JPS6054435A - Exposing method for x-ray - Google Patents

Abstract

PURPOSE:To transfer an ultrafine mask pattern to a lower layer resist in high resolution by superposing a low sensitivity negative resist of the prescribed thickness on a high sensitivity negative resist, and exposing X-ray in a suitable amount. CONSTITUTION:High and low sensitivity negative resists 9, 8 of a wafer 5 are superposed, the thickness of the layer 8 is formed slightly thicker than several thousands Angstrom of flying distance in the layer 8 of photon Auger electron emitted from an Au pattern 7 of an X-ray mask 4, the X-ray is emitted in the suitable exposure amount in the film thickness reference of the resist 9, and the mask pattern 7 is transferred through the upper layer 8 to the lower layer 9. In this case, the layer 8 is acted as a buffer layer to the photon Auger electron 10 emitted from the Au 7 to absorb the electron to advance decomposition reaction, the layer 8 is all dissolved by development, and the layer 9 which is crosslinked by 100% is selectively retained. According to this structure high resolution copy of submicron order width can be performed, and the influence of secondary electron can be removed at the resist side. Accordingly, the degree of freedom can be given to the design of the X-ray.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray exposure method in the field of X-ray lithography that is effective for copying fine patterns of 1 μm or less.

The promise of X-ray lithography, which uses soft X-rays as a technology for copying high-resolution patterns, has been recognized in the electronics industry.
Letters (Electronlcs Letters)
Since its publication in Vol. 8, No. 4, pp. 102-104 (1972), research and development regarding X-ray phosphorography has been vigorously pursued, and in recent years has come quite close to the practical stage.

The present inventor noticed one important problem in the course of research and development of X-ray lithography for many years.

It relates to the effect of photoelectrons and Auger electrons emitted from the X-ray absorber pattern of the X-ray mask, especially Mask-L. However, the points regarding photoelectron and Auger electron emission were made in the publication Journal published in 1975.
Journal of Vacuum Science Fist and Fist Technology
and Technology) Volume 12 No. 6 No. 1
It is published on pages 329-1331. In this paper, R
When using an h target (wavelength of - line is 4.6λ), Pd target (wavelength of Lα line is 114.37 A), etc., the viewpoint of the effect of continuous X-rays, which are high energy components that are emitted more The effects of photoelectrons and Auger electrons are pointed out in .

The inventor has developed an M target (the wavelength of the Kα ray is 8.34^
), S1 target (k-line wavelength is 7.13^), MO
Met (the wavelength of Lα ray is 5.41 A), and P
In the process of studying the effects of photoelectrons and Auger electrons emitted from an X-ray mask in more detail using a d target, etc., we discovered an experimental result that seems to be a new problem. FIG. 1 shows the sensitivity characteristics of a negative resist to explain the nature of the problem. In Figure 1,
In addition to the transfer using an X-ray mask, the XII! The dose is Dl
(residual film rate 0), and the X-ray dose to the resist directly under the part without pattern &
0 qb)) 1) Increasing the residual film rate of the negative resist as much as possible has the effect of suppressing swelling during development, resulting in high resolution. From this point of view, the present inventor attempted to form a fine pattern. Using Stmet, the mask contrast of the used X-ray mask pattern with respect to blood relatives was determined from calculations while conducting transfer experiments in the case where it was sufficient to obtain D1 vs. D8 in Figure 1. It has been found that the obtained contrast ratio is hardly realized in actual transfer. That is, the first
According to the exposure conditions set in the figure, if the X-ray dose to the resist layer located directly under the part without a pattern is set to D2, the calculated X-ray dose should be DI directly under the All-in-one. It is. However, if we calculate backwards from the remaining film, the X-rays to the resist layer directly below the AI pattern)'-
S i was much larger than D□, and this X-ray dose i DI was applied to the resist. This is because photoelectrons and Auger electrons are emitted from the X-ray absorber pattern and are applied to the resist directly under the overexposed cancer pattern.

The present inventor conducted a transfer experiment in vacuum (<4 The result is that ~50 pieces of remaining film is the limit. In a vacuum, the range of photoelectrons and Auger electrons emitted from the M pattern is large, and it is thought that their influence on the resist is more significant.

Although it is difficult to accurately evaluate the barrage of photoelectrons and Auger electrons (secondary electrons) generated from the fabric pattern,
Based on the experimental results, tb shows the negative resist (PGMM) residual film thickness characteristic diagram when using a Pd radiation source as shown in Figure 2. 1) P of dLa line at all data points
The dose amount for GMA was set at 130 mJ4-.

In Figure #42, when there is no X-ray mask (data indicated by landmarks), that is, when X-rays are directly irradiated to 1) GMA, the residual film thickness of PGMA gradually decreases as the pressure of the lightless W surrounding increases. do.

On the other hand, when the PGMA resist is irradiated with X-rays through an X-ray mask with a thin Au layer (17 nm thick) on the surface (data marked with II), l) the residual film thickness of GMA' is approximately It shows a certain value and also has an extremely high residual film rate (90 inches or more). As mentioned above, this means that M
A large amount of photoelectrons and Auger electrons are emitted from the surface, and the PG
This is thought to be due to excessive exposure to the MA resist.

Excessive exposure of the resist by photoelectrons and Auger electrons emitted from any pattern as described above is a serious problem from the viewpoint of realizing accurate copying of fine patterns. In other words, in actual X-ray exposure transfer, it is not possible to set the X-ray dose to obtain a high residual film, and the large increase in the residual film thickness is caused by the formation of fine resist patterns (particularly submic μ-width patterns). This is a major obstacle.

The purpose of the present invention is to solve these conventional problems, and to eliminate photoelectrons and Auger electrons (
An object of the present invention is to provide an X-ray exposure method that avoids the adverse effects of secondary electrons and can more accurately copy fine patterns in X-ray phosphorography. That is, in the present invention, the resist is coated on the workpiece by transmitting it through an X-ray mask equipped with an X-ray absorber pattern. In the X-ray exposure method, resist layers are applied to the workpiece in two layers, with a high-sensitivity negative resist layer on the lower layer and a low-sensitivity negative resist layer on the -L layer, and - on the upper resist layer. The film thickness is made slightly thicker than the range within the resist layer of the secondary electrons emitted from the X-ray absorber pattern, and the upper resist layer is used as a buffer layer for controlling the secondary electrons. X-rays are irradiated with an appropriate exposure amount based on the film of the layer, and the pattern of the X-ray mask is transferred to the lower resist layer by passing through the upper resist layer, and the secondary electrons are absorbed by the upper resist layer. This is an X-ray exposure method characterized by the following.

The present invention will be described below with reference to drawings showing embodiments.

Figure 3 61. , X, 11! FIG. 2 is a schematic diagram showing an example of an exposure method. In the X-ray exposure method according to the present invention, X-rays are emitted from the X-ray source 10X@extraction window 2.

The X-ray mask 4 includes a mask substrate 6 that is highly transparent to the X-ray flux, and an X-ray absorber (Au) formed on the mask substrate.
It consists of pattern 7.

The above configuration is the same as the conventional one. In the present invention, the workpiece (wafer) 5 is arranged in two layers, with the high-sensitivity negative resist layer 9 on the bottom and the low-sensitivity negative resist layer 8 on the top. Apply.

Here, the thickness of the upper low-sensitivity resist layer 8 will be mentioned. The range of photoelectrons and Auger electrons emitted from the X-ray absorber pattern 7 is within the resist layer 8 in the energy range from α rays (1,49 to 6 V) to PdLa rays (2,84 Key). It is thought to be approximately several thousand amps. In addition, the experimental formula regarding the range of electrons is, for example, 19
Fujika, Status, Solidi published in 1974 (
Phys, atat, aol, (a)) volume 26, pages 525-535. Therefore, the thickness of the upper resist layer 8 is determined by photoelectrons and Auger electrons (secondary electrons).
The upper resist layer 8 is set to be slightly thicker than the range of several thousand^, and the upper resist layer 8 is used as a buffer layer for photoelectrons and Auger electrons.

In addition, the sensitivity difference between the resists used for the upper l/cyst layer 8 and the lower resist layer is such that the sensitivity of the upper resist layer 8 is 100
It is preferable that the sensitivity of the lower resist layer 9 is on the order of 10 millijoules and on the order of 10 millijoules, but depending on the rise sensitivity of the resist used, as mentioned above, the sensitivity of the lower resist layer 9 may differ. There is no problem even if the resist layer 8 becomes smaller.For the low-sensitivity resist layer 8, use the product name CMS (manufactured by Toyo IW Tatsuji Co., Ltd.) or the product name JS.
RM section 5-E (can use resists such as Nippon Synthetic Rubber (marked line) - resist with high blade sensitivity) Jm 9 has product name PGMA (Tokyo Ohka (marked line), product name 5EL-N (
Resists such as SOMAR KOGYO ■ [) can be used. However, even if it is used as a low-sensitivity resist, 2
When different kinds of resists have the above-mentioned sensitivity difference, the one with relatively higher sensitivity can be used as the lower resist layer 9, and the one with lower sensitivity can be used as the upper resist layer 8.Vl: Of course.

Furthermore, in the present invention, X-rays are irradiated with an appropriate exposure amount based on the film thickness of the lower resist layer 9, and the pattern 7 of the X-ray mask 4 is transferred to the lower resist 1m 9 by passing through the upper resist layer 8. At the same time, the secondary electrons 10 are absorbed into the upper resist layer 8. The pattern 7 is transferred by the X-ray exposure transfer using the X-ray mask 4.
At this time, as mentioned above, a large number of photoelectrons and
Auger electrons 10 are emitted. These photoelectrons and Auger electrons expose the upper negative resist layer 8, but since the upper negative resist layer 8 has low sensitivity, no electron-sensitive reaction (crosslinking) occurs. This point is a feature of the present invention,
This point will be explained in more detail.

FIG. 4 is a detailed view of the X-ray mask and the upper and lower resist layers.The upper negative resist layer 8 is R8, the lower negative resist layer 9 is R, and the area directly below the hs pattern 7 is region 2.
The area directly below where there is no thin pattern is defined as area I. In Figure 5,
Sensitivity characteristics indicating the exposure state of resist layers R1 and R* in region 1.1 are shown. As shown in FIG. 5 (1), in the lower resist layer Ft of region i, +J: The amount is D2 and the remaining film rate t, I:
It is 0. Upper resist layer 11)
-Dx is much larger than I) due to the photoelectrons and Auger electrons emitted from the pattern 7.

As shown in FIG. 3 (II), in region (2), the xH dose of the lower resist layer R8 is Dl and the residual film rate is 0, and the X-ray dose of the upper resist layer R8 is D8. The remaining film rate is 0. Therefore, when one X&1 transfer is performed under such settings, the upper resist layer 8 is transferred to the secondary '
Acts as a buffer layer for electrons and absorbs them.
In order to
A pattern of 0% is obtained. At this time, the two-part resist layer R8 has a remaining film ratio θ% and does not remain.

However, in the development process, all of the upper resist layer is dissolved, leaving only the 100% crosslinked portion of the lower resist layer R80.

In addition, the 21-thick film resist structure of the present invention is suitable for X-ray radiation ↓? For example, electron beam exposure is impossible due to the proximity effect.

As explained above, according to the present invention, high-resolution copying with a submicron width in the 11th CX-ray lithography can be more reliably performed. Second, since secondary electrons are allowed to be emitted from the X-ray mask and the influence of secondary electrons is removed on the resist side, there is no restriction on the design of the X-ray mask.
It has the effect of providing flexibility in its design, and thirdly, providing flexibility in system design such as exposure conditions for X-green exposure.

[Brief explanation of the drawing]

Figure 1 is a sensitivity characteristic diagram showing the excess exposure effect due to secondary electrons in negative resists, which is a problem with the conventional technology;
The figures are the same (a diagram showing the residual film characteristics of PGMA, Figure 3 is a schematic diagram of the X1m exposure method which is an embodiment of the present invention, Figure 4 is a detailed diagram of the iX1liij mask and resist configuration, Figures 5 (1) and (II) are sensitivity characteristic diagrams in a negative two-layer structure explaining the present invention in detail. 1... X-ray source, 2... X-ray extraction window, 3...・X-ray flux, 4... X-ray mask, 5... Workpiece, 6...
Mask substrate, 7...X 1) Absorber pattern, 8...
・Negative resist layer, 9...Negative resist layer, 1o
...Photoelectronics/Auger Electronics Special R1/Applicant 11 Denki Co., Ltd. No. 1η'l) Small tree Figure 5 X-ray dose amount X-ray dose amount

Claims (1)

[Claims] (1) X-ray exposure in which X-ray flux from an X-ray source is transmitted through an X-ray mask equipped with an X# absorber pattern to a resist coated on a workpiece, and the pattern of the X-ray mask is transferred to the resist. In this method, resist layers are coated on the workpiece in two layers, with a high-sensitivity negative resist layer as the lower layer and a low-sensitivity negative resist layer as the upper layer, and the film thickness of the upper resist layer is set to the X-ray absorbing layer. The upper resist layer is made slightly thicker than the range of the secondary electrons emitted from the body pattern within the resist layer, and the upper resist layer is used as a buffer layer for the secondary electrons. X-rays are irradiated with the exposure amount, and the X-rays are transmitted through the upper resist layer and onto the lower resist layer.
An X-ray exposure method characterized by transferring a pattern of a ray mask and absorbing secondary electrons into an upper resist layer.