JPH05197160A - 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 resist pattern even when the half-tone phase shift method is used. CONSTITUTION:In the pattern forming method exposing and developing a photosensitive resin film 23 formed on a Si substrate 22 with an exposure mask formed with a mask pattern 21 made of a semi-transparent material (Si) giving the optical phase difference to transmitted light to form the desired pattern on a translucent substrate (SiO2) 20, a positive type resist is used for the photosensitive resin film 23, the resist 23 is bleached in a developer of 2.38%-TAMAH for 30 sec before exposure, and spin-drying is performed after washing to form a surface insoluble film 24.

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 manufacturing a semiconductor manufacturing apparatus, 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 the present time. If the wavelength of the exposure light source is changed in this way, it will take a considerable period of time from the material development to the 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 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 mask pattern edge portion 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, according to 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, in particular, when a positive resist is used, the 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 to suppress the decrease in the residual film rate, which occurs when a positive resist is used in the halftone phase shift method, by hardening the resist.

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 positive resist is used as the photosensitive resin film, and the surface of the resist is developed before the development of this resist. It is characterized in that a curing process is performed on the.

Further, the present invention (claim 2) uses an exposure mask in which a mask pattern made of a semitransparent film which gives an optical phase difference to transmitted light is formed on a transparent substrate.
With respect to the surface of the light source or the radius L of the secondary light source made uniform by the optical system, the radius d from the center satisfying the relationship of 0 <d <L
In the pattern forming method of forming a desired pattern by exposing and developing the photosensitive resin film formed on the semiconductor substrate by the annular illumination in which the part of is formed as the dark part,
A positive resist is used as the photosensitive resin film, and the surface of the resist is subjected to a curing treatment before the resist is developed.

Preferred embodiments of the present invention include the following (1) to (5). (1) As a semi-transparent film, the phase difference between the light transmitted through the semi-transparent film and the light transmitted only through the transparent substrate is (180 × (2n
+1) ± 10: Select a material and film thickness that satisfy the relationship within n = integer) °.

(2) As a resist curing treatment, the resist surface is immersed in an alkaline solution or an organic alkali developing solution before exposure, and further washed with water to form an insolubilized film on the resist surface.

(3) As a resist curing treatment, an insolubilized film is formed on the resist surface by irradiating the resist surface with ultraviolet light having photosensitivity in an atmosphere having a water content of less than 10% after exposure.

(4) The amplitude transmittance T of the mask pattern is set so as to satisfy the following expression with respect to the amplitude transmittance T ₀ of the light transmitting portion. 0.01 × T ₀ ≦ T ≦ 0.16 × T ₀

(5) For annular illumination, a first condensing optical system such as a fly's-eye lens for condensing light from the light source and the light condensed by the first condensing optical system are made uniform. And a second condensing optical system for condensing the light homogenized by the homogenizing optical system to irradiate the mask, and projection optics for projecting the light transmitted through the mask onto the semiconductor substrate. And a projection exposure apparatus having a system.

[0019]

There are a method of forming an insolubilized film on the surface of the photosensitive resin and a method of controlling the optical image to improve the film reduction caused by using the positive regist.
There are several methods for insolubilizing the photosensitive resin material. As one of the methods, there is a method of immersing the surface of the photosensitive resin film in an alkaline solution or an organic alkali developing solution to increase the relative concentration of elemental sulfur on the surface of the film to reduce the solubility. As another method of insolubilizing, there is a method of irradiating the resist film with ultraviolet light having photosensitivity in an atmosphere containing almost no water. This method forms a surface cross-linked film, and it is possible to further increase the insolubility by heating.

Here, when the insolubilized film is formed on the surface of the photosensitive resin, the insolubilized film can be removed at the time of development with a sufficient exposure amount in the portion to be exposed. On the other hand, the insolubilized film cannot be removed if the exposure amount is small in the portion that should not be exposed when the halftone mask is used. Therefore, when the halftone mask is used, it is possible to suppress film loss in a portion that should not be exposed, and it is possible to form a pattern having a good shape by eliminating the depression at the central portion of the pattern.

Further, although there is an annular illumination technique as a method for improving the characteristics of the residual film by an optical method, it is difficult to completely maintain the residual film even in this method. Therefore, in this case as well, it is preferable to perform the above-mentioned processing.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a schematic block diagram showing a projection exposure apparatus used in each embodiment method 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 forming 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, and the cross-sectional shape becomes a good pattern shape because the side wall approaches the vertical direction, but the resolution in a fine pattern deteriorates and resolution may be possible. The focus range becomes narrow. On the other hand, when the σ value is large, the resolution in a fine pattern and the focus range that can be resolved are slightly improved, 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 in order 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 step 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 coated on the resist (SAL601) 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 (11) formed at this time
Refractive index n = 4.57 for the g-line of the mercury lamp of 1)
Then, the phase difference with respect to the light transmitting portion is 180 ° and the amplitude transmittance is 15
% Satisfied.

Using this projection exposure mask, the numerical aperture NA
= 0.54 and a coherence factor σ = 0.5 were used to perform exposure. As for the photosensitive resin film, as shown in FIG. 2B, a cresol novolak naphthoquinonediazide positive resist 23 having a thickness of 1.3 μm is formed on a Si substrate 22, and baking is performed at 90 ° C. for 5 minutes. It is a thing. Then, before exposing this to tetramethylammonium hydroxide (TMAH)
It is exposed to a 2.38% developer for 30 seconds, washed with water, and then spin-dried. As shown in FIG.
Is formed.

Next, using the above-mentioned projection exposure mask, a positive resist 23 was exposed as shown in FIG. 2 (d). Here, 25 indicates an exposed region. Then, development is performed for 50 seconds at 2.38% TMAH, and
As shown in (e), a resist pattern 26 was formed. At this time, due to the presence of the insolubilized film 24, there was no inconvenience such as the depression of the central portion of the residual resist pattern. In this method, it is also effective to further perform baking at 110 ° C. for 1 minute before development.

Through the above steps, the resolution of the 0.45 μm pattern with the focus margin of 0.8 μm when using the halftone mask was improved to 1.0 μm by forming the surface insolubilized film.

Next, an experiment was conducted in which the halftone mask used in this example and the photosensitive resin film subjected to the surface insolubilization treatment were used, and ring illumination was also used. The annular illumination was performed with respect to the diameter L of the fly's eye lens group with the radius d = 0.65 L shielded from the center. It was confirmed that when a ring-shaped illumination and a halftone mask were combined, a 0.45 μm pattern resolved with a focus margin of 1.3 μm was improved to 1.7 μm by forming a surface insolubilized film.

As described above, according to the method of this embodiment, when the resist 23 is exposed by the halftone phase shift method, the surface of the resist 23 is preliminarily dipped in the TMAH developing solution and washed with water so that the surface of the resist 23 is exposed. Insolubilized film 24
Is formed. Therefore, it is possible to suppress the 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.

FIG. 3 is a sectional view showing a resist pattern forming step according to the second embodiment of the present invention. In this example, first, as shown in FIG. 3A, a cresol novolac naphthoquinonediazide positive resist 33 having a thickness of 1.3 μm was formed on a Si substrate 32 and baked at 90 ° C. for 5 minutes. This substrate was exposed as shown in FIG. 3B using the halftone mask shown in FIG. 2A. Here, 35 indicates an exposure area.

The halftone mask used here is one in which Si is sputtered on a quartz substrate in an N ₂ atmosphere while controlling the film thickness to 80 nm. Phase difference 180 for the light transmitting part
°, intensity transmittance 13% is satisfied.

Next, a mercury lamp of 250 to 330 nm
While irradiating the resist 33 with the light of N _{2 in the} atmosphere
Baking was carried out at 0 ° C. for 2 minutes to form a crosslinked film (insolubilized film) 34 on the surface of the unexposed portion as shown in FIG.
At this time, the water content in the nitrogen atmosphere was about 5%.
Further, the insolubilized film 34 was formed only in the portion where the exposure amount was small.

Then, TMAH was developed with 2.38% developer to obtain 5
Development was performed for 0 seconds to form a resist pattern 36 as shown in FIG. By this method, a 0.40 μm pattern was resolved with a focus margin of 0.6 μm when a halftone mask was used, but was improved to 1.2 μm by forming a surface insolubilized film.

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's eye lens group and the radius d =
0.65 L was shielded. It was confirmed that the 0.4 μm pattern resolved with the focus margin of 1.2 μm when combined with the ring illumination and the halftone mask was improved to 1.9 μm by forming the surface insolubilized film. FIG. 4 is a sectional view showing a resist pattern forming step according to the third embodiment of the present invention.

In this embodiment, first, as shown in FIG. 4A, a negative resist 43 having polyvinyl alcohol as a resin component is formed on the Si substrate 42 to have a thickness of 1.3 μm.
Baking was performed at 0 ° C. for 5 minutes. For this substrate, the halftone mask shown in FIG.
Exposure was performed as shown in (b). Here, 45 indicates an exposure area.

The halftone mask used here was formed by sputtering Si on a quartz substrate in an N ₂ atmosphere while controlling the film thickness to 80 nm, and the Si film formed at this time was exposed to light from the i-line of a mercury lamp. Phase difference 180 with respect to the transmission part
°, intensity transmittance 13% is satisfied.

Next, after baking at 130 ° C. for 2 minutes, development with a TMAH 2.38% developing solution for 120 seconds was performed to form a resist pattern 46 as shown in FIG. 4C. Here, since the residue 47 was generated in the space portion, the substrate was placed in a chamber capable of further vacuuming,
After sufficiently drawing a vacuum, oxygen gas was injected at a flow rate of 20 sccm to cause discharge and exposed to oxygen plasma for 20 seconds to remove the residue 47 as shown in FIG. 4 (d). At this time, the film thickness of the resist pattern was slightly reduced, but there was no problem in terms of accuracy.

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's eye lens group and the radius d =
0.65 L was shielded. Also in this case, a good resist pattern having no residue in the space portion was obtained by exposing it to plasma or radicals containing oxygen atoms after forming the resist pattern.

The present invention is not limited to the above embodiments. In the first embodiment, as the hardening treatment of the positive resist, the treatment with the TAM developer was performed before the exposure, but the treatment liquid is not limited to TAM, and an alkaline solution or an organic alkali developing solution can be used. Further, in the second embodiment, as the positive resist curing treatment, baking was performed while exposing the resist in a N ₂ atmosphere after exposure to light of a mercury lamp.
The same effect can be obtained if the resist is irradiated with ultraviolet light having photosensitivity in an atmosphere of less than 0%. In addition, various modifications can be made without departing from the scope of the present invention.

[0041]

As described in detail above, according to the present invention, a phenomenon which is a problem in the halftone phase shift method, that is, a positive type resist is used by subjecting the resist to a curing effect treatment before development. In this case, it is possible to suppress the film loss in the central portion of the resist pattern and form a good resist pattern. 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 each embodiment of the present invention,

FIG. 2 is a sectional view showing a resist pattern forming step according to the first embodiment,

FIG. 3 is a sectional view showing a resist pattern forming step according to the second embodiment.

FIG. 4 is a sectional view showing a resist pattern forming process according to a third embodiment.

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

FIG. 6 is a diagram for explaining a problem caused by 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 ... SiO ₂ substrate (transparent substrate), 21 ... Si pattern , 22, 32, 42 ... Si substrate, 23, 33, 43 ... Positive resist, 24, 34 ... Surface insolubilized film, 25, 35, 35 ... Exposed region, 26, 36 ... Resist pattern.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01L 21/027 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 for forming a desired pattern by exposing and developing a resin film, a positive resist is used as the photosensitive resin film, and a curing treatment is applied to the surface of the resist before development of the resist. A method for forming a pattern. 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 for developing a desired pattern, a positive resist is used as the photosensitive resin film, and a hardening treatment is performed on the surface of the resist before the resist is developed. Method.