified semi-transparent film forming method according to the present invention will be described with reference to FIG.

  FIGS. 3A to 3C are schematic views for explaining the process of forming the modified semi-transparent film 4 according to the embodiment of the present invention, and FIG. 3A is a modified semi-transparent film on a flat glass substrate. FIGS. 3B and 3C are cross-sectional views taken along lines X2-X2 and Y1-Y1 in FIG. 3A, respectively, illustrating a state where the light-transmitting film 4 is formed.

  As shown in this figure, when the modified semi-transparent film 4 is formed, the deposition is first performed in the widest range, and then the deposition is performed in a slightly narrow range while making the centers substantially coincide with each other. It is changed to deposit. In carrying out the vapor phase growth method, when using an optical CVD apparatus, it is relatively easy to gradually narrow the deposition range.

  In this way, as shown in FIGS. 3A to 3C, the gradation portion G is formed on the entire peripheral edge of the modified semi-transparent film. The gradation part G is configured so that the transmittance is higher as it is closer to the boundary with the light transmitting part. The gradation of the gradation portion G varies depending on the number of scans at the time of film formation. However, the gradation portion G does not necessarily have a smooth taper shape, and may have a relatively rough step shape. On the other hand, in the central portion C formed inside the gradation portion G, conditions such as the film thickness are adjusted so that the transmittance with respect to the wavelength of the exposure light of the exposure apparatus is the same as that of the initial semi-transparent film.

  As shown in FIG. 2C, the modified semi-transparent film 4 having the gradation portion G is formed on the light-shielding film pattern 2a and further irradiated with laser light. By removing unnecessary portions, a modified semi-transparent film pattern 4a is formed (FIG. 2D).

  The laser zapping mark 5 is formed at the site where the modified semi-transparent film is laser zapped, but the laser zapping mark 5 is formed at the site where the gradation portion G is left without performing the laser zapping. Never happen.

  When a modified semi-transparent film is deposited after exposing a part of the transparent substrate in order to remove the defect D, the exposed part is overlapped with an area slightly wider than the initial semi-transparent film. In this way, it may be deposited. This is because it is easy to ensure redundancy and to easily secure the area of the gradation portion G.

  FIG. 2D shows a state where the formation of the modified semi-transparent film pattern 4a is completed. As shown in this figure, the defect D in the semi-translucent portion is completely removed. As described above, the gradation portion G is formed on the entire peripheral portion immediately after the modified semi-transparent film 4 is formed. However, if necessary, unnecessary portions are laser zapped with laser light. FIG. 2D shows that the gradation portion G is left in a part of the pattern 4a of the modified semi-transparent film. However, the laser zapping step may be omitted after a necessary and sufficient film forming range is defined without forming a redundant region when the modified semi-transparent film 4 is formed.

  FIG. 4A is an enlarged cross-sectional view taken along line X3-X3 shown in FIG. On the transparent part 1 where the glass substrate is exposed, a light-shielding film pattern 2a and a modified semi-transparent film pattern 4a are formed, and a gradation part G is formed in at least a part of the boundary region with the light-transmitting part 1. Is shown. Moreover, as shown in this figure, exposure light is irradiated from the back surface side of a glass substrate.

  FIG. 4B shows a cross-sectional view of the resist pattern after exposure and development using the multi-tone photomask shown in FIG. In the example of the resist pattern in FIG. 4B, the resist film thickness is the thickest at the portion corresponding to the light-shielding film pattern 2a having the lowest transmittance, and the film thickness at the portion corresponding to the modified translucent film pattern 4a. Is thinner than the light-shielding film, and the film thickness corresponding to the transparent part 1 having the highest transmittance has all the resist removed, but corresponds to the gradation part G formed at the pattern edge part of the semi-transparent film. In the resist pattern edge portion 14b, the film thickness changes from a stepped shape to a tapered shape.

  As described above, the multi-tone photomask correction method according to the embodiment of the present invention is configured such that, in the process of forming the corrected semi-transparent film, the transmittance is higher as the boundary with the transparent portion is closer. By providing the gradation portion, it is possible to avoid the “abnormal transmittance portion (FIG. 5B) 114b” from being formed in the resist pattern edge portion.

  The present invention has a great industrial applicability with respect to the production of a multi-tone photomask, particularly in that it can provide a technique for improving the accuracy of defect correction.

(A)-(b) is the schematic explaining the correction process of the multi-tone photomask which concerns on embodiment of this invention. (C)-(d) is the schematic explaining the correction process of the multi-tone photomask which concerns on embodiment of this invention. (A)-(c) is the schematic explaining the formation process of the correction semi-transparent film 4 which concerns on embodiment of this invention, Fig.3 (a) is a correction semi-translucent on a flat glass substrate. FIGS. 3B and 3C are cross-sectional views taken along lines X2-X2 and Y1-Y1 in FIG. 3A, respectively, illustrating a state where the film 4 is formed. (A) is an expanded sectional view of the X3-X3 line shown in FIG.2 (d). FIG. 4B is a cross-sectional view of the resist pattern after exposure and development using the multi-tone photomask shown in FIG. (A) is a cross-sectional view taken along the line X1-X1 of the modified multi-tone photomask (see FIG. 7 (d)) obtained by the conventional modification method (FIGS. 6 and 7), and (b) is ( It is sectional drawing of the resist pattern 111a obtained after an exposure and image development process using the multi-tone photomask of a). (A)-(b) is the schematic explaining the correction process of the conventional multi-tone photomask. (C)-(d) is the schematic explaining the correction process of the conventional multi-tone photomask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Transparent part 2a, 102a Light shielding film pattern 3a, 103a Initial semi-transparent film pattern 4, 104 Modified semi-transparent film 4a, 104a Modified semi-transparent film pattern 5, 105 Laser zapping mark 11a, 111a Resist Pattern 14b Stepped or tapered resist pattern edge (corrected pattern)
114b resist pattern edge (abnormal pattern)
R1, R2 correction area G gradation part

Claims (9)

A translucent part, a light shielding part, and a semi-translucent part are provided on a transparent substrate, the semi-translucent part is formed by a pattern of a semi-translucent film, and the semi-translucent film is a boundary with the translucent part A multi-tone photomask having a gradation portion configured so that a transmittance is higher in at least a part of a region as it is closer to a boundary with the light transmitting portion. The semi-transparent film in the semi-translucent portion includes a first semi-transparent film and a second semi-transparent film formed by a film formation method different from the first semi-transparent film, 2. The multi-tone photomask according to claim 1, wherein the second semi-transparent film is adjusted to be substantially equal to the transmittance of the first semi-transparent film in a region other than the gradation portion. 3. The multi-tone photomask according to claim 1, wherein a film thickness of the semi-transparent film in the gradation portion is thinner toward an end portion. 3. The film according to claim 2, wherein the second semi-transparent film is a film locally formed so as to include the removed region after a part of the first semi-transparent film is removed. Multi-tone photomask. 5. The multi-tone photomask according to claim 2, wherein the second semi-transparent film is a film formed by a vapor deposition method. 6. The multi-tone photomask according to claim 5, wherein the gradation portion is obtained by stepwise changing a film formation range of the vapor phase growth. A method for correcting a multi-tone photomask in which a transparent part, a light shielding part, and a semi-transparent part are provided on a transparent substrate, wherein a transparent substrate is removed by removing a region including a defect in the semi-transparent part. And a step of forming a modified semi-transparent film so as to include the exposed partial region, and then forming the modified semi-transparent film while shifting an end portion thereof. A method for correcting a multi-tone photomask including 8. The method of correcting a multi-tone photomask according to claim 7, further comprising a step of selectively removing a part of the modified semi-transparent film. 9. The edge of the modified semi-transparent film is an edge of a pattern of the modified semi-transparent film isolated on the source electrode and drain electrode forming region and other translucent parts of the thin film transistor having a source and a drain. The correction method of the multi-tone mask of description.

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