In photolithography, haze prevention is of critical importance to integrated circuit chip manufacturers. Numerous
studies have established that the presence of ammonia in the photolithography tool can cause haze to form on
optical surfaces resulting in permanent damage to costly deep ultra-violet optics. Ammonia is emitted into wafer
fab air by various semiconductor processes including coating steps in the track and CMP. The workers in the
clean room also emit a significant amount of ammonia. Chemical filters are typically used to remove airborne
contamination from critical locations but their lifetime and coverage cannot offer complete protection.
Therefore, constant or periodic monitoring of airborne ammonia at parts-per-trillion (ppt) levels is critical to
insure the integrity of the lithography process. Real time monitoring can insure that an accidental ammonia
release in the clean room is detected before any optics is damaged.
We have developed a transportable, highly accurate, highly specific, real-time trace gas monitor that detects
ammonia using Cavity Ring-Down Spectroscopy (CRDS). The trace gas monitor requires no calibration gas
standards, and can measure ammonia with 200 ppt sensitivity in five minutes with little or no baseline drift. In
addition, the high spectral resolution of CRDS makes the analyzer less susceptible to interference from other
gases when compared to other detection methods.
In this paper we describe the monitor, focus on its performance, discuss the results of a careful comparison with
ion chromatography (IC), and present field data measured inside the aligner and the reticule stocker at a semiconductor fab.
In the semiconductor industry, control of ammonia at the parts-per-billion concentration level is critical to insure the integrity of the lithography process. Ammonia is emitted into wafer fab air by various semiconductor processes including CVD, wafer cleaning, coater tracks, and CMP, as well as from outdoor air. Exposure to even low parts-per-billion concentrations of ammonia during the photolithography process can lead to yield loss and unscheduled equipment downtime. Picarro, Inc. has developed a field-deployable, real time, ambient gas analyzer capable of continuously monitoring parts-per-trillion levels of ammonia in situ, and in real-time, thereby allowing a user to directly monitor ammonia levels in sensitive photo-lithography equipment.
Cavity ring-down spectroscopy (CRDS) can provide high sensitivity, high precision, and absolute calibration in a wide range of environments. We report on a compact cavity ring-down spectrometer that can measure atmospheric toxic industrial compounds such as hydrides and hydrazines. The ring-down spectrometer is fully contained in two 5 ¼" tall, 19" wide rack mount enclosures and utilizes a robust, near-infrared, fiber-coupled tunable diode laser. The instrument has a baseline sensitivity of 8 x 10-11 cm-1/Hz½. We will present the results of this study, which demonstrates the capability to detect toxic gases such as arsine, silane, and hydrazine (simulated using ammonia) in air at parts per billion (ppb) concentrations in less than 1 minute. We will also present results on CRDS instrument performance, including zero drift, precision, absolute accuracy, and linearity over a wide range of environmental operating conditions.
We report on cavity-enhanced second-harmonic generation of 488 nm radiation in a 5 mm long periodically poled KTiOPO4 (PPKTP) crystal pumped by the output of a single-mode 976 nm semiconductor external cavity laser. At a pump laser output power of 660 mW, a mode-matching efficiency into an enhancement cavity of 65 % was observed. A maximum power of 156 mW at 488 nm was generated in the enhancement cavity of which 130 mW was coupled out. Under these pump laser conditions an overall optical conversion efficiency of 20 % and an overall electrical to optical efficiency of 9 % was measured. Both the spatial and spectral properties of the 488 nm beam are of very high quality. Typically, a near-diffraction-limited beam with M2<1.1 is produced with low astigmatism and little ellipticity.
We report on robustness testing of a highly reliable frequency-doubled, external cavity semiconductor laser (DECSL). The laser module has been demonstrated to survive 6G operating vibration swept from 100 Hz to 500 Hz at 0.25 octaves/min. Impact shock to destruction was performed, and the unit passed operating specifications up to 300G. Good pointing stability and laser start times are shown as a function of repeated environmental temperature cycling between operating extremes.
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