Date: Jan 15, 2000 Source: MDA (
click here to go to the source)
A visible and near-infrared absorption spectrometer that offers very high detection sensitivities can be used as a microcontamination and water vapor sensor in semiconductor manufacturing, according to Los Gatos Research (LGR; Mountain View, CA). The device uses small, continuous-wave indium gallium arsenide (InGaAs) lasers and a novel cavity ringdown detection (CRD) geometry to detect water vapor in amounts less than 1 part-per-billion--levels considered to be 10 to 100 times more sensitive than current detection methods. It is compact in size (less than a cubic foot) and can be connected easily to gas lines outside of a vacuum chamber.
In semiconductor manufacturing, water vapor can interfere with the high-vacuum chemical reactions used to process materials. In addition, when water interacts with some corrosive gases, resulting acids can damage the containers and the pipes that store and supply the gases to the process reactors. This corrosion can produce microscopic particles that ultimately damage semiconductors by causing short-circuits--a recurring industry problem that significantly increases manufacturing costs due to process delays and low yields. Looking to achieve the ultimate process purity for semiconductors, BMDO funded LGR and its partner SRI Inter-national under a 1997 BMDO STTR Phase II to develop this technology. The funding helped the team to finalize the design of the CRD geometry, which is key to the device's part-per-billion sensitivity.
The CRD geometry is an effective method of increasing the optical path length of the spectrometer. An axial cell is used with mirrors at both ends to confine and internally reflect the light from the InGaAs lasers. By reflecting the laser back and forth within the cell, the effective path length is increased to as much as 10 kilometers, and the path length is directly proportional to detection sensitivity.
