KR20090087153A - Half-tone phase shift blankmask, photomask and it's manufacturing method - Google Patents

Abstract

A half-tone phase shift blank mask, photomask and its manufacturing method are provided to improve the density and line edge roughness of the thin film by using the DC-RF coupled sputtering method. The phase shift layer is formed on the transparent substrate(10). The phase shift layer consists of multilayer more than the single layer or two layers. The light-shielding layer(50) is formed on the phase shift layer. The reflection barrier layer(60) is formed on the light-shielding layer. The resist film is formed on the reflection barrier layer. The target for the single layer phase shift layer is made of metal more than one kind and/or the transition metal. The first phase inversion film(20) includes tantalum(Ta) and/or chrome(Cr). The first phase inversion film is formed at the upper part of the transparent substrate.

Description

Halftone phase inversion blank mask, photomask and manufacturing method thereof {HALF-TONE PHASE SHIFT BLANKMASK, PHOTOMASK AND IT'S MANUFACTURING METHOD}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a half-tone phase shift blank mask capable of realizing a high precision critical dimension (CD) in a semiconductor photo-lithography process. The present invention relates to an appropriate halftone phase inversion mask and a blank mask of the material, which can be applied to ArF (193 nm) lithography and ArF immersion lithography that can realize a minimum line width.

Due to the high integration of semiconductor integrated circuits, the importance of photolithography technology, which is a core process of semiconductor manufacturers, is becoming increasingly important.

The photolithography technology has shortened the exposure wavelength with 436 nm g-line, 365 nm i-line, 248 nm KrF, and 193 nm ArF to improve the resolution of the pattern process.

However, shortening the exposure wavelength greatly contributed to the improvement of the resolution, but adversely affects the depth of focus (DoF), causing a lot of burden on the design of the optical system including the lens.

Accordingly, in order to solve the above problems, a phase inversion mask has been developed that simultaneously improves the resolution and the depth of focus by modifying the phase of the exposure light passing through the transmission part by using the phase inversion film as the transflective portion.

The phase inversion film includes a reversal phase inversion film useful for line and space patterns, and a halftone phase inversion film effective for isolation patterns or contact holes. To facilitate control, MoSiN, MoSiO, MoSiON, and MoSiCON, a single layer of molybdenum silicide (MoSi) series, have been developed and are currently being used as phase inversion films for 6% ArF.

However, current single-layer molybdenum silicide material uses the same silicide-based material as SiO ₂ , the main component of the substrate, which makes it difficult to control etching with the substrate during dry etching, thereby preventing damage to the substrate. It has a problem that causes it.

In addition, the single-layer molybdenum silicide material is vulnerable to ammonia contained in Standard Cleaning 1 (SC 1) used in the cleaning process of the photomask, and the predetermined thickness is changed due to the change of the thickness of the phase inversion film when the repeated cleaning process is applied. It has a disadvantage that it cannot be used beyond the transmittance and phase amount of.

As a result, current single-layer molybdenum silicide materials cannot remove all sulfuric acid and ammonia components used in the cleaning process due to their weak chemical resistance characteristics, and growth defects on the surface are continuously observed when the exposure energy of 193 nm or below ArF is continuously irradiated. It shows the problem that occurs.

In addition to the above problems, low stress, defect free, roughness, conductivity, and the like are increasingly being refined and refined to achieve high precision CD of 90 nm or less in order to refine the adhesion and pattern of the thin film.

The present invention provides a method for manufacturing a halftone phase inversion blank mask formed of a single film and / or two or more layers in the manufacture of a halftone phase inversion blank mask applied to an exposure wavelength below ArF in order to solve the above problems. In particular, through the DC-RF coupled sputtering method, the density, chemical resistance, uniformity, growth defects (Haze), surface roughness (Roughness), stress, LER, and defects of the thin film can be improved. One way is to provide a high quality halftone phase inversion blank mask.

In order to achieve the above object, a characteristic of the method for manufacturing a halftone phase inversion blank mask according to the present invention has a phase inversion film of a semi-transmissive portion on a transparent substrate, and the phase inversion film is the first phase inversion film alone and / or the second phase. It is composed of an inverted film, characterized in that the light-shielding film and the anti-reflection film is sequentially deposited thereon and a halftone phase inversion blank mask formed with a resist film.

In particular, in the case of the halftone phase inversion blank mask manufacturing process according to the present invention, a1) forming a phase inversion film on a transparent substrate; b1) forming a light shielding film on the phase inversion film formed in step a1); c1) forming an anti-reflection film on the light shielding film formed in step b1); d1) forming a resist film on the anti-reflection film formed in step c1) to manufacture a halftone phase inversion blank mask.

In the manufacturing process, the phase inversion film sequentially stacked if necessary, may be composed of one or more phase inversion film, to reduce the defects of the crystalline of the phase inversion film, improve the chemical resistance, 30% or less in the exposure wavelength It is possible to form one or more layers on the top or at the interface or the bottom of the reflectance control of.

In the step a1), the transparent substrate is a transparent substrate selected from synthetic quartz, calcium fluoride (CaF2), and fluorine-doped quartz (F-Doped Quartz).

In the step a1), the flatness of the transparent substrate is 0.3 μm or less and the center line average roughness is 0.3 nm Ra or less.

When the energy of the exposure wavelength is irradiated on the transparent substrate in step a1), the transmittance change is within 0.5%.

In general, the transparent substrate has a transmittance of 88% or more in the exposure wavelength.

However, due to defects occurring in the production stage of the substrate and / or the manufacturing process of the transparent substrate, the energy of the exposure wavelength is transferred to the wafer using the completed photomask after the patterning process of the blank mask. This causes a problem in that the transmittance of the transparent substrate portion is changed to cause unwanted defects.

Therefore, in order to prevent defects caused by fluctuations in the transmittance, the transparent substrate should use a transparent substrate having excellent light resistance to exposure energy, and in particular, the change in transmittance due to repeated energy irradiation with respect to exposure light is within 0.5%. Should be used to prevent defects.

The birefringence generated when applying the transparent substrate to the immersion lithography in step a1) is 3 nm / 6.35 mm or less, and the birefringence in the area of 152 × 152 cm with a size of 6 × 6 × 0.25 inch The change range (Range) is characterized in that 3nm / (152 × 152cm) or less.

Transparent substrates used in immersion exposure techniques cause CD errors due to their birefringence. This problem is due to the fact that the numerical aperture (NA), such as 365 nm i-line and 248 nm KrF applied in conventional vacuum lithography, is smaller than the NA of the immersion exposure technology. It was not a problem because it was larger than the Pattern Error Size.

However, as the increase in NA and the size of the resolution to be realized in ArF Lithography become less than 90 nm, a problem of CD error due to birefringence of a substrate is increasing.

The CD error due to the birefringence has a characteristic that the longer the optical path length is proportional to the size of the maximum CD error. In this relationship, the transparent substrate having the largest thickness in the blank mask has the influence of the largest birefringence. do.

Therefore, the birefringence of the transparent substrate must be controlled to realize high resolution. Therefore, the birefringence of the transparent substrate of less than 3nm / 6.35mm is required, more preferably, the transparent substrate to which the birefringence of 1nm / 6.35mm is applied.

In addition, in birefringence, the uniformity (Uniformity) also plays an important role in the formation of the fine pattern.

Therefore, the uniformity range of the birefringence must also be controlled, and the birefringence uniformity range should also be applied to 3 nm / (152 × 152 cm) or less, and more preferably, to use a transparent substrate having 1 nm / (152 × 152 cm) applied. .

In the step b1 ~ d1), the phase inversion film, the light shielding film, the anti-reflection film is formed by vacuum deposition, preferably DC sputtering, RF sputtering, DC-RF Coupled sputtering, ion beam sputtering, ion plating and One or more methods selected from atomic layer deposition are possible.

In the step b1 ~ d1), in particular, in order to improve the density (Density), stress, growth defects (Haze), particles, chemical resistance, conductivity, surface roughness, uniformity of the thin film is deposited by applying the DC-RF Coupled sputtering method Characterized in that.

The DC-RF Coupled Sputtering method makes it easy to discharge at low voltage by using high frequency of RF to make thin film deposited during DC sputtering using high frequency of RF, and also makes high quality thin film density and uniformity under the influence of high frequency. It is possible to produce a tone type phase inversion blank mask.

In addition, when applying the DC-RF Coupled sputtering method, the Atomic Shot Peening generated during the deposition by the general DC sputtering method is reduced to reduce the film stress.

Therefore, when the thin film is deposited by the DC-RF coupled sputtering method, the density, uniformity, etc. can be further improved by the conventional general DC and / or RF sputtering method, and also the stress is reduced, thereby growing growth defects. It is possible to improve particles, chemical resistance, surface roughness, conductivity, and LER, thereby enabling the production of high quality halftone phase inversion blank masks.

In the step b1 ~ d1), the phase inversion film, the light shielding film, the reflective film can be formed through DC or RF and / or DC-RF Coupled magnetron reactive sputtering, in this case argon (Ar), helium (He), neon (Ne) and at least one inert gas selected from the group consisting of xenon (Xe), oxygen (O 2), nitrogen (N ₂ ), carbon monoxide (CO), carbon dioxide (CO ₂ ), nitrogen dioxide (NO ₂₎ ), At least one reactive gas selected from the group consisting of nitrogen monoxide (NO), nitrous oxide (N ₂ O), ammonia (NH ₃ ) and methane (CH ₄ ).

When the single-phase phase inversion film is formed in step b1), the sputter target material used for forming the phase inversion film includes at least one metal and / or transition metal and silicon.

In the target of the single-phase phase inversion film, the metal and / or transition metal may be composed of one or more selected from aluminum, titanium, vanadium, chromium, zirconium, niobium, molybdenum, lanthanum, tantalum, and tungsten. .

When the single-phase phase inversion film is formed in step b1), it is characterized in that at least one selected from oxide, nitride, carbide, oxynitride, oxidized carbide, nitride carbide, oxycarbide nitride using the target used.

In the sputter target used to form the single-phase phase inversion film in step b1), the composition ratio of the target is 1 to 50 at% of at least one metal and / or transition metal, 50 to 95 at% of silicon, and 0 to 50 at% of oxygen. , Nitrogen is 0 to 50 at%, and carbon is 0 to 50 at%.

In step b1), the film composition ratio of the single layer phase inversion is 5-30 at% of one or more metals and / or transition metals, 35-65 at% silicon, 5-35 at% nitrogen, and 0-5 at% oxygen. It features.

When the phase inversion film has a two-layer structure in step b1), the first phase inversion film formed on the substrate is 0.5 at an exposure wavelength at which an extinction coefficient k value of 157 nm to 200 nm is selected for efficient control of transmission and reflection. It is characterized by being 2.0.

In the phase inversion film, the first phase inversion film should have a function of controlling the transmittance and the reflectance at the same time, and this characteristic is related to the extinction coefficient k value.

Therefore, in order to control the transmittance and reflectance, the extinction coefficient k value at the exposure wavelength should be relatively higher than that of the second phase inversion layer stacked on the first phase inversion layer.

However, when the extinction coefficient k of the first phase inversion film becomes larger than 2.0 at the exposure wavelength, there is a problem in that the reflectance is increased at the exposure wavelength at the same thickness.

On the other hand, when the extinction coefficient k is 0.5 or less in exposure light, efficient transmittance and reflectance control becomes difficult. Therefore, appropriate adjustment of the extinction coefficient k value is necessary.

In the step b1), when the phase inversion film has a two-layer structure, a layer for controlling the reflectance is formed on the first phase inversion film and the second phase inversion film or on top, bottom, or interface to control the reflectance of the phase inversion film. It can be characterized by.

The film for controlling the reflectance may include the same kind of material used in the first phase inversion film, and may form nitrides, oxides, carbides, oxynitrides, oxidized carbides, nitrides, oxynitrides and transition metals and metals. Through this, at least one reflection adjusting layer having a function of controlling the reflectance to 30% or less at the exposure wavelength can be formed.

In the step b1), when the phase inversion film has a two-layer structure, a material that can be used as the first phase inversion film essentially includes tantalum (Ta) and / or chromium (Cr), and a single and additional transition thereof. A sputtering target composed of a metal and one or more selected elements of the metal can form one or more selected from oxides, nitrides, carbides, oxynitrides, oxidized carbides, nitrides and oxynitrides, and thus the composition ratio of the thin film It is characterized by 10-10% of the total metal component, 0-70% of nitrogen, 0-70% of oxygen and 0-70% of carbon.

When the phase inversion film has a two-layer structure in step b1), a chlorine gas is used as a gas used in the dry etching of the first phase inversion film.

The transparent substrate under the first phase inversion film has a characteristic of being etched when using a dry etching gas whose main component is fluorine-based gas due to SiO ₂ .

Therefore, in order to prevent damage of the transparent substrate, the first phase inversion film has a property of being etched with a chlorine-based gas to simultaneously serve as an etching stopper.

When the phase inversion film has a two-layer structure in step b1), the etching selectivity of the first phase inversion film with respect to the transparent substrate is 1: 2 or more.

The first phase inversion film is required to control transmittance and reflectance, and also simultaneously serves as an etch stopper for over etching of the second phase inversion film stacked on the first phase inversion film. You should be able to.

In addition, the dry substrate of the first phase inversion film should have a property that the transparent substrate should not be damaged during over etching.

Therefore, the dry phase of the first phase inversion film is required to have a selectivity of 1: 2 or more for the transparent substrate, and more preferably, a material of 1: 5 or more.

When the phase inversion film has a two-layer structure in step b1), the size of the optical energy bandgap of the first phase inversion film is 3 eV or less.

In the step b1), when the phase inversion film has a two-layer structure, the second phase inversion film is formed of oxides, nitrides, carbides through a sputtering target containing one or more transition metals including essentially silicide and / or hafnium. It is characterized by forming at least one selected from oxynitride, oxycarbide, nitride, oxynitride.

In the step b1), when the phase inversion film has a two-layer structure, the second phase inversion film essentially includes hafnium, and includes at least one transition metal and metal, through which oxides, nitrides, carbides, and oxides are formed. It is characterized by forming at least one selected from nitride, oxidized carbide, nitride carbide and oxidized carbide.

In the step b1), when the phase inversion film has a two-layer structure, the second phase inversion film mainly has a function of controlling the phase and is characterized by little variation in transmittance with respect to thickness.

In the step b1), when the phase inversion film has a two-layer structure, the target for the second phase inversion film may be made of hafnium silicide (HfSi), and the composition ratio of the target is 5 to 95 at% of hafnium (Hf), Silicide (Silicide) is characterized in that it can be adjusted in the range of 5 ~ 95at%.

In the step b1), when the phase inversion film has a two-layer structure, the target for the second phase inversion film may be made of hafnium aluminum (HfAl), and the composition ratio of the target is 5 to 95 at% of hafnium (Hf), Aluminum (Al) is characterized in that it can be adjusted in the range of 5 ~ 95at%.

In the step b1), when the phase inversion film has a two-layer structure, the target for the second phase inversion film is 10 to 90 at% of the metal content when configured using a silicide target containing one or more metals, silicide (Silicide) is characterized in that it can be adjusted in the range of 10 ~ 90at%.

In the step b1), when the phase inversion film has a two-layer structure, the dielectric constant of the second phase inversion film is characterized in that the material of 3 to 8.

In the step b1), when the phase inversion film has a two-layer structure, the composition ratio of the second phase inversion film is 10 to 30 at% of metal, 10 to 60 at% of silicide, and 10 to 80 at% of oxygen.

In the step b1), when the phase inversion film has a two-layer structure, the composition ratio of the second phase inversion film is 5 to 50 at% of hafnium, 5 to 50 at% of aluminum, and 10 to 90 at% of oxygen.

In the step b1), when the phase inversion film has a two-layer structure, the extinction coefficient k of the second phase inversion film is 0.1 to 0.5.

In the step b1), when the phase inversion film has a two-layer structure, the refractive index n of the second phase inversion film is 1.5 to 3.0.

In the step b1), when the phase inversion film has a two-layer structure, the gas used for dry etching of the second phase inversion film can be selectively etched by both fluorine gas and chlorine gas.

In the step b1), when the phase inversion film has a two-layer structure, the thickness of the second phase inversion film is 500 to 1500 mW.

In the step b1), when the thickness of the phase inversion film formed on the transparent substrate is d ₁ , the birefringence is 5nm / (6.35 + d ₁ mm) or less.

In the step b1), before, during or after the formation of the phase inversion film, a heat treatment process, a plasma surface treatment, and a flash lamp surface treatment may be performed.

The heat treatment process, the plasma surface treatment, and the flash lamp surface treatment have an effect of improving the thin film density and improving the thin film uniformity in the step of stabilizing after the thin film is formed.

As such a heat treatment method, a rapid thermal process (RTP), a hot plate, a furnace, or the like may be used.

Through this heat treatment method, the density of the thin film can be improved and the impurity ions contained in the thin film can be removed.

Through heat treatment, a thin oxide film of tens of angstroms is formed on the surface, and the oxidative protective layer serves to reduce the adsorption of airborne molecular contamination (AMC) sources known to cause growth defects from the outside. do.

In addition, plasma treatment using oxygen serves to reduce the concentration of air molecules and reduce the stress of the thin film by activating and removing impurity ions and organic substances adsorbed on the thin film surface. Similarly, the surface treatment by the flash lamp also has the effect of reducing the stress and chemical resistance of the thin film.

In the step b1), the density of the phase inversion film is characterized in that 2 to 10g / cm ³ .

In the step b1), the center line average roughness of the phase inversion film is characterized in that 0.1 to 5nmRa.

In step b1), the chemical resistance of the phase inversion film is changed to sulfuric acid and SC 1 (ammonia: hydrogen peroxide: ultrapure water = 1: 1: 5) during 2 hours of immersion within 1% of the exposure wavelength, and the amount of phase change It is characterized by being within 1 degree.

In the step b1), the growth defect of the phase inversion film does not occur when the 5kJ ArF Laser irradiation.

In the step b1), the number of particles generated after the deposition of the phase inversion film, there is no more than 1.0㎛, 0.5 ~ 1.0㎛ is characterized in that less than 10, 0.1 ~ 0.5㎛ less than 20.

In the step b1), impurity ions and volatile organic compounds (VOCs) detected when analyzing the concentration of air molecules after deposition of the phase inversion film using ion chromatography (IC) and ATD GC / MS ) Is a total amount of 10ppbv to 5ppmv / (6inch × 6inch × 0.25inch) or less.

In the step b1), the flatness after the deposition of the phase inversion film is within ± 1㎛ compared to before deposition.

In the step c1), the light shielding film is formed of chromium (Cr), molybdenum (Mo), molybdenum silicide (MoSi), molybdenum tantalum silicide (MoTaSi), tantalum (Ta), and tantalum tungsten (TaW). It may be used, and the reactive gas may be used to form oxides, nitrides, carbides, oxynitrides, oxidized carbides, nitrides and oxynitrides.

In the d1) step, the anti-reflection film is formed of chromium (Cr), molybdenum (Mo), molybdenum silicide (MoSi), molybdenum tantalum silicide (MoTaSi), tantalum (Ta) and tantalum tungsten (TaW). It may be used, and the reactive gas may be used to form oxides, nitrides, carbides, oxynitrides, oxidized carbides, nitride carbides, oxynitrides.

In the step b1 ~ d1), the sheet resistance of any one or more thin films selected from a phase shift film, a light shielding film, an antireflection film is 1Ω / □ to 1MΩ / □ characterized in that.

According to the present invention by the above configuration, in the manufacture of the half-tone phase inversion film blank mask has excellent quality by improving the film density, air molecular contamination, Stress, sheet resistance, Roughness, chemical resistance, particles, growth defects It is possible to manufacture a halftone phase inverted blank mask, and thus an excellent photomask can be produced.

Examples The present invention will be described in detail by way of examples, but the examples are used only for the purpose of illustrating and explaining the present invention, and are not used to limit the scope of the present invention as defined in the meaning or claims. .

Therefore, it will be appreciated that various modifications and equivalent other embodiments may be made from those skilled in the art.

Therefore, the true technical protection scope of the present invention will be defined by the technical details of the claims.

The following Example 1 and Comparative Example 1 shows the result of deposition under the same conditions in order to measure the uniformity and density of the thin film according to the deposition method.

(Example 1)

In the present Example 1, a tantalum (Ta) and hafnium silicide (HfSi) target as a first phase inversion film and a second phase inversion film and a 6 × 6 layer using a molybdenum tantalum silicide (MoTaSi) target as a single phase inversion film The thin film density was measured after each thin film was deposited using a DC-RF Coupled Magnetron Sputter apparatus on a 0.25 inch transparent substrate.

First, DC-RF coupled sputtering conditions using a tantalum target were deposited using argon (Ar) gas only at DC power of 50-1.5 kW and pressure of 1.5-5 mtorr, and RF was deposited at a frequency of 10-20 MHz.

After that, using n & k Analyzer 1512RT equipment from n & k Technology, the transmittance of 49 points of 7 x 7 was measured. The result was 22.1% at 193nm and the range was 0.14%.

Similarly, HfSi (20: 80at%) target is applied with DC-RF Coupled Sputtering method to form HfSiO thin film using argon (Ar) and oxygen (O2) gas at 50 ~ 1.5kW DC power and 1.5 ~ 5mtorr pressure. It was deposited on a transparent substrate. The transmittance of the deposited HfSiO was measured by n & k Analyzer 1512RT in the same manner, and measured as 85.1% at 193nm, and the range was 0.16%.

In the same manner as above, MoTaSiN was deposited on a transparent substrate using argon (Ar) and nitrogen (N ₂ ) gases using a MoTaSi target, and a transmittance of 5.6% at 193 nm was 0.12%.

As a result of measuring the density of the thin film of Ta, HfSiO and MoTaSiN using XRR equipment, Ta was 5.2cm ² / gram, HfSiO was 4.3cm ² / gram MoTaSiN was 4.8cm ² / gram.

(Comparative Example 1)

The following Comparative Example 1 was deposited using DC and RF sputtering using the same target to compare Example 1 above.

The measured transmittance of Ta was 23.1% at 193 nm and 0.52% Range. The transmittance of HfSiO was 85.3% at 193 nm, 0.65% Range, and 0.32% MoTaSiN at 193 nm and 5.5% Range. Indicated.

In addition, as a result of measuring the thin film density of Ta, HfSiO and MoTaSiN using XRR equipment, Ta showed 3.6cm ² / gram, HfSiO 3.2cm ² / gram and MoTaSiN 3.3cm ² / gram.

Through Example 1 and Comparative Example 1, it can be seen that the thin film deposited through the DC-RF Coupled Sputter has improved uniformity and thin film density than the thin film deposited by the general DC and RF Sputter.

(Example 2)

Next, the chemical resistance evaluation of Ta, HfSiO and MoTaSiN produced by Example 1 and Comparative Example 1 was carried out as follows. At this time, sulfuric acid was immersed at 85 ° C. for 2 hours, and SC 1 and ozone water (O ₃ ) were immersed at 23 ° C. for 2 hours. After that, the change in transmittance and thickness at 193 nm were examined.

Before chemical resistance test After chemical resistance test Sulfuric acid SC 1 O ₃ Transmittance @ 193nm Thickness Transmittance @ 193nm Thickness Transmittance @ 193nm Thickness Transmittance @ 193nm Thickness  Example 1 Ta 22.1 116 22.2 114 22.2 113 22.2 115 HfSiO 85.1 723 85.2 717 85.2 716 85.2 720 MoTaSiN 5.6 676 5.6 676 5.7 673 5.6 675  Comparative Example 1 Ta 23.1 111 23.6 103 23.7 102 23.4 109 HfSiO 85.3 720 85.5 708 85.8 702 85.5 712 MoTaSiN 5.5 679 5.6 675 5.9 669 5.6 675

Table 1 Results of chemical resistance

Example 2 will be described with reference to Table 1. First, chemical resistance tests were performed on Ta, HfSiO, and MoTaSiN having different thin film densities according to the sputtering conditions of Example 1 and Comparative Example 1. Chemical resistance was carried out for sulfuric acid, SC 1 and ozone water (O ₃ ).

As a result of the experiment, Ta according to Example 1 showed a change in transmittance after immersion in sulfuric acid, SC 1 and ozone water increased by 0.1% at 193 nm, and the thickness was decreased by 1 to 3 Å. In addition, HfSiO also showed a change in transmittance of 0.1% and a thickness of 3 ~ 6Å.

In the same way, MoTaSiN showed a change in transmittance of 0.1% and a change in thickness of 1 ~ 3Å.

However, as a result of measuring the change of transmittance and thickness of Ta, HfSiO and MoTaSiN according to Comparative Example 1, first, the change of transmittance according to sulfuric acid and SC 1 was 0.3-0.6%, and the thickness change was 2-9 2. , HfSiO showed a change of transmittance of 0.2 ~ 0.5% and a change of thickness of 8 ~ 18Å.

All of the above results can be applied to the half-tone phase inversion blank mask, but it can be seen that the thin film density is excellent by the DC-RF coupled sputtering method according to Example 1 having high quality half-tone phase inversion film characteristics.

The above results indicate that the higher the film density by the DC-RF Coupled sputtering method, the less diffusion and adsorption of ammonia components contained in sulfuric acid and SC 1, and thus the chemical resistance change is improved compared to the conventional DC and RF Sputter method. there was.

The method for improving the density of the thin film can be divided into external and internal improvement methods, and the internal method can improve the thin film density by changing process conditions.

That is, by maintaining the pressure at high vacuum during sputtering to increase the mean free path, the ion energy may be increased to improve the density, and may also be possible by changing the reactive gas. However, these internal conditions can be improved due to system limitations, but it can be confirmed through experiments that the improvement is relatively small compared to the DC-RF Coupled Sputter method. In addition, the DC-RF Coupled Sputter method is a method that can deposit the particles more uniformly and stably during deposition by applying RF high frequency to the chamber particles from the target to the substrate by the DC Sputter method. Therefore, preferably through the DC-RF Coupled Sputter method, it is desirable to further improve the thin film density through internal gas and pressure adjustment.

More preferably, by applying an external improvement method, it is possible to stabilize the thin film and improve the thin film density by using Furnace, RTP, Hot-Plate, Plasma, and the like.

(Example 3)

In Example 3, the center line average roughness of the thin films according to Example 1 and Comparative Example 1 was measured using an AFM equipment.

Example 1 Comparative Example 1 Ta HfSiO MoTaSiN Ta HfSiO MoTaSiN Center Line Average Roughness 0.32nmRa 0.52 nm Ra 0.35nmRa 0.52 nm Ra 0.92 nm Ra 0.53 nm Ra

Table 2 Surface Roughness Measurement Results

As a result of measuring centerline average roughness according to Example 3 with reference to Table 2, the centerline average roughness values of Ta, HfSiO, and MoTaSiN of Example 1 by DC-RF Coupled Sputtering showed 0.32nmRa, 0.52nmRa, and 0.35nmRa. Ta, HfSiO and MoTaSiN of Comparative Example 1 by DC and RF sputtering was 0.52nmRa, 0.92nmRa and 0.53nmRa it was confirmed that the relatively better.

The relatively low surface roughness by DC-RF coupled sputtering indicates less surface energy, and the lower surface energy indicates a smaller probability of particles adsorbing during external environmental and internal processes. In addition, the adsorption of air pollutant sources (AMC) by the surface energy is also reduced, thereby reducing the occurrence of growth defects (Haze).

Moreover, the surface roughness of the thin film affects the surface tension, and this surface tension has a great influence on the stress of the thin film. Therefore, in order to reduce the stress of the thin film, the surface roughness should be low, and in improving the surface roughness, it can be seen that the improvement by the method by DC-RF coupled sputtering.

(Example 4)

Example 4 uses the gas chromatography / mass spectrometer (GC / MS) and ion chromatography (Ion Chromatograph; IC) to determine the concentration of air molecules in the thin film used in Example 2. Co-analysis.

IC (ppb) GC / MS (ppb)  Sum SO _x NH ₄ Etc BHT A / H Etc  Example 1 Ta 20 42 240 N / D 420 380 1,102 HfSiO 30 20 320 N / D 280 730 1,380 MoTaSiN 20 30 220 N / D 200 210 680  Comparative Example 1 Ta 40 62 490 N / D 480 560 1,632 HfSiO 150 37 580 N / D 490 880 2,137 MoTaSiN 60 50 400 N / D 410 650 1,570

Table 3 Air Molecular Pollution Analysis Results

Table 3 shows the results of analyzing the air molecule contamination concentrations of the thin films according to Example 2 immersed in sulfuric acid and SC 1. Each Ta, HfSiO and MoTaSiN was produced through the process according to Example 1 and Comparative Example 1, after immersing in sulfuric acid and SC 1 through Example 2 and then washed with ultrapure water.

Ion analysis was performed using ICS-3000 equipment, and outgas was analyzed using ATD-GC / MS equipment. As a result of analysis of air molecule contamination concentration, Ta showed a difference of 530 ppbv in Example 1 and Comparative Example 1, HfSiO showed a difference in concentration of 757 ppbv, and MoTaSiN showed a difference in concentration of 890 ppbv. That is, the concentration difference indicates a concentration that provides a source of growth defects when the photomask is manufactured and then irradiated with an ArF laser in a wafer shop.

Moreover, the concentration of these air molecules is not only dependent on numerical values but also on the adsorption and diffusion distances of the impurity ions and outgases by the density of the thin film. It can be seen that.

The results show the same results as the density, chemical resistance, and centerline average roughness measurement results of the thin films analyzed in Examples 1 to 3, and in order to reduce the growth defects through the DC-RF coupled sputtering method is excellent. Able to know.

(Example 5)

In Example 5, the birefringence was measured after depositing the thin films according to Example 1 and Comparative Example 1 on a transparent substrate. In this case, the birefringence of the transparent substrate used was measured to be 2.32nm / 6.35mm, and the uniformity range was 2.03nm / (152 x 152cm).

Example 1 Comparative Example 1 Ta HfSiO MoTaSiN Ta HfSiO MoTaSiN Average Range Average Range Average Range Average Range Average Range Average Range Birefringence 2.41 2.09 2.44 2.13 2.42 2.00 3.01 2.64 3.09 2.79 2.62 2.68

Table 4 Birefringence Measurement Results

With reference to Table 4, the fifth embodiment is described as follows. As a result of measuring birefringence at 193 nm after depositing a thin film on the transparent substrate, the variation in birefringence values of Ta, HfSiO and MoTaSiN according to Example 1 showed a maximum increase of 0.12 nm compared to the birefringence of 2.32 nm / 6.35 mm of the transparent substrate. It was. However, the increase in birefringence according to Comparative Example 1 showed an increase of up to 0.77 nm, indicating an increase of about 6 times. In addition, in terms of uniformity, the maximum uniformity of 0.1 nm was changed for Ta, HfSiO, and MoTaSiN according to Example 1, but the uniformity was greatly changed for Ta, HfSiO, and MoTaSiN, up to 0.76 nm.

These results indicate that the birefringence is also greatly affected by the density of the thin film, the stabilization of the thin film composition, and the surface stress. In particular, the birefringence of the transparent substrate is the largest, but the birefringence difference is different depending on the deposited thin film. It can be seen from this experiment that occurs.

That is, the birefringence is also affected by the uniformity, low surface energy, and thin film density of the thin film composition based on the thin film density, uniformity, and center line average roughness results of Examples 1 and 3, and the CD of 65 nm or less of high precision is affected. In order to apply to the implementation and immersion lithography, it can be seen that the DC-RF coupled sputtering method is superior to the general sputtering method according to the comparative example.

(Example 6)

In Example 6, the refractive index and the extinction coefficient of Ta and HfSiO according to Example 1 were measured by using an ellipsometer to implement a two-layered phase reversal film. First, a refractive index measurement at 193 nm using Ta's ellipsometer showed n = 1.94 and a refractive index at 193 nm of HfSiO showed n = 2.01.

This refractive index is an important index for determining the thickness of the entire phase inversion film. Therefore, the present inventors varied the composition ratio of the HfSi target, and measured as follows using an ellipsometer.

at% pellicle n @ 193nm k @ 193nm Si SiO 1.57 0.02 Hf: Si = 20: 80 HfSiO 2.01 0.06 Hf: Si = 60: 40 HfSiO 2.22 0.13 Hf: Si = 80: 20 HfSiO 2.39 0.25 Hf HfO 2.76 0.37

Table 5. Results of Measurement of Refractive Index and Extinction Coefficient According to Composition Ratio of HfSi

Referring to Table 5, the refractive index and the extinction coefficient according to the HfSi target composition ratio according to the sixth embodiment, it can be seen that the refractive index n varies from 2.01 to 2.39 depending on the composition ratio of Hf and Si. Such a composition ratio was limited to typical composition ratios, and based on these composition ratios, halftone phase inversion films of two-layer films having various thicknesses and combinations could be formed.

First, in the case of HfO, the refractive index is n = 2.76 at 193 nm, indicating that the refractive index is quite high. However, the extinction coefficient k is shown to be relatively 0.37, it is determined that the transmittance is relatively low. On the other hand, SiO has a low refractive index n = 1.57 at 193 nm, similar to that of a synthetic quartz glass substrate, but a low extinction coefficient. Therefore, it can be confirmed that the thickness and phase shift can be adjusted through various composition ratios based on these results.

(Example 7)

In Example 7, the first phase shift film was formed using a Ta target, and then the second phase shift film was sequentially stacked using a HfSi (20:80 at%) target, and then transmittance and reflectance were measured. At this time, the thickness of the Ta target was variously adjusted to control the reflectance, and the thickness of HfSiO was also changed to keep the phase displacement constant.

Ta thickness Transmittance Reflectance @ 193nm Phase amount (degrees) @ 193nm  Remarks 193nm 365nm One 70 19.3% 67.2% 23.1% 178.2 X 2 90 15.3% 51.2% 23.7% 179.3 O 3 110 10.1% 43.2% 24.2% 177.8 O 4 130 8.3% 30.2% 25.7% 180.3 O 5 150 7.0% 29.3% 27.2% 178.3 O 6 170 5.7% 27.2% 29.3% 177.3 O 7 190 4.6% 26.3% 35.1% 177.8 X 8 210 2.3% 25.7% 43.2% 179.2 X

Table 6. Measurement of transmittance and reflectance according to the thickness of the first phase displacement film

Table 6 above shows the results of measuring transmittance and reflectance according to the thickness of Ta, which is the first phase shift film. First, the transmittance change of the total phase inversion film according to the thickness range of Ta to 70 to 210 ~ according to Nos. 1 to 8 was observed. The transmittance is 67.2%, which may cause problems in inspection sensitivity. On the other hand, in case of 7, 8, the reflectance is 35.1% and 43.2% in the exposure wavelength at the thickness of 190 and 210Å of Ta, which may have a problem of re-reflection during wafer transfer.

Therefore, the inventors were able to confirm that various transmittances can be controlled along the thickness of Ta according to 2 to 6.

(Example 8)

In Example 8, after the formation of the first phase shift film, TaON having the same material as the main component was deposited in the range of 10 to 100 Å for the 7 and 8 that were not used due to the reflectivity in Example 7, The thickness of the phase shift film was reduced to 50 ~ 110Å.

Ta + TaON Transmittance reflectivity Phase amount Remarks Thickness 193nm 365nm @ 193nm @ 193nm 7 187 5.5% 34.3% 28.1% 176.3 8 204 5.7% 29.7% 29.3% 178.1

Table 7. Transmittance Change and Reflectance Measurement Results after Anti-reflective Film Deposition

This Example 8 is demonstrated with reference to Table 7. First, in Example 7, as the thickness of Ta is increased, the reflectance is higher than 30%, and TaON after deposition of the first phase inversion film using the same target for No. 7, 8, which may cause a pattern error due to re-reflection during wafer transfer. The reflection adjusting layer of was deposited sequentially. The combined thickness of the first phase inversion film and the reflection adjustment layer was fabricated similarly to Nos. 7, and 8, and the thickness ratios of Ta and TaON were adjusted for reflectance control. This resulted in the formation of a two-layered phase inversion film with a transmittance of 5.5% in the conventional exposure wavelength, 34.4% in the inspection wavelength, and a reflectance in the exposure wavelength below 30%, with a phase amount within 175 degrees.

Therefore, it was confirmed through the present example that the surface reflectance can be sufficiently adjusted by forming the reflection adjustment layer. The formation of the reflection control layer is not limited to the first phase inversion film, but the position of the second phase inversion film is appropriately positioned between the substrate and the first phase inversion film, the top of the first phase inversion film, and the top of the second phase inversion film. Can be on site.

(Example 9)

Next, the light blocking film, the antireflection film, and the resist were sequentially stacked on the halftone phase inversion film prepared in Example 7, and then dry etching was performed for pattern formation.

First, dry etching of HfSiO was performed at 300 W and 55 mtorr using SF ₆ and / or CHF ₄ and O ₂ gas, and an additional 30 seconds was added to the Over Etching Time. Thereafter, dry etching of the first phase shift layer was performed in the same condition as 300 W and 55 mtorr using a gas mixed with Cl ₂ and O ₂ , and an additional 30 seconds was added to the over etching time.

As a result, the pattern profile was very good at 88.5 degrees, and the average line roughness of 0.42nmRa was found to be no damage as measured by AFM to measure damage damage of the transparent substrate.

(Example 10)

Next, the flatness of the halftone phase inversion film prepared according to Example 7 was sequentially laminated with the light blocking film and the antireflection film, and the flatness was measured using the Flatmaster. The degree was measured.

DC-RF Coupled Sputter DC, RF Sputter Remarks Board 0.28 μm 0.28 μm 2-layer phase inversion film Ta 0.29㎛ 0.35 μm HfSiO 0.32 μm 0.53 μm Shading 0.34 μm 0.75 μm Antireflection film 0.34 μm 0.82 μm 1 layer phase inversion film MoTaSiN 0.30㎛ 0.37 μm Shading 0.32 μm 0.50㎛ Antireflection film 0.32 μm 0.51 μm

Table 8. Flatness Variation

Table 8 shows the deposition method by the DC-RF Coupled sputter according to Example 10 and the flatness change according to the deposition on the DC and RF sputter.

First, as a result of the flatness change according to the two-layered phase inversion film, the flatness value of the thin film deposited by DC-RF coupled sputter increased 0.06㎛ compared to the substrate. 9 times the difference in flatness.

Similarly, in the case of MoTaSiN, which is a single phase reversal film, the flatness value of the thin film deposited by DC-RF coupled sputter increased by 0.04㎛ compared to the substrate, and by 0.23㎛ increased by the deposition by DC and RF Sputter. It showed a relatively high flatness change. This flatness change can indirectly confirm the state of the thin film stress, it can be seen that the method by the DC-RF Coupled sputtering can implement a low stress.

(Example 11)

Next, the particles were measured according to the sequence of thin film deposition using the GM-3000 equipment for particle measurement for the thin film used in Example 10.

DC-RF Coupled Sputter Particle Size Sum 0.1 ~ 0.5㎛ 0.5 ~ 1.0㎛ 1.0 ㎛ or more Board 3 One 0 4 First phase inversion film Ta 3 One 0 4 Second phase inversion film (HfSiO) 10 3 0 13 Shading 15 5 0 20 Antireflection film 17 8 0 25 DC, RF Sputter 0.1 ~ 0.5㎛ 0.5 ~ 1.0㎛ 1.0 ㎛ or more Sum Board 2 One 0 3 First phase inversion film Ta 6 One 0 7 Second phase inversion film (HfSiO) 21 6 One 19 Shading 29 10 3 33 Antireflection film 35 12 5 41

Table 9-1. Particle Measurement Results of a Two-Layer Halftone Phase Inverted Blank Mask

Table 9-1 shows the results of measuring the particles according to the thin film deposition on the two-layer halftone type blank mask according to Example 11 using the GM 3000 equipment. As a result of the measurement, when the thin film was deposited by DC-RF Coupled Sputter, the particle increase up to the last layer of anti-reflective layer was sequentially increased from 0.1 to 0.5㎛ size, and the number of particles increased by 14, but 0.1 ~ 0.5 by DC and RF Sputter. The number of μm particles has been shown to increase by 33. Similarly, the particle number of 0.5 ~ 1.0㎛ size also showed 7 particle increase when using DC-RF Coupled Sputter, but DC, RF Sputter method showed 11 particle increase.

This resulted in the effect that the particles are suppressed compared to the DC, RF sputtering method of particles through the DC-RF Coupled sputtering method.

DC-RF Coupled Sputter Particle Size Sum 0.1 ~ 0.5㎛ 0.5 ~ 1.0㎛ 1.0 ㎛ or more Board One 0 0 One Phase Inversion Film (MoTaSiN) 3 One 0 4 Shading 5 One 0 6 Antireflection film 6 One 0 7 DC, RF Sputter 0.1 ~ 0.5㎛ 0.5 ~ 1.0㎛ 1.0 ㎛ or more Sum Board 2 One 0 3 Phase Inversion Film (MoTaSiN) 6 2 0 8 Shading 10 3 One 14 Antireflection film 13 3 One 17

Table 9-2. Particle Measurement Results of Single-Layer Halftone Phase Inverted Blank Masks

Table 9-2 shows the results of measuring the particles according to the thin film deposition on the single-film halftone type blank mask according to Example 11 using the GM 3000 equipment. As a result of the measurement, when the thin film was deposited by DC-RF Coupled Sputter, the particle increase up to the last anti-reflective layer laminated sequentially compared to the substrate showed 0.1 ~ 0.5㎛ size particle number increased by 5, but 0.1 ~ 0.5 by DC, RF Sputter The number of μm particles shows an increase of eleven. Similarly, the particle number of 0.5 ~ 1.0㎛ size also showed one particle increase when using DC-RF Coupled Sputter, but DC, RF Sputter method showed two particle increase.

Through this, the thin film deposition method through the DC-RF Coupled sputtering method showed that the particles are suppressed compared to the conventional DC and RF sputtering methods.

(Example 12)

The following Example 12 evaluates the line edge roughness of 17 points for the 1.0 μm Line & Space Pattern for the evaluation of the same halftone phase inversion blank mask made of the DC-RF Coupled sputtering method and DC and RF sputtering. It was. As a result, the halftone phase inverted blank mask produced by DC-RF Coupled sputter method showed 20nm under and showed excellent LER result, while the halftone phase inverted blank mask by DC and RF sputter method showed LER result which exceeded 43nm. It was.

(Example 13)

Next Example 13 is a 193nm Laser to identify the growth defects generated in the half-tone phase inversion photomask fabricated by the DC-RF Coupled sputter method and the same half-tone phase inversion blank mask made of DC, RF sputter After irradiating 5kJ at 4mJ and 60Hz, the number of growth defects generated through electron microscopy was measured.

As a result of the measurement, growth defects did not occur in the half-tone phase inversion photomask fabricated by DC-RF Coupled Sputter method, but 8 various growth defects were observed in half-tone phase inversion photomask fabricated by general DC and RF Sputter method. It became.

1 is a cross-sectional view of a two-layer film halftone type phase inversion blank mask produced by the present invention.

2 is a cross-sectional view of a single film halftone type phase inversion blank mask produced by the present invention.

<Explanation of symbols for main parts of drawing>

10: transparent substrate

20: first phase inversion film

30: second phase inversion film

40: single phase inversion film

50: light shielding film

60: antireflection film

100: 2-layer film halftone type phase inversion blank mask

200: single layer halftone phase inversion blank mask

Claims (28)

Transparent substrate; A phase inversion film on the transparent substrate; A light blocking film on the phase inversion film; An anti-reflection film on the light shielding film; And A resist film on the anti-reflection film, The phase inversion film, the light shielding film, or the anti-reflection film is a halftone phase inversion blank mask, characterized in that formed by applying a DC-RF Coupled sputtering method. The method of claim 1 A halftone phase inverted blank mask, characterized in that the phase inversion film formed by the DC-RF Coupled sputtering method is formed of a single film or a multilayer of two or more layers. The method of claim 2, A half-tone phase inversion blank mask comprising at least one type of metal and / or transition metal, wherein the target is used for forming a single phase reversal film. The method of claim 2, The target used in forming the single-phase phase inversion film is a halftone phase inversion blank mask, characterized in that at least one of aluminum, titanium, vanadium, chromium, zirconium, niobium, molybdenum, lanthanum, tantalum, and tungsten is included. . The method of claim 1, The single-phase phase inversion film formed by the DC-RF Coupled Sputtering method is a phase inversion blank mask characterized in that it is formed of at least one selected from oxides, nitrides, carbides, oxynitrides, oxidized carbides, nitrides and oxynitrides of metals. . The method of claim 2, The composition ratio of the single-phase phase inversion film formed by the DC-RF coupled sputtering method is 1 to 50 at% of metal, 50 to 95 at% of silicon, 0 to 50 at% of oxygen, 0 to 50 at% of nitrogen, and 0 to 50 at% of carbon A phase inversion blank mask, characterized in that%. The method of claim 2, The phase inversion of a single film phase inversion is 5-30 at% of at least one metal and / or transition metal, 35-65 at% of silicon, 5-35 at% of nitrogen, and 0-5 at% of oxygen. Blank Mask. The method according to claim 1 or 2, A phase inversion blank mask, wherein when the phase inversion film has a two-layer structure, the extinction coefficient k of the first phase inversion film formed on the substrate is 0.5 to 2.0 at a selected exposure wavelength of 157 nm to 200 nm. The method according to claim 1 or 2, When the phase inversion film has a two-layer structure, the first phase inversion film formed on the substrate essentially includes tantalum (Ta) and / or chromium (Cr), and a single and at least one selected of transition metals or metals thereof. A phase inversion blank mask comprising forming one or more selected from oxides, nitrides, carbides, oxynitrides, oxidized carbides, nitrides and oxynitrides through a sputtering target composed of elements. The method of claim 9, A blank mask, characterized in that the composition ratio of the first phase inversion film formed on the substrate is 10 to 100% of metal, 0 to 70% of nitrogen, 0 to 70% of oxygen, and 0 to 70% of carbon. The method of claim 9, The phase inversion blank mask, wherein the gas used in the dry etching of the first phase inversion film formed on the substrate is a chlorine-based gas. The method of claim 9, The phase inversion blank mask of claim 1, wherein an etching selectivity of the first phase inversion film formed on the substrate is 1: 2 or more. The method of claim 9, A phase inversion blank mask, wherein the size of the optical energy bandgap of the first phase inversion film formed on the substrate is 3 eV or less. The method of claim 2, When the phase inversion film has a two-layer structure, the second phase inversion film is formed of oxides, nitrides, carbides, oxynitrides, oxides, or the like through a sputtering target containing one or more transition metals, which essentially includes silicide and / or hafnium. A phase reversal blank mask comprising at least one selected from carbides, nitrides and oxynitrides. The method of claim 2, When the phase inversion film has a two-layer structure, the target for the second phase inversion film may be composed of hafnium silicide (HfSi), and the composition ratio of the target is 5 to 95 at% of hafnium (Hf) and 5 to silicide (Silicide). Phase inverted blank mask, characterized in that adjustable in the range of ~ 95at%. The method of claim 2, When the phase inversion film has a two-layer structure, the target for the second phase inversion film may be made of hafnium aluminum (HfAl), and the composition ratio of the target is 5 to 95 at% of hafnium (Hf) and 5 of aluminum (Al). Phase inverted blank mask, characterized in that adjustable in the range of ~ 95at%. The method of claim 2, When the phase inversion film has a two-layer structure, the target for the second phase inversion film is 10 to 90 at% of the metal content and 10 to silicide (Silicide) when the target for the second phase inversion film is formed using a silicide target containing at least one metal. Phase inverted blank mask, characterized in that adjustable in the range of 90at%. The method of claim 2, A phase inversion blank mask, wherein when the phase inversion film has a two-layer structure, the dielectric constant of the second phase inversion film is 3 to 8. The method of claim 2, When the phase inversion film has a two-layer structure, the composition ratio of the second phase inversion film is 10 to 30 at% of metal, 10 to 60 at% of silicide, and 10 to 80 at% of oxygen. The method of claim 2, When the phase inversion film has a two-layer structure, the composition ratio of the second phase inversion film is 5 to 50 at% of hafnium, 5 to 50 at% of aluminum, and 10 to 90 at% of oxygen. The method of claim 2, A phase inversion blank mask, wherein the extinction coefficient k of the second phase inversion film is 0.1 to 0.5 when the phase inversion film has a two-layer structure. The method of claim 2, The refractive index n of the second phase inversion film when the phase inversion film has a two-layer structure is 1.5 to 3.0, characterized in that the phase inversion blank mask. The method of claim 2, When the phase inversion film has a two-layer structure, the thickness of the second phase inversion film is 500 to 1500 mW. The method of claim 1, A phase inversion blank mask, wherein the heat treatment step, plasma surface treatment, and flash lamp surface treatment are selectively performed before, during or after the formation of the phase inversion film. The method of claim 1, A phase inversion blank mask, wherein the density of the phase inversion film is 2 to 10 grams / cm 3. The method of claim 1, A phase inversion blank mask, wherein the center line average roughness of the phase inversion film is 0.1 to 5 nm Ra. The method of claim 1, A phase inversion blank mask, wherein the number of particles generated after deposition of the phase inversion film is 1.0 μm or more, and 0.5 to 1.0 μm is less than 10, and 0.1 to 0.5 μm is less than 20. The method of claim 1, The total amount of impurity ions and volatile organic compounds (VOCs) detected when analyzing the concentration of air molecules after deposition of the phase shift film using ion chromatography (IC) and ATD GC / MS is in the range of 10 ppbv to A phase inversion blank mask, characterized in that less than 5ppmv / (6inch x 6inch x 0.25inch).

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