JPH0723959B2 - Pattern transfer mask and method of use - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithographic technique for transferring a highly accurate pattern such as a semiconductor integrated circuit pattern, and particularly to a pattern capable of highly accurately aligning a wafer and a mask. It relates to transfer masks and can be applied to various lithographic techniques such as photolithography, X-ray lithography, and electron beam lithography.

[Background of the Invention]

A conventional method for aligning a wafer and a transfer mask in pattern transfer is described in, for example, Precision Machinery, Vol. 46, No. 8,
As described in pages 1003 to 8 (1983) (see FIG. 2), the position detecting marks 5 and 6 formed on the wafer 4 are irradiated with light 9 and the reflected light is detected.
In this case, the reflected light is as shown in FIG. Here, 5'or 5 "is the intensity of light reflected by the mark 5,
Reference numeral 6'denotes the intensity of the reflected light which is reduced by scattering the reflected light by the mark 6 having a rough surface, and 11 'shows the absorber 2 on the mask.
And C is the slice level of the reflected light intensity 5'or 5 "of the mark 5. When the reflected light from the mark 5 is 5 ', it can be detected correctly, but according to the process. The reflected light from the mark 5 may be reduced to a slice level C or lower as in 5 ″, which makes alignment impossible. At this time, even if the amplification degree of the detection circuit is increased, the ratio of 5 ″ and 6 ′ is small, and stable alignment is impossible. Further, in this method, the actually measured reflected light intensity 11 ′ 2 has an asymmetrical shape as shown in FIG. 2C due to aberrations of the illumination optical system and the detection optical system. When the slice level is changed from C to C ', the mask position shifts by δ. In addition, a wafer process step for forming the mark 6 having a rough surface is required, which causes an increase in cost.If the reflectance of the mark 6 is high, the intensity of reflected light as in the aluminum layer forming step is increased. When the intensity is strong, the reflected light intensity 6'becomes the same level as the reflected light intensity 11 'by the absorber, and it becomes difficult to detect the position.

Such a thing is well known especially in the manufacturing process of the semiconductor integrated device using the X-ray lithography technique.

[Object of the Invention]

An object of the present invention is to provide a pattern transfer mask that facilitates alignment when transferring a large number of patterns to one pattern transfer material.

[Outline of Invention]

The present inventor has found that stable alignment can be achieved by reducing the light reflected by the absorber 2 formed on the substrate 1. For example, as shown in FIG. 1, a transfer mask is provided with a thin film 3 between a substrate 1 and a radiation absorber 2,
The inventor has invented a novel mask that greatly reduces the light 11 reflected by the absorber 2 and a position detection method using the same. That is, for example, when the refractive index of the substrate 1 and the thin film 3 are substantially equal to each other, and the refractive index is n and the sum of the thicknesses of the substrate 1 and the thin film 3 is d, the intensity I of the reflected light 11 is the wavelength of the detection light 9. λ, the refractive index of the absorber 2 with respect to the wavelength is ng, and the refractive index of the atmosphere is no. When the detection light 9 is vertically incident, However Becomes Therefore, if the sum of the thicknesses of the substrate 1 and the thin film 3 is d / 2 [lambda] / 2n or an odd multiple thereof, I can be reduced.

Further, when the mark 8 formed on the wafer is formed to have a step or a boundary with the wafer surface, for example, the step 18 can provide a sharp position signal such as 18 'in FIG. 1 (b). Found. In this case, since the reflected light intensity 11 'by the absorber is extremely small, the position signal 18'
Can be detected with high accuracy and easily.

Even if the thin film 3 is not provided, the thickness d'of the substrate 1 (N 'is the refractive index for the wavelength λ of the substrate), the reflected light 11' is reduced.

The gist of the present invention lies in the following two points.

(1) An absorber that absorbs the irradiation light is provided on a part of the surface of the first film that transmits the irradiation light, and the first film is
A pattern transfer mask having a film thickness that reduces the intensity of reflected light from the absorber of the irradiation light that has passed through the first film and entered the absorber.

(2) (a) An absorber that absorbs the irradiation light is provided on a part of the surface of the first film that transmits the irradiation light, and the first film passes through the first film. A pattern transfer mask having a film thickness that reduces the intensity of the reflected light from the absorber of the irradiation light incident on the absorber is prepared near the pattern transfer object having a position detection mark on the surface thereof. And (b) irradiating the pattern transfer material with the irradiation light through the pattern transfer mask and detecting reflected light of the irradiation light from the pattern transfer mask and the pattern transfer object, A pattern transfer mask, which comprises a step of detecting a relative position between the pattern transfer object and the pattern transfer mask by a reflected light signal from the absorber and a reflected light signal from the position detection mark. How to use.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 3 is a sectional view of a transfer mask according to the present invention.
The mask 20 comprises a support 25, a thin film substrate 1 having a high X-ray transmittance, a thin film 3 for preventing reflection, and an X-ray absorber 2. As the thin film 3, chrome oxide was used.

A method of aligning the wafer and the mask using this transfer mask will be described with reference to FIG.

FIG. 4 shows a detection optical system by the epi-illumination method. The irradiation light from the light source 23 irradiates the X-ray mask 20 and the semiconductor wafer 4 through the beam splitter 7 and the objective lens 15.
Then, the reflected light from the wafer 4 and the mask 20 is detected by the detector.
The light intensity is detected by 10 as shown in FIG. 4 (b).

The reflected light intensity 16 from the semiconductor substrate 4 is extremely brighter than the reflected light intensity 11 'from the alignment absorber 2 formed on the transfer mask 20. Further, since the signal 18 'due to the mark 8 on the wafer 4 also appears clearly, the relative position between the mask 20 and the wafer 4 can be easily detected. That is, from the reflected light intensities 16 and 11 ', the position of the mask 20
The position of the wafer 4 can be detected from 18 '. According to this method, as the semiconductor process progresses, even if the reflectance from the semiconductor substrate is reduced, the reflected light intensity is 11 '
By increasing the gain of detector 10 as long as 16 is large,
It is possible to obtain a clear position signal as shown in FIG.
Therefore, even when the reflected light 16 of the semiconductor substrate is large as in the aluminum layer forming step, a correct position signal can be obtained.

A similar effect was obtained even when the pattern formed by the absorber 2 was a so-called Fresnel zone target pattern.

In addition, although it is not always necessary to make the detection light incident perpendicularly on the transfer mask surface, it goes without saying that the above-mentioned mathematical formulas and conditions are different in that case.

Further, the thin film 3 need not be provided on the entire surface of the mask, and may be provided only between the absorber 2 and the substrate 1.

According to the present embodiment, the positions of the X-ray mask and the semiconductor wafer can be accurately detected regardless of the reflectance of the semiconductor substrate, which has an effect of improving the yield in manufacturing semiconductor devices.

〔The invention's effect〕

According to the present invention, since the intensity of the reflected light from the absorber can be reduced, the reflected light from the pattern-transferred object of the irradiation light applied to the pattern-transferred object through the mask can be accurately detected. For example, if the present invention is used when there is a registration mark or the like on the pattern transfer material, the mark position can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a positional relationship between a transfer mask according to the present invention, a wafer, and reflected light intensity, FIG. 2 is a view for explaining a conventional technique, FIG. 3 is a sectional view of a transfer mask of an embodiment, and FIG. 4 is a diagram used for explaining the embodiment. 1 ... Mask substrate, 2 ... Mask absorber, 3 ... Antireflection thin film, 4 ... Transferred object (wafer, etc.), 5, 6, 8 ...
Marks on wafer surface, 5 ', 5 ", 6', 8 '... Reflected light signal of wafer mark, 7 ... Beam splitter, 9 ... Position detection light, 10 ... Detector, 14 ... Absorber Light reflected by, 15
...... Support, 4 ', 16 ...... Reflected light intensity on wafer surface, 18 ...
… Steps or boundaries of marks on wafer, 18 ′ …… Wafer position signal, 20 …… Transfer mask.

Claims (5)

[Claims] 1. An absorber that absorbs the irradiation light is provided on a part of the surface of the first film that transmits the irradiation light, and the first film passes through the first film and is A pattern transfer mask having a film thickness that reduces the intensity of the reflected light from the absorber of the irradiation light incident on the absorber. 2. The film thickness d of the first film is (Λ: wavelength of the irradiation light, m: natural number, n: refractive index of the first film with respect to the wavelength of the irradiation light), wherein the mask for pattern transfer according to claim 1. . 3. A second film which transmits the irradiation light is provided between the first film and the absorber, and a sum of film thicknesses of the first film and the second film is , A thickness that reduces the intensity of reflected light from the absorber of the irradiation light that has passed through the first film and the second film and is incident on the absorber. The pattern transfer mask according to claim 1. 4. The index of refraction of the first film and the index of refraction of the second film are substantially equal, and the sum d'of the film thicknesses of the first film and the second film is (Λ: wavelength of the irradiation light, m: natural number, n: refractive index of the first film and the second film with respect to the wavelength of the irradiation light). The described pattern transfer mask. 5. A method of using a pattern transfer mask, which comprises the following steps. (A) An absorber that absorbs the irradiation light is provided on a part of the surface of the first film that transmits the irradiation light, and the first film is
A pattern transfer mask having a film thickness that reduces the intensity of reflected light from the absorber of the irradiation light that has passed through the first film and entered the absorber is provided with a position detection mark on its surface. A step of preparing in the vicinity of the pattern transfer material. (B) the absorber is irradiated with the irradiation light through the pattern transfer mask and the reflected light of the irradiation light from the pattern transfer mask and the pattern transfer is detected, Detecting the relative position of the pattern transfer object and the pattern transfer mask by the reflected light signal from the position detection mark and the reflected light signal from the position detection mark.