JP2018124466A - Defect correction method of phase shift mask - Google Patents

Abstract

A defect correction method for a phase shift mask is provided. Step S1 of measuring a position and size of a defect portion with respect to a photomask substrate having a pattern including a defect portion formed of a phase shift film on a transparent substrate; A step S2 for determining whether or not the size of the defect portion is 1.0 μm × 1.0 μm or more, and a step P2 for depositing a light shielding film on the defect portion when the determination result is NO. It is characterized by that. [Selection] Figure 1

Description

  The present invention relates to a method for correcting defects generated in a phase shift mask used mainly in the manufacture of flat panel display devices, and a photomask having defects corrected.

  A phase shift mask (PSM) is a photomask whose resolution is improved by a phase shift effect. A phase shift film used for a phase shift mask is usually a semi-transmissive film having a transmittance of about 1 to 10 [%] and an effect of inverting (or shifting) the phase.

  In general, in the case of a so-called binary mask in which only a light shielding film pattern is formed on a transparent glass substrate, a region including a defect is locally shaped and removed (trimmed) by laser zapping, or the light shielding film is formed by a photo-CVD method or the like. A technique for locally depositing a light-shielding film on a shaped and removed part or a pattern defect (hereinafter, the pattern defect may be referred to as a white defect) has been established with relatively high positional accuracy. Correction was possible according to the size and type of the defect.

In Patent Document 1, in a defect correction method for a phase shift photomask having a light shielding pattern and a phase shifter pattern, a light shielding layer and a phase shift layer are patterned and formed at predetermined positions, and then laser light is applied to a missing portion of the phase shifter pattern. A defect correcting method for a phase shift photomask is disclosed, in which a SiO ₂ film is selectively deposited by the photo CVD method used. Patent Document 2 discloses a defect correction method for a gray tone mask.

JP2009-020312 JP2008-216346 JP2014-074827

  However, the phase shift mask applied to the flat panel display device is a special film in that the two parameters of the transmittance and the phase shift amount are controlled by the film thickness. . In the experiments of the present inventors, in order to correct a disconnection defect (2.0 μm × 4.0 μm) of a 2.0 μm width line pattern as shown in the optical reflection image of the photomask in FIG. When a light-shielding film of the same size was deposited by the CVD method, the line width at the corrected portion was locally narrowed as shown in the SEM image after exposure as shown in FIG. I could not. In another experiment in which the light shielding film was replaced with a phase shift film, the line width was further reduced. This indicates that correction of the phase shift film is extremely difficult.

  That is, even if the defect portion can be shaped and removed accurately by laser zapping, a phase shift film having exactly the same optical characteristics as the surrounding film in the phase difference and transmittance is deposited at that position with accurate position accuracy. It was extremely difficult.

  This reason is mainly due to the difference in the deposition method of the phase shift film and the defect correction film. That is, the phase difference is controlled by the film thickness, but the deposition method is different between the phase shift film and the defect correction film, and strictly speaking, the composition is also different, so the phase difference is not necessarily the same even if the film thickness is the same. Because it will not be.

  When a film having different optical characteristics is deposited on the defective portion of the pattern, there is a difference in the light interference effect between the surrounding phase shift film and the deposited film formed on the defective portion, which is formed by transfer exposure. Pattern formation defects were likely to occur in the pattern.

  In view of the above problems, it is a primary object of the present invention to provide an optimal defect correction method according to the size and type of a defect.

  In the first phase shift mask defect correcting method according to the present invention, the position and size of a defect portion are measured with respect to a photomask substrate having a pattern including the defect portion formed of a phase shift film on a transparent substrate. Step S1, determining whether the size of the defective portion on the phase shift film is 1.0 μm × 1.0 μm or more, and if the determination result is NO, And a step P1 of depositing a light-shielding film filling the defect portion.

In the second phase shift mask defect correcting method according to the present invention, the position and size of a defect portion are measured with respect to a photomask substrate having a pattern including the defect portion formed of a phase shift film on a transparent substrate. Step S1, step S2 for determining whether or not the size of the defect on the phase shift film is 1.0 μm × 1.0 μm or more, and if the determination result in step S2 is YES, In step S3 for determining whether or not there is a disconnection, and the determination result in step S3 is NO (that is, no disconnection),
A step P2-1 of depositing a light shielding film in a rectangular shape while overlapping with a pattern edge portion of the phase shift film adjacent to the defect portion;
A step P2-2 of shaping and removing the phase shift film around the defect portion into a rectangular shape so as to include only the other defect portion while leaving the non-disconnected pattern edge portion in the defect portion,
The overlap width O (O1, O2) is set to 1.0 μm or less.

In the third phase shift mask defect correcting method according to the present invention, the position and size of the white defect are measured with respect to a photomask substrate having a pattern including a white defect formed of a phase shift film on a transparent substrate. If the determination result in step S1, the step S2 for determining whether the defect size on the phase shift film is 1.0 μm × 1.0 μm or more, and the determination result in the step S2 is YES, further disconnection Step S3 for determining whether or not, and when the determination result of Step S3 is YES (that is, disconnection),
A step P3-1 of depositing a light shielding film in a region T that includes the defect portion and covers the defect portion while overlapping with an edge portion of the single-layer phase shift film adjacent to the defect portion;
A step P3-2 of shaping and removing the light shielding film with an error Δt of 0.1 μm ± 0.1 μm of the pattern width before the pattern width before correction;
Including
The overlap width O (O3, O4) is 1.0 μm or less.

  The first to third phase shift masks described above are based on the premise that the pattern of the phase shift mask film is directly formed on the transparent substrate, but the pattern of the light shielding film is formed on the transparent substrate. The defect correction method of the present invention can also be applied to an “edge-enhanced phase shift mask” (Patent Document 3) in which a phase shift film is deposited on the pattern of the light-shielding film, particularly at the pattern edge portion. is there.

  According to the present invention, it is possible to correct a defect even for a phase shift mask that is inherently difficult to correct.

The flowchart which shows the procedure of the defect correction method of the phase shift mask by 1st Embodiment. The top view and sectional drawing of a phase shift mask which show a mode that the pinhole defect by 1st Embodiment was formed The top view and sectional drawing of a phase shift mask which show a mode that correction of the pinhole defect by 1st Embodiment was completed The top view and enlarged plan view of the phase shift mask which show a mode that the non-disconnection defect by 1st Embodiment was formed The top view and enlarged plan view of the phase shift mask which show a mode that the correction | amendment of the unbroken defect by 1st Embodiment was completed The top view and enlarged plan view of the phase shift mask which show a mode that the disconnection defect by 1st Embodiment was formed The enlarged plan view of the phase shift mask which shows a mode that correction of the disconnection defect by 1st Embodiment was completed The optical reflection image of the phase shift mask and the pattern after exposure (pinhole defects: A, B, non-breaking defects C, D) showing that the defect correction according to the first embodiment is completed. Optical reflection image of phase shift mask showing a state where correction of disconnection defect according to the first embodiment is completed (when overlap is insufficient: A, when overlap is excessive: B) Optical reflection image and post-exposure pattern of phase shift mask when disconnection defect is corrected by conventional method

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, none of the following embodiments gives a limited interpretation in the recognition of the gist of the present invention. The same or similar members are denoted by the same reference numerals, and the description thereof may be omitted.

(First Embodiment)-Basic Concept of the Present Invention (Modification of Single Layer PSM)-
FIG. 1 is a flowchart showing a procedure for correcting a defect of a phase shift mask according to the first embodiment of the present invention. The defect correction in the present invention refers to correction of a white defect unless otherwise specified. However, in order to simplify the description, the phase shift mask will be described on the assumption that a single-layer phase shift film pattern is formed on a transparent substrate. The embodiment will be described.

1. Correction of pinhole defects (first correction method)
When correcting a pinhole defect, first, the target photomask substrate is put on an inspection machine, and the position and size of the defect portion are measured (step S1). Next, it is determined whether or not the size of the defective portion on the phase shift film is 1.0 μm × 1.0 μm or more (step S2). If the determination result is NO (that is, if the size of the defect portion is equal to or smaller than a predetermined value, as a process 1 (P1), a means such as a photo-CVD method can be used to specify the position of the film on the defect portion, A light shielding film having substantially the same size is deposited so as to fill the defect portion.

  Here, the determination result in step S2 is NO, which means that the defect portion formed on the pattern formed of the phase shift film is a minute white defect called a so-called pinhole defect. . In this case, since the influence on the exposure is inherently small, if the periphery including the defect is shaped and removed (trimmed) by the laser zapping process, the optical characteristics are adversely affected. Therefore, trimming is not performed, and step P1 for depositing a light shielding film on the defective portion is performed as it is, and then only the film formation residue is removed as necessary. As a result, minute white defects formed on the pattern formed by the phase shift film are covered with a light-shielding film having a large film thickness. Even if the defect portion of the film is replaced with a light-shielding film, the exposure is hardly affected.

  Removal of the film-forming residue is not necessary in correcting pinhole defects. However, as will be described later, in the “defect related to the edge”, a trimming process in accordance with the peripheral edge is required.

  The light-shielding film used here may have an optical density of 3.0 or more. For example, a chromium film is preferable, but is not limited to this. The material may be used. In addition, when selecting a light-shielding film to be locally formed in a region including a defective portion, it is preferable to appropriately select a material in which a residue is difficult to remain when evaporated by a subsequent laser zapping process.

  Note that “the effect on exposure hardly occurs” should be discussed on the premise of the wavelength of exposure light and the target line width. Forming a pattern with a minimum line width of about 2 μm to 3 μm on the premise of exposure light composed of mixed light or monochromatic light of h-line, i-line (ultraviolet light of wavelength 365 [nm] to 436 [nm]) It is assumed. Under this assumption, a pinhole defect having a size of 1.0 μm × 1.0 μm or less exceeds the resolution limit, so it can be said that “the influence on exposure hardly occurs”. This is a premise common to the present invention, including defect correction methods for the second and third phase shift masks described later.

  In addition, when a film-forming residue (film shift of the phase shift film) is confirmed as an independent dot-like defect in the defective part, it is preferable to shape and remove the film-forming residue by a known method such as a laser zapping process. .

  FIG. 2A is an enlarged plan view showing a state in which the pattern of the phase shift film 12 is formed on the transparent substrate 11 such as synthetic quartz glass. The phase shift film is a semi-transmissive film having a transmissivity of about 1 to 10 [%] as a typical value and having the effect of inverting or shifting the phase, and the pattern is a typical line and space pattern. Is shown. However, an actual pattern is not necessarily such a pattern, and is not limited to a line-and-space pattern. A pinhole defect d1 of 1.0 μm × 1.0 μm or less exists on the pattern of the phase shift film 12.

  FIG. 2B is a cross-sectional view taken along line XX in FIG. It can be seen that the pinhole defect d1 having a diameter L1 formed on the phase shift film 12 reaches the transparent substrate 11. A photomask inspection machine measures the position and size of defects using an optical technique. Usually, when inspecting a single-layer semi-transmissive film, the result of transmitted illumination is given priority. Even if a defect is confirmed by reflected illumination, correction is not required if it is not transmitted by transmitted illumination. Then, if it is determined by the transmitted illumination that the pinhole defect has a size of 1.0 μm × 1.0 μm or less, a light shielding film is locally deposited only on this portion by the photo-CVD method, and FIG. The state shown in FIG. 3B is reached, and the defect correction ends.

  Even if the light shielding film is formed in a part of the portion where the phase shift film is to be formed, since the size thereof is less than the resolution limit of the exposure machine, there is almost no influence after the exposure, rather, The defect is corrected more than when the pinhole defect is left as it is.

  FIG. 8A shows an optical reflection image of a single-phase phase shift mask including white defects (pinhole defects) having a size of 1.0 μm × 1.0 μm, and FIG. The SEM image which observed the pattern after the exposure after applying this correction method is shown. The pattern after exposure could be corrected almost normally by correcting the size equal to the defect size with the light shielding film without performing trimming.

2. Correction of non-breaking defects (second correction method)
When correcting a non-breaking defect, it is a case where the determination result of the above step S2 is YES (size is 1.0 μm × 1.0 μm or more), and further, step S3 for determining whether or not it is disconnected is necessary. It becomes. Here, with regard to the distinction between “disconnected” and “non-disconnected”, it is realistic to set the following criteria.

  FIG. 4A shows a pattern having a phase shift film defect d2 on the line pattern. FIG. 4B is an enlarged view around the deficient portion d2 surrounded by the alternate long and short dash line in FIG. Although the size of the defective portion d2 exceeds 1.0 μm × 1.0 μm, the pattern width Lr in the portion where the pattern is narrowest in the vicinity of the defective portion with respect to the pattern width Lo remains at 1 μm or more, so that the disconnection has occurred. Judge that there is no.

  If the determination result in step S3 is NO (that is, no disconnection), the light shielding film is deposited in the region T while overlapping the pattern edge portion of the phase shift film adjacent to the deficient portion d2 (step P2-1). . At this time, the overlap width O (O1, O2) is set to 1.0 μm or less.

  Next, as shown in FIG. 5, the phase shift film around the defect portion is shaped and removed in a rectangular shape so as to include only the other defect portion while leaving the pattern edge portion on the non-breaking side in the defect portion. (Step P2-2). This step is called trimming. In FIG. 4B, a region Z to be trimmed is shown by a broken line. As shown in FIG. 5B, the defect correction is completed by shaping and removing the light-shielding film in a rectangular shape so as to include the defect portion of the white defect while remaining as the remaining portion R. Needless to say, it is necessary not to remove adjacent patterns during trimming.

  As described above, when the target pattern is a pattern including a non-disconnection defect, a reference for distinguishing between “non-disconnection” and “disconnection” is provided in advance. In the above-described example, when the size of the pattern width Lr (distance from the end of the pattern to the end of the defective portion) other than the defective portion is 1 μm or less, even if an unbroken portion remains, “ It is determined as “disconnection”, and “correction of disconnection defect” (third correction method) described later is applied. The point here is that even if there is a defect portion with a defect size exceeding 1.0 μm × 1.0 μm on the pattern, the pattern has a pattern width of at least 1 μm or more. In order to repair the portion, a light-shielding film having a transmittance of 0 is embedded.

  However, because it cannot be said to be a line pattern, such as an electrode pattern, it may not always be appropriate to distinguish between “disconnected” or “non-disconnected”, but this correction method is based on the size of the missing part and the remaining part. Is applicable. That is, the present correction method can be applied if there is a defect portion with a defect size exceeding 1.0 μm × 1.0 μm and the pattern remains 1 μm or more.

  FIG. 8C shows an optical reflection image of a single-layer phase shift mask including white defects (non-disconnection defects) having a size of 2.0 μm × 2.0 μm, and FIG. The SEM image which observed the pattern after the exposure after applying this correction method is shown. By forming a film so as to cover the defective part and trimming only the left edge of the defective part, the line width can be corrected to be equal to the normal part. As described above, with respect to the non-breaking defect of the phase shift film, the defect can be corrected by trimming only one side where the pattern width is secured while replacing the defect portion with the light shielding film. Strictly, a thinning of about 20 nm was confirmed by exposure with the modified photomask, but the effect was slight and it was at a level that would not cause a problem in practice.

3. About disconnection defect correction (third correction method)
When correcting the disconnection defect, the determination result of step S2 is YES (size is 1.0 μm × 1.0 μm or more), and further, step S3 for determining whether or not the disconnection is necessary is necessary. Become. Here, the criterion for determining whether or not “disconnected” is “disconnected” is as described above.

  That is, when the pattern width Lr other than the defective portion is smaller than a predetermined reference value (for example, 1 μm) with respect to the pattern width Lo, not only when it is physically disconnected but also when it is not completely disconnected. Is determined to be “disconnected”.

  FIG. 6A shows a pattern having a phase shift film defect d3 on the line pattern. FIG. 6B is an enlarged view around the deficient portion d3 surrounded by the alternate long and short dash line in FIG. The defect d3 exceeds 1.0 μm × 1.0 μm and is disconnected. That is, the determination result of step S3 is YES (that is, disconnection).

  At this time, as shown in FIG. 7A, a light-shielding film is deposited in a region T that includes the defect portion d3 and overlaps the pattern edge portion of the phase shift film adjacent to the defect portion while covering the defect portion. (Step P3-1). Trimming may be performed before the light shielding film is deposited. At this time, as shown in the figure, the size of the overlap width O (O3, O4) of the region T and the end E of the defect portion is adjusted to be 1.0 μm or less.

  Next, as shown in FIG. 7B, the defect correction is completed by shaping and removing the edge portions on both sides of the light-shielding film into a rectangular shape while remaining as the remaining portion R. At this time, the pattern is removed so as to remain wider than the pattern width by the width Δt. Since the defect portion of the phase shift film having a large area such as a disconnection defect is replaced with a light shielding film, the magnitude of the difference Δt from the design value of the pattern width greatly affects the line width after exposure.

  The error allowed for the difference Δt from the design value of this pattern width necessary for reducing the thinning or thickening of the pattern after exposure obtained from the experiment is 0.1 ± 0.1 μm, that is, the original The optimum difference from the pattern size was 0.0 μm to +0.2 μm.

  FIG. 9A shows an optical reflection image of a single layer phase shift mask including white defects (disconnection defects) having a size of 2.0 μm × 4.0 μm. In this example, since the overlap was insufficient, leakage light was generated from the gap, resulting in pattern thinning. FIG. 9B shows the overlap width O (O3, O4) as +0.4 μm in a single-layer phase shift mask including white defects (disconnection defects) having a size of 2.0 μm × 4.0 μm. In this case, an optical reflection image is shown. In this case, the local line width is increased.

  Therefore, it is important to ensure overlap when forming the light shielding film and to correct the line width within a predetermined range after the light shielding film is formed.

4). Limit of defect correction The defect that can correct the defect of the phase shift mask with the light shielding film has a limit depending on the size or the site of the defect. The accuracy of the current laser zapping is about 0.1 μm and the line width is assumed to be about 2 to 3 μm. Therefore, if there is a defect portion of 10 μm × 10 μm or more, it is judged as NG, and the phase shift mask is produced again. .

Second Embodiment-Application to Edge-Enhanced Phase Shift Mask-
A two-layer phase shift mask in which a light shielding film pattern is provided on a transparent substrate and a phase shift film is deposited on a portion where the line width is likely to be thin, such as a pattern edge portion (in this specification, “edge-enhanced phase shift mask”) The correction method of the present invention is also applicable.

Since the first light-shielding film is not different from a normal binary mask when the pattern formation of the first light-shielding film is completed, it can be corrected by applying the conventional technique.
The defect correction method described in the first embodiment can be applied to the white defect generated when the second phase shift film is formed.

(Other embodiments)
The correction of the white defect is as described in the first and second embodiments, but the correction of the “black defect” caused by the foreign matter or the film thickness abnormality of the phase shift film is known. After removing the corresponding part by a removal method, for example, laser zapping, artificially forming a “white defect”, the white defect correction method according to the present invention is applied according to the size and part of the white defect. That's fine. The criteria for determining the size and part of the white defect are just as described in the present invention.

  According to the present invention, defects in the phase shift mask that have been difficult to be corrected can be corrected. Therefore, the industrial applicability is extremely large.

11 Transparent substrate 12 Phase shift film d1 Pinhole defect (white defect of 1.0 μm × 1.0 μm or less)
d2 Non-breaking defect d3 Disconnection defect O (O1-O4) Overlap width Δt Difference from design value of pattern width

Claims (8)

  Step S1 of measuring the position and size of the defect portion on the photomask substrate having a pattern including the defect portion formed of the phase shift film on the transparent substrate, and the size of the defect portion on the phase shift film Step S2 for determining whether or not is 1.0 μm × 1.0 μm or more, and, if the determination result is NO, a step P1 for depositing a light-shielding film filling the defect portion on the defect portion A defect correction method comprising: Step S1 of measuring the position and size of the defect portion on the photomask substrate having a pattern including the defect portion formed of the phase shift film on the transparent substrate, and the size of the defect portion on the phase shift film Step S2 for determining whether or not is 1.0 μm × 1.0 μm or more, and if the determination result in Step S2 is YES, Step S3 for determining whether or not there is a disconnection, and Step When the determination result of S3 is NO (that is, no disconnection),
A step P2-1 for depositing a light shielding film in a rectangular shape while overlapping with a pattern edge portion of the phase shift film adjacent to the defect portion;
A step P2-2 of shaping and removing the phase shift film around the defect portion into a rectangular shape so as to include only the other defect portion while leaving the non-disconnected pattern edge portion in the defect portion,
A defect correction method for a phase shift mask, wherein the overlap width O (O1, O2) is 1.0 μm or less. Step S1 of measuring the position and size of a white defect on a photomask substrate having a pattern including a white defect formed of a phase shift film on a transparent substrate; and the defect size on the phase shift film is 1. Step S2 for determining whether or not 0 μm × 1.0 μm or more, and if the determination result in Step S2 is YES, Step S3 for determining whether or not there is a disconnection, and the determination in Step S3 If the result is YES (ie disconnection)
A step P3-1 of depositing a light shielding film in a region T that includes the defect portion and covers the defect portion while overlapping with an edge portion of the single-layer phase shift film adjacent to the defect portion;
A step P3-2 of shaping and removing the light shielding film with an error Δt of 0.1 μm ± 0.1 μm of the pattern width before the pattern width before correction;
Including
A defect correction method for a phase shift mask, wherein the overlap width O (O3, O4) is 1.0 μm or less. A phase shift mask for a photomask in which a pattern of a phase shift film is formed on a transparent substrate,
A phase shift mask including a defect correction film formed of a light shielding film on the pattern. A phase shift mask for a photomask in which a light shielding film pattern and a phase shift film pattern are formed in this order on a transparent substrate,
A phase shift mask including a defect correction film formed of a light shielding film on the pattern.   6. The phase shift mask according to claim 4, wherein the light shielding film is embedded so as to cover a defect portion of the pattern of the phase shift film.   The overlap width between the lower phase shift film and the upper light shielding film when the size of the pattern defect portion is larger than 1.0 μm × 1.0 μm and the pattern defect portion is determined not to be disconnected. 7. The phase shift mask according to claim 6, wherein O (O1, O2) is controlled to 1.0 μm or less.   When it is determined that the defective portion of the pattern is disconnected, the overlap width O (O3, O4) between the lower phase shift film and the upper light shielding film in the defective portion is controlled to 1.0 μm or less. 7. The phase shift according to claim 6, wherein the difference Δt between the width of the light-shielding film deposited in the defect portion and the design value of the pattern width in the defect portion is controlled to 0.1 μm ± 0.1 μm. mask.

Images