Characteristics of Excimer Laser-Annealed Polycrystalline Silicon on Polymer layers

폴리머 위에 엑시머 레이저 방법으로 결정화된 다결정 실리콘의 특성

Abstract

In this work, we investigated a low temperature polycrystalline silicon (LTPS) thin film transistors fabrication process on polymer layers. Dehydrogenation and activation processes were performed by a furnace annealing at a temperature of $430^{\circ}C$ for 2 hr. The crystallization of amorphous silicon films was formed by excimer laser annealing (ELA) method. The p-type device performance, fabricated by polycrystalline silicon (poly-Si) films, shows a very good performance with field effect mobility of $77cm^2/V{\cdot}s$ and on/off ratio current ratio > $10^7$. We believe that the poly-Si formed by a LTPS process may be well suited for fabrication of poly-Si TFTs for bendable panel displays such as AMOLED that require circuit integration.

본 논문은 유기물로 이루어진 폴리머 기판상에 저온 다결정 실리콘 박막트랜지스터 제조방법에 대해 연구하였다. 먼저, 폴리머 기판에 화학증착방식으로 비결정 실리콘 박막을 증착하였고, 열처리 장치인 퍼니스로 탈수소 및 활성화 공정을 430도에서 2시간동안 진행하였다. 이후 엑시머 레이저를 이용하여 결정화를 진행하여 다결정 실리콘 반도체 막을 제조하였다. 이 박막은 박막트랜지스터 제작을 위한 활성층으로 사용하였다. 제작된 p형 박막트랜지스터는 이동도 $77cm^2/V{\cdot}s$, on/off 전류비는 $10^7$이상의 동작특성을 보였고, 이는 결정화된 박막내부에 결함 농도가 낮음을 의미한다. 이 결과로 유기물 기판상에 엑시머 레이저로 형성된 다결정 실리콘으로 제작된 전자소자는 플렉서블 AMOLED 디스플레이 회로 형성에 최적의 기술임을 알 수 있다.

Fig. 1. Photographs showing (a) Samsung Galaxy S6 Edge, (b) Samsung Gear S2 Classic, and (c) Samsung Galaxy Tab S 8.4-inch.

Fig. 2. Flexible AMOLED panels of (a) LG display and (b)Samsung display.

Fig. 3. Images of (a) Spin coater (Rotation speed: 0~8000 rpm, Hold time: 1~999 sec, Sample size: up to 4 inch) and (b) Furnace (Temperature: up to 1000 ^oC, Atmosphere: N₂, Ar, Air) equipments.

Fig. 5. Images of (a) PECVD (RF frequency: 13.56 MHz, Process temperature: 100~400 ^oC) and (b) ELA (Wavelength: 308 nm, Frequency: up to 300 Hz) equipments.

Fig. 6. Images of (a) 50-nm amorphous silicon and (b)50-nm polycrystalline silicon film crystallized by XeCl laser processing.

Fig. 8. Images of (a) Sputter (RF frequency: 13.56 MHz, Temperature: up to 150 ^oC) and (b) Ion shower (Acceleration voltage: 1 kV~15 kV, phosphorous (P) or boron (B) doping) equipments.

Fig. 9. Structure of a p-type TFT device.

Fig. 10. Temperature evolution after 10 seconds of laser pulse-on process: temperature gradient of the a-Si/multilayer film/polymer layer.

Fig. 11. Pixel circuit design. The green arrow indicates the direction of the current flowing in the OLED by the driving thin film transistor.

Fig. 13. Transfer curve of (a) before and (b) after delamination for p-type TFTs.

Fig. 12. Image of probe station (Voltage: -200V~200V, Current level: < 10¹² A) equipment.

Fig. 4. (a) Polymer solution (Fully imidized and excellently chemical resistance, Viscosity: 60∼80 Pa) and (b) Polymer film (Thickness: 15 μm, color: yellowish) coated on glass substrate.

Fig. 7. (a) SEM plane-view image and (b) AFM surface topography for poly-Si films in the laser irradiation area.

Table 1. Measured device parameters of the p-type TFTs for W/L = 7/7 μm. Values averaged over nine TFTs.