JP2002313707A - Method of forming euv-ray reflecting film, euv mask blank, and reflective mask for euv exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of particles due to abnormal discharge during sputtering at the time of forming an EUV-ray reflecting multilayer film. SOLUTION: The occurrence of particles caused by electric field concentration during sputtering is suppressed by raising the electric conductivity of an Si target used at the time of forming the EUV-ray reflecting multilayer film by sputtering by doping the film with doping elements by appropriately controlling the kinds and amounts of the doping elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a multilayer film for EUV light reflection used for light exposure of EUV light used in semiconductor manufacturing and the like, the multilayer film, and an EU using the multilayer film.
The present invention relates to a V mask blank and a reflective mask for EUV exposure using the multilayer film. The EU described in the present invention
V (Extreme Ultra Violet) light refers to light in a wavelength band of a soft X-ray region or a vacuum ultraviolet region, and specifically, light having a wavelength of about 0.2 to 100 nm.

[0002]

2. Description of the Related Art Conventionally, in the semiconductor industry, a photolithography method using visible light or ultraviolet light has been used as a technique for transferring a fine pattern necessary for forming an integrated circuit having a fine pattern on a Si substrate or the like. I came. However, while miniaturization of semiconductor devices is accelerating, shortening the wavelength of conventional light exposure is approaching the exposure limit. In the case of light exposure, the resolution limit of the pattern is 1/1 of the exposure wavelength.
It is said to be ₂ even if an F ₂ laser (157 nm) is used.
The limit is expected to be about 0 nm. So as 70nm after exposure technique, having a shorter wavelength than the F ₂ laser EU
Promising is EUV lithography (hereinafter referred to as “EUVL”), which is an exposure technique using V light (13 nm).

The principle of EUVL image formation is the same as that of photolithography. However, since EUV light absorbs a large amount of all substances and has a refractive index close to 1, refractive optical systems such as light exposure cannot be used. , All use a reflective optical system. At this time, a reflective mask for exposure is generally used at this time.

As described above, in EUVL, a reflection film of EUV light is frequently used. At present, in EUVL with an exposure wavelength of 10 to 20 nm, this EUV
As a light reflection film, a multilayer film composed of Mo and Si is often used. As materials capable of obtaining a high reflectance in the above-mentioned wavelength region, Ru / Si, Mo / Be, Mo compound / Si compound, Si / Nb Periodic multilayer film, Si / Mo / Ru periodic multilayer film, Si / Mo / Ru / Mo periodic multilayer film, and Si / R
A u / Mo / Ru periodic multilayer film can also be used.
However, the optimum film thickness and the like differ depending on the material. In the following description of the present invention, the case of a multilayer film made of Mo and Si is taken as an example. In the case of a multilayer film composed of Mo and Si, a DC film is first formed by a DC magnetron sputtering method using an Si target in an Ar gas atmosphere.
Then, using a Mo target, an Mo film is formed under an Ar gas atmosphere, and this is one cycle, and after stacking 30 to 60 cycles, preferably 40 cycles, a Si film is finally formed. A reflective film for EUV light is manufactured.

[0005]

However, according to the above-described process, when sputtering is performed using a Si target, particles are generated, and the particles adhere to the EUV light reflecting film during film formation, thereby impairing the uniformity of the film. There is a problem that a film defect occurs. Then, a reflective mask for EUV exposure that requires high transfer accuracy for a fine pattern of several tens of nm is manufactured using the reflective film to which the particles are adhered, and the mask is used to apply EU to a desired substrate.
When patterning is performed by VL, the particles cause pattern defects, which adversely affects the transfer accuracy of the pattern and lowers the yield of semiconductor products. Therefore, a film forming method that does not generate particles in the film forming process is required.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on the causes of the generation of particles, and as a result, the following has become clear. That is, local electric field concentration occurs on the irregularities generated on the surface of the Si target during sputtering, and abnormal discharge occurs. This abnormal discharge caused particles to be generated. Therefore, the present inventors have conceived that it is possible to prepare a Si target that does not generate particles in a film forming process by sputtering by doping an element that increases the conductivity of Si into the Si target based on the above-described elucidation results. It is completed.

That is, a first aspect of the present invention is to suppress the particles generated by electric field concentration by increasing the electric conductivity of a Si target in a film formation using sputtering of a Si layer in a multilayer film including a Si layer used for EUV light reflection. It is characterized in that the sputtering is performed using a Si target doped with a doping element that satisfies the requirement of suppressing film formation defects due to adhesion of particles, ensuring that the reflectance of the EUV light reflection is within a predetermined range, and satisfying the above requirements.
This is a method for forming a UV light reflection film.

[0008] A second aspect of the present invention relates to Si used for EUV light reflection.
In film formation using sputtering of a Si layer in a multilayer film including a layer, Li, Be,
B, P, Sc, Ti, V, Se, Rb, Sr, Zr, N
b, Mo, Ru, Rh, La, Ce, Pr, Na, M
g, Al, Cr, Mn, Fe, Co, Ni, Cu, G
a, Ge, As, Y, Pb, Ba, Nd, Sm, Eu,
Gd, Tb, Ho, Er, Lu, Ta, W, Re, O
Doping with at least one element selected from the group consisting of s, Ir, and Pt suppresses generated particles and suppresses film-forming defects due to adhesion of the particles, and sets the reflectance of EUV light reflection within a predetermined range. And a sputtering method using a Si target that satisfies the following conditions.

A third invention is an EUV mask blank using an EUV light reflecting film formed by the film forming method according to the first or second invention.

A fourth aspect of the present invention is a reflective mask for EUV exposure, characterized by using an EUV light reflecting film formed by the film forming method according to the first or second aspect.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present inventors have clarified that the cause of particles that cause pattern defects in film formation is abnormal discharge of a Si target.
As a measure to suppress this abnormal discharge, Si
Of doping with an element that increases the electrical conductivity of. Here, this process will be described in more detail. In other words, the cause of the abnormal discharge of the Si target is not due to the crystal state of the Si target, but to the conductive state of the Si target, particularly due to the presence of a locally low conductive portion of the Si target. is there.

The inventors of the present application made use of the fact that Si is a genuine semiconductor in which the electrical conductivity changes greatly due to a small amount of doping elements, thereby increasing the electrical conductivity.
By finding an appropriate doping element that satisfies that the reflectance of the reflection of V light can be maintained within a predetermined range and the amount of doping, it has been conceived that Si sputtering in which generation of particles is suppressed can be realized. More preferably, the conductivity of the Si layer formed by sputtering using the Si target having the increased conductivity is also improved, so that charge-up during sputtering is suppressed, and the adhesion of dust is suppressed. The effect of prevention was also obtained.

(Selection of Doping Element) In order to select the doping element, various elements are added to the Si target in an amount of 1-2.
The following analysis was performed on the optical effect when mol% doping was performed. First, the optical effect that is a problem in the present invention is the reflectance of the Si film formed on the Mo / Si multilayer film. The reflectance is the imaginary part of the complex refractive index of the Si film described below. Has been determined to be almost determined.

Here, the imaginary part of the complex refractive index will be described. The diffraction phenomenon occurring in the crystal is caused by the scattering factor f of the atoms. Here, each substance forming the multilayer film is regarded as a uniform medium in the wavelength order of EUV light, and if a scattering factor is linked to a refractive index on the medium, scattering occurs only at the layer interface. Therefore, theoretically, in a multilayer film composed of a single layer having a steep interface, an equation considering reflection from all the interfaces may be set. That is, each single layer is a uniform film having a complex refractive index n. At this time, the contribution from the atoms is formulated as follows.

(Equation 1) Here, n: real part of optical refractive index, k: imaginary part of optical refractive index, r ₀ = e ² / mc ² = 2.82 × 10 ⁻¹³ cm: classical electron radius, λ: wavelength of light, N _q : number of atoms in 1 cm ^{3 of} element q, f (0): forward scattering cross section of element q. However, in Equation 1, the correlation between atoms and electrons involved in the structure existing in the solid is ignored. Here, this approximation is effective when the energy of the photon is around 100 ev or away from the absorption edge. _Nq can be obtained from the following relational expression. N _q = N × N _a / m _q where N: density (g / cm ³ ), m _q : atomic weight of element q,
N _a: Avogadro's number, it is.

Using the above equation (1), L
1 mol% or 2 mol% of each element from i to Ra
FIG. 1 shows simulated values of the complex refractive index when doped, and FIGS. 2 and 3 show graphs of the values. However, λ = 13.5 nm. As is apparent from FIGS.
In the case of doping by ol%, the real part of the complex refractive index does not show a large change only to the extent that the third digit changes. On the other hand, the imaginary part of the complex refractive index, which means the absorption coefficient, changes greatly. From the above simulation results, it has been found that the requirement for the element to be doped into the Si target may be an element having a small imaginary part in the complex refractive index after doping.

For example, when a pattern is transferred onto a desired substrate by EUVL, the angle of incidence of EUV light on the multilayer film is 2.0.
If an optical system of 5 deg is used, non-doped Si
And a multilayer film formed by Mo (period length 7.0 nm, Γ =
0.40, ⁴⁰ periods, (Si / Mo) ⁴⁰ / Si) is 0.
708 shows the reflectance. Here, Γ means, for example, Si and Mo
In the multilayer film formed by
Mo when the thickness of the layer in one cycle formed by the layer is 1
This is a value indicating the thickness of the layer. Incidentally, in a multilayer film formed of Si and Mo, when Γ = 0.40, the wavelength is 13.5.
The reflectivity for EUV light of nm is maximized.

Here, as described above, for example, Si and M
o (multilayer film with period length 7.0 nm, Γ = 0.
The real part of the complex refractive index of the Si layer in (40/40 periods, (Si / Mo) ⁴⁰ / Si) has a very small effect on the reflectivity of this film, so that the S element doped with the doping element
The inventors conceived that the reflectance of the multilayer film formed from i and Mo can be approximated as the relationship with the imaginary part of the complex refractive index of the Si layer, and this was obtained by simulation. FIG. 5 shows the obtained relationship. As is apparent from FIG. 5, the imaginary part of the complex refractive index of the Si layer of the multilayer film has a linear relationship with the reflectance of the multilayer film. From this relationship, the reflectivity of the multilayer film when the selected doping element was doped in a desired amount could be made predictable.

Further, from FIG. 5, the relationship between the reduction ratio of the reflectance of the multilayer film and the imaginary part of the complex refractive index of the Si layer when the doping element is doped is as shown in FIG. That is,
For example, a multilayer film (period length 7.0) formed of Si and Mo
nm, Γ = 0.40, ⁴⁰ periods, (Si / Mo) ⁴⁰ / S
In the case of i), if the decrease in the reflectance is allowed to be about 10% as compared with the case where the Si layer without the doping element is used, the complex of the Si layer doped with the doping element can be obtained from FIG. The imaginary part of the refractive index is -0.003
It can be derived that 86 or more is sufficient. Similarly, if the decrease in the reflectance is allowed to about 2%, it can be derived from FIG. 6 that the imaginary part of the complex refractive index of the Si layer doped with the doping element should be -0.00219 or more.

From the above, it is apparent from the relationship between Equation 1 and FIG. 5 that the element to be doped and the doping amount thereof can be derived if the allowable rate of decrease in reflectance is determined in advance. became. Based on the derivation result, the doping element and the doping amount for ensuring the reflectance of EUV light reflection in a predetermined range and suppressing the number of particles adhering on the Si layer to a desired number or less can be determined. It may be obtained experimentally.

Li, Be, B, P, C are examples of elements that satisfy this requirement and can be doped at a high concentration of 2 mol% or more.
a, Sc, Ti, V, Se, Rb, Sr, Zr, Nb,
Mo, Tc, Ru, Rh, La, Ce, Pr, etc. were found. Similarly, examples of elements that satisfy this requirement and can be doped at a concentration of about 1 mol% include Na, Mg, Al,
Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, A
s, Y, Pb, Ba, Nd, Pm, Sm, Eu, Gd,
Tb, Ho, Er, Lu, Ta, W, Re, Os, I
r, Pt, etc. were found.

From the above dopable elements, an appropriate doping element can be selected in consideration of availability, raw material cost, and ease of doping a Si target. For example, elements such as B, Al, P, and Ga are considered preferable elements from the above viewpoint. Therefore, each of these four elements is doped into Si by 2 mol%, and the period length is 7 n.
A Mo / Si multilayer film having m periods of 40 cycles was formed on a Si substrate, and the reflectance when EUV light was incident on the multilayer film at different incident angles was simulated. The result is shown in FIG. It was shown to. As a result, the incident angle of EUV light is 0 to 15
In deg, it was found that each of the EUV light reflecting films having the Si layer doped with 2 mol% of each of the above four elements had almost the same reflectance as the EUV light reflecting film having the non-doped Si layer.

On the other hand, from the examples of the dopable elements, T
i, Al and B are selected as doping elements, and Ti: 2
mol%, Al: 1 mol%, B: 2 mol%, a Si target was prepared, and a Si film was formed. FIG. 7 shows the resistance value of the bulk body of the Si target, the manufacturing method, the density of the bulk body, and the resistance value of the formed Si layer. According to the results, when compared with the resistance value of the Si target bulk body, it is reduced to about 1/10 or less for B-doped and about 1/2 for Al-doped, but is increased about twice for Ti-doped. I have. This is because the non-doped Si target is manufactured by a melting method,
It is considered that the target is manufactured by a sintering method due to a difference in manufacturing method. In general, a bulk body produced by a sintering method has many pores, and its density is 70% of that of a fusion target as shown in FIG. Therefore, for example, Ti
In the case of doping, as described above, it is considered that the resistance value of the target bulk body apparently increased about twice.

However, here, the beginning of the “embodiment of the invention”
As described in the previous section, "The source of abnormal discharge of the Si target
This is due to the conduction state of the Si target,
That the conductivity of the Si target is low
Is due. "it is conceivable that. And this local S
The conductivity of the i target is equivalent to the conductivity of the deposited Si layer
It is considered that the value of S
Comparing the resistance values of the i-layer, it was found that
Bottom, about 1/30 in Al doping, 1/2 in Ti doping
It is as follows. As a result, the conductive state of the Si target
In particular, the conductivity of the Si target is locally improved,
Even when using a shifted Si target, sputtering
No abnormal discharge was observed during the test, and the
30 particles / cm ^TwoIt was below. Sa
In addition, charge-up during sputtering is suppressed,
It also has the effect of preventing the adhesion of mi

The Si doped with these doping elements
An EUV mask blank was manufactured using an EUV light reflecting multilayer film formed using a target. And this EU
Design rule is 0.07 using V mask blank
A reflective mask for EUV exposure of a 16 Gbit-DRAM of μm was manufactured. Exposure transfer was performed by EUVL using the manufactured reflective mask for EUV exposure, and it was confirmed that it had good transfer characteristics with high accuracy and few defects. It was confirmed that by transferring a pattern onto a desired substrate using a mold mask, a semiconductor device such as an LSI having a high degree of integration can be produced with a high yield.

(Example 1) In the case where a Si target doped with B is used. B on Si (purity 99.99%) powder
(Purity: 99.7%), 2.5 mol% doped, compacted into a disk having a diameter of 3 inches and a thickness of 10 mm, and then sintered under a reducing atmosphere. As a result, Si crystal doped with 2 mol% of B was obtained. was gotten. A backing plate was bonded to this Si crystal to produce a sputtering target. Using this Si target doped with B, a Mo / Si multilayer film was formed on a glass substrate by a sputtering method. Glass substrate using a SiO ₂ -TiO ₂ glass 6 inch square. Sputtering is performed using a DC magnetron sputtering method. First, a Si film is formed under an atmosphere of 0.1 Pa of Ar gas using a prepared Si target doped with B, and then 0.1 Pa of Ar gas is formed using an Mo target. A Mo film was formed under the atmosphere described above. At this time, the thickness of one Si layer is 2.7 nm, and the thickness of one Mo layer is 4.2 nm.
, And this was taken as one cycle to form a Mo / Si multilayer film of 40 cycles. 7. The uppermost layer is a Mo oxidation preventing layer.
A 0 nm Si layer was formed.

As a result, no abnormal discharge was observed during the sputtering for forming the Si layer. The number of generated particles was 3.6 / cm ² . In addition, the number of generated particles is obtained by measuring particles having a diameter of 3 μm or more existing in the form of a multilayer film by a particle counter (KLA-Tencor, Surfscan 6220). The decrease in reflectance was 0.1%.

(Embodiment 2) In the case where a Si target doped with Al is used. Doping element B in Example 1,
2.5 mol% dope to Al powder (purity 99.9%),
A multilayer film was formed on a glass substrate in the same manner as in Example 1 except that 1 mol% of dope was used. As a result, no abnormal discharge was observed during the sputtering for forming the Si layer. The number of generated particles was 14.0 / cm ² . The decrease in reflectance was 0.2%.

(Embodiment 3) The multilayer film formed in each of Embodiments 1 and ₂ was formed by using an SiO ₂ target and using an Ar gas of 0.1 P
a by RF magnetron sputtering in an atmosphere of
An intermediate layer composed of an O ₂ film was formed to a thickness of 0.05 μm.
On this intermediate layer, a film containing Ta and B was formed as a EUV absorption layer to a thickness of 0.1 μm by a DC magnetron sputtering method to obtain an EUV mask blank. This EU
Design rule is 0.07μ using V mask blank
m having a pattern for 16Gbit DRAM
A reflective mask for V exposure was manufactured by the following method.

First, an EB resist was coated on an EUV mask blank, and a resist pattern was formed by EB drawing. Using this resist pattern as a mask, the intermediate layer as an etching stopper layer, the EUV absorbing film containing Ta and B is dry-etched using chlorine,
An absorption pattern was formed on the UV mask blank. Further, the intermediate layer exposed on the multilayer film is removed with a diluted hydrofluoric acid solution, and the resist remaining on the absorption pattern is removed.
A V mask was obtained. When exposure transfer was performed by EUVL using the obtained reflective mask for EUV exposure,
It was confirmed that it had good transfer characteristics with high accuracy and few defects.

(Comparative Example) A case where a Si target not doped with a doping element is used. A Si target (purity 99.99%) was prepared by a melting method, and a multilayer film was formed on a glass substrate as in Example 1. As a result, abnormal discharge was observed during the sputtering for forming the Si layer. The number of generated particles was 61.6 particles / cm ² .

[0031]

As described above in detail, the present invention suppresses the generation of particles on the Si target used for sputtering in the formation of the EUV light reflection multilayer film having the Si layer, and the reflectance of the EUV light reflection is reduced. A doping element which can be ensured in a predetermined range was found and doped. When a film was formed by sputtering using this Si target, generation of particles could be suppressed, and as a result, an EUV light reflecting multilayer film having a small amount of particles attached could be obtained.

[Brief description of the drawings]

FIG. 1 is a table of a complex refractive index when an Si target is doped with each element.

FIG. 2 is a graph showing a real part of a complex refractive index when each element is doped into a Si target.

FIG. 3 is a graph showing an imaginary part of a complex refractive index when each element is doped into a Si target.

FIG. 4 is a graph showing a change in reflectance of a Si / Mo multilayer film formed by doping each doping element into a Si target.

FIG. 5 is a graph showing the relationship between the reflectance of a Si / Mo multilayer film doped with a doping element and the imaginary part of the complex refractive index of the Si layer.

FIG. 6 is a table showing a relationship between a reduction ratio of a reflectance of a Si / Mo multilayer film doped with a doping element and an imaginary part in a complex refractive index of the Si layer.

FIG. 7 is a table showing a resistance value, a density, and a resistance value of a formed Si layer of a target bulk when a Si target is doped with each doping element.

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Claims (4)

[Claims] In a multilayer film including a Si layer used for EUV light reflection, in forming a Si layer by sputtering, the conductivity of a Si target is increased to suppress particles generated due to electric field concentration and to form a film by adhesion of particles. The film formation of the EUV light reflecting film is characterized in that the film defect is suppressed, the reflectance of the EUV light reflection can be secured in a predetermined range, and sputtering is performed using a Si target doped with a doping element that satisfies. Membrane method. 2. A method according to claim 1, wherein in forming the Si layer in the multilayer film including the Si layer used for EUV light reflection by sputtering, Li, Be, B, P, Sc, T
i, V, Se, Rb, Sr, Zr, Nb, Mo, Ru,
Rh, La, Ce, Pr, Na, Mg, Al, Cr, M
n, Fe, Co, Ni, Cu, Ga, Ge, As, Y,
Pb, Ba, Nd, Sm, Eu, Gd, Tb, Ho, E
doping at least one element selected from the group consisting of r, Lu, Ta, W, Re, Os, Ir, and Pt, thereby suppressing generated particles and suppressing film formation defects due to adhesion of the particles; and A method for forming an EUV light reflecting film, characterized in that sputtering is performed using a Si target that satisfies that the reflectivity of EUV light reflection can be maintained within a predetermined range. 3. An EU using an EUV light reflecting film formed by the film forming method according to claim 1 or 2.
V mask blank. 4. An EU comprising an EUV light reflecting film formed by the film forming method according to claim 1 or 2.
Reflective mask for V exposure.