Patent Number: 051669625
Section: claims

1. An X-ray mask comprising: an X-ray transmitting substrate having a structure in which a plurality of different layers consisting of a same material and having different compositions are stacked;  an X-ray absorber formed on one surface of said substrate and having a predetermined pattern; and  a support frame arranged on a peripheral portion of said substrate.  forming an X-ray transmitting substrate by a CVD method while changing the flow rate of at least one type of a gas of gases used during the film formation so that said X-ray transmitting substrate has a structure in which a plurality of different layers consisting of a same material and having different compositions are stacked;  forming an X-ray absorber having a predetermined pattern on one surface of said substrate; and  forming a support frame on a peripheral portion of said substrate.  an X-ray transmitting substrate having a structure in which a plurality of different layers consisting of a same material and having different compositions are stacked,  an X-ray absorber formed on one surface of said substrate and having a predetermined pattern, and  a support frame arranged on a peripheral portion of said substrate, comprising the steps of:  forming a first alignment mark on said substrate by using the same material as said X-ray absorber;  forming a second alignment mark on a wafer, said second mark having a pattern corresponding to said first mark;  coating an X-ray resist on said wafer;  arranging said mask above said wafer such that said first and second marks are substantially aligned with each other;  radiating visible light onto a region including said second mark of said wafer through a region including said first mark of said wafer, and aligning the positions of said mask and said wafer with each other while detecting reflected light;  radiating X-rays onto said resist on said wafer through said mask after the alignment between said mask and said wafer, thereby transferring said X-ray absorber pattern of said mask;  developing the transferred resist to form a resist pattern; and  processing said wafer by using said resist pattern. 2. A mask according to claim 1, wherein said substrate is constituted by a plurality of SiC layers having different C/Si composition ratios. 3. A mask according to claim 2, wherein said substrate comprises surface layers formed on both the outermost portions of said substrate, and the ratio of C to Si in said surface layers is larger than the ratio of C to Si in the entire substrate. 4. A mask according to claim 3, wherein said substrate comprises a single central layer sandwiched between said surface layers, and the ratio of C to Si in said surface layers is larger than the ratio of C to Si in said central layer. 5. A method of manufacturing an X-ray mask, comprising the steps of: 6. A method according to claim 5, wherein said substrate consists of SiC formed by using a first gas containing Si and a second gas containing C. 7. A method according to claim 6, wherein during the substrate formation, the flow rate of said first gas is fixed while the flow rate of said second gas or a diluted gas mixture of said second gas is changed. 8. A method according to claim 7, wherein said substrate comprises surface layers formed on both the outermost portions of said substrate, and the formation of said surface layers is performed essentially by increasing the flow rate of said second gas. 9. A method according to claim 6, wherein during the substrate formation, the flow rate of said second gas is fixed while the flow rate of said first gas or a diluted gas mixture of said first gas is changed. 10. A method according to claim 9, wherein said substrate comprises surface layers formed on both the outermost portions of said substrate, and the formation of said surface layers is performed essentially by decreasing the flow rate of said first gas. 11. A method according to claim 6, wherein said first ga comprises one material selected from the group consisting of silane, dichlorosilane, trichlorosilane, tetrachlorosilane, silicon tetrafluoride, and disilane, and said second gas comprises one material selected from the group consisting of methane, ethane, ethylene, acetylene, and propane. 12. A method according to claim 6, wherein a third gas comprising one material selected from the group consisting of arsine, phosphine, fluorine, chlorine, hydrogen chloride, and diborane is used together with said first and second gases during the substrate formation. 13. An exposure method using an X-ray mask comprising: 14. A method according to claim 13, wherein the visible light is laser light. 15. A method according to claim 13, wherein the first and second marks are diffraction grating-like marks.