JP3450848B2 - Photomask blank, glass substrate for photomask blank, and photomask - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a photomask mask blank, which is a material of a phototomask used as a mask for exposure of a fine pattern in the production of LSI, etc., and a phototomask production using this inspection method. The present invention relates to a method and a photomask manufactured by this manufacturing method.

[0002]

2. Description of the Related Art As semiconductor devices become highly integrated, projection exposure techniques used in lithography processes are required to have finer transfer patterns and higher resolution.

A photomask used as a mask when performing this projection exposure is one in which a fine pattern for exposure consisting of a light transmitting portion and a light shielding portion is formed on a transparent substrate. In this fine pattern, it is necessary that the individual patterns have a precise positional relationship with respect to the reference position. The accuracy of this positional relationship requires higher accuracy in proportion to the finer pattern and higher resolution of the pattern.

This fine pattern is usually formed by forming a resist film on a photomask blank having a light-shielding film formed on the surface of a transparent substrate and subjecting the resist film to electron beam exposure for drawing a fine pattern with an electron beam. After that, it is formed by developing and etching. This electron beam drawing is performed by holding the photomask blank on the moving stage, storing the pattern to be drawn in the computer as coordinate data, and controlling the irradiation position of the electron beam and the position of the moving stage based on this coordinate data. .

Here, exposure is performed by this electron beam drawing,
The fine pattern actually formed on the photomask blank by development and etching and the fine pattern indicated by the coordinate data must match exactly. If pattern transfer is performed using a photomask that does not match with a precision higher than a predetermined value, a large number of defective semiconductor products will be manufactured. Therefore, with respect to the manufactured photomask, an inspection is performed as to whether or not the actually formed fine pattern and the fine pattern indicated by the coordinate data match with each other with a precision higher than a predetermined accuracy. In this inspection, the coordinate value of the mark attached to the predetermined coordinate position during electron beam drawing is measured by a coordinate measuring machine, and the measured coordinate value of this mark and the corresponding mark coordinate value of the coordinate data are collated. Then, it is inspected whether or not they match with each other with a precision higher than a predetermined level. Photomasks that fail this inspection are considered defective.

There are various possible causes for failing this inspection, and one of them is the flatness of the main surface of the photomask blank. That is, if the surface (main surface) of the photomask blank on which the fine pattern is formed does not have a flatness above a certain level, it is impossible to form an accurate fine pattern even if the electron beam drawing accuracy is improved. Can not. Therefore, conventionally, the flatness of the photomask blank is inspected by a flatness measuring device, and the photomask blank having a flatness of a predetermined level or less is rejected as a defective product before the electron beam writing process is performed. Was omitted.

Here, the photomask blank is
It is a material for photomasks obtained at an intermediate stage of manufacturing a photomask and broadly refers to a material before it is completed as a photomask, but a photomask blank at a certain stage is an independent product as a material for a photomask. In many cases, it is treated as.

[0008]

By the way, even if a photomask is manufactured using a photomask blank having a flatness equal to or higher than a predetermined level by the above-mentioned flatness inspection, the coordinate position accuracy is obtained in the obtained photomask. There is a problem that defective products are often mixed due to the above defects. For this reason, attempts have been made to set a strict standard of flatness, but it has been found that even if the standard is stricter than a predetermined level, the yield is significantly deteriorated, and the defect rate is hardly improved.

According to the research conducted by the present inventor, when the flatness of the photomask blank is equal to or higher than a predetermined level, the coordinate position of the fine pattern formed by the uneven shape even if the flatness is constant. It was found that the accuracy depends greatly, and even if the flatness is improved, the coordinate position accuracy cannot be improved in proportion thereto.

The present invention has been made under the background described above, and a photomask blank inspecting method capable of accurately determining the quality of a photomask blank, and a photomask having high productivity using this inspecting method. An object of the present invention is to provide a photomask manufacturing method that can be manufactured and a photomask manufactured by this manufacturing method.

[0011]

In order to solve the above-mentioned problems, a method of inspecting a photomask blank according to the present invention includes (1) a photomask formed by forming a transfer fine pattern on a porous substrate. A method of inspecting a photomask blank for determining the quality of a photomask blank used as a material, comprising measuring an uneven shape of a main surface of the photomask blank, the uneven shape of the main surface being substantially parallel to the main surface. A plane substantially parallel to the reference plane, or a simple concave curved surface shape in which the height distribution of the main surface shows a smooth increasing tendency from the center of the main surface toward the periphery, Or, a configuration characterized by determining whether the height distribution of the main surface is a simple convex curved surface shape showing a smooth decreasing tendency from the center of the main surface toward the peripheral edge. It was.

The method of manufacturing a photomask according to the present invention comprises (2) a light-shielding film forming step of forming a light-shielding film on a light-transmitting substrate, and a resist film forming step of forming a resist film on the light-shielding film. A resist film exposure / development step in which the resist film is subjected to fine pattern exposure and development;
A method of manufacturing a photomask, comprising: an etching step of removing a part of a light-shielding film in a fine pattern to form a fine pattern including a light-transmitting portion and a light-shielding portion on a main surface of a light-transmitting substrate. In a step prior to the exposure / development step, a photomask blank inspection step of inspecting the photomask blank including the transparent substrate by the method of configuration 1 is provided.

Furthermore, the photomask blank according to the present invention is (3) a photomask blank used as a material for a photomask in which a transfer fine pattern is formed on a porous substrate, and has an uneven shape on the main surface. Is a plane substantially parallel to a reference plane substantially parallel to the main surface,
Or, the height distribution of the main surface is a simple concave curved surface shape showing a smooth increasing tendency from the center of the main surface toward the periphery, or the height distribution of the main surface is The configuration is characterized by a simple convex curved surface shape showing a smooth decreasing tendency from the center to the periphery.

The glass substrate for a photomask blank according to the present invention is (4) a glass substrate for a photomask blank used as a light-transmitting substrate of the photomask blank of the constitution 3, in which the irregular shape of the main surface is , A plane that is substantially parallel to a reference plane that is substantially parallel to the main surface,
Or, the height distribution of the main surface is a simple concave curved surface shape showing a smooth increasing tendency from the center of the main surface toward the periphery, or the height distribution of the main surface is The configuration is characterized by a simple convex curved surface shape showing a smooth decreasing tendency from the center to the periphery.

[0015]

In the above structure 1, when the flatness of the main surface of the photomask blank is not less than a certain level, the unevenness of the main surface of the photomask blank is It is a plane that is substantially parallel to a reference plane that is substantially parallel to the main surface, or a simple concave curved surface in which the height distribution of the main surface shows a smooth increasing tendency from the center of the main surface toward the periphery. In the case of a shape, or when the height distribution of the main surface is a simple convex curved surface shape showing a smooth decreasing tendency from the center of the main surface toward the periphery,
If it is a non-defective product, and if it is not so, for example, if it has a so-called twisted curved surface shape in which a convex curved surface and a concave curved surface are combined, it is determined to be a defective product.

As described above, the fact that the quality of the photomask blank can be accurately determined by the curved surface shape has been clarified by the research by the present inventor. That is,
The curved surface shape of the main surface of a large number of photomask blanks having the same flatness was measured in advance by a flatness measuring device, a photomask was manufactured using these photomask blanks, and the coordinate position accuracy of each was measured. However, it has been clarified that the quality of the coordinate position accuracy and the curved surface shape of the main surface of the photomask blank have the above-described relatively simple correlation.

According to the inspection method of Structure 1, the accuracy of the inspection can be significantly improved as compared with the conventional inspection using only the flatness measurement.

Further, according to the constitution 2, the productivity can be remarkably improved without deteriorating the yield.

Further, according to the configurations 3 and 4, the photomask blank and the glass substrate for the photomask blank which are non-defective can be almost always obtained.

[0020]

1 to 6 are explanatory views of a photomask blank inspecting method according to an embodiment of the present invention.
3 is a diagram showing a main surface of a photomask blank having a substantially convex curved surface shape with respect to a reference plane, FIG. 2 is a diagram showing contour line distribution of the main surface of the photomask blank shown in FIG. 1, and FIG. Is a diagram showing a main surface of a photomask blank having a substantially simple concave curved surface shape with respect to a reference plane,
FIG. 4 is a view showing a contour line distribution of the main surface of the photomask blank shown in FIG. 3, FIG. 5 is a view showing the main surface of the photomask blank having a curved surface shape twisted with respect to a reference plane, and FIG. 6 is a view showing a contour line distribution on the main surface of the photomask blank shown in FIG. Hereinafter, a photomask blank inspection method, a photomask manufacturing method, a photomask blank, and a photomask blank glass substrate according to one embodiment will be described in detail with reference to these drawings. In the following description, a photomask blank inspection method will be described along with a description of a photomask manufacturing method.
The photomask blank and the glass substrate for the photomask blank will be described. The manufacturing process of the photomask is
The process includes photomask blank manufacturing, photomask blank inspection, resist coating, electron beam exposure, development, etching, and resist stripping / cleaning. Each step will be described below.

Photomask blank manufacturing process First, a chromium film (light-shielding film) having a thickness of 650 Å is formed on the surface (main surface) of a quartz glass substrate of 5 inches × 5 inches × 0.09 inches by a sputtering method. Obtain a photomask blank.

Photomask blank inspecting step Next, the uneven shape of the main surface of the photomask blank obtained by the above steps is measured, and the uneven shape of the main surface is substantially parallel to a reference plane substantially parallel to the main surface. Are parallel planes,
Or, the height distribution of the main surface is a simple concave curved surface shape showing a smooth increasing tendency from the center of the main surface toward the periphery, or the height distribution of the main surface is The quality is inspected based on whether or not the shape is a simple convex curved surface showing a smooth decreasing tendency from the center to the periphery. If the irregular shape of the main surface is a plane that is substantially parallel to a reference plane that is substantially parallel to the main surface, or has a substantially simple convex or concave curved surface shape, then it is a good product (pass). If not, for example, if it has a twisted curved surface shape such as a combination of a convex curved surface and a concave curved surface, it is determined as a defective product (failed). The photomask blank determined to be non-defective and the glass substrate used for manufacturing the photomask blank constitute a photomask blank and a glass substrate for a photomask blank according to an embodiment of the present invention. Moreover, the reason why the photomask blank on which the chrome film is formed is inspected without performing the inspection at the stage of the glass substrate is that since the chrome film is a metal film, the formation of the chrome film causes some distortion on the main surface of the substrate. Since there is a possibility that the unevenness of the main surface of the substrate may be slightly different from that of the glass substrate, the inspection is performed at this stage in order to maintain the inspection accuracy better. . Since the resist is an organic film, there is no risk of distortion in the resist forming process, which is the subsequent process.

The unevenness of the photomask blank is measured by a flatness measuring device (for example, Auto Select which is a flatness measuring device manufactured by General Signal Company).
8010 etc.). This flatness measuring device is capable of measuring unevenness of each point on the surface with respect to the reference plane with a resolution of 0.1 μm or more, and subjecting the measured data to image processing to display or print out a contour line distribution or a perspective view. is there.

FIGS. 1 to 6 show an example in which the unevenness shape of the main surface of the photomask blank is measured by this flatness measuring device and a perspective view and a contour map thereof are printed out. In these drawings, reference numeral 1 is a main surface of the photomask blank, reference numeral 2 is a reference plane, and the reference plane 2 is a plane parallel to the xy plane substantially parallel to the main surface 1. Further, the unevenness of the main surface 1 refers to the magnitude (height difference) of the distance in the z-axis direction with respect to the reference plane 2. Furthermore, the height difference for each contour line is 0.3 μm.
Is.

In the example shown in FIGS. 1 and 2, the main surface 1
The concave-convex shape is a simple curved surface shape that is almost simple with respect to the reference plane 2. Therefore, this photomask blank is determined to be non-defective (pass).

Further, in the example shown in FIGS. 3 and 4, the concave and convex shape of the main surface 1 is a substantially simple concave curved surface shape with respect to the reference plane 2. Therefore, this photomask blank is also determined to be non-defective (pass).

On the other hand, in the example shown in FIGS. 5 and 6, the uneven shape of the main surface 1 has a curved surface shape twisted with respect to the reference plane 2. Therefore, this photomask blank is determined to be a defective product (fail).

The above determination can be made easily by visually observing the image displayed by the flatness measuring device or the printed out drawing, but it can be automatically made by an appropriate image processing operation. Is also possible. That is, for example, the xyz coordinate axes are set as shown in the figure, two of the four sides of the main surface 1 facing each other with a large change in height are selected, and the highest point and the lowest point of one side are respectively set to H1max,
A straight line L1 connecting these points is set as H1min. Next, on the other side, H1max, H1min and their x
Two points having the same coordinates are set as H2max and H2min, and a straight line L2 connecting these points is set. Then, when the main surface 1 is a plane that is substantially parallel to the reference plane 2 or has a curved surface shape that is a substantially simple convex or concave shape, the straight lines L1 and L2 with respect to the reference plane 2 The slopes are substantially the same or the positive and negative slopes are the same. On the other hand, when the main surface 2 has a twisted curved surface shape in which a convex curved surface and a concave curved surface are combined, the positive and negative inclinations of the straight lines L1 and L2 with respect to the reference plane 2 are different. become. Therefore, the determination can be automatically performed by performing the above processing by the image data processing operation. Further, for example, by setting the reference plane 2 at an appropriate position on the z-axis and processing the distribution of the distance of the main surface with respect to the reference plane in the z-axis direction by a statistical method, the curved surface shape can be more accurately discriminated. It is also conceivable that the judgment is made by using

Resist Forming Step Next, an electron beam resist (EBR-9HS31 manufactured by Toray Industries, Inc.) is applied by a spin coater on the main surface of the photomask blank that has passed the inspection of the photomask blank, and then dried to form chromium. Thickness 5 on the surface of the membrane
An electron beam resist film of 500 Å is formed.

Electron Beam Exposure Step Next, the photomask blank on which the electron beam resist film is formed is subjected to electron beam exposure by an electron beam exposure apparatus. This electron beam exposure apparatus stores a pattern to be drawn in a computer as coordinate data, and controls the irradiation position of the electron beam and the position of the moving stage on a photomask blank held on the moving stage based on the coordinate data. A fine pattern is drawn by irradiating an electron beam. The coordinate position accuracy of this electron beam drawing is extremely high, and if the main surface of the photomask blank to be drawn is a completely flat surface, the accuracy of 0.1 μm or less can be maintained relatively easily.

Resist development, etching and resist
Peeling Step Next, the photomask blank after electron beam exposure is subjected to a development treatment and a baking treatment to form a fine pattern of the resist film. Then, using this resist film as a mask,
165 g of ceric ammonium nitrate and perchloric acid (7
(0%) 12 ml of pure water was added to 1000 ml of an etching solution to etch the chrome film to remove a part of the chrome film in a fine pattern.
An exposure fine pattern including a light transmitting portion and a light shielding portion is formed. After that, the resist film remaining on the chromium film is peeled off, washed and dried to obtain a photomask.

According to the above-described manufacturing method, it is possible to obtain a high-quality photomask with high productivity while preventing a decrease in yield. Further, according to the above-described inspection method, it is possible to perform an inspection with high accuracy, and it is possible to improve the yield of photomask manufacturing because a good product is not a defective product and a defective product is not a good product. Became.

Next, the coordinate position accuracy of each photomask manufactured by using both the photomask blanks judged to be non-defective and defective by the photomask blank inspection method according to the above-described embodiment is checked, and one execution is performed. A part of the result of confirming the reliability of the inspection method of the example will be described.

7, FIG. 9, FIG. 11, FIG. 13, FIG. 15, FIG. 17, FIG. 19, and FIG. 21, the unevenness shape of the main surface of different photomask blanks is measured by a flatness measuring device and printed out. It is a figure. Of these, the photomask blanks shown in FIGS. 7, 9, and 11 are determined as non-defective products, and the photomask blanks shown in FIGS.
The photomask blanks shown in FIGS. 19 and 21 are judged to be defective.

8, FIG. 10, FIG. 12, FIG. 14, FIG. 16, FIG. 18, FIG. 18, FIG.
FIG. 22 shows the results of examining the coordinate position accuracy of each photomask manufactured using the photomask blanks shown in FIGS. 9, 11, 13, 15, 17, 19, and 21.

The coordinate position accuracy was measured as follows. First, a predetermined mark is attached at the time of electron beam drawing. This mark has four points X1, X2, Y1 and Y2 which are reference points for defining the xy coordinate axes, and P1, P2, P3 and P4 which are representative points of each part of the fine pattern.
, P5 and P6. Each of these points is included in the coordinate data stored in the computer. Each of these marks is formed as a mark on the photomask when the photomask is completed. Since these marks are also used as alignment marks when transferring using a photomask, they are formed during normal photomask production. Here, the mark was used.

Next, the coordinate position of each mark of the photomask manufactured using each of the above photomask blanks is measured using a laser interference type coordinate measuring machine. This coordinate measurement is performed as follows. First, the X formed on the photomask
1, X2, Y1, Y2, P1, P2, P3, P4, P5,
10 points of P6 are measured by the coordinate measuring machine, and the measured coordinate values are plotted on arbitrary two-dimensional coordinates of the computer of the coordinate measuring machine. 8, 10, 12, 14, and 1
6, FIG. 18, FIG. 20 and FIG. 22, each point indicated by a cross indicates the measured coordinate value. Next, the amount of deviation between this measured coordinate value and the set coordinate value stored in the electron beam exposure apparatus is obtained. If this displacement is large, the coordinate position accuracy will be poor. The amount of deviation is measured as follows. First, point X1 according to the measured coordinate values of the coordinate measuring machine
Let the straight line connecting X2 and X2 be the x-axis. Next, set a straight line passing through the point Y1 and orthogonal to the x-axis, and set this as the y-axis,
The intersection of the set x-axis and y-axis is set as the virtual origin O. In this way, after setting the xy coordinate axes and the virtual origin in the coordinate measuring machine, next, the set coordinate values of each point stored in the electron beam drawing apparatus are loaded into the coordinate measuring machine, and the mutual xy coordinate axes are acquired. After making the origins coincident with each other, the deviation amount of each corresponding point is measured. 8, 10, 12, and 1
4, FIG. 16, FIG. 18, FIG. 20 and FIG. 22, each point indicated by ● is a coordinate value set in the electron beam exposure apparatus,
The distance between the mark points and the mark points is the amount of coordinate deviation (indicated by the arrow in the figure).

As a result of the measurement as described above, as is apparent from the figure, the photomask manufactured by using the photomask blank determined to be non-defective in the inspection uses the photomask blank determined to be defective. It was found that the ratio of the number of coordinate shifts within the allowable error range was significantly larger than that of the manufactured photomask.

In the above-mentioned one embodiment, the case where quartz glass is used as the translucent substrate has been suggested, but this is glass such as soda lime glass, aluminoborosilicate glass, borosilicate glass, or sapphire. Alternatively, it can be applied to other transparent substrate materials.

In the above-described embodiment, the photomask blank inspection step is carried out after the chromium film is formed on the quartz glass substrate. However, this can be done before forming the chromium film or by applying resist. You may go later.

[0041]

As described above in detail, according to the present invention, the uneven shape of the main surface of the photomask blank is measured, and the uneven shape of the main surface is substantially parallel to the reference plane substantially parallel to the main surface. The quality of the photomask blank is judged by whether it is parallel planes or has a curved surface shape that is almost simple convex or concave, and it is judged as a non-defective product. A good quality photomask can be obtained.

[Brief description of drawings]

FIG. 1 is a view showing a main surface of a photomask blank having a substantially simple curved surface shape with respect to a reference plane.

FIG. 2 is a diagram showing a contour line distribution on the main surface of the photomask blank shown in FIG.

FIG. 3 is a view showing a main surface of a photomask blank in which a reference plane has a substantially simple concave curved surface shape.

FIG. 4 is a diagram showing a contour line distribution on the main surface of the photomask blank shown in FIG.

FIG. 5 is a view showing a main surface of a photomask blank having a curved surface shape twisted with respect to a reference plane.

6 is a diagram showing a contour line distribution on the main surface of the photomask blank shown in FIG.

FIG. 7 is a diagram in which a concavo-convex shape on the main surface of the photomask blank is measured by a flatness measuring device and printed out.

8 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG.

FIG. 9 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

FIG. 10 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG.

FIG. 11 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

FIG. 12 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG. 11.

FIG. 13 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

FIG. 14 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG.

FIG. 15 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

16 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG.

FIG. 17 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

FIG. 18 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG. 17.

FIG. 19 is a diagram in which the uneven shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

20 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG.

FIG. 21 is a diagram in which the concavo-convex shape of the main surface of the photomask blank is measured by a flatness measuring device and printed out.

22 is a diagram showing the results of examining the coordinate position accuracy of a photomask manufactured using the photomask blank shown in FIG. 21.

[Explanation of symbols]

1 ... Main surface, 2 ... Reference plane.

Claims (2)

(57) [Claims] 1. A fine pattern for transfer is formed on a transparent substrate.
Used as a transparent substrate for a photomask
It is a method of inspecting the glass substrate to judge the quality of the glass substrate.
The main surface of a glass substrate with a flatness above a certain level
The uneven shape of the main surface is measured by measuring the uneven shape of
A plane that is substantially parallel to a reference plane that is substantially parallel to the surface,
Alternatively, the height distribution of the main surface is from the center of the main surface to the periphery.
Simple concave curved shape showing a smooth increasing trend toward
Or the height distribution of the main surface is
A simple showing a smooth decreasing direction from the center to the periphery
Determining pass / fail based on whether or not it is a convex curved surface shape
A method for inspecting a glass substrate, comprising: 2. The method for inspecting a glass substrate according to claim 1.
Where x, y are included in the reference plane, x,
The y and z orthogonal coordinate axes are set, and among the four sides of the main surface,
Select two opposing sides that have a sharp change in elevation, the highest on one side
These points and the lowest point are defined as H1max and H1min, respectively.
Set a straight line L1 connecting the points and place it on the other side
And two points whose x coordinate is the same as H1max and H1min.
Let H2max and H2min be the straight line L2 connecting these points.
Then, the inclinations of the straight lines L1 and L2 with respect to the reference plane 2 are almost the same.
If the same or the same positive and negative slopes,
The surface is a plane substantially parallel to the reference plane 2, or
Is a simple curved surface that is convex or concave
The method of inspecting glass substrates is characterized by
Law.