JP7219010B2 - phase shift mask blank - Google Patents

Description

The present invention relates to a phase shift photomask blank for manufacturing a phase shift photomask used in the manufacture of semiconductor devices and the like, and a phase shift photomask manufacturing method using the same.

2. Description of the Related Art Along with the recent miniaturization of semiconductor devices, there is a demand for improvement in the resolution of a transferred pattern by projection exposure using a photomask. One method for improving the resolution is the phase shift method. The phase shift method is to obtain a transfer pattern with high contrast by setting the phase of the light transmitted through the photomask opening and the phase of the semi-transmitted light in the area adjacent to the opening to be inverted by approximately 180 degrees. is possible. A photomask used in the phase shift method is called a phase shift photomask (hereinafter abbreviated as a phase shift mask).

A general method of manufacturing a phase shift mask is performed as follows. First, a resist layer is formed on a light shielding film made of a chromium-based film formed on a phase shift film such as molybdenum silicon (MoSi) of a phase shift mask blank, and a circuit pattern is drawn using an electron beam and developed. A resist pattern is formed. Next, using this resist pattern as an etching mask, the light-shielding film is etched using an oxygen-containing chlorine-based gas to form a light-shielding film pattern. is etched to form a phase shift film pattern.

A technique for improving the resolution of the phase shift film pattern includes thinning the resist layer. However, the thickness of the light-shielding film needs to be about 40 to 60 nm in order to secure the optical density of the light-shielding frame formed around the mask. is limited. The light-shielding frame plays a role of preventing exposure light from leaking out of the exposure area and exposing the wafer when the mask pattern is transferred.

Therefore, a technique has been proposed in which a hard mask layer resistant to oxygen-containing chlorine-based gas used for etching the light-shielding film is formed on the light-shielding film (Patent Document 1). FIG. 2 shows the structure of a phase shift mask blank 50 having a hard mask layer 5 on a light shielding film 3. As shown in FIG. 2 (and FIG. 1, which will be described later), the form having the resist layer 7 is shown, but the form before the resist layer 7 is usually also called a blank (here, a phase shift mask blank). , both forms are also referred to herein as blanks.

As the hard mask layer 5, a material that can be etched with a fluorine-based gas and has a high etching resistance to a chlorine-based gas, such as silicon oxide (SiOx) or silicon oxynitride (SiON), is usually selected. Therefore, the hard mask layer 5 itself can be made thinner because the thickness of the hard mask layer 5 is not reduced by the oxygen-containing chlorine-based gas used for etching the light-shielding film 3 . Therefore, the originally expected concept is that the thickness of the resist layer 7 used on the hard mask layer 5 can be reduced and the resolution of the resist can be improved.

However, in the structure in which the resist layer 7 is formed directly on the hard mask layer 5, the adhesion of the resist layer 7 to the material of the hard mask layer 5 such as SiOx is poor, and the resist pattern collapses during the development process. Therefore, it is usually necessary to perform a hydrophobic treatment on the surface of the hard mask layer 5 to increase the adhesion to the resist layer 7 . HMDS (hexamethylenedisilazane) or the like is generally used for this hydrophobic treatment. For the above reasons, the conventional phase shift mask blank 50 must have the structure having the hydrophobizing layer 6 between the hard mask layer 5 and the resist layer 7, as shown in FIG.

JP 2010-267836 A

Hydrophobic treatment with HMDS, if the time is too long, the probability of appearance defects increases, and if it is too short, the adhesion with the resist is insufficient and the resist pattern collapses, so the optimal conditions are determined and set. Must. In addition, the process is difficult to control and unstable because the conditions need to be optimized each time the state of the apparatus or the HMDS liquid changes.

If the resist film thickness is increased in accordance with product specifications, resist pattern collapse is more likely to occur, and the trade-off between resolution and appearance defects becomes even more severe. Conversely, if the resist film is made thinner in order to improve the resolution, the film thickness of the etching mask becomes thinner, which restricts the etching time and deteriorates the dimensional accuracy.

As described above, the low adhesion of the resist layer to the current hard mask layer such as SiOx and the instability of the optimum conditions for HMDS processing to compensate for it are the reasons for the improvement of the resolution and dimensional accuracy of the resist pattern. Furthermore, with the goal of reducing appearance defects, it makes the manufacture of phase shift masks difficult.

The present invention has been made in view of the above problems, and its object is to improve the adhesion of the resist without using HMDS, to easily cope with changes in the film thickness of the resist, and to improve the mask pattern. To provide a phase shift mask manufacturing method and a phase shift mask blank used in the method, in which the resolution and dimensional accuracy of a mask are improved and appearance defects caused by HMDS are improved.

In order to solve the above problems, the phase shift mask blank according to the present invention is
having a substrate transparent to an exposure wavelength, a phase shift film, a light shielding film, and a hard mask layer in this order;
The hard mask layer has a first hard mask layer and a second hard mask layer from the side closer to the light shielding film,
The second hard mask layer is a composite compound containing two or more kinds of metal elements, and is formed of a material that is more easily etched by dry etching with a chlorine-based gas than by dry etching with a fluorine-based gas. It is a mask blank.

2. The phase shift mask blank according to claim 1, wherein said second hard mask layer contains at least one metal element selected from the group consisting of chromium, aluminum, zirconium, hafnium and tin. A mask blank is preferred.

Further, the phase shift mask blank according to the present invention is preferably the phase shift mask blank according to claim 1 or 2, wherein the second hard mask layer further contains at least one selected from oxygen, nitrogen and carbon. .

A method for manufacturing a phase shift mask blank according to the present invention is a method for manufacturing a phase shift mask using the phase shift mask blank according to any one of claims 1 to 3,
forming a pattern of the second hard mask layer by dry etching using a chlorine-based gas using a resist pattern formed on the second hard mask layer as a mask; and forming a pattern of the second hard mask layer as a mask. As a step of forming a pattern of the first hard mask layer by dry etching using a fluorine-based gas;
The method of manufacturing a phase shift mask includes the step of forming the pattern of the light shielding film by dry etching using a chlorine-based gas using the pattern of the first hard mask layer as a mask.

According to the phase shift mask blank of the present invention, the adhesion of the resist is improved without using HMDS, it becomes easy to cope with changes in the film thickness of the resist, and the hard mask layer serves as an etching mask for the phase shift film. Since the etching precision is improved, the resolution and dimensional precision of the mask pattern are improved. At the same time, it is possible to manufacture a phase shift mask with improved appearance defects caused by HMDS.

1 is a schematic cross-sectional view of an embodiment of a phase shift mask blank of the present invention; FIG. 1 is a schematic cross-sectional view of a conventional phase shift mask blank; FIG. FIG. 10 is a schematic cross-sectional view showing steps from resist coating to formation of a second hard mask pattern in the manufacturing process of a phase shift mask using the phase shift mask blank of the present invention. 4A and 4B are schematic cross-sectional views showing steps from forming a first hard mask pattern to forming a phase shift pattern subsequent to FIG. FIG. 5 is a schematic cross-sectional view showing steps from the second resist application to the formation of a light-shielding frame subsequent to FIG. 4 in the phase shift mask production process using the phase shift mask blank of the present invention.

Embodiments of a phase shift type photomask blank of the present invention and a method of manufacturing a phase shift mask using the same will be described below with reference to the drawings. Identical components are denoted by the same reference numerals unless there is a reason for convenience. In addition, in the drawings used in the following description, in order to make the features easier to understand, there are cases in which the characteristic parts are shown in an enlarged manner, and the dimensional ratio of each component is not the same as the actual one.

[Phase shift mask blank]
FIG. 1 shows a schematic cross-sectional view of an embodiment of the phase shift mask blank of the present invention. Here, the resist layer 7 is provided, but as described above, the form without the resist layer 7 (before coating) may be used.

The phase shift mask blank 10 of the present invention comprises a transparent substrate 1 having transparency to an exposure wavelength, at least a phase shift film 2 on the transparent substrate 1, and a light shielding film 3 formed on the phase shift film 2. and a hard mask layer formed on the light shielding film 3, and the hard mask layers are laminated in order of the first hard mask layer 4-1 and the second hard mask layer 4-2 from the side close to the light shielding film 3. It has a layered structure.

In the phase shift mask blank 10 of the present invention, the first hard mask layer 4-1 is etched with a fluorine-based gas such as silicon oxide (SiOx) and is made of a material having high etching resistance to chlorine-based gas.

The second hard mask layer 4-2 is etched by dry etching using a chlorine-based gas, and is made of a material that is difficult to etch by dry etching using a fluorine-based gas. This allows the second hard mask layer 4-2 to serve as an etching mask for the first hard mask layer 4-1 when etching the first hard mask layer 4-1 with a fluorine-based gas.

The second hard mask layer 4-2 needs to improve adhesion to the resist layer 7. FIG. At the same time, the second hard mask layer 4-2 must be made of a material that is easily etched by dry etching using a chlorine-based gas and difficult to etch by dry etching using a fluorine-based gas. For that purpose, the second hard mask layer 4-2 contains at least one metal element as a main component. In addition, the boiling point of the chloride or acid chloride of the main metal element among the contained metal elements is desirably not more than half the boiling point of the fluoride of the metal element.
The forms (chemical formulas) of fluorides, oxides, and acid chlorides are not limited to one type. Just do it.

Generally, in dry etching, an introduced gas collides with electrons in plasma to generate active radicals and reactive ions dissociated into various forms to cause etching. Here, it is known that the more a volatile product with a low boiling point is formed on the etching surface, the easier it is to etch. The index is the boiling point and vapor pressure of the reaction product of the material to be etched and the introduced gas. That is, the lower the boiling point of the reaction product, the higher the vapor pressure and the easier it is to be exhausted.

In view of the above, metals that meet the conditions of the second hard mask layer 4-2 in the embodiment of the present invention were investigated. Table 1 shows the boiling points of typical fluorides, chlorides, and acid chlorides of metal elements that are suitable candidates for the material of the second hard mask layer 4-2. The numerical values in Table 1 summarize values found in various literatures (CRC Handbook of Chemistry and Physics, 78th. Edition, etc.) and websites.

In all metal elements shown in Table 1, the boiling points of chlorides (Cr is an acid chloride of CrO ₂ Cl ₂ ) are half or less that of fluorides of the metal elements. That is, the main metal element in the second hard mask layer 4-2 in the present invention is preferably selected from the group consisting of chromium, aluminum, zirconium, hafnium and tin.

The second hard mask layer 4-2 may contain two or more kinds of chromium, aluminum, zirconium, hafnium, and tin instead of one kind. In addition, as long as it functions as an etching mask when etching the first hard mask layer 4-1, the second most abundant element may be an element other than chromium, aluminum, zirconium, hafnium, and tin. It may be oxygen, nitrogen or carbon. Crystallinity, electrical properties, etchability, washing solution resistance and the like can be adjusted by using these composite compounds.

For example, in order to lower the electric resistance, it is better not to contain oxygen or nitrogen, but in order to increase the cleaning solution resistance, it is preferable to contain oxygen or nitrogen. In general, metal oxides and metal nitrides with a stoichiometric ratio contain a large amount of oxygen and nitrogen and often have high electrical resistance. It is preferable to use a material or a metal oxynitride.

When the light-shielding film 3 is made of a chromium-based material, a chromium-based material containing chromium as the main metal element is also selected for the second hard mask layer 4-2. As a result, the second hard mask layer 4-2 is also etched at an etching rate similar to that of etching the light shielding film 3, and the step of removing the second hard mask layer 4-2 can be eliminated. That is, it becomes possible to improve the efficiency of the process. If the second hard mask layer 4-2 is made of a chromium-based material, the film thickness can be 2 nm to 10 nm, and can be made even thicker if the specifications do not require resolution. Further, when the thickness is 2 nm, a resist film thickness of about 40 to 60 nm is sufficient, and the resolution of the resist can be further improved.

As described above, in the phase shift mask blank of this embodiment, by introducing the second hard mask layer containing a metal element as a main component, the adhesion of the resist is improved without using HMDS. In addition, by selecting a material that has suitable dry etching characteristics with respect to gas species, it becomes easy to cope with changes in film thickness, such as thinning or thickening of the resist. In addition, appearance defects caused by HMDS are reduced. Furthermore, in this embodiment, the second layer from the surface is provided with a silicon layer which is not expected to have a light shielding property. Therefore, it is not necessary to thicken the chromium layer of the surface layer (that is, the first layer), and it can be made as thin as possible. This makes it possible to thin the resist layer that is subsequently formed on the surface layer. As a result, the effects of miniaturization of the pattern and prevention of side etching can be obtained.

Other elements constituting the phase shift mask blank of the embodiment of the present invention will be described below.

(transparent substrate)
Although the material of the transparent substrate 1 having transparency to the exposure wavelength is not particularly limited, quartz glass, aluminosilicate glass, or the like can be used.

(Phase shift film)
The material of the phase shift film 2 is preferably silicon or molybdenum oxide, nitride, oxynitride, or a combination thereof. ratio and phase difference can be obtained. The transmittance value is desirably 2% or more and 40% or less in accordance with the specifications of the final photomask product. If it falls below the lower limit of 2%, it will not be effective even though it is substantially the same as the existing binary mask. If the upper limit of 40% is exceeded, the effect of the mask is lowered, which is also not preferable. In this embodiment, around 6% is set as a suitable value. It is desirable that the value of the phase difference is 170 degrees or more and 190 degrees or less. The film thickness is set to 30 nm or more and 80 nm or less because it also contributes to the transmittance. In addition, it is necessary to be able to etch with a fluorine-based gas and to have etching resistance with an oxygen-containing chlorine-based gas. This is to prevent the phase shift film, which is the lower layer, from being excessively shaved when the light shielding film 3, which is the upper layer of the phase shift film 2, is etched with an oxygen-containing chlorine-based gas.

(Light shielding film)
The material of the light shielding film 3 preferably contains any one of chromium oxide, nitride and oxynitride. The light-shielding frame formed by the light-shielding film 3 has an optical density of 2 or more, preferably 3 or more together with the phase shift film, in order to prevent exposure light from leaking outside the exposure region during mask pattern transfer and exposing the wafer. It is necessary to set the film thickness as follows. In addition, it must be possible to etch with an oxygen-containing chlorine-based gas, and at the same time must have etching resistance with a fluorine-based gas. The reason for this is the same as that for the phase shift film 2 described above. When the first hard mask layer 4-1, which is the upper layer, is etched with a fluorine-based gas, the light shielding film 3, which is the lower layer, is excessively shaved. This is to prevent

The phase shift mask blank of the present embodiment is produced by using a sputtering technique to form a phase shift film 2, a light shielding film 3, a first hard mask layer 4-1 and a second hard mask layer 4- on a transparent substrate 1. 2 are formed sequentially.

[Manufacturing method of phase shift mask]
FIG. 3 is a schematic cross-sectional view showing steps from resist coating to second hard mask pattern formation in the phase shift mask manufacturing process using the phase shift mask blank of the embodiment of the present invention. FIG. 3(a) shows that the phase shift mask blank of the present invention is prepared, and a chemically amplified or chemically amplified layer reacting with an electron beam (or a laser, hereinafter represented by an electron beam) is applied to the surface of the second hard mask layer 4-2. It is a form coated with a non-chemically amplified resist (assumed to be a negative type). Thereafter, an electron beam is irradiated so as to form a desired circuit pattern, and the resist in the portion not irradiated with the electron beam is removed with an alkaline developer or the like, thereby forming a resist pattern 7a as shown in FIG. 3(b). do. When a positive resist is used, the resist in the electron beam-irradiated portion is removed by development.

Next, as shown in FIG. 3C, using the resist pattern 7a as an etching mask, the second hard mask layer 4-2 is dry-etched using a chlorine-based etching gas to form the second hard mask pattern 4-2a. Form.

FIG. 4 is a schematic cross-sectional view showing steps from forming a first hard mask pattern to forming a phase shift film pattern subsequent to FIG. be. First, using the resist pattern 7a and the second hard mask pattern 4-2a as an etching mask, or after removing the resist pattern 7a and using the second hard mask pattern 4-2a as an etching mask, a fluorine-based etching gas is used to perform etching as shown in FIG. As in a), the first hard mask layer 4-1 is dry etched to form a first hard mask pattern 4-1a.

Next, using the second hard mask pattern 4-2a and the first hard mask pattern 4-1a as an etching mask (FIG. 4A), or using the first hard mask pattern 4-1a as an etching mask (FIG. 4B )), the light-shielding film 3 is dry-etched using a chlorine-based etching gas containing oxygen (when the light-shielding film 3 is Cr-based) to form a light-shielding film pattern 3a (FIG. 4(c)). When the second hard mask pattern 4-2a and the first hard mask pattern 4-1a are used as etching masks, the second hard mask pattern 4-2a disappears due to the chlorine-based etching gas during this process, and thereafter the first hard mask pattern 4-2a disappears. The hard mask pattern 4-1a becomes an etching mask.

Next, after removing the first hard mask pattern 4-1a (or leaving it as it is), as shown in FIG. Then, a phase shift film pattern 2a having a light shielding film pattern 3a is formed. At this time, when the phase shift film 2 is dry-etched while leaving the first hard mask pattern 4-1a, the first hard mask pattern 4-1a is mostly lost by the fluorine-based etching gas in the middle of the process. The light shielding film pattern 3a becomes an etching mask. Although the light-shielding film pattern 3a is reduced by an amount corresponding to an etching mask, it is formed in advance with a film thickness capable of ensuring a necessary optical density after the film reduction.

5A and 5B are schematic cross-sectional views showing steps from the second resist application to the formation of a light shielding frame subsequent to FIG. As shown in FIG. 5(a), a positive resist (or negative resist) 8 is applied to the surface of the configuration shown in FIG. 4(d). After that, electron beam irradiation (or laser irradiation or light exposure) and development are performed so that the resist remains only on the outer peripheral portion of the mask, thereby forming a second resist pattern 8a as shown in FIG. 5(b). After that, the light shielding film pattern 3a other than the area that will become the light shielding frame 3b is removed by etching to form a shape as shown in FIG. 5(c). Finally, the excess resist pattern 8a is removed to complete the phase shift mask 100 (FIG. 5 (
d)).

As described above, in the method for manufacturing a phase shift mask according to the present embodiment, in etching the first hard mask layer such as SiOx corresponding to the hard mask layer 5 (see FIG. 2) of the conventional phase shift mask blank, conventionally, the resist pattern has to be used as a mask, the resist pattern or the second hard mask pattern can be selectively used as an etching mask. Therefore, it becomes easier to change the film thickness of the resist to make it thinner or thicker, and the etching accuracy of the hard mask layer, which serves as an etching mask for the phase shift film, is improved, so that the resolution and dimensional accuracy of the mask pattern are improved. do.

Reference Signs List 1 Transparent substrate 2 Phase shift film 2a Phase shift film pattern 3 Light shielding film 3a Light shielding film pattern 3b Light shielding frame 4-1 First hardware Mask layer 4-1a First hard mask pattern 4-2 Second hard mask layer 4-2a Second hard mask pattern 5 Hard mask layer 6 Hydrophobic treatment layer 7 Resist layer 7a Resist pattern 8 Second resist layer 8a Second resist pattern 10 Phase shift mask blank (present invention)
50 ... phase shift mask blank (conventional)
100... phase shift mask

Claims (2)

a substrate transparent to the exposure wavelength;
a phase shift film;
a light shielding film;
a hard mask layer, in this order;
The hard mask layer has a first hard mask layer and a second hard mask layer from the side closer to the light shielding film,
The first hard mask layer is made of silicon oxide,
The second hard mask layer is a composite compound containing two or more kinds of metal elements, and is formed of a material that is more easily etched by dry etching with a chlorine-based gas than by dry etching with a fluorine-based gas ,
The phase shift mask blank , wherein the composite compound contains at least two metal elements selected from chromium, aluminum, zirconium, hafnium, and tin . 2. The phase shift mask blank of claim 1, wherein the second hard mask layer further contains at least one selected from oxygen, nitrogen and carbon.

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