JP3047823B2 - Exposure mask and pattern forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an exposure mask for reduced projection exposure and a method for forming a fine pattern using the same.

[0001]

2. Description of the Related Art With the recent increase in the degree of integration of semiconductor integrated circuits, finer circuit patterns have been required. For example, in a 64 Mb DRAM, a gate length of 0.3 is required.
A transistor of 5 μm or less is required. At present, as this fine processing technology, the i-line of a mercury lamp (wavelength 365 n
m) is used as the exposure light source,
Recently, KrF excimer laser light (wavelength: 248 nm) has begun to be used as an exposure light source.

In a conventional fine pattern forming method using a positive type photoresist, a positive type photoresist is first applied on a semiconductor substrate, and then a desired integrated circuit pattern is formed of a light shielding film such as Cr. The photomask drawn by the above is irradiated with ultraviolet light, and the pattern is imaged on the photoresist through a projection lens. Subsequently, a post-exposure bake treatment is performed as necessary, and then development is performed using an organic alkali developer to form a fine pattern of a resist (FIGS. 2B and 2C).

In a conventional pattern forming method, a high NA of an exposure apparatus and a high performance of a photoresist are required.
Although pattern miniaturization has been achieved steadily,
On the other hand, with the miniaturization, the problem that the size variation due to the pattern density, that is, the effect of the optical proximity effect is large has become apparent.

[0004]

The problem of the optical proximity effect in the conventional pattern forming method is that a line pattern having the same line width, such as a gate electrode forming step, has a 1: 1 ratio.
Existing in the same mask at different distances between adjacent patterns from a line-and-space (L & S) level to an isolated line, and the area of the pattern portion is 50 in the photomask.
In a process as small as less than 10% (FIG. 2a), this is a particularly serious problem.

[0005] The cause is considered as follows. In the conventional case, the space between the patterns becomes a light transmitting portion on the mask. The change in the space width means a change in the area of the light transmitting portion, and the amount of diffracted light passing through the projection optical system itself changes greatly. For this reason, the optical image on the image plane changes greatly depending on the pattern density, and a strong optical proximity effect occurs.

As a method of reducing the optical proximity effect, there has been proposed a method of correcting the dimension or shape of a pattern on a photomask so that the completed dimension of the pattern becomes a constant value (for example, see Japanese Patent Application Laid-Open No. H03-36549). These methods are complicated and require a lot of time and labor for designing, manufacturing or inspecting a photomask.

An object of the present invention is to solve the above-mentioned problems and to provide an exposure mask capable of easily forming a pattern with high dimensional accuracy and a pattern forming method using the exposure mask.

[0008]

The exposure mask of the present invention comprises:
The pattern consisting of the light transmitting part formed on the exposure mask
Lighting with a coherence factor between 0.4 and 0.9
An exposure mask for transferring on a negative photoresist formed on a substrate using light , wherein the pattern has a plurality of types of distances between adjacent patterns, and the area occupied by the pattern formed by the light transmitting portion is It is characterized by being less than 50% of the area of the light irradiation area of the exposure mask.

Further, in the pattern forming method of the present invention, the step of forming a negative photoresist film on a substrate and the step of forming a pattern comprising a light transmitting portion formed on an exposure mask to a plurality of types of distances between adjacent patterns. And the area occupied by the pattern is 50 times the area of the light-irradiated area of the exposure mask.
% By using an exposure mask having a coherence factor of 0.4 to 0.9 using an exposure mask having a coherence factor of less than 0.4%, and a step of developing the photoresist film. . (Action)
FIG. 1 shows a bright pattern forming method. Pattern of the present invention
In the forming method, as shown in FIG.
The pattern portion becomes the light transmitting portion 12 on the mask, and the pattern
The space between the electrodes becomes the light shielding portion 11 on the mask. Spec
Even if the source width changes, only the area of the light shielding part changes.
Of the light transmitting part corresponding to the line pattern part of the same line width.
The area does not change.

For this reason, the change in the optical image on the image plane due to the pattern density is small, and when a pattern is formed using a negative photoresist as shown in FIGS. The effect is reduced.

In particular, in order to effectively reduce the optical proximity effect, the coherence factor (σ) of the exposure apparatus must be set to 0.4.
It is known from the calculation result of the optical image that it is desirable to set the value to 0.9 or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of the present invention will be described with reference to the drawings. FIG. 3 schematically shows a photomask used in the present embodiment. A space 32 (light-shielding portion) 31 is set to 0.25 μm for a line 32 (light-transmitting portion) having a width of 0.25 μm.
From 1 μm to 1 μm.

Using a KrF excimer laser as an exposure light source,
Chemical amplification type spin-coated to a thickness of 0.7 μm on a Si substrate by changing the numerical aperture (NA) of the reduction projection exposure apparatus to 0.5 and changing the coherence factor (σ) from 0.4 to 0.9. Was exposed to the negative photoresist. Subsequently, a post-exposure bake was performed and a pattern was formed by alkali development. The exposure amount was such that an L & S pattern of line / space = 0.25 μm / 0.25 μm was formed as designed.

As a result, as shown in FIG.
In any case of 0.9, the dimensional variation due to the optical proximity effect was suppressed to less than 10% of the design size.

On the other hand, when a conventional pattern forming method, that is, a photomask and a positive photoresist in which a line pattern portion is formed by a light shielding portion and a space portion is formed by a light transmitting portion, the following results are obtained.

Using a photomask shown in FIG. 4, that is, a photomask in which the brightness is reversed from that in FIG. 3, a pattern was formed on a chemically amplified positive resist under the same conditions as in the above embodiment. In this case, as shown in FIG. 6, except for the condition of σ = 0.7, the dimensional variation due to the optical proximity effect is 10 times the design dimension.
%, And particularly at σ of 0.6 or less, the dimensional change was very remarkable. (Embodiment 2) As another example, the result when the σ is fixed to 0.7 and the NA is changed from 0.45 to 0.55 in the above embodiment is as follows.

In the method of the present invention, as shown in FIG.
Even if A was changed, the effect of the optical proximity effect was hardly observed, and it was confirmed that the dimensional control accuracy was excellent.

On the other hand, in the conventional method, when the NA was reduced to 0.45 as shown in FIG. 8, remarkable thinning due to the optical proximity effect was observed.

In the two embodiments described above, the case where the line width of the pattern is constant has been described. However, the present invention is effective even when patterns having different line widths coexist on the same mask. Needless to say,

[0020]

As described above, according to the method of the present invention, the dimensional fluctuation due to the optical proximity effect can be reduced.
Both dimensional control accuracy and exposure latitude are greatly improved.

[Brief description of the drawings]

FIG. 1 is a view for explaining a pattern forming method of the present invention.

FIG. 2 is a diagram illustrating a conventional pattern forming method.

FIG. 3 is a schematic view of a photomask according to the method of the present invention.

FIG. 4 is a schematic view of a photomask according to a conventional method.

FIG. 5 is a diagram showing the optical proximity effect of the method of the present invention in Example 1.

FIG. 6 is a diagram showing an optical proximity effect of a conventional method.

FIG. 7 is a diagram showing the optical proximity effect of the method of the present invention in Embodiment 2.

FIG. 8 is a diagram showing the optical proximity effect of the conventional method.

[Explanation of symbols]

10, 20, 30, 40 Photomask 11, 21, 31, 42 Light-shielding part 12, 22, 32, 41 Light-transmitting part 13, 23 Glass substrate 14, 24 Light-shielding film 15 Negative photoresist 25 Positive photoresist 16, 26 semiconductor substrate 17, 27 ultraviolet light or far ultraviolet light 18, 28 resist pattern

Claims (3)

(57) [Claims] 1. A pattern comprising a light transmitting portion formed on an exposure mask and having a coherence factor of 0.4 or more.
In an exposure mask that is transferred onto a negative photoresist formed on a substrate using illumination light of 0.9 or less, the pattern has a plurality of types of distances between adjacent patterns, and is formed of a light transmitting portion. An exposure mask, wherein the occupied area is less than 50% of the area of the light irradiation area of the exposure mask. 2. The exposure mask according to claim 1, wherein a line width of the light transmitting portion is the same between the patterns. 3. A step of forming a negative type photoresist film on a substrate, and a pattern comprising a light transmitting portion formed on an exposure mask has a plurality of types of distances between adjacent patterns and occupies the pattern. The photoresist film is coated with a coherence factor of 0.4 using an exposure mask whose area is less than 50% of the area of the light irradiation area of the exposure mask.
A pattern forming method, comprising: a step of exposing with an illumination light of 0.9 or less and a step of developing the photoresist film.