JPS6055337A - Method of exposure to x-rays - Google Patents

Abstract

PURPOSE:To copy micropatterns more precisely in X-ray lithography by coating the material to be treated, such as wafer, first with a low-sensitive negative type resist as a lower layer, and second, a high sensitive positive type resist in a specified thickness as an upper layer to form two coating layers. CONSTITUTION:The material to be treated, such as wafer 5, is coated with a low sensitive negative type resist layer 9 as a lower layer, and a high sensitive positive type resist layer 8 as an upper layer to form two coating layers. The film thickness of this resist layer 8 is set to a value little thicker than the transit distance of photoelectrons and Auger electrons (secondary electrons) of several hundred nm to use the layer 8 as a buffer layer against the secondary electrons. The coated wafer 5 is irradiated with a proper exact amt. of X-rays based on the film thickness of the lower resist layer 9, the X-rays are transmitted through the upper resist layer 8, and form an X-ray mask pattern in the lower resist layer 9. A large number of photoelectrons and Auger electrons 10 emitted from an Au pattern 7 are absorbed with the layer 8. As a result, all the layer 8 is dissolved in a development step to leave only the 100% cross-linked parts of the layer 9, and a copy having submicron wide high resolution can be ensured in this X-ray lithography.

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 phosphorography using soft X-rays as a technology for copying high-resolution patterns has been demonstrated in electronics and
Letters (Electronics 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 inventor of the present invention has been concerned with one important problem in the course of research and development of X-ray phosphorography for many years. it is,
This field relates to the effects of photoelectrons and Auger electrons emitted from an X-ray mask, particularly an X-ray absorber pattern on the mask. However, the point regarding photoelectron/Auger electron emission was first published in 1975 in the journal Op Vacuum Science and Technology (Jour).
nal of Vacuum 5ci-ence an
d Technology) Volume ν No. 6 No. 1329
It is published on pages 1331 to 1331. However, in this paper,
Bhfi-get (the wavelength of LIC1 line is 4.6^), P
When using a d target (wavelength of - line is 4.37), etc., the effect of photoelectrons and Auger electrons has been pointed out from the viewpoint of the effect of continuous X-rays, which are high-energy components that are emitted in large quantities. There is.

The inventor has set M target (the wavelength of the flow line is 8.34 people).
, Si target (wavelength of flow line is 7.13 people), M
.

In the process of researching the effects of photoelectrons and Auger electrons emitted from an X-ray mask over a wide range of areas and in more detail using a target (the wavelength of the Omi line is 5.41) and a Pd target, we discovered new problems. I found some experimental facts.

FIG. 1 shows the sensitivity characteristics of a negative resist to explain the problem. In Figure 1, during transfer using an X-ray mask, the X-ray dose to the resist directly under the pattern, which is an X-ray absorber, is Di (remaining film rate 0).
In addition, we are considering the case where the exposure conditions are set so that the X-ray dose to the resist directly under the part where there is no An pattern is Dl (remaining film rate 100 cm). 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. The present inventor attempted to form a fine pattern from this point of view. Using a Si target, the mask contrast for the M pattern of the X-ray mask used is obtained from calculations while conducting transfer experiments in the case where it is sufficient to obtain Dl vs. It was discovered that the above contrast ratio is hardly achieved in actual transfer. In other words, according to the exposure conditions set in Figure 1, the X-ray dose to the resist located directly under the part where there is no AI pattern is adjusted. , the calculated X-ray dose should be J'j: DI just below the pattern. However, when calculating backwards from the remaining film, the X-ray dose to the resist directly below the pattern is much higher than Dl.
3, and this X-ray dose D3 was applied to the resist. This is due to the fact that photoelectrons and Auger electrons are emitted from the X-ray absorber pattern, and excess exposure is given to the resist directly under the photosensitive pattern.

The present inventor conducted transfer experiments in vacuum (<4X10-Torr), but for certain types of negative resists,
Due to the above effect, exposure with 100% film remaining could not be realized (although it was possible based on calculations), and the result was that ~50% film remaining was the limit. In a vacuum, the range of photoelectrons and Auger electrons emitted from a thin pattern is large, and it is thought that their influence on the resist is more significant.

Although it is difficult to accurately evaluate the amount of photoelectrons and Auger electrons (secondary electrons) generated from the Au pattern, the inventors have determined from experimental results that the negative resist A characteristic diagram of residual film thickness of PGMA was obtained. The dose of PdLa line to PGMA at all data points was set to 130 mJ/crl. When there is no X-ray mask (data indicated by marks), that is, when X-rays are directly irradiated to PGMA, the remaining film thickness of PGMA gradually decreases as the pressure of the exposure atmosphere increases. On the other hand, when the P soldering resist is irradiated with X-rays through an X-ray mask with a thin oil film (17 nm thick) on the entire surface (data indicated by H), the residual film thickness of PGMA remains almost constant regardless of the pressure. Moreover, extremely high residual &', X ratio (90
or more). This is considered to be because, as described above, a large amount of photoelectrons and Auger are emitted from the oil surface, resulting in excessive exposure of the η4A resist.

The overexposure of the resist by photoelectrons and Auger electrons emitted from the 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 a higher X-ray dose to obtain a high residual thickness, and the large increase in residual film thickness is caused by a fine resist pattern (a submicro width pattern in lt'i). It is a major cina disorder in the formation of.

The purpose of the present invention is to solve the conventional problems, and to avoid the adverse effects of photoelectrons and Auger electrons generated from an X-ray mask, and to make it possible to copy fine patterns in X-ray phosphorography with n1 degree of accuracy. An object of the present invention is to provide a line exposure method.

That is, the present invention transmits an X-ray beam from an X-ray source to a resist coated on a workpiece by transmitting it through an X-ray mask equipped with an X-ray absorber pattern, and transfers the pattern of the X-ray mask onto the resist. In the X-ray exposure method, resist layers are applied to the workpiece in two layers, with a low-sensitivity negative resist layer as the lower layer and a high-sensitivity positive resist layer as the upper layer, and a film of the upper positive resist layer. The thickness is made slightly thicker than the range within the resist layer of secondary electrons emitted by the X-ray absorber pattern, the upper positive resist layer is used as a buffer layer for secondary electrons, and the lower negative resist layer is used as a buffer layer for secondary electrons. X-rays are irradiated with an appropriate exposure amount based on the film thickness of the shape resist layer, and pass through the upper resist layer to form an X-ray mask pattern on the lower negative resist layer, and the secondary electrons are transferred to the upper resist layer. This is an Xa exposure method characterized by absorbing Xa into a layer.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic diagram showing an embodiment of the X-ray exposure method according to the present invention. In the X-ray exposure method according to the present invention,
An X-ray flux 3 is emitted from the X-ray extraction window 2 of the radiation source 1, and the
The beam 3 passes through an X-ray mask 4 and is irradiated onto a workpiece (wafer) 5 coated with resist. X-ray mask 4
consists of a mask substrate 6 having high transmittance to X-ray flux, and an X-ray absorber pattern 7 formed on the mask substrate. The above points are the same as before. In the present invention, the workpiece (wafer) 5 has a low-sensitivity negative resist layer 9.
The high-sensitivity positive resist layer 8 is placed on the bottom and the high-sensitivity positive resist layer 8 is placed on the top, respectively, and coated in two layers, upper and lower.

Here, the film thickness of the upper highly sensitive positive resist layer 8 will be considered. The range of photoelectrons and Auger electrons emitted from the X-ray absorber pattern 7 is JKa line (1,49Ke
In the energy range from y ) to the PdLa line (2,84 Kev), it is considered to be approximately several thousand A in the resist layer 8. In addition, the experimental formula etc. regarding the range of an electron are shown, for example in Phys.5tat, 5ol(a), Vol. 26, page 525-5≦5 published in 1974. Therefore, the thickness of the upper positive resist layer 8 is set to be a little thicker than the range of photoelectrons and Auger electrons (secondary electrons), which is several thousand^, and the upper positive resist layer 8 is used as a buffer layer for secondary electrons. used as Further, the upper positive resist layer 8 and the lower negative resist layer 9 are on the order of 100 millijoules,
It is desirable to set it to the order of one digit, but depending on the rise sensitivity of the resist used, the above-mentioned upper and lower resist) 1
There is no problem even if the difference in sensitivity of 5 is reduced. Further, a resist such as FBM (product name) (manufactured by Daikin Industries, Ltd.) can be used for the high-sensitivity upper positive resist layer 8, and a resist such as product name CMS (manufactured by Toyo Soda Industries, Ltd.) can be used for the lower negative-tone resist layer 9, which has -1 low sensitivity. ), product name JSRMIVIES-E (manufactured by Japan Synthetic Rubber), etc. can be used.

Furthermore, in the present invention, X-rays are irradiated with an appropriate exposure amount based on the film thickness of the lower resist layer, and are transmitted through the upper resist layer to form an X-ray mask pattern on the lower resist layer 9. The next electron is absorbed into the upper resist layer 8. The M pattern 7 is transferred by X-ray exposure transfer using an X-ray mask, and at this time, as mentioned above, a large number of photoelectrons/Auger electrons 1o are emitted from the M pattern 7. The upper resist layer 8 is exposed to light, but since this upper resist layer 8 is highly sensitive, a sufficient decomposition reaction of the resist occurs, and the entire upper resist layer is dissolved during development. This point is a feature of the present invention, and will be explained in more detail. FIG. 4 is a detailed view of the X-ray mask and two resist layers. The upper positive resist layer 8 is R, and the lower negative resist layer 9 is R.
8. The region directly below the p-77 is defined as region II, and the region directly below where there is no Au pattern is defined as region I. FIG. 5 shows the sensitivity characteristics indicating the exposure state of the resist layer Rs - Rt in region 1, I[. □ As shown in FIG. The X-ray dose is Dl, the residual film rate is 1.0, and the upper resist layer R
In No. 3, the X-ray dose is D2 and the residual film rate is 0. The X-ray dose of the upper resist layer is much greater than that of the lower resist layer due to photoelectrons and Auger electrons emitted from the M pattern. Fifth
As shown in the figure (If), in the lower resist layer R□ of region (■), the remaining film rate is 0 at an X-ray dose of D2, and in the upper resist layer island, the X-ray dose is rAs at D2.
The rate is O. Therefore, when one X-ray transfer is performed under such settings, the upper positive resist layer R2 acts as a buffer layer for secondary electrons, and the lower negative resist layer R1 has a residual film rate of 100 cm. A pattern is obtained. At this time, the upper resist layer island does not remain because the remaining film rate is θ%. That is, in the development step, the upper resist layer & is completely dissolved, leaving only the 100% crosslinked portion of the lower resist layer R1.

Note that the two-layer thick film (JIJ) formation of the present invention is possible in X-ray lithography, but is impossible in, for example, electron beam exposure due to the proximity effect.

As explained above, according to the present invention, firstly, high M image resolution copying of submicron width in X-ray phosphorography can be more reliably performed. Second, since secondary electrons are allowed to be emitted from the X-ray mask and the influence of the secondary electrons is removed on the resist side, there is no restriction on the design of the X-ray mask, and Proposition 1 has a high degree of freedom. Thirdly, it has the effect of providing flexibility in system design such as the exposure atmosphere for X-ray exposure.

[Brief explanation of the drawing]

Figure 1 is a sensitivity characteristic diagram showing the excess exposure effect due to secondary electrons in the negative resist, which is a problem with the conventional technology.
The figures are the same < A figure showing the residual film characteristics of PGMA, Figure 3 is a schematic diagram of an X-ray exposure method that is an embodiment of the present invention,
Figure 4 is a detailed diagram of the X-ray mask and resist N formation, Figure 5 (
1) and (II) are sensitivity characteristic diagrams in a negative-type positive-type two-layer structure in which the present invention is explained in detail. DESCRIPTION OF SYMBOLS 1... X-ray source, 2... X-ray extraction window, 3... X-ray flux, 4... X-ray mask, 5... Workpiece, 6...
Mask substrate, 7... X-ray absorber pattern, 8... Positive resist, 9... Negative resist layer, 10...
Photoelectrons/Auger electrons - Figure 5 X-ray dose x section g - input amount - 22 (

Claims (1)

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