In combinatorial method, combinatorial evaluation of thin film library has not been established enough, so efficiency of searching by this method is limited. One of property which has not been available combinatorial evaluation is crystallization temperature (Tx). Conventionally, Tx is measured using differential scanning calorimeter (DSC), but it is impossible to apply to the thin film library. Because its one sample size is 1×1 mm, thickness is several micrometers, and 1,089 samples (33columns and 33 rows) are integrated on one library, so the samples are too small to measure using DSC. In this study, an alternative method using infrared thermography is presented for combinatorial evaluation of Tx. This device detects infrared energy radiated from an object and its temperature can be calculated using its own emissivity.
In crystallization point, electrical resistivity change is lead with structure change, and this derives emissivity change. Low electrical resistivity means less free electron that is low reflectivity and high emissivity. In heating test, while emissivity keeps constant, T-Ta curve (T: true sample temperature, Ta: apparent temperature measured by thermography) gradient is constant, but the point of Tx, T-Ta curve gradient changes by change of emissivity. Therefore transformation point can be detected by T-Ta curve gradient change. This method can be applied to thin film library, because the method requires only observation of sample surface.
PtSi and PdCuSi amorphous alloys were employed to confirm this method. First, homogeneous amorphous alloy thin films were deposited on alumina wafer (20×20mm). Each of these samples was then heated in vacuum chamber with monitoring infrared images and electrical resistivity, in-situ. Obvious emissivity change could be detected at the same temperature of electrical resistivity change. This temperature also agrees enough with DSC results. In case of Pt67Si33, emissivity change was detected at 511K, and DSC result shows Tx at 516K, there is only 5K error between these values. At this temperature, both electrical resistivity and emissivity decreased and it agrees with the theory. Sample crystallization was confirmed after heating test by X-ray diffraction.
Measurement on the thin film library was then considered. A quarter thin film library was used, 256 samples (16×16) are integrated and each sample size is 1×1mm separated 0.2mm grid made by sputtering on alumina wafer. For first inspection, all samples were same composition PdCuSi amorphous alloy. Every 3×3 samples, center sample were blank, i.e. alumina surface, its emissivity is stable so the surface indicated reference temperature of around samples. Alumina emissivity was calibrated using a thermo couple on the sample wafer. 184 samples in the all samples were measured at one time, Tx can be detected in all 184 samples and these value errors ranged in 15K. Therefore, this method has a great of potential in combinatorial method.