A Parallel Detecting, Spectroscopic Ellipsometer for Intelligent Process Control of Continuously Deposited CIGS Films

Abstract

Advanced materials processing involves active control of fabrication and real-time monitoring of the final product. Sensors must be an integral part of the overall material processing system. ITN Energy Systems, Inc. and the Colorado School of Mines have developed a Parallel Detection, Spectroscopic Ellipsometer (PDSE) sensor for in-situ, real-time characterization and process control of multi-layered vapor deposited films. By measuring changes in the polarization state of reflecting light as a function of wavelength (250 to 5000 nm), the PDSE sensor determines the complex reflectance and/or the ellipsometric amplitude and phase. The PDSE provides cost-effective in-line sensing for film process control through detection of critical product variables that directly relate to film performance including: film thickness, optical excitation states, impurity concentrations, conductivity/resistance, intermixing at interfaces, microstructure, surface roughness, void fraction, defects, and grain size. The PDSE sensor is an optical probe with no moving parts that can measure the optical properties of thin films in as little as 3 msec with sensitivity to films less than a monolayer in thickness. We will use this PDSE system to provide real time process control of vapor deposited CuInGaSe2 (CIGS) films on a continuous flexible substrate. Initial results from CIGS films indicate that the PDSE has the sensitivity and accuracy to provide intelligent process control. The remaining challenge is to develop interpretive algorithms; the amount and quality of information required will determine their complexity. In addition, with the inception of in-situ, real-time monitoring, we hope to enable minimal data analysis approaches1 that provide extremely useful information with minimum interpretive algorithm development.

In Situ Sensors for CIGS Deposition and Manufacture

“…Accurate measurement is verified by ex-situ comparison with scanning electron micrograph (SEM) cross-section and energy dispersive spectroscopy (EDS). 20,21 Moving, flexible, or softened substrates require active maintenance of sensor alignment. the atomic ratio Cu/(In+Ga)) exceeds one 13,14,15 due to the formation of Cu 2-x Se on the film surface.…”

In situ diagnostic methods for thin‐film fabrication: utilization of heat radiation and light scattering

“…The absolute temperature was determined by a thermocouple behind the Table I. Real-time monitoring methods that have been applied for fabrication of GIGS films, and their major features Method Probe Features Thermocouple 12 Temperature Composition Conductivity 27 Metal contacts Electrical properties Optical emission spectroscopy 28 Plasma or electron Source flux X-ray diffraction 29 X-ray Crystalline phases, etc. Rutherford back scattering 30 Ion beam Phases, interdiffusion Ellipsometry 31 Polarized light Composition, thickness, surface structure, bandgap, etc. X-ray fluorescence 32 X-ray Composition, thickness Pyrometer 15,16 Heat radiation Composition, thickness Laser light scattering (LLS) 17 Laser beam Composition, thickness, surface structure Spectroscopic light scattering (SLS) 18,19 White light Composition, thickness, surface structure, bandgap, etc.…”

In-Situ Sensors for Process Control of CuIn(Ga)Se2 Module Deposition: Final Report, August 15, 2001

“…Slight variations in sample-to-sensor distance -or in x-ray tube currenthave little effect on interpretation and can be corrected for using the substrate signal. In contrast, techniques based on reflection (R) -including ellipsometry 17 -require precise alignment of optical source, sample, and detector. The isotropic emission also implies, however, that intensity decreases with the square of the distance to the sample, yielding a ~1/r 4 overall dependence of signal on sensor-to-sample distance, when the fall-off in intensity from the x-ray source is included.…”