JPH0580491A - Production of phase shift mask - Google Patents

Abstract

PURPOSE:To stably produce the phase shift mask which is formed to allow the end point of the dry etching of shifters to be easily obtd., prevents charge-up in a stage for electron beam plotting, consequently decreases the fluctuations in the thickness of the shifters, can utilize the effect of shifting the phases to the max. extent and is good in overlap plotting. CONSTITUTION:The process for producing the phase shift mask by using a substrate formed with light shielding layer patterns has a stage for successively providing an etching stopper layer 3, a shifter layer 4, a conductive layer 5, and a resist on the substrate 1 formed with the light shielding layer patterns, a stage for dry etching the conductive layer 5 and the shifter layer 4 after forming resist patterns and a stage for peeling the resist patterns and the conductive layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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 2 made of chromium or the like is formed on a substrate 1 made of a transparent material as shown in FIG. 6 (a), and patterning is performed by an ordinary lithography method to form a pattern in which the light-shielding layer 2 is partially removed. After the shifter layer 4 is formed thereon (see FIG. 6B) (see FIG. 6B).
By patterning the shifter layer by the lithographic method, the phase shift mask as shown in FIG. 6D is completed. The superposing step of forming the shifter layer pattern in accordance with the light shielding layer pattern is important in the manufacturing process of the phase shift mask.

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

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 shifter and the substrate are the same kind of material. Therefore, it becomes difficult to determine the end point during etching of the shifter layer. That is, if over-etching is performed to obtain a shifter having a good pattern shape, the thickness of the shifter layer may vary due to the problem of etching the substrate and the difference in the etching rate in the substrate due to the characteristics of the dry etching apparatus. There will be a problem. 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 shifter layer and the resist are both dielectrics and have poor conductivity, they are not drawn in the resist during overlay drawing with an electron beam for patterning the resist for etching the shifter layer. The electrons incident on the can not be conducted and diffused, causing a charge-up phenomenon, and a normal pattern cannot be drawn.
The overlay drawing of the shifter pattern formation did not work.

Each of these methods for solving the problem that the etching thickness becomes nonuniform during etching of the shifter and the charge-up phenomenon have been individually proposed.

As a conventional technique for uniform etching, it has been proposed to provide an etching stopper layer between the shifter 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. Therefore, in JP-A-3-71133 and JP-A-3-78747, fluorides, chlorides or aluminum oxides (Al oxides) of alkali metals and alkaline earth metals are used as etching stopper layers.
₂ O ₃ ) is described. By using these etching topper layers, the detection of the etching end point was facilitated, and the substrate was never 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 a process is described in JP-A-2-211450 and JP-A-2-140743. The invention has a problem that the thickness of the shifter layer cannot be sufficiently controlled because the etching end point cannot be determined in the etching for forming the shifter.

[0011]

The present invention makes it possible to easily obtain the end point of the dry etching of the shifter in the phase shift mask as described above, and to prevent the charge-up phenomenon in the electron beam writing process. It is an object of the present invention to provide a stable manufacturing method of a phase shift mask that can prevent the fluctuations of the shifter thickness and can maximize the effect of shifting the phase, and that has good overlay drawing. To do.

[0012]

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

More specifically, an etching stopper layer, a shifter layer, a conductive layer, and a resist are sequentially provided on a substrate having a light-shielding layer pattern formed thereon to form a resist pattern,
A method of manufacturing a phase shift mask, characterized in that the resist pattern and the conductive layer are peeled off after dry-etching the conductive layer and the 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. The performance of the phase shift mask varies depending on the order of formation.

In the method of manufacturing a phase shift mask according to the present invention, an etching stopper layer is formed on the entire pattern surface of a photomask obtained by a normal photomask manufacturing process, and a conductive layer is formed on the shifter layer. The film is 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.

Further, there is a feature that the transmittance of light is not reduced when the phase shift mask is used because the conductive layer is peeled off in the final step.

The method of manufacturing the phase shift mask of the present invention will be described in detail below. 1 to 5 show a method of manufacturing the phase shift mask of the present invention. The drawings are examples for explanation, and the present invention is not limited by these drawings.

FIG. 1 shows a mask obtained by patterning the light shielding layer 2 on the substrate 1. As the substrate 1, glass such as quartz glass or low-expansion glass having a small positional distortion is usually used. Since the light-shielding layer can be patterned by a usual method, it is preferable to use a metal film containing chromium as a main component. The etching stopper layer 3, the shifter layer 4, the conductive layer 5, and the resist 6 are sequentially formed on the mask of FIG. 1 to obtain FIG.

The etching stopper layer 3 is a layer of the shifter layer 4.
Provided to stop the latching without reaching the substrate
It has high transparency and is suitable for etching the shifter layer.
Then SiO₂It is necessary to obtain a sufficient selection ratio
It As an example, alumina (Al ₂O₃), Magnesias
Pinel (MgAl₂O_Four), Zirconia (ZrO₂)etc
Is mentioned.

The shifter layer 4 needs to have an appropriate film thickness in order to shift the phase of incident light depending on the difference in refractive index. For the shifter layer 4, SiO ₂ or organic polymer can be used. The amount of phase shift is determined by the film thickness of the shifter layer and the refractive index of the material of the shifter layer. For example, a refractive index of 1.4 is obtained by using a light source of i-line (wavelength 365 nm) using SiO _2.
7 When the amount of phase shift is 180 °, the film thickness of the shifter layer is about 390 nm.

The conductive layer 5 need only be conductive so as to prevent a charge-up phenomenon during superposition drawing 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 6 is used as a mask when patterning the lower light shielding layer 5 and the shifter layer 4. An electron beam resist is usually used as the resist, and a conductive layer 5 is provided below the resist in order to prevent a charge-up phenomenon during writing. 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. 3 shows the mask after the resist 6 is developed and the conductive layer 5 is etched using the resist pattern as a mask.

Subsequently, the shifter layer 4 is etched using the pattern of the resist 6 as a mask. SiO on the shifter layer 4
_When an inorganic substance such as ₂ is used, it can be etched by a dry etching method such as reactive ion etching. When an organic polymer compound is used for the shifter layer 4, wet etching can be performed using an organic solvent or an alkaline solution. The mask after etching is shown in FIG.

FIG. 5 shows a mask in which the resist 6 and the conductive layer 5 are peeled off to complete the pattern formation of the shifter layer 4.

[0026]

EXAMPLES Examples of the present invention will be described below. A photomask having a light-shielding pattern containing chromium as a main component on a substrate made of quartz glass was obtained by a conventional method. continue,
An aluminum oxide thin film was formed to a thickness of about 20 nm as an etching stopper layer by RF sputtering using aluminum oxide as a sputtering target and argon as a sputtering gas.

Next, a SiO ₂ film to be a shifter layer was formed by RF sputtering with a target of SiO ₂ and a sputtering gas of a mixed gas of argon and oxygen. 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 = 365 /
From the relationship of 2, the film thickness was set to about 390 nm.

Subsequently, a metal tantalum film having a thickness of 5 nm was formed as a conductive layer on the SiO ₂ film by sputtering.

Next, an electron beam curable resist (made by Shipley Microelectronics, trade name SAL-601E) is used.
R7) was coated on the entire surface, and a resist pattern was formed by ordinary steps such as electron beam drawing, development, and baking. Using this resist pattern as a mask, the tantalum film of the conductive layer is first etched by a 30% sodium hydroxide aqueous solution,
It was performed with a 10: 1 mixture of hydrogen peroxide water. Then, by reactive ion etching using C ₂ F ₆ gas,
The shifter layer was etched. The aluminum oxide thin film was not etched under this condition, and the quartz glass substrate was not etched. After that, the remaining resist was removed by oxygen gas plasma, and the tantalum of the conductive layer was dissolved by the above aqueous solution to obtain a phase shift mask.

[0030]

According to the method of manufacturing a phase shift mask according to the present invention, the etching stopper layer for dry etching has sufficient etching resistance. Therefore, it is possible to provide the phase shift mask in which the shift of the phase difference from the design value due to the etching of the substrate during the dry etching of the shifter layer and the variation of the phase difference due to the in-plane variation of the dry etching rate are suppressed. Further, since the etching stopper layer is on the light shielding layer pattern, the light shielding layer pattern is protected.

Further, by forming a conductive layer,
Since the charge-up phenomenon can be prevented at the time of overlapping writing for patterning the shifter layer, the electron beam is not affected and good pattern writing can be performed. Further, in the method for manufacturing a phase shift mask of the present invention, the conductive layer is peeled off in the final step, so that the light transmittance does not decrease due to the conductive layer when the phase shift mask is used.

[0032]

[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.

6A to 6D are cross-sectional views showing a conventional manufacturing method in the order of steps.

[Explanation of symbols]

 1 substrate 2 light-shielding layer 3 etching stopper layer 4 shifter layer 5 conductive layer 6 shifter layer patterning resist

Claims (1)

[Claims] 1. A method of manufacturing a phase shift mask using a substrate on which a light shielding layer pattern is formed, comprising: (a) an etching stopper layer, a shifter layer, a conductive layer, a resist on the substrate on which the light shielding layer pattern is formed. A phase shift mask comprising: a step of sequentially forming a resist pattern, a step of dry-etching the conductive layer and the shifter layer after forming a resist pattern, and a step of (c) peeling the resist pattern and the conductive layer. Manufacturing method.