JPH1069064A - Production of halftone phase shift mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a halftone phase shift mask comprising a metal silicide such as molybdenum silicide by which the CD (line width of a mask) and phase difference can be independently controlled and a mask of high accuracy which satisfies requirements for both of the CD and phase difference can be obtd. SOLUTION: After a MoSiN film pattern 32a is formed by dry etching by using a resist pattern 33a as a mask, the phase difference and DC are measured. When the phase difference is satisfactory but the CD is required to be more accurate for the designed value, the etching conditions are changed to control only the CD while the phase difference is kept, and then a dry etching process is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used when a fine pattern such as an LSI is transferred by a projection exposure apparatus, and in particular, to a halftone phase in which resolution is improved by giving a phase difference between exposure lights. The present invention relates to a method for manufacturing a shift mask.

[0002]

2. Description of the Related Art In the manufacture of a semiconductor LSI, a phase shift mask is used as one of photomasks serving as a fine pattern transfer mask. This phase shift mask is designed to improve the resolution of a transfer pattern by giving a phase difference between exposure lights passing through the mask. As one of the phase shift masks, a phase shift mask described in JP-A-4-136854 is known as a mask particularly suitable for transferring an isolated hole or space pattern.

This phase shift mask is formed on a transparent substrate,
By forming a semi-transparent film that transmits light having an intensity that does not substantially contribute to exposure and shifts the phase of light passing therethrough, and selectively removing a part of the semi-transparent film, A mask pattern having a light-transmitting portion that transmits light having an intensity that substantially contributes to exposure and a semi-light-transmitting portion that transmits light having an intensity that does not substantially contribute to exposure is formed. This phase shift mask shifts the phase of light passing through the semi-transparent portion, and the phase of light passing through the semi-transparent portion is substantially inverted with respect to the phase of light passing through the translucent portion. With such a relationship, the light that has passed through the vicinity of the boundary between the light-transmitting portion and the semi-light-transmitting portion and diverted by diffraction cancels each other, so that the contrast at the boundary portion can be maintained well. This is called a halftone phase shift mask.

In this phase shift mask, when the wavelength of the exposure light is λ and the refractive index of the semi-transparent film to the exposure light is n, the value of the thickness t of the semi-transparent film is generally t = λ / It is usually set to a value that satisfies {2 (n-1)}, and the transmittance of the semi-transparent film at the wavelength of the exposure light is set to about 1 to 50%.

The above-mentioned semi-transparent film has a two-layer structure,
The phase difference was adjusted mainly with an SOG (coating glass: spin-on-glass) film, and the transmittance was determined with a thin chromium film. However, the above-described structure has several problems in producing a mask pattern. that is,
Since the SOG film and the chromium film have different film forming methods and pattern processing methods, defects are likely to occur during the process, and since SOG has a small refractive index, the required film thickness for inverting the phase with exposure light is normal. It is thicker than a light-shielding film and is difficult to process. Further, SOG has low mechanical strength and poor adhesion to a chromium film, so that film is easily peeled off.

Therefore, in order to solve these problems, a single-layer film has been developed in which the phase difference and the transmittance can be simultaneously controlled by one film. Chromium-based and molybdenum silicide-based compositions are generally used as the composition of the single-layer film, and chromium-based oxide films and chromium oxynitride films are known. (MoSiO), nitrided molybdenum and silicon (MoSiN), oxynitrided molybdenum and silicon (MoSiON), oxycarbonized molybdenum and silicon (MoSiOC), oxycarbonitrided molybdenum and silicon (MoSiOCN), etc. Have been. More specifically, MoSiN is composed of metal-bonded MoSi and a nitride of Mo or Si. These single-layer films are formed by a reactive sputtering method using a chromium or molybdenum silicide target. For the formation of the mask pattern, wet etching or dry etching is used for chromium, and dry etching is used for molybdenum silicide.

In order to maximize the characteristics of the phase shift mask, it is ideal that the amount of phase shift is 180 °, but in practice, it is desirable to be within a range of about ± 3 °. Since the single-layer halftone phase shift mask controls the phase difference and the transmittance simultaneously with one film, the manufacture of the halftone phase shift mask blank requires high-precision control of the film quality and thickness. . Also, the line width of the mask (CD: Critical Dime)
Also, higher accuracy is required for the masks as compared with ordinary masks.

[0010] Usually, the production of a mask using a chromium-based photomask blank is performed by the steps shown in FIG. 7. First, as shown in FIG. 7A, a chromium film 12 is formed on a transparent substrate 11 by a sputtering method or the like, and a resist 13 is applied thereon to obtain a photomask blank. Next, as shown in FIG. 7B, the resist 13 is exposed and developed to obtain a resist pattern 13a. After that, using the resist pattern 13a as a mask, FIG.
The chromium film 12 is etched to form a chromium film pattern 12a as shown in FIG.
By removing the resist pattern 13a as shown in (d), a photomask is completed. Such a process is the same in the case of using a molybdenum silicide-based photomask blank.

Here, for the chromium-based etching, for example, wet etching with ceric ammonium nitrate or dry etching with Cl ₂ , CCl ₄ or the like is used. In the case of molybdenum silicide, a dry etching technique using CF ₄ or the like is used. In these processes, in the case of molybdenum silicide,
What is not a problem with a normal mask is a problem with a halftone phase shift mask.

The reason is that, in the case of chromium-based etching, any of the above-mentioned chemicals and gases is resistant to the substrate glass, and is hardly etched. That is, while the etching selectivity between chromium and glass is several tens to several hundreds, the molybdenum In the case of silicide, the glass is also slightly etched (selectivity is about several to several tens). In the case of a normal mask, even if the substrate glass is slightly dug, there is no effect on the actual use of the mask.
Since the glass has a phase difference of °, the amount of phase calculated from the refractive index of the glass and the etched depth changes when the glass is etched.

However, this problem can be avoided by designing a halftone film in which the amount of etching of the glass (that is, the amount of phase shift) is calculated in advance.
Japanese Patent Application Laid-Open No. 7-56317 discloses that a deviation from a target phase difference is corrected by using this fact, and a phase shift mask with high accuracy can be obtained.

[0012]

However, in the case of chromium-based etching, the etching time is added to increase the etching time in the lateral direction, and the etching is finished more than the designed dimension of the patterned resist. If the CD can be controlled, the substrate glass is hardly affected, whereas the molybdenum silicide-based material similarly finishes over the designed dimensions and simultaneously etches the substrate glass.

FIG. 8 and FIG. 9 are diagrams showing such a situation. FIG. 8 shows a case of chromium-based, and FIG. 9 shows a case of molybdenum silicide-based. Chromium film pattern 22 or molybdenum silicide film pattern 2 using resist pattern 21 as a mask
In the case of chromium shown in FIG. 8, when chrome film pattern 22 is additionally etched, the chrome film pattern 22 is over-etched by side etching as shown in FIG. 8B, but the glass substrate 24 is hardly affected. In the case of molybdenum silicide, the molybdenum silicide film pattern 23 is over-finished and the glass substrate 24 is etched at the same time as shown in FIG. In other words, in the halftone phase shift mask, the phase difference between CD and CD can be controlled independently in the chromium system, but not in the molybdenum silicide system, and a highly accurate mask with a value satisfying both the CD and the phase difference can be obtained. There was a problem that it could not be done.

[0014]

Means for Solving the Problems The present invention (first present invention)
In order to solve the above-mentioned problem, a semi-translucent film having a predetermined phase shift amount and transmittance is formed on a transparent substrate, and the semi-translucent film is dry-etched using a resist pattern as a mask. A step of forming a film pattern and, when the phase difference or the line width obtained as a result of this step exceeds an allowable range, change the etching conditions so that only the exceeding requirement is adjusted to be within the allowable range. And a step of adding dry etching to the half-tone phase shift mask.

According to the second aspect of the present invention, a semi-transparent film having a predetermined phase shift and a predetermined transmittance is formed on a transparent substrate.
The semi-light-transmitting film is dry-etched using the resist pattern as a mask to form a semi-light-transmitting film pattern, and when the phase difference and line width obtained as a result of this step exceed the allowable range, both of the steps are performed. Adjusting the etching conditions so that both are within the allowable range, and adding dry etching.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a method for manufacturing a halftone phase shift mask according to the present invention will be described below in detail with reference to the accompanying drawings. Before that, an outline of the present invention will be described.

According to the first aspect of the present invention, in a metal silicide halftone phase shift mask such as molybdenum silicide, a phase difference between a CD and a phase difference can be controlled as independently as possible to obtain a highly accurate mask having a value satisfying both the CD and the phase difference. I will provide a.

In general, the control parameters of dry etching mainly include gas type, pressure, and RF power.
Various conditions can be set by the combination, and there are optimal conditions according to the purpose.

In the case where radicals are the main component of the reaction, the progress of etching is isotropic as shown in FIG. 2 as in the case of wet etching as a reaction mechanism.

On the other hand, when ions are the main component of the etching reaction, the mask is excellent in mask transferability because of utilizing the straightness of the ions, and anisotropic etching is performed as shown in FIG. When etching a molybdenum silicide-based semi-transparent film, the apparatus is an RIE (reactive ion etching) apparatus using parallel plate electrodes, and both active ions and radicals contribute to the etching. Etching is performed under conditions having the following properties. Therefore, depending on the setting of the conditions, the reaction can be changed to a reaction mainly composed of radicals (isotropic etching) or a reaction mainly composed of ions (anisotropic etching).

FIG. 4 shows that CF ₄ / O ₂ = 95 as a gas.
The change in the etching rate of MoSiN (molybdenum and silicon nitride) and the quartz substrate (QZ) when the pressure was changed at / 5 sccm and RF power of 100 W. FIG. 5 shows the pressure of the side etching amount. Show dependencies. As is clear from both figures, when the pressure is high, the etching rate of MoSiN is high and quartz is low, and the etching is isotropic, and the rate of increase in the amount of side etching when the etching time is extended becomes large.
Conversely, when the pressure is low, the relationship between the etching rates is reversed, resulting in anisotropic etching, and the rate of increase in the side etching amount is small even if the etching time is extended,
Since the etching rate of quartz is high, the phase difference increases corresponding to the etching amount.

Therefore, if the above-mentioned properties are applied, it is possible to control the CD and the phase difference almost independently. That is, first, etching is performed by taking into account the amount of digging of the quartz substrate under somewhat anisotropic conditions, and in this step, if the CD is smaller than the design value, the amount of digging of quartz is small and the amount of side etching is large. If etching is added under isotropic conditions, only the CD can be adjusted without changing the phase difference.
Conversely, when the CD is as designed and the phase difference is slightly lower,
Conversely, if the etching is added under the same conditions, the CD can be dug almost without changing the CD and the phase difference can be adjusted.

Under the etching conditions in which the pressure is set low and the anisotropy is increased, the etching of the resist proceeds and the selectivity tends to decrease. Therefore, as another method, the pressure is fixed and the gas type is changed. It may be. CF ₄ above
If, for example, CHF ₃ or the like having a higher deposition property is used as an additional gas, the side etching amount, that is, the CD can be made substantially constant by the side wall protection effect. FIG. 6 shows the dependency of the amount of side etching on the amount of CHF ₃ added.

In the second aspect of the present invention, when both the CD and the phase difference do not fall within the allowable range, the two are adjusted so as to fall within the allowable range. I can do it. That is, as a result of the first etching step, when the CD is thinner than the design value and the phase difference is low, if the etching is added under the condition that both of them are adjusted, both the CD and the phase difference are reduced. Both can be adjusted to be within acceptable ranges.

Next, a first embodiment of the present invention will be described with reference to FIG. In the first embodiment, first, FIG.
As shown in FIG. 7, a 950 nm-thick MoSiN film 32 of nitrided molybdenum and silicon is formed as a semi-transparent film on a transparent substrate 31 made of quartz glass whose main surface is mirror-polished by a sputtering method. Next, a positive electron beam resist (ZEP810: manufactured by Zeon Corporation) 33 for forming a pattern of the MoSiN film 32 is applied thereon by spin coating to a thickness of 500 nm and dried. Next, electron beam writing is selectively performed on the positive type electron beam resist 33 and developed to form a resist pattern forming resist pattern 33a of the MoSiN film 32 as shown in FIG. 1B.

Next, using a parallel plate electrode type dry etching apparatus with the resist pattern 33a as a mask, MoS
The iN film 32 is etched under the following conditions (etching condition 1) to form a MoSiN film pattern 32a as shown in FIG. Etching conditions 1 Gas: CF ₄ / O ₂ = 95/5 sccm RF power: 100 W Pressure: 0.15 Torr Time: 60 sec

Next, the CD is temporarily measured by a transmission type CD measuring machine while the resist pattern 33a is kept as it is. In this case, the CD after stripping can be estimated before stripping the resist by checking the CD conversion difference between the state with the resist and the stripped resist in advance. At this time,
It was estimated that the CD after removing the resist was 1.90 μm with respect to the designed value of 2.00 μm. Further, a part of the resist outside the main pattern was peeled off, and the phase difference was measured to be 181.0 °.

Here, in order to finish the mask with high accuracy, it is necessary to make only the CD close to the design value without changing the phase difference. Therefore, additional etching is performed under the following conditions (etching condition 2). Etching condition 2 Gas: CF ₄ / O ₂ = 95/5 sccm RF power: 100 W Pressure: 0.3 Torr Time: 7 sec

Here, from FIG. 4 and FIG.
Under the condition of orr, the side etching rate is 0.01
5 μm / sec, etching rate of quartz glass is 0.5
Since it is known that it is 8 ° / sec, by adding etching under the above conditions, the CD value after the resist is stripped is advanced by 0.105 μm and is 2.005 μm, and the phase difference is 0.3.
(The refractive index of quartz glass at a wavelength of 248 nm is 1.508, which is 13.5 ° per degree), which is 181.30 °, and the CD is set to the design value while the phase difference remains almost constant. I was able to get closer.

Next, a second embodiment of the present invention will be described. In the second embodiment, the steps are exactly the same as those in the first embodiment up to the etching under the etching condition 1. Next, the CD is temporarily measured with the transmission type CD measuring machine while keeping the resist pattern 33a as it is. At this time, the CD after removing the resist is 1.99 with respect to the design value of 2.00 μm.
It was estimated to be μm. When the resist was partially removed outside the main pattern and the phase difference was measured.
Was 5.0 °.

Here, in order to finish the mask with high precision, it is necessary to make the phase difference close to the design value without changing the CD. Therefore, etching is additionally performed under the following conditions (etching condition 3). Etching condition 3 Gas: CF ₄ / O ₂ = 95/5 sccm RF power: 100 W Pressure: 0.075 Torr Time: 21 sec

Here, FIG. 4 and FIG.
Under the condition of 5 Torr, the side etching rate is 0.5.
0015 μm / sec, and the etching rate of quartz glass was found to be 3.2 ° / sec.
The value advances by 0.03 μm to 2.02 μm, and the phase difference is 5.0.
In this case, the phase difference is set to 180.0 ° (the refractive index of quartz glass at a wavelength of 248 nm is 1.508, which is 13.5 ° per 1 °). Could be approached.

Next, a third embodiment of the present invention will be described. In the third embodiment, the steps up to the etching under the etching condition 1 are exactly the same as those in the first embodiment. Next, the CD is temporarily measured with the transmission type CD measuring machine while keeping the resist pattern 33a as it is. At this time, it was presumed that the CD after the resist was stripped was exactly 2.00 μm with respect to the design value of 2.00 μm. In addition, a part of the resist outside the main pattern was peeled off, and the phase difference was measured to be 176.0 °.

Here, in order to finish the mask with high accuracy, it is necessary to make the phase difference close to the design value without changing the CD. Therefore, at a constant pressure, CH
Etching is additionally performed under the condition (etching condition 4) to which F ₃ gas is added. Etching condition 4 Gas: CF ₄ / CHF ₃ / O ₂ = 85/10/5 sccm RF power: 100 W Pressure: 0.15 Torr Time: 50 sec

Here, it is known from FIG. 6 that the side etching rate is 0.0004 μm / sec and the quartz glass etching rate is 1.1 ° / sec under the above conditions. By adding, the CD value after the resist is stripped is advanced by 0.02 μm to 2.02 μm, and the phase difference is advanced by 4.0 ° (where the wavelength 2
Assuming that the refractive index of quartz glass at 48 nm is 1.508, it becomes 13.5 ° per 1 °) (180.0 °), and the CD can be kept almost constant and the phase difference can be brought close to the design value.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the steps are exactly the same as those in the first embodiment up to the etching under the etching condition 1. Next, the CD is temporarily measured with the transmission type CD measuring machine while keeping the resist pattern 33a as it is. At this time, the CD after removing the resist was 1.95 with respect to the design value of 2.00 μm.
It was estimated to be μm. When the resist was partially removed outside the main pattern and the phase difference was measured.
3.0 °.

Here, in order to finish the mask with high precision, it is necessary to make both the CD and the phase difference close to the design values. Therefore, additional etching is performed under the following conditions (etching condition 5). Etching condition 5 Gas: CF ₄ / O ₂ = 95/5 sccm RF power: 100 W Pressure: 0.15 Torr Time: 76 sec

Here, from FIG. 4 and FIG.
Under the condition of Torr, the side etching rate is 0.0
It has been found that the etching rate of the quartz glass is 1.42 ° / sec.
The D value advances by 0.4 μm to 1.99 μm, and the phase difference is 8.0.
(The refractive index of quartz glass at a wavelength of 248 nm is 1.508, which is 13.5 ° per 1 °), which is 181.0 °, so that both the CD and the phase difference can be close to the design values. did it.

In the above embodiment, nitrided molybdenum and silicon (MoSiN) are used as the semi-transparent film.
Was used, but oxidized molybdenum and silicon (Mo)
SiO), oxynitrided molybdenum and silicon (M
oSiON) can also be used. Further, instead of molybdenum (Mo), tungsten (W), chromium (Cr), tantalum (T
Metal silicide using a) or the like can also be used.
Further, a two-layer film such as molybdenum silicide and SOG may be used instead of the single-layer film. The same as the above embodiment can be performed by using these other films.

Further, in the third embodiment, CHF ₃ was added as a gas having a strong deposition property, but C ₂ F ₆ and C ₄ F
A gas such as ₈ or CH ₂ F ₂ can also be used.

In each of the above embodiments, quartz glass is used as the transparent substrate. However, other glass such as soda lime glass, aluminoborosilicate glass, and borosilicate glass may be used. it can. However, in that case, a process corresponding to the refractive index, etching rate, and the like of the material is required.

Further, when forming a resist pattern, light exposure may be used in addition to the method using electron beam lithography. In this case, it is needless to say that a resist according to the exposure conditions is used.

[0043]

As described above, according to the method of manufacturing a halftone phase shift mask of the present invention, in manufacturing a halftone phase shift mask of a metal silicide system such as molybdenum silicide, the CD and the phase difference can be controlled independently. As a result, a highly accurate mask having a value satisfying both the CD and the phase difference can be obtained. Further, according to the present invention, even when both the CD and the phase difference are not within the allowable range, both the CD and the phase difference can be kept within the allowable range by additional etching, and a highly accurate mask can be obtained. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a method for manufacturing a halftone phase shift mask according to the present invention.

FIG. 2 is a sectional view showing isotropic etching.

FIG. 3 is a cross-sectional view showing anisotropic etching.

FIG. 4 is a characteristic diagram showing pressure dependency of an etching rate.

FIG. 5 is a characteristic diagram showing pressure dependency of a side etching amount.

FIG. 6 is a characteristic diagram showing the dependence of the amount of side etching on the addition of CHF ₃ .

FIG. 7 is a cross-sectional view showing mask production using a chromium-based photomask blank.

FIG. 8 is a cross-sectional view showing a state during chromium-based etching.

FIG. 9 is a cross-sectional view showing a state of molybdenum silicide-based etching.

[Explanation of symbols]

 31 transparent substrate 32 MoSiN film 32a MoSiN film pattern 33a resist pattern

Claims (6)

[Claims] 1. A semi-transparent film having a predetermined amount of phase shift and transmittance is formed on a transparent substrate, and the semi-transparent film is dry-etched using a resist pattern as a mask to form a semi-transparent film pattern. When the phase difference or line width obtained as a result of the above step exceeds the allowable range, dry etching is added by changing the etching conditions so that only the exceeding requirement is adjusted to be within the allowable range. A method for manufacturing a halftone phase shift mask. 2. A semi-transparent film having a predetermined amount of phase shift and transmittance is formed on a transparent substrate, and the semi-transparent film is dry-etched using a resist pattern as a mask to form a semi-transparent film pattern. When the phase difference and the line width obtained as a result of the step exceed the allowable range, dry etching is added by changing the etching conditions so that both are adjusted so that both are within the allowable range. And a method for manufacturing a halftone phase shift mask. 3. The method of manufacturing a halftone phase shift mask according to claim 1, wherein the etching condition is changed by pressure. 4. The method for manufacturing a halftone phase shift mask according to claim 1, wherein the etching conditions are changed depending on a gas type. 5. The method for manufacturing a halftone phase shift mask according to claim 1, wherein the translucent film is made of oxidized transition metal and silicon, nitrided transition metal and silicon, and oxynitrided. A method of manufacturing a halftone phase shift mask, wherein the halftone phase shift mask is a thin film of any one of transition metals and silicon. 6. The method of manufacturing a halftone phase shift mask according to claim 5, wherein the transition metal is molybdenum.