JPH0743888A - Photomask blank and photomask - Google Patents

Abstract

PURPOSE:To uniformalize the etching quantity (side etching quantity) of phase shift layers in a direction parallel with a transparent substrate at the time of wet etching by changing etching characteristics in a film thickness direction. CONSTITUTION:A first layer of the phase shift layer 5 is formed on the transparent substrate 1 and further, a second layer of the phase shift layer 6 is formed on the first layer of the phase shift layer 5. Shifter parts 7 and shifter apertures 8 are formed as well. A sputter film forming device by a DC magnetron system is used for production thereof. Chromium is sputtered and deposited by evaporation from a chromium target and two layers of the phase shifter films consisting of a halftone chromium oxide are formed on the transparent substrate 1 by reactive sputtering using oxygen and CH4 as reactive gases and changing film forming conditions. The etching characteristics and optical characteristics are changed in the film thickness direction by changing film quality and film thickness with each of the respective phase shift layers 5, 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask blank and a photomask used in a projection exposure apparatus.

[0002]

2. Description of the Related Art An example of a conventional phase shift photomask is shown in FIG. 4, in which a light shielding layer 3 is formed on the surface of a transparent substrate 1 and further on the light shielding layer 3. A transparent or translucent phase shifter layer 2 is made. In that case, the transparent or semi-transparent phase shifter layer 2 plays a role of phase shift, and the light shielding layer 3 plays a role of suppressing light transmittance. The light shielding layer 3 is made of a light shielding film such as Cr or molybdenum silicide film.

Another example is shown in FIG. 5, in which only a single semitransparent phase shifter layer 2 is formed on the surface of a transparent substrate 1. In that case, the single-layer semitransparent phase shifter layer 2 has both the role of phase shift and the role of adjusting the light transmittance. Therefore, in another example, a light-shielding layer is not used, and the light transmittance at the exposure wavelength λ is controlled to be equal to or lower than the photosensitivity of the photoresist by controlling the light transmittance by the light absorption of the halftone phase shifter. ing.

In such and another example, the shifter layer 2 has a target phase shift φ (usually π radian) of φ = 2π · (n ₁ −1) · d ₁ / λ. The thickness d ₁ of the shifter layer 2 is set so as to satisfy 1). Therefore, from the equation (1), d ₁ is as follows. d ₁ = φ · λ / 2π · (n ₁ −1) ··· (2)

[0005]

One example and another example of a conventional phase shift photomask is that wet etching is performed to form the shifter opening 8.
As shown in FIG. 6, the boundary of the shifter opening 8 becomes blunt due to the isotropicity of the wet etching. Therefore, the shifter opening 8 has to be formed by dry etching.

Further, in an example of a conventional phase shift photomask, the phase shifter layer 2 and the light shielding layer 3 are made of different materials, so that the film forming process and the dry etching process are complicated in the photomask manufacturing process. It caused a troublesome problem.

Another example is a semitransparent phase shifter layer 2
Therefore, the film forming process and the dry etching process are simplified in the photomask manufacturing process, and the labor can be saved. However, since it is a single layer, the design of the optical film lacks flexibility.
Therefore, for example, when the extinction coefficient k does not fall below a certain limit for an exposure wavelength of a short wavelength such as an oxide or oxynitride of chromium or molybdenum silicide, the optical parameter dependence of the light transmittance T causes However, there is a problem that it is not possible to suppress a decrease in light transmittance. Further, even when a low-tone or high-reflectance halftone photomask is required, the reflectance is uniquely determined when it is a single layer.

An object of the present invention is to solve the problems of the prior art and to cut the pattern of the phase shift photomask by wet etching, and to transmit the light even if the phase shifter layer has a large absorption coefficient. Can be made higher, and further, it is possible to manufacture a halftone photomask with low reflectance or high reflectance, and
(EN) Provided are a photomask blank and a photomask which have a simple photomask manufacturing process and are labor-saving.

[0009]

In order to achieve the above object, a photomask blank and a photomask of the present invention have two or more phase shift layers formed on a transparent substrate, and each phase shift layer has a phase shift layer. It is characterized in that the etching characteristics and the optical characteristics are changed in the film thickness direction by changing the film quality and the film thickness.

[0010]

In the present invention, since the etching characteristics are changed in the direction of film thickness, the amount of etching of the phase shift layer in the direction parallel to the transparent substrate surface (referred to as side etching amount) is made uniform during wet etching. It becomes possible to form a sharp pattern by wet etching.

Further, since the optical characteristics are changed in the direction of the film thickness, the transmittance loss due to the reflection of incident light in the phase shift layer is reduced, and the phase shift layer having a large extinction coefficient can be used for the material. Also makes it possible to increase the transmittance.

Furthermore, a photomask blank and a photomask having a low reflectance or a high reflectance can be easily manufactured.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. A photomask blank and a photomask of an embodiment of the present invention are shown in FIG. 1, in which a first phase shift layer 5 is formed on a transparent substrate 1, and the first layer A second phase shift layer 6 is formed on the phase shift layer 5. In addition,
In the figure, 7 is a shifter portion, and 8 is a shifter opening portion.

In the manufacture of such an embodiment, a DC magnetron type sputtering film forming apparatus is used, and chromium is sputter-deposited from a chromium target, and reactive sputtering using oxygen and CH ₄ is used as a reactive gas. On the transparent substrate 1, the film forming conditions were changed to form a two-layer phase shifter film made of halftone chrome oxide.

The substrate holder of the sputtering device is 153
It is possible to mount 14 quartz transparent substrates 1 of mm square in the circumferential direction, and in order to make the film thickness distribution uniform, 1.5 min.
The film was formed by rotating at a rotation speed of rotation. The substrate temperature at that time is 100 ° C. The first phase shifter layer has Ar flow of 40 sccm and O ₂ flow of 7 sccm, and the sputtering pressure is 2
mTorr, sputtering voltage 417V, sputtering current 2.5A, film formation for 10 minutes, layer thickness 65.5 nm
Formed. The deposition rate of spin film formation is 6.25 nm / mi
n, which is 94 nm / min in terms of static film formation. The film thickness is 62.5 nm.

The film quality obtained under the film forming conditions of the first layer is n ₁ = 2.5 and k ₁ = 0.5 in the optical constants n ₁ -ik ₁ .
The wet etching rate is 174 nm / min in the layer thickness direction and 1620 nm / min in the direction perpendicular to the layer thickness direction (referred to as side etching).

The wet etching solution is cerium ammonium nitrate 165 gr, 70% with respect to 1 liter of water.
An aqueous solution containing 42 ml of perchloric acid at a liquid temperature of 20
℃ was made.

Immediately after the formation of the first layer, the second layer was successively formed under different film forming conditions, and the second halftone chromic acid carbonized layer was formed to a thickness of 62.5 nm.

The film forming conditions for the second layer are as follows. The reaction gas flow rate is Ar; 27 sccm, O ₂ ; 4.4 sccc
m, CH ₄ ; 3 sccm, sputtering pressure is 2 mTorr
r, sputter voltage is 425 V, sputter current is 2.5
A, the film formation time is 14.5 minutes. The deposition rate of the rotary film formation is 4.3 nm / min, and it is 65 nm / m in terms of static film formation.
in. The substrate temperature is 200 ° C.

The film quality obtained under the film forming conditions for the second layer has optical constants n ₂ -ik ₂ of n ₂ = 2.0 and k ₂ = 0.5.
8, the wet etching rate is 132 nm / min in the layer thickness direction, and 960 nm / min in the direction perpendicular to the layer thickness direction (referred to as side etching). The film thickness is 62.5 nm.

AZ1500 photoresist is applied to a phase photomask blank in which a second phase shift layer is formed on a transparent substrate 1, and an exposure phenomenon is performed to form a linear resist pattern having a line width of 2 μm. Etching time is 1 minute. Wet etching was performed.

The cross-sectional shape of the phase shift photomask after wet etching is shown diagrammatically in FIG. Figure 2
In the figure, 9 is a resist layer.

Incidentally, this phase shift photomask has 1
It was possible to perform etching under the same dry etching conditions as the single-layer halftone phase shift photomask having the same film quality as the first layer and the single layer halftone phase shift photomask having the same film quality. That is, a parallel plate type RF ion etching apparatus is used, an operating pressure is 0.3 Torr, and a reaction gas C is used.
H ₂ Cl ₂ and O ₂ at 25 sccm and 75 s, respectively
When the etching was performed at ccm, the etching could be performed in about 4 minutes.

The i-line light transmittance T of the two-layer phase shift layer photomask was 6.38%, the reflectance was 12.9%, and the phase shift angle φ ₀ was 180 °.

In such an embodiment, the wet etching shape was improved as shown in FIG. 2 because the side etching rate of the second layer was smaller than the side etching rate of the first layer. Is uniformized. In addition, the transmittance, reflectance and phase shift angle of this halftone phase shift mask match the calculated values from the measured optical constants and film thickness.

By the way, although this embodiment relates to two halftone phase shift layers, it is possible to design and manufacture three or more halftone phase shift layers in the same manner. FIG. 3 shows a three-layer halftone phase shift layer having a reduced reflectance and an improved transmittance. Comparing the characteristics of the three-layer halftone phase shift layer with the characteristics of a conventional single-layer film having the same film thickness and an optical constant equal to the average value of the three-layer halftone phase shift layer, the three-layer halftone phase shift layer is compared. Tone phase shift layer reflectance R = 1
In contrast to 3.4% and the transmittance T = 9.74%, the reflectance R = 10.23% and the transmittance T = 9.5% in the single layer film, which can increase the reflectance and improve the transmittance. It turns out to be effective. The phase shift angles are both 180 °. In addition, make multiple layers,
By using the enhanced reflection film, it is possible to suppress the transmittance even in a wavelength range where the extinction coefficient k is small. In FIG. 3, 10 is a third phase shift layer.

In the film structure of this three-layer film, n ₁ = 2.5, k ₁ = 0.5, d, where the optical constant and film thickness of the j-th layer are n _j -k _j and d _j , respectively. ₁ = 325Å n ₂ = 2.3, k ₂ = 0.42, d ₂ = 706.5Å n ₃ = 2.07, k ₃ = 0.4, d ₃ = 392.5Å Total film thickness d = d ₁ + D ₂ + d ₃ = 1424Å, and the average value of the optical constants of the three-layer film, the optical constants of the single-layer film having the same film thickness, and the film thickness are: n = 2.282, k = 0.4327, d = 1424
Å The incident direction of light is from the back surface of the substrate.

[0028]

According to the present invention, since the etching characteristics are changed in the film thickness direction, the amount of etching in the direction parallel to the transparent substrate surface of the phase shift layer (referred to as the side etching amount) during wet etching is It becomes possible to make uniform, and a sharp pattern can be formed even by wet etching.

Further, since the optical characteristics are changed in the direction of the film thickness, the transmittance loss due to the reflection of incident light in the phase shift layer is reduced, and the phase shift layer having a large extinction coefficient can be used for the material. Also makes it possible to increase the transmittance.

Further, a photomask blank and a photomask having a low reflectance or a high reflectance can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view showing a cross-sectional shape after wet etching according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of an example of a conventional phase shift photomask.

FIG. 5 is an explanatory diagram of another example of a conventional phase shift photomask.

FIG. 6 is an explanatory diagram showing a cross-sectional shape of a conventional phase shift photomask after wet etching.

[Explanation of symbols]

 1-Transparent substrate 2--Semi-transparent phase shifter layer 3--Light-shielding layer 5--First phase shift layer 6-・ Second phase shift layer 7 ・ ・ ・ Shifter section 8 ・ ・ ・ Shifter opening 9 ・ ・ ・ ・ Resist layer 10 ・ ・ ・ ・ ・ Third phase shift layer

Claims (1)

[Claims] 1. A two or more phase shift layer is formed on a transparent substrate, the film quality and film thickness are changed for each phase shift layer, and etching characteristics and optical characteristics are changed in the film thickness direction. Photomask blanks and photomasks characterized by being present.