Patent Number: 052767248
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for exposing a substrate like a semiconductor wafer to X-rays in the lithographic process in the manufacture of semiconductor devices, and more particularly, to an X-ray transmitting window which forms a partitioning wall of two vessels having a relative pressure difference and which transmits X-rays so as to allow X-rays to be transferred between the vessels. 2. Description of the Related Art There is an increasing demand for fine circuit patterns in order to provide high-density and high-performance semiconductor integrated circuits. The possibility of formation of fine patterns on the order of 0.1 .mu.m or less is the primary reason for developing X-ray lithography. A promising high-output X-ray source employed in such an X-ray lithography is SOR (synchrotron orbital radiation). In X-ray lithography which employs SOR, X-rays generated under a high vacuum of about 10.sup.-10 Torr are irradiated onto a sample, such as a semiconductor wafer, generally placed in an atmosphere having 1 atm. To achieve this, an X-ray transmitting window made of a material having a high X-ray transmittance, such as beryllium (Be), is provided between the SOR source and the sample chamber. For the reason mentioned above, a pressure difference substantially equal to 1 atm is applied to the X-ray transmitting window. In the case of an X-ray transmitting window made of a Be plate and having an opening area of, for example, 30 mm.times.30 mm, such a pressure difference can be resisted if the thickness is about 0.2 mm. However, such a Be X-ray transmitting window has the following drawbacks. (1) 10 .ANG. X-rays which pass through Be are attenuated at about 0.2 dB/.mu.m. This attenuation rate increases as the wavelength increases. Thus, the use of X-rays of short wavelengths in x-ray lithography is advantageous from the viewpoint of transmittance. However, X-ray absorber (which may be a gold film) on the exposure mask readily transmits X-rays of short wavelengths. Consequently, in X-ray lithography, the contrast of the X-ray absorber patterns is reduced, making exposure of fine patterns difficult. Thus, the use of a Be X-ray transmitting window which is as thin as possible and of X-rays of long wavelengths is desired. To achieve these objectives, it is necessary for the thickness of the Be X-ray transmitting window to be reduced to 1/10th or less of that of the conventional window. (2) To achieve a high throughput in X-ray lithography, it is desired to increase the opening area of the X-ray transmitting window to about several tens of millimeters x several tens of millimeters. Currently, it is very difficult to provide a Be X-ray transmitting window which satisfies the aforementioned requirements. SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray transmitting window which exhibits a high transmittance to X-rays having long wavelengths of 10 .ANG. or above, which has an opening area whose side dimension is several tens of millimeters, and which can withstand a pressure difference of about 1 atm. Another object of the present invention is to provide an X-ray exposure apparatus having two vessels which are connected to each other through the partitioning wall formed of the abovementioned window, so that, in a source connected to one of the vessels, an SOR is generated, and in another vessel, a sample like a silicon wafer coated with a resist film is exposed to an X-ray of the SOR transmitted through the window. To achieve the above object, an X-ray transmitting window according to the present invention is a plate-like member formed by joining a large number of juxtaposed capillary tubes, each having an inner diameter of about several tens of .mu.m, parallel to each other. The smaller the inner diameter of each of the capillary tubes and the larger the length thereof, the greater the pressure difference obtained at the two sides of the window. That is, it is possible to produce a vacuum at one side of the window and an atmospheric pressure at the other side thereof. However, a decrease in the inner diameter of the thin tubes and an increase in the length thereof reduces the transmittance of the window. Thus, the inner diameter and length (the thickness of the window) of the capillary tubes are determined with the practical pressure difference and transmittance taken into consideration. The size of the window is determined such that the window withstands that pressure difference.