JP2004318088A - Photomask blank, photomask and method for manufacturing photomask blank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photomask blank producing a photomask having sufficiently low line edge roughness of an etching pattern, and to provide a photomask using the blank and a method for manufacturing a photomask blank. <P>SOLUTION: In the photomask blank having a multilayer film composed of four or more layers having different compositions from one another other on a substrate, the composition on the interface between the above layers is gently inclined. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photomask blank used for manufacturing a semiconductor integrated circuit and the like, a photomask, and a method for manufacturing a photomask blank.

  Photomasks used for a wide range of applications including the manufacture of semiconductor integrated circuits such as ICs, LSIs, and VLSIs are basically photomasks having a light-shielding film containing chromium as a main component on a light-transmitting substrate. A predetermined pattern is formed on the light-shielding film of the blank by applying a photolithography method and using ultraviolet rays, electron beams, or the like. In recent years, pattern miniaturization has rapidly progressed in response to market demands for higher integration of semiconductor integrated circuits and the like, and this has been dealt with by shortening the exposure wavelength. However, while shortening the exposure wavelength improves resolution, it also causes a decrease in the depth of focus, resulting in a decrease in process stability and a negative effect on product yield.

One effective pattern transfer method for such a problem is a phase shift method, and a phase shift mask is used as a mask for transferring a fine pattern.
This phase shift mask (halftone type phase shift mask) includes, for example, as shown in FIGS. 9A and 9B, a phase shifter part b forming a pattern portion on the mask, and a phase shifter b. The non-existing substrate is composed of the exposed portion a, and the phase difference between the light passing through both is set to about 180 °, so that the light intensity at the interference portion becomes zero due to the interference of the light at the pattern boundary. And the contrast of the transferred image can be improved. In addition, by using the phase shift method, it is possible to increase the depth of focus for obtaining the required resolution, as compared with a case where a normal mask having a general light shielding pattern made of a chrome film or the like is used. It is possible to improve the resolution and the margin of the exposure process.

  The above-mentioned phase shift masks can be practically roughly classified into a complete transmission type phase shift mask and a halftone type phase shift mask depending on the light transmission characteristics of the phase shifter. The complete transmission type phase shift mask is a mask in which the light transmittance of the phase shifter portion is equivalent to that of the substrate exposed portion and which is transparent to the exposure wavelength. In the halftone phase shift mask, the light transmittance of the phase shifter is about several% to several tens% of the exposed part of the substrate.

  FIG. 1 shows a basic structure of a halftone type phase shift mask blank, and FIG. 2 shows a basic structure of a halftone type phase shift mask. The halftone phase shift mask blank of FIG. 1 has a halftone phase shift film 2 formed on almost the entire surface of a transparent substrate 1. The halftone type phase shift mask of FIG. 2 is obtained by patterning the phase shift film 2 and includes a phase shifter 2a for forming a pattern portion on the substrate 1 and a substrate exposed portion 1a having no phase shifter. . Here, the light transmitted through the phase shifter 2a is phase-shifted with respect to the light transmitted through the substrate exposing portion 1a, and the transmittance of the phase shifter 2a is set to a light intensity that is not sensitive to the resist on the substrate to be transferred. Is set. Therefore, it has a light blocking function of substantially blocking exposure light.

  As the halftone type phase shift mask, there is a single layer type halftone type phase shift mask which has a simple structure and is easy to manufacture. As this single-layer halftone type phase shift mask, one having a phase shifter made of a MoSi-based material such as MoSiO and MoSiON described in JP-A-7-140635 (Patent Document 1) has been proposed. .

  What is important in the phase shift mask blank used for such a phase shift mask is that while satisfying optical characteristics such as transmittance, reflectance, and refractive index at the exposure wavelength to be used, and durability such as chemical resistance. That is, low defects must be realized.

  However, in the single-layer halftone phase shift film, when the optical characteristics are set to a desired value, the film composition is uniquely determined. Therefore, it is possible to obtain a phase shift film satisfying other required characteristics. It was difficult.

  In order to avoid this problem, a phase shift multilayer film having a plurality of layers satisfying optical characteristics and a plurality of layers satisfying other characteristics such as chemical resistance has been proposed. However, the phase shift film composed of a plurality of films has a problem that a step is easily generated on the side surface of the etching pattern at the time of pattern formation, and line edge roughness is deteriorated.

  Furthermore, when a plurality of films having different compositions are laminated in addition to the phase shift film as described above to have one function, for example, a reflection film is formed by alternately laminating films having different compositions. Although there are photomasks of the type, similar problems are encountered in such a case.

JP-A-7-140635

  The present invention has been made to solve the above problems, and provides a photomask blank that provides a photomask having sufficiently small line edge roughness of an etching pattern, a photomask using the same, and a method of manufacturing a photomask blank. The purpose is to do.

  The inventor of the present invention has conducted intensive studies to solve the above-described problems, and as a result, has found that a photomask blank having a structure in which a multilayer film having four or more layers is formed on a substrate, and the composition of adjacent films in the multilayer film is different. In the present invention, it is found that a photomask blank capable of drawing a mask pattern with a small line edge roughness and a photomask using the same can be obtained by gently tilting the composition of the interface of each film constituting the multilayer film. I've reached the point.

That is, the present invention provides the following photomask blank, a photomask, and a method for manufacturing a photomask blank.
Claim 1:
A photomask blank having a multilayer film composed of four or more layers having different compositions on a substrate, wherein the composition of the interface between the respective layers is gently inclined.
Claim 2:
2. The photomask blank according to claim 1, wherein the multilayer film is formed of a film containing a metal silicide and a compound of oxygen and / or nitrogen as main components.
Claim 3:
The photomask blank according to claim 1, wherein the multilayer film is provided with one or more films mainly containing molybdenum silicide oxynitride.
Claim 4:
The multilayer film is a phase shift film, and a chromium-based light-shielding film or a chrome-based antireflection film, or a multilayer film in which at least one of these chrome-based light-shielding films and chromium-based antireflection films are laminated on the multilayer film is formed. The photomask blank according to claim 1, wherein:
Claim 5:
When performing sputtering film formation using a sputtering film forming apparatus having a plurality of targets having different compositions, a film having a different composition is obtained by gradually changing a combination of powers applied to the plurality of targets near an interface of each layer. The method for producing a photomask blank according to claim 1, wherein a plurality of layers are formed.
Claim 6:
6. The method according to claim 5, wherein the combination of the targets is a metal silicide target and a silicon target.
Claim 7:
The method for manufacturing a photomask blank according to claim 5, wherein the combination of the targets is a metal target and a silicon target.
Claim 8:
When a multilayer film is formed by sputtering with a plurality of targets, the power gradient period when gradually changing the combination of power applied to the targets near the interface between the layers is 10% of the time required to complete the film formation of each layer. The method for manufacturing a photomask blank according to any one of claims 5 to 7, wherein:
Claim 9:
A photomask, wherein the multilayer film of the photomask blank according to claim 1 is patterned.

  In this case, according to the present invention, in a photomask blank having a structure in which four or more layers of different compositions are provided on a substrate, the composition of the interface of each film is gently inclined. Then, when a pattern is formed on the multilayer film and a photomask is manufactured, a mask pattern with sufficiently reduced line edge roughness can be obtained.

  Further, by forming a phase shift film with the above-mentioned multilayer film, and forming a chromium-based light-shielding film or a chromium-based antireflection film or a multilayer film in which at least one of each of these is laminated on the phase shift film, Together with this, more precise patterning becomes possible, and it is possible to sufficiently cope with further miniaturization and higher integration of semiconductor integrated circuits.

  According to the present invention, even in a photomask blank having a structure in which a plurality of films having different compositions are stacked, it is possible to suppress line edge roughness when a mask pattern is formed on the stacked film by etching.

Hereinafter, the present invention will be described in more detail.
The photomask blank according to the present invention is obtained by forming a multilayer film composed of four or more layers on a substrate such as quartz or CaF ₂ through which exposure light is transmitted or a substrate such as a high flatness substrate having a thermal expansion coefficient of 1 ppm / ° C. or less. It is provided in.

  The multilayer film of the present invention can be applied to a phase shift film, or can be used as a film having optical properties such as a reflection film or a semi-transmission film.

  When used as a phase shift film, a phase shift multilayer film 2 made of a metal silicide compound is formed on a substrate 1 as shown in FIG. In this case, the phase shift mask according to the present invention is formed by patterning a phase shift multilayer film of a phase shift mask blank, and as shown in FIG. 2, a first light transmitting portion is formed between the patterned phase shifter portions. The (substrate exposed portion) 1a and the patterned phase shift multilayer film (phase shifter portion) 2 become the second light transmitting portion 2a.

  The phase shift mask blank can be formed on a transparent substrate by a reactive sputtering method using a sputtering gas containing an oxygen source gas and / or a nitrogen source gas, and has a transmittance of several% to exposure light. A metal silicide having tens of% (particularly preferably 3 to 40%), and having a phase difference of 180 ° ± 5 ° with respect to the light transmitted through the phase shifter part with respect to the light transmitted only through the transparent substrate It is preferable that a phase shift multilayer film formed from an oxide, nitride or oxynitride is provided.

  Here, as the metal silicide target, it is preferable to use molybdenum silicide, from which a dense and high-purity target can be easily obtained, and the phase shift multilayer film is a film containing a compound of molybdenum silicide as a main component, particularly, It is desirable to include one or more layers. It is also preferable that an oxide, nitride, or oxynitride film of molybdenum silicide and a silicon oxide, nitride, or oxynitride film are alternately stacked. In addition, when the multilayer film of the present invention is used as a laminated film such as a reflective film, it is desirable to form a structure in which films of different compositions such as Si and Mo are regularly laminated.

  The multilayer film of the present invention is composed of four or more layers. With less than four layers, the line edge roughness cannot be sufficiently reduced even if the composition and / or composition ratio of the film interface is inclined. The upper limit of the number of layers is appropriately selected and is not particularly limited, but is usually 200 layers or less, particularly 100 layers or less.

  In this case, in the present invention, the above-mentioned layers have different compositions from each other, and the composition is gently inclined at the interface between the layers. Here, the difference in composition includes not only the case where the constituent elements constituting each layer are different, but also the case where the composition ratio is different even if the constituent elements are the same.

  The term “gradient in composition” means that the composition of one layer may change continuously from the composition of one layer to the composition of the other layer between adjacent layers, or may change stepwise. As described above, the composition may be changed in 10 to 50 steps.

  As shown in FIG. 10, the thickness d of the inclined region 7 in which the composition is gently inclined is equal to the thickness d of the inclined region 7 of the single-layer film 6 having the composition changed through the inclined region 7. It is preferable that d / D ≧ 0.1 of the thickness D including the thickness D, that is, d / D ≧ 0.1. Although the upper limit of d / D can be appropriately selected, it is usually d / D ≦ 1, particularly d / D = 0.5. If d / D <0.1, the line edge roughness may be poor. Note that the thickness D is preferably 3 to 600 °, particularly preferably 10 to 300 °. Further, the total thickness of the multilayer film is preferably 30 to 2000 °.

  The method of manufacturing the multilayer film will be described in more detail. First, a plurality of targets having various compositions such as a combination of a metal silicide target such as molybdenum silicide and a silicon target or a combination of a metal target such as molybdenum and a silicon target are provided in one sputtering chamber. Provide.

  Only one target may be discharged and sputtered per layer, or a plurality of targets may be simultaneously discharged and sputtered to form a film while synthesizing film components scattered from each target (generally co-sputtering). )). At this time, the substrate is desirably rotated so that the film components from the respective targets are uniformly mixed. A desired film composition can be obtained by adjusting the discharge power applied to each target.

  In this case, when a multilayer film is formed by sputtering with the plurality of targets, the power gradient period when gradually changing the combination of powers applied to the targets near the interface between the layers is not changed until the film formation of each layer is completed. It is preferably at least 10% of the time, more preferably 20 to 50%.

  A multilayer film is manufactured by using such a film forming apparatus. The discharge power of each target is gradually changed from a predetermined period before the film formation of one layer is completed, and the composition of the next film is formed. Adjust so that As a result, a structure in which the composition and / or composition ratio near the interface between the layers is gradually and gradually obtained is obtained.

  Here, such a graded layer can be obtained by adjusting the discharge power to the target, but by continuously changing the discharge power to the target, the grade in which the composition is substantially continuously changed is obtained. A film is obtained, and a gradient film whose composition changes stepwise is obtained by changing the discharge power stepwise or intermittently.

  In the present invention, the sputtering method may be a method using a DC power supply or a method using a high-frequency power supply, and may be a magnetron sputtering method or a conventional method.

  The composition of the sputtering gas is appropriately set so that a multilayer film formed by depositing an inert gas such as argon and xenon and, if necessary, a nitrogen gas, an oxygen gas, various nitrogen oxide gases, and a carbon oxide gas has a desired composition. Should be added to

  When configuring a phase shift film, when it is desired to increase the transmittance of the formed phase shift film, the amount of gas containing oxygen or nitrogen added to the sputtering gas is adjusted so that a large amount of oxygen and nitrogen are taken into the film. It can be prepared by an increasing method, a method using a sputtering target to which oxygen or nitrogen is added in advance in a large amount, or the like. Specifically, when a film of molybdenum silicide oxynitride (MoSiON) is formed, it is preferable to use molybdenum silicide as a target and perform reactive sputtering with a sputtering gas containing an argon gas, a nitrogen gas, and an oxygen gas as a sputtering gas. preferable.

  The same applies when an oxide or nitride of molybdenum silicide or another metal (for example, zirconium) is used instead of molybdenum.

  Here, the composition of the oxide, nitride and oxynitride (oxynitride) of the metal silicide is more than Me (metal such as Mo and Zr) = 0 atomic% and 25 atomic% or less, preferably 0.2 to 0.2 atomic%. It is preferable to appropriately select from the range of 25 atomic%, Si = 10 to 33 atomic%, O = 0 to 67 atomic%, and N = 0 to 57 atomic%.

  More specifically, in the case of an oxide of molybdenum silicide (MoSiO), it is preferable that Mo is more than 0 atomic% and 25 atomic% or less, Si is 10 to 33 atomic%, and O is 33 to 67 atomic%. In the case of a nitride of molybdenum silicide (MoSiN), Mo is preferably more than 0 atomic% and 25 atomic% or less, Si is 10 to 42 atomic%, and N is 33 to 58 atomic%. In the case of nitride (MoSiON), it is preferable that Mo = 0.2 to 25 atomic%, Si = 10 to 57 atomic%, O = 1 to 60 atomic%, and N = 6 to 57 atomic%. In the case of silicon oxide, nitride, and oxynitride, it is preferable that Mo = 0 atomic% in the above composition.

  On the other hand, when a laminated film is formed of a metal film and has a function of a reflection film, for example, a metal such as Mo, Zr, Ti, Al, Au, Cu, Ag, Cr, Ni, Co, Pd, Pt, or Si is used. Any combination may be used, and a single substance may be laminated, or an alloy containing 1 to 50 atomic% of another metal atom may be combined and laminated. Above all, a combination of Mo and Si is preferable. In this case, a single element of Mo and Si may be laminated, or if necessary, a Mo alloy film containing 1 to 50 atomic% of another metal element and another Mo element. A Si alloy film containing 1 to 50 atomic% of a metal element may be laminated.

  In the present invention, a chromium-based light-shielding film 3 is provided on the phase shift multilayer film 2 as shown in FIG. 3, or the reflection from the chrome-based light-shielding film 3 is reduced as shown in FIG. The chrome-based anti-reflection film 4 can be formed on the chrome-based light-shielding film 3. Further, as shown in FIG. 5, a phase shift multilayer film 2, a first chrome-based antireflection film 4, a chrome-based light-shielding film 3, and a second chrome-based antireflection film 4 'are formed in this order from the substrate 1 side. You can also.

  In this case, it is preferable to use chromium oxycarbide (CrOC), chromium oxynitride carbide (CrONC), or a laminate thereof as the chromium-based light-shielding film or chromium-based antireflection film.

  Such a chromium-based light-shielding film or chromium-based antireflection film uses a target in which chromium alone or chromium is added with any one of oxygen, nitrogen, and carbon, or a combination thereof, to an inert gas such as argon or krypton. A film can be formed by reactive sputtering using a sputtering gas to which carbon dioxide gas or the like is added as a carbon source.

Specifically, when a CrONC film is formed, as a sputtering gas, a gas containing carbon such as CH ₄ , CO ₂ , CO, a gas containing nitrogen such as NO, NO ₂ , N ₂ , and a gas containing CO ₂ , NO, O _2, or other gases containing oxygen, or a mixture of these gases with an inert gas such as Ar, Ne, or Kr can also be used. In particular, it is preferable to use a CO ₂ gas as the carbon source gas and the oxygen source gas from the viewpoints of the in-plane uniformity of the substrate and the controllability during production. As an introduction method, various sputtering gases may be separately introduced into the chamber, or several gases may be introduced together or all gases may be mixed and introduced.

  In the CrOC film, Cr is 20 to 95 atomic%, particularly 30 to 85 atomic%, C is 1 to 30 atomic%, particularly 5 to 20 atomic%, O is 1 to 60 atomic%, particularly 5 to 50 atomic%. It is preferable that the CrONC film has a Cr content of 20 to 95 at%, particularly 30 to 80 at%, C of 1 to 20 at%, particularly 2 to 15 at%, O of 1 to 60 at%, It is particularly preferred that 5 to 50 atomic% and N be 1 to 30 atomic%, particularly 3 to 20 atomic%.

  The photomask of the present invention is obtained by patterning a multilayer film of the photomask blank obtained as described above.

  Specifically, when manufacturing a photomask as shown in FIG. 2, as shown in FIG. 6A, after forming the multilayer film 12 on the substrate 11 as described above, a resist film is formed. 6B, the resist film 13 is patterned by lithography as shown in FIG. 6B, and the multilayer film 12 is etched as shown in FIG. As shown in (D), a method of removing the resist film 13 can be adopted. In this case, application, patterning (exposure, development), etching, and removal of the resist film can be performed by a known method.

  When a chromium-based light-shielding film and / or a chromium-based antireflection film (chrome-based film) is formed on the phase shift multilayer film, the light-shielding film and / or the antireflection film in a region necessary for exposure are removed by etching. Then, after exposing the phase shift multilayer film to the surface, the phase shift multilayer film is patterned in the same manner as described above, whereby a phase shift mask in which the chrome-based light-shielding film 3 remains on the outer peripheral edge side of the substrate as shown in FIG. Obtainable. In addition, a resist is applied on the chromium-based film, patterning is performed, the chromium-based film and the phase shift multilayer film are patterned by etching, and only the chromium-based film in a region necessary for exposure is removed by selective etching. Alternatively, a photomask can be obtained by exposing the phase shift pattern to the surface.

  Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1]
As a multilayer film, an alternate laminated film of a molybdenum silicide oxynitride (MoSiON) film and a silicon oxynitride (SiON) film was formed.

For the film formation, a DC sputtering apparatus provided with two targets 22a and 22b as shown in FIG. 8 was used. A MoSi _3.5 target was used as the target 22a for the MoSiON film, and a Si target was used as the target 22b for the SiON film. In addition, a mixed gas of Ar = 20 cm ³ / min, N ₂ = 100 cm ³ / min, and O ₂ = 5 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

On a quartz substrate, first, a discharge power of 1000 W was applied to a MoSi _3.5 target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first layer film to a thickness of 270 °. Subsequently, the discharge power of the MoSi _3.5 target was gradually reduced, while the discharge power of the Si target was gradually increased. When reaching 305 ° from the start of the formation of the MoSiON film, the discharge power of the MoSi _3.5 target was set to 0 W, the discharge power of the Si target was changed to 1000 W, and the transition to the formation of the SiON film was completed. . By the above method, a gradient composition region having a d / D of 0.1 was formed.

Next, while gradually decreasing the discharge power of the Si target to 0 W, the discharge power of the MoSi _3.5 target was gradually increased to 1000 W. Thereafter, the films were alternately laminated by the same operation. A total of four multilayer films were obtained.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. Observation of the obtained pattern and measurement of LER of the multilayer film showed an excellent value of 10 nm.

[Example 2]
As a multilayer film, an alternate laminated film of a MoSiON film and a SiON film was formed.
For the film formation, a DC sputtering apparatus provided with two targets as shown in FIG. 8 was used. A MoSi _3.5 target was used as a target for the MoSiON film, and a Si target was used as a target for the SiON film. In addition, a mixed gas of Ar = 20 cm ³ / min, N ₂ = 100 cm ³ / min, and O ₂ = 5 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

On the quartz substrate, first, a discharge power of 1000 W was applied to a MoSi _3.5 target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first layer film to a thickness of 240 °. Subsequently, the discharge power of the MoSi _3.5 target was gradually reduced, while the discharge power of the Si target was gradually increased. When the temperature reached 310 ° after the start of the formation of the MoSiON film, the discharge power of the MoSi _3.5 target was set to 0 W, the discharge power of the Si target was changed to 1000 W, and the transition to the formation of the SiON film was completed. . By the above method, a gradient composition region having d / D of 0.2 was formed.

Next, while gradually decreasing the discharge power of the Si target to 0 W, the discharge power of the MoSi _3.5 target was gradually increased to 1000 W. Thereafter, the films were alternately laminated by the same operation. A total of four multilayer films were obtained.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. Observation of the obtained pattern and measurement of LER of the multilayer film showed an excellent value of 8 nm.

[Example 3]
As a multilayer film, an alternate laminated film of a MoSiON film and a SiON film was formed.
For the film formation, a DC sputtering apparatus provided with two targets as shown in FIG. 8 was used. A MoSi _3.5 target was used as a target for the MoSiON film, and a Si target was used as a target for the SiON film. In addition, a mixed gas of Ar = 20 cm ³ / min, N ₂ = 100 cm ³ / min, and O ₂ = 5 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

On a quartz substrate, first, a discharge power of 1000 W was applied to a MoSi _3.5 target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first layer film to a thickness of 190 °. Subsequently, the discharge power of the MoSi _3.5 target was gradually reduced, while the discharge power of the Si target was gradually increased. When reaching 203 ° after the start of the formation of the MoSiON film, the discharge power of the MoSi _3.5 target was set to 0 W, the discharge power of the Si target was changed to 1000 W, and the transition to the formation of the SiON film was completed. . By the above method, a gradient composition region having a d / D of 0.1 was formed.

Next, while gradually decreasing the discharge power of the Si target to 0 W, the discharge power of the MoSi _3.5 target was gradually increased to 1000 W. Thereafter, the films were alternately laminated by the same operation. A multilayer film having a total of six layers was obtained.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. Observation of the obtained pattern and measurement of LER of the multilayer film showed an excellent value of 9 nm.

[Example 4]
As a multilayer film, an alternate laminated film of a molybdenum (Mo) film and a silicon (Si) film was formed.
For the film formation, a DC sputtering apparatus provided with two targets as shown in FIG. 8 was used. A Mo target was used as a target for the Mo film, and a Si target was used as a target for the Si film. Ar = 70 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

  First, on a quartz substrate, a 1000 W discharge power was applied to a Mo target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first-layer film to a thickness of 27 °. Subsequently, the discharge power of the Mo target was gradually reduced while the discharge power of the Si target was gradually increased. When the temperature reached 34 ° after the start of the formation of the Mo film, the discharge power of the Mo target was set to 0 W and the discharge power of the Si target was changed to 1000 W, and the transition to the formation of the Si film was completed. By the above method, a gradient composition region having a d / D of 0.1 was formed.

  Next, an operation of gradually decreasing the discharge power of the Si target to 0 W while gradually increasing the discharge power of the Mo target to 1000 W is performed. A multilayer film of 40 layers was obtained.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. Observation of the obtained pattern and measurement of LER of the multilayer film showed an excellent value of 6 nm.

[Comparative Example 1]
As a multilayer film, a laminated film of a MoSiON film and a SiON film was formed.
For the film formation, a DC sputtering apparatus provided with two targets as shown in FIG. 8 was used. A MoSi _3.5 target was used as a target for the MoSiON film, and a Si target was used as a target for the SiON film. In addition, a mixed gas of Ar = 20 cm ³ / min, N ₂ = 100 cm ³ / min, and O ₂ = 5 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

First, on a quartz substrate, a discharge power of 1000 W was applied to a MoSi _3.5 target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first layer film to a thickness of 540 °. Subsequently, the discharge power of the MoSi _3.5 target was gradually reduced, while the discharge power of the Si target was gradually increased. When the temperature reached 610 ° after the start of the formation of the MoSiON film, the discharge power of the MoSi _3.5 target was set to 0 W, the discharge power of the Si target was changed to 1000 W, and the transition to the formation of the SiON film was completed. . By the above method, a gradient composition region having a d / D of 0.1 was formed, and then a second layer film was formed.
The films were stacked by the above operation to obtain a multilayer film having a total of two layers.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. When the obtained pattern was observed and the LER of the multilayer film was measured, it was 18 nm, which was not sufficient.

[Comparative Example 2]
As a multilayer film, an alternate laminated film of a MoSiON film and a SiON film was formed.
For the film formation, a DC sputtering apparatus provided with two targets as shown in FIG. 8 was used. A MoSi _3.5 target was used as a target for the MoSiON film, and a Si target was used as a target for the SiON film. In addition, a mixed gas of Ar = 20 cm ³ / min, N ₂ = 100 cm ³ / min, and O ₂ = 5 cm ³ / min was introduced as a sputtering gas. At this time, the gas pressure during sputtering was set to 0.2 Pa.

On a quartz substrate, first, a discharge power of 1000 W was applied to a MoSi _3.5 target, and a sputter film was formed while rotating the substrate at 30 rpm to form a first layer film to a thickness of 300 °. Next, the discharge power of the Si target was changed to be 1000 W, and a SiON film was formed. D / D was set to 0 by the above method.
Films were alternately laminated by the same operation, and finally a multilayer film having a total of four layers was obtained.

Evaluation of Line Edge Roughness (LER) A resist film 13 is formed on the multilayer film obtained under the above conditions as shown in FIG. 6A, and the resist film 13 is formed as shown in FIG. Then, after the multilayer film 12 was dry-etched as shown in FIG. 6C, the resist film 13 was peeled off as shown in FIG. 6D. When the obtained pattern was observed and the LER of the multilayer film was measured, it was 16 nm, which was not sufficient.

Table 1 summarizes the results of the above Examples and Comparative Examples.
From these results, it was confirmed that the multilayer film of the present invention had sufficiently small line edge roughness and was very useful as a photomask.

FIG. 2 is a cross-sectional view of a phase shift mask blank according to one embodiment of the present invention. It is sectional drawing of the same phase shift mask. 1 is a cross-sectional view of a phase shift mask blank provided with a chrome-based light-shielding film according to one embodiment of the present invention. 1 is a cross-sectional view of a phase shift mask blank provided with a chrome-based light-shielding film and a chrome-based antireflection film according to one embodiment of the present invention. It is sectional drawing of the same other phase shift mask blank. It is explanatory drawing which showed the manufacturing method of the phase shift mask, (A) is the state which formed the resist film, (B) was the state which patterned the resist film, (C) was the state which performed etching, (D) FIG. 3 is a schematic sectional view in a state where a resist film is removed. It is sectional drawing which shows the other Example of a phase shift mask. It is the schematic of the direct-current sputtering apparatus used in the Example. (A), (B) is a figure explaining the principle of a halftone type phase shift mask, (B) is the elements on larger scale of the X section of (A). It is a conceptual diagram of the structure and composition change of the multilayer film of this invention.

Explanation of reference numerals

1,11,21 substrate 12 multilayer film 2 phase shift film (phase shift multilayer film)
Reference Signs List 3 Chromium-based light-shielding film 4, 4 'Chrome-based antireflection film 5 Multilayer film 6 Single-layer film in multilayer film 7 Gradient region of composition 8 Concentration curve of each film composition 1a Substrate exposed portion 2a Second light transmitting portion (phase shifter) Part)
13 Resist film 22a, 22b Target

Claims (9)

  A photomask blank having a multilayer film composed of four or more layers having different compositions on a substrate, wherein the composition of the interface between the respective layers is gently inclined.   2. The photomask blank according to claim 1, wherein the multilayer film is formed of a film containing a metal silicide and a compound of oxygen and / or nitrogen as main components.   The photomask blank according to claim 1, wherein the multilayer film is provided with one or more films mainly containing molybdenum silicide oxynitride.   The multilayer film is a phase shift film, and a chromium-based light-shielding film or a chrome-based antireflection film, or a multilayer film in which at least one of these chrome-based light-shielding films and chromium-based antireflection films are laminated on the multilayer film is formed. The photomask blank according to claim 1, wherein:   When performing sputtering film formation using a sputtering film forming apparatus having a plurality of targets having different compositions, a film having a different composition is obtained by gradually changing a combination of powers applied to the plurality of targets near an interface of each layer. The method for producing a photomask blank according to claim 1, wherein a plurality of layers are formed.   6. The method according to claim 5, wherein the combination of the targets is a metal silicide target and a silicon target.   The method for manufacturing a photomask blank according to claim 5, wherein the combination of the targets is a metal target and a silicon target.   When a multilayer film is formed by sputtering with a plurality of targets, the power gradient period when gradually changing the combination of power applied to the targets near the interface between the layers is 10% of the time required to complete the film formation of each layer. The method for manufacturing a photomask blank according to any one of claims 5 to 7, wherein: A photomask, wherein the multilayer film of the photomask blank according to claim 1 is patterned.

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