JP2001291661A - Method of manufacturing reflection type mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the removement of a most upper layer of a reflector formed of a multilayer film, by overetching and also prevent the formation of a relatively large taper on the sidewall of a pattern of a SiO2 buffer film and the consequent projection of a bottom edge of the taper from a bottom edge of an absorber. SOLUTION: A Ta absorber 13 is kept in a reactive ion-overetched state, until a part of the SiO2 buffer film 12 is removed. The SiO2 buffer film 12 is removed in two stages through reactive sputter underetching and wet etching. In the first stage, the SiO2 buffer film 12 is reactive sputter underetched, to such a degree that α-Si 11a in the lower layer is not exposed. In the second stage, the rest of the SiO2 buffer film is removed by diluted hydrogen fluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a reflection type mask for transferring a pattern of a semiconductor integrated circuit to a substrate by reduction projection exposure, and particularly to an extreme ultraviolet (EUV).
The present invention relates to a method for manufacturing a lithography reflective mask.

[0002]

2. Description of the Related Art With the miniaturization of semiconductor integrated circuit elements,
EUV lithography having a wavelength of 3 to 30 nm is used for improving resolution. Since the refractive index of a transmission material for EUV is very close to 1, a reduction projection optical system using a reflecting mirror is used instead of a refracting lens, and a reflection type mask is used.

In the manufacture of this mask, a low-expansion glass or Si substrate is laminated on a substrate of Mo and Si alternately, which reflects nearly 70% of the light when the EUV wavelength is 13.5 nm. A reflector is formed, and a T _{2 serving} as an absorber 13 is formed thereon via SiO _{2 serving} as a buffer layer.
is formed, and a resist (not shown) is applied thereon to complete a mask blank.

The resist is selectively exposed to an electron beam based on a desired circuit pattern and then developed,
An etching mask having a desired pattern is formed.

Using this mask, a Ta absorber and SiO 2
_{The two} buffer films are selectively etched, and the etching mask is removed.

[0006] Conventionally, a Ta absorber is first replaced with S by plasma etching using a chlorine-based gas as a reactive gas.
It was selectively removed until the iO ₂ buffer film (stopper film) was exposed.

Next, the SiO ₂ buffer film was selectively removed by plasma etching using a fluorine-based gas as a reactive gas.

Thereafter, the resist mask was removed by plasma ashing or the like to complete a reflection type mask.

[0009]

However, since the uppermost layer is terminated with α-Si as a protective film of the multilayer reflector, over-etching occurs in the plasma etching step of the SiO ₂ buffer film. Buffer film thickness is 40 ~
In contrast to 50 nm, the uppermost layer α-Si has a very thin film thickness of 10 nm or less in order to reduce the absorption of EUV light. There is a problem that the reflectance is reduced.

[0010] On the other hand, if a wet etching an SiO ₂ buffer layer hydrofluoric acid or the like, as shown in FIG. 7 (B), because although lower α-Si11a are not removed by etching, isotropic etching, SiO ₂ A relatively large taper is formed on the pattern side wall of the buffer film 12, and its bottom edge BE projects outward from the bottom edge of the absorber 13, so that the EUV light reflectance near the pattern side wall is reduced.

In view of the above problems, it is an object of the present invention to prevent the uppermost layer of a multilayer film reflector from being removed by over-etching, and to provide a relatively large layer on the pattern side wall of the SiO ₂ buffer film. It is an object of the present invention to provide a method of manufacturing a reflective mask which is tapered so as to prevent its bottom edge from projecting outward from the bottom edge of the absorber.

[0012]

According to the method of manufacturing a reflection type mask according to the present invention, an S film is formed on a multilayer reflector.
An absorber film is formed via the iO ₂ buffer film, and after removing the absorber film by etching on the substrate on which the etching mask is formed, the SiO ₂ buffer film is removed by etching, In the step of removing the etching mask, in the step of etching the absorber film,
Reactive ion over-etching with a first reactive gas, thereby depositing a first deposit containing a compound of the substance of the absorber and the first reactive gas on the side wall of the SiO ₂ buffer film, _{In the} step of etching the _two- buffer film, reactive sputter under-etching is performed with a second reactive gas, whereby the second substance containing the compound of the second reactive gas is formed on the surface of the first deposit and the surface of the SiO ₂ buffer film. The deposits are deposited and then the remaining SiO ₂ buffer film is removed by wet etching with a reactive liquid having a higher solubility for the second deposits than for the first deposits.

According to this method, since the SiO ₂ buffer film is wet-etched after the reactive sputter under-etching, it is possible to prevent the uppermost layer of the multilayer film reflector from being removed by over-etching. .

[0014] The etchant is a long time to penetrate into SiO ₂ buffer layer sidewalls, since the etching progresses in this portion is delayed than that of the buffer layer surface is formed on the pattern side of the SiO ₂ buffer layer This makes it possible to prevent the bottom edge of the buffer film from projecting outward from the bottom edge of the absorber.

[0015] Other objects, configurations and effects of the present invention will become apparent from the following description.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a reflective mask according to an embodiment of the present invention will be described below with reference to the drawings. Corresponding identical or similar components in a plurality of figures are given the same or similar reference numerals.

In this method of manufacturing a reflection type mask, FIG.
As shown in (A), the SiO ₂ buffer film 12 is subjected to reactive sputter underetching and wet etching while the Ta absorber 13 is subjected to reactive ion overetching until a part of the SiO ₂ buffer film 12 is removed. It is characterized in that it is removed in two stages. That is, in the first stage, the SiO ₂ buffer film 12 is
Reactive sputter under-etching is performed until the surface 11a is not exposed, as shown in FIG. 1C. In the second stage, the remaining SiO ₂ buffer film is removed with dilute hydrofluoric acid.

Next, this method will be described in detail.

When the absorber 13 is reactive ion-etched with a chlorine-based gas, as shown in FIG. 1B, a deposit 15 such as a chloride of Ta adheres so as to protect the pattern side wall, and anisotropically. Etching is performed. The SiO ₂ buffer film 12 is over-etched, and the deposits 15 adhere to the surface thereof as well.

[0020] caused to act dilute hydrofluoric acid in this state as the etching solution of the SiO ₂ buffer layer 12, for deposits 15 is a chloride mainly Ta, dilute hydrofluoric acid permeates into SiO ₂ buffer layer 12 Slowly, the etching rate becomes slow. In this case, since the etching rates in the vertical and horizontal directions are equal, the side wall of the SiO ₂ buffer film 12 is
A relatively large tapered shape is obtained as shown in FIG.

In order to avoid this, the part 1 in FIG.
B from the state of FIG.
Reactive under-etching using nitrogen-based gas
Then, the state shown in FIG. This etching
Then, on the pattern surface, carbon or carbon fluoride
The deposit 16 adheres to the pattern side wall and SiO _Two
Part of the buffer film 12 is removed. SiO_Twobuffer
The deposit 15 deposited on the surface layer of the film 12 is
15 which is removed by the
Remains due to the side wall protection effect of fluorine gas plasma
I do.

In this state, when diluted hydrofluoric acid is allowed to act as an etchant, the absorber 13 and the buffer film pattern 12a are formed.
The adhering matter 15 remains on the pattern side wall near the boundary with the pattern, so that the time required for the etchant to penetrate into the buffer film pattern 12a becomes longer, and the etching progress in this part is delayed. On the other hand, since the surface of the buffer film 12 is only covered with the deposit 16 of carbon or carbon fluoride, the etching of the buffer film 12 proceeds relatively faster than that of the pattern 12a.

FIG. 2 shows SiO 2 covered only by the deposit 15.
₄ is a graph showing experimental results of the etching depth versus the etching time when the _2- buffer film and the SiO ₂ buffer film covered only by the deposit 16 are wet-etched with a 3.3% dilute hydrofluoric acid solution. .

From FIG. 2, it can be seen that when the SiO ₂ buffer film is covered only with the deposit 15, the etching start time of the SiO ₂ buffer film is delayed, and much time is required to obtain the same etching depth.

From the above, the remaining S is diluted with dilute hydrofluoric acid.
The iO ₂ buffer film can be removed with a small taper on the side wall, thereby preventing the bottom edge of the SiO ₂ buffer film from projecting outward from the bottom edge of the absorber, and thus preventing EUV. Light reflectance can be prevented from decreasing near the pattern wall.

[0026]

Next, an example of an embodiment of the above-mentioned method of manufacturing a reflective mask will be described.

(1) Preparation of Mask Blank—FIG. 3A On a Si wafer substrate 10 having a diameter of 6 inches, a pair of Mo and Si having a period length of 6.9 nm is used as an EUV light reflecting portion.
A multilayer reflector 11 was formed in which 0 layers were stacked. However,
The uppermost layer is an 8 nm α-Si protective film 11a. A 40 nm SiO ₂ film was formed thereon as a buffer film 12 by RF magnetron sputtering. Further, Ta was deposited to a thickness of 100 nm as the absorber 13 by DC magnetron sputtering. Since the crystal structure of Ta was columnar, the Ta particles collided with the underlying SiO ₂ buffer film 12 due to sputtering and penetrated to form a mixed layer of 1 nm or less.

(2) Formation of etching mask 14—FIG.
(B) In order to form an etching mask on the absorber 13, ZEP70 manufactured by Zeon Corporation was used as a resist by spin coating.
Is applied to a thickness of 330 nm, and 150
Baking was performed at 3 ° C. for 3 minutes. Next, a desired mask pattern was drawn on the resist by an electron beam drawing method.
After that, the spin developing method was used to develop Zeon Z
The pattern was developed using ED500, methyl isobutyl ketone as the rinse.

(3) Reactive ion overetching of the absorber 13-FIGS. 1 (A) and 1 (B) 20.0 ml / min of Cl ₂ gas and 80.0 ml / m
Using a reactive mixed gas with a BCl ₃ gas in, the pressure is set to 0.5 Pa, and the Ta absorber 13 is subjected to reactive ion etching until the surface layer of the SiO ₂ buffer film (stopper film) 12 is completely exposed. did. Microwave power is 60
0 W and RF power was 30 W. The etching time is
This was the time when the Ta absorber 13 could be etched by 150%.

(4) Reactive sputter underetching of the SiO ₂ buffer film 12-FIG. 4 (A) Ar gas at 200.0 ml / min and 10.0 ml / m
extent to using in C ₄ F ₈ gas and 20.0 ml / min reactive mixture gas of O ₂ gas, and then the pressure 1.0 Pa, the SiO ₂ buffer layer 12 is the surface of the α-Si11a not exposed Until the reactive sputter under etching was performed. The microwave power was 400 W and the RF power was 15 W.

(5) Wet etching of SiO ₂ buffer residual film 12-FIG. 4B In order to determine the etching time of the SiO ₂ buffer residual film 12, the relationship between the concentration of hydrofluoric acid (HF) and the etching rate was examined. .

FIG. 6 shows that when the immersion time is 10 seconds,
Shows the experimental results of SiO ₂ etching depth for hydrofluoric acid concentration.

From FIG. 6, the hydrofluoric acid concentration in wet etching was determined to be 3.3%. Because the film thickness is 40nm
This is because the controllability is very good when SiO ₂ is etched in several tens of seconds.

The remaining film thickness of the SiO ₂ buffer film 12 is set to 4.6.
When the thickness was set to nm, the substrate was immersed in an HF solution having a concentration of 3.3% for 30 seconds to obtain a favorable pattern shape of the SiO ₂ buffer film 12 with a small taper due to side etching.

In the direction parallel to the substrate, the absorber 13 and the SiO ₂ buffer residual film 1 are etched by side etching.
The shape 2 is, for example, as shown in FIG. In order to represent the amount of side etching, the bottom edge of the absorber 13 is defined as the origin, and the direction parallel to the substrate and inside the edge is defined as the X axis. Then, the X coordinates of the top edge and the bottom edge of the SiO ₂ buffer residual film 12 are set to TE and BE, respectively.
Expressed by FIG. 7A shows a case where TE>BE> 0, and FIG. 7B shows a case where TE>0> BE.

FIG. 8 shows an experimental result of the edge position X with respect to the etching time of the SiO ₂ buffer film 12. TE
1 to TE3 and BE1 to BE3 each have a SiO ₂ buffer residual film 12 of 21.0% by the dry etching.
nm, 12.8 nm, and 4.6 nm, the top edge position TE when performing the above wet etching.
And the bottom edge position BE.

As is clear from FIG. 8, when the etching time is fixed at 30 seconds, the SiO ₂ to be etched is
The thickness of the buffer residual film 12 is 12.8 nm or 4.6 nm.
In any case, the bottom edge position BE is about 5 nm.

Therefore, if the target value of the SiO film thickness before wet etching is (12.8 + 4.6) / 2 = 8.
If it is 7 nm, the actual value is ± 4.1 nm from the target value.
The bottom edge position BE is 5 nm
Degree.

Assuming that the deposition error of the SiO ₂ buffer film 12 having a thickness of 40 nm is ± 2 nm, the dry etching error of the SiO ₂ buffer film 12 after the Ta absorber 13 is over-etched is within ± 2 nm. In this case, the sum of both errors is within the above range of ± 4.1 nm. This dry etching error corresponds to about ± 7.6% with respect to the dry etching amount of the SiO ₂ buffer film 12 (35−8.7 = 26.3 nm). This value can be sufficiently realized by a commercially available plasma etching apparatus.

In general, in order to obtain a good pattern shape of the SiO ₂ buffer film 12 with a small taper due to side etching, when the concentration of the HF solution is 3.3%, the immersion time is generally set to the remaining SiO ₂ buffer. It has been found that a value obtained by adding a time equal to or less than the etching time for the thickness of the buffer film 12 may be determined.

Since the resist (ZEP7000) used for the etching mask is dissolved with hydrofluoric acid, a fresh etching solution is continuously supplied to the mask to prevent the dissolved resist from affecting the etching rate. There is a need to. For this reason, wet etching equipment includes
It is desirable to use a spray or paddle method.

(6) Removal of the etching mask 14-FIG.
Finally, the remaining etching mask 14 is
It was removed by plasma ashing with the reactive gas of No. ₂ .

The present invention also includes various modifications.

For example, the absorber 13 only needs to absorb incident light, and may be a heavy metal such as W, Pt, Au or Ge.

The multilayer reflector 11 is made of Cr, Ni, Mo, R
a film of a heavy element such as u, Rh, W or Re;
A multilayer pair of a film of a light element such as C or Si,
What is necessary is to reflect the incident light when the Bragg reflection condition is satisfied.

The substrate 10 may be glass as long as the surface is optically polished to such an extent that the reflectivity of the multilayer film reflector 11 is not reduced and the reflectivity is not reduced.

The buffer film 12 is made of a CVD (chemical vap).
Alternatively, the film may be formed in a temperature range in which the multilayer film reflector 11 is not destroyed, for example, 150 ° C. or lower. When the SiO ₂ buffer film 12 having a different film quality is formed, ammonium fluoride may be added to dilute hydrofluoric acid in order to increase the wet etching rate.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a characteristic portion of an embodiment of the present invention;
(A) is a schematic cross-sectional view showing a state in which the absorber 13 has been subjected to reactive ion overetching in the production of the reflection mask, (B) is an enlarged cross-sectional view of the portion 1B in (A), and (C).
FIG. 4 is a cross-sectional view showing a state in which the SiO ₂ buffer film 12 is further subjected to reactive sputter underetching from the state of FIG.

[2], and SiO ₂ buffer film covered only deposit 15, and a SiO ₂ buffer layer which covered only deposit 16, in the case of wet etching at a concentration 3.3% dilute hydrofluoric acid solution 4 is a graph showing experimental results of etching depth versus etching time.

FIG. 3A is a schematic sectional view of a mask blank,
(B) is a schematic sectional view showing a state where an etching mask is formed on this mask blank.

FIG. 4A is a schematic cross-sectional view showing a state after the reactive sputter underetching of the SiO ₂ buffer film 12 with respect to the state of FIG. 1A, and FIG. 4B is a state after further wet etching; It is a schematic sectional drawing which shows a state.

FIG. 5 shows an etching mask 14 for the state of FIG.
FIG. 4 is a schematic cross-sectional view showing a state after removing.

FIG. 6 is a graph showing experimental results of etching depth of SiO ₂ with respect to hydrofluoric acid concentration when the immersion time is 10 seconds.

FIG. 7 shows a tapered Si formed by side etching.
FIG. 4 is an explanatory diagram of a top edge position TE and a bottom edge position BE of the O ₂ buffer film with respect to a bottom edge of the absorber 13;

FIG. 8: Reactive sputter underetched SiO
₉ is a graph showing experimental results of edge position X with respect to wet etching time of _two buffer films.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 11 Multilayer reflector 11a Protective film 12 Buffer film 12a Buffer film pattern 13 Absorber 14 Etching mask 15, 16 Deposit

Claims (5)

[Claims] An absorber film is formed on a multilayer reflector via a SiO ₂ buffer film, and after removing the absorber film by etching on a substrate on which an etching mask is formed, the SiO ₂ buffer layer is removed by etching, further reflection type mask manufacturing method of removing the etching mask, the etching process of the absorber film, and reactive ion overetching the first reactive gas, thereby SiO ₂ A first deposit containing a compound of the substance of the absorber and the first reactive gas is attached to a side wall of the buffer film. In the step of etching the SiO ₂ buffer film, reactive sputtering is performed with a second reactive gas. Under etching
Thereby, the second deposit containing the compound of the second reactive gas is attached to the surface of the first deposit and the surface of the SiO ₂ buffer film. Next, the remaining SiO ₂ buffer film is A method for manufacturing a reflection type mask, comprising: removing by wet etching with a reactive liquid having a higher solubility for a kimono than for the first deposit. 2. The absorber film is Ta, the first reactive gas is a chlorine-based gas, and the first deposit is mainly T
a, the second reactive gas is a fluorine-based gas, the second deposit contains a carbon fluoride-based substance, and the reactive liquid is dilute hydrofluoric acid. The method for manufacturing a reflective mask according to claim 1. 3. The method according to claim ₂ , wherein the time of the wet etching is a value obtained by adding a time equal to or less than the time for etching the thickness of the remaining SiO ₂ buffer film. Method for manufacturing a reflective mask. 4. The method according to claim 3, wherein the concentration of the diluted hydrofluoric acid is about 3.3%. 5. The multilayer film according to claim 1, wherein a pair of Mo and Si is laminated a plurality of times, and an uppermost layer is α-Si thicker than the pair of Si.
The method for manufacturing a reflective mask according to claim 1, wherein: