氨電漿對下閘極多晶矽薄膜電晶體之影響

Abstract

首先，本研究深入探討氨電漿對於下閘極多晶矽薄膜電晶體鈍化效應之影響。這些元件經過數種條件的氨電漿製程，包括不同階段、不同製程時間長度，以及不同功率的電漿製程。 相較於沒有經過電漿製程的元件，pre-SPC-treatment會使元件電性變差，而post-SPC-treatment及after-AA-treatment會提升元件電性。經過pre-SPC-treatment的元件有最差的電性表現，而經過after-AA-treatment的元件則有最好的電性表現。雖然after-AA-treatment是鈍化缺陷最有效率的方式，但是相較於post-SPC-treatment，經過after-AA-treatment的元件也受到最嚴重的離子轟擊傷害。此外，較長時間或是較高功率的電漿製程，可以較有效地提升元件電性、抑制電流突增效應(Kink Effect)。較高功率的電漿製程也可以較有效地提升閘極氧化層的品質。 隨後，本研究探討退火製程對於已接受過電漿製程之多晶矽薄膜電晶體的影響。我們推測在氮氣的環境之下，退火或許可以消除乾蝕刻期間，在閘極氧化層中產生的電洞缺陷。此外，經過退火的元件，其電性表現主要受到幾個機制影響，分別是： (1)退火消除閘極氧化層中的電洞缺陷、(2)退火製程期間，氮自由基及氫自由基被釋出，並喪失鈍化效應、(3)退火製程後，殘餘的鈍化效應、(4)氨電漿製程中所造成的電漿傷害。

First, the passivation effect of NH3 plasma treatment on bottom gate poly-Si TFTs is thoroughly discussed. The poly-Si TFTs are exposed to NH3 plasma with several conditions, including diverse stages, various plasma treatment time, and different plasma power. Compared with the sample without any plasma treatment, pre-SPC-treatment degrades device performance; however, post-SPC-treatment and after-AA-treatment improve device performance. The poly-Si TFTs with pre-SPC-treatment exhibit the worst performance, and those with after-AA-treatment ones exhibit the best performance than the counterparts. Although after-AA-treatment is the most efficient technique to passivate traps, the poly-Si TFTs with after-AA-treatment suffer from the heaviest ion bombardment damage than those with post-SPC-treatment ones. In addition, longer plasma treatment time or higher plasma power will enhance performance and alleviate kink effect more effectively. The plasma treatment with higher plasma power will also strengthen the bulk oxide quality more significantly. Second, the impacts of post-metal-annealing on plasma-treated poly-Si TFTs are systematically investigated. We hypothesize that PMA in N2 ambient is a method to annihilate the hole traps in the gate oxide generated by plasma dry etching. Moreover, the performance of the poly-Si TFTs with PMA are mainly attributed to the combination of following mechanisms: 1) the elimination of the hole traps in the gate oxide by PMA, 2) the out-diffusion of nitrogen and hydrogen radicals during PMA processing, 3) the remaining passivation effect by NH3 plasma, and 4) the plasma-induced damage by NH3 plasma.