計畫名稱：精進高壓高抗腐超流體系統發展矽與三五族材料之高縱橫比類乾蝕刻製程及磊晶層剝離技術
執行起迄：2017/08/01~2018/07/31
總核定金額：975,000元
中文摘要：磊晶層剝離技術(epitaxial lift-off, ELO)，乃本研究獲得單晶矽奈米薄膜(Monocrystalline Silicon Nanomembrane, c-SiNM)之主要方法。然傳統濕式蝕刻ELO製程之瓶頸，其蝕刻效率主要是受擴散速度限制，而不是反應速度限制；且伴隨因水溶液表面張力，引起薄膜皺摺與裂痕問題。深究「磊晶層剝離技術」之技術瓶頸，發現其蝕刻效率主要是受擴散速度限制，而不是反應速度限制，超流體具極低黏滯力、極高擴散速率及幾乎為零之表面張力等特點，受其「液氣共存」之特殊性啟發，本研究建置開發具高抗腐能力之『水浴溫控雙腔體超臨界流體蝕刻系統』及相關製程能力，且將其導入於磊晶層剝離技術上，透過調整製程步驟與條件，優化製程參數，於超流體條件下，以無水或低含水之低濃度氫氟酸(HF)，於無維持層結構幫忙下，展演以超流體技術實現III-V族薄膜與奈米矽薄膜之高效磊晶層剝離技術。本研究針對矽之金屬輔助蝕刻技術，設計建置一套鐵氟龍蝕刻載具，以石墨為電極，透過外部電壓調整樣品之蝕刻電流密度，達調控蝕刻反應速率與蝕刻機制之目的。實驗上，首先於P+‒Si基板上，觀察其微米柱樣品於不同金屬催化層厚度下(Au = 12、22、32及42nm)，其「金屬輔助化學蝕刻」之效應；爾後，利用不同金厚度之P+−Si (Au = 32nm & 20 nm)及N−Si樣品(Au = 15nm)，研究其對於不同蝕刻液配比(HF/H2O2)與不同蝕刻時間下，其微米柱與微米洞之蝕刻形貌與蝕刻深度；另外，本研究於蝕刻時，導入電壓調變機制，透過調整樣品於順偏蝕刻或逆偏蝕刻，觀察其操作於電洞或電子注入下，對於其樣品之蝕刻影響與作用機制，並比較有無氧化劑(H2O2)介入之差異。 矽基材料，利用金屬輔助化學蝕刻技術，輔以偏壓電洞調控技術，已具準直微米級矽穿孔能力，奈米柱之深寬比亦可達200左右。但若要進一步將穿孔能力進階至次微米級甚至奈米等級，亦或欲將奈米柱之深寬比更向上提升，將遭遇濕蝕刻技術本質能力的限制。此一瓶頸，同發展「磊晶層剝離技術」所遭遇的困難。本研究完成一內腔及上蓋以鐵氟龍包覆保護之高壓腔體之細部設計與建置，輔以耐壓抗腐高分子管路與閥件，克服低濃度氫氟酸與雙氧水混入高壓二氧化碳操作下，耐腐合金腔體，因微腐蝕引起的製程污染問題，以提升系統穩定性進而擴展其應用，作為超流體下發展金屬輔助化學蝕刻技術之關鍵設備，以求未來能突破當前研究限制，獲得研究進展。
英文摘要：For fast flexible electronics, transferrable mono-crystalline Si (c-Si) nanomembranes (NMs) become the most attractive candidate, owing to their material uniformity, mechanical flexibility and durability, electrical properties similar to the bulk Si, easy handling and processing, and low cost. Unfortunately, c-Si can’t directly be grown on a flexible polyimide (PI) substrate due to its high crystalline temperature. For sub-ten micrometer free-standing c-Si membranes, it can be obtained by immersing the Si wafers in KOH solution with a concentration of 50 wt% at 90°C for different duration of time to obtain different thickness (etching rate ~ 1.3 μm/min). However, the way for obtaining c-Si nanomembranes (c-SiNMs) is still quite limited. Currently, the main method for obtaining c-SiNMs is selectively to remove the tiny sandwiched SiO2 layer of the SOI (Silicon on Insulator) by using high concentrated hydrofluoric (HF) acid – called epitaxial lift-off process (ELO). It exists many limitations, including low lateral etching rate (LER) in liquid, film wrinkling and cracking issues (i.e. c-SiNMs maintained issues). Looking into the bottleneck of traditional ELO technology by wet etching method, people found its LER is mainly dominant by diffusion-limited instead of reaction-rate-limited. In other words, the primal reason for manipulating etching rate is dependent on the solubility of reaction residues and the exchanging rate of fresh etchant solution in the etching tunnel. In order to break those bottlenecks, we were inspired by those specific characteristics from supercritical fluids, including extremely low viscosity, ultra-high diffusion speed and zero surface tension – which has extremely potential to bring breakthrough in developing ELO technology. Therefore, in the beginning of this study, a highly corrosion-resistance and HF-compatible supercritical fluids (SCFs) etching system was established for developing SCFs etching process and to demonstrate its specifics on lifting out of III-V thin-film and SiNMs. To introduce MaCEtch for etching Silicon, we designed and built up a Teflon holder assembly as the etch setup – using high density graphite as the electrodes. Overall, we can directly apply voltage into the samples from etchant – to control the etching current density, etching rate and etching mechanism. In experimental, P+-Si samples with micro?pillar but having different Au film thickness (12, 22, 32 and 42nm) as metal catalyses were firstly introduced into MaCEtch to clarify how the metal thickness influence in MaCEtch. Then, two kinds of samples with different Au thickness, P+?Si (Au = 32nm & 20nm) and N?Si (Au = 15nm), were etching under various etchant ratio (HF/H2O2) with different etching time to investigate their etched surface morphology and etching depth for micro-pillar and micro-hole. In addition, we further operate the samples under reverse bias or forward bias to inject electron or hole during etching to study the etching mechanism under bias and current-driving. We also show its results difference when the etchant has no Oxidant (H2O2) involved. Eventually, our work in pioneer can become the valuable foundation for developing SCFs etching technology and bring inspired in the field of photonics, Silicon industry, etc.