JP4951813B2 - Blank for halftone phase shift mask - Google Patents

Description

[0001]
BACKGROUND 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 photomask, and particularly, between exposure light passing through the photomask. The present invention relates to a halftone phase shift mask and a halftone phase shift mask blank which improve the resolution of a transfer pattern by giving a phase difference to the halftone phase shift mask.
[0002]
[Prior art]
In a semiconductor manufacturing process, a photomask is used as a mask at the time of pattern exposure for forming a fine pattern on a Si wafer or the like. One type of photomask is a phase shift mask using a phase shift method.
The phase shift method is one of the techniques for improving the resolution when transferring a fine pattern, and has been actively developed. In principle, by providing a phase shift unit in the adjacent area on the mask pattern so that the phase difference between the transmitted light is 180 degrees, the transmitted light is diffracted and interferes with each other to reduce the light intensity at the boundary. As a result, the resolution of the transfer pattern is improved.
As a result, it has the effect of improving the resolution and the depth of focus of a fine pattern that is remarkably superior to that of a normal photomask.
[0003]
A halftone phase shift mask has been developed as a kind of the phase shift mask as described above. The halftone phase shift mask is composed of a transmissive portion that transmits light having a strength that contributes to exposure and a semi-transmissive portion that does not substantially contribute to exposure, and a mask pattern formed on a transparent substrate. By making the transflective part have a phase reversal action of transmitted light and a light shielding function within the pattern below the resist sensitivity, the light passing near the boundary between the transmissive part and the transflective part cancels each other out. In this way, the edge shape of the light intensity is sharpened, the resolution and the depth of focus are improved, and the mask pattern is faithfully transferred onto the wafer.
[0004]
In recent years, in order to further improve the resolution of the mask pattern transferred onto the wafer, a high-transmittance halftone mask has been proposed in which the light transmittance at the semi-transmissive portion is increased. The high-transmittance halftone mask has a high transmissivity in the semi-transmitting part, and the intensity of light that is transmitted with the phase reversed is also increased. For this reason, the phase canceling effect is enhanced, and the resolution at the time of transferring the mask pattern onto the Si wafer is improved.
[0005]
[Problems to be solved by the invention]
In the halftone phase shift mask and blank for halftone phase shift mask, the phase change amount and transmittance at the exposure wavelength at the time of pattern exposure, which are the original optical characteristics of the phase shift mask, satisfy the desired conditions. In addition to satisfying, it is necessary that the reflectance at the exposure wavelength is reduced, and that the reflectance at the inspection wavelength at the time of pattern inspection is increased (the transmittance is reduced). .
This is because if the reflectivity of the photomask at the exposure wavelength is high, multiple reflection occurs between the photomask and the wafer during exposure, and the mask pattern transfer accuracy decreases.
[0006]
In the inspection / dimension measurement of the phase shift mask, the inspection wavelength is light having a wavelength longer than the exposure wavelength when exposure is performed using the halftone phase shift mask. For example, the exposure wavelength is 248 nm (KrF In the case of laser), the inspection wavelength is ultraviolet light such as i-line (wavelength 365 nm) of a high-pressure mercury lamp. This is because if the reflectance with respect to the inspection wavelength is low (the transmittance is high), the contrast between the transmission part (transparent substrate) and the semi-transmission part is lowered, which causes a problem that inspection / dimension measurement becomes difficult. .
Ideally, it is desirable to use light having the same wavelength as the exposure wavelength for inspection / dimension measurement. However, since the cost of generating a short wavelength increases, the exposure wavelength becomes shorter year by year. The inspection wavelength is longer than the exposure wavelength.
[0007]
In order to avoid the above problems, antireflection technology on the photomask surface has been studied. In the halftone phase shift mask, for example, a thin film material with low reflectance is used as a material for forming the semi-transmissive portion. It has been studied for use.
However, especially in dealing with shortening the exposure wavelength or increasing the transmittance at the exposure wavelength, the reflectance at the exposure wavelength is increased by controlling the phase difference and the transmittance at the exposure wavelength. Therefore, problems such as low reflectance at the inspection wavelength (increased transmittance) are likely to occur.
[0008]
In order to solve the above problems, the present invention selects a material for forming a semi-transmissive portion and optically controls it, thereby improving the mask pattern transfer accuracy and facilitating inspection. It is an object of the present invention to provide a blank for a phase shift mask and a halftone phase shift mask using the same.
[0009]
[Means for Solving the Problems]
In the present invention, the refractive index of the light-shielding film at the exposure wavelength of the blank for a halftone phase shift mask in which the light-shielding film and the transparent film are sequentially formed on the transparent substrate is the refractive index of the transparent film. more, and the light-shielding film and Ri main constituent element is zirconium silicide der of the transparent film, a reactive sputtering method upper layer transparent film on a transparent substrate by the lower two layers of the light-shielding film in blank halftone phase shift mask film Ru are deposited, the spectral reflectance curve as a region that includes the exposure wavelength of blank the halftone phase shift mask, the minimum point is sandwiched between the inflection point Is a blank for a halftone type phase shift mask. For this reason, it has an antireflection effect on the exposure wavelength, and not only can prevent deterioration of pattern accuracy due to multiple reflections when transferring a mask pattern onto a wafer, but also when forming a film on a transparent substrate. By simply changing the conditions and the like, the lower layer film and the upper layer film can be formed continuously, and the production efficiency can be dramatically improved. For example, the sputtering method is known as the most suitable method for manufacturing a mask blank. In this case, the same sputtering target is used, and the lower layer can be formed only by changing the conditions during film formation, for example, the atmosphere such as the oxygen flow rate. The film and the upper layer film can be formed continuously.
[0011]
Further, the present invention provides a light-shielding film and a refractive index of the light-shielding film at an exposure wavelength of a blank for a halftone phase shift mask in which a transparent film is sequentially formed on a transparent substrate. greater than the refractive index, and the main constituent elements of the transparent film and the light-shielding film is zirconium silicide der is, the upper layer on a transparent substrate by reactive sputtering a transparent film, the lower the light-shielding film in blank halftone phase shift mask two-layer film is Ru are deposited, the spectral reflection as a region that includes an exposure wavelength of blank the halftone phase shift mask, the minimum point is sandwiched between the inflection point A blank for a halftone phase shift mask, wherein a rate curve is set. For this reason, a reduction in reflectance at the exposure wavelength can be achieved, and a reduction in mask pattern accuracy due to multiple reflections can be prevented, and the inspection wavelength is included in the vicinity of the wavelength that gives the maximum point of the spectral reflectance. -The contrast between the transmissive part and the semi-transmissive part necessary for dimension measurement can be obtained.
[0012]
The halftone phase shift mask blank according to the present invention is characterized in that, in the blank for a halftone phase shift mask according to the above invention, the minimum point and the exposure wavelength of the halftone phase shift mask substantially coincide. It is.
For this reason, reflection during exposure can be minimized.
[0013]
Further, according to the present invention, in the blank for a halftone phase shift mask according to the invention, the exposure wavelength of the halftone phase shift mask is 157 nm (F2 laser), 193 nm (ArF laser), 248 nm (KrF laser), 365 nm. (I-line) 436 nm (g-line) selected from any one of the inflection points in the spectral reflectance curve of the halftone phase shift mask blank and including the exposure wavelength. 193 nm, 248 nm, 257 nm, 325 nm (He—Cd laser), 365 nm, 436 nm, 488 nm (Ar laser), 546 nm (e line), 633 nm (He—Ne laser), 780 nm (Ga−) As laser) in the order of the exposure wavelength, the same as the selected exposure wavelength. Fourth step long from one stage of a wavelength, to include any of the exposure wavelength, a blank halftone phase shift mask, wherein a spectral reflectance curve is set.
Furthermore, the exposure wavelength of the halftone phase shift mask is selected from any one of 157 nm (F2 laser), 193 nm (ArF laser), 248 nm (KrF laser), 365 nm (i-line), and 436 nm (g-line), A region between inflection points including the exposure wavelength in the spectral reflectance curve of the halftone phase shift mask blank, and having a minimum point between the inflection points, 193 nm, 248 nm, 257 nm, 325 nm (He -Cd laser), 365 nm, 436 nm, 488 nm (Ar laser), 546 nm (e-line), 633 nm (He-Ne laser), and 780 nm (Ga-As laser) in the order of the exposure wavelengths, If the same exposure wavelength does not exist, exposure is one to four steps longer than the most recent exposure wavelength To include any length is a blank halftone phase shift mask, wherein a spectral reflectance curve is set.
[0014]
For example, when the exposure wavelength is 157 nm, since the same wavelength does not exist, one of the wavelengths 193 nm or 193 nm which is the latest wavelength is longer by one to four steps, that is, any of the wavelengths of 248 nm, 257 nm, 325 nm and 365 nm. in region including the exposure wavelength between inflection point in the spectral reflectance curve, so as to sandwich the maximum point between the inflection point, is that the spectral reflectance curve is set.
[0015]
By way of further example, when the exposure wavelength is 193nm, the same wavelength a is 193nm fourth step longer wavelengths from one step than, i.e. 248 nm, 257 nm, 325 nm, is one of wavelengths of 365 nm, the spectral reflectance curve In the region where the exposure wavelength is included between the inflection points , the spectral reflectance curve is set so as to sandwich the maximum point between the inflection points .
[0016]
For this reason, it is selected from wavelengths of 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, 436 nm, 488 nm, 546 nm, 633 nm, and 780 nm,
The selected fourth step long from one stage of the exposure wavelength and the same wavelength, one of the exposure wavelength,
If the same exposure wavelength and exposure wavelength selected is not present, the four-stage long from one step than the most recent exposure wavelength or the last wavelength in one of the exposure wavelength, performing the inspection of the halftone phase shift mask Is possible. That is, since the reflectance becomes high at the inspection wavelength, the contrast necessary for the inspection can be obtained, and the inspection can be performed with high accuracy. Specifically, the inspection is represented by pattern dimension measurement, pattern chipping, pattern remaining, and the like.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below based on one embodiment.
FIG. 1A is a cross-sectional view showing one embodiment of the structure of a halftone phase shift mask blank according to the present invention. FIGS. 1B and 1C are sectional views showing an example of the manufacturing process of the halftone phase shift mask according to the present invention and an example of the manufactured halftone phase shift mask.
FIG. 2 is an explanatory view of antireflection by a three-layer film or a two-layer film on a transparent substrate.
[0020]
Below, the refractive index of the thin film currently formed in the blank for halftone type phase shift masks by this invention, and the halftone type phase shift mask, a film thickness, and its relationship are demonstrated.
In general, the light transmittance and reflectance of a transparent two-layer film formed on a transparent substrate are the optical constants (refractive index, extinction coefficient) and film thickness of these films, and the substrate, exposure atmosphere (usually It depends on the refractive index of air) and is determined as a result of multiple interference in the film.
[0021]
The conditions for reducing the reflectance of the transparent two-layer film formed on the transparent substrate to 0, that is, the antireflection conditions are, for example, three layers including the transparent substrate assuming normal incidence as shown in FIG. Considering the structure, if the refractive indices of layer 1, layer 2, layer 3 and air are n1, n2, n3 and n0, respectively,
n2 / n1 = √ (n3 / n0) (1)
In addition, when the film thicknesses of the layer 1 having the refractive index n1 and the layer 2 having the refractive index n2 are d1 and d2, respectively.
d1 = (2m + 1) λ / 8n1 (m = 0, 1, 2,...)
d2 = (2m + 1) λ / 8n2 (m = 0, 1, 2,...)
(2)
It is.
[0022]
If the above mathematical formulas (1) and (2) are satisfied, the reflectance is zero. Similarly, in the case where the layer 2 is a metallic film, if the film is formed so as to satisfy n0 <n2 / n1 <n3 even if the mathematical expressions (1) and (2) are not completely satisfied, a certain degree An antireflection effect can be obtained.
[0023]
In this way, if the formulas (1) and (2) are satisfied, the reflectance can be kept low. For example, when synthetic quartz is used as the transparent substrate, the refractive index is n3 = 1.5 at the exposure wavelength. Because
n2 / n1 = √n3 = 1.22
Therefore, n2> n1 is a necessary condition.
[0024]
As shown in FIG. 1A, the blank for halftone phase shift mask of the present invention has a transparent film (1) as an upper film and a light-shielding film (2) as a lower layer on a transparent substrate (3). It was produced by forming a two-layer film as a film.
Therefore, the halftone phase shift mask blank has a three-layer structure including the light-shielding film (2) and the transparent film (1) including the transparent substrate (3), and the optical constants of the respective layers are different. In particular, the entire phase change amount and transmittance with respect to the exposure wavelength are set to desired values, and the antireflection condition is satisfied.
In order to make the optical constants of the respective layers different, different materials may be used when forming the transparent film and the light-shielding film, or the film forming conditions may be changed using the same material.
[0025]
As a material for forming the transparent film and the light-shielding film of the halftone phase shift mask blank, for example, materials having Zr and Si as main constituent elements can be cited, but Hf, Ti, Mo, etc. other than Zr Since the same tendency is seen also in other metals, it is also possible to use these metals.
[0026]
【Example】
Hereinafter, a blank for a halftone phase shift mask of the present invention and a halftone phase shift mask using the same will be described with reference to examples.
<Example 1>
In the first embodiment, the configuration and manufacturing process of the halftone phase shift mask blank and the halftone phase shift mask shown in FIG. 1 will be described.
A zirconium silicide target was used on a transparent substrate (3) made of a quartz substrate having a refractive index n = 1.51 and an extinction coefficient k = 0 (wavelength λ = 248 nm, hereinafter the same), and an appropriate amount of oxygen was added to argon gas. Film formation was performed by a reactive sputtering method to form a light-shielding film (2). At this time, the thickness of the light-shielding film was 42.3 nm.
The optical constant of the light-shielding film (2) was confirmed in advance by a preliminary experiment and had a refractive index n = 2.33 and an extinction coefficient k = 0.73.
[0027]
Next, a film is formed on the light-shielding film (2) by the reactive sputtering method using the same zirconium silicide target as that used to form the light-shielding film, and an appropriate amount of oxygen is added to argon gas. ) Was formed. The film thickness of the transparent film at this time was 92.7 nm.
The optical constant of the transparent film (1) was previously confirmed by a preliminary experiment, and the refractive index n = 1.94 and the extinction coefficient k = 0.
[0028]
In this way, by using a zirconium silicide target on a quartz substrate and forming a two-layer film having a transparent film as an upper layer and a light-shielding film as a lower layer, KrF laser exposure having a structure as shown in FIG. A phase shift halftone mask blank corresponding to high transmittance having a phase difference of 180.21 degrees with respect to light (wavelength 248 nm) and a transmittance of 20.12% was obtained.
[0029]
FIG. 3 shows a spectral transmittance curve and a spectral reflectance curve of the above halftone phase shift mask blank.
The spectral reflectance has local maximums near wavelengths of 200 nm and 330 nm, and local minimums near wavelengths of 250 nm and 550 nm. In addition, there are inflection points near wavelengths of 220 nm, 270 nm, and 420 nm.
At this time, an exposure wavelength of 248 nm (during KrF excimer laser exposure) is included in a wavelength region including a minimum point near the wavelength of 250 nm and inflection points near the wavelengths of 220 nm and 270 nm.
[0030]
The inspection wavelength 365 nm (high-pressure mercury lamp i-line) is included in a wavelength region including a maximum point near 330 nm and inflection points near wavelengths 270 nm and 420 nm. Furthermore, the reflectance at an exposure wavelength of 248 nm (at the time of KrF excimer laser exposure) is 0.25%, and the influence of multiple reflection at the time of exposure can be sufficiently reduced. Further, the reflectance at an inspection wavelength of 365 nm (high pressure mercury lamp i-line) is 27.1%, and the transmittance is 30.3%, so that a contrast necessary for inspection can be obtained.
[0031]
Next, as shown in FIG. 1B, a resist is applied to the blank for halftone phase shift mask thus obtained, and a resist pattern (4) is formed through a resist process such as exposure and development. , Dry etching, and stripping of the resist pattern to form a light-shielding film pattern (2a) and a transparent film pattern (1a) on the transparent substrate (3) as shown in FIG. A tone type phase shift mask was obtained.
The dry etching conditions are as follows. An RIE apparatus was used as the dry etching apparatus.
Etching gas: BCl3
・ Pressure: 10 Pa (transparent film), 20 Pa (light-shielding film)
・ High frequency output: 125W (transparent film), 60W (light-shielding film)
It should be noted that the etching can be performed even when other chlorine gas or fluorine gas is used as the etching gas.
[0032]
In the present invention, the refractive index of the light-shielding film at the exposure wavelength of the blank for a halftone phase shift mask in which the light-shielding film and the transparent film are sequentially formed on the transparent substrate is the refractive index of the transparent film. more, and the light-shielding film and Ri main constituent element is zirconium silicide der of the transparent film, a reactive sputtering method upper layer transparent film on a transparent substrate by the lower two layers of the light-shielding film in blank halftone phase shift mask film Ru are deposited, the spectral reflectance curve as a region that includes the exposure wavelength of blank the halftone phase shift mask, the minimum point is sandwiched between the inflection point Since this is a blank for halftone phase shift masks, it has an antireflection effect on the exposure wavelength. Not only the halftone phase shift mask blank to prevent a decrease in pattern accuracy, since the main constituent elements of the principal constituent elements and transparency film of the light-shielding film is identical zirconium silicide, a film on a transparent substrate By simply changing the manufacturing conditions when forming, the lower layer film and the upper layer film can be formed continuously, and the manufacturing efficiency can be drastically improved.
[0034]
Further, the present invention provides a light-shielding film and a refractive index of the light-shielding film at an exposure wavelength of a blank for a halftone phase shift mask in which a transparent film is sequentially formed on a transparent substrate. Greater than the refractive index, and
Wherein Ri main constituent element is zirconium silicide der of the light-shielding film and the transparent film, a reactive sputtering method upper layer transparent film on a transparent substrate by a two-layer film and the light-shielding film lower layer Ru are deposited In the halftone phase shift mask blank, the spectral reflectance curve is set so that the minimum point is sandwiched between the inflection points in the region including the exposure wavelength of the halftone phase shift mask blank. The reflectance at the exposure wavelength can be reduced, and the contrast between the transmissive part and the semi-transmissive part necessary for inspection / dimension measurement can be obtained. Further, according to the present invention, since the minimum wavelength and the exposure wavelength of the halftone phase shift mask substantially coincide, reflection during exposure can be minimized.
[0035]
Further, in the present invention, the exposure wavelength is selected from any of 157 nm (F2 laser), 193 nm (ArF laser), 248 nm (KrF laser), 365 nm (i line), and 436 nm (g line), and the halftone type In the region between the inflection points including the selected exposure wavelength of the spectral reflectance curve of the blank for phase shift mask , a minimum point is sandwiched between the inflection points, 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, Since the spectral reflectance curve is set so that one of the wavelengths longer by one to four steps than the same wavelength as the exposure wavelength in the order of the exposure wavelengths of 436 nm, 488 nm, 546 nm, 633 nm, and 780 nm , Reflectivity is high at the inspection wavelength, the contrast required for inspection can be obtained, and high-precision inspection is possible. The ability.
[Brief description of the drawings]
FIG. 1A is a cross-sectional view showing one embodiment of the structure of a halftone phase shift mask blank according to the present invention.
FIG. 6B is a manufacturing process diagram of the halftone phase shift mask according to the present invention.
(C) is sectional drawing which shows an example of the halftone type | mold phase shift mask by this invention.
FIG. 2 is an explanatory diagram of antireflection by a two-layer film.
FIG. 3 is a spectral transmittance curve and a spectral reflectance curve of a halftone phase shift mask blank.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Transparent film 1a ... Transparent film pattern 2 ... Light-shielding film 2a ... Light-shielding film pattern 3 ... Transparent substrate (synthetic quartz)
4 ... resist pattern 5 ... layer 1
6 ... Layer 2
7 ... Layer 3
8 ... Incident light 9 ... Reflected light

Claims (4)

The refractive index of the light-shielding film at the exposure wavelength of the halftone phase shift mask blank in which the light-shielding film and the transparent film are sequentially formed on the transparent substrate is larger than the refractive index of the transparent film, wherein Ri main constituent element is zirconium silicide der of the light-shielding film and the transparent film, a reactive sputtering method upper layer transparent film on a transparent substrate by a two-layer film and the light-shielding film lower layer Ru are deposited In the halftone phase shift mask blank, the spectral reflectance curve is set so that the minimum point is sandwiched between the inflection points in the region including the exposure wavelength of the halftone phase shift mask blank. A blank for a halftone phase shift mask.   2. The half according to claim 1, wherein in the halftone phase shift mask blank, a minimum point of the spectral reflectance curve and an exposure wavelength of 157 nm, 193 nm, 248 nm, 365 nm, or 436 nm substantially coincide with each other. Blank for tone type phase shift mask.   The exposure wavelength of the halftone phase shift mask blank is selected from any of 157 nm, 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, and 436 nm, and the exposure of the spectral reflectance curve of the halftone phase shift mask blank is performed. In the region between the inflection points including the wavelength, a minimum point is sandwiched between the inflection points, and in the order of the exposure wavelengths of 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, 436 nm, 488 nm, 546 nm, 633 nm, and 780 nm, 3. The spectral reflectance curve is set so that any one of the exposure wavelengths that are one to four steps longer than the selected exposure wavelength is included. A blank for a halftone phase shift mask according to claim 1.   The exposure wavelength of the halftone phase shift mask blank is selected from any of 157 nm, 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, and 436 nm, and the spectral reflectance curve of the halftone phase shift mask blank In the region between the inflection points including the exposure wavelength, the minimum point is sandwiched between the inflection points, and in the order of the exposure wavelengths of 193 nm, 248 nm, 257 nm, 325 nm, 365 nm, 436 nm, 488 nm, 546 nm, 633 nm, 780 nm, If the same exposure wavelength as the selected exposure wavelength does not exist, the spectral reflectance curve is set so as to include one of the exposure wavelengths that is one to four steps longer than the most recent exposure wavelength. The halftone type according to any one of claims 1 to 2, characterized in that: Blank for a phase shift mask.

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