JPH06250381A - Mask plate for photoexposing and its production - Google Patents

Abstract

PURPOSE:To provide the mask plate for photoexposing which can be easily produced and has durability and a high resolving power by providing the inside of a transparent substrate with grooves having fine ruggedness in the bottom, to form translucent regions and specifying the phase difference between the transmitted light rays of these regions and transparent regions to a substantially specific value. CONSTITUTION:A resist for electron beams is applied on a quartz substrate 1 and desired patterns are plotted thereon by an electron beam plotter. Resist patterns 6 are obtd. after development. In succession, the phase shift regions 3 are formed by a reactive ion etching method using these patterns 6 as a mask. Further, the etching is executed by changing the etching conditions to conditions under which gaseous hydrocarbon is added, to form the extremely fine ruggedness 4 in the bottoms of the phase shift regions 3. The optimum value exists at the depth of the phase shift regions 3 by the wavelength of exposing light and the refractive index of the transparent substrate. The depth is adjusted by the etching time in such a manner that the substantial phase difference attains 180 deg.. The resist is thereafter removed and the mask plate 9 for photoexposing is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical exposure mask plate used for manufacturing semiconductor devices and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the field of semiconductors, processing technology is becoming finer as the degree of integration increases. In order to form a micron-order fine pattern, an optical exposure technique is used in which a mask pattern is reduced and transferred (1/5 times, etc.) to a photosensitive resin (resist) applied on a semiconductor substrate. 1Mbit (megabit) currently mass-produced
DRAM (Dynamic RAM) and 4Mbit DRAM
The minimum line widths in the above are 1.2 μm and 0.8 μm, respectively. Most of the photolithography equipment (stepper) that produces these uses the 436 nm emission line emitted from the ultra-high pressure mercury lamp called the g-line, and some have started to use the 365 nm emission line emitted from the lamp called the i-line. ing.

64 MbitD scheduled for mass production in the future
In RAM and 256 Mbit DRAM, the required minimum line widths are 0.3 μm and 0.2 μm, respectively. In order to mass-produce these semiconductor devices, development of a photolithography technique with higher resolution is required. In order to improve the resolution by shortening the wavelength of the exposure light, instead of the g-line, i
Line, and the use of a krypton-fluorine (KrF) excimer laser at 248 nm is under consideration.

In these exposure apparatuses, a mask having an opaque pattern usually formed of a metal thin film on a transparent substrate such as quartz is irradiated with light from the back surface, and the light flux passing through the mask is reduced through a projection lens. The image is formed on the substrate. As the pattern size approaches the wavelength, the contrast of the light image on the substrate becomes worse due to the diffraction of light at the pattern edge, and a resolution far worse than the limit resolution determined by the numerical aperture (NA) and wavelength of the lens can be realized. Not not. Recently, the following three phase shift methods have been proposed which improve the pattern structure on the mask to increase the contrast of the optical image and dramatically improve the practical resolution.

A phase shift mask is used in the phase shift method. The first example is shown in FIG. Reference numeral 11 is a quartz substrate that is transparent to the exposure wavelength, and 12 is a chromium thin film that blocks exposure light. A thin film (phase shift film) 13 is transparent to exposure light, and its film thickness Ts has the following relationship with the refractive index n and the exposure wavelength λ. Ts = λ / {2 · (n−1)} (1) This condition is set so that the phase of the exposure light transmitted through the thin film 13 is shifted by exactly a half wavelength. Openings 14, 1
Reference numeral 5 generally corresponds to the opening of the mask, and the opening 15 is arranged together with the phase shift film 13.

In the present phase shift mask, the phase of the light transmitted through the opening 14 and the phase of the light transmitted through the opening 15 are different by 180 degrees, so the light wave diffracted from the opening 14 and the light wave diffracted from the opening 15 cancel each other out. In the projection plane, the opening 14,
15 Each of the light bleeding is suppressed and the contrast of the projected image is improved. Next, a second example will be shown with reference to FIG.

In FIG. 6, 21 is a quartz substrate transparent to the exposure wavelength, and 22 is a chrome thin film that blocks the exposure light. Reference numeral 23 is a resist film which serves as a phase shift film, and the film thickness thereof satisfies the relationship of the expression (1). In the manufacturing process of this mask, after forming the opening 24 with a resist (not shown) with an electron beam drawing apparatus, the chromium film 22 is etched,
After removing the chromium film in the opening 24, a resist 23 which is a phase shift film is applied, and the opening 24 is formed in the phase shift film 23 by exposing the transparent substrate 21 side with far ultraviolet rays using the chromium film 22 as a mask. Form. afterwards,
By etching the chromium film under the phase shift film 23, the opening of the chromium film 22 becomes larger than 24, and a region 25 covered with the resist film is formed in the peripheral portion of the chromium film.

The phase of the light transmitted through the area 25 and the phase of the light transmitted through the area 24 are different by 180 degrees, and when the two overlap in the projected image, they cancel each other, so that the leakage of light from the area 24 to the peripheral portion is suppressed. To be done. Therefore, the light intensity distribution on the image plane becomes very sharp, and the practical resolution can be improved. A third example will be shown with reference to FIG.

In FIG. 7, reference numeral 31 is a quartz substrate transparent to the exposure wavelength, and 33 is a transparent film serving as a phase shift film, and the film thickness thereof satisfies the relation of the expression (1). In the process of forming this mask, a resist (not shown) is applied on the phase shift film 33, a desired pattern is drawn by an electron beam drawing apparatus, and then a resist pattern 36 is obtained by development by a usual method (FIG. 7A). Using the resist pattern 36 thus obtained as a mask, the phase shift film 3
Process 3 (Fig. 7b).

[0010]

The first method of the above-mentioned conventional phase shift methods improves the contrast of the pattern projected on the resist by the phase shift mask, so that the practical resolution is greatly improved. However, in order to manufacture a mask as shown in FIG. 5, after drawing a first resist image for forming a chrome pattern by an electron beam drawing apparatus, a second resist image for defining a phase shift film is formed. There must be. 2 electron beam drawing that requires a long time
It is necessary to perform the second pattern on the first pattern with high precision in addition to the need to perform it once, and there is a problem that the mask fabrication becomes technically difficult and at the same time the cost becomes high.

The second method does not increase the number of drawing times of the electron beam exposure apparatus, but the mask manufacturing process is complicated. Further, since the resist film left as the phase shift film is a brittle material, it is difficult to perform cleaning for removing dust on the mask, which is not a practical method.

In the third method, the phase of the light transmitted through the phase shift film 33 and the phase of the light transmitted through the transparent substrate are different by 180 °,
The light intensity on the resist surface has a dark portion at the boundary between the phase shift portion and the transparent substrate. In particular, by controlling the width of the phase shift film 33, the same effect as that of a conventional mask using an opaque light-shielding film can be obtained for the phase of light after passing through the mask and the light intensity on the resist surface. When such a shifter shading type phase shift mask is used for exposure by the resist i-line stepper, it is 0.20 μm on the projection memory surface.
When a phase shift film having a width (1.0 μm on the mask surface) is used, the shifter acts as a light shielding part. Now, considering the resolution of 0.55 μm pitch line and space patterns, the spacing between adjacent shifters is 0.35 μ in terms of conversion on the resist surface.
m, about the same as the light source wavelength of 365 nm, 0.6
It can be seen that the line & space pattern of the μm pitch is almost impossible to be resolved like the conventional mask.

Similarly, when it is used for exposure by a stepper using a KrF excimer laser as a light source, it is 0.1 on the projection surface.
When a shifter having a width of 5 μm (0.75 μm on the mask surface) is used, the shifter acts as a light shielding portion. 0.4 μm now
Considering the resolution of pitch line & space, the spacing between adjacent shifters is 0.25 μm when converted on the projection plane,
It is almost the same as the light source wavelength of 248 nm, and it can be seen that the line & space pattern of 0.4 μm pitch is almost impossible to be resolved like the conventional mask. Therefore, this mask is easy to make, but the resolution is improved by about 10%.
There is a problem that about 20% is not sufficient.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical exposure mask plate which is easy to manufacture, has durability, and has high resolution, and a manufacturing method thereof. .

[0015]

According to the present invention, a groove having fine irregularities at the bottom is provided in a substrate transparent to visible light or ultraviolet light to form a semi-transparent region for the light. Provided is a mask plate for light exposure, which is characterized in that the phase difference between the translucent region and the remaining transparent region with respect to transmitted light is substantially 180 °.

The transparent substrate can be made of, for example, a SiO ₂ compound. Examples of SiO ₂ compounds include glass and quartz. The semi-transparent region is for forming a non-exposed region, and the substantial light transmittance of the exposure light is 10 with respect to the light transmittance of the transparent region.
~ 90%. This light transmittance is achieved as a result of the incident light (exposure light) being scattered by the extremely fine irregularities formed on the incident surface of the exposure light.

The number of protrusions is usually 1000-5.
It is 000 pieces / mm ² , and the height difference of irregularities is usually 3 to 10 nm.
Is. The transparent area is for forming an exposure area, and the incident surface of the exposure light is smooth. The light passing through the semitransparent region and the transparent region, respectively, in order to enhance the resolution, it is preferable that the diffracted lights interfere with each other in the vicinity of the boundary of the respective regions to cancel each other, and the phase difference is substantially It may be 180 °.

In order for the phase difference to be substantially 180 °, the semitransparent region and the transparent region must be incident light (exposure light).
A distance corresponding to the equation (1) mλ / {2 · (n-1)} (1) (where m is a positive odd number, λ is the wavelength of the exposure light, and n is the refractive index of the substrate) in the incident direction of It is preferable to have an optical path difference of

The light exposure mask plate of the present invention is, for example, as follows.
Can be manufactured as follows. Ie on the surface
SiO with a resist pattern₂C on the system substrate
HF ₃Or CF_FourAnd H₂The first air consisting of a mixed gas of
Etching is performed using a etching gas to obtain approximately formula (I) mλ / {2 (n-1)} (I) (where m is a positive odd number, λ is the wavelength of light, and n is the refraction of the substrate).
The groove with a depth corresponding to the
After the first etching gas of 0.5-10 vol%
Using a second etching gas mixed with a hydrocarbon gas
Etch again to expose the bottom surface at a depth corresponding to formula (I).
For light exposure by forming fine unevenness that reflects light to complete the groove
Manufacture mask plate.

The first etching gas is used to pre-form a groove in the substrate, and CHF ₃ or CF _{4 is used.}
A mixed gas of H ₂ and H ₂ is used. A small amount of O _{2 in} this gas
Can also be mixed. The preformed groove has a smooth bottom surface and a depth of approximately (I) mλ = {2 (n-1)} (1) (where m is a positive odd number, λ is the wavelength of light, and n is the substrate). (Which is the refractive index of), but is specifically set to be 10 to 50 nm shallower than the distance of the formula (I).

The second etching gas is used to form the light-reflecting unevenness on the bottom surface of the groove to complete the groove, and the first etching gas contains 0.5 to 10 vol%.
It is preferably prepared by mixing 1 to 2 vol% of hydrocarbon gas. As the hydrocarbon gas, for example, methane, ethane or the like can be used. The amount of hydrocarbons mixed is 10v
If it is ol% or more, the unevenness becomes large and becomes non-uniform, which is not preferable.

This etching is usually performed to a depth of 10 to 50 nm, and the groove is completed by making the depth of the groove correspond to the distance of the formula (I). The obtained light exposure mask plate is placed in a projection exposure apparatus, and used, for example, so that a wafer having a photosensitive material formed on its surface is exposed to light transmitted through the mask plate.

[0023]

The operation of the light exposure mask obtained by the present invention will be described with reference to FIG. FIG. 1A is an enlarged schematic view of the vicinity of the boundary between the transparent substrate and the phase shift region. 1 is a region other than the groove of the substrate, 2 is a groove region (phase shift region), 3 is a groove depth, 4 Are fine irregularities.

The depth 3 of the phase shift region has an optimum value depending on the wavelength of the exposure light and the refractive index of the transparent substrate as shown in Table 1 according to the formula (I). The condition is that the phase of light passing through the semitransparent region of the groove having the unevenness of 180 ° differs by 180 °, but in reality, the substantial phase difference may be 180 °, so the depth 3 of the phase shift region is as follows. It may be an odd multiple of the depth shown in Table 1.

[0025]

[Table 1] Light passing through the phase shift region 2 of this mask is scattered by the fine irregularities 4, and as a result, the transmittance of the phase shift region 2 becomes smaller than that of the transparent substrate region 1 other than the groove. The amplitude distribution of the light passing through the mask in this way is shown in FIG.
As shown in (b), the phase of the light passing through the transparent region 1 other than the groove is positive, whereas the phase of the light passing through the phase shift region 2 is inverted and has a negative sign. When this light is projected on the sample substrate through the lens, as shown in FIG. 1 (c),
Since the phase is inverted at the boundary between the transparent substrate region 1 and the phase shift region 2 other than the groove, the light intensity is almost 0 immediately below. Therefore, the spread of the light intensity distribution is suppressed, and a fine pattern with high contrast can be formed.

[0026]

【Example】

Embodiment 1 An embodiment of the present invention will be described with reference to FIG. An electron beam resist is applied onto the quartz substrate 1, a desired pattern is drawn by an electron beam drawing device, and a resist pattern 6 is obtained after development (FIG. 2a).

Then, using the resist pattern 6 as a mask, the phase shift region 3 is formed by the ordinary reactive ion etching method (RIE) (FIG. 2b). Further, the etching condition is changed to a condition in which a hydrocarbon gas is added to carry out etching to form extremely fine irregularities 4 on the bottom of the phase shift region 3 (FIG. 2c). The depth of the phase shift region 3 thus formed is adjusted by the etching time so as to have the value shown in Table 1 above according to the wavelength of the exposure light according to the above formula (I).

The first etching depth is adjusted so that the second etching depth is 10 nm to 50 nm. Then, the resist is removed to complete the light exposure mask plate 9 (FIG. 2d). In the present embodiment, the electron beam resist was used to form the pattern by electron beam writing, but the same result can be obtained even if the photoresist is used to form the pattern by the light exposure method.

In the method shown in Table 1, the depth of the phase shift region shown in Table 1 is such that the end portions of the phase shift region 3 formed by etching the resist pattern 6 and the substrate are formed at an angle close to vertical. Is preferred.

Second Embodiment A second embodiment of the present invention will be described with reference to FIG. A metal thin film 7 having a thickness of about 100 nm is deposited on a quartz mask substrate 1, and an electron beam resist 8 is applied thereon (FIG. 3a). A desired pattern is drawn by an electron beam drawing device to obtain a resist pattern 8'after development (Fig. 3b).

Then, using the resist pattern 7 as a mask, the metal thin film 7 is etched by the usual reactive ion etching method (RIE) or liquid phase etching method to form a pattern (FIG. 3c). Then, RIE is performed using the resist pattern 8'and the metal thin film pattern 7'as a mask.
To form the phase shift region 3. Further, the etching conditions are changed to form ultrafine irregularities 4 on the bottom of the phase shift region 3 (FIG. 3d). The depth of the phase shift region 3 thus formed is adjusted by the etching time so as to have the values shown in Table 1. After that, the resist and the metal thin film are peeled off to obtain a desired mask plate for light exposure (FIG. 3).
e).

The relationship between the first etching depth and the second etching depth and the substantial depth of the phase shift region are the same as in the first embodiment. Kr according to this embodiment
F Excimer laser (light source wavelength = 248 nm) In the process of manufacturing a mask plate for light exposure for a stepper, a 100 nm thick Cr film is deposited as a metal thin film on a quartz substrate, and a 500 nm positive type resist is used as a pattern forming resist. A resist was used. In this example, the RIE method was used to form the phase shift region using the resist and the metal thin film as a mask. These process technologies are known in the IC manufacturing process.

FIG. 4 shows the calculation result of the light intensity distribution of the 0.2 μm line-and-space pattern on the resist surface when using the light exposure mask formed by the above materials and steps. It can be seen that the contrast is improved when the semitransparent phase shift is used as compared with the case where the transparent phase shift mask is used. Actually, using this mask, NA = 0.4
The KrF excimer laser stepper No. 5 was used to optimize the exposure amount, and then an exposure test was performed. With the conventional mask, 0.
Although the resolution of the line and space of 25 μm was the limit, it was possible to resolve the line and space of 0.2 μm with this mask, and it was confirmed that the resolution was improved by 10% or more.

Various materials and methods other than the above materials and methods can be used in the manufacturing process of this embodiment. As the mask material for forming the phase shift region, in addition to Cr used in the present embodiment, metals such as Al, W, Ti and Cu, alloys such as Al-Si and W-Si, that is, a transparent substrate, Any material can be used as long as the etching selection ratio can be realized.

Further, by determining the depth of the phase shift region according to Table 1, it is possible to deal with the case where the wavelength of the exposure light source changes. For example, the i-line (3
65nm) In the stepper, the depth of the phase shift region is 397nm.
Similar results are obtained by setting to.

[0036]

According to the present invention, it is possible to provide a mask plate for light exposure, which can transfer a fine pattern with high resolution, is easy to manufacture, and has a high durability, and a method for manufacturing the same.

[Brief description of drawings]

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

FIG. 2 is an explanatory view of the manufacturing process of the light exposure mask plate manufactured in the example of the present invention.

FIG. 3 is an explanatory view of the manufacturing process of the light exposure mask plate manufactured in the example of the present invention.

FIG. 4 is an explanatory diagram of relative light intensity on a sample substrate when light exposure is performed using the light exposure mask plate of the present invention.

FIG. 5 is an explanatory view of a conventional light exposure mask plate.

FIG. 6 is an explanatory diagram of a conventional light exposure mask plate.

FIG. 7 is an explanatory diagram of a conventional light exposure mask plate.

[Explanation of symbols]

 1 Quartz Substrate 3 Phase Shift Region 4 Fine Asperity 6 Resist Pattern 7 Metal Thin Film 8 Resist Layer 9 Photoexposure Mask Plate

Claims (3)

[Claims] 1. A substrate, which is transparent to visible light or ultraviolet light, is provided with a groove having fine irregularities at the bottom to form a semi-transparent region, and the semi-transparent region is formed. The phase difference for the transmitted light with the remaining transparent region is substantially 18
A mask plate for light exposure, which is set at 0 °. 2. A semi-transparent area is 1 for a transparent area.
The light exposure mask plate according to claim 1, which has a light transmittance of 0 to 90%. 3. An S having a resist pattern formed on its surface
An io ₂ -based substrate is etched by using a first etching gas composed of CHF ₃ or a mixed gas of CF ₄ and H ₂ , and is approximately expressed by the formula (I) mλ / {2 (n-1)} (I) ( However, m is a positive odd number, λ is the wavelength of light, and n is the refractive index of the substrate. A groove having a depth corresponding to the distance is preliminarily formed, and then 0.5 to 10 vol% is added to the first etching gas. Etching again using a second etching gas mixed with the hydrocarbon gas described in (1) above to form fine irregularities for reflecting light on the bottom surface at a depth corresponding to the formula (I) to complete the groove, and a mask for light exposure A method of manufacturing a mask plate for light exposure, which comprises manufacturing a plate.