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Retrograde Profile for X-Ray Masks by Molecular Beam Epitaxy

IP.com Disclosure Number: IPCOM000038485D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+3]

Abstract

X-ray lithography involves fabricating thin, structurally stable masks. One approach is the use of thin silicon membranes that support a gold absorbing layer that is patterned, as desired. This is achieved by using the process depicted in Fig. 1 wherein an oxide diffusion mask is defined to stop boron diffusion in selected areas. Then, in Fig. 2, a heavy boron-doped layer is diffused on both sides of the mask, and acts as an etch stop. In Fig. 3, the oxide is stripped away and then the film is etched as shown in Fig. 4. The boron-doped films are under tensile stress which is required for mechanical stability of the mask. The optical properties of the boron-doped membrane are compromised by the defects in the film that result from the high doping level.

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Retrograde Profile for X-Ray Masks by Molecular Beam Epitaxy

X-ray lithography involves fabricating thin, structurally stable masks. One approach is the use of thin silicon membranes that support a gold absorbing layer that is patterned, as desired. This is achieved by using the process depicted in Fig. 1 wherein an oxide diffusion mask is defined to stop boron diffusion in selected areas. Then, in Fig. 2, a heavy boron-doped layer is diffused on both sides of the mask, and acts as an etch stop. In Fig. 3, the oxide is stripped away and then the film is etched as shown in Fig. 4. The boron-doped films are under tensile stress which is required for mechanical stability of the mask. The optical properties of the boron-doped membrane are compromised by the defects in the film that result from the high doping level. The mechanical strength of the membrane is also decreased due to micro- cracks and lattice defects that propagate after mask fabrication. Unfortunately, the high doping level throughout the film is made necessary because the diffusion process and the fact that a high concentration of boron is needed to provide an etch stop. This means that an even higher concentration is needed near the surface to drive the dopant in, resulting in an excessively doped membrane, that exhibits the degraded qualities mentioned above. An improved method is now provided in which the boron doping is not performed throughout the membrane thickness. The final mask structure is shown in Fig. 5. Here, a supporting silicon membrane 10 is deposited on substrate 12 which...