表面通道P型金氧半場效電晶體之硼穿透效應及閘極結構之研究

Abstract

在本論文中，我們提出以SAP結構用於以BF2佈植之P型閘極表面通道P型金 氧半場效電晶體，來捕捉氟原子以遏止硼穿透效應。藉由捕捉氟於非晶矽 層中，以減少因氟所造成硼在閘極氧化層中擴散速率增強的效應，我們可 達到阻止硼擴散的目的。複晶矽閘極空乏效應並不因此非晶矽層而更嚴重 。閘極氧化層的可靠性也不因使用此閘極結構而有所影響。和硼穿透效應 有關，並對短通道P型閘極之P型金氧半場效電晶體的臨界電壓有所影響的 反短通道效應，也在本論文中提出討論。當硼穿透效應愈明顯時，此反短 通道效應也愈嚴重。此效應相信是由於在高溫過程中，氟增強硼在閘極氧 化層中的擴散速率所造成，並可由二維製程模擬程式模擬驗證。此外，我 們以SIMS和TEM分析氧對P型閘極之微結構和硼擴散的影響。結果發現，在 沉積SAS 結構時，由於成長中斷，造成一層非常薄的氧化層在兩層非晶矽 的界面，也使得SAS 的晶粒較小。此界面氧化層形成氧原子的擴散障礙， 造成在SAS 結構中有較高的氧濃度，並因而減緩了SAS 結構的結晶速率。 在高溫退火後，此界面氧化層可以吸收大量的氟原子，因而減少硼擴散增 強效應，並進而遏止硼穿透效應的發生。最後，對於矽閘極結構在P 型閘 極中對遏止硼穿透效應的影響，我們做一深入的研究。瞭解閘極材料及界 面雜質聚積效應對遏止硼穿透的效應的影響。並對不同閘極結構對P 型閘 極元件的特性及可靠度做仔細的研究。氮化閘極氧化層對遏止硼穿透效應 的效果也做一討論。結果發現，使用非晶矽為 P型閘極材料，可以有效地 遏止硼穿透效應，並且有較低的閘極阻值。 We have studied the effects of trapping fluorine in BF2 implanted gate electrode to suppress the boron penetration by the proposed SAP gate structure for the surface-channel PMOSFET. The retarda- tion of boron diffusion is caused by trapping of fluorine in the amorphous layer due to lower diffusion rate of fluorine in such layer. Device performance is not degraded by using this gate structure. The boron- penetration-dependent RSCE on the threshold voltage for short channel p+-gated PMOSFETs was also studided. The RSCE becomes more significant with enhanced boron penetration . Fluorine enhanced boron diffusion in the gate oxide is believed to account for the RSCE, which is confirmed by using a two-dimen- sional process simulator. Effects of oxygen impurity on the microstructure and fluorine diffusion in BF2-implanted amorphous- Si p+-gated PMOS capacitors are also characterized by SIMS and TEM. Higher oxygen concentration retards the crystallization and the fluorine diffusion. Finally, effects of materials and struc- tures of the gate electrode on suppressing boron diffusion are examined in detail. The suppression of boron penetration by the nitrided oxide is also considered. Results show that the amor- phous-Si is a promising gate material for future dual-gate CMOS process.