JPH0787174B2 - Pattern formation method - Google Patents

Description

The present invention relates to a pattern forming method for forming a fine resist pattern by a reduction projection exposure method.

[Outline of Invention]

According to the present invention, when a fine photoresist pattern formed by arranging the constituent elements of the pattern with an interval of the minimum resolution line width or less is formed by the reduction projection exposure method, the exposure pattern is at an interval larger than the minimum resolution line width. By dividing the exposure pattern into a plurality of exposure patterns and performing reduction projection exposure for each exposure pattern, a pattern having an interval smaller than the minimum resolution line width can be clearly formed with high resolution.

[Conventional technology]

BACKGROUND ART In the formation of various fine patterns including semiconductor manufacturing technology, photolithography by applying photographic technology, that is, processing technology by forming a photoresist pattern is widely used.

Recently, for example, pattern exposure for obtaining a photoresist pattern used in a process of forming a fine circuit element with a pattern of about 1 μm, such as in a very large semiconductor integrated circuit (VLSI), is performed by contacting an exposure mask with the photoresist film. The reduced projection exposure method, which has many advantages over the so-called contact transfer method, has been widely used (for example, Semiconductor World 1
982, 5.P.58-82).

Generally, when manufacturing a fine device such as a semiconductor device, a plurality of devices, for example, VLSI devices are formed in an array on a common semiconductor wafer, and then the wafer is divided into individual device parts to simultaneously form a plurality of semiconductor devices. The method of obtaining is adopted. Therefore, in the photolithography technique used for manufacturing a semiconductor device, usually, the same photoresist pattern is repeatedly arranged in two directions X and Y which are orthogonal to each other on a wafer.

In the reduction projection exposure method, these patterns are formed individually. A method of forming a resist pattern by this projection exposure method will be described with reference to FIG. In the figure, (1) shows, for example, a semiconductor wafer on which a photoresist pattern is to be formed. In this case, the photoresist film (2) is applied on the wafer (1) and placed on the moving stage (3). This moving stage (3) is shown in FIG.
In FIG. 1, required intermittent movement can be performed in the Y direction orthogonal to the paper surface. This moving stage
For example, it can move with high accuracy of about ± 0.02 μm.

Then, a predetermined pattern exposure is performed by reduction exposure on the photoresist film (2) on the wafer (1) at one movement position of the movement stage (3), and this pattern exposure is performed for each movement of the stage (3). At the position, a plurality of exposure patterns (8) are arranged on the wafer (1) in the X and Y directions, respectively, as shown in FIG.

In the reduction exposure, as shown in FIG. 1, light from a light source (4) such as a mercury lamp is passed through a required optical lens system (5),
An original image (6) having a magnified optical image of a target exposure pattern (8), a so-called reticle, is irradiated, and the optical image is contracted and irradiated onto a photoresist film (2) by a contracting lens system (7) to form a photoresist film. The fine exposure pattern (8) is formed in (2). This exposure is performed at the position where the moving stage (3) is intermittently moved by a predetermined amount with respect to X and Y as described above, and a plurality of fine exposure patterns (8) are shown in the X and Y directions as shown in FIG. A plurality of arrays are formed in each.

Then, in practice, the photoresist film (2) is subjected to a development treatment to remove each exposed portion or unexposed portion of the fine exposed pattern (8) to form a resist pattern of a desired pattern.

This photoresist pattern is used, for example, as an etching resist, and selectively etches, for example, a metal layer deposited on the wafer (1), a diffusion mask layer, or the like to form, for example, an electrode or a wiring pattern or a diffusion mask. Use for pattern formation.

As described above, the reduction projection exposure method forms a plurality of exposure patterns individually, but has many advantages over the so-called contact transfer method in which a plurality of exposure patterns are exposed at the same time. . That is, in the case of the contact transfer method, the exposure optical mask is directly adhered to the entire surface of the resist film (2), and the exposure process is simultaneously performed on the entire surface of the resist film. In this case, however, scratches may occur such as foreign matter such as dust entering between the exposure optical mask and the resist film (2), and the exposure optical mask is severely damaged and cannot be used repeatedly. Since it is difficult to completely adhere the film and the resist film to each other over the entire surface, there arises such a disadvantage that the transfer accuracy of the pattern is deteriorated.

The reduction projection exposure method described above has an advantage that these problems can be solved.

However, such a reduction projection exposure method also causes a problem in miniaturization of the photoresist pattern. That is, in the reduction projection exposure method, the resolution is limited by the diffraction of light. The minimum resolution line width in this case is It is known to be given in. However,
Here, k is a proportional constant in consideration of the pattern forming process and is generally given as k = 0.8, λ is the exposure wavelength, and NA is the numerical aperture of the reduction projection lens system. Now for example λ = 0.436
When μm, NA = 0.42, the minimum resolution linewidth is 0.83μ
m.

Therefore, for example, when pattern exposure is performed by an array of pattern constituent elements having a line width of 0.5 μm and a spacing smaller than the minimum resolution line width by this reduction projection exposure method,
Due to the light diffraction, the contrast of the light intensity between the exposed portion and the non-exposed portion becomes insufficient, and it becomes difficult to form a pattern by a clear arrangement of the pattern constituent elements.

Then, in order to reduce the minimum resolution line width itself, the exposure wavelength λ should be reduced as is clear from the equation (1), or
By increasing the numerical aperture NA. However, in practice, if the exposure wavelength λ is too small, the light absorption in the lens becomes large, or the exposure sensitivity of the photoresist is lowered, so there is a limit to the reduction of the wavelength λ, and the aperture of the lens system is limited. Since there is a restriction on the number NA as well, the minimum resolution line width cannot be sufficiently reduced, and it is not possible to sufficiently meet the current requirements such as the formation of a fine pattern with a width of 0.5 μm and an interval. Is occurring.

[Problems to be solved by the invention]

In the formation of a photoresist pattern by the above-described reduction projection exposure method, the present invention addresses the problem of the constraint of the minimum resolution line width, and the distance between the constituent elements of the target photoresist pattern is not more than the minimum resolution line width. Therefore, it is possible to reliably form the constituent elements of the fine photoresist pattern.

[Means for solving problems]

According to the present invention, in the pattern exposure of the pattern forming method for forming a photoresist pattern by the reduction projection exposure method, the distance between the constituent elements of the intended photoresist pattern is the numerical aperture NA or the exposure wavelength of the reduction projection lens in the reduction projection exposure. When it is less than or equal to the minimum resolution line width determined by λ, the exposure pattern for the photoresist is divided into a plurality of exposure patterns by extraction of constituent elements at intervals larger than the above-mentioned minimum resolution line width, and these are divided. Reduction projection exposure is performed for each pattern of each set to form one fine exposure pattern.

[Action]

According to the above-described method of the present invention, even though a photoresist pattern having a pattern interval equal to or smaller than the minimum resolution line width is formed, a pattern having a large interval equal to or larger than the minimum resolution line width for each exposure. As a result, the exposure is performed a plurality of times to expose the pattern in which all the constituent elements that form the target pattern are arranged, so that the reduction in contrast is avoided, and the exposure is excellent in sharpness, and therefore clear. Therefore, it is possible to form a fine exposure pattern and thus a photoresist pattern having excellent sharpness.

〔Example〕

Also in the pattern forming method according to the present invention, that is, the photoresist pattern forming method, the fine exposure pattern (8) is formed by the pattern forming method by the reduction projection exposure method described in FIG. As shown in FIG. 2, the same fine exposure pattern (8) is arrayed in the X and Y directions of the common resist film (2) by intermittent transfer in the Y and Y directions. However, in the present invention, a plurality of exposure steps are taken in forming each fine exposure pattern (8), that is, for one fine exposure pattern (8).

Now, for example, as shown by hatching in FIG. 3 to show the exposed portion S, the interval corresponding to the interval of the target pattern constituting element is the interval D which is the minimum resolution line width or less, A case will be described in which an exposure pattern (8) in which stripe-shaped exposure portions S having an exposure width W corresponding to the interval between the constituent elements of the pattern are arranged is exposed on the photoresist film (2). In this case, as shown in FIGS. 4A and 4B, an exposure pattern, that is, a photoresist film (2) corresponding to a pattern in which every other constituent element (stripe) of the target pattern is extracted. To the first and second exposure patterns (8A) and (8B) respectively extracted from the stripe-shaped exposure portions S described with reference to FIG. 3, and exposed by superposing them by two exposures. By doing so, the exposure pattern (8) shown in FIG. 3 is formed on the photoresist film (2). In this example, the first and second exposure patterns (8A) and (8B) are substantially the same pattern in which the exposure portions S each having the width W are arranged at the interval of 2D + W. In this case, a magnified optical image forming either one of the exposure patterns (8A) or (8B) is used as the original image (6) described in FIG. Then, when forming each one exposure pattern (8), a first exposure operation and a second exposure operation are performed, respectively. That is, in the first exposure operation, the original image (6) is subjected to the reduced projection light described in FIG. 1 on the photoresist film (2) to expose the exposure pattern (8A) or (8B) in FIG. Then, the stage (3) is moved so that the exposure pattern is moved by the distance (W + D) on the photoresist film (2) in the direction orthogonal to the stripe direction of the exposed portion S, and the second exposure operation is performed. I do.

In this way, the desired exposure pattern (8) of FIG. 3 is obtained by the first and second exposure operations. In this way, each exposure pattern (8) is transferred to the stage (3).
If it is performed at each intermittent transition position in the X and Y directions, a plurality of exposure patterns (8) are formed in the X and Y directions, respectively, as shown in FIG.

By subjecting the photoresist film (2) on which the exposure pattern (8) has been formed in this way to a developing process, a desired resist pattern can be formed.

According to such a method, even when the width W and the interval D of the exposure pattern (8) are smaller than the minimum resolution line width determined in the reduced projection exposure, the exposure pattern in each of the first and second exposure operations ( As shown in FIGS. 4A and 4B, 8A) and (8B) are pattern exposures with an interval of (2D + W), so (2D + W) is larger than the minimum resolution line width in the reduced projection exposure. With the intervals, high-contrast exposure can be performed in each of the first and second exposure operations.

Further, this will be explained with reference to the above-mentioned first and second
The exposure intensity distribution in the direction orthogonal to the stripe exposure portion S on the photoresist surface in each exposure operation has a peak at the center of the width W as shown in FIG. 5, and this peak portion is (2D + W). The distribution is arranged with a pitch.
In this case, if the pitch, that is, the exposure interval (2D + W) is equal to or more than the minimum resolution line width, the interference effect between the exposed parts due to the diffraction of light becomes small, and the peak of each exposure becomes steep and its contrast That is, the exposure peak value Im
Contrast C determined by ax and minimum value Imin, Is large. That is, for example, as shown in FIG. 6, when pattern exposure is performed with a distance D smaller than the minimum resolution line width corresponding to the finally obtained exposure pattern (8),
Due to mutual interference, the difference between Imax and Imin becomes small and the waveform of the exposure distribution becomes blunt, so that the contrast C becomes small.
Therefore, the photoresist pattern formed by exposure as shown in FIG. 6 becomes a pattern with poor sharpness and low sharpness, or it becomes substantially impossible to form a fine pattern of the photoresist pattern.

That is, for example, when the exposure pattern (8) having W = 0.5 μm and D = 0.5 μm is exposed, the period is 1.0 μm, whereas according to the present invention, the exposure is performed in each of the first and second exposures. Since the exposure interval (2D + W) = 1.5 μm, the period is 2.0 μm, which is twice as long as the conventional single exposure, and the contrast is improved by reducing the pattern density. It can be inferred from the fact that the lens can be regarded as a low-band filter whose transmittance decreases monotonically with respect to the spatial frequency when considered by Fourier optics.

As described above, according to the method of the present invention, the contrast of the exposure pattern can be increased, but it is also possible to combine a process having a light intensity contrast amplification effect to obtain a higher contrast.

In the above example, the pattern formation is performed by dividing the exposure into the first and second exposures, but the exposure may be performed in a plurality of divisions more than two. .

〔The invention's effect〕

As described above, according to the method of the present invention, even a fine pattern having a pattern interval smaller than the minimum resolution line width can be exposed with high contrast, so that it is possible to form a fine pattern by reduced projection exposure with excellent sharpness. To do.

According to the present invention, a plurality of exposures, for example, the first and second exposures are performed. Depending on the pattern, both exposures are substantially the same pattern (8A) as in the embodiment.
With (8B), the relative position between the photoresist film (2) and the projected optical image, that is, the original image (6), is moved by the moving stage (3) to perform each reduction projection exposure. However, in actuality, as described at the beginning, the moving accuracy of the moving stage (3) is as high as ± 0.02 μm, and therefore there is no fear that the relative movement will cause a decrease in accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory view of a reduction projection exposure method, FIG. 2 is a plan view showing an example of an arrangement pattern of an exposure pattern of a resist film, FIG. 3 is a plan view of an example of an exposure pattern, and FIGS. First
FIG. 5 is an exposure intensity distribution diagram according to the present invention, and FIG. 6 is an exposure intensity distribution diagram of a conventional method. (1) wafer, (2) photoresist film, (3)
Is a moving stage, (4) is a light source, (5) is an optical system,
(6) is an original image, (8) is a fine exposure pattern, and (8A) and (8B) are first and second exposure patterns.

Claims (1)

[Claims] 1. A pattern forming method for forming a pattern on a photoresist by a reduced projection exposure method, wherein a component of a target photoresist pattern has an interval of not more than a minimum resolution line width of the reduced projection exposure method. , The exposure pattern for the photoresist is divided into a plurality of exposure patterns by extracting the constituent elements of the constituent elements at intervals larger than the minimum resolution line width, and reducing each of the divided sets of patterns. A pattern forming method, characterized in that projection exposure is performed to form a photoresist pattern.