JP2007094435A - Method for manufacturing photomask blank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method or the like for manufacturing a photomask blank capable of efficiently reducing film stress. <P>SOLUTION: The method for manufacturing the photomask blank having at least a film for forming a mask pattern on a transparent substrate comprises a film forming process for sputter-forming the film for forming the mask pattern by containing at least helium gas in sputtering atmosphere and a process for heating the transparent substrate during or after the film forming process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a photomask blank for manufacturing a lithography mask such as a photomask used in a lithography process in manufacturing a semiconductor device or the like, and is particularly suitable for a KrF excimer laser, an ArF excimer laser, and an F ₂ excimer laser. The present invention relates to a halftone phase shift mask blank and a manufacturing method thereof.

  In recent years, there is a contradictory relationship between the two important characteristics required for photolithography, high resolution and securing of the focal depth, and it is not possible to improve the practical resolution only by increasing the NA of the exposure apparatus lens and shortening the wavelength. (Non-Patent Document 1 etc.).

Under such circumstances, phase shift lithography is attracting attention as a next-generation photolithography technique, and a part of it has been put into practical use. Phase shift lithography is a method that improves the resolution of optical lithography by changing only the mask without changing the optical system. By providing a phase difference between the exposure light that passes through the photomask, interference between the transmitted light and each other is achieved. The resolution can be improved dramatically by using.
The phase shift mask is a mask having both light intensity information and phase information, and various types such as a Levenson type, an auxiliary pattern type, and a self-alignment type (edge enhancement type) are known. These phase shift masks have a complicated structure and require advanced techniques for manufacturing as compared with conventional photomasks having only light intensity information.

As one of the phase shift masks, a phase shift mask called a so-called halftone phase shift mask has been put into practical use in recent years.
In this halftone type phase shift mask, the light semi-transmissive portion has two functions of a light shielding function for substantially blocking exposure light and a phase shift function for shifting (usually inverting) the light phase. Therefore, it is not necessary to separately form the light shielding film pattern and the phase shift film pattern, and the structure is simple and the manufacturing is easy.
In the halftone phase shift mask, the mask pattern is processed by the dry etching process. However, in the method of realizing the light shielding function and the phase shift function in separate layers, the layer having the light shielding function and the layer having the phase shift function are separated. Both require a high degree of control to obtain a good pattern shape. On the other hand, since a single etching process can be used by configuring a single-layer light semi-transmissive part having both a light shielding function and a phase shift function, the mask manufacturing process can be simplified and easily improved. It is possible to obtain a pattern shape.

As shown in FIG. 1, the halftone phase shift mask has a light transmission portion (transparent substrate exposed portion) 200 that transmits light having a strength that substantially contributes to exposure through a mask pattern formed on the transparent substrate 100. And a light semi-transmissive part (light-shielding part / phase shifter part) 300 that transmits light of intensity that does not substantially contribute to exposure (FIG. 5A) and transmits through this light semi-transmissive part. By shifting the phase of the light so that the phase of the light transmitted through the light semi-transmissive portion is substantially inverted with respect to the phase of the light transmitted through the light transmissive portion ((b) in the figure). ), The light passing through the vicinity of the boundary between the light semi-transmission part and the light transmission part and wrapping around each other by the diffraction phenomenon cancels each other, and the light intensity at the boundary part is almost zero, and the contrast of the boundary part Ie improve resolution Than it (Fig. (C)).
In addition, the above-described halftone phase shift mask and the light semi-transmissive portion and the light semi-transmissive film (phase shift layer) in the blank are used as a pretreatment or cleaning solution such as cleaning in the mask manufacturing process and cleaning when using the mask. It is necessary to have sufficient durability against an acid solution such as sulfuric acid and sufficient durability against an alkaline solution such as ammonia.
Further, regarding a phase shift mask that can realize these required optimum characteristics in a single-layer light semi-transmissive portion, proposals have been made regarding molybdenum silicide oxynitride films (Patent Document 1, Patent Document 2, and Patent Document 3). ing.
Monthly Semiconductor World 1990.12, Applied Physics, Volume 60, November (1991) JP-A-6-214792 Patent No. 2878143 Japanese Patent No. 2989156

By the way, as the wavelength of the laser used for exposure is shortened from i-line (365 nm) or KrF excimer laser (248 nm) to ArF excimer laser (193 nm), the phase angle shift with respect to the same change in film thickness increases. Therefore, it is necessary to improve the durability of the phase shift mask with respect to the acid solution and the alkali solution as the wavelength of exposure is shortened.
In addition, since the energy of the laser light is increased by shortening the wavelength of the laser used for the exposure, the damage of the light translucent part due to the exposure is increased, and within the service life period required for the phase shift mask, There is a problem that a deviation occurs in the set transmittance and phase difference.
On the other hand, with the miniaturization of semiconductor circuits and the like, the wavelength of the exposure light source used for lithography has been shortened, and the NA of the exposure apparatus lens has been increased. In order to ensure the depth of focus, the flatness required for the photomask has become increasingly severe. In recent years, the flatness is required to be 0.3 to 0.5 μm or less. The flatness of the photomask depends on the bending strength of the transparent substrate, the flatness of the substrate before film formation, and the internal stress of the film forming the circuit pattern, etc. Among these, the inside of the film forming the circuit pattern in particular Stress has become a major problem.
Under these circumstances, an application by the applicant of the present application (specialized) is to improve the density of the light translucent portion in order to improve the acid resistance, alkali resistance, and excimer laser irradiation resistance of the phase shift mask. Application 2001-246080). This application discloses a method for lowering the pressure of an atmosphere containing argon and a reactive gas used when forming a film constituting the light semi-transmissive portion by sputtering in order to improve the density of the light semi-transmissive portion. ing.
Furthermore, in the above application, based on the fact that the internal stress of the film increases when the pressure of the atmosphere in which the sputtering is performed is reduced, the light semitransmissive film is compressed by performing a heat treatment after forming the light semitransmissive film. A method of relieving stress is disclosed. On the other hand, in the above-mentioned application, a very high temperature heat treatment (for example, 600 ° C.) may be required to obtain a predetermined stress, and a method capable of efficiently reducing the compressive stress by the heat treatment has been required.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a method capable of effectively reducing the stress of a thin film forming a pattern.

The present invention has the following configuration.
(Configuration 1) In a method for producing a photomask blank having at least a film for forming a mask pattern on a transparent substrate,
In the method, at least one layer of the film for forming the mask pattern is formed by sputter film formation by containing at least helium gas in a sputtering atmosphere, and the transparent substrate is formed during or after the film formation process. And a step of heating the photomask blank.
(Structure 2) The photo according to structure 1, wherein in the film forming step, the film for forming the mask pattern is formed by sputtering using a mixed gas of argon and helium as a sputtering gas. Mask blank manufacturing method. (Configuration 3) The photomask blank is a halftone phase shift mask blank, and the film for forming the mask pattern has a predetermined transmittance with respect to the exposure light and the exposure light with respect to the transparent substrate. 3. The method for producing a photomask blank according to Configuration 1 or 2, wherein the photomask blank is a light semi-transmissive film composed of one layer or two or more layers whose phase is shifted by a predetermined amount.
(Structure 4) The light semitransmissive film is selected from Structures 1 to 3 including a film made of a material containing silicon and nitrogen and / or oxygen, or a metal, silicon, and nitrogen and / or oxygen. The manufacturing method of the photomask blank described in 1.
(Structure 5) The photomask blank manufacturing method according to one selected from Structures 1 to 4, wherein a heat treatment temperature in the step of heating the transparent substrate is 180 ° C. or higher.
(Structure 6) A photomask manufactured using the photomask blank according to structures 1 to 5.

Hereinafter, the present invention will be described in detail.
The present invention provides a photomask blank manufacturing method having at least a film for forming a mask pattern on a transparent substrate.
In the method, at least one layer of the film for forming the mask pattern is formed by sputter film formation by containing at least helium gas in a sputtering atmosphere, and the transparent substrate is formed during or after the film formation process. (Step 1).
In the present invention, argon was conventionally used as a sputtering gas by the inventors' experiment, but by replacing part or all of argon with helium, compression was achieved compared to the case of using conventional argon. This is achieved by reducing the stress. It has also been found that compressive stress is more effectively reduced by performing heat treatment during or after film formation. This is presumed to be because helium that tends to volatilize is present in the film in advance and helium is volatilized by the heat treatment, so that the compressive stress in the film is relaxed.

In the present invention, the preferable sputtering pressure is preferably 0.20 to 0.40 Pascal, more preferably 0.23 to 0.35 Pascal, and most preferably 0.25 to 0.31 Pascal. When the pressure of the sputtering atmosphere is as low as the above range, the density of the light semi-transmissive film can be improved and the film can be densified. The densification of the thin film has the effect of improving the chemical resistance, acid resistance, and excimer laser resistance against acid and alkali, and further improves the pattern accuracy in a fine pattern. If it is below the above range, the internal stress of the film may become so large that it cannot be improved by heat treatment, and the stability of film formation may be affected.
In the present invention, when the film for forming the mask pattern includes a film having at least one compressive stress property, the compressive stress of the film having the compressive stress property can be reduced. The compressive stress property means that the stress shown when only Ar is used as the sputtering gas is the compressive stress.
As will be described later, when the film showing the compressive stress property for forming the mask pattern on the transparent substrate has a multilayer structure, it is preferable that at least one layer is sputtered within the above sputtering pressure range. It is more preferable to perform sputtering in the above sputtering pressure range.

In the present invention, a preferable sputtering gas in the sputtering atmosphere is a mixed gas of an inert gas such as argon and helium. Note that another inert gas can be used instead of argon, and another inert gas can be added to the mixed gas of argon and helium.
A preferable sputtering gas content when performing reactive sputtering by adding a reactive gas such as nitrogen or oxygen to the sputtering atmosphere is 25 to 34%. When the lower limit is exceeded, the stress reduction effect is reduced, and when the upper limit is exceeded, the sputtering rate is reduced and productivity is reduced. About Ar, it is 5 to 15%. If the lower limit is exceeded, the optical characteristics become extremely unstable, and if the upper limit is exceeded, the sputtering rate decreases and the productivity decreases.

In the present invention, examples of a film for forming a mask pattern on a transparent substrate include a light semi-transmissive film in a halftone phase shift mask and a light shielding film in a photomask.
Here, as the light semi-transmissive film in the halftone phase shift mask, a light semi-transmissive film having a single layer structure, for example, two layers or more of a low-transmittance layer and a high-transmittance layer are stacked, and a phase angle and transmission A light semi-transmissive film having a multilayer structure designed to have a desired value is included.
As a light semi-transmissive film having a single layer structure, a material containing oxygen and / or nitrogen in metal and silicon (silicon), or a material containing carbon and / or fluorine and / or hydrogen in these, chromium oxide, chromium fluoride, etc. However, those substantially consisting of metal, silicon, and nitrogen and / or oxygen are preferable. Examples of the metal mentioned here include one or more metals selected from titanium, vanadium, niobium, molybdenum, tantalum, and tungsten. A commonly used metal is molybdenum, but molybdenum is particularly excellent in transmittance controllability and target density among the above metals. Titanium, vanadium, and niobium have excellent durability against alkaline solutions, but are slightly inferior to molybdenum in target density. Tantalum is superior in durability against alkali solutions and target density, but slightly inferior to molybdenum in controllability of transmittance. Tungsten has similar properties to molybdenum, but is slightly inferior to molybdenum in the discharge characteristics during sputtering.
As the light semi-transmissive film having a multilayer structure, as the high-transmittance layer, a high-transmittance layer substantially composed of silicon and nitrogen and / or oxygen, or metal (metal in the light semi-transmissive film having the single layer structure) As well as a high transmittance layer substantially composed of silicon and nitrogen and / or oxygen, and the low transmittance layer is one or two of chromium, molybdenum, tantalum, titanium, tungsten, hafnium, zirconium, etc. A metal film made of an alloy of more than one kind, or an oxide, nitride, oxynitride, silicide or the like of these metals or alloys is preferable.
As the light shielding film in the photomask, a light shielding film having a single layer or a multilayer structure made of chromium, a chromium compound containing oxygen, nitrogen, carbon, or the like in chromium, other chromium compounds, or the like can be given.
In the present invention, when a film for forming a mask pattern on a transparent substrate has a multilayer structure, at least a film exhibiting compressive stress properties is sputtered by containing at least helium gas in a sputtering atmosphere. It is preferable. Note that a film made of a material containing silicon and nitrogen and / or oxygen or a metal, silicon and / or nitrogen or oxygen usually has compressive stress properties.

In the present invention, the heat treatment temperature in the step of heating the transparent substrate during or after the film formation step is 180 ° C. or more from the viewpoint of effectively volatilizing helium in the film and effectively relieving the compressive stress in the film. Preferably, 200 degreeC or more, 300 degreeC or more, and 400 degreeC or more are more preferable. However, since it takes a long time to reach the heat in the heat treatment apparatus and it becomes more difficult to manage the apparatus at a high temperature, it is preferably 500 ° C. or less practically.
Note that the atmosphere for the heat treatment can be air or an inert gas such as nitrogen or argon. In the case of a gas containing oxygen such as the atmosphere, the characteristics of the light semi-transmissive film may be slightly changed by heat treatment. Therefore, when the light semi-transmissive film is formed, the change is taken into consideration. It is preferable to do. When it is desired to avoid a change in film characteristics due to the heat treatment, it is preferable to perform the heat treatment in an inert gas atmosphere. In particular, in the case of a heat treatment at a high temperature (for example, 380 ° C. or higher), the amount of change in the film characteristics is large, so that the inertness is inactive. It is desirable to perform heat treatment in a gas atmosphere.

(Example)
Hereinafter, the present invention will be described in detail using examples.
Example 1
In this embodiment, the effect of using helium as a sputtering gas and the effect of heat treatment after film formation will be described.
Using a DC magnetron sputtering apparatus as shown in FIG. 2, a single-layer semi-transparent film consisting essentially of molybdenum, silicon and nitrogen is formed on a transparent substrate to produce a halftone phase shift mask blank. did.
This DC magnetron sputtering apparatus has a vacuum chamber 1, and a magnetron cathode 2 and a substrate holder 3 are arranged inside the vacuum chamber 1. A sputtering target 5 bonded to a backing plate 4 is attached to the magnetron cathode 2. The backing plate 4 is cooled directly or indirectly by a water cooling mechanism. The magnetron cathode 2, the backing plate 4, and the sputtering target 5 are electrically coupled. A transparent substrate 6 is attached to the substrate holder 3.
The vacuum chamber 1 is exhausted by a vacuum pump through an exhaust port 7. After reaching a degree of vacuum that does not affect the characteristics of the film formed by the atmosphere in the vacuum chamber, a mixed gas containing nitrogen is introduced from the gas inlet 8 and a negative voltage is applied to the magnetron cathode 2 using the DC power source 9. Sputtering is performed. The pressure inside the vacuum chamber 1 is measured by a pressure gauge 10.
Using a molybdenum silicide target (Mo: Si = 20: 80), the flow rate of a mixed gas of Ar, N ₂ and He as a sputtering gas is Ar: 10 sccm, N ₂ : 80 sccm, and He: 0, 9, 18, No heat treatment after film formation, after heat treatment at 200 ° C., on a phase shift mask blank formed with a light semi-transmissive film (phase angle: 182-184 °, transmittance 5-6%) under six conditions of 36, 54, and 69 sccm And 400 ° C. heat treatment were performed, and the internal stress of the light semi-transmissive film was evaluated. The internal stress of the light semi-transmissive film was evaluated by measuring the amount of change in flatness of the transparent substrate before and after the formation of the light semi-transmissive film.
The flatness was measured over a 146 mm square range excluding the edge 3 mm of the synthetic quartz substrate (152 mm × 152 mm × 6.35 mm), and was defined as the difference in height between the highest and lowest points from the average surface of the substrate. . The flatness of the transparent substrate was measured using an interferometer (manufactured by TROPEL: FlatMaster 200).
FIG. 3 shows the relationship between the amount of He introduced into the sputtering gas and the amount of change in flatness with respect to each blank subjected to no heat treatment after film formation, after heat treatment at 200 ° C., and after heat treatment at 400 ° C. The flatness change amount in FIG. 3 indicates a positive change amount, that is, compressive stress.
As is apparent from FIG. 3, it can be seen that the amount of change in flatness tends to be reduced by introducing He into the sputtering gas, and the amount of change in flatness can be further reduced by further heat treatment. From this, it is shown that the compressive stress of the light translucent film could be reduced.

(Example 2)
In the present embodiment, an example will be described in which a halftone phase shift mask blank for a KrF excimer laser (248 nm) having a single-layer light semi-transmissive film substantially composed of molybdenum, silicon, and nitrogen is described.
Using the same sputtering apparatus of Example 1, Mo: Si = 20: 80 as a sputtering target, argon, nitrogen, and helium (gas flow rates: Ar = 10 sccm, N ₂ = 80 sccm, He = 40 sccm) as sputtering gas. The light semitransmissive film was formed by adjusting the film forming pressure to 0.28 Pa so that the phase angle of the light semitransmissive film was approximately 180 °. The flatness at that time was 1.3 μm.
Then, heat processing was performed for 30 minutes at 250 degreeC using the heat processing apparatus.
The obtained halftone phase shift mask blank had a transmittance for exposure light of 6%, a phase angle of approximately 180 °, and a flatness of 0.6 μm, which satisfied the required value.
Further, the required values of the chemical resistance (acid resistance, alkali resistance, functional water resistance) and light resistance (KrF excimer laser) were almost satisfied.

(Example 3)
In this example, an example in which a halftone phase shift mask blank for an ArF excimer laser (193 nm) having a single-layer light semi-transmissive film substantially composed of molybdenum, silicon, and nitrogen will be described.
Using the same sputtering apparatus of Example 1, Mo: Si = 10: 90 as a sputtering target, argon, nitrogen, and helium (gas flow rates: Ar = 10 sccm, N ₂ = 80 sccm, He = 40 sccm) as sputtering gas. The light semitransmissive film was formed by adjusting the film forming pressure to 0.25 Pa so that the phase angle of the light semitransmissive film was approximately 180 °. The flatness at that time was 1.3 μm.
Then, heat processing was performed for 30 minutes at 250 degreeC using the heat processing apparatus.
The obtained halftone phase shift mask blank had a transmittance for exposure light of 6%, a phase angle of approximately 180 °, and a flatness of 0.6 μm, which satisfied the required value.
Further, the required values of the chemical resistance (acid resistance, alkali resistance, functional water resistance) and light resistance (ArF excimer laser) were almost satisfied.

Example 4
A resist film (baking temperature: 190 ° C. for ArF, 180 ° C. for KrF) was formed on the light semitransmissive film of the phase shift mask blank of Examples 2 and 3, and a resist pattern was formed by pattern exposure and development. Next, the exposed portion was removed by etching (dry etching with CF ₄ + O ₂ gas) to obtain a light semi-transmissive film pattern (holes, dots, etc.), that is, a light semi-transmissive portion. After removing the resist, it is immersed in 98% sulfuric acid (H ₂ SO ₄ ) at 100 ° C. for 15 minutes, washed with sulfuric acid, rinsed with pure water, etc., and a phase shift mask for ArF excimer laser and for KrF excimer laser Obtained a phase shift mask.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments.

For example, not only a halftone phase shift mask or blank having a single-layer light semi-transmissive film, but also a half-tone phase shift mask or blank having a light semi-transmissive film having a multilayer structure, or a single-layer or multilayer light-shielding film The present invention can also be applied to photomasks and photomask blanks having
The present invention can also be applied to a halftone phase shift mask or blank for an F ₂ excimer laser (157 nm) comprising a single-layer light semi-transmissive portion or light semi-transmissive film, and further a reaction during sputtering. Using oxygen gas as a reactive gas, for example, a light semi-transmissive part or light semi-transmissive film having a single layer or multilayer structure including a film containing silicon and oxygen such as MoSiO, MoSiON, NiSiON, PdSiON, SiON, and SiO is formed. In particular, the present invention can be applied.

(The invention's effect)
As described above, according to the present invention, sputtering film formation is performed by containing at least helium gas in the sputtering atmosphere, and the transparent substrate (thin film formed by sputtering film formation) is heated during or after the film formation. Thus, the film stress can be efficiently reduced.

It is a figure for demonstrating the transfer principle of a halftone type phase shift mask. It is a schematic diagram of the DC magnetron sputtering apparatus used in the Example. It is a figure which shows the relationship between He introduction amount and flatness variation | change_quantity.

Explanation of symbols

100 Transparent substrate 200 Light transmission part 300 Light semi-transmission part

Claims (6)

In a method for producing a photomask blank having at least a film for forming a mask pattern on a transparent substrate,
In the method, at least one layer of the film for forming the mask pattern is formed by sputter film formation by containing at least helium gas in a sputtering atmosphere, and the transparent substrate is formed during or after the film formation process. And a step of heating the photomask blank. 2. The photomask blank according to claim 1, wherein in the film formation step, a film for forming the mask pattern is formed by sputtering using a mixed gas of argon and helium as a sputtering gas. Production method. The photomask blank is a halftone phase shift mask blank, and the film for forming the mask pattern has a predetermined transmittance with respect to the exposure light and a predetermined amount of the phase of the exposure light with respect to the transparent substrate. 3. The method for producing a photomask blank according to claim 1, wherein the photomask blank is a light semi-transmissive film composed of one or more layers to be shifted. 4. The light semi-transmissive film includes a film made of a material containing silicon and nitrogen and / or oxygen, or a metal, silicon, and nitrogen and / or oxygen. The manufacturing method of the photomask blank of description. The method for producing a photomask blank according to claim 1, wherein a heat treatment temperature in the step of heating the transparent substrate is 180 ° C. or higher. A photomask manufactured using the photomask blank according to claim 1.

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