| 摘要: | 純鎢因具備極高熔點、良好導電導熱性、低熱膨脹係數與優異耐蝕性，廣泛應用於半導體製程、高溫熱場與關鍵功能零組件；然而其硬脆與高模數特性使傳統切削、研磨與拋光在薄化加工中不僅效率受限，亦容易引入加工變質層並造成厚度不均。本研究建立純鎢電解減薄系統，採定電流密度加工並加入工件旋轉以提升排渣能力，並結合電場與流場模擬分析輔助模具流道與電極配置設計。電場以 COMSOL 電流模組模擬，流場與粒子追蹤以 ANSYS Fluent（ k-ω SST）分析。模擬結果顯示：加入犧牲材可將邊緣效應外移，使工件有效區域之電場分布更均勻；工件轉速提升可降低排渣時間，但由於旋轉與主流方向在兩側形成加速與減速的不對稱流速分布，排渣效率存在最佳操作轉速。實驗以 5 wt.% NaOH（、極間 1.0 mm 及固定轉速條件下，探討不同加工電流密度與加工時間之影響；平面度 PV）與粗糙度 Sa）以表面 3D 輪廓量測儀量測三吋有效面積，TTV 與厚度變化以 U
型外徑分厘卡量測，移除量以重量差換算移除率與電流效率，並輔以 SEM 與 EDS 分析加工前後之表面微觀形貌與元素組成變化。結果顯示材料移除量隨電流密度與時間呈穩定且近線性的增長趨勢，且電流效率維持於高水準，顯示製程具高效率與良好穩定性，後續可依目標減薄量調整加工時間以滿足需求。平面度改善度多為負但未出現大幅惡化，高度分布可觀察到邊緣效應並隨加工時間增強；延長時間亦無法進一步改善Sa（。 SEM 顯示加工後表面形成連續且完整之蝕刻痕跡，呈階梯狀微觀溶解特徵；EDS 則顯示加工後表面含氧比例下降，表示表面氧化層比例降低。綜合加工效率與品質指標，本研究選定較高電流密度條件作為較佳參數，並以工件旋轉與外擴犧牲材作為提升排渣與電場均勻性的關鍵設計。;Pure tungsten possesses an extremely high melting point, excellent electrical and
thermal conductivity, a low coefficient of thermal expansion, and superior corrosion
resistance, making it widely used in semiconductor manufacturing, high-temperature
thermal fields, and critical functional components. However, its high hardness, brittleness,
and elastic modulus limit the efficiency of conventional cutting, grinding, and polishing
processes during thinning operations. These methods also tend to introduce a damaged
surface layer and cause thickness non-uniformity.
In this study, an electrolytic thinning system for pure tungsten was developed.
Constant current density machining combined with workpiece rotation was adopted to
enhance debris removal. Electrical-field and flow-field simulations were integrated to
assist in the design of mold flow channels and electrode configurations. The electric field
was simulated using the Electric Currents module in COMSOL, while the flow field and
particle tracking were analyzed using ANSYS Fluent with the k–ω SST turbulence model.
Simulation results indicate that the introduction of a sacrificial material shifts the
edge effect outward, leading to a more uniform electric-field distribution within the
effective processing region of the workpiece. Increasing the workpiece rotational speed
reduces debris residence time; however, due to the interaction between rotation and the
main flow direction, asymmetric acceleration and deceleration regions develop on
opposite sides of the workpiece. Consequently, an optimal rotational speed exists for
maximizing debris removal efficiency.
Experiments were conducted using a 5 wt.% NaOH electrolyte, an interelectrode
gap of 1.0 mm, and a constant rotational speed, while varying the machining current
density and machining time. Flatness (PV) and surface roughness (Sa) were measured
over the effective three-inch area using a 3D surface profilometer. Total thickness
ii
variation (TTV) and thickness change were measured using a U-type outside micrometer.
Material removal was calculated from weight differences and converted into removal
rates and current efficiency. Surface morphology and elemental composition before and
after machining were further analyzed using SEM and EDS.
The results show that material removal increased steadily and approximately linearly
with both current density and machining time. Current efficiency remained at a high level,
indicating that the process provides both high efficiency and good stability. The required
thinning depth can therefore be achieved by adjusting machining time according to
application needs. Flatness improvement was mostly negative but without severe
degradation. Height distribution maps revealed pronounced edge effects that intensified
with longer machining times. Prolonged machining did not further improve surface
roughness (Sa). SEM observations showed continuous and intact etching traces after
machining, exhibiting a step-like micro-dissolution morphology. EDS results indicated a
reduction in oxygen content on the machined surface, suggesting a decrease in the surface
oxide layer.
Considering both machining efficiency and quality indicators, a higher current
density condition was selected as the optimal parameter. Workpiece rotation and an
extended sacrificial material were identified as key design strategies for improving debris
removal and achieving a more uniform electric-field distribution. |
