Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is widely used to analyze the surface contamination of LCD panels. To analyze the panel surface, the sample must be separated to TFT (thin film transistor) and CF (color filter). This preparation sometimes results in contaminating the sample. Siloxane contamination could not alone distinguish between defect and contamination of sample preparation. We evaluate the siloxane spreading by comparing cooling sample preparation/cooling measurement and room temperature preparation/measurement by TOF-SIMS imaging observation. It is found that cooling sample preparation and cooling measurement is to reduce the spread of siloxane contamination. (C) 2002 Elsevier Science B.V. All rights reserved.