Use of deep reactive ion etching in the fabrication of high-efficiency high-resolution crystal x-ray analyzers

Spherically bent silicon crystal x-ray analyzers have been employed in high-resolution inelastic x-ray scattering experiments to increase the counting efficiency due to the small cross-section of the inelastic scattering processes of interest. [1] In these bent analyzers, strain causes a distribution of lattice spacing, limiting the achievable energy resolution. Hence, the silicon wafers were diced using precision diamond saws into an array of ~1x1 mm2 blocks, and then acid etched to remove the saw damage, leaving blocks ~0.6x0.6 mm2 glued to a spherical concave substrate. With this method, meV energy resolution has been demonstrated with a bending radius of 6.5 m. [2] We seek to optimize the dicing process using the technique of deep reactive ion etching (DRIE) to develop highly efficient crystal analyzers. Ideally, each individual block subtends an angle that matches the acceptance (Darwin width) of the silicon reflection. This requires block sizes of about 500 μm2. DRIE offers the flexibility of selecting the block size, with finely controlled groove widths (i.e., minimal loss of material), and hence the possibility of controlling the energy width. We have made a prototype analyzer using DRIE with block size of 470 μm2, groove widths of 30 μm, and about 500 μm deep. The wafer was then bent and glued to a glass substrate with 2-meter radius. Tests showed encouraging results, with the DRIE analyzer performing at the 100 meV level. Details of the process and further refinements will be discussed.