Research On Characteristics Of Photolithography Medium And Lithography Method With Sub-wavelength Resolution

Optical lithography is one of the foundations of miniaturization of integrated circuit and study of the microscopic quantum world. It has become the key technology to fabricate microelectronic device and optoelectronic device. At present, the photolithography used has many limits such as expensive, complex, low output and so on. This paper mainly focuses on the characteristics of photolithography medium and lithography method with sub-wavelength resolution. We mainly research the design of365nm LED and its application in lithography, the characteristics of the photolithography medium with sub-wavelength resolution, and sub-wavelength gratings inscribed by surface plasmons(SPs) and waveguide modes interference lithography. The developmental lithography based on365nm LED with10nm FWDH can realize a Micro-Nano scale lithography with high efficiency, energy conservation and environmental protection. The study on characteristics of X AR-N7700/30commercial resist and azobenzene copolymer film with cyano group provides for foundations of sub-wavelength lithography by SPs and waveguide modes interference. The first proposed sub-wavelength lithography by waveguide modes interference has the advantages of low cost and with no mask. It can inscribe large area sub-wavelength gratings, of which the period of can be effectively controlled by the thickness of the resist film, the excited modes of the electromagnetic field. Using the azobenzene polymer as a new sub-wavelength photolithographic medium has the advantages with simple workmanship and the inscribed structure can be erased and reconstructed. This paper is significant in Micro-Nano scale lithography, and especially in fabrication of sub-wavelength gratings.The details of this thesis are listed following:1. The arrangements of365nm ultraviolet LED point light sources with4×4array in a plan and focusing lens are designed and optimized. Area light source with uniform illumination in exposure plan at the working distance is achieved. Lithography experiment with contact exposure method is realized with the optimized365nm LED area light source with a FWDH of10nm. The lithographic patterns are consistent with the mask.2. Using365nm wave band light sources as the exposure sources, SEM, step tester, AFM and ellipsometry, the chemical and physical characteristics of photolithography medium X AR-N7700/30resist with sub-wavelength resolution are studied. The developing velocity of the unexposed part of the resist is23.15nm/s, and that is1.85nm/s for the exposed part. In the condition of postbaking temperature with115degrees for5minutes and the undiluted developing liquid, the contrast of the resist is as high as2.38. When the resist is undiluted, the thickness of the spin coating resist film is260-450nm. When the developing liquid is diluted to weight concentration70%and50%, the thickness of the resist film is150-210nm and90-150nm respectively. When the developing liquid is diluted to weight concentration30%, the thickness of the film is45-48nm. One dimension gratings by325nm laser and442nm laser respectively are inscribed. The absorption spectrum and refractive index of the azobenzene copolymer film with cyano group are measured. Surface relief gratings based on the film are inscribed by the interference of442nm beam and532nm beam respectively.3. We propose a sub-wavelength lithography structure by exciting SPs and waveguide modes interference lithography, which is based on prism, refractive matching oil, substrate, metal film, resist and air multi-layer. The structure can effectively avoid the pollution of the resist resulted by refractive matching oil. When the thickness of the resist film is less than the critical thickness, SPs modes can be excited to inscribe the sub-wavelength gratings. While the thickness of the resist film is thicker than the critical thickness, waveguide modes can be excited to inscibe the sub-wavelength gratings. Both the TE and TM polarized light can excite waveguide modes, and the electromagnetic field of waveguide modes is mainly distribute in the layer of the resist film. The interference of waveguide modes of TM1、TE0can be used to inscribe monolayer sub-wavelength gratings, while the interference of high order waveguide modes can inscribe multilayer sub-wavelength gratings. In this lithography structure, we can effectively adjust the period of the sub-wavelength gratings by changing the thickness of the resist film and picking different modes of the electromagnetic field. The lithography structure has the advantages of low cost and with no mask.4. We use the azobenzene copolymer film with cyano group as a new optical lithography medium. By optimizing the lithography structure parameters and light path, we successfully realize large area sub-wavelength gratings inscribed by SPs interference and waveguide modes interference excited by532nm and442nm respectively. When the thickness of the polymer film is55nm and the exposure light is532nm laser, the sub-wavelength gratings with a period of190nm is inscribed, and characteristic size of the gratings is95nm, which is smaller than1/5of the excited laser wavelength. When the thickness of the polymer film is165nm and343nm, the inscribed sub-wavelength gratings has a characteristic size of108nm and103nm respectively, which are fabricated by TE0、TM1waveguide modes interference lithography respectively. When the thickness of azo-polymer film is17nm and the exposure light is442nm laser, the sub-wavelength gratings with a characteristic size of90nm is inscribed by SPs interference lithography. When the thickness of the polymer film is100nm and208nm, the inscribed sub-wavelength gratings has a characteristic size of95nm and94nm respectively, which are fabricated by TE0、 TM1waveguide modes interference lithography. For the azobenzene polymer has a higher absorbance at442nm light band than that at532nm, The gratings inscribed by SPs interference lithography and waveguide modes interference lithography excited by442nm laser are smoother than that inscribe by532nm laser. The strongest electromagnetic field of SPs is mainly distributed on the interface of metal film and the polymer film. The needed exposure time is relatively longer, while the strongest electromagnetic field is mainly distributed in the layer of the polymer film, and the needed exposure time is relatively shorter. What’s more, the uniformity of the gratings inscribed by waveguide modes interference is better than that of SPs interference lithography. Experimental results are consistent with the numerical calculation, which verifies our method. Using the azobenzene polymer as a new sub-wavelength photolithographic medium has the advantages of simple workmanship and the inscribed structure can be erased and reconstructed.5. The absorbance of the azobenzene copolymer film with cyano group at365nm LED light is effectively modulated by532nm laser. When the silver nanocubes are dropped onto the surface of the polymer film, the modulation degree is significantly higher than that without the nanoparticles in the same intensity of532nm laser due to the field enhancement of excitation of surface plasmons. The super-resolution lithography would be developed based on the enhancement absorbance modulation by the excitation of surface plasmons is discussed.The innovations of this thesis are shown as following:1. The arrangements of365nm ultraviolet LED point light sources array and focusing lens are designed and optimized. Area light source with uniform illumination in exposure plan at the working distance is achieved. Lithography experiment with contact exposure method is realized with the optimized365nm LED area light source with a FWDH of10nm. The lithographic patterns are consistent with the mask. The LED light source can be used in Micro-Nano scale lithography with advantages of simple structure, energy conservation, environmental protection and low cost.2. Firstly propose the sub-wavelength lithography by waveguide modes interference. The large area sub-wavelength gratings can be inscribed by this technology. When the thickness of the resist film is less than the critical thickness, SPs modes can be excited to inscribe the sub-wavelength gratings. While the thickness of the resist film is thicker than the critical thickness, waveguide modes can be excited to inscribe the sub-wavelength gratings. The interference of waveguide modes of TM1、 TEo can be used to inscribe monolayer sub-wavelength gratings, while the interference of high order waveguide modes can inscribe multilayer sub-wavelength gratings. Using the proposed lithography structure, the period of the sub-wavelength gratings can be effectively adjusted by changing the thickness of the resist film and picking different modes of the electromagnetic field. The lithography structure has the advantages of low cost and with no mask.3. Using the azobenzene copolymer film with cyano group as a new optical lithography medium, large area sub-wavelength surface relief gratings are successfully inscribed by SPs interference and waveguide modes interference. When the thickness of azo-polymer film is17nm and the exposure light is442nm laser, the sub-wavelength gratings with a characteristic size of90nm is inscribed by SPs interference lithography. When the thickness of the polymer film is100nm and208nm, the inscribed sub-wavelength gratings has a characteristic size of95nm and94nm respectively, which are fabricated by TE0、TM1waveguide modes interference lithography. Using the azobenzene polymer as a new sub-wavelength photolithographic medium has the advantages of simple workmanship and the inscribed structure can be erased and reconstructed.