The present and foregoing application claim priority to Japanese Application No. P2000-221289 filed Jul. 21, 2000. All of the foregoing applications are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a light exposure method for performing extremely fine machining in, for example, the field of semiconductors.
2. Description of Related Art
In e.g., the filed of semiconductors, in order to cope with the tendency towards higher integration of semiconductor devices, it is becoming incumbent to establish a new process technique enabling the machining of an extremely fine pattern of, for example, 0.1 xcexcm or less.
For machining a fine pattern, the so-called lithographic technique is indispensable. Thus, in order to enable the ultra-fine machining through improvement in optical resolution to cope with the tendency towards shorter wavelengths of the exposure light, development of a new light exposure technique employing the extreme ultraviolet (EUV) in the vicinity of 7 to 16 nm wavelength, in addition to the ultraviolet light such as KrF (krypton fluorine) or ArF (argon fluorine) or the conventional mercury lamp, is proceeding energetically.
However, in the wavelength range of the extreme ultraviolet (EUV), the light undergoes marked optical absorption with the routine resist material, such that the illuminated light fails to reach a lower portion of the resist layer. The result is that a resist pattern of an optimum rectangular shape cannot be prepared, thus deteriorating the resist pattern.
Such deterioration in the resist pattern obstructs the ultra-fine machining, and hence it is desired to suppress such deterioration. Although it is currently practiced to reduce the film thickness of the resist layer to e.g., less than 150 nm to improve the light transmittance of the resist layer in its entirety. However, if the film thickness of the resist layer is reduced, etching resistance tends to be insufficient.
It is therefore an object of the present invention to provide a light exposure method which resolves the problem of light transmittance of the resist layer in the wavelength range of the extreme ultraviolet (EUV) to enable finer machining than was heretofore possible.
According to the present invention, there is provided a light exposure method for selectively exposing a resist layer with one of X-rays containing soft X-rays, vacuum ultraviolet light rays and ultraviolet rays containing extreme ultraviolet light rays for patterning the resist layer to a pre-set shape, in which the method includes the step of employing, as a high molecular material forming the resist layer, a high molecular material having the oxygen content ratio (no) and density (xcfx81) satisfying the following equations (1) and/or (2):                     ρ        ≤                              3.66            xc3x97                          {                                                12.011                  xc3x97                                                            (                                              1                        -                                                  n                          0                                                                    )                                        /                    2                                                  +                                  15.9994                  xc3x97                                      n                    0                                                  +                                  1.00794                  xc3x97                                                            (                                              1                        -                                                  n                          0                                                                    )                                        /                    2                                                              }                                                          32.4297              xc3x97                                                (                                      1                    -                                          n                      0                                                        )                                /                2                                      +                          126.595              xc3x97                              n                0                                      +                          1.3607              xc3x97                                                (                                      1                    -                                          n                      0                                                        )                                /                2                                                                        (        1        )                                ρ        ≤                              3.66            xc3x97                          {                                                12.011                  xc3x97                                                            (                                              1                        -                                                  n                          0                                                                    )                                        /                    3                                                  +                                  15.9994                  xc3x97                                      n                    0                                                  +                                  1.00794                  xc3x97                                      (                                          1                      -                                              n                        0                                                              )                                    xc3x97                                      2                    /                    3                                                              }                                                          32.4297              xc3x97                                                (                                      1                    -                                          n                      0                                                        )                                /                3                                      +                          126.595              xc3x97                              n                0                                      +                          1.3607              xc3x97                              (                                  1                  -                                      n                    0                                                  )                            ⁢                              2                /                3                                                                        (        2        )            
and forming the high molecular material as a coating to form the resist layer having a film thickness not less than 250 nm.
It should be noted that the oxygen content ratio (no) is based not on the weight ratio but on the ratio of the numbers of atoms.
In a high molecular material forming the resist layer, the presence of oxygen atoms is indispensable for manifestation of resist characteristics. In the high molecular material, the portion which undergoes chemical reactions due to the irradiated light to cause changes in the physical properties of an irradiated portion and an unirradiated portion to manifest resist characteristics is necessarily a group containing oxygen, such as ester groups, phenol groups, alcoholic groups and carboxylic groups.
In the wavelength range of the extreme ultraviolet (EUV) light rays, optical absorption for oxygen is larger than that for carbon or hydrogen and accounts for the lowering of the light transmittance of the high molecular material. The value of optical absorption for one oxygen atom is of an extremely large value which is approximately three times that for one carbon atom and approximately 50 to 100 times that for one hydrogen atom.
In the present invention, since the high molecular material having the pre-set oxygen content ratio no and density xcfx81 is used, the proportion of the oxygen atoms in the constituent atoms of the high molecular material is of a relatively small value. Thus, the optical absorption in the entire high molecular material is suppressed, such that, if the film thickness of the resist layer is of a thicker value of, for example, 250 nm, sufficient light transmittance may be achieved in manifesting resist characteristics.
Moreover, since the film thickness of the resist layer is set to not less than 250 nm, the etching resistance of the resist layer can be improved.
According to the present invention, in which the high molecular material having the pre-set oxygen content ratio n0 and density xcfx81 is used, it is possible to produce a resist pattern of an optimum shape even with the thick resist layer having a film thickness not less than 250 nm. In addition, since the film thickness of the resist layer is set to not less than 250 nm, it is possible to construct a lithographic process having excellent etching resistance to assure ultra-fine machining more intricate than was heretofore possible.
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