JPH09289148A - Mask for x-ray exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lighten the influence of multireflection and perform highly accurate alignment by providing an opaque film region which prevents the penetration of an alignment beam, being provided on a reflection preventive film region which transmits an alignment light and besides does not reflect an alignment light. SOLUTION: An opaque film region 20 is made on a reflection preventive film in the region where a mask mark 4 is provided. A difference in level is adjusted in advance so that the luminous intensity of a diffracted light 10 may be maximum or optimum. Then, applying an incident light 9 to the mask mark 4 will let one part of the incident light transmit the mask mark 4 being a diffractive grating and diffract. Then, it is reflected on the face of a semiconductor wafer 6, and it transmits again an X-ray transmitting board 1, and become diffracted lights 21 and 22. The diffracted lights 21 and 22 are both attenuated for their luminous intensity by the opaque film region 20, so they hardly contribute to the interference with the diffracted light 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray exposure mask for forming a highly precise fine pattern used when manufacturing a semiconductor IC, LSI or the like by X-ray exposure.

[0002]

2. Description of the Related Art With the high integration of semiconductor ICs and LSI patterns, it is indispensable to advance the technology for forming fine patterns with high precision on a wafer. Various exposure methods such as an X-ray exposure method, an electron beam exposure method, and an ultraviolet exposure method have been used as conventional techniques for forming a fine pattern. Among these exposure methods, the X-ray exposure method is a highly precise fine pattern. Is considered to be advantageous for the formation of

In the X-ray exposure method, photo-Auger electrons generated by irradiating an X-ray-sensitive polymer with X-rays are bonded to the polymer,
This is an exposure method that induces cleavage and utilizes the change in the dissolution rate of a polymer in a solvent in an X-ray-irradiated portion and an unirradiated portion. As described above, the X-ray exposure method is very useful for the formation of high-precision fine patterns because of the use of X-rays with excellent straightness and the small interaction range of the energy of photo-Auger electrons on the polymer. It is one of the excellent exposure methods.
The conventional X-ray exposure method will be described below.

FIG. 4 is a sectional view showing the structure of a conventional X-ray exposure mask. In the figure, 1 is an X-ray transparent substrate that is a thin film formed of a substance having a small X-ray transmission attenuation amount, 2 is a support column that supports the X-ray transparent substrate 1, and 3 is an X-ray transparent substrate 1.
An X-ray absorption layer formed of a substance that does not transmit X-rays and forms a semiconductor integrated circuit pattern, and 4 is a mask mark that is a diffraction grating that is formed by the X-ray absorption layer 3 and is provided around the semiconductor integrated circuit pattern. Reference numeral 5 denotes an alignment transmission window which is a part of the X-ray transmission substrate 1 and transmits the alignment light.

Since the alignment light near the visible light region such as the semiconductor laser light and the He-Ne laser light is transmitted through the alignment transmission window 5 at the time of alignment, the X-ray transmission substrate 1 is made of only X-rays. Instead, it is necessary to use a material having a small transmission attenuation for these rays.
For example, when using X-rays having a wavelength of 4 to 15Å, the materials are Al ₂ O ₃ , Si, Si ₃ N ₄ , SiC,
SiO _{2 and the} like are suitable.

Further, the reinforcing column 2 needs to keep the X-ray transparent substrate 1 flat and maintain mechanical strength in order to facilitate the handling of the X-ray transparent substrate 1. The material is Si or SiO _2.
Etc. are used. Furthermore, the X-ray absorption layer 3 is a thin film, and it is necessary to increase the transmission attenuation of X-rays.
Heavy metals such as Ta, Au and Pt are used as the material.

FIG. 5 is an explanatory view showing how the X-ray exposure mask according to FIG. 4 is aligned.
No. 826 is disclosed. In the figure, the same reference numerals as those in FIG. 4 indicate the same parts, 6 is a semiconductor wafer, 7 is a wafer mark which is a step of a substrate formed on the semiconductor wafer 6, and 8 and 9 are incident light by alignment light.
Reference numerals 10 and 11 denote diffracted lights of incident lights 8 and 9, and 12 denotes an X-ray photosensitive polymer film (X-ray resist) formed on the semiconductor wafer 6.

The pattern thus formed by the X-ray absorbing layer 3 is transferred to the X-ray photosensitive polymer film 12 by irradiating it with X-rays. After that, the ion etching method,
A semiconductor integrated circuit pattern is formed by using a plating method or the like.
The resolution of the transferred pattern depends on the distance between the semiconductor wafer 6 and the X-ray transparent substrate 1 (hereinafter referred to as the gap),
It is greatly affected by the accuracy of alignment (hereinafter referred to as alignment) between the semiconductor wafer 6 and the X-ray transparent substrate 1. For example, in order to form a fine pattern of 0.1 to 0.3 μm, it is necessary to set the gap to 10 to 30 μm.

Although there are several types of alignment, the optical heterodyne interferometry method using a diffraction grating as an alignment mark is known to be capable of highly accurate alignment. This method is applied to the semiconductor wafer 6
The amount of positional deviation between the X-ray transmission substrate 1 and the X-ray transmission substrate 1 is detected from the phase difference of the beat signal of the diffracted light that has undergone optical heterodyne interference. Specifically, both the mask mark 4 which is a diffraction grating formed on the X-ray transparent substrate 1 and the wafer mark 7 which is a diffraction grating formed on the semiconductor wafer 6 are provided with lasers of two kinds of wavelengths. Lights 8 and 9 (incident light) are emitted. Then, the diffracted light 10 generated by the incident lights 8 and 9,
11 is photoelectrically converted to obtain a beat signal, the phase difference between them is detected, and alignment is performed.

By the way, since the gap between the semiconductor wafer 6 and the X-ray transparent substrate 1 is only several tens of μm as described above,
Multiple reflections due to alignment light may occur during alignment. FIG. 6 is an explanatory diagram showing multiple reflection in the X-ray exposure mask according to FIG. 9A shows the multiple reflection caused by the incident light 9 applied to the mask mark 4, and FIG. 9B shows the incident light 9 applied to the wafer mark 7.
13 shows multiple reflections caused by, and 13 to 16 are unnecessary diffracted lights caused by the multiple reflections.

Undesired diffracted light due to these multiple reflections is generated in accordance with a minute change in the gap, and the intensity changes with a gap change of λ / 2 (λ: wavelength of alignment light) as one cycle. As a result, this intensity fluctuation appears as an amplitude fluctuation of the beat signal, destabilizing the phase difference detection signal,
It has a drawback that the alignment accuracy is deteriorated.

[0012]

As described above, since the conventional X-ray exposure mask produces a highly precise fine pattern,
The semiconductor wafer is arranged at a position very close to the gap of several tens of μm. Therefore, multiple reflection causes unnecessary diffracted light to interfere with the diffracted light originally used for alignment, and the amplitude of the detected beat signal fluctuates, resulting in deterioration of alignment accuracy. There was a point. The present invention is intended to solve such a problem, and an object of the present invention is to provide an X-ray exposure mask capable of reducing the influence of multiple reflection and performing highly accurate alignment.

[0013]

In order to achieve such an object, an X-ray exposure mask according to the present invention is provided on a mask alignment mark to transmit alignment light and not reflect alignment light. An antireflection film region and an opaque film region which is provided on the antireflection film region and prevents transmission of alignment light are provided. With this configuration, the present invention can prevent multiple reflection due to alignment light.

[0014]

Next, details of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 denote the same parts.

Reference numeral 19 denotes an antireflection film region made of a material having a high alignment light transmittance and a small amount of alignment light reflection. Then, the antireflection film region 19 is
It is composed of a single layer made of a single substance or a plurality of layers made of different substances, and is formed on the mask mark 4 and the alignment transmission window 5.

Reference numeral 20 is an opaque film region made of a substance which is difficult to transmit alignment light. The opaque film region 20 is composed of a single layer made of a single substance or a plurality of layers made of different substances, and is formed on the antireflection film region 5 in the region where the mask mark 4 is provided. Has been done.

FIG. 2A is an explanatory view showing multiple reflection caused by the incident light 9 applied to the mask mark 4, and FIG. 2B is an explanatory diagram showing multiple reflection caused by the incident light 9 applied to the wafer mark 7. Is. In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same or equivalent components, and 21 to 24 are unnecessary diffracted light generated by the multiple reflection of the incident light 9, and d1 is the step of the antireflection film region 19.

Regarding the operation of the present invention having the above configuration,
The mask mark 4 and the wafer mark 7 will be described in detail. First, in FIG. 2A, the step d1 is adjusted in advance so that the light intensity of the diffracted light 10 is maximum or optimal. When the mask mark 4 is irradiated with the incident light 9, a part of the incident light 9 is transmitted and diffracted through the mask mark 4 which is a diffraction grating and is reflected on the surface of the semiconductor wafer 6,
The light is again transmitted through the X-ray transparent substrate 1 to become diffracted lights 21 and 22. Since the diffracted lights 21 and 22 are attenuated in light intensity by the opaque film region 20, they hardly contribute to the interference with the diffracted light 10.

Next, in FIG. 2B, the incident light 9 irradiated on the alignment transmission window 5 is transmitted to the wafer mark 7 on the semiconductor wafer 6 through the X-ray transmission substrate 1 and the antireflection film region 19. Is irradiated. A part of the incident light 9 is reflected and diffracted by the wafer mark 7, and then the X-ray transparent substrate 1
Is reflected by the semiconductor wafer 6 to become diffracted light 23, 24. Since the diffracted lights 23 and 24 pass through the alignment transmission window 5 without being reflected, they hardly contribute to the interference with the diffracted light 11.

The antireflection film region 19 may be provided on both sides of the alignment transmission window 5, and the entire surface of the X-ray transmission substrate 1 (one side, or, as long as it does not interfere with the transmission of X-rays).
It may be provided on both sides. The transmittance of the alignment light in the alignment transmission window 5 is at least 70 to 80%.
It is enough if there is. The same material as the X-ray absorption layer 3 may be used for the opaque film region 20. The antireflection film region 19 and the opaque film region 20 can be formed using a technique such as a resist process, a process layer deposition process, an etching process, a lift-off process, etc. used in a semiconductor manufacturing process.

FIG. 3 is an explanatory view showing another embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same or equivalent components, 5a is a transmission window for alignment whose thickness is adjusted to d2, and 23 to 24 are unnecessary diffracted light by the incident light 9. Now, the transmittance in the alignment transmission window 5 is determined by the wavelength of incident light, the film thickness of the alignment transmission window 5, X
It is determined by the refractive index and the like of the linear transmission substrate 1. Therefore, as shown in the same figure, the thickness d2 of the alignment transmission window 5a is
By adjusting, the transmittance of the incident light 9 can be optimized. That is, instead of FIG.
Can be used in combination with FIG. If the antireflection film region 19 is further provided on the alignment transmission window 5a on one side or both sides, multiple reflection can be prevented more effectively.

[0022]

As described above, according to the present invention, by providing the antireflection film region and the opaque film region, the alignment light is multiply reflected between the X-ray exposure mask and the semiconductor wafer, and unnecessary diffraction occurs. It is possible to prevent the generation of light, stabilize the phase difference signal, and realize highly accurate alignment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of an X-ray exposure mask according to the present invention.

FIG. 2 is an explanatory diagram showing multiple reflection by the X-ray exposure method according to FIG.

FIG. 3 is a sectional view showing another embodiment of an X-ray exposure mask according to the present invention.

FIG. 4 is a sectional view showing the structure of a conventional X-ray exposure mask.

5 is an explanatory diagram showing an X-ray exposure method according to FIG.

6 is an explanatory diagram of multiple reflection by the X-ray exposure method according to FIG.

[Explanation of symbols]

1 ... X-ray transparent substrate, 2 ... Reinforcing columns, 3 ... X-ray absorbing layer, 4
... mask mark, 5 ... alignment transmission window, 6 ... semiconductor wafer, 7 ... wafer mark, 8, 9 ... incident light, 10,
11 ... Diffracted light, 12 ... X-ray photosensitive polymer film (X-ray resist), 13-16, 21-24 ... Unnecessary diffracted light, 19 ...
Antireflection film region, 20 ... Opaque film region.

Claims (7)

[Claims] 1. An X-ray exposure mask comprising: an X-ray transparent substrate that transmits X-rays; and a mask alignment mark formed on the X-ray transparent substrate and comprising an X-ray absorbing layer. In the above, an anti-reflection film region is provided on the mask alignment mark to transmit the alignment light and does not reflect the alignment light, and an opaque film region provided on the anti-reflection film region to prevent the transmission of the alignment light. X characterized by
Line exposure mask. 2. The X-ray exposure mask according to claim 1, wherein the mask alignment mark is a diffraction grating formed by a substrate step on an X-ray transparent substrate. 3. The mask for X-ray exposure according to claim 1, further comprising: a transmission window for alignment in a predetermined region which transmits alignment light, at a predetermined position of the X-ray transmission substrate. 4. The mask for X-ray exposure according to claim 3, wherein the thickness of the alignment transmission window is adjusted according to the transmittance of alignment light. 5. An X-ray exposure mask according to claim 1, wherein the antireflection film region is provided on either one side or both sides of the alignment transmission window. . 6. The opaque film region according to claim 1, wherein the opaque film region is formed by one of a single layer made of a substance that does not transmit alignment light and a plurality of layers. X-ray exposure mask. 7. The antireflection film region according to claim 1, wherein the antireflection film region is a single layer or a plurality of layers made of a substance that transmits X-rays and alignment light but does not reflect alignment light. An X-ray exposure mask, which is formed by either one of them.