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Failure analysis of liquid crystal display panel by time-of-flight secondary ion mass spectrometry
Applied Surface Science 203±204 (2003) 836±841
Failure analysis of liquid crystal display panel by time-of-¯ight secondary ion mass spectrometry S. Miyaki*, A. Yoshida, Y. Yamamoto, K. Takeuchi Surface and Material Science Laboratory, ITES Co., Ltd., 800, Ichimiyake Yasu-cho Yasu-gun Shiga-ken, 520-2392, Japan
Abstract Time-of-¯ight 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 ®lm transistor) and CF (color ®lter). 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. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Time-of-¯ight secondary ion mass spectrometry; Liquid crystal display; Mapping; Cooling sample preparation; Siloxane; Surface contamination
1. Introduction Time-of-¯ight secondary ion mass spectrometry (TOF-SIMS) is widely used to analyze the surface contamination of LCD panel [1]. The cell of LCD panel consists of thin ®lm transistor (TFT) and color ®lter (CF). The cell gap between TFT and CF is less than 10 mm, which is kept by sealant with ®ller, and ®lled with liquid crystal. The cell inside surface of TFT and CF is covered with alignment ®lm, polyimide. To analyze the local failure of LCD panel, TOF-SIMS imaging observation is the most effective method using both the wide stage raster and the narrow beam raster. In the step of cell separation, it is important to be aware that the contamination is not spread on the *
Corresponding author. Tel.: 81-77-587-9161; fax: 81-77-587-9199. E-mail address: [email protected] (S. Miyaki).
alignment ®lm. Usually the whole cell is cooled with liquid nitrogen not only to analyze volatile organic material but also to stick the contamination on the surface of the local failure region. We investigated the effect of cooling to reduce spreading and stick the material on the local region, using TOF-SIMS imaging observation. 2. Experimental PDMS is easily diffused material for LCD analysis [2]. Hexamethylcyclotrisiloxane is used as the contamination material. Fig. 1 shows the schematic illustration of LCD sample preparation. LCD panel is cut to 12 mm square with sealed area, which has opening gap in three sides. The opposite side of the seal is dipped in siloxane solution in ethanol for 1 min, and dried for 1 h. Sample is cooled in the liquid nitrogen bath and picked up, then separated by razor blades.
0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 2 ) 0 0 8 1 6 - 4
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
837
Fig. 1. Schematic illustration of LCD failure analysis procedure.
Sample separation by using razor blades is carefully executed to avoid slipping on TFT and CF. This sample is compare with the one operated at the room temperature (RT). All the measurements are performed with IONTOF TOF-SIMS IV equipped with 25 keV Ga ®eld emission ion source, cold ®nger cooling system, and image observation by stage raster. The images are obtained 7 mm 7 mm under stage raster. During the imaging observation with cooling, sample temperature rises from 150 to 170 K in 30 min [3]. Fig. 2 shows the relation between imaging region and the dipped area.
Fig. 2. Relation between measurement region and dipped area.
Fig. 3. TOF-SIMS positive spectrum with cooling preparation.
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S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
3. Results and discussion Fig. 3 shows the RT measuring spectrum obtained on the surface cooled in liquid nitrogen before opening the cell without dipping. Hydrogen ion fragments are scarcely visible, and other fragments are the same as with RT preparation. This means that H2O, humidity of the air, is little adsorbed at the surface of liquid crystal, or desorbed during pumping. Cooling measurement below 160 K is detected. Hydrogen ion fragments covered by frost, contamination of H2O cannot be avoided. It is dif®cult to analyze the LCD degradation by humidity invasion into the cell. Fig. 4 shows the layout of measured images. C2 H5 ion and CF ion are liquid crystal fragments. Figs. 5 and 6 show the images of the sample prepared at RT and the sample prepared with cooling. Fig. 7 shows the imaging map of cooling preparation sample with cooling measurement. Table 1 shows
Fig. 4. Imaging map fragment layout from Figs. 5±8.
the semi-quantitative spread of siloxane contamination distribution. The difference between RT preparation and cooling preparation seems that siloxane contamination spreads from the air, because siloxane distributes randomly on the sample. Cooling preparation reduces vaporization of siloxane. Cooling measurement after cooling preparation is the most effective
Fig. 5. Image map with RT preparation.
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
839
Fig. 6. Image map with cooling preparation.
to reduce the contamination spread, because siloxane is detected near the dipped area. Fig. 8 shows the images of the sample which was dipped entirely in siloxane solution for 2 days, and which was measured by cooling system after cooling preparation. In this map, top center is the edge of the sample, and siloxane is detected all over the measure-
ment region. It is assumed that siloxane diffusion into the gap is not so fast as the one on the opened surface compared with partial dipped experiment, therefore siloxane contamination is mainly spread from the air and along the surface, and is not spread quickly into liquid crystal or along the interface of alignment ®lm.
Table 1 Semi-quantitative spread of siloxane contamination Experimental temperature
Size of contamination area
Sample preparation TOF-SIMS measurement
Intensity of siloxane Dipped region
Center region
RT
RT Cooling
Large ±
Strong ±
Strong ±
Fig. 5 ±
Cooling
RT Cooling
Medium Small
Strong Medium
Weak Weak
Fig. 6 Fig. 7
Fig. 7. Image map by cooling system.
Fig. 8. Image map dipped for long time in siloxane.
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
4. Conclusions Sample preparation at RT induces contamination on the surface widely. Cooling sample preparation reduces contamination during the preparation. The edge of actual LCD samples are molded by silicon rubber. To prevent siloxane contamination, cooling measurement after cooling preparation is effective to reduce the spread of contamination for LCD failure analysis. And we think cooling preparation makes the
841
various defect materials in LCD stick on the local failure region simultaneously. References [1] H. Takatsuji, Mater. Sci. Semicond. Process. 4 (1±3) (2001) 309. [2] M. Deimel, H. Rulle, V. Liebing, A. Benninghoven, Proceedings of SIMS X, Wiley, New York, 1997, p. 755. [3] E. Niehuis, T. Heller, C. Bendel, J. Zehnpfenning, Proceedings of SIMS XI, Wiley, New York, 1998, p. 779.
Failure analysis of liquid crystal display panel by time-of-¯ight secondary ion mass spectrometry S. Miyaki*, A. Yoshida, Y. Yamamoto, K. Takeuchi Surface and Material Science Laboratory, ITES Co., Ltd., 800, Ichimiyake Yasu-cho Yasu-gun Shiga-ken, 520-2392, Japan
Abstract Time-of-¯ight 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 ®lm transistor) and CF (color ®lter). 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. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Time-of-¯ight secondary ion mass spectrometry; Liquid crystal display; Mapping; Cooling sample preparation; Siloxane; Surface contamination
1. Introduction Time-of-¯ight secondary ion mass spectrometry (TOF-SIMS) is widely used to analyze the surface contamination of LCD panel [1]. The cell of LCD panel consists of thin ®lm transistor (TFT) and color ®lter (CF). The cell gap between TFT and CF is less than 10 mm, which is kept by sealant with ®ller, and ®lled with liquid crystal. The cell inside surface of TFT and CF is covered with alignment ®lm, polyimide. To analyze the local failure of LCD panel, TOF-SIMS imaging observation is the most effective method using both the wide stage raster and the narrow beam raster. In the step of cell separation, it is important to be aware that the contamination is not spread on the *
Corresponding author. Tel.: 81-77-587-9161; fax: 81-77-587-9199. E-mail address: [email protected] (S. Miyaki).
alignment ®lm. Usually the whole cell is cooled with liquid nitrogen not only to analyze volatile organic material but also to stick the contamination on the surface of the local failure region. We investigated the effect of cooling to reduce spreading and stick the material on the local region, using TOF-SIMS imaging observation. 2. Experimental PDMS is easily diffused material for LCD analysis [2]. Hexamethylcyclotrisiloxane is used as the contamination material. Fig. 1 shows the schematic illustration of LCD sample preparation. LCD panel is cut to 12 mm square with sealed area, which has opening gap in three sides. The opposite side of the seal is dipped in siloxane solution in ethanol for 1 min, and dried for 1 h. Sample is cooled in the liquid nitrogen bath and picked up, then separated by razor blades.
0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 2 ) 0 0 8 1 6 - 4
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
837
Fig. 1. Schematic illustration of LCD failure analysis procedure.
Sample separation by using razor blades is carefully executed to avoid slipping on TFT and CF. This sample is compare with the one operated at the room temperature (RT). All the measurements are performed with IONTOF TOF-SIMS IV equipped with 25 keV Ga ®eld emission ion source, cold ®nger cooling system, and image observation by stage raster. The images are obtained 7 mm 7 mm under stage raster. During the imaging observation with cooling, sample temperature rises from 150 to 170 K in 30 min [3]. Fig. 2 shows the relation between imaging region and the dipped area.
Fig. 2. Relation between measurement region and dipped area.
Fig. 3. TOF-SIMS positive spectrum with cooling preparation.
838
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
3. Results and discussion Fig. 3 shows the RT measuring spectrum obtained on the surface cooled in liquid nitrogen before opening the cell without dipping. Hydrogen ion fragments are scarcely visible, and other fragments are the same as with RT preparation. This means that H2O, humidity of the air, is little adsorbed at the surface of liquid crystal, or desorbed during pumping. Cooling measurement below 160 K is detected. Hydrogen ion fragments covered by frost, contamination of H2O cannot be avoided. It is dif®cult to analyze the LCD degradation by humidity invasion into the cell. Fig. 4 shows the layout of measured images. C2 H5 ion and CF ion are liquid crystal fragments. Figs. 5 and 6 show the images of the sample prepared at RT and the sample prepared with cooling. Fig. 7 shows the imaging map of cooling preparation sample with cooling measurement. Table 1 shows
Fig. 4. Imaging map fragment layout from Figs. 5±8.
the semi-quantitative spread of siloxane contamination distribution. The difference between RT preparation and cooling preparation seems that siloxane contamination spreads from the air, because siloxane distributes randomly on the sample. Cooling preparation reduces vaporization of siloxane. Cooling measurement after cooling preparation is the most effective
Fig. 5. Image map with RT preparation.
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
839
Fig. 6. Image map with cooling preparation.
to reduce the contamination spread, because siloxane is detected near the dipped area. Fig. 8 shows the images of the sample which was dipped entirely in siloxane solution for 2 days, and which was measured by cooling system after cooling preparation. In this map, top center is the edge of the sample, and siloxane is detected all over the measure-
ment region. It is assumed that siloxane diffusion into the gap is not so fast as the one on the opened surface compared with partial dipped experiment, therefore siloxane contamination is mainly spread from the air and along the surface, and is not spread quickly into liquid crystal or along the interface of alignment ®lm.
Table 1 Semi-quantitative spread of siloxane contamination Experimental temperature
Size of contamination area
Sample preparation TOF-SIMS measurement
Intensity of siloxane Dipped region
Center region
RT
RT Cooling
Large ±
Strong ±
Strong ±
Fig. 5 ±
Cooling
RT Cooling
Medium Small
Strong Medium
Weak Weak
Fig. 6 Fig. 7
Fig. 7. Image map by cooling system.
Fig. 8. Image map dipped for long time in siloxane.
S. Miyaki et al. / Applied Surface Science 203±204 (2003) 836±841
4. Conclusions Sample preparation at RT induces contamination on the surface widely. Cooling sample preparation reduces contamination during the preparation. The edge of actual LCD samples are molded by silicon rubber. To prevent siloxane contamination, cooling measurement after cooling preparation is effective to reduce the spread of contamination for LCD failure analysis. And we think cooling preparation makes the
841
various defect materials in LCD stick on the local failure region simultaneously. References [1] H. Takatsuji, Mater. Sci. Semicond. Process. 4 (1±3) (2001) 309. [2] M. Deimel, H. Rulle, V. Liebing, A. Benninghoven, Proceedings of SIMS X, Wiley, New York, 1997, p. 755. [3] E. Niehuis, T. Heller, C. Bendel, J. Zehnpfenning, Proceedings of SIMS XI, Wiley, New York, 1998, p. 779.