C-2 X-光能量散佈能譜- 7B/7 積碳與輻射損傷(B)-輻射損傷

 C-2-7 輻射損傷(Radiation damage) 

在發展出楔形研磨拋光法之前，用手工研磨拋光法製備TEM試片的過程，包含局部磨薄的渦穴研磨，然後氬離子減薄。如果渦穴研磨不足，離子減薄的時間過長，氬離子會損傷TEM試片，如圖C-32所示。圖C-32(a)用渦穴研磨拋光至小於10微米的厚度，氬離子減薄時間小於一小時，6H-SiC/Ti界面完好清晰。圖C-32(b)用渦穴研磨拋光至大於30微米的厚度，氬離子減薄時間約為八小時，在試片最薄處，接近6H-SiC/Ti界面的鈦磊晶層已被非晶質化。這是TEM試片的第一階段輻射損傷，是為離子輻射損傷，主要是離子轟擊過程中，動量轉移造成原子脫離原來的晶格位置，使晶體變成非晶質。

Before wedge polish method being developed, the process of manual grinding and polishing TEM specimens includes dimple grinding for local thinning and argon ion milling. Samples will be damaged if dimpling is insufficient and ion milling time is too long, as shown in Figure C-32. The HRTEM image shown in Figure C-32(a) was from a TEM sample well dimpled to be thinner than 10 um, and the corresponding ion milling time was less than 1 hour. The BF image shown in Figure C-32(b) was from a TEM sample dimpled to be about 30 um, and the corresponding ion milling time was about 8 hours. The mechanism of first stage TEM specimen radiation damage is momentum transfer that causes atoms shifting from their lattice positions and amorphization during ion bombardment. 

圖C-32 6H-SiC/Ti TEM試片。手工研磨拋光+渦穴研磨後，離子減薄。(a)離子減薄時間小於1小時；(b)離子減薄時間約8小時；(c) (b)中方塊區域的放大圖。

TEM試片的第二階段輻射損傷發生在TEM分析中，如果將電子束集中照射局部區域過久，也會造成輻射損傷，此時是電子輻射損傷，電子的質量很小，所以電子輻射損傷主要是當少數電子由動能轉換成熱能造成的。固態無機材料的界面和晶界，是TEM試片中相對上較容易遭受輻射損傷的區域。半導體TEM試片分析中，低介電係數材料和光阻層最容易遭受此加熱式的輻射損傷。圖C-33顯示在長時間用電子束集中連續照射後，造成6H-SiC/Ti界面逐漸非晶質化，非晶質層從試片邊緣逐漸延伸入試片，非晶質層厚度逐漸變厚。

The second radiation occurs during TEM analysis. The radiation damage is caused by converging the electron beam to illuminate the specimen locally. The mass of electrons is small, so the damage mechanism in this stage is a transformation from kinetic energy to heat when electrons are trapped in the specimen. Grain boundaries and interfaces are positions where have higher energy and prone to being damaged by heat for solid state inorganic materials. For TEM specimens of semiconductor devices, layers of low K materials and PR are phases easy to be radiation damaged by thermal energy. Images shown in Figure C-33 display that the interface of 6H-SiC/Ti were amorphized by continuous electron beam illumination. The amorphous layer extended from the edge into the specimen, and was getting thickness gradually.

圖C-33  高溫熱處理後的6H-SiC/Ti TEM試片經電子束集中連續照射後，界面非晶質化的變化。(a) t = 0；(b) t = 6 分鐘；(c) t = 10 分鐘。