JPS60222849A - X-ray exposure method - Google Patents

Abstract

PURPOSE:To enable a negative resist having constant high sensitivity to be used in in whatever exposure atom. it is used, by forming a thin metallic film high in ionization tendency as the uppermost layer of an X-ray resist and exposing this layer. CONSTITUTION:The thin film 7 made of a metal, such as K, Na, Mg, Al, or Zn, is formed on the X-ray resist 3. Since these metals have high ionization tendency and oxides tend to be formed on the surface in the air, oxygen in the air reacts with the metal film 7, and prevented from intruding into the resist 3 by interrupting it on the surface of the metal film 7. In another words, this film 7 serves as a kind of reducing agent, absorbs the oxygen in the air to form a stable film serviceable as a protective film, and prevents it from intrusion into the layer 3. The figure illustrates an X-ray source 1, an X-ray mask 2, an X-ray flux 5. As a result, allowance is given for development of the X-ray resist, and freedom can be given to the design of the system of X-ray exposure, such as exposure atm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray exposure method in the field of X-ray phosphorography, which is effective in transferring fine patterns of 1 μf or less.

(Prior art and its problems) X-ray exposure technology is expected to be an extremely promising transfer technology in the future due to its reliable high resolution of submicron width patterns, and active research and development is currently being carried out in various places. It is being said. The present inventor has been involved in research on X-ray exposure technology for a long time, and has discovered one important problem. Figure 1 shows characteristics that indicate experimental facts that are considered to be problematic. This figure shows the exposure atmosphere for the remaining film thickness of PGMA (
In this case, air) shows pressure dependence.

Depending on the dose of MoLα radiation, in a low pressure air atmosphere ~
It was set at 5 5 ml T/C< to obtain a residual film thickness of 60 inches.

As the pressure increases, absorption of characteristic X-rays increases in the air atmosphere, so in that case, the exposure time was increased so that a dose of 55 mJy(i) was applied to the P()MA resist.

As can be seen from the figure, as the pressure increases, the residual film thickness of P(IMA) decreases considerably.This phenomenon of negative resist, that is, the reduction reaction of crosslinking due to increase in air pressure, is explained in detail by the mechanism. Although this has not been fully elucidated, it has been experimentally confirmed that it is an effect of oxygen in the air.For example, in the 1975 publication Journal of Vacuum Science and Technology, .

Vac, Sci, Technol,) Volume 12, No. 1
A similar effect is pointed out on page 329. In Figure 1, the fact that the PGMA residual film thickness decreases as the air pressure increases means that the sensitivity of the P (3MA resist) decreases as the pressure increases. The remaining film thickness at that time was reduced to about 35% from the value of about 55 inches at pressure.

Such a phenomenon is a major problem in X-ray exposure technology from the following viewpoints. Currently, the exposure atmosphere of the X-ray exposure system can be vacuum, He gas, or atmosphere (air), but it has not been determined that only one of them is possible.

The pressure range shown in Figure 1 is in the low vacuum region of 67 to 2670 pa, but the fact that the residual film thickness fluctuates in response to pressure changes is a problem in the fabrication of devices that require the entire culm to have a specified residual film thickness. . However, if the pressure of the exposure atmosphere is determined, a constant residual film thickness can always be obtained, but in this case, it is necessary to provide an additional mechanism for controlling the pressure of the atmosphere to a constant value. The above is the first point.

The second point is related to the atmospheric exposure method. The atmospheric exposure method is superior in the ease of designing and configuring the Xi exposure system, and is considered to be a very promising exposure method in the future. This advantage is particularly easy to take advantage of in step-and-repeat systems. However, as can be seen from Figure 1, in the atmosphere (~1
0', Pa), the sensitivity is expected to decrease considerably. This is because, as mentioned above, the cross-linking reduction reaction caused by oxygen slows down, resulting in a dog-like appearance). The decrease in resist sensitivity is
This is a serious problem because it is directly related to the throughput of X-ray exposure. A major challenge for the future of X-ray exposure is to increase throughput, and one major means of achieving this high throughput is the development of H1 high-sensitivity X-ray resists. It is often obtained in high-sensitivity t/resists and BVC negative resists.

However, if such a high-sensitivity negative resist exhibits a decrease in sensitivity due to the y-ambience dependence as shown in FIG. 1, it is a major problem.

In FIG. 2, PdLa rays (wavelength 4.
A pressure dependence similar to that described above with 37A) is shown. The dose amount was 130 m and the resist was <P()MA, the same as in FIG. A similar phenomenon is observed in this case as well, and the above interpretation applies as is.

(Object of the Invention) An object of the present invention is to provide a new X-ray exposure method that eliminates such conventional drawbacks and can use a negative resist that exhibits a constant high sensitivity regardless of the exposure atmosphere. It is in.

(Structure of the Invention) That is, according to the present invention, in an X-ray exposure method in which a workpiece coated with an X-ray resist is irradiated with X-rays emitted from an X-ray source through an X-ray mask, the upper layer of the X-ray resist is As* Cap N a r M g *A
4. Zn, Fe, N i + 3 n + P
An X-ray exposure method is obtained which is characterized in that a thin metal film having a high ionization tendency, such as d# or Cu, is formed and exposed.

(Example) The configuration of the present invention will be described below with reference to the drawings.

Third: The figure is a schematic diagram showing an embodiment of the X-ray exposure method according to the present invention. The basic configuration consists of an X-ray source 1, an X-ray mask 2, and a workpiece 4 coated with an X-ray resist 3. An X'a flux 5 emitted from an X-ray source 1 is irradiated onto an X-ray resist 3 through an X-ray mask 2. At this time, the X-ray flux is absorbed by the absorber pattern portion 6 (usually made of Au) on the X-ray mask and does not reach the resist surface below. Here, the exposure atmosphere between the X-ray mask 2 and the X-ray resist 3 may be vacuum, ) Ie gas, or air;
Let us discuss the case of air).

In the case of the atmosphere, the sensitivity of high-sensitivity X-ray negative resists is significantly reduced due to the influence of a large amount of oxygen. Therefore, the present invention adopts a configuration in which a thin metal film 7 is newly formed on the X-ray resist 3. As this metal film, K, Ca + N
a * Mg , A l * Znr F e + N
1rPd or Cu is used. These metals have a strong tendency to ionize and easily form oxides on their surfaces in the air. The key point here is that by forming a thin film of metal on an X-ray resist, oxygen in the air reacts with the metal film, and the reaction occurs on the surface of the metal (or the entire thin metal layer). This prevents oxygen from passing through to the X1liI resist. In other words, these thin metal films act as a kind of reducing agent, absorbing oxygen from the air and turning into stable oxides, forming a kind of protective film that prevents oxygen from penetrating into the inner X-ray resist layer. . By skillfully utilizing the characteristics of metals that have a strong tendency to ionize, oxygen can be taken in only in a thin metal film and oxygen can be prevented from entering the X-ray resist, and the object of the present invention has been achieved. Ru.

In other words, the fact that the condition of the X-ray resist, which is unaffected by oxygen in the atmosphere (air), which is the worst issue, can be improved to 7i means that it is possible to obtain a negative resist that exhibits a constant high sensitivity regardless of the exposure atmosphere. .

The thickness of the thin metal film may vary slightly depending on the type of metal, but it is in the range of several tens to several thousand amps. If it is necessary to remove a thin metal film after X-ray exposure and before developing the X-ray resist, appropriate dry etching (for example, 0□.

This can easily be done by a method such as using Ar gas) or wet etching.

(Effects of the Invention) As explained above, according to the present invention, firstly, high-throughput X-ray radiation using a high-sensitivity negative X-ray resist can be achieved regardless of the exposure atmosphere; Greater tolerance can be given when developing sensitive X-ray resists (i.e., there is no need to consider lower sensitivity due to reaction with oxygen), and thirdly, there is greater freedom in system design such as the exposure atmosphere for X-ray exposure. It has the effect of giving strength.

[Brief explanation of drawings]

Figures 1 and 2 show the exposure atmosphere (air) of the remaining film thickness (i.e. sensitivity) of the negative resist, which is a problem with the conventional technology.
FIG. 3, a diagram showing pressure dependence, is a schematic diagram for explaining an X-ray exposure method that is an embodiment of the present invention.

Claims (1)

[Claims] (1) X1FJ emitted from the X-ray source! An X-ray exposure method in which a workpiece coated with an X-ray resist is irradiated with X-rays through an X-ray mask, the X-rays being exposed after forming a thin metal film with a high ionization tendency as an upper layer of the X-ray resist. Sabamitsu method.