探索小间隙结构的氧化物-氮化物-氧化物扇贝行为及氟碳或氢氟碳等离子体处理后的化学分析

Sang-Jin Chung, Pingshan Luan, Minjoon Park, Andrew Metz, Gottlieb S. Oehrlein
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引用次数: 0

摘要

在高纵横比接触蚀刻过程中,氧化物-氮化物-氧化物(ONO)堆叠层在垂直侧壁上的扇贝现象很常见,其特征是氧化物层和氮化物层在不同蚀刻速率下的水平蚀刻。为了了解ONO扇贝在复杂等离子体化学中的作用机制,研究用单一氟碳化合物(FC)或氢氟碳化合物(HFC)气体处理的二氧化硅和氮化硅的表面化学是至关重要的。为了模拟SiO2和Si3N4侧壁的各向异性刻蚀,我们采用水平沟槽结构研究了FC (Ar/C4F8)、HFC (Ar/CH3F、CH2F2或CH3F)、FC/HFC (Ar/C4F8/CH2F2)或FC/H2 (Ar/C4F8/H2)等离子体产生的中性自由基的影响,当宽高比(Ar)高达25时。为了消除离子的影响,采用电感耦合等离子体处理氧化物和氮化物沟槽结构。利用椭偏仪研究了薄膜厚度随AR的变化规律。此外,对Ar/C4F8和Ar/CH2F2等离子体处理的氧化物和氮化物衬底进行了x射线光电子能谱(XPS)测量,测量地点包括沟槽结构外、沟槽入口附近(Ar = 4.3)和沟槽深处(Ar = 12.9)。我们发现了沟槽侧壁的各种响应,包括FC沉积和自发蚀刻,它们反映了(1)FC和HFC气体的性质,(2)暴露表面的性质,以及(3)相对于沟槽入口的位置。总的来说,蚀刻和沉积模式系统地变化取决于前驱体气体。我们发现ONO在不同氩弧度下的扇贝是依赖于等离子体化学的。氧化物呈现出二元侧壁轮廓,要么全部沉积在沟槽内(通过FC和FC/H2处理),要么蚀刻(HFC和FC/HFC)。在较高的AR下,沉积和蚀刻都呈现出稳定的衰减。在氮化物衬底上,HFC前驱体在入口附近观察到蚀刻,高F:C比的HFC前驱体(如CHF3)在较高的AR下出现最大的净蚀刻。对Ar/C4F8和Ar/CH2F2处理过的表面进行的XPS测量表明,Ar/C4F8总体上在沟槽内外沉积了富氟膜,而Ar/CH2F2主要沉积了交联膜(除沟槽入口附近外),沟槽深处有一层特别薄的石墨状膜。
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Exploring oxide-nitride-oxide scalloping behavior with small gap structure and chemical analysis after fluorocarbon or hydrofluorocarbon plasma processing
The scalloping of oxide-nitride-oxide (ONO) stacked layers on vertical sidewalls during high-aspect-ratio contact etch is commonly seen and characterized by the horizontal etching of oxide and nitride layers at different etch rates. To understand the mechanisms of ONO scalloping in complex plasma chemistry, it is crucial to examine the surface chemistry of silicon dioxide and silicon nitride processed with single fluorocarbon (FC) or hydrofluorocarbon (HFC) gases. To simulate the isotropic etching of SiO2 and Si3N4 sidewalls, we use a horizontal trench structure to study the effect of neutral radicals produced by FC (Ar/C4F8), HFC (Ar/CH3F, CH2F2, or CH3F), FC/HFC (Ar/C4F8/CH2F2), or FC/H2 (Ar/C4F8/H2), plasma for aspect-ratio (AR) up to 25. To eliminate the effect of ions, oxide and nitride trench structures were treated by inductively coupled plasma. The changes in the film thickness as a function of AR were probed by ellipsometry. Additionally, x-ray photoelectron spectroscopy (XPS) measurements on oxide and nitride substrates processed by Ar/C4F8 and Ar/CH2F2 plasma were performed at various locations: outside of the trench structure, near the trench entrance (AR = 4.3), and deeper in the trench (AR = 12.9). We find a variety of responses of the trench sidewalls including both FC deposition and spontaneous etching which reflect (1) the nature of the FC and HFC gases, (2) the nature of the surfaces being exposed, and (3) the position relative to the trench entrance. Overall, both the etching and deposition patterns varied systematically depending on the precursor gas. We found that the ONO scalloping at different ARs is plasma chemistry dependent. Oxide showed a binary sidewall profile, with either all deposition inside of the trench (with FC and FC/H2 processing) or etching (HFC and FC/HFC). Both profiles showed a steady attenuation of either the deposition or etching at higher AR. On the nitride substrate, etching was observed near the entrance for HFC precursors, and maximum net etching occurred at higher AR for high F:C ratio HFC precursors like CHF3. XPS measurements performed with Ar/C4F8 and Ar/CH2F2 treated surfaces showed that Ar/C4F8 overall deposited a fluorine-rich film outside and inside of the trench, while Ar/CH2F2 mostly deposited a cross-linked film (except near the trench entrance) with an especially thin graphitic-like film deep inside the trench.
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