JP3102386B2 - Photomask manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask for a projection exposure apparatus, and more particularly to a method for manufacturing a photomask used for forming a fine pattern in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art At present, in a manufacturing process of a semiconductor device, an optical lithography technique is mainly used to form a pattern on a semiconductor substrate. In the optical lithography technology, a photomask (an exposure original plate on which a pattern including a transparent region and a light-shielding region is formed by a reduction projection exposure apparatus. When the reduction ratio is not 1: 1, it is also particularly called a reticle. A pattern of the photosensitive resin can be obtained by transferring the pattern of the photosensitive resin on a semiconductor substrate coated with the photosensitive resin and developing the pattern.

[0003] In the conventional optical lithography technology, mainly the development of an exposure apparatus, especially the high N
A has responded to miniaturization of semiconductor element patterns. Here, NA (numerical aperture) corresponds to how much light the lens can collect, and the larger the value, the more light that can be collected, and the better the performance of the lens. As is generally well known as the Rayleigh equation, the critical resolution (the size of the critical fine pattern that can be resolved) and NA are R = K1 ×
There is a relationship of λ / NA (where K1 is a constant that depends on the process such as the performance of the photosensitive resin). As the NA increases, the limit resolution becomes finer.

[0004] However, although the resolution is improved by increasing the NA of the exposure apparatus, the depth of focus (the range in which the displacement of the focal position can be tolerated) decreases, and it becomes difficult to further miniaturize the focal depth. Was. Again, although the actual physical description is omitted, the depth of focus DOF and NA have the relationship DOF = K2 × λ / NA2 (where K2 is a process-dependent constant) as the Rayleigh equation as before. It is known to hold. That is, as the NA is increased, the depth of focus becomes narrower, and a slight shift of the focal position cannot be tolerated.

Accordingly, various super-resolution techniques have been studied. In general, the super-resolution technique is a technique for improving the light intensity distribution on the image plane by controlling the transmittance and the phase on the pupil plane of the illumination optical system, the photomask, and the projection lens system.

[0006] Among various super-resolution methods, the improvement of resolution characteristics by optimizing the illumination optical system, that is, the so-called modified illumination method is highly realistic and has attracted particular attention in recent years.

[0007] With the proposal of various super-resolution techniques, the limit of optical lithography has reached below the exposure wavelength. However, in the pattern formation near the resolution limit, the optical proximity effect (Optical proximity effect) is used.
The influence of t) has become significant. The optical proximity effect is a phenomenon in which a pattern is affected by another pattern around the pattern, and the shape and dimensions change. Therefore, the optical proximity correction (Optical Proximity Corre)
ction: hereinafter referred to as OPC) has been actively studied. This is a method of obtaining a desired photosensitive resin pattern by deforming the mask pattern in advance, contrary to the deformation of the photosensitive resin pattern.
In the OPC method, a method of simply changing the size of a mask pattern (a method of changing a mask bias or a part of the size of a pattern is particularly distinguished from a jog method), or disposing a fine pattern smaller than the resolution limit at a corner of the pattern. There are methods such as hat and self.

[0008]

However, in the conventional optical proximity effect correction, since the dimensions of the mask pattern are changed, there has been a problem that the pattern dimensions can be changed only at certain intervals. The mask data creation and the exposure data of the drawing apparatus are all created so as to be on a grid at equal intervals in both the x and y directions. This grid size is determined by the limitation in the mask drawing apparatus. That is, the dimension cannot be guaranteed unless it is equal to or larger than the minimum beam size of the mask drawing apparatus.

As the grid mask drawing apparatus, an electron beam drawing apparatus is mainly used, and the minimum beam size is about 0.05 μm. In this case, if the reduction ratio of the exposure apparatus is 1/5, it is possible to design with a 0.01 μm grid on the image plane (on the semiconductor substrate). However, in a mask drawing apparatus, it is not practical to draw a beam by narrowing the beam to a minimum value, and this minimum grid is not often used. This is because, as the beam diameter is reduced, the time for writing the same area increases in inverse proportion to the square of the dimension, and it takes one day or more to write the entire mask with the minimum beam diameter.

In such a long-time drawing, the stability of the drawing apparatus greatly affects the mask accuracy. Therefore, the pattern dimension increment that can be stably formed on the mask is 0.1 μm, and the design of the semiconductor element requires
A grid size of about ０．０ of 0.02 μm was used. Therefore, when the dimension of the transfer pattern is reduced due to the optical proximity effect, adding a mask bias may make the transfer pattern too large.On the other hand, it is necessary to control the transfer pattern dimension in steps smaller than the grid when drawing the mask. And it was.

[0011] Due to such a limitation of the grid, the OPC method cannot be applied in some cases. For example, in the linearity of the contact hole pattern described below, the problem of the grid of the mask dimension occurs. Here, the relationship between the mask dimension and the dimension of the obtained photosensitive resin pattern is called linearity. And
It is well known that a hole pattern has a large dimensional variation (poor linearity) at least twice as large as a line pattern.

FIGS. 9A and 9B show 0.2 μm and 0.25 μm in KrF excimer laser exposure (NA = 0.55, coherent factor σ = 0.8).
3 shows a light intensity distribution simulation of the hole pattern of FIG. FIG. 10 shows the relationship between the mask pattern size obtained from the light intensity distribution simulation and the pattern size transferred to the photosensitive resin.

Here, the size of the hole pattern of 0.2 μm is adjusted to the design value. Such a relationship between the mask dimension and the transfer dimension is called linearity. Here, the size of the photosensitive resin pattern is a certain value or more (slice level) from the result of the light intensity distribution simulation.
The dimensions were determined using a simple development model in which the photosensitive resin was removed by development at a light intensity of: Then, the slice level was set to a value at which the 0.2 hole pattern became 0.2 μm. The dimension between the mask pattern (value on the semiconductor substrate: 1/5) and the photosensitive resin pattern does not have an ideal linear relationship, and the larger the mask dimension, the larger the dimension deviates.

If the linearity is poor, 0.2
It is difficult to form a hole pattern of 0.25 μm and a hole pattern of 0.25 μm at the same time.
It became larger than 29 μm. If the mask size for the 0.25 μm hole pattern is 0.225 μm, a 0.25 μm photosensitive resin pattern can be obtained.
In this case, it was impossible to create a mask because of the grid at the time of mask drawing.

On the other hand, if an OPC method such as dialogue is used,
The size of the hole pattern can be changed in finer increments depending on the size of the serif. However, there is a problem that the dimensions are not stable because the serif is fine. In particular, there has been known a problem that when a serif pattern is applied to a field connection of an electron beam lithography apparatus, dimensions are extremely changed. As the size of the serif decreases, the size of the hole pattern transferred to the photosensitive resin decreases. The hole pattern has a smaller depth of focus than a line pattern of the same size, and the smaller the size, the further the depth of focus is reduced. Therefore, it has been difficult to use serifs in the hole pattern.

By improving the linearity of the hole pattern, the manufacturing margin of the semiconductor device is expanded. For example, if the hole pattern is too large, there is a problem that adjacent patterns come into contact with each other, and if the hole pattern is too small, there is a problem that junction resistance increases and the depth of focus decreases.

An object of the present invention is to provide a method of manufacturing a photomask which improves the linearity of a hole pattern without using a fine pattern such as serifs.

[0018]

In order to achieve the above object, a method of manufacturing a photomask according to the present invention has a plurality of types of hole patterns having different dimensions from each other, and the hole patterns are formed by a photosensitive resin by transmitted illumination. A plurality of types of hole pattern dimensions are respectively determined from a relationship with a desired transfer dimension, so that the desired mask pattern does not fit on a grid.
If the mask pattern is smaller than the desired mask pattern and
To create design data, and over-exposure
Finish the desired mask pattern by drawing
The desired mask pattern is on the grid
Creates design data of the desired mask pattern,
The desired mask is formed by drawing by normal exposure.
The pattern is finished to form a plurality of types of hole patterns.

Further , among the plurality of types of hole patterns,
At least one type of hole pattern is a hole pattern
Create double exposure data inside the data of
Double exposure of the data portion for double exposure
To set .

According to the present invention, in a mask having holes having different sizes, a small-size hole pattern is first designed to be smaller than a desired size so as to ride on a grid. For example, when the above-described hole patterns of 0.2 μm and 0.25 μm are simultaneously opened on the semiconductor substrate, the hole pattern of 0.25 μm needs to be 0.225 μm on the mask. However, a grid size of 0.
If it is not 005 μm, data of 0.225 μm cannot be created. Such a fine grid cannot be used due to the limitation of the mask drawing apparatus. Therefore, 0.25μ
The hole pattern of m is also on the grid on the data 0.2
μm. Then, when the mask is drawn, the exposure amount is made larger than that of the other patterns to enlarge the pattern to a desired size.

As described above, the dimensions of the photosensitive resin pattern formed on the semiconductor substrate can be more accurately controlled by setting the mask dimensions in steps smaller than the mask data and the grid size of the drawing apparatus.

In particular, in the optical proximity effect correction, a photosensitive resin pattern having a desired size is formed on a semiconductor substrate by changing a mask size. However, conventionally, there is a limitation on a grid size at the time of data creation and mask drawing. Therefore, the dimension of the photosensitive resin pattern could not be controlled in steps smaller than the grid size.

In the photomask manufacturing method of the present invention, since the dimensions are partially changed depending on the exposure amount,
A mask having a desired size can be manufactured by controlling the size in an analog manner, not in a digital manner as in the related art.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing data for manufacturing a photomask according to an embodiment of the present invention, and FIG.
FIG. 2 is a diagram showing a mask pattern created by using the data shown in FIG. 1. Here, as the exposure apparatus, a KrF excimer having a reduction ratio of 1/5 (mask pattern size: pattern size on an image forming surface = 5: 1), a numerical aperture NA = 0.55, and a coherent factor σ = 0.8. A laser (wavelength λ = 248 nm) exposure apparatus is used.

The grid for mask design is 0.025.
In the following description, it is assumed that hole patterns of 0.2 μm and 0.25 μm (on the image plane) are formed simultaneously. Hereinafter, in this description, the dimension on the mask is also described by a value on the semiconductor substrate (the actual mask pattern dimension is five times the value).

In FIG. 1, a 0.2 μm hole (for opening) pattern 1 and a 0.25 μm hole (for opening) pattern 2 are both 0.2 μm data 11 on design (CAD) data. And 0.25
In the μm hole pattern 2, double exposure data 12 (0.15 μm data) is further created inside.

When converting the design data for the mask drawing apparatus, the double exposure data 12 (0.15 μm
(Data) portion is double-exposed. In general, in the mask drawing data conversion, a process is performed to prevent double exposure of a connected portion of each pattern even if the connected portion overlaps. However, in the present invention, processing of this overlapping portion is performed. First, double exposure is performed.

FIG. 2 shows a mask pattern in which a mask is created using the drawing data. The mask pattern is a chrome light-shielding film 1 formed on the transparent substrate 101.
In FIG. 02, the chromium light-shielding film in the design data portion was removed to form an opening. Here, exposure is performed by adjusting the exposure amount to the hole pattern 1 of 0.2 μm. At this time, the 0.25 μm hole pattern 2 in which the inside is double-exposed is overexposed, so that the size is increased to 0.225 μm. The value of 0.225 μm is a dimension obtained from the linearity shown in FIG. 0.2 μm on mask
In order to obtain a 0.25 μm photosensitive resin pattern under the condition that a 0.2 μm photosensitive resin pattern can be obtained as a hole pattern, it is necessary to set the vertical axis (photosensitive resin pattern dimension) of FIG.
A line is drawn horizontally from the position of 25 μm, the intersection with the linearity curve is determined, and the horizontal axis (mask dimension) of the intersection is read, indicating that a 0.225 μm hole pattern is necessary. Therefore, when exposure is performed on the substrate coated with the photosensitive resin using this mask, as shown in FIG.
The hole pattern 1 and the 0.25 μm hole pattern can be simultaneously formed on the photosensitive resin 103 with high accuracy.

When the pattern is enlarged by performing double exposure in this manner, the dimensions can be controlled by the shape and area of the superposition.

In this case, the data for double exposure is arranged inside the 0.2 μm data, but other methods of double exposure are possible. For example, as shown in FIG. 5, data 22 for double exposure may be arranged at a constant width on the outer periphery of the 0.2 μm data 11. Further, as shown in FIG. 6, if the data 32 for double exposure is arranged at the four corners of the 0.2 μm hole pattern 11, not only the control of the pattern size but also the rounding of the corner can be improved.

(Embodiment 2) Next, Embodiment 2 of the present invention
Will be described. Here, the design of a photomask for forming hole patterns of 0.2 μm and 0.25 μm on a semiconductor substrate under the same exposure conditions as in the first embodiment will be described.

FIG. 7 shows design data used in the present mask manufacturing method. Here, both the 0.2 μm hole (for opening) pattern 1 and the 0.25 μm hole pattern 2 are 0.2 μm data 11 in the design (CAD) data.
a and 11b. Further, in the present embodiment, when the drawing apparatus has a proximity correction mechanism (for example, shot rank correction: a function of setting an exposure amount for each pattern) without performing double exposure, the same applies. The effect is obtained.

That is, 0.25 which enlarges the pattern
A special exposure rank is set for the μm hole pattern 2, and the 0.2 μm data 11b is set to be 20% over-exposed to the same 0.2 μm data 11a. Therefore, when mask drawing is performed using the present mask drawing data, the 0.25 μm hole pattern 2 can be processed into a 0.225 μm hole pattern on the mask. Therefore, when exposure is performed using this mask, hole patterns of 0.2 μm and 0.25 μm can be simultaneously formed in the photosensitive resin.

The proximity effect correction means that the pattern size fluctuates due to the density of the pattern at the time of drawing a mask. For this purpose, a method of separately setting the exposure amount of a specific pattern is used. Therefore, this is a method of forming a mask pattern based on design data. In the present invention, this function is used to form a pattern that does not ride on the grid. For this purpose, design data is created with dimensions smaller than the desired mask pattern (not on the grid) and on the grid. Then, the film is fattened by the amount of exposure light to finish a desired mask pattern. The design data is reduced when the exposure amount of the photosensitive resin pattern at the time of mask drawing is low (under exposure)
If it is higher (overexposure), the shape will be better,
This is because the dimensional accuracy is good.

(Embodiment 3) Next, Embodiment 3 of the present invention.
Will be described. Here, the design of a photomask for forming hole patterns of 0.2 μm and 0.25 μm on a semiconductor substrate under the same exposure conditions as in Embodiment 1 will be described.

FIG. 8 shows design data used in the present mask manufacturing method. Here, both the 0.2 μm hole (for opening) pattern 1 and the 0.25 μm hole pattern 2 are 0.2 μm data 11 in the design (CAD) data.
a and 11. However, in this embodiment, without performing double exposure, the 0.25 μm hole pattern 2 has
A fine pattern having a size that cannot be resolved by the drawing apparatus is formed. Here, the size of one grid (0.
(025 μm square) pattern is arranged every other grid.

When this CAD data is drawn by a mask drawing apparatus, this fine pattern is not resolved, and the pattern shape is enlarged by 1/2 grid on each side. Therefore, 0.25
The μm hole pattern is 0.225 in the mask pattern.
μm, which is 0.25 μm when transferred onto a semiconductor substrate.
m holes can be formed.

[0039]

As described above, according to the present invention, a mask pattern that does not ride on the grid is formed by temporarily resizing a pattern once and further over-exposing the pattern to form a desired pattern on a semiconductor substrate. A photosensitive resin pattern having dimensions can be obtained. Therefore, there is an effect that the linearity can be corrected in finer increments than the limit of the grid size at the time of manufacturing the mask, and the effect of improving the dimensional accuracy is particularly great in a hole pattern with poor linearity.

[Brief description of the drawings]

FIG. 1 is a diagram showing design data used in a photomask manufacturing method according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a mask pattern obtained by the photomask manufacturing method according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a relationship (linearity) between a mask pattern dimension and a photosensitive resin pattern dimension used in the photomask manufacturing method of the present invention.

FIG. 4 is a plan view showing a photosensitive resin pattern on the semiconductor substrate obtained by using the photomask according to the first embodiment of the present invention.

FIG. 5 is a diagram showing another example of design data used in the photomask manufacturing method of the present invention.

FIG. 6 is a diagram showing another example of design data used in the photomask manufacturing method of the present invention.

FIG. 7 is a diagram showing design data used in a method for manufacturing a photomask according to Embodiment 2 of the present invention.

FIG. 8 is a view showing design data used in a photomask manufacturing method according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a light intensity distribution obtained by using a conventional photomask.

FIG. 10 is a diagram showing the linearity of a hole pattern obtained by a conventional photomask.

[Explanation of symbols]

 1 0.2 μm hole pattern 2 0.25 μm hole pattern 11, 11a, 11b 2 μm data 12, 22, 32 Double exposure data 13 Fine pattern 101 Transparent substrate 102 Light shielding film 103 Photosensitive resin

Continuation of the front page (56) References JP-A-10-256124 (JP, A) JP-A-5-36595 (JP, A) JP-A-1-181422 (JP, A) JP-A-63-17526 (JP) JP-A-63-293822 (JP, A) JP-A-5-11433 (JP, A) JP-A-3-48420 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) H01L 21/027 G03F 1/08

Claims (2)

(57) [Claims] 1. A method of manufacturing a photomask having a plurality of types of hole patterns having different sizes from each other and transferring the hole patterns to a photosensitive resin by transmitted illumination, wherein the plurality of types of hole patterns are transferred to a desired transfer size. The desired mask pattern does not fit on the grid
Is smaller than the desired mask pattern and
To create the design data and draw by over-exposure.
Finish the desired mask pattern by painting
If the desired mask pattern is on the grid,
Create design data for the desired mask pattern and
The desired mask pattern is drawn by drawing light.
A plurality of types of hole patterns. 2. At least one type of hole pattern among the plurality of types of hole patterns further creates double exposure data inside the hole pattern data, and double exposes the double exposure data portion. 2. The method for manufacturing a photomask according to claim 1, wherein the exposure amount is set according to: