JPH05281702A - Production of phase shift mask - Google Patents

Abstract

PURPOSE:To provide a process for manufacture capable of easily producing the phase shift mask of particularly a chromiumless type (or edge light shielding type) among phase shift masks satisfying the following requirements; the patterns formed by projection exposing high contrast and high resolution and there is no need for providing a conductive layer during the production process. CONSTITUTION:Light shielding layer patterns 2 are provided on a transparent substrate 1 and further, a transparent thin-film layer is provided on at least the region provided with the light shielding layer patterns 2. A negative type photoresist layer 4 is then formed thereon. After this negative type photoresist layer 4 is subjected to patterning by a photolithography method exposing the layer from behind the transparent substrate, the transparent thin-film layer is etched and thereafter, the light shielding layer patterns 2 and the negative photoresist patterns 4' are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is particularly applicable to LSIs and VLSs.
The present invention relates to a method for manufacturing a phase shift mask used as an original image for duplication of a circuit arrangement when a semiconductor integrated circuit represented by I or the like is manufactured by applying a photolithography method,
More specifically, the present invention relates to a manufacturing method for a so-called chromeless type (or edge shading type) phase shift mask.

[0002]

2. Description of the Related Art The phase shift mask referred to in the present invention is
The technique can be applied to both so-called photomasks and reticles. However, in recent years, it is usually often used as the latter reticle.
Here, in general, the reticle is used as an original image for duplication of a circuit layout in the manufacturing process of a semiconductor integrated circuit, but in particular, it is a generic term for those that are used by being mounted in a reduction projection exposure apparatus. The reduction ratio is usually selected from 1/4 to 1/10 and used. The photomask is used as an original image for duplication of the circuit arrangement like the reticle, and is generically referred to as a photomask which is used by being mounted in a projection exposure apparatus of equal size.

When a conventional photomask or reticle is used for the projection exposure of a fine pattern in the manufacturing process of the semiconductor integrated circuit, when the projection exposure light passes through the adjacent openings, diffraction occurs to interfere with each other. Although they match, the phases of these transmitted projection exposure lights are the same at any part, so the light intensities are overlapped, and the resolution of the pattern projected onto the surface of the photoresist provided on the wafer is reduced. Degradation will occur.

This is a semiconductor integrated circuit in which the miniaturization of the target pattern is extremely rapidly changing from sub-micron to quarter-micron and below.
The technique of accurately forming and producing with a desired accuracy has a problem in that it is extremely difficult to perform by conventional optical photography using a projection exposure optical system. This is because, as the size of the target fine pattern is closer to the wavelength of the projection exposure light, the deterioration of the resolution tends to be stronger rapidly. In principle, it was impossible to resolve the pattern.

Therefore, by shifting the phases of the projection lights passing through the adjacent patterns, preferably by inverting the phases by 180 degrees, the intensities of the projection exposure lights which interfere with each other are canceled to cancel out the fine patterns as described above. A phase shift mask using a phase shift technique for improving the resolution of has been developed and attracted attention.

According to this, since the phase is sharply inverted (preferably 180 degrees inverted) at the edge portion of the phase shift layer pattern, the light contrast is emphasized at the edge portion, and the phase is below the wavelength of the projection exposure light. An extremely fine pattern can be resolved.

(FIGS. 2A to 2D) and (FIG. 3A)
(D) shows a phase shift mask of a chromeless type or an edge light shielding type,
The conventional manufacturing method is shown. FIG. 2A shows a case where the phase shift layer pattern 3 ′ is directly formed on the transparent substrate 1, and FIG. 3A shows an etching stop layer 7 provided on the transparent substrate 1. The figure shows the case where the phase shift layer pattern 3'is provided thereon.

In FIG. 2A, the phase shift layer 3, the electron beam resist film 5 and the conductive layer 6 are provided in this order on the transparent substrate 1, and electron beam drawing 9 is performed. Then, a resist pattern 5'is formed by a lithography process (FIG. 2B), the phase shift layer 3 is dry-etched (FIG. 2C), and then the conductive layer 6 and the resist pattern 5'are removed. By doing so, a phase shift mask is obtained (FIG. 2 (d)).

3A to 3D, steps similar to those in FIG. 2 are performed, but here, in particular, as a structure, a dry etching stop layer is provided between the transparent substrate 1 and the phase shift layer 3. Since 7 is provided in advance, the end point of the etching of the phase shift layer 3 can be controlled and detected in a self-aligned manner (FIG. 2).
As compared with the case described above, the phase shift layer pattern 3 ′ can be formed more accurately and accurately with ease.

However, in the conventional manufacturing method, the contrast of the mask pattern and the dry etching accuracy of the phase shift layer pattern to be formed have contradictory characteristics.

That is, in (FIG. 2), since the transparent substrate 1 and the phase shift layer 3 which is the member to be etched are in direct contact with each other, the phase shift prepared in advance when dry etching is performed. It is very difficult to stop the dry etching only in the layer portion, and there is a problem that the lower transparent substrate is also dry etched.

On the other hand, in FIG. 3, since the etching stopper layer 7 is provided, the etching action does not reach the transparent substrate. The characteristic required as the material of the etching stop layer is that the dry etching rate is extremely slow as compared with the material of the phase shift layer, that is, the dry etching selection ratio is large. However, the etching stop layer made of a material satisfying this is
Compared with both the transparent substrate and the phase shift layer pattern, the transmission performance for the projection exposure light is generally inferior, and in the case of (FIG. 3), the light-shielding portion and the transmission portion obtained as the projection pattern. There was a problem that the contrast with was much worse than that of (Fig. 2).

Conventionally, a synthetic quartz substrate has been used as a transparent substrate, and its transmission performance in the visible light region and the ultraviolet light region is very excellent. Further, conventionally, silicon dioxide (SiO ₂ ) or SOG (spin on glass) has been used as a material for the phase shift layer pattern, and both have excellent transmissivity. On the other hand, as a material of the etching stop layer, silicon nitride (Si ₃ N ₄ ) alumina (Al ₂ O ₃ ) and the like have been proposed. It did not reach any material of the layer pattern, and this became a limiting factor, resulting in the reduction of the contrast of the projection pattern as described above.

Further, in patterning the phase shift layer, in order to perform electron beam drawing on the electron beam resist film on the phase shift layer, for example, as shown in (FIG. 2) and (FIG. 3),
A conductive layer must be provided on the electron beam resist film.
However, according to this, alteration of these material properties due to chemical reaction occurring at the interface between the conductive layer and the electron beam resist film,
There is a possibility that problems such as adhesion of stains to the electron beam resist film may occur when the conductive layer is removed.

The purpose of providing the conductive layer is to prevent deterioration of drawing accuracy and precision of electron beam drawing. This is because the transparent substrate, the phase shift layer and the electron beam resist film are usually made of an insulating material. Therefore, if electron beam drawing is performed without providing a conductive layer, charge up by electron beam irradiation is performed. This is because the occurrence of the (charging) phenomenon hinders the electron beam, which originally had a straightness, from blocking it, making it impossible to draw an accurate and highly accurate pattern.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is, in particular, of a chromeless type (or edge shading type) among phase shift masks. To provide a manufacturing method capable of easily obtaining a phase shift mask satisfying the above conditions, in which a projected and exposed pattern has high contrast and high resolution, and further, it is not necessary to provide a conductive layer in the manufacturing process. It is in.

[0017]

To achieve the above object, the means provided by the present invention is to provide a phase difference to at least partially coherent light incident on a patterned transparent substrate. In a method of manufacturing a so-called phase shift mask used in a photolithography method, a light-shielding pattern is provided on a transparent substrate, a transparent thin film layer is further provided on at least the region where the light-shielding pattern is provided, and then a negative-type photomask is formed thereon. Forming a resist film,
After patterning the negative photoresist film by the photolithography method of exposing from the back surface of the transparent substrate, the transparent thin film layer is etched, and then the light shielding pattern and the patterned negative photoresist film are removed. It is a method of manufacturing a phase shift mask characterized by removing.

The chromeless type (or edge light-shielding type) phase shift mask according to the present invention is originally a pattern which is projected and exposed, and the pattern along the edge of the phase shift layer pattern is originally obtained with high resolution. It is suitable for projecting a ring-shaped pattern or a line pattern on a wafer.

The present invention will be described in more detail below with reference to the drawings.

As shown in FIG. 1E, the chromeless type (or edge light shielding type) phase shift mask has a transparent substrate 1 and a phase shift layer pattern 3'which is also made of a transparent material formed on it. There is no light-shielding pattern like a normal photomask (or reticle).

However, when projection exposure is performed by using a chromeless type (or edge shading type) phase shift mask for the photolithography method, the amplitude of the projection exposure light is inverted due to the phase shift layer pattern, The projection exposure lights cancel each other out only in the region along the edge of the phase shift layer pattern, and as a result, the exposure pattern projected on the wafer surface is formed as a ring-shaped or linear light-shielded pattern. It Moreover, at this time, a sharp contrast can be provided along the edge of the phase shift layer pattern, and an extremely fine resist pattern can be formed. The projected exposure pattern becomes the ring shape or the linear shape largely depending on the width of the phase shift layer pattern itself, and when the width is wider than a certain degree, it becomes a ring shape.
Also, if the width is narrower than some other degree, it becomes linear.

Here, the phase shift layer pattern is formed such that the phase difference of the projection exposure light is inverted by 180 degrees with respect to the portion where the phase shift layer pattern is not present. The condition at this time is d = λ / {2 (n-1)}, where n is the refractive index of the phase shift layer pattern member and d is the film thickness of the phase shift layer pattern with respect to the wavelength λ of the projection exposure light. It is given clearly and simply by the formula.

FIGS. 1A to 1E are explanatory views relating to the present invention and a method of manufacturing the phase shift mask having the structure shown in FIG. 1E.

First, the light shielding pattern 2 is formed on the transparent substrate 1 by a known electron beam lithography method (see FIG. 1).
(See (a)). The transparent substrate 1 is made of an optically transparent material such as quartz glass which has been used as a conventional photomask substrate, and its thickness is not particularly limited, but it is usually taken into consideration in view of ease of handling and cost. Is 1.5 to 7.
The thing of about 0 mm is used.

The light-shielding pattern 2 may be made of a light-shielding material such as chromium or chromium oxide used for ordinary photomask blanks, but it is necessary to have an optical density in an appropriate range because it has a light-shielding property during the manufacturing process. Usually 2.0-4.
About 0 is preferable, and in connection therewith, the film thickness of the light shielding pattern is appropriately about 20 to 200 nm. In the electron beam lithography method, as is well known, an electron beam resist is coated on a substrate and is drawn by using an electron beam drawing apparatus, so that it is necessary to provide a conductive layer at least during the manufacturing process. Since it is a conductive material itself, it is not necessary to separately provide a conductive layer.

Next, a phase shift layer 3 is formed so as to cover the entire surface having the light shielding pattern 2, and then a negative photoresist 4 is deposited on the phase shift layer 3. Then, using the light-shielding pattern 2 as a mask pattern, the exposure 8 from the rear surface of the transparent substrate 1 (not particularly limited, for example, g
The negative photoresist is selectively exposed by performing line exposure (also good) (FIG. 1B).

The material of the phase shift layer 3 may be optically transparent, such as SiO ₂ or SOG, but is not particularly limited thereto. The thickness of the phase shift layer 3 is formed so that the phase difference of the projection exposure light transmitted through the phase shift layer pattern portion becomes 180 degrees as described above. For example, the refractive index n of the phase shift layer is 1. Four
7 (SiO ₂ ) and the exposure wavelength λ is 365 nm, the film thickness d is 390 nm according to the above relational expression. The method for forming the phase shift layer 3 is not particularly limited, but a known method represented by a sputtering method, a vapor deposition method, an ion plating method, a CVD method, a spin coating method, or the like may be used. it can.

The photoresist 4 is a negative photoresist for semiconductors, and is usually applied to a thickness of about 500 nm. The resist thickness is not particularly limited to this, and is 300 to 2
It may be about 000 nm, and the type of resist may be a negative photoresist. The exposure 8 from the back surface of the transparent substrate 1 is performed by appropriately setting a light source wavelength and an exposure amount that have a resolution sufficient for pattern formation in a lithography process using the photoresist 4.

FIG. 1C is a diagram in which a resist pattern 4'is formed through the photolithography process after exposure in FIG. 1B. Since the resist pattern 4'is a negative type photoresist, the light shielding pattern 2 is formed. Gives an inverted pattern.

Next, the phase shift layer 3 is etched by a dry etching method to form a phase shift layer pattern 3 '(FIG. 1 (d)). In this dry etching process, the light-shielding layer pattern 2 functions as an etching stop layer in a self-aligning manner, and when a proper etching depth is achieved, the light-shielding pattern 2 is exposed and etching is stopped at the same time. A known method may be used for the dry etching step. For example, when the phase shift layer is SiO ₂ , dry etching can be performed by using a reactive ion etching apparatus using Freon gas as an etching gas. However, the etching method is not limited to this, and a method with good anisotropy may be used to expose the light shielding layer.

Next, the exposed light-shielding layer pattern 2 is removed and the resist pattern 4'is further removed, thereby completing the chromeless type phase shift mask shown in FIG. 1 (e). A method such as wet etching may be used to remove the light-shielding layer pattern 2, and a known stripping method such as a plasma asher or a stripping solution may be used to remove the resist pattern 4 ′.

[0032]

According to the present invention, since neither the etching stop layer nor the conductive layer remains as the final product, the transmission performance does not deteriorate as in the conventional case. Further, dry etching can be performed by the thin film used as the light shielding pattern. Since it stops in a self-aligning manner at an appropriate etching condition, the etching depth can be controlled accurately, and since the light-shielding layer functions as a conductive layer during pattern writing in the first step, drawing accuracy deterioration due to charge-up It is possible to form a precise and highly accurate light-shielding pattern, and when forming a phase shift layer pattern, there is no need to provide a conductive film.

[0033]

The present invention will be described in more detail with reference to the following examples.

A washed synthetic quartz glass substrate (thickness: 2.
3 mm), a low reflection light-shielding film (film thickness 100 nm) in which a chromium film and a chromium oxide film are laminated in this order is formed by a sputtering method, and a positive electron beam resist (manufactured by Chisso Corporation: (Trade name: PBS) is applied to a thickness of about 500 nm by a spin coating method, and after a predetermined baking treatment, an acceleration voltage of 10 kV and a dose amount of about 2.5 μC / cm ² are used by using a raster scan type electron beam drawing apparatus. After drawing a predetermined pattern by the above, development processing was performed to obtain a resist pattern.

After further performing a predetermined baking process, the light shielding pattern is formed by wet etching the low reflection light shielding film using the ceric ammonium nitrate etchant with the resist pattern as a mask pattern. The phase shift mask intermediate having the structure shown in FIG. 1A was obtained by stripping the resist pattern with a stripping solution.

Next, a 390-nm-thick Si film as a phase shift layer is formed on the entire surface of the substrate including the light-shielding pattern and the transmission portion.
An O ₂ film is formed by a sputtering method, a negative photoresist is applied on the O ₂ film to a thickness of about 500 nm, and a baking process is performed. Then, the master mask side (light source side) of the contact exposure apparatus is provided with a substrate rear surface. And exposed (Fig. 1
(B)). Then, development processing was performed to form a resist pattern using the light shielding pattern itself of the substrate as a mask pattern. The resist pattern formed at this time is a reverse pattern because a negative resist was used (see FIG. 1).
(C)).

Next, a parallel plate type reactive ion etching apparatus was used to dry-etch the phase shift layer using the resist pattern as a mask. The dry etching conditions were C ₂ F ₆ and H ₂ gas, the gas pressure ratio was C ₂ F ₆ : H ₂ = 10: 1, the electric power was 300 W, and the gas pressure was 0.03 Torr. The etching time at this time was about 15 minutes, and the etching was performed until the SiO ₂ etching reached the set bottom surface and the light-shielding pattern was sufficiently exposed (FIG. 2D). Then, the exposed light shielding pattern was removed by immersing it in a wet etching solution (an aqueous solution of cerium ammonium nitrate and perchloric acid). Furthermore, the resist pattern was peeled off with a peeling solution (Fig. 1).
The phase shift mask shown in (e) was obtained.

[0038]

As described in detail above, according to the method of manufacturing a phase shift mask according to the present invention, since neither the etching stop layer nor the conductive layer remains as the final product, the transmission performance is deteriorated as in the conventional case. In addition, since the thin film used as the light-shielding pattern stops dry etching in a self-aligned manner at an appropriate etching condition, the etching depth can be accurately controlled, and the pattern drawing in the first step can be performed. In that case, since the light-shielding layer functions as a conductive layer, it is possible to form an accurate and highly accurate light-shielding pattern without deterioration in drawing accuracy due to charge-up. And, it is necessary to provide a conductive film when forming the phase shift layer pattern. There is no From the above, among the phase shift masks, especially for the chromeless type (or edge light shielding type), the pattern projected and exposed on the photoresist surface on the wafer has high contrast and high resolution, and moreover, during the manufacturing process. It was possible to provide a manufacturing method capable of easily obtaining a phase shift mask that does not require a conductive layer.

[0039]

[Brief description of drawings]

1A to 1E are sectional views showing a method of manufacturing a chromeless phase shift mask of the present invention in the order of steps.

2A to 2D are cross-sectional views showing a method of manufacturing a conventional chromeless phase shift mask in the order of steps.

3A to 3D are cross-sectional views showing another method of manufacturing the chromeless phase shift mask of the present invention in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 2 ... Shading layer pattern 3 ... Phase shift layer 3 '... Phase shift layer pattern 4 ... Negative photoresist layer 4' ... Negative photoresist pattern 5 ... ..Electron beam resist layer 5 '... Electron beam resist pattern 6 ... Conductive layer 7 ... Etching stop layer 8 ... Exposure 9 ... Electron beam exposure

Claims (1)

[Claims] 1. A method of manufacturing a so-called phase shift mask which is used in a photolithography method by imparting a phase difference to at least partially coherent light incident on a transparent substrate on which a pattern is formed, and a light shielding pattern on the transparent substrate. And a transparent thin film layer is further provided on at least the region where the light shielding pattern is provided, and then a negative photoresist film is formed on the transparent thin film layer, and the negative photoresist is exposed by the photolithography method from the back surface of the transparent substrate. A method of manufacturing a phase shift mask, comprising: patterning a resist film, etching the transparent thin film layer, and thereafter removing the light-shielding pattern and the patterned negative photoresist film.