JP2010078769A - Selecting method and manufacturing method for photomask blanks, and manufacturing method for photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a selecting method and a manufacturing method for photomask blank in which a photomasks with small change in flatness and shape before and after a pellicle is stuck is manufactured. <P>SOLUTION: The selecting method for photomask blanks selects photomask blanks each having a height difference of ≤0.15 μm between two points symmetrical about the center of the photomask blank as a point of symmetry in an area wherein the pellicle is stuck or a variance of ≤0.20 μm in height at a point on a concentric circle having its center at the center of the photomask blank. Also, the method of manufacturing the photomask blanks by preparing a substrate for a photomask which has a predetermined value of height difference between two optional points symmetrical about the center of the substrate for the photomask as a point of symmetry in the area where the pellicle is stuck or variance in height at the point on the concentric circle having its center at the center of the substrate for the photomask. The manufacturing method for the photomask uses the selected or manufactured one. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a selection method and a manufacturing method of a photomask blank used in a photolithography process in semiconductor device manufacturing and the like, and a photomask manufacturing method using the photomask blank.

  In recent years, with the high integration of integrated circuits such as DRAMs, the demand for miniaturization of circuit design pattern rules is increasing day by day. As the integration of semiconductor devices increases, the demand for miniaturization in the photolithography process has increased, and the device design rules have already been miniaturized to 0.1 μm or less, and the requirement for pattern dimensional accuracy has reached 10 nm or less. ing. As a result, many problems have arisen in processing accuracy in the photolithography process used in the semiconductor manufacturing process.

  One of these problems is the flatness of the photomask used in the lithography process, which is one of the factors involved in increasing the accuracy of the pattern forming process. Along with miniaturization, the depth of focus allowed by the resist is becoming shallower, and it is important that the flatness of the photomask, which is one of the causes of defocusing, is small.

In order to reduce defocusing in lithography, it is necessary to accurately position the mask pattern corresponding to the original image so that the exposure pattern can be drawn at a predetermined position and width within an allowable error during wafer exposure. That is, ideally, it is desired that a light-shielding film pattern, a phase shift film pattern, and the like are formed on a photomask substrate having extremely good flatness.
However, when the photomask is mounted in the wafer exposure apparatus, the photomask is vacuum chucked by chucking the photomask with a vacuum chuck on the mask stage of the wafer exposure apparatus, as disclosed in Patent Document 1. Depending on the surface shape of the part, the entire surface shape of the photomask may be greatly deformed. In order to improve this, Patent Document 1 discloses a method for taking into account the deformation of the photomask due to the chucking in advance by performing a simulation.

  Incidentally, a photomask is generally manufactured through the following steps. That is, first, on a transparent substrate (hereinafter referred to as a photomask substrate), a light shielding film, a translucent film, a phase shift film or the like is formed alone or in combination (in this specification, on this photomask substrate A photomask blank having a film formed in (5) is referred to as a blank film). Next, a resist is applied onto the photomask blanks, a resist film is processed by lithography, a mask pattern is formed using the resist film as an etching mask, and then the resist film is peeled to manufacture a photomask. Thereafter, a pellicle film is formed as a dust-proof cover so as to cover the mask pattern. The pellicle film is a transparent thin film made of nitrocellulose, cellulose acetate, or the like, and is attached to the pellicle frame. The pellicle frame is made of an aluminum alloy, stainless steel, polyethylene, or the like, and is generally made of an aluminum alloy. The pellicle frame is attached to the photomask with an adhesive layer made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin or the like.

  However, even when the flatness of the photomask blank is sufficiently reduced, the mask pattern is formed by lithography, and then the pellicle frame is pasted to deteriorate the flatness of the photomask and distort the mask pattern. There was a thing. Further, when exposure is performed in such a state that the mask pattern is distorted, there is a problem that the exposure accuracy cannot be secured. Furthermore, due to the progress of miniaturization of pattern rules in recent years and the reduction of the depth of focus, the influence of the deformation of the photomask due to the attachment of the pellicle cannot be ignored.

JP 2003-50458 A

  The present invention has been made in view of such a problem, and a method for selecting and manufacturing a photomask blank capable of manufacturing a photomask with a small change in flatness and shape before and after attaching a pellicle, and It aims at providing the manufacturing method of the photomask using the photomask blanks selected or manufactured by these.

  In order to achieve the above object, the present invention provides a method for selecting a photomask blank in which a blanks film is formed on a photomask substrate, wherein the pellicle is attached within the surface on which the blanks film is formed. The photomask blank is selected as a non-defective photomask blank having a point difference of 0.15 μm or less with respect to the center of the photomask blank. A photomask blank selection method is provided (claim 1).

  In such a region where the blank film is formed, in the region where the pellicle is pasted, the height difference between the two points that are point-symmetrical with respect to the center of the photomask blank is any two points. If the photomask blank selection method is to select a photomask blank of 0.15 μm or less as a non-defective product, it is possible to select a photomask blank having a small change in flatness and shape before and after the pellicle is attached. With such a photomask blank, a photomask having a small change in flatness and shape before and after attaching the pellicle can be manufactured.

  Further, the present invention is a method for selecting a photomask blank in which a blanks film is formed on a photomask substrate, and in the region where the pellicle is attached within the surface on which the blanks film is formed, A photomask blank having a height variation at a point on a concentric circle centered on the center of any photomask blank that intersects is 0.20 μm or less on any circle is selected as a non-defective photomask A method for selecting blanks is provided (claim 2).

  In such a region where the blank film is formed, in the region where the pellicle is pasted, the height variation at a point on a concentric circle centering on the center of any photomask blank intersecting with the region is Even in the photomask blank selection method for selecting a photomask blank having a diameter of 0.20 μm or less as a good product even on a circle, a photomask blank having a small change in flatness and shape before and after the pellicle is attached is selected as a good product. be able to.

  In addition, the present invention is a method for manufacturing a photomask blank, and at least as a photomask substrate, any arbitrary point-symmetrical relationship with the center of the photomask substrate in a region where a pellicle is attached as a symmetry point A photomask substrate having a predetermined difference in height difference between two points or a height variation at a point on a concentric circle centered on the center of the photomask substrate is prepared, and a blanks is formed on the surface of the photomask substrate. A photomask blank manufacturing method is provided, wherein a photomask blank is manufactured by forming a film.

  As described above, the photomask substrate is centered on the height difference of two arbitrary points that are point-symmetrical with respect to the center of the photomask substrate in the region where the pellicle is attached or the center of the photomask substrate. If a photomask blank manufacturing method for preparing a photomask substrate in which a variation in height at a point on the concentric circle is a predetermined value and forming a blanks film on the substrate, flatness and before and after attaching a pellicle Photomask blanks having a small shape change can be manufactured. With such a photomask blank, a photomask having a small change in flatness and shape before and after attaching the pellicle can be manufactured.

  In this case, the photomask substrate to be prepared is a photomask substrate in which the height difference between any two points that are point-symmetric with respect to the center of the photomask substrate is 0.15 μm or less. (Claim 4) The photomask substrate to be prepared is a photomask substrate having a height variation of 0.20 μm or less at a point on a concentric circle centered on the center of the photomask substrate. (Claim 5) is preferable.

  In this way, the photomask substrate to be prepared is a photomask substrate or photomask substrate in which the height difference between any two points that are point-symmetrical with respect to the center of the photomask substrate is 0.15 μm or less. If the variation in height at points on concentric circles centered on the center of the substrate is 0.20 μm or less, photomask blanks with less change in flatness and shape before and after the pellicle is attached can be manufactured more reliably. can do.

  According to another aspect of the present invention, there is provided a photomask manufacturing method, wherein the photomask blank selected by any of the above photomask blank selection methods is used to form a mask pattern by lithography to manufacture a photomask. (6) A photomask is manufactured by forming a mask pattern by lithography on the photomask blank manufactured by any of the above-described photomask blank manufacturing methods, and manufacturing the photomask A method is provided (claim 7).

  In this way, a photomask is manufactured using the photomask blank selected by any one of the above photomask blank selection methods or the photomask blank manufactured by any one of the above photomask blank manufacturing methods. For example, a photomask having a small change in flatness and shape before and after attaching the pellicle can be manufactured. In such a photomask, the change in flatness and shape due to the attachment of the pellicle is small, so that the mask pattern as designed can be stably used in the exposure process after the pellicle is attached. .

According to the photomask blank selection method and photomask blank manufacturing method of the present invention, it is possible to select or manufacture a photomask blank that can manufacture a photomask having a small change in flatness and shape before and after attaching a pellicle. .
In addition, according to the photomask manufacturing method of the present invention, a photomask having a small change in flatness and shape before and after the pellicle is attached can be manufactured. With such a photomask, the change in flatness and shape due to the attachment of the pellicle is small, so that the mask pattern as designed can be stably used in the exposure process after the pellicle is attached.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
As described above, even when the flatness of the photomask blank is sufficiently small, the photomask flatness is deteriorated by attaching the pellicle frame after forming the mask pattern by lithography, and the mask pattern. If the mask pattern is distorted as described above, exposure accuracy cannot be ensured.

In particular, when the flatness (TTV, Total Thickness Variation) of the photomask changes by 0.05 μm or more, the shape changes greatly and the influence is large.
Therefore, the present inventor conducted intensive experiments and studies to obtain photomask blanks that do not cause deterioration of the flatness of the photomask and distortion of the mask pattern stably after the pellicle frame is attached.

  In general, when a pellicle is attached to a photomask, the pellicle is deformed so as to be pulled by the shape of the photomask. At this time, the photomask is also deformed by being pulled by the pellicle. The deformation of the pellicle does not affect the image distortion, but the deformation of the photomask greatly affects the image accuracy even with a slight distortion. Therefore, if the pellicle is prevented from being distorted, the photomask will not be deformed. The surface on which the pellicle adheres to the photomask, that is, the surface of the pellicle frame that adheres to the photomask (also referred to as the pellicle surface) is rougher than the photomask, and the adhesive sheet intervenes. The distortion with a local range is not caused by adhesion with the photomask, and the plane is formed on the four sides of the pellicle frame to generate the distortion. This researcher pays attention to this point and uses a symmetrical shape with the center of the photomask as a reference point to cancel out the distortion of each facing pellicle frame, resulting in less distortion in the photomask. Found that you can get.

  In other words, regardless of the shape of the pellicle, if the flatness and shape of the area where the pellicle is to be attached (pellicle attachment area) is controlled by paying attention to its symmetry, the photomask blank can be Thus, it was found that the flatness and shape of the photomask blanks are hardly changed, and exposure with the original pattern can be stably performed.

  The present inventor has further studied based on these findings, and in any region where the pellicle of the photomask blank is to be attached, any two points having a point-symmetrical relationship with the center of the photomask blank as the symmetry point. The inventors have conceived that the flatness of the photomask blanks should be controlled on the basis of the height difference and the height variation at a point on a concentric circle centered on the center of the photomask blanks, and the present invention has been completed.

  Hereinafter, the present invention will be described in more detail with reference to the drawings, but the present invention is not limited thereto.

First, with reference to FIG. 2, the positional relationship of each element used for the definition of the photomask blank etc. in this invention is demonstrated.
FIG. 2A is a cross-sectional view of the photomask blank with the pellicle attached. The photomask blank 10 has a blanks film 12 formed on a photomask substrate 11. The material of the photomask substrate 11 may be any material that is substantially transparent to the exposure wavelength, and specifically, synthetic quartz or the like is used. The blanks film 12 is formed by combining a light shielding film, a translucent film, a phase shift film, or the like alone or in combination.
Moreover, there is no restriction | limiting in particular in the magnitude | size of the photomask blank 10 which can apply this invention, the material of the blanks film | membrane 12, a multilayer structure, a film thickness.

In an actual photomask manufacturing process, a mask pattern is formed on the blank film 12 by lithography or the like, and the pellicle 30 is pasted after forming the photomask. However, in FIG. 2A, the pellicle 30 is attached to the photomask blank 10 for convenience. The state of pasting was shown.
The pellicle 30 is mainly composed of a pellicle film 32 that is a dust-proof film, and a pellicle frame 31 for uniformly stretching the pellicle film 32 and fixing it to a photomask. The pellicle film 32 is made of a transparent thin film made of nitrocellulose, cellulose acetate or the like. The pellicle frame 31 is made of an aluminum alloy, stainless steel, polyethylene, or the like, and is generally made of an aluminum alloy. The pellicle frame 31 is attached to the photomask with an adhesive layer (not shown) made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin, or the like.
The present invention is not particularly limited by the material and dimensions of the pellicle film, pellicle frame, adhesive layer and the like.

FIG. 2B shows a schematic diagram when the surface of the blanks film 12 of the photomask blank 10 is viewed from the pellicle 30 side.
In FIG. 2B, a portion (pellicle attachment region) 51 where the pellicle frame 31 is attached by the adhesive layer is shown. The pellicle attachment area 51 is an area in the photomask blank 10 where the pellicle frame 31 is attached after forming a mask pattern to form a photomask.

The present invention can be applied if the planar shape of the surface of the photomask blank 10 on which the blanks film 12 is formed is such that the center O of the photomask blank 10 can be defined. In the case of a square as shown in FIG. 2B, the center of the photomask blank 10 coincides with the intersection of two diagonal lines (D).
In general, the center of the rectangle formed by the pellicle attaching region 51 is coincident with the center of the photomask blank 10. In general, after the blanks film 12 is formed on the photomask substrate 11, flattening of the photomask substrate 11 and the photomask blank 10 is performed in order to perform a relaxation process such as a heat treatment for relaxing the film stress of the blanks film 12. Sex is almost the same.

  The present invention manages the flatness with the center O of the photomask blank 10 as a symmetric point in the pellicle attachment region 51 of the photomask blank 10. Specifically, there are the following two modes.

(First aspect)
In the pellicle pasting region 51 (the region where the pellicle is to be pasted) 51 of the photomask blank 10, the height difference between the two points that are point-symmetrical with respect to the center O of the photomask blank 10 is arbitrary two points. A small shape is assumed for each set. Specifically, it is 0.15 μm or less, more preferably 0.10 μm or less, for an arbitrary set of two points.
Here, the two points having a point-symmetrical relationship with respect to the center O of the photomask blank 10 as a symmetric point are a set of the point A and the point A ′ as illustrated in FIG. A set of points B ′.

(Second embodiment)
In the pellicle attaching region 51 of the photomask blank 10, the height variation at a point on a concentric circle with the center O of the photomask blank 10 as the center is small. Specifically, for a certain concentric circle, the height variation of all points on the concentric circle is set to 0.20 μm or less so that this condition is satisfied for all concentric circles (ie, diameter). The height variation is preferably 0.15 μm or less.

This is illustrated in FIG. 1 (b).
Circles C ₁ , C ₂ , and C _{3 in} FIG. 1B are concentric circles centered on the center O of the photomask blank 10. Of the points on each of the concentric circles C ₁ , C ₂ , and C ₃ , the portions of the respective pellicle attachment regions 51 (solid line portions of C ₁ , C ₂ , and C ₃ ) need only satisfy a predetermined variation.

  By doing so, it is possible to minimize the amount of deformation of the photomask that occurs when the photomask blank 10 is used as a photomask and the pellicle 30 is attached to the photomask.

  And if it is such a photomask blank 10, the photomask with a small flatness and shape change before and after sticking a pellicle can be manufactured. In such a photomask, the change in flatness and shape caused by attaching the pellicle is small, so that the mask pattern as designed can be stably used in the exposure process after attaching the pellicle. it can.

The photomask blanks 10 having such a shape can be realized by measuring the shape in advance and selecting and using only those having a predetermined shape.
In addition, the shape of such a photomask is measured in advance when manufacturing a photomask substrate, the amount of in-plane polishing for obtaining a predetermined shape is determined, and partial polishing or adjustment of the polishing load is performed. It is also possible to create a predetermined shape. A photomask blank is formed by forming, on such a photomask substrate, a light shielding film and / or a phase shift film mainly containing Cr, metal silicide, and oxygen and nitrogen.

  Note that the light shielding film and the phase shift film may have a multilayer structure such as an antireflection film or an etching stopper. These films generally have stress, and the amount of deformation of the photomask substrate due to the film varies depending on the amount of film remaining (coverage) when the photomask is formed. Therefore, the film stress is preferably as small as possible. In particular, when it is 0.3 GPa or less, the deformation amount of the photomask substrate is suppressed, which is preferable. When it is necessary to use a film having a large film stress, it is preferable to consider the coverage in advance, and it is sufficient that the shape of the photomask when the pellicle frame after pattern formation is pasted has the predetermined shape.

  Furthermore, if the photomask shape when the photomask when the pellicle is formed is chucked to the exposure machine, the photomask shape is less than a predetermined deformation amount, a predetermined flatness can be obtained even if the exposure machine is chucked. Is preferable. Accordingly, the shape of the photomask substrate 11 is considered in advance in consideration of the film stress of the photomask blanks 10 or the blanks film 12 so that the photomask on which the pellicle 30 is formed has a predetermined shape when chucked by the exposure machine. Is more preferable if it is determined in advance.

  ADVANTAGE OF THE INVENTION According to this invention, the photomask blank in which distortion by pellicle sticking was prevented effectively is provided. With such a photomask blank, a photomask having a small change in flatness and shape before and after attaching the pellicle can be manufactured. With such a photomask, the change in flatness and shape due to the attachment of the pellicle is small, so that the mask pattern as designed can be stably used in the exposure process after the pellicle is attached.

As the pattern rule becomes finer, a position error due to deformation of the photomask becomes a problem. The present invention is particularly effective when the pattern line width is 65 nm or less.
The exposure wavelength used in the photomask manufactured from the photomask blank according to the present invention is not particularly limited. However, the shorter the exposure wavelength, the shallower the focal depth, the more effective the present invention. The 248 nm or less, particularly 193 nm. The present invention is effective for the following exposure wavelengths.

  EXAMPLES Hereinafter, although an Example and comparative example of this invention are given and this invention is demonstrated more concretely, this invention is not limited to these.

Example 1
First, the following were prepared as photomask blanks 10. That is, the photomask substrate 11 is a 152 mm square synthetic quartz substrate, and the blanks film 12 is a halftone film (HT film) made of MoSiON with a thickness of 460 angstroms (Å) and the entire surface of the photomask substrate 11. The film was formed by a sputtering apparatus.
In addition, the area | region (pellicle adhesion area | region) 52 which is going to affix the pellicle of the photomask blanks 10, and its inner area are 100 mm x 132 mm.

Next, the flatness of the photomask blanks 10 before attaching the pellicle was measured using an UltraFlat 200M manufactured by Tropel as a flatness measuring machine.
As a result, the flatness (TTV) of the area 52 inside the region to which the pellicle of the photomask blank 10 before the pellicle 30 is to be pasted (pellicle pasting region) is 0.16 μm, and the photomask blanks The height difference at any two points in the pellicle attaching region 51 that is point-symmetric from the center O of 10 was within 0.14 μm (FIG. 3A).

Next, the pellicle 30 was attached to the photomask blanks 10. The flatness of the photomask blank 10 after this pellicle attachment was measured in the same manner as before the pellicle attachment.
As a result, the flatness (TTV) in the range 52 inside the region where the pellicle was affixed (the pellicle affixing region) was almost unchanged at 0.19 μm (FIG. 3B). Moreover, there was almost no change in the shape of the photomask blanks 10.

(Example 2)
First, a photomask blank 10 having the same dimensions and blank film as in Example 1 was prepared.

Next, the flatness of the photomask blanks 10 before attaching the pellicle was measured in the same manner as in Example 1.
As a result, the flatness (TTV) of the range 52 inside the pellicle attachment region of the photomask blank 10 before attaching the pellicle is 0.22 μm, and the high point at a concentric point from the center O of the photomask blank 10 is shown. The variation in thickness was within 0.14 μm in the pellicle pasting region 51 for any diameter portion (FIG. 4A).

Next, the same pellicle 30 as in Example 1 was attached, and the flatness of the photomask blank 10 after the pellicle was attached was measured in the same manner as in Example 1.
As a result, the flatness (TTV) in the range 52 inside the pellicle attachment region was not substantially changed to 0.21 μm (FIG. 4B). Moreover, there was almost no change in the shape of the photomask blanks 10.

(Comparative Example 1)
First, a photomask blank 10 having the same dimensions and blank film as in Example 1 was prepared.

Next, the flatness of the photomask blanks 10 before attaching the pellicle was measured in the same manner as in Example 1.
As a result, the flatness (TTV) of the range 52 inside the pellicle pasting region of the photomask blank 10 before the pellicle pasting is 0.25 μm and is concentric from the center O of the photomask blank 10. The variation in height was within 0.21 μm in the pellicle attachment region 51 for any diameter portion (FIG. 5A).

Next, the same pellicle 30 as in Example 1 was attached, and the flatness (TTV) of the photomask blank 10 after the pellicle was attached was measured in the same manner as in Example 1.
As a result, the flatness in the range 52 inside the pellicle attachment region was greatly changed to 0.39 μm, and the shape of the photomask blanks 10 was also changed (FIG. 5B).

  From the results of Examples 1 and 2 and Comparative Example 1, the flatness of the photomask blanks before and after attaching the pellicle by setting the flatness of the photomask blanks within a predetermined range by paying attention to symmetry as in the present invention. It can also be seen that photomask blanks with a small change in shape can be produced.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

It is the schematic explaining flatness distribution which the photomask blank which concerns on this invention requires. It is the schematic explaining the positional relationship of a photomask blank and a pellicle sticking area | region, (a) is sectional drawing of the state which affixed the pellicle to the photomask blank, (b) is the blanks film | membrane surface of a photomask blank FIG. It is a figure which shows distribution of the flatness of the photomask blank measured in Example 1, (a), (b) is before pellicle sticking and after pellicle sticking, respectively. It is a figure which shows distribution of the flatness of the photomask blank measured in Example 2, (a), (b) is before pellicle sticking and after pellicle sticking, respectively. It is a figure which shows distribution of the flatness of the photomask blank measured in the comparative example 1, (a), (b) is before pellicle sticking and after pellicle sticking, respectively.

Explanation of symbols

10 ... Photomask blanks, 11 ... Photomask substrate,
12 ... Blanks membrane,
30 ... Pellicle, 31 ... Pellicle frame, 32 ... Pellicle membrane,
51 ... Pellicle pasting area 52: Range inside the pellicle pasting area,
O ... Center of photomask blanks, D ... Diagonal line.

Claims (7)

  A method for selecting a photomask blank in which a blanks film is formed on a photomask substrate, wherein the center of the photomask blanks is a symmetric point in a region where a pellicle is pasted in a surface on which the blanks film is formed A photomask blank selection method comprising: selecting a photomask blank having a height difference between two points having a point-symmetrical relation as 0.15 μm or less at any two points as a non-defective product.   A method for selecting a photomask blank in which a blanks film is formed on a photomask substrate, wherein any photomask that intersects with the pellicle in a region where a pellicle is attached in a surface on which the blanks film is formed A photomask blank selection method, wherein a photomask blank having a height variation at a point on a concentric circle centered on the center of the blank is 0.20 μm or less on any circle is selected as a good product. A method for producing photomask blanks, at least,
As a photomask substrate, a height difference between two arbitrary points that are point-symmetrical with respect to the center of the photomask substrate in the region where the pellicle is attached or a concentric circle centered on the center of the photomask substrate Prepare a photomask substrate whose height variation at the upper point is a predetermined value,
A method for producing a photomask blank, comprising producing a blank film on a surface of the photomask substrate to produce the photomask blank.   The photomask substrate to be prepared is a photomask substrate in which the height difference between any two points that are point-symmetric with respect to the center of the photomask substrate is 0.15 μm or less. The manufacturing method of the photomask blank of Claim 3.   4. The photomask substrate to be prepared is a photomask substrate having a height variation of 0.20 μm or less at a point on a concentric circle centered on the center of the photomask substrate. The manufacturing method of the photomask blanks as described in 1 ..   A photomask manufacturing method, comprising: using a photomask blank selected by the photomask blank selection method according to claim 1 or 2; and forming a mask pattern by lithography to manufacture the photomask.   A photomask is manufactured by forming a mask pattern by lithography on the photomask blank manufactured by the method of manufacturing a photomask blank according to any one of claims 3 to 5. Manufacturing method.

Images