JP3042728B2 - X-ray mask and X-ray exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray
The present invention relates to a line mask and an X-ray exposure method.

[0002]

2. Description of the Related Art Generally, an X-ray mask used for X-ray exposure is formed by forming an X-ray absorber pattern composed of an absorber layer for absorbing X-rays on a membrane film which transmits X-rays well. I have. In 1: 1 close proximity X-ray exposure using the present X-ray mask, the thickness of the absorber layer is determined by the mask contrast (X-ray transmittance of the portion without the absorber pattern / X-ray transmission of the absorber pattern portion). Rate), its thickness is an important factor influencing the exposure characteristics. The mask contrast is expressed as 1 / exp (−μm), where t (nm) is the thickness of the absorber layer and μ (1 / nm) is the linear absorption coefficient for the irradiated X-ray.
t). Conventionally, the higher the contrast,
It was thought that the exposure characteristics such as the resolution of the X-ray exposure, the dimensional control of the transfer pattern, and the exposure margin would be improved. Therefore, the absorber layer should be formed as thick as possible within the range where the absorber pattern can be formed. It had been. In this case, the contrast is generally 7 to 10 as a criterion. For example, when tantalum (Ta) is used as the absorber material,
The contrast is about 7 with respect to the synchrotron radiation having a thickness of 0.65 μm and a center wavelength of 0.8 nm, and the thickness of the absorber layer should be 0.65 μm or more so as to secure this contrast at least. Was created. However, the criterion for this contrast is derived based on a large pattern in which the planar size of the absorber pattern is 1 μm or more, and the influence of X-ray diffraction and mutual interference, which becomes remarkable in close exposure of a fine pattern, is determined. The accompanying change in the effective exposure contrast was not taken into account.

[0003]

In the conventional X-ray exposure using a high-contrast X-ray mask, even if the proximity gap (distance between the mask and the wafer) is 30 μm or more, the planar size is 0.3 μm or more. The transfer pattern was successfully transferred. However, for patterns smaller than 0.3 μm, the resolution deteriorates rapidly due to the influence of X-ray diffraction and interference, and there is a problem that pattern transfer of 0.2 μm or less is particularly difficult. For this reason, in order to transfer a pattern of 0.2 μm or less using a conventional X-ray mask, it was necessary to reduce the proximity gap to about 10 μm, which is impractical.

An object of the present invention is to provide an X-ray mask and an X-ray exposure method which have a high effective exposure contrast in a large proximity gap of 20 μm or more for a pattern having a size of 0.3 μm or less, and as a result, a high resolution. Is to provide.

[0005]

According to the present invention, 0.3 μm
In order to reversely utilize the influence of X-ray diffraction and mutual interference in the proximity exposure of the following fine pattern, irradiation X
Controlling the line phase shift change amount {360 (1-n) t / λ} and mask contrast {1 / exp (-μt)} by the thickness t of the absorber layer to increase the effective exposure contrast. It is characterized by.

[0006]

According to the present invention, the proximity gap is 2
Since the effective exposure contrast for a pattern of 0.3 μm or less can be increased even under a large condition of 0 μm or more, the resolution characteristics obtained by X-ray exposure using this mask are different from those of a conventional X-ray mask. It is better. In particular,
Patterns of 0.2 μm or less can be easily resolved. In addition, since the thickness of the absorber layer can be made thinner than before, an X-ray mask and an X-ray exposure method which can be easily processed even with a fine pattern and have high processing accuracy can be obtained.

[0007]

EXAMPLES The present invention will be described more specifically with reference to the following examples. Embodiment 1 FIG. 1 is a diagram showing a first embodiment according to the present invention. FIG.
In the figure, reference numeral 1 denotes an absorber layer, 2 denotes a membrane, 3 denotes an X-ray mask having these as basic components, and an absorber pattern 4 is formed on this mask. 4 is the line width L
_This is a line-and-space absorber pattern in which the line pattern _4a is repeated at a constant interval _L4b . Here, a cross-sectional view is shown. The absorber layer 1 was made of tantalum (Ta), and the membrane 2 was made of 2 μm silicon nitride (SiN). The size L _4a of the absorber pattern 4 is 0.15 μm, and its space width L _4b is also 0.15 μm. The thickness t ₄ of the absorber layer 1 corresponding to the absorber pattern 4 is a phase change amount | 36 with respect to synchrotron radiation having a peak wavelength of 0.8 nm.
0 (1-n) t / λ | is 83 degrees, mask contrast 1
/ Exp (-μt) 0.3μ so that becomes 2.45
m. At this time, the refractive index n of tantalum is 0.1.
99939, linear absorption coefficient μ is 0.00298711 / nm
It is.

In preparing the present X-ray mask, first,
2 μm thick silicon nitride film on both sides of silicon substrate by CVD
After forming to a film thickness, tantalum is
μm, and subsequently silicon dioxide (Si
O ₂ ) was formed by ECR to a thickness of 0.2 μm. An EB resist is applied to the substrate, and an absorber pattern 4 is applied by EB exposure.
Exposure was performed to leave only the upper resist. Using this resist pattern as an etching mask, silicon dioxide is
Etched with E. Further, tantalum was etched by RIE using silicon dioxide as an etching mask. Finally, the silicon substrate was removed from the back side of the substrate by wet etching using the silicon nitride film as an etching mask. In this mask manufacturing process, the absorber pattern 4
Since the thickness of tantalum at the time of formation of the thin film is as thin as 0.3 μm, the etching characteristics are good, and the conventional problems such as pattern collapse and non-uniformity at the pattern edge are eliminated.
Although the pattern size was small, the pattern shape and the dimensional accuracy were formed well.

Using the present X-ray mask 3, pattern transfer was performed with an X-ray exposure apparatus utilizing synchrotron radiation having a peak wavelength of 0.8 nm. The gap between the mask and the wafer was controlled at 30 μm. As an exposure resist, F
BM-G (positive resist) was applied at 1 μm. When this mask is used, the variation range of the exposure amount capable of transferring the absorber pattern 4 of 0.15 μm onto the resist pattern is 80 to 110.
A large value of mJ / cm ² was obtained.

On the other hand, when a conventional mask is used, 3
Under the exposure condition with a gap of 0 μm, it was impossible to transfer the absorber pattern 4 to the resist pattern.

The reason why the transfer characteristics are improved when the present X-ray mask is used as described above will be described below. FIG. 2 shows a general example of a transmitted X-ray intensity distribution transmitted through an X-ray mask in X-ray exposure. The X-ray intensity when there is no mask absorber pattern is set to 1. X-ray 30μ transmitted through membrane
Diffraction occurs according to the gap of m. Further, the X-rays transmitted through the absorber layer have a phase change of {360 (1-n) t / λ} at the same time as the intensity attenuation {1-exp (-μt)} times. Furthermore, these X-rays interfere with each other. The range of the diffraction and the interference depends on the wavelength and the gap of the X-ray. In the case of the X-ray wavelength and the gap in the present embodiment, the range in which the influence is most significant is 0.2 at most from the pattern edge.
μm. Therefore, the effect of X-ray diffraction and mutual interference increases as the pattern size decreases, and the transmitted X-ray intensity distribution changes. In some cases, an intensity reversal phenomenon as shown in FIGS. 2A and 2B occurs, and a resist pattern faithful to the mask pattern cannot be obtained. However, if the amount of phase change and the amount of attenuation (mask contrast and dependence) are selected to optimal values as in the present invention, the effects of diffraction and interference can be reversed, and X-rays faithful to the mask pattern can be used. An intensity distribution is obtained. As a result, 0.
Even with a fine pattern of 3 μm or less, the effective exposure contrast can be improved. As shown in FIG. 2C, when the range in which the X-ray intensity distribution faithful to the mask pattern is obtained is defined as the exposure amount margin C, the minimum of the X-ray intensity at the position (a) where the reversal phenomenon occurs is obtained. When the value is a and the maximum value of the X-ray intensity at the position (b) is b, i) a is 1
When smaller than C = a / b, ii) When a is larger than 1, c = 1 / b.

FIGS. 3A and 3B show the relationship between the exposure amount margin and the mask contrast and the phase change amount.
(A) shows the results when the proximity gap is 30 μm, and (b) shows the results when the proximity gap is 20 μm. In these figures,
,,, And are the cases where the line width and the space width of the line pattern are 0.2 μm, 0.15 μm, and 0.1 μm, respectively. As is clear from these results, the exposure amount margin is about 2.5 for mask contrast and about 8 for phase change.
It has a maximum value at 0 degree, a mask contrast of 1 to 4 and a phase change amount of 30 to 120 degrees are extremely high as compared with other conditions. Therefore, if the thickness of the absorber layer is controlled so as to satisfy this condition, even when the proximity gap is as large as 20 to 30 μm, the thickness is 0.1 to 0.2 μm.
Thus, a fine pattern of m can be satisfactorily transferred. When the absorber layer is tantalum, the film thickness satisfying this condition is 75 to 450 nm.

In this embodiment, an example was described in which the material of the absorber layer was tantalum. However, if the conditions of the phase change amount and the mask contrast in the absorber layer satisfy the above conditions, gold is used. It is clear that the same effect can be obtained by using tungsten, tungsten, and other materials.

[0014]

As described in detail above, the X of the present invention
When a line mask is used, a fine pattern of 0.3 μm or less can be accurately transferred with a large proximity gap of 20 μm or more. Further, since the thickness of the absorber layer can be reduced, the production of the X-ray mask is easier than before and the accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 shows transmission X transmitted through an X-ray mask in X-ray exposure.
It is a figure showing a general example of a line intensity distribution.

FIG. 3 is a diagram illustrating a relationship between an exposure amount margin and a mask contrast and a phase change amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absorber layer 2 Membrane 3 X-ray mask 4 Absorber pattern

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Isato Matsuda 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-62-262428 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 1/16

Claims (2)

(57) [Claims] 1. An X-ray mask having an X-ray transmitting pattern formed by a membrane film transmitting X-rays and an X-ray absorbing layer formed on the membrane film. (Nm), when the refractive index of the absorber layer for this wavelength is n and the linear absorption coefficient is μ (1 / nm), the thickness t (nm) of the X-ray absorber layer is 30 <| 3.
An X-ray mask set to satisfy the following condition: 60 (1-n) t / λ | <120 and 1 <1 / exp (−μt) <4. 2. A peak wavelength of X-rays to be irradiated using an X-ray mask having a membrane film transmitting X-rays and an X-ray absorber pattern formed of an X-ray absorber layer formed on the membrane film. Is λ (nm), the refractive index of the absorber layer with respect to this wavelength is n, and the linear absorption coefficient is μ (1 / nm), the thickness t (nm) of the X-ray absorber layer is 30 < ｜ 3
An X-ray exposure method, wherein pattern transfer is performed under a condition satisfying 60 (1-n) t / λ | <120 and 1 <1 / exp (−μt) <4.