Responsivity Uniformity Enhancements for Backside-Illuminated Charge-CoupledDevices (BICCDs) by Excimer Laser-Assisted Etching

摘要

BICCDs are solid-state electronic imaging devices which read out image chargesfrom wells in an array of pixels. The substrate below the pixel array is typically thinned by chemically etching (100)-oriented silicon using a potassium hydroxide (KOH) etch. The potassium hydroxide anisotropically etches to the (111) crystallographic plane in silicon, leaving smooth sidewalls at an angle of 54.7 degrees to the image plane. This smooth surface acts as a mirror to reflect extraneous light onto the image plane of the BICCD, causing spurious images and reducing the responsivity uniformity (RU) of the devices. We have developed a noncontact excimer laser-assisted process to promote a chemical reaction between a halocarbon ambient and the silicon. The laser-assisted chemical reaction results in a roughened (textured) surface which behaves as a light sink. The use of a nonreactive ambient allows us to texture the sidewalls of prepackaged and pretested devices. The sidewalls of fully functional BICCD die have been textured in a Freon-115 (chloropentafluoroethane) ambient by directing 5000 pulses with laser fluence of about 0.75 J/sq cm upon them. The RU of the devices as well as the background level (fat-zero) are dramatically improved.