具原子層沉積之高介値常數絕緣層金氧半電容之光響應研究

本文是以原子層沉積系統(Atomic Layer Deposition, ALD)將高介値常數的二氧化鉿(HfO2)成長在P-type的矽基板上來當作金氧半材料中的閘極氧化層，並以濺鍍的方式將氧化銦錫(ITO)覆蓋在二氧化鉿薄膜上來做為閘極導電層。利用氧化銦錫為透明導體的特性，以可見光光源來照射元件，利用電容-電壓曲線之量測技術於室溫下分析，比較照光前、照光時、照光後的金氧半電容元件(MOSC)的電性差異，並利用高能輻射照射對二氧化鉿產生陷阱能階進一步觀察光響應的物理機制。在電容-電壓的量測結果中，我們觀察到從反轉區掃描到聚集區的C-V曲線，只要掃描時電壓有經過聚集區，這時候便會有電洞注入到氧化層而被氧化層內的缺陷所捕捉，造成後續量測平帶電壓大幅的往左偏移，顯見在聚集區之偏壓所造成的電洞捕捉效應主宰了輻射前之C-V行為。而在掃描中照光的同時，雖有大量電子捕捉現象，但當光源關閉後，則僅有少量電子殘留在HFO2中，造成C-V偏移量與未照光情況下相比有小幅度變小的現象。在聚集區掃描到反轉區方向的電容電壓特性曲線中，我們觀察到此時平帶電壓的偏移量比起從反轉區掃描到聚集區有明顯偏左的現象。我們認為是因為在聚集區的時候，電洞已經先進入到氧化層中被捕捉完畢了，所以接下來的量測只要沒有產生新的缺陷，平帶電壓就不會有明顯偏移的現象了。在經過高能輻射的照射之後，二氧化鉿中捕捉電子的缺陷型態數量增加，使電洞捕捉與電子捕捉的現象共存，讓平帶電壓左移的量變小，在照光的情況下甚至有C-V曲線幾乎沒有偏移的情況產生。

關鍵字

原子層沉積；高k值介質；二氧化鉿；光照射；輻射

並列摘要

In this thesis, metal-oxide-semiconductor capacitors (MOSC) with high-k dielectric HfO2 deposited by atomic layer deposition (ALD) were fabricated, and indium tin oxide (ITO) prepared by sputtering was used as the gate metal material. By taking advantage of the transparent and conductive characteristics of the indium tin oxide, the MOSC was shined with visible light and its capacitance-voltage (C-V) characteristic was measured before and after illumination. Photo-response of the MOSC subjected to high-energy γ-ray irradiation was also carried out in this work such that the charge trapping mechanism of the HfO2 high-k dielectric under visible light illumination can be realized. During the C-V measurements swept from inversion to accumulation, we found large flat-band voltage shift to the left in the C-V curves due to holes injection into the oxide as long as the sweep voltage reaches the accumulation region. This indicates that hole-trapping near the HfO2/Si interface in accumulation is the dominant effectbefore the MOSC being subjected to irradiation. Large amount of electron trapping is observed when the MOSC is subjected to visible light illumination. Compared with the pre-illuminated C-V characteristics, there is a small difference in the flat-band voltage shift in the C-V curves obtained after the light is turned off due to some electron-trapping occurred in the oxide during previous light illumination. This electron-trapping was caused by electrons injection near the HfO2/Si interface when the sweep voltage was in inversion region during light illumination. For the post-illuminated C-V measurements swept from accumulation to inversion, only negligible flat-band voltage shift was found when comparing with the pre-illuminated C-V curves. In this case, it is believed that holes were already trapped by the trapping center in the oxide when the sweep voltage starting at the accumulation region. For the MOSC subjected to γ-ray irradiation, the increase of electron-trapping inside the HfO2 layer caused by irradiation cancels the hole-trapping due to the sweep voltage at accumulation, which makes the post-illuminated C-V curves shift only slightly to the left or even no shift at all when compared with the pre-illuminated C-V curves.

並列關鍵字

atomic layer deposition ； high-k dielectric ； HfO2 ； light illumination ； irradiation

參考文獻

[1] J. Robertson, “Band offsets of wide-band-gap oxides and implications for future electronic devices”, J. Vac. Sci. Technol., vol. 18, pp. 1785-1791, 2000