JPH05107734A - Production of phase shift mask - Google Patents

Abstract

PURPOSE:To produce a phase shift mask having reduced unevenness in the thickness of the pattern of the phase shifter layer, capable of making the best use of phase shift effect and ensuring satisfactory plotting in a superposed state. CONSTITUTION:An etching stopper layer 2 and a light shielding layer 3 are successively formed on a substrate 1 and the layer 3 is patterned. A phase shifter layer 5, an electric conductive layer 6 and a resist are successively formed on the resulting pattern 3, the resist 7 is drawn to form a resist pattern 7 for the phase shifter layer 5 and the layer 5 is etched to produce a phase shift mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photomask (hereinafter referred to as a phase shift mask) having a transparent shifter for increasing the resolution by giving a phase difference to illumination light passing through an opening.

[0002]

2. Description of the Related Art In the manufacture of semiconductor integrated circuits, with the progress of photolithography technology and the miniaturization of devices, the demand for higher resolution of photomasks is increasing more and more. Approaching. Generally, the resolution limit is given by kλ / NA, where λ is the wavelength of light and NA is the numerical aperture of the lens (k is a constant). There is a method of using. However, in order to change the illumination wavelength, it is necessary to change the entire optical system of the exposure apparatus, which requires a great deal of labor. Apart from this, a phase shift method is known in which a resolving power exceeding the above-mentioned limit is obtained by giving a phase difference to adjacent openings of a mask (Japanese Patent Publication No. 62-50811 and Japanese Patent Laid-Open No. 58-17374).
(See Japanese Patent Publication No. 4).

In the phase shift mask used in the phase shift method, d = λ / 2 (n-1); d = shifter film thickness, λ
= Wavelength and n = refractive index of the shifter, the shift amount is 180 ° and the phase shift effect is the highest when the shifter film thickness satisfies the relationship.

An example of a conventional method of manufacturing a phase shift mask will be described below with reference to FIG. A light-shielding layer (3) of chromium or the like is formed on a transparent substrate (1) as shown in FIG. 9 (a), and patterning is performed by an ordinary lithography method.
A pattern is formed by partially removing the light-shielding layer (3) (see FIG. 9B), a phase shifter layer (5) is formed thereon (see FIG. 9C), and a phase is formed by a lithography method. By patterning the shifter layer, a phase shift mask as shown in FIG. 9D is completed. The superposing step of forming the pattern of the phase shifter layer according to the light shielding layer pattern is important in the manufacturing process of the phase shift mask.

As a material for the above-mentioned phase shifter layer (transparent film), it is desirable that it should have sufficient transparency at the wavelength of illumination light and have sufficient resistance to scrubbing and the like. As a material that can satisfy
Silicon dioxide (hereinafter referred to as SiO ₂ ) may be used.

Although SiO ₂ can be etched by either wet etching or dry etching, dry etching is advantageous because anisotropic etching can be performed when forming a fine pattern. However, as a substrate for a phase shift mask, a silica glass (S
Since iO ₂ ) is used, the phase shifter layer and the substrate are the same kind of material. Therefore, it becomes difficult to determine the end point when the transparent film is etched. That is, if overetching is performed to obtain a phase shifter layer pattern with a good pattern shape, the substrate may be etched, and the thickness of the transparent film may vary due to the difference in the etching rate in the substrate due to the characteristics of the dry etching device. There is a problem that causes Any of these problems leads to the phase difference deviating from 180 ° in the substrate, and the characteristics of the phase shift method cannot be fully utilized.

Further, since the materials of the above-mentioned phase shifter layer and the resist are both dielectrics and have poor conductivity, the resist is used in overlay drawing with an electron beam for patterning the resist for etching the phase shifter layer. Electrons incident inside could not be conducted and diffused, and a charge-up phenomenon occurred, so that a normal pattern was not drawn and overlay drawing of the shifter pattern formation was not successful.

[0008] Each of these methods for solving the problem that the etching thickness is nonuniform during etching of the phase shifter layer and the method for solving the charge-up phenomenon have been proposed individually.

As a technique for uniform etching, it has been proposed to provide an etching stopper layer between the phase shifter layer and the substrate. As a material having a large selection ratio with respect to SiO ₂ , SixNy, poly-Si and the like are considered. This etching stopper layer must remain transparent at the wavelength of the light used, as it will remain in the finally completed mask. However,
In SixNy, poly-Si and the like, there has been a problem that the transmittance of ultraviolet light is lowered and the contrast of the mask is lowered. For this reason, JP-A-3-
71133, Japanese Patent Laid-Open No. 3-78747, a fluoride, chloride or aluminum oxide (Al) of an alkali metal or an alkaline earth metal is used as an etching stopper layer.
₂ O ₃ ) is described. By using these etching stopper layers, it becomes easy to detect the etching end point and the substrate is not etched. However, in these methods, a charge-up phenomenon occurred and drawing could not be performed normally.

As a conventional technique for preventing the charge-up phenomenon, a method of forming a conductive film in the process is described in JP-A-2-211450 and JP-A-2-140743. In the above, there is a problem that the thickness of the phase shifter layer cannot be sufficiently controlled because the etching end point cannot be determined in the etching for forming the phase shifter layer pattern. Furthermore, when the conductive layer remains on the phase shift mask, there is a problem that the light intensity is reduced due to absorption during exposure.

[0011]

SUMMARY OF THE INVENTION The present invention makes it possible to easily obtain the end point of dry etching of the phase shifter layer in the phase shift mask as described above and to charge up in the electron beam writing process. (EN) A method for stably manufacturing a phase shift mask which prevents the phenomenon and consequently minimizes the variation in the thickness of the phase shifter layer and maximizes the effect of shifting the phase, and which is excellent in overlay drawing. The purpose is to

[0012]

The present invention has been made in view of the above problems, and in a method of manufacturing a phase shift mask which gives a phase difference to illumination light passing through an opening,
It is characterized by providing an etching stopper layer when forming a phase shifter layer pattern for giving a phase difference, and further providing a conductive layer for preventing a charge-up phenomenon during electron beam writing.

In particular, an etching stopper layer and a light shielding layer are sequentially formed on a substrate to form a light shielding layer pattern, a phase shifter layer, a conductive layer and a resist are sequentially formed, and then the resist is drawn to form the phase shifter. Forming a resist pattern for layers,
A method for manufacturing a phase shift mask, which comprises etching the phase shifter layer.

[0014]

In the method of manufacturing the phase shift mask, it is necessary to form the conductive layer for preventing the charge-up phenomenon and the etching stopper layer for the uniformity of etching. There is a difference in the performance of the completed phase shift mask depending on the formation order of the.

In the method of manufacturing the phase shift mask according to the present invention, the conductive layer and the etching stopper layer are formed. Therefore, it is possible to prevent a charge-up phenomenon at the time of overlapping writing with an electron beam, to write a normal pattern, and to easily identify the etching end point during dry etching.

The method of manufacturing the phase shift mask of the present invention will be described in detail below. 1 to 8 show a method of manufacturing the phase shift mask of the present invention. The drawings are examples for description, and the present invention is not limited to the drawings.

FIG. 1 shows a blank in which an etching stopper layer (2), a light shielding layer (3) and a light shielding layer patterning resist (4) are sequentially formed on a substrate (1).

As the substrate (1), glass such as quartz glass or low expansion glass having a small positional distortion is usually used.

The etching stopper layer (2) is provided in order to stop the etching of the phase shifter layer without reaching the substrate, and it has high transparency and can take a sufficient selection ratio with SiO ₂ when etching the phase shifter layer. It is necessary. Examples include alumina (Al ₂ O ₃ ), magnesia spinel (MgAl ₂ O ₄ ), zirconia (Zr
O ₂ ) and the like.

Since the light shielding layer (3) can be patterned by a usual method, it is preferable to use a metal film containing chromium as a main component.

As the resist (4), an electron beam drawing resist or a photo-sensitive resist can be used.

The resist (4) is patterned (see FIG. 2), the light-shielding layer is etched using the resist pattern as a mask (see FIG. 3), and then the resist is removed to obtain the mask of FIG.

Then, a phase shifter layer (5), a conductive layer (6) and a phase shifter layer patterning resist (7) are formed on the light shielding layer pattern (see FIG. 5).

The phase shifter layer (5) is required to have an appropriate thickness in order to shift the phase of incident light due to the difference in refractive index. SiO ₂ or an organic polymer can be used for the phase shifter layer (5). The phase shift amount is determined by the refractive index and film thickness of the phase shifter layer, for example using a SiO ₂ i
Using a line (wavelength 365 nm) light source, the refractive index is 1.
47, when the phase shift amount is 180 °, the film thickness of the phase shifter layer is about 390 nm.

The conductive layer (6) only needs to have conductivity for preventing a charge-up phenomenon at the time of drawing by superimposing with an electron beam, and a metal thin film, an organic conductive material or the like can be used.

In the present invention, the resist (7) is used as a mask when patterning the lower phase shifter layer (5) and the conductive layer (6). An electron beam resist is usually used as the resist (7), and a conductive layer (6) is provided below the resist (7) in order to prevent a charge-up phenomenon during drawing. Whether the resist is a positive type resist or a negative type resist, a similar pattern can be formed by only changing the electron beam drawing portion.

FIG. 6 shows the state of the mask after patterning the resist and etching the conductive layer (6).

Subsequently, the phase shifter layer (5) is etched by using the resist (7) pattern as a mask. When an inorganic material such as SiO ₂ is used for the phase shifter layer (5), it can be etched by a dry etching method such as reactive ion etching. Since the etching is stopped by the etching stopper layer, the end point can be easily determined. Further, even when the etching rate has in-plane variation, the phase shifter layer can be etched up to the etching stopper layer in all in-plane by performing etching for a sufficient time, and therefore in-plane variation can be prevented. When an organic polymer compound is used for the phase shifter layer (5), wet etching can be performed using an organic solvent, an alkaline solution or the like. The mask after etching is shown in FIG.

FIG. 8 shows a mask in which the resist (7) and the conductive layer (6) which have been used as a mask are removed to complete the formation of the phase shifter layer pattern.

[0030]

EXAMPLES Examples of the present invention will be described below. An aluminum oxide thin film having a thickness of about 20 nm was formed as an etching stopper layer by RF sputtering using aluminum oxide as a sputtering target and argon as a sputtering gas on a substrate made of quartz glass.

Next, the light-shielding layer was formed by depositing chromium to a thickness of about 100 nm by sputtering. Then, a positive type electron beam resist (PBS, manufactured by Chisso Co.) was applied on the light-shielding layer.
Coating was performed to a thickness of 00 nm, and drawing was performed under the conditions of an acceleration voltage of 10 kV and a dose amount of about ² μC / cm ² . Development was performed with a dedicated developer, and after predetermined baking and descum, chromium was wet-etched with an etching solution containing cerium ammonium nitrate as a main component using the resist pattern as a mask to form a light-shielding layer pattern. Finally, the resist was removed with a dedicated stripping solution.

Next, a SiO ₂ film to be a phase shifter layer was formed by RF sputtering using SiO ₂ as a target and a mixed gas of argon and oxygen as a sputtering gas. The refractive index of this film is 1.47. For example, when used in the i-line of a mercury lamp (wavelength 365 nm), (n-1) d = 3.
From the relationship of 65/2, the film thickness was set to about 390 nm.

Subsequently, a metal tantalum film is formed as a conductive layer by 5
A film having a thickness of nm was formed by sputtering.

Next, an electron beam curable resist (trade name SA, manufactured by Shipley Microelectronics Co., Ltd.) is formed on the conductive layer.
L-601ER7) was coated on the entire surface, and the pattern of the phase shifter layer was formed by a usual process such as electron beam drawing, development, and baking. Since there is a conductive layer in the lower layer, there is no disturbance of the electron beam at the time of electron beam drawing and high-precision drawing is possible. Using this resist as a mask, the tantalum of the conductive layer was etched with a mixed solution of 30% sodium hydroxide aqueous solution and hydrogen peroxide solution 10: 1. After that, the phase shifter layer was etched by reactive ion etching using C ₂ F ₆ gas. The aluminum oxide thin film is not etched under this condition, and the quartz glass substrate is not etched. After that, the remaining resist was removed by oxygen gas plasma, and the tantalum of the conductive layer was removed by the above mixed solution to obtain a phase shift mask.

[0035]

According to the method of manufacturing a phase shift mask of the present invention, since the etching stopper layer for dry etching has sufficient etching resistance, the substrate is also etched during the dry etching of the phase shifter layer. It is possible to provide a phase shift mask in which the deviation of the phase difference from the design value and the variation of the phase difference due to the in-plane variation of the dry etching rate are suppressed.

Further, by forming the conductive layer, the charge-up phenomenon can be prevented at the time of overlay writing for patterning the phase shifter layer, so that the electron beam is not affected and good pattern writing can be performed.

Further, in the manufacturing method of the present invention, since the conductive layer is removed in the final step, light absorption by the conductive layer does not occur when the phase shift mask is used, and a sufficient exposure intensity can be obtained.

[0038]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of manufacturing a phase shift mask of the present invention in the order of steps.

FIG. 2 is a cross-sectional view showing a method of manufacturing a phase shift mask of the present invention in the order of steps.

FIG. 3 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

FIG. 4 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

FIG. 5 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

FIG. 6 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

FIG. 7 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

FIG. 8 is a cross-sectional view showing the method of manufacturing the phase shift mask of the present invention in the order of steps.

9A to 9D are sectional views showing a conventional manufacturing method in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Etching stopper layer 3 Light-shielding layer 4 Light-shielding layer patterning resist 5 Phase shifter layer 6 Conductive layer 7 Phase shifter layer patterning resist

Claims (1)

[Claims] 1. A method of manufacturing a phase shift mask, comprising: (a) a step of sequentially forming an etching stopper layer and a light shielding layer on a substrate; (b) forming a light shielding layer pattern, a phase shifter layer, a conductive layer and a resist. And (c) drawing a resist to form a resist pattern for the phase shifter layer and etching the phase shifter layer, the method for producing a phase shift mask.