C-3 電子能量損失能譜(EELS) – 同素異形體與試片厚度效應

C-3-6 成份映像 – 同素異形體與試片厚度效應

C-3-4節中，圖C-41顯示EELS能譜可以區分矽的矽元素和二氧化矽的矽元素，二者L邊刃的起始能量和近邊刃微細結構明顯不同。在半導體元件的顯微結構中有多處純矽與二氧化矽相鄰的結構，EELS的成份映像技術是否可以區分它們? 圖C-46顯示純元素矽和二氧化矽的矽的分佈在EELS成份映像是可以分離的，只要三個攝像的能窗位置和寬度設置適當。

Figure C-41 in paragraph C-3-4 shows that the Si L_2,3 edges of element Si and the oxidated Si can be clearly distinguished in EELS spectra. They are different in both threshold energy and near edge fine structure. There are many sites where Si and SiO₂ are next to each other in semiconductor devices. Can they be distinguished by EELS mapping? Figure C-46 states that the distribution of Si/Si and Si/SiO₂ can be mapped separately by adequately setting those three energy windows.

圖C-46 矽的EELS成分映像圖。(a)明場像；(b)氧元素成份映像圖；(c)單晶矽和多晶矽的矽元素成份映像圖；(d)二氧化矽的矽元素成份映像圖。Ref[1]

做EELS分析的TEM試片相對上要偏薄，盡量避免入射電子產生多重散射，造成近邊刃微細結構失真。多重散射也會影響EELS成分映像圖的品質，如圖C-47所示。圖C-47(b)明場像中的鎢栓中間的縫清晰可見，而圖C-47(a)明場中的鎢栓中間的縫則只隱約可見，經驗上得知，對應圖C-47(a)的試片比對應圖C-47(b)的試片厚。因此在鈦元素成份映像圖中，薄試片(圖C-47(d))中的TiN層和Ti層的對比清晰許多。

The thickness of TEM specimen for EELS analysis needs to be thin enough to avoid multi scattering for incident electrons. Multi scattering will smear out near edge fine structure of characteristic edges of elements. Quality of EELS elemental maps will be decreased too when multi scattering occurs, as shown in Figure C-47. The seam in Figure C-47(a) is not as clear as that in Figure C-47(b). This indicates that the specimen thickness of Figure C-47(b) is thinner than that of Figure C-47(a) by experience. The contrast between the Ti layer and the TiN layer is higher in the elemental map of the thin specimen (Figure C-47(d)) than those in the thick specimen (Figure C-47(c)).

圖C-47 EELS成分映像圖的試片厚度效應。(a)厚試片的明場像；(b)薄試片的明場像；(c)厚試片的鈦元素成份映像圖；(d)薄試片的鈦元素成份映像圖。

參考文獻

1] J. S. Bow, W. T. Chang, Y. M. Tsou, H. S. Chou, and C. Chiou, Proc. ISTFA, 101-105 (2002).