JP2018010080A - Phase shift type photomask blank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase shift type photomask blank including a hard mask layer that has a low sheet resistance value and prevents degradation in position accuracy by charging when a pattern is formed by use of an electron beam drawing device, in a phase shift type photomask blank having a phase shift film, a light-shielding film and a hard mask layer formed on a substrate.SOLUTION: The phase shift type photomask blank includes a hard mask layer that can be dry-etched by a fluorine-based gas but substantially cannot be dry-etched by chlorine-based etching containing oxygen and that has a sheet resistance value of 200 Ω/(unit square) or less in a sheet form having a thickness of 5 nm. A fluoride in the hard mask layer has a boiling point of 250°C or lower, and an oxide and a chloride in the hard mask layer have a boiling point of 400°C or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a phase shift photomask blank for producing a phase shift photomask used in the manufacture of semiconductor devices and the like.

  With the recent miniaturization of semiconductor elements, there is a demand for improved transfer pattern resolution by projection exposure using a photomask. One method for improving the resolution is a phase shift method. The phase shift method can obtain a transfer pattern with high contrast by adjusting the phase of the transmitted light at the photomask opening and the phase of the transmitted light at the portion adjacent to the opening to be inverted by approximately 180 degrees. It is possible. A photomask used for the phase shift method is called a phase shift photomask.

  A general method for manufacturing a phase shift photomask is to first form a resist film on a light shielding film made of a chromium-based film on a phase shift film such as molybdenum silicon (MoSi) of a phase shift photomask blank, and then use an electron beam. A circuit pattern is drawn using, and developed to form a resist pattern. 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, and further using the fluorine-based gas as a light-shielding film pattern as an etching mask, a phase shift film Is etched to form a phase shift film pattern.

  As a technique for improving the resolution of the phase shift film pattern, there is a resist thinning. However, the film thickness of the light-shielding film is required to be about 40 to 60 nm in order to ensure the optical density of the light-shielding frame formed on the outer peripheral portion of the mask. There are limits. The light shielding frame has a role of preventing a phenomenon in which exposure light leaks out of the exposure area when the mask pattern is transferred and the wafer is exposed.

  In view of this, a technique has been proposed in which a hard mask layer that is resistant to oxygen-containing chlorine-based gas used during light-shielding film etching is formed on the light-shielding film (Patent Document 1). Since the hard mask layer is not reduced by the oxygen-containing chlorine gas used when etching the light shielding film, the hard mask layer itself can be made thin. Therefore, it is possible to reduce the thickness of the resist used on the hard mask layer.

JP 2010-267836 A

  However, since the conventional hard mask layer is made of a material mainly composed of silicon oxide, the sheet resistance value is high, and when the mask pattern is formed by using an electron beam drawing apparatus, the position accuracy of the pattern deteriorates due to charging. There is a problem of doing.

In order to solve the above-mentioned problem, the present invention described in claim 1
A phase comprising a substrate transparent to an exposure wavelength, a phase shift film formed on the substrate, a light shielding film formed on the phase shift film, and a hard mask layer formed on the light shielding film. A shift type photomask blank,
The hard mask layer can be dry-etched with a fluorine-based gas,
And it is not substantially dry etched by chlorine-containing etching containing oxygen,
The sheet resistance value when the film thickness is 5 nm is 200Ω / □ or less, which is a phase shift photomask blank.

  The present invention according to claim 2 is the phase shift photomask blank according to claim 1, wherein the boiling point of the fluoride in the hard mask layer is 250 ° C. or less.

  The present invention described in claim 3 is the phase shift photomask blank according to claim 1 or 2, wherein the boiling point of the oxide and chloride of the hard mask layer is 400 ° C or higher. It is.

  The invention according to claim 4 is characterized in that the hard mask layer contains at least one selected from the group consisting of ruthenium, tantalum, titanium, vanadium, iridium, tungsten, and molybdenum. The phase-shifting photomask blank described in any one of the items is used.

  The present invention according to claim 5 is the phase shift photomask blank according to claim 4, wherein the hard mask layer further contains at least one selected from oxygen, nitrogen, and carbon. It is.

  According to the present invention, it is possible to prevent charging at the time of electron beam drawing, and it is possible to improve the positional accuracy of the pattern. By providing the hard mask layer, the resist can be thinned, and a phase shift photomask having a circuit pattern with high resolution can be manufactured.

It is a schematic cross section concerning an embodiment of a phase shift type photomask blank of the present invention. It is a schematic cross section which shows from a resist application to light shielding film pattern formation among the manufacturing processes of the phase shift type photomask using the phase shift type photomask blank of this invention. FIG. 3 is a schematic cross-sectional view illustrating a process from the formation of a light shielding film pattern to the formation of a light shielding frame, continued from FIG. It is a schematic cross section of a phase shift type photomask manufactured using the phase shift type photomask blank of the present invention.

  Hereinafter, embodiments of the phase shift photomask blank of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the same component unless there is a reason for convenience, and the overlapping description is abbreviate | omitted. Also, in the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner, and the dimensional ratios of the respective constituent elements are not the same as the actual ones.

A phase shift photomask blank 100 shown in FIG. 1 includes a substrate 11 transparent to an exposure wavelength, a phase shift film 12 formed on the substrate 11, and a light shielding film formed on the phase shift film 12. 13 and a hard mask layer 14 formed on the light shielding film 13. Less than,
Each component will be described.

<Board>
The material of the substrate 11 that is transparent with respect to the exposure wavelength is not particularly limited, and quartz glass, aluminosilicate glass, or the like can be used.

<Phase shift film>
The material of the phase shift film 12 is preferably an oxide, nitride, oxynitride of silicon or molybdenum, or a composite thereof, and the desired transmission with respect to the exposure wavelength can be achieved by adjusting the content ratio and film thickness. Rate 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, the retardation value is desirably 170 degrees or more and 190 degrees or less, and the film thickness is 30 nm or more. It is desirable to set it to 80 nm or less. In addition, etching with a fluorine-based gas is possible, and it is necessary to have etching resistance with an oxygen-containing chlorine-based gas. This is because when the light shielding film 13 that is the upper layer of the phase shift film 12 is etched with a chlorine-containing gas containing oxygen, the phase shift film that is the lower layer is prevented from being excessively shaved.

<Light shielding film>
The material of the light shielding film 13 preferably includes any one of chromium oxide, nitride, and oxynitride. The light shielding frame formed by the light shielding film 13 has an optical density of 2 or more, preferably 3 or more in combination with the phase shift film, in order to prevent a phenomenon in which exposure light leaks out of the exposure area during mask pattern transfer and exposes the wafer. Thus, it is necessary to set the film thickness. Moreover, it is necessary to be able to perform etching with an oxygen-containing chlorine-based gas, and at the same time, it is necessary to have etching resistance with a fluorine-based gas. This is for the same reason as the phase shift mask 12 described above, in order to prevent the light shielding film 13 as the lower layer from being excessively shaved when the hard mask layer 14 as the upper layer is etched with a fluorine-based gas. is there.

<Hard mask layer>
The hard mask layer 14 used in the phase shift photomask blank 100 of the present invention can be etched with a fluorine-based gas, and substantially with an oxygen-containing chlorine-based gas for etching a light shielding film mainly composed of chromium as a lower layer. This material is not etched. At the same time, in order to prevent charging at the time of drawing a circuit pattern by the electron beam drawing apparatus, the sheet resistance value when the film thickness is 5 nm is a material having a resistance of 200Ω / □ or less. Here, if the electrical resistivity of the thin film is ρ (Ω · m) and the film thickness is t (m), the sheet resistance Rs (Ω / □) is described as the following equation (1).
Rs = ρ / t (1)
Usually, since the structure of an ultrathin film changes with film thickness, sheet resistance is dependent on film thickness.

As a material for the hard mask layer 14, a material mainly composed of silicon oxide has been mainstream, but this material has a high sheet resistance value. Specifically, the sheet resistance value when the thickness of the silicon oxide film is 5 nm is 2.0 × 10 ¹³ Ω / □ or more. For this reason, charging is likely to occur during electron beam drawing, and the positional accuracy of the mask pattern deteriorates.

  The hard mask layer 14 used in the phase shift photomask blank 100 of the present invention has a sheet resistance value of 200 Ω / □ or less when the film thickness is 5 nm, can be etched using a fluorine-based gas, and contains oxygen. Therefore, it is preferable that the fluoride has a boiling point of 250 ° C. or lower and the oxides and chlorides have a boiling point of 400 ° C. or higher. In addition, although the form (chemical formula) of fluoride, oxide, and chloride is not necessarily one kind, in the present invention, the boiling point of at least one kind of fluoride is 250 ° C. or less, and all stoichiometrically possible It means that the boiling point of the oxide and chloride in the form is 400 ° C. or higher.

  In dry etching, the introduced gas collides with electrons in the plasma, and active radicals and reactive ions dissociated into various forms are generated to cause etching. However, low-boiling volatile products are formed on the etching surface. It is easy to etch, and the index is the boiling point and vapor pressure of the reaction product by the material to be etched and the introduced gas.

  For example, for rhenium, the sheet resistance value of rhenium with a film thickness of 5 nm is about 67.6 Ω / □, and the boiling point of the fluorine compound is about 33.8 ° C. These are the conditions required for the material of the hard mask layer of the present invention. Is enough. On the other hand, since the boiling point of the oxygen compound is about 250 ° C., the oxygen compound is easily etched by oxygen added to the chlorine gas at the time of etching the light shielding film. Therefore, rhenium is not suitable for the hard mask layer of the present invention.

  In view of the above, when a metal that meets the conditions of the hard mask layer in the present invention is selected, examples include ruthenium, tantalum, titanium, vanadium, iridium, tungsten, and molybdenum. A material containing at least one metal selected from the group consisting of these, or a material containing at least one selected from oxygen, nitrogen, and carbon can also be used.

  When oxygen and / or nitrogen is contained, the lower the sheet resistance, the better the content of oxygen and nitrogen, but the higher the resistance to the cleaning solution, the higher the oxygen and nitrogen content. good. In general, metal oxides and metal nitrides with stoichiometric ratios often have high oxygen and nitrogen contents and high sheet resistance, so metal oxides and metal nitridings that contain more metal than stoichiometric ratios. And metal oxynitrides are preferred for the hard mask layer.

  Here, taking iridium as an example of the material of the hard mask layer, the sheet resistance value when the thickness is 5 nm is about 9.4Ω / □. The boiling point of the fluorine compound of iridium is about 53 ° C. and does not react with chlorine gas and oxygen gas, so that all the conditions required for the hard mask layer of the present invention are satisfied.

  The hard mask layer 14 is desirably 15 nm or less in order to realize high resolution, that is, to make the resist thin, and may be slightly etched during etching of the light shielding film. It is desirable that

<Method for Producing Phase Shift Photomask Using Phase Shift Photomask Blank of the Present Invention>
FIG. 2 is a cross-sectional view of the steps up to the step of forming only the light-shielding film pattern 13a on the phase shift film 12 in the process of manufacturing the phase shift photomask 101 shown in FIG. First, a phase shift photomask blank 100 is prepared, and a chemically amplified or non-chemically amplified negative resist 15a that reacts with an electron beam is applied to the surface of the hard mask layer 14 (FIG. 2A). Then, an electron beam is irradiated so as to form a desired circuit pattern, and a resist pattern 15c as shown in FIG. 2B is formed by removing a portion of the resist not irradiated with the electron beam with an alkali developer or the like. To do. If a positive resist is used, the resist exposed to the electron beam is removed by development.

  Subsequently, as shown in FIG. 2C, the hard mask layer 14 is dry etched using the fluorine-based etching gas 16a using the resist pattern 15c as an etching mask. Thereafter, as shown in FIG. 2D, the light shielding film 13 is dry-etched using a chlorine-based etching gas 16b containing oxygen. In the middle of this, the resist pattern 15c generally disappears, and thereafter, the hard mask layer pattern 14a becomes an etching mask.

  Further, as shown in FIG. 2E, the remaining resist pattern 15c is completely removed, and then the hard mask layer pattern 14a is peeled and removed, whereby the phase shift film 12 as shown in FIG. A form having the light shielding film pattern 13a is formed.

  FIG. 3 is a cross-sectional view of the process after the formation of the light shielding film pattern 13a following FIG. 2 in the manufacturing process of the phase shift photomask 101 shown in FIG. As shown in FIG. 3A, the phase shift film 12 is dry-etched using a fluorine-based etching gas 16c using the light-shielding film pattern 13a as an etching mask. Thereby, a phase shift film pattern 12a as shown in FIG. 3B is formed.

  Next, as shown in FIG. 3C, a positive resist (or negative resist) 15b is applied to the surface in the form of FIG. 3B. Thereafter, a resist pattern 15d as shown in FIG. 3D is formed by electron beam irradiation (or laser irradiation or light exposure) so that the resist remains only in the outer peripheral portion of the mask. The reason for adopting such a configuration is to finally form the light shielding frame 13c on the outer periphery of the mask. The light-shielding film pattern 13a other than the region of the light-shielding frame 13c is removed by etching, and a form as shown in FIG. Finally, the excessive resist pattern 15d is peeled and removed, whereby the phase shift photomask 101 is completed.

  Hereinafter, the phase shift type photomask blank of the present invention and an embodiment in which a phase shift type photomask is manufactured using the same will be described.

First, the difference in sheet resistance between the conventional hard mask layer mainly composed of silicon oxide and the hard mask layer using iridium oxide used in this example was examined. All the hard mask layers had a thickness of 5 nm. While the sheet resistance of the conventional hard mask layer was not measurable with a four-terminal method sheet resistance measuring machine (1.0 × 10 ⁹ Ω / □ or more), the sheet resistance of the hard mask layer of the present invention was 200 Ω / □. An improvement was seen.

  Next, the phase shift photomask blank 100 shown in FIG. 1 was produced. That is, a molybdenum silicon film having a film thickness of 72 nm is formed on the quartz substrate 11 as the phase shift film 12, the transmittance is about 6% with respect to ArF exposure light having a wavelength of 193 nm, and the phase difference after masking is 180 degrees. It was made to become. Further, a 50 nm-thick chromium oxynitride film was formed thereon as the light-shielding film 13 so that the optical density combined with the phase shift film 12 was about 3. Further, the iridium compound having a film thickness of 5 nm was formed thereon as the hard mask layer 14 to prepare a phase shift photomask blank 100 (FIG. 1).

  Next, in order to form a circuit pattern, a chemically amplified negative resist 15a (FEN271: manufactured by Fuji Film Electronics Material) was applied to the surface of the phase shift photomask blank 100 with a film thickness of 84 nm (FIG. 2A). ). A desired circuit pattern was drawn using an electron beam drawing machine (JBX9000: manufactured by JEOL), and then a baking process was performed at 110 ° C. for 10 minutes, followed by a development process, thereby forming a resist pattern 15c (FIG. 2 (b)).

Subsequently, the hard mask layer 14 was etched using CF ₄ plasma using a dry etching apparatus (FIG. 2C). Further, while maintaining the vacuum state in the same apparatus, the light shielding film 13 was continuously etched using Cl ₂ plasma containing O ₂ gas (FIG. 2D). Then, the surplus resist pattern 15c is removed with a stripping solution (treatment solution containing hydrogen fluoride, organic solvent, and water) (FIG. 2E), and the surplus hard mask layer pattern 14a is added to SF ₆ with Ar. The circuit pattern which has the light shielding film pattern 13a on the phase shift film 12 was formed by peeling by the dry etching performed (FIG. 2F).

Next, the phase shift film 12 was etched using CF ₄ plasma using the light shielding film pattern 13a as an etching mask (FIG. 3B). Next, positive i-line resist 15b (AR80: manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to the surface with a film thickness of 500 nm (FIG. 3C). Next, using a laser drawing machine (ALTA3100: manufactured by Applied Materials), a region other than the region where the light shielding frame is to be formed was drawn and developed to form a resist pattern 15d (FIG. 3D). Next, by using Cl ₂ plasma containing O ₂ gas, the light shielding film pattern 13a other than the region that becomes the light shielding frame 13c is removed to form the light shielding film pattern 13b (FIG. 3E), and finally the resist pattern 15d is formed. The light shielding frame 13c was formed by peeling and removing with a peeling liquid (treatment liquid containing hydrogen fluoride, an organic solvent, and water), and the phase shift photomask 101 was manufactured (FIG. 3F).

  In the phase shift photomask blank of the present invention, since the sheet resistance of the hard mask layer was as low as 200 Ω / □, the positional deviation due to charging at the time of electron beam drawing compared to the phase shift photomask using the conventional hard mask layer Was suppressed and the positional accuracy was improved.

11 Substrate 12 Phase shift film 12a Phase shift film pattern 13 Light shielding film 13a, 13b Light shielding film pattern 13c Light shielding frame 14 Hard mask layer 14a Hard mask layer pattern 15a, 15b Resist 15c, 15d Resist pattern 16a-16c Etching gas 100 Phase shift type Photomask blank 101 Phase shift type photomask

Claims (5)

A phase comprising a substrate transparent to an exposure wavelength, a phase shift film formed on the substrate, a light shielding film formed on the phase shift film, and a hard mask layer formed on the light shielding film. A shift type photomask blank,
The hard mask layer can be dry-etched with a fluorine-based gas,
And it is not substantially dry etched by chlorine-containing etching containing oxygen,
A phase shift photomask blank having a sheet resistance value of 200 Ω / □ or less when the film thickness is 5 nm.   The phase shift photomask blank according to claim 1, wherein the boiling point of the fluoride in the hard mask layer is 250 ° C or lower.   The phase shift photomask blank according to claim 1 or 2, wherein the boiling point of the oxide and chloride of the hard mask layer is 400 ° C or higher.   The phase shift type according to any one of claims 1 to 3, wherein the hard mask layer includes at least one selected from the group consisting of ruthenium, tantalum, titanium, vanadium, iridium, tungsten, and molybdenum. Photomask blank.   The phase shift photomask blank according to claim 4, wherein the hard mask layer further includes at least one selected from oxygen, nitrogen, and carbon.

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