X-ray mask membranes

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... 

As a boron nitride film, a B-C-N passivation film can also be deposited by plasma-enhanced CVD in semiconductor devices [9], and hydrogenated boron nitride carbide films are applied for X-ray mask membranes. The radiofrequency (13.56 MHz) plasma-enhanced CVD process uses B2H6, CH4, and Ng or NH3 as source gases, or in a sputtering process with a boron target, CH4, N2, and Ar are used [10 to 18]. A B-C-N mixed phase can also be prepared by N" ion implantation into B4C at 100 keV [19]. 

A mask consisting of a pattern made with an x-ray absorbing material on a thin x-ray transparent membrane,... 

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. 42. Diagram of a mask used for 1 1 proximity x-ray Hthography. These thin-membrane masks, required for optimum transmission when using patterned metal absorbers, must remain free of distortion to maintain pattern fideHty during exposure.

LIGA mask consists of supporting membrane which is a low-density material and near transparent to the hard X-ray and high-density metal patterns which absorb most of the X-ray photon energy so that it becomes opaque to the X-ray. The requirements on the supporting membrane of a LIGA mask are ... 

A surface covered with a photoresist and a gold mask can be irradiated with high-intensity, well-collimated X-rays that degrade the exposed regions of the polymer. The degraded polymer is removed to create a primary template. Galvanoforming produces a secondary metallic template that is used as a mold for a polymer membrane with homogenous pores (Fig. 2). 

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