X-ray masks

The x-ray mask represents perhaps the most difficult component to fabricate in the x-ray lithographic system. Watts and Maldonado (77) have outlined the requirements for a mask capable of replicating VLSI patterns in a production environment as follows ... 

In another report, instead of direct x-ray ablation, an x-ray mask, which was 10-pm-thick Au on a Kapton film, was employed to ablate a PMMA wafer. Then the ablated PMMA wafer was developed. For sealing, a PMMA cover was first spin-coated with a 2-pm layer of poly(butyl methacrylate-co-methyl methacrylate) and then thermally bonded to the PMMA plate (120°C for 1 h) [200]. 

The X-ray masks consist of a thin membrane (e.g., 3-pm titanium or 30-pm beryllium) together with absorbers consisting of X-ray opaque gold layers that are more than 10 pm in thickness in order to achieve the required mask contrast. Within the irradiated sections of the resist layer, the polymer chains are destroyed reducing their molecular weight. In most experiments polymethyl methacrylate (PMMA) is used as the X-ray resist. 

An optically generated x-ray mask is itself one of the key features of LIGA, producing the necessary high contrast with a thick (>10 pm) gold absorber on materials membrane consist of low atomic number elements [27], The absorber mask is patterned using polymethyl methacrylate (PMMA) resists exposed by electron-beam lithography (e-beam) or from an intermediate mask that relies on an e-beam exposure... 

Fig. 1 X-ray absorption spectra calculated for the metals (Au, W, Ta, and Cu) which are mainly used as the absorbers for x-ray masks...

Although photoresists remain the dominant resists used in the fabrication of all kinds of IC devices, electron-beam resists are widely used in the fabrication of photomasks and x-ray masks, as well as in niche applications in the fabrication of exploratory research devices. 

P.A. Seese, K.D. Cummings, D.J. Resnik, A.W. Yanfo, W.A. Johnson, G.M. Weiss, and J.P. Wallace, Accelerated radiation damage testing of x ray mask membrane materials, Proc. SPIE... 

An electron beam patterning was abo performed on plasmapcdymerized CuAA films [117-118]. Morita and Hattori [97] described a dry litogiaphy inocess involving an X-ray mask formed by gold-doped plasma polymerization of dyrraie. 

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