JP2000091194A - Exposure method and reflection-type mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To align a reflection-type mask and a sample by forming a mark for alignment on a multilayer film, applying light to the mark, and utilizing light being reflected from the mark. SOLUTION: A multilayer film 2 is laminated on a substrate 1. A middle layer 3 and an absorption body 4 are successively laminated on the multilayer film 2. Then, a resist pattern is formed by using the electron beam lithography method as an etching mask, and the absorption body 4 is eliminated by dry etching. After that, a resist is eliminated by oxygen plasma ashing, the middle layer 3 being exposed is eliminated by wet etching, and a desired pattern 5 and a mark 6 for alignment are formed. Light is applied to a mark 6, and the reflection-type mask and the sample are aligned by using light being reflected from the mark 6, thus overlapping a transfer pattern using a reflection- type mask with a simple manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithography technique in a manufacturing process of a semiconductor integrated circuit or the like, and particularly to an extreme ultraviolet lithography technique using a reflection type mask.

[0002]

2. Description of the Related Art As a technique for mass-producing semiconductor integrated circuits, a lithography technique using ultraviolet light or far ultraviolet light as a light source is used. In this method, a circuit pattern formed on a transmission mask is transferred to a wafer via a projection optical system including a refractive lens. The most important performance of lithography technology is the minimum pattern size that can be transferred to the wafer,
That is, the resolution. Generally, resolution is proportional to the wavelength of exposure light and inversely proportional to the numerical aperture (NA) of the projection optical system.
For example, a 248 nm wavelength KrF excimer laser beam and N
Using a projection optical system of A0.65, a resolution of about 0.2 μm is obtained. In order to further advance the miniaturization of semiconductor integrated circuits, a lithography technique using an ArF excimer laser beam having a wavelength of 193 nm as a light source has been developed, but the practical resolution is limited to about 0.13 μm.

On the other hand, the exposure light is adjusted to 3 to 30 in the extreme ultraviolet region.
If the wavelength is shortened to nm, a resolution of 0.1 μm or less can be realized. However, since the optical constants of all the substances are extremely close to 1 in the extreme ultraviolet region, the projection optical system must be constituted by a reflecting mirror instead of a refractive lens. In recent years, high reflectivity has been obtained by using a multilayer film in which a large number of two types of thin films having different optical constants are alternately stacked. Therefore, an extreme ultraviolet lithography technique using a multilayer reflector has been developed. Since the absorption coefficient of all substances is large in the extreme ultraviolet light region, a reflection mask using a multilayer film is required instead of a transmission mask.

Incidentally, a semiconductor integrated circuit is manufactured by superimposing a large number of circuit patterns on a wafer in a predetermined positional relationship. Therefore, in order to overlap the circuit pattern formed in the previous step and the circuit pattern to be transferred from now on, the alignment between the mask and the wafer is very important. Generally, the overlay accuracy needs to be 1/3 or less of the pattern size.

A reflective mask that can be positioned is Jo.
urnal of VacuumScience an
d Technology Vol. B14 p. 41
88 (1996). FIG. 6 (a)
The structure is shown. On the substrate 61, two optical constants different from each other are set.
A multilayer film 62 formed by alternately laminating many types of thin films is formed. Since the phase of the reflected light at each interface of the multilayer film matches the exposure light in the extreme ultraviolet region, a high reflectance can be obtained. A pattern 63 made of a material having a low reflectance is formed on the multilayer film. On the other hand, the alignment mark 64 is made of the same substance as the pattern, and is formed on the substrate. At a wavelength in the visible light region, the reflectivity of the mark is higher than the reflectivity of the substrate. Therefore, the mark is irradiated with visible light, and the position of the mark is detected using the reflected light.

FIG. 6B shows the structure of a reflective mask described in Japanese Patent Laid-Open No. 5-82420. Substrate 6
5, a pattern portion 66 made of a multilayer film and an alignment mark 67 made of the multilayer film are formed. At the wavelength of the exposure light in the extreme ultraviolet region, the reflectivity of the mark is higher than the reflectivity of the substrate. Therefore, the mark is irradiated with light having the same wavelength as the exposure light, and the position of the mark is detected using the reflected light.

[0007]

In the conventional manufacturing process of the first reflective mask, the multilayer film in the area where the mark is to be formed is partially removed, and then a substance is laminated on the entire surface. Partially removed to form patterns and marks. In this case, since the multilayer film and the substance are separately removed, there is a problem that the manufacturing process is complicated. On the other hand, in the second conventional reflective mask, a mark is formed by partially removing the multilayer film. Here, if the pattern is formed by partially removing the multilayer film simultaneously with the formation of the mark, the manufacturing process is simple. However, when the originally necessary multilayer film is removed, there is a problem that it is difficult to correct the pattern. Therefore, a method of laminating a material on the multilayer film and partially removing the material to form a pattern is conceivable. However, since the pattern and the mark are formed separately, there is a problem that the manufacturing process is complicated. Was.

It is an object of the present invention to provide an exposure method capable of superimposing transfer patterns using a reflective mask whose manufacturing process is simple. The object of the present invention is
An object of the present invention is to provide a reflective mask that allows transfer patterns to be superposed and has a simple manufacturing process. Still another object of the present invention is to provide a semiconductor integrated circuit manufactured by using the above exposure method.

[0009]

In order to solve the above-mentioned problems, an exposure method according to the present invention comprises a step of irradiating an exposure light in an extreme ultraviolet region to a reflection type mask, and a step of projecting a pattern of the reflection type mask by a projection optical system. Transferring to a sample through a system, the reflective mask has a mark formed on the multilayer film, irradiates the mark with light, and uses the light reflected from the mark to form the mark. This is for positioning the reflective mask and the sample.

Further, the reflection type mask of the present invention is a reflection type mask to which exposure light in an extreme ultraviolet region is irradiated, wherein a mark for positioning is formed on the multilayer film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an exposure method comprising the steps of irradiating exposure light in the extreme ultraviolet region to a reflective mask and transferring the pattern of the reflective mask to a sample via a projection optical system. In the method, the reflective mask has a mark formed on a multilayer film, irradiating the mark with light, and performing alignment between the reflective mask and the sample using light reflected from the mark. It is characterized by.

The multilayer film is formed by alternately laminating a large number of two types of thin films having different optical constants. Since the phase of the reflected light at each interface of the multilayer film matches the exposure light, a high reflectance can be obtained. A material having a low reflectance is laminated on the multilayer film, and the material is partially removed to form a pattern and a mark at the same time. At the wavelength of the exposure light, the reflectivity of the mark is smaller than the reflectivity of the surrounding multilayer film. Therefore,
The mark is irradiated with light having the same wavelength as the exposure light, and the position of the mark can be detected using the reflected light. At a wavelength different from that of the exposure light, the reflectivity of the mark is smaller or larger than the reflectivity of the surrounding multilayer film. Therefore, it is also possible to irradiate the mark with light having a wavelength different from that of the exposure light and detect the position of the mark using the reflected light. This makes it possible to superimpose transfer patterns using a reflective mask whose manufacturing process is simple.

FIG. 1 shows a first embodiment of the structure of the reflection type mask of the present invention. The substrate 1 is a flat plate of fused quartz, and is ultra-smoothly polished to a surface roughness of 0.2 nm. The multilayer film 2 is composed of a Mo thin film having a thickness of 2.7 nm and a Mo thin film having a thickness of 4.0 nm.
And 40 thin layers alternately laminated with each other. On the multilayer film, a pattern 5 composed of the intermediate layer 3 and the absorber 4
And marks 6 for alignment. The intermediate layer is a 10 nm thick SiO ₂ thin film, and the absorber is 100 nm thick.
Is a Cr thin film. As described below, the intermediate layer has a function of protecting the multilayer film when removing the absorber.

The wavelength of the exposure light is 13 nm, and the incident angle is 5 °. In this case, the reflected light at each interface of the multilayer film reinforces each other, and a reflectance of 70% is obtained. On the other hand, the absorber is opaque and the reflectance is 0.07%. As described above, the ratio between the reflectance of the multilayer film and the reflectance of the pattern is sufficiently large to perform pattern transfer.

When the mark is irradiated with light in order to align the mask and the wafer, the contrast C of the mark is defined by the following equation, where R1 is the reflectivity of the multilayer film and R2 is the reflectivity of the mark. .

C = | R1−R2 | / (R1 + R2) (1) When light with a wavelength of 13 nm is irradiated within an incident angle range of 0 ° to 10 °, the reflectivity of the multilayer film is 70% and the reflectivity of the mark is Is 0.
Since it is 07%, a contrast of 99.8% is obtained. In addition, a wavelength of 633 nm in an incident angle range of 0 ° to 10 °.
When the He—Ne laser beam is applied, the reflectivity of the multilayer film is 39% and the reflectivity of the mark is 65%, so that a contrast of 25% can be obtained. As described above, since the reflectivity of the mark is different from the reflectivity of the surrounding multilayer film, the position of the mark can be detected with high accuracy using the reflected light.

FIG. 2 shows an embodiment of a manufacturing method for the above-mentioned reflective mask. A Mo / Si multilayer film 2 having a cycle length of 6.7 nm and a 40-layer pair was stacked on a fused quartz substrate 1 by an ion beam sputtering method. On the multilayer film, an intermediate layer 3 of a 10-nm-thick SiO ₂ thin film and an absorber 4 of a 100-nm-thick Cr thin film were sequentially laminated by magnetron sputtering (FIG. 2A). Next, a resist pattern 7 was formed by using an electron beam drawing method (FIG. 2B). Using this resist as an etching mask, the absorber 4 was removed by dry etching using a mixed gas of Cl ₂ and O ₂ (FIG. 2C). Here, since the multilayer film 2 was protected by the intermediate layer 3, no damage occurred. Thereafter, the resist 5 was removed by oxygen plasma ashing. further,
The exposed intermediate layer 3 was removed by wet etching using hydrofluoric acid to form a mark for alignment with a desired pattern (FIG. 2D).

Next, a second embodiment relating to the structure of the reflection type mask of the present invention will be described with reference to FIG. This is one in which the reflectivity of the mark is made smaller than the reflectivity of the surrounding multilayer film with respect to the He-Ne laser light having a wavelength of 633 nm. The substrate 1 is a flat plate of fused quartz, and the multilayer film 2 is a Mo / Si multilayer film having a periodic length of 6.7 nm and 40 layers. On the multilayer film, a pattern 5 composed of the intermediate layer 3, the absorber 4, and the surface layer 8 and a mark 6 for alignment are formed.
The intermediate layer is a 10 nm thick SiO ₂ thin film, and the absorber is
00 nm Cr thin film, surface layer is 78 nm thick Si ₃ N ₄
It is a thin film. At a wavelength of 13 nm of the exposure light, the transmittance of the surface layer is 28%, while the reflectance of the absorber is 0.07%.
Therefore, the ratio between the reflectivity of the multilayer film and the reflectivity of the pattern is large enough to perform pattern transfer. On the other hand, at a wavelength of 633 nm, the surface layer is transparent. Now, consider the case where the refractive index of the surface layer is n, the thickness is h, and the mark is irradiated with light of wavelength λ from vacuum at an incident angle θ. The condition that the reflected light from the interface between the vacuum and the surface layer and the reflected light from the interface between the surface layer and the absorber are weakened by the following equation. Here, m is an integer of 0 or more.

N × h = (2m + 1) × cos θ × λ / 4 (2) where n = 2.0, h = 78 nm, λ = 633 nm
Therefore, if m = 0 and θ = 0 ° to 10 °, the above expression is satisfied. In this case, the reflectivity of the mark is smaller than that in the case where light is directly irradiated from the vacuum to the absorber. Specifically, since the reflectivity of the mark is 16% and the reflectivity of the multilayer film is 39%, the contrast of the mark is 42%. Thus, for He-Ne laser light,
Since the contrast of this embodiment is larger than that of the first embodiment, the position of the mark can be detected with higher accuracy.

The above-mentioned reflective mask was mounted on the extreme ultraviolet light exposure apparatus shown in FIG. 4 to transfer a pattern. The pattern of the semiconductor integrated circuit is formed on the reflective mask, and the size of the pattern is 0.4 μm.

First, the configuration of the exposure apparatus will be described. The reflection mask 42 and the wafer 44 are respectively placed on the mask stage 4
5 and the wafer stage 46. Extreme ultraviolet light having a wavelength of 13 nm emitted from the light source 40 irradiates the reflective mask via the illumination optical system 41. The coherence factor is 0.6. The pattern formed on the reflective mask is transferred to the resist on the wafer via the projection optical system 43. The magnification of the projection optical system is 1/4, and the NA is 0.1. The projection optical system is configured to be rotated about the optical axis, and a diffraction-limited resolution of 0.07 μm can be obtained in an arc region equidistant from the optical axis. This arc region is 30 m in the longitudinal direction (circumferential direction) on the wafer.
m, 1 mm in the width direction (radial direction). Therefore, the exposure field is limited to this circular arc region, and the mask stage and the wafer stage are synchronously scanned at a speed ratio of 4: 1 to transfer the pattern on the entire surface of the reflective mask onto the wafer.

Now, marks 471 and 47 of the reflection type mask
2, mask alignment systems 481,
482 are arranged. As the shape of this mark,
A linear pattern or a cross pattern is used. A reference mark plate 49 is fixed to the wafer stage.
The reference mark plate is provided on the reference mark plate at an interval obtained by multiplying the mark interval of the reflective mask by the magnification of the projection optical system.
502 is formed. The mask alignment system is H
An e-Ne laser beam is used as a light source, and a mark on a reflective mask and a reference mark are simultaneously detected. Here, although the He-Ne laser beam passes through the projection optical system, no chromatic aberration occurs because the projection optical system is constituted only by the reflecting mirror. On the other hand, an off-axis wafer alignment system 51 is arranged near the projection optical system. The wafer alignment system uses a He-Ne laser beam as a light source to detect a mark on the wafer.

The alignment between the reflective mask and the wafer is performed as follows.
Proceed as follows. First, the mask alignment system 481 measures the amount of positional deviation between the mark 471 of the reflective mask and the reference mark 501, and the mask alignment system 482 measures the amount of positional deviation between the mark 472 of the reflective mask and the reference mark 502. Thus, the position of the pattern of the reflective mask in the coordinate system of the wafer stage is obtained. Next, the distance between the center of the exposure field of the projection optical system and the center of the detection area of the wafer alignment system, that is, the baseline amount is measured. Then, the position of the mark on the wafer is measured by the wafer alignment system. Based on these measurement results, the relative position between the pattern of the reflective mask and the pattern of the wafer is obtained, and the wafer stage is driven to complete the alignment. By this exposure method, 3
In the area of 0 × 30 mm, a pattern having a size of 0.1 μm was transferred with an overlay accuracy of 25 nm.

In the present embodiment, the mark of the reflective mask is irradiated with the He-Ne laser light, but the light of the same wavelength as the broadband light or the exposure light from the halogen lamp may be irradiated. Furthermore, besides the above-mentioned off-axis method,
A so-called TTL method or TTR method can also be used.

Next, an example of manufacturing a semiconductor integrated circuit using the exposure method of the present invention will be described with reference to FIG. A field oxide film 76 was formed on a p-type substrate 77 by an ordinary method, and an oxide film 75 and a polycrystalline silicon film 74 were formed thereon. After that, by resist coating, exposure using the aforementioned reflective mask and extreme ultraviolet light exposure device, and development processing,
Resist patterns 731 and 732 were formed (FIG. 5).
a). Using the resist pattern as a mask, oxide film 7
5. The polycrystalline silicon film 74 was processed by dry etching, the resist was removed, and polycrystalline Si / SiO ₂ gates 781 and 782 were formed (FIG. 5B). Thereafter, high concentration n + layers 791, 792, 793 were formed by ion implantation (FIG. 5c). FIG. 5D is a plan view of the formed gate, and the gate could be formed with high overlay accuracy. Thereafter, a semiconductor integrated circuit having good electric characteristics was manufactured through a normal electrode forming step and a wiring step.

It should be noted that the present invention is not limited to the above-described embodiment, and the material of the multilayer film may be Cr, Ni, M
Heavy elements such as o, Ru, Rh, W, and Re and their compounds may be combined with light elements such as Be, B, C, and Si and their compounds. Al, C
You may use r, Ni, Ta, W, etc. and its compound. The material of the surface layer is SiO ₂ , Al ₂ O ₃ , Ti
O ₂ , Ta ₂ O ₅ or the like may be used. Since Al ₂ O ₃ and Ta ₂ O ₅ are opaque in the extreme ultraviolet region, they can be used as absorbers. In addition, as a gas for dry etching in manufacturing a mask, a suitable fluorine-based or chlorine-based gas can be used. Further, it goes without saying that the wavelength of the exposure light is not limited to 13 nm, but can be applied to any wavelength in the extreme ultraviolet light range of 3 to 30 nm.

[0027]

As described in detail above, in the lithography technique using extreme ultraviolet light as a light source, transfer patterns can be superposed using a reflective mask whose manufacturing process is simple.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment of the structure of a reflective mask according to the present invention.

FIG. 2 is a view for explaining an embodiment relating to a method of manufacturing a reflection type mask of the present invention.

FIG. 3 is a view for explaining a second embodiment relating to the structure of the reflection type mask of the present invention.

FIG. 4 is a diagram illustrating a configuration of an extreme ultraviolet light exposure apparatus.

FIG. 5 is a view for explaining an embodiment relating to the manufacture of a semiconductor integrated circuit using the exposure method of the present invention.

FIG. 6 is a diagram illustrating the structure of a conventional reflective mask.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Multilayer film, 3 ... Intermediate layer, 4 ... Absorber, 5 ...
Pattern, 6 ... mark.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiromasa Yamanashi 1-280 Higashi-Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. F-term in Hitachi Central Research Laboratory (reference) 5F046 AA25 BA05 CA04 CA08 CB02 CB17 CB25 CC01 CC02 EA02 EA03 EB02 EB03 FA03 FA20

Claims (9)

[Claims] 1. An exposure method comprising: irradiating exposure light in an extreme ultraviolet region onto a reflective mask; and transferring a pattern of the reflective mask to a sample via a projection optical system. The mask has marks formed on the multilayer film,
An exposure method, comprising irradiating the mark with light and performing alignment between the reflective mask and the sample using light reflected from the mark. 2. An exposure method according to claim 1, wherein said reflective mask has a pattern formed on said multilayer film, and said pattern material and said mark material are the same. . 3. The exposure method according to claim 1, wherein the mark is formed by laminating at least two kinds of substances, and a surface layer of the mark is transparent at at least one wavelength of light for irradiating the mark. An exposure method, comprising: 4. The exposure method according to claim 3, wherein the wavelength of light for irradiating the mark is λ, the incident angle is θ, the refractive index of the surface layer of the mark is n, the thickness is h, and m is 0 or more. Where n × h = (2m + 1) × cos θ × λ / 4. 5. A reflective mask irradiated with exposure light in an extreme ultraviolet region, wherein a mark for positioning is formed on a multilayer film. 6. A reflective mask according to claim 5, wherein a pattern is formed on said multilayer film, and a material of said pattern and a material of said mark are the same. 7. The reflection type mask according to claim 5, wherein said mark is formed by laminating at least two kinds of substances.
A reflective mask, wherein a surface layer of the mark is transparent at at least one wavelength in the range of 400 nm to 800 nm. 8. A method of manufacturing a reflection type mask to be irradiated with exposure light in an extreme ultraviolet region, wherein at least a step of laminating a substance on the multilayer film, the step of removing the substance and aligning the pattern with a pattern are performed. Forming a mark. 9. A semiconductor integrated circuit manufactured by the exposure method according to claim 1. Description: