JPH05197144A - Pattern forming method - Google Patents

Abstract

PURPOSE:To provide the pattern forming method capable of suppressing the film reduction at the center section of a resist pattern and capable of forming the good pattern even when the half-tone phase shift method is used. CONSTITUTION:In the pattern forming method performing exposure and development for a photosensitive resin film 23 formed on a Si substrate 22 with an exposure mask formed with a mask pattern made of a semi-transparent material (Si) 21 giving the optical phase difference to the transmitted light on a translucent substrate (SiO2) 20 to form a desired pattern, a positive type resist keeping the film remaining ratio of 90% or above when the whole surface of the photosensitive resin film 23 is irradiated with the same light intensity as the maximum light intensity E' obtained at the center section of the mask pattern while the light intensity E corresponding to the image intensity Ie at the edge portion of the pattern is given is used for the photosensitive resin film 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithography process in a semiconductor manufacturing apparatus manufacturing process, and more particularly to a resist pattern forming method for exposing a resist by a halftone phase shift method.

[0002]

2. Description of the Related Art With the progress of semiconductor technology, semiconductor devices, and eventually semiconductor elements, are being accelerated and highly integrated. Along with this, the need for miniaturization of patterns is increasing more and more, and miniaturization and high precision of pattern dimensions are also required.

For the purpose of satisfying this demand, short-wavelength light such as far-ultraviolet light has been used as an exposure light source. However, Kr is about to be used in the next-generation exposure light source.
Although a chemically amplified resist is being developed as a resist material for the process using the 248 nm oscillation line of the F excimer laser, it is still in the research stage and it is still difficult to put it to practical use at this point. In this way, when the wavelength of the exposure light source is changed, it is necessary from the material development to the practical use, and thus it takes a long time before it is put into practical use.

In recent years, attempts have been made to miniaturize the exposure light source without changing it. One of the methods is the phase shift method. In this method, a phase inversion layer is partially provided in the light transmitting portion to eliminate the influence of diffraction of light from an adjacent pattern and improve the pattern accuracy. There are several types of this phase shift method, and the Levenson type, which is formed by alternately providing the phase difference between two adjacent light transmitting portions by 180 °, is particularly known.

However, it is difficult for the Levenson type phase shift method to exert its effect when three or more patterns are adjacent to each other. That is, the optical phase difference between the two patterns is 1
At 80 °, the other pattern is in phase with one of the previous two patterns, resulting in a phase difference of 1
There is a problem in that patterns of 80 ° are resolved, but patterns of 0 ° in phase difference are not resolved. In order to solve this problem, it is necessary to fundamentally rethink the device design, and it is quite difficult to put it into practical use immediately.

On the other hand, there is a halftone method as a method using the phase shift method and requiring no device design change. The principle of the halftone phase shift method is shown in FIG. In the halftone mask, the mask pattern 51 formed on the transparent substrate 50 is formed of a semitransparent film. This translucent film transmits the exposure light with an amplitude transmittance of 1 to 16%, and the phase difference of the light transmitted through the mask pattern is 1 with respect to the transmission portion.
The film thickness was adjusted so as to be within 80 ± 10 °. By doing so, it becomes possible to make the light intensity on the wafer corresponding to the edge portion of the mask pattern steep and improve the resolution. That is, a steep image intensity (shifter edge effect) at the edge portion is obtained by the optical phase inversion effect at the pattern edge portion, and the sidewall angle of the resist pattern is improved.

However, in the halftone phase shift method, while the resolution performance of the edge portion is improved, the phenomenon caused by the light transmission of the mask pattern is unavoidable. That is, when the positive type resist is used, the film thickness is reduced in the central portion of the resist pattern, and when the negative type resist is used, the residual film is generated in the space portion.

FIG. 6 shows a pattern shape (a) when a large area pattern formed using a positive resist is exposed by a normal Cr mask and a pattern shape when exposed by a halftone phase shift method. (B) is shown. In the halftone mask, since a small amount of light is transmitted in the dark part, in a comparatively large pattern, film loss occurs in the central part of the pattern as shown in (b).

[0009]

As described above, in the conventional halftone phase shift method, the side wall angle of the resist pattern is improved by using the semitransparent film having a certain degree of transparency in the light shielding portion. However, there has been a problem that a phenomenon caused by the mask pattern transmitting light, particularly when a positive resist is used, the film thickness of the central portion of the resist pattern is reduced.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to suppress film loss in the central portion of a resist pattern even when the halftone phase shift method is used. Another object of the present invention is to provide a pattern forming method capable of forming a good resist pattern.

[0011]

The essence of the present invention is that the use of a positive type resist having a high contrast with respect to the amount of exposure causes a film loss in the central portion of the resist pattern, which is a problem in the halftone phase shift method. It is to prevent the phenomenon.

That is, according to the present invention (claim 1), a semiconductor substrate is formed by using an exposure mask having a mask pattern made of a semitransparent material which gives an optical phase difference to transmitted light on a transparent substrate. In a pattern forming method of forming a desired pattern by exposing and developing a photosensitive resin film formed on a substrate, a light intensity Ic (this When the light intensity E) corresponding to the image intensity Ie of the portion corresponding to the edge is given, the maximum light intensity obtained at the central portion of the mask pattern is E ′, and the light intensity equal to this light intensity E ′. This is a method in which a positive resist whose residual film ratio maintains a desired value or more when irradiated on the entire surface of the photosensitive resin film is used.

Further, the present invention (claim 2) uses an exposure mask in which a mask pattern made of a semitransparent material which gives an optical phase difference to transmitted light is formed on a transparent substrate, and an optical system is used. Formed on the semiconductor substrate by annular illumination in which a dark portion is formed with a radius of d from the center satisfying the relation of 0 <d <L with respect to the surface of the light source or the radius L of the secondary light source uniformized by In a pattern forming method of forming a desired pattern by exposing and developing a photosensitive resin film, a light intensity Ic (corresponding to an edge at this time) at which a desired pattern is resolved as a desired dimension as a photosensitive resin film. When the light intensity E) corresponding to the partial image intensity Ie is given, the maximum light intensity obtained at the central portion of the mask pattern is E ′, and the light intensity equal to this light intensity E ′ is applied to the entire surface of the photosensitive resin film. Residual film when irradiated There is a method to use a positive type resist to maintain the above desired value.

Here, the contrast of the positive resist with respect to the exposure amount can be improved by, for example, increasing the composition ratio of the low molecular weight resin in the resist.

[0015]

FIG. 3 shows a halftone mask substrate and an image intensity distribution when a line & space pattern is exposed using the substrate. The halftone mask substrate is a quartz substrate 30.
It is configured by forming a pattern 31 of a semitransparent film on the top. Comparing the image intensity distribution with the halftone mask, it can be seen that 31 which originally should be shielded has image intensity.
In order to process the resist pattern with respect to the mask with high dimensional accuracy, the light intensity E corresponding to the image intensity Ie of the portion corresponding to the edge of the semitransparent film 31 may be given. At this time,
The light intensity E'corresponding to the image intensity Id at the center of the portion to be shielded is E '= E * Id / Ie (1)

It is represented by Exposure is performed using a halftone mask substrate, and at this time, in order that the residual film ratio of the positive resist pattern is equal to or more than a desired amount, the light intensity E ′ shown above is required.
In the above, it is necessary that the residual film rate T ′ of the resist is not less than the desired residual film rate T. As a guideline, it is desirable to select the resist to be used with the γ characteristic expressed by the equation (2) by using the residual film rate T ′ of the resist at the light intensity E ′. It is necessary to use a resist that satisfies the relational expression represented by the desired residual film rate T. γ = T ′ / log ₁₀ (E / E ′) (2) γ = T ′ / log ₁₀ (E / E ′) ≧ T / log ₁₀ (E / E ′) = γ ′ ... (3)

As an example, two types of positive resists having sensitivity characteristics shown in FIG. 4 will be compared. Now, it is assumed that the residual film rate needs to be 90% or more. Also, E ′ = 0.
Suppose there is a 5E relationship. At this time, T / log
₁₀ (E / E ') = 3.0. First resist 41
Then, when the exposure amount E corresponding to Ie is given, the exposure amount E '
The residual film rate is maintained at 100%, and the γ value obtained by Eq. (2) is 3.3, which is a large value compared to 3.0. In this case, even if the mask portion has a light intensity, the above-mentioned FIG.
A good resist pattern without film reduction as shown in (a) can be obtained. However, in the case of the second resist 42, the residual film rate can be maintained at only 70% at the exposure amount E '. Actually, the γ characteristic of this resist is 2.3, which is smaller than that of 3.0, and in this case, the resist pattern has a film thickness reduction at the pattern center as shown in FIG. 6B. When performing exposure using a halftone mask in this way,
The selection of the resist is important, and when the exposure dose E for processing the desired pattern with high dimensional accuracy is given, it is necessary to use a resist that can maintain the residual film rate even if the exposure dose E ′ shown in equation (1) is given. is necessary.

[0018]

The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in the method of one embodiment of the present invention. As the lamp of the light source, a mercury lamp g line 436 nm, h line 405 nm, i
Other than line 365nm, excimer laser exposure (KrF
Etc.) are used. Then, they become uniformized light by an optical system including an optical integrator (fly-eye lens) and the like in order to improve irradiation uniformity.
FIG. 1 shows the luminous flux after passing through the optical system. In the figure, 1 is a homogenized light beam (secondary light source), 2 and 3 are aperture stops, 4 is a secondary light source irradiation optical system, 5 is a projection optical system, 6 is a mask, and 7 is a wafer.

In such a reduction projection exposure apparatus,
The pattern formation characteristics (resolution, depth of focus, etc.) are determined by the NA (NA = sin θ) of the projection optical system 5 and the coherency σ (σ = sin φ / sin δ) of the illumination light. N
The larger A is, the higher the resolution is, but the depth of focus is decreased. Further, when the coherency σ value becomes small, the edge of the pattern is emphasized, so that the side wall becomes closer to the vertical side and the cross-sectional shape becomes a good pattern shape, but the resolution in a fine pattern becomes poor and resolution can be achieved. The focus range becomes narrow. On the other hand, if the σ value is large, the resolution in a fine pattern and the focus range that can be resolved are slightly better, but the sidewall inclination of the pattern cross section is gentle, and in the case of a thick resist, the cross-sectional shape is trapezoidal or triangular. Therefore, as a relatively balanced σ value, σ = 0.5 to 0.7 is fixedly set. σ
Since the size of the light source surface of the secondary light source 1 may be determined to set the value, a circular aperture stop 2 for setting the σ value is generally placed immediately after the light source surface of the secondary light source 1.

FIG. 2 is a sectional view showing a resist pattern forming process according to the first embodiment of the present invention. The projection exposure mask (halftone mask) 6 is formed by forming a pattern 21 of a Si film (semitransparent film) on a SiO ₂ substrate (transparent substrate) 20, as shown in FIG. 2A. Specifically, the Si film 21 is formed on the SiO ₂ substrate 20 to a thickness of 61.
of the electron beam resist (SAL601) with a film thickness of 0.5 μm, and a coatable organic conductive film is further coated thereon and exposed to the electron beam. Then, it was developed to form a resist pattern. Further, using this resist as a mask, the Si film 21 is subjected to chemical dry etching (CDE) to remove unnecessary portions of Si.
Was created by removing. The Si film formed at this time has a refractive index n = 4.57 with respect to the g-line of a mercury lamp, and has a phase difference of 180 ° with respect to the light transmitting portion and an amplitude transmittance of 15%.

When an exposure amount E for accurately processing a desired 0.6 μm pattern is applied using this mask, the maximum light intensity at the center of the large area corresponding to the halftone mask at this time is 0. It was confirmed to correspond to 59E. Further, 90% or more is required as the residual film characteristic of the large area pattern.

Using this projection exposure mask, numerical aperture NA
= 0.54 and a coherence factor σ = 0.5 were used to perform the exposure. As for the photosensitive resin film, as shown in FIG. 2B, a cresol novolak naphthoquinone diazide positive resist 23 was formed to 1.3 μm on a Si substrate 22 and baked at 90 ° C. for 5 minutes. It is a thing. The positive type resist used here was 5.2 whose initial film thickness was standardized to 1 and which greatly exceeded the γ'characteristic of 3.92 defined by the equation (2).

Then, using the above-mentioned projection exposure mask, a positive resist 23 was exposed as shown in FIG. 2 (c). Here, 25 is an original exposure area, and 26 is an exposed area which should be originally shielded from light. Next, tetramethylammonium hydroxide (TMAH)
Development was performed with a 2.38% solution for 50 seconds to form a resist pattern 27 as shown in FIG.

In this method, 110 ° C. before development,
It is also effective to carry out further baking for 1 minute. Through the above process, the focus margin is 0.6 μm pattern.
The resolution was 2.1 μm with high accuracy, and the residual film rate of the large area pattern was maintained at 95% at this time.

The halftone mask used in this embodiment,
Next, an experiment was carried out in which ring illumination was also used. The ring-shaped illumination is based on the diameter L of the fly-eye lens group, and the radius d =
0.65 L was shielded. When the annular illumination and the halftone mask were combined, the 0.6 μm pattern resolved with a focus margin of 2.6 μm.

As described above, according to this embodiment,
By selecting and using a positive resist satisfying the expression (3), it is possible to prevent the phenomenon of film loss in the central portion of the resist pattern, which is a problem in the halftone phase shift method. Therefore, a good resist pattern can be formed, and the accuracy of the subsequent pattern processing can be improved.

The present invention is not limited to the above embodiment. In the examples, a cresol novolak naphthoquinonediazide positive resist resist was used as the photosensitive resin, but the present invention is not limited to this, and the contrast with respect to the exposure amount is high, and any resist satisfying the above formula (3) can be used. Is. Further, even in the case of an ordinary resist, it is possible to satisfy the expression (3) by increasing the resin composition ratio of the low molecular weight. Other,
Various modifications can be implemented without departing from the scope of the present invention.

[0029]

As described above, according to the present invention, by using a positive resist having a high contrast with respect to the exposure amount, the film reduction in the central portion of the resist pattern, which is a problem when the halftone phase shift method is used, is achieved. Can be suppressed, and a good resist pattern can be formed. The present invention is also effective when a halftone mask is combined with annular illumination exposure.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in an embodiment method of the present invention,

FIG. 2 is a sectional view showing a resist pattern forming step according to an embodiment of the present invention,

FIG. 3 is a diagram showing a relationship between a halftone mask substrate and an image intensity distribution,

FIG. 4 is a diagram showing sensitivity characteristics of two types of positive resists;

FIG. 5 is a diagram for explaining the principle of the halftone phase shift method,

FIG. 6 is a diagram for explaining a problem of the halftone phase shift method.

[Explanation of symbols]

1 ... Secondary light source, 2, 3 ... Aperture stop, 4 ... Secondary light source irradiation optical system, 5 ... Projection optical system, 6 ... Mask, 7 ... Wafer, 20, 30 ... SiO ₂ substrate (transparent substrate), 21, 31 ... Si film (semitransparent film), 22 ... Si substrate, 23 ... Positive resist, 25, 26 ... Exposure region, 27 ... Resist pattern, 41 ... Resist pattern obtained using first resist, 42 ... A resist pattern obtained by using the resist of 2.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 8831-4M H01L 21/30 341 S 7352-4M 361 F

Claims (2)

[Claims] 1. A photosensitive material formed on a semiconductor substrate using an exposure mask having a mask pattern made of a semitransparent material that gives an optical phase difference to transmitted light on a transparent substrate. In a pattern forming method of exposing and developing a resin film to create a desired pattern, as a photosensitive resin film, a light intensity Ic at which a desired pattern is resolved according to a desired dimension (at a portion corresponding to an edge at this time). When the light intensity E) corresponding to the image intensity Ie is given, the maximum light intensity obtained at the center of the mask pattern is E ′, and the entire surface of the photosensitive resin film is irradiated with a light intensity equivalent to this light intensity E ′. In this case, a pattern forming method is characterized in that a positive resist whose residual film ratio is maintained at a desired value or more is used. 2. A surface of a light source made uniform by an optical system using an exposure mask having a mask pattern made of a semitransparent material which gives an optical phase difference to transmitted light on a transparent substrate. Alternatively, with respect to the radius L of the secondary light source, the photosensitive resin film formed on the semiconductor substrate is exposed to light by the annular illumination in which a portion having a radius d from the center satisfying the relationship of 0 <d <L is formed as a dark portion. In a pattern forming method of developing to form a desired pattern, as a photosensitive resin film, a light intensity Ic at which a desired pattern is resolved according to a desired dimension (corresponding to an image intensity Ie of a portion corresponding to an edge at this time) When the light intensity E) is given, the maximum light intensity obtained at the central portion of the mask pattern is E ′, and when the entire surface of the photosensitive resin film is irradiated with a light intensity equivalent to this light intensity E ′, the residual film ratio is A port that maintains the desired value or more A pattern forming method characterized by using a di-type resist.