JP2003084418A - Halftone phase shifting mask and blank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a halftone phase shifting mask having the objective transmittance and phase contrast, less liable to cause particle defects and having high chemical stability without using a metal silicide compound using Si atoms or a metal fluoride with respect to a halftone phase shifting mask having regions transparent to light for exposure and translucent regions comprising a monolayer translucent film 2 whose phase and transmittance have been controlled on a glass substrate 1 and to provide a halftone phase shifting mask blank for fabricating the halftone phase shifting mask. SOLUTION: Principal constituent elements comprised in the translucent film layer 2 are aluminum and oxygen and the ratio of the number of oxygen atoms is <=60%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask for exposure transfer used in a photolithography process in a semiconductor manufacturing process and a photomask blank for manufacturing the same, and more particularly to a halftone type phase shift. The present invention relates to a mask or a halftone type phase shift mask blank.

[Prior art]

Along with the rapid miniaturization of semiconductor devices in recent years, the lithography technology for transferring a mask pattern onto a Si wafer has also advanced at the same time. In order to improve resolution, the reduction projection exposure apparatus (stepper) uses a KrF excimer laser (wavelength 248 nm) and an ArF excimer laser (wavelength 1 after i-line (wavelength 365 nm).
The wavelength is steadily shortening to the deep ultraviolet region such as 93 nm) and further to the vacuum ultraviolet region of the F2 laser (wavelength 157 nm).

The phase shift method is one of the resolution improving techniques in the lithography technique, and has been actively developed. In principle, by providing a phase shift part in adjacent areas on the mask so that the transmitted light is 180 degrees, the light intensity at the boundary is weakened when the transmitted light is diffracted and interferes with each other. As to improve the resolution of the transfer pattern. As a result, it has the effect of improving the resolution and the depth of focus of a fine pattern, which are dramatically superior to those of a normal photomask.

The phase shift method as described above is based on IBM's Le.
Proposed by Venson et al., JP-A-58-173
No. 744, and Japanese Patent Publication No. 62-50811 in principle, Levenson type and halftone type are known. In particular, the halftone phase shift mask (hereinafter referred to as the halftone mask) has a function of reversing the phase of the transmitted light in the semitransparent film and a light shielding property below the sensitivity of the resist inside the pattern, and thus the transmitted light intensity. It has the effect of making the edge shape steep and improving the resolution and depth of focus characteristics and faithfully transferring the mask pattern onto the wafer, and is particularly effective in improving the resolution of the isolated pattern.

In the halftone mask, a semi-transparent layer that gives a phase difference and a transmittance is a single-layer halftone mask made of one kind of thin film material and a semi-transparent layer that gives a phase difference and a transmittance. There are multilayer halftone masks composed of more than one kind of thin film material. The simplest structure of the multi-layer type halftone mask is a two-layer type halftone mask in which the phase difference and the transmittance are separately controlled by one kind of thin film material.

In a halftone mask (including mask blanks hereinafter), the transmittance of ultraviolet rays, which is the exposure wavelength, is generally 5 to 15%, the reflectance is 25% or less, and the transmittance at the inspection wavelength is Must be 40% or less. The reason for this is that if the reflectance at the exposure wavelength is high, the exposure accuracy will be reduced due to multiple reflection between the mask and the wafer during projection transfer. In addition, the mask inspection and dimension measurement are mainly 365n.
Visible light of m (i line) or ultraviolet ray of 257 nm is used, but if the transmittance for this inspection wavelength exceeds 40%,
This is because the contrast between the transmissive portion (glass substrate) and the semi-transparent film portion is lowered, which causes a problem that inspection / dimension measurement becomes difficult.

As a measure for realizing the above-mentioned necessary conditions, that is, transparency in the ultraviolet region having a short wavelength and flat spectral characteristics up to the visible light region, as a semitransparent film material for a halftone mask. Is proposed as a metal silicide such as MoSi or a metal fluoride such as CrF.
It has been used in line exposure and KrF exposure.

Not only the halftone mask but also a photomask blank material is formed by a sputtering method which is excellent in adhesion to a glass substrate. In order to realize similar spectral characteristics in future ArF exposure and further F2 exposure, it becomes necessary to increase the transmittance in the shorter wavelength region. Therefore, in the halftone due to the metal silicide, Si (silicon)
A method of increasing the composition ratio of SiO ₂ and increasing the small absorption of SiO ₂ and SiN components is adopted. However, since Si has low conductivity, there is a problem in that the number of particle defects in the film rapidly increases when sputtering film formation is performed with a large Si composition ratio.

[0009] Further, it has been reported that metal fluorides such as CrF and the like are originally insufficient in chemical stability and have insufficient irradiation resistance in ArF exposure, and it is further used in F2 exposure having higher energy. It will be difficult.

DISCLOSURE OF THE INVENTION The present invention has a target transmittance and a phase difference without using a metal silicide compound using Si or a metal fluoride, and is less likely to cause particle defects, and is chemically An object is to provide a halftone mask having high stability and a halftone mask blank for manufacturing the halftone mask.

[Means for Solving the Problems]

In order to solve the above problems, the present invention provides a halftone mask and a halftone mask blank in which the kind of elements constituting the semitransparent film is related to the film properties such as optical properties and particle defects. It is decided in consideration. The means are listed below.

The invention according to claim 1 of the present invention comprises a half having a transparent region for exposure light and a semi-transparent region consisting of a single-layer semi-transparent film whose phase and transmittance are controlled, on a glass substrate. A tone type phase shift mask, wherein the main constituent elements contained in the semitransparent film layer are aluminum and oxygen, and the atomic ratio of oxygen is 60% or less. Is.

According to a second aspect of the present invention, the main elements constituting the semitransparent film layer are aluminum and oxygen, and the halftone type phase shift mask according to the first aspect is produced. For this purpose, a halftone type phase shift mask blank is used.

According to a third aspect of the present invention, the atomic ratio of oxygen is 40% to 50% with respect to the total atomic ratio of aluminum and oxygen which are the main elements constituting the semitransparent film layer.
The halftone phase shift mask according to claim 1, wherein

According to a fourth aspect of the present invention, the atomic ratio of oxygen is 40% to 50% with respect to the atomic ratio of aluminum and oxygen, which are the main elements constituting the semitransparent film layer.
The halftone phase shift mask blank according to claim 2, wherein

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Silicon is a so-called semiconductor material and has a high insulating property. For this reason, a charging phenomenon is likely to occur, and abnormal sputtering is likely to occur during sputtering using this phenomenon. This increases defects. In the present invention, the use of aluminum makes it possible to reduce the above-mentioned particle defects in the film because it is a conductor. Also, since aluminum oxide is used, unlike metal fluoride, alumina (Al ₂ O ₃ )
Therefore, the irradiation resistance in exposure is also high.

FIG. 3 is a plot of optical constants (n: refractive index, k: extinction coefficient) of various materials at a wavelength of 157 nm. Here, assuming that the film is a homogeneous thin film and the interface is not roughened, the transmittance (T) and reflectance (R) of the thin film are generally the optical constant (n, k) and the film thickness (d) of the thin film, And is uniquely determined by the refractive index (ns) of the transparent substrate and expressed by the following equation (normal incidence is assumed, λ is the wavelength). T = t ^* t ^** ns * 100 ... R = r ^* r ^** 100 ... t = 2 / (m1 + m2 * ns + m3 + m4 ^* ns) t ^* is t and r ^* is the complex conjugate of r. r = (m1 + m2.ns-m3-m4.ns) / (m1
+ M2 · ns + m3 + m4 · ns) m1 = cos δ m2 = sin δ / (n−k · I) · I m3 = sin δ · (n−k · I) · I m4 = cos δ = 2π (n−k · I) d / λ I represents an imaginary unit. Further, in the halftone mask, the phase difference is an important amount, but the phase difference PS (degree) can be approximated by the following linear expression. PS = 360x (n-1) xd / λ ...

As can be seen from the formula, it is desirable to use a thin film material having a large refractive index n in order to reduce the film thickness d for obtaining the desired phase difference of 180 degrees in the halftone mask. Further, the extinction coefficient k is an amount that mainly affects the transmittance, and has the following equation with the absorption coefficient μ of light by the thin film. μ = 4πk / λ

3 and 4 are plots of optical constants of various materials at wavelengths of 157 nm and 193 nm, respectively. The solid lines are n and k for the transmittances of 5% and 15%, respectively, when the phase difference is 180 degrees in a single layer film.
It is a line connecting the conditions, and therefore, the material within this solid line can be the thin film material of the single-layer halftone mask. However, as can be seen from the figure, it is difficult for a single metal thin film to fall within this range. Therefore, it is necessary to reduce k as an oxide or a nitride (approximately k = about 0.5) and optimize the contents of oxygen and nitrogen.

Conventionally, by using an oxynitride of a metal silicide such as MoSi or a metal fluoride such as CrF, k
I've been using small materials. That is, as can be seen from FIGS. 3 and 4, metal fluoride originally has very small k. Furthermore, oxynitride thin films of metal silicide are generally made of Si.
It is possible to reduce k by the amount including the components of O ₂ and SiN. However, in these films, when the composition ratio of Si is increased, Si has low conductivity, and therefore, there is a problem that particle defects in the film rapidly increase due to induction of abnormal discharge during sputtering film formation.

Therefore, in the present invention, instead of using Si, attention is paid to the fact that k of Al ₂ O ₃ and AlN is small, and Al
Oxynitride is used. Of these, Al ₂ O ₃ originally has a low k, so that it can be used as a single-layer halftone at both wavelengths of 157 nm and 193 nm by reducing the O (oxygen) composition ratio. Therefore, by setting the atomic ratio of O ₂ to 60% or less, it can be used as a halftone. On the other hand, AlN can be used as a single-layer halftone at a wavelength of 157 nm by decreasing the N (nitrogen) composition ratio, and can be used at a wavelength of 193 nm by increasing the N (nitrogen) composition ratio.

By selecting the oxynitride of Al as described above, the effect of reducing k, which is mainly caused by Al ₂ O ₃ and AlN, can be obtained. Among them, in the present invention, the oxygen content is particularly specified. I will do it. The reason why oxygen is used instead of nitrogen is that AlN is inferior to Al ₂ O ₃ in resistance to an acid or alkali cleaning liquid, and therefore it is desirable that nitrogen is not contained as much as possible.

FIG. 1 is a schematic view showing the structure of the halftone mask of the present invention in cross section. FIG. 1 shows a single-layer type halftone mask, in which a kind of mask pattern of a semitransparent film layer 2 defined in claim 1 or 3 of the present invention is formed on a glass substrate 1.

FIG. 2 is a schematic view showing the structure of the halftone mask blank of the present invention in cross section. This is a mask blank for producing the halftone mask of the present invention defined in claim 2 or 4, and after this, steps of resist coating, electron beam or laser drawing, dry etching, etc. It becomes a halftone mask. Note that after FIG. 2, a form in which a resist is applied or a form in which a light-shielding film is provided on a halftone film for a three-color type may be referred to as a mask blank, but it does not affect the gist of the present invention. However, it is included in the scope of the present invention.

【Example】

Here, of the halftone masks of the present invention, an example in which a single layer type halftone mask for F2 (wavelength 157 nm) exposure was prepared using a semitransparent film layer whose main elements are aluminum and oxygen. explain.

First, using an Al target as a cathode,
A reactive sputtering film formation experiment was carried out in which O ₂ gas was added to Ar, and several Al _x O _y films having different composition ratios were formed. The composition ratio was changed by the O ₂ / Ar flow rate ratio. Further, the optical constant (n, k) of the formed film was examined by an ellipsometer. Target: Al Film forming atmosphere: Ar + O ₂ = 40 [SCCM] (reactive sputtering) O ₂ = 3.0, 5.0 [SCCM] (O ₂ / (Ar + O ₂ ) × 100 = 7.5% to 12. 5%) Pressure: 0.25 [Pa] Power: DC300 [W] Target-substrate distance: 200 [mm]

The wavelength of the film produced as described above is 157 nm.
The optical constants (n, k) at were measured with an ellipsometer. The permeability of the film, that is, the magnitude of k is greatly affected by the O content, but for a film with an oxygen flow rate of 5 [SCCM], the exposure wavelength used for mask inspection and size measurement such as wavelengths of 365 nm and 248 nm. K in the range is 0.
It is close to 0, which is 005 to 0.008, and the transmittance at the wavelength of the inspection region is extremely high, so it is difficult to use it in a single layer. Therefore, it was decided to use a film with an oxygen flow rate of 3 [SCCM] to form a single-layer halftone film. As a result of analysis by X-ray photoelectron spectroscopy, the film with an oxygen flow rate of 3 was found to have 47% oxygen and 53% aluminum.

A film having an oxygen flow rate of 3 [SCCM] was selected as a thin film for forming a single-layer halftone mask.
First, this film was formed to a thickness of 1030Å on a transparent synthetic quartz substrate to prepare a single-layer film blank. Further, an electron beam resist was applied on this single-layer film blank and baked. After that, ordinary electron beam drawing was performed and development was performed to form a resist pattern. Then, using this resist pattern as a mask, RIE (reactive ion etching) with BCl ₃ gas was performed, and then the resist was peeled off to complete the halftone mask of the present invention. The transmittance of the single-layer halftone mask thus manufactured is 7%,
The phase difference was 179 degrees, which cleared the target value. Also,
The ratio of the number of O atoms to the total number of atoms of Al and O in the formed single-layer halftone film was 46.9%, which was within the range of the present invention.

[0028]

As described in detail above, according to the halftone type phase shift mask and blank of the present invention, the target transmittance can be obtained without using a metal silicide compound using Si atoms or a metal fluoride. It is possible to obtain a halftone mask that has a phase difference, is less likely to cause particle defects, and has high chemical stability, and a halftone mask blank for producing the halftone mask.

[Brief description of drawings]

FIG. 1 is a partial schematic view showing a cross section of an embodiment of a halftone mask of the present invention.

FIG. 2 is a partial schematic view showing a cross section of an embodiment of a halftone mask blank of the present invention.

FIG. 3 is a diagram showing optical constants of various materials at a wavelength of 157 nm.

FIG. 4 is a diagram showing optical constants of various materials at a wavelength of 193 nm.

[Explanation of symbols]

1 ... Glass substrate 2 ... Semi-transparent film layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Haraguchi             1-5-1 Taito, Taito-ku, Tokyo Toppan stamp             Imprint Co., Ltd. (72) Inventor Tsukasa Yamazaki             1-5-1 Taito, Taito-ku, Tokyo Toppan stamp             Imprint Co., Ltd. F-term (reference) 2H095 BB03 BC05

Claims (4)

[Claims] 1. A halftone phase shift mask having a region transparent to exposure light on a glass substrate and a semitransparent region composed of a single-layer semitransparent film whose phase and transmittance are controlled. The main constituent elements contained in the semitransparent film layer are aluminum and oxygen, and the atomic ratio of oxygen is 60.
% Or less, a halftone type phase shift mask. 2. A halftone type phase shift mask for producing a halftone type phase shift mask according to claim 1, wherein the main elements constituting the semitransparent film layer are aluminum and oxygen. blank. 3. The atomic number ratio of oxygen is 40% to 50% with respect to the atomic ratio of aluminum and oxygen which are the main elements constituting the semitransparent film layer. Halftone type phase shift mask. 4. The atomic number ratio of oxygen is 40% to 50% with respect to the atomic ratio of the total of aluminum and oxygen which are the main elements constituting the semitransparent film layer. Halftone type phase shift mask blank.