国立台湾海洋大学机械与机电工程学系(2).pdf

1 2005/3/6吳志偉吳志偉1 NTOU Aquatic NEMS Research Center Engineering Science for MEMS Design and Fabrication 吳志偉 國立台灣海洋大學機械與機電工程學系 Tel02-24622192-3253 Email wuchihwemail.ntou.edu.tw 2005/3/6吳志偉吳志偉2 NTOU Aquatic NEMS Research Center Atomic structure of MatterAtomic structure of Matter Everything on our Earth is made from 96 stable and 12 unstable elements. The basic structure of an atom involves a nucleus and the orbiting electrons. The nucleus consists of protons and neutrons. The difference in atomic structures results in different properties of the elements. 2 2005/3/6吳志偉吳志偉3 NTOU Aquatic NEMS Research Center Atomic structure of MatterAtomic structure of Matter Electrons can exist in more than one orbit. They can be moved from one orbit to another orbit with a change of energy. The outer orbit has a 23A diameter, which is about 1000 times greater than nucleus. In a neutral state, the total numbers of protons and electrons in an atom are equal to each other. The total number of electrons is designated as the element number or atomic number of the specific material in a periodic table. Each element contains a specific number of protons, and no two elements have the same number of protons. Elements with the same number of electrons at the outer orbit have similar properties. Atoms seek to combine with other atoms to create the stable condition of a full outer orbit. 2005/3/6吳志偉吳志偉4 NTOU Aquatic NEMS Research Center Ions and IonizationIons and Ionization An ion is an electrically charged atom or molecule. Ionization is the process of producing ions. Electrolysis processes Electron beam Ionization energy is defined as the energy needed to remove the outermost electron from an atom of the ionized medium. An ionization of a gas requires approximately 50 to 100 electro voltseV, 1.6x10-19J 3 2005/3/6吳志偉吳志偉5 NTOU Aquatic NEMS Research Center Doping of semiconductorsDoping of semiconductors According to the material’s ability to conduct electricity, there are three types of engineering materials that we use frequently for electromechanical systems. Conducting, insulation or dielectric, semiconducting materials 2005/3/6吳志偉吳志偉6 NTOU Aquatic NEMS Research Center DopingDoping The process of turning semiconducting materials to be electrically conducting. By virtue of the foreign impurity , one may control both the intensity and path of electric current flow through the semiconductor materials. In NEMS, doping of semiconducting materials can alter the material’s resistance to chemical or physical etching. Doping of silicon is thus often used as a barrier to etching as an “etching stop”. http//www.ndl.gov.tw/ICFAB_CLASSROOM/MULTI_MEDIA/index.htm 4 2005/3/6吳志偉吳志偉7 NTOU Aquatic NEMS Research Center DopingDoping Objective To determine the electric properties n or p type To improve properties, such as wear and corrosion To create an etching barrier, such as boron or phosphorous Dopants Boron -1 Phosphorous 1 Arsenic 1 Antimony 1 s Diffusion Ion implantation 2005/3/6吳志偉吳志偉8 NTOU Aquatic NEMS Research Center P- / N- type DopingP- / N- type Doping 在矽晶體中摻入三族元素,由於和矽 原子鍵結需要四個電子,三族元素原 子僅可供應三個電子,因而形成了一 個電子的空缺,我們稱之為電洞.當 外加一個電壓時,電洞向負電位處移 動,形成了電的傳導.此摻雜的區域 即稱為正型區p-type region,主 要的傳導載子carrier為電洞. http//www.ndl.gov.tw/ICFAB_CLAS SROOM/MULTI_MEDIA/index.htm 在矽晶體中摻入五族元素,由於要和 矽鍵結需要四個電子,五族元素原子 卻可提供五個電子,摻雜原子多出了 一個電子,當外加一個電壓時,電子 向正電位處移動,形成了電的傳導. 此摻雜的區域即稱為負型區n- type region,主要的傳導載子 carrier為電子。 5 2005/3/6吳志偉吳志偉9 NTOU Aquatic NEMS Research Center Doping of silicon for conductivityDoping of silicon for conductivity The degree of the increased conductivity can be related to the reduction of electrical resistivity in the material. The heavier the dose in the doping, the less the resistuvuty and thus the more electrically conductive the silicon becomes. 2005/3/6吳志偉吳志偉10 NTOU Aquatic NEMS Research Center The diffusion processThe diffusion process The diffusion process is the introduction of a controlled amount of foreign material into selected region of another materials. In genera, diffusion can take place with liquids to solids, gas to solids, and liquids to liquids. In reality, the duration of diffusion, that is the time t into the diffusion process, plays an important role in the variation of the concentration of liquid A. Fick’s law is used as the basis for mathematical modeling of diffusion processes. Gas, concentration, Solid, concentration, x X 0 Concentration of gas at x Nx 0 ,, 0 or a xa x aa CC C CC xxx − ∆ ∝∝ − −∆ 6 2005/3/6吳志偉吳志偉11 NTOU Aquatic NEMS Research Center The diffusion processThe diffusion process In doping of semiconductors by diffusion, the semiconductor substrates usually are heated to a carefully selected temperature, and the dopant is made available at the surface of the substrate. The dopant can diffuse into the substrate until a maximum concentration is reached. The maximum concentration of dopant through diffusion is called solid solubilitysolid solubility. 2005/3/6吳志偉吳志偉12 NTOU Aquatic NEMS Research Center The diffusion processThe diffusion process F atoms or molecules, or ion flux, of the foreign materials to be diffused into the substrate material D diffusion coefficient, or diffusivity, of the foreign material in the substrate material N concentration of the foreign material in the substrate The square root of the diffusion coefficients, d1/2, for selected material. x xN DF ∂ ∂ − Silicon substrate Mask High temp. dopant gas 7 2005/3/6吳志偉吳志偉13 NTOU Aquatic NEMS Research Center The diffusion processThe diffusion process The concentration N can be determined by solving the diffusion equation derived from Fick’s law. where Nx,t the concentration of the foreign material at a depth x into the substrate at time t, and Nsthe solid solubility at the diffusion temperature. x txN D t txN 2 2 ,, ∂ ∂ ∂ ∂       Dt x erfctxN Ns 2 , Initial condition Nx,0 0 for no dopant in substrate initially, Boundary conditions N0,t Ns, concentration of the dopant at the substrate surface, N∞,t 0, no dopant diffused in far away distance from the substrate surface. 2005/3/6吳志偉吳志偉14 NTOU Aquatic NEMS Research Center 擴散設備擴散設備 擴散製程一般都是在爐管 中進行，在高溫的爐管中 放入晶圓，使擴散源得以 擴散進入晶圓內部。其機 台主要為爐管設備。 http//www.ndl.gov.tw/ICFAB_CLASS ROOM/MULTI_MEDIA/index.htm 8 2005/3/6吳志偉吳志偉15 NTOU Aquatic NEMS Research Center 量測技術量測技術 將試片磨出斜角1-5度及加入化學染色方式來達成。 磨完後再經1-2分鐘之後，會發現p型區域之顏色會 比n型區域來得深，再利用光學干涉條紋即可讀出接 面深度。 接面深度量測 Ref 張俊彥, 積體電路製程及設備技術手冊, p. 302 N type8g CuSO4‧5H2O, 10cc. 49 HF P type100 cc. HFHNO3HFHNO31冰醋酸 1310 2005/3/6吳志偉吳志偉16 NTOU Aquatic NEMS Research Center 離子佈植簡介離子佈植簡介 傳統的高溫擴散技術因雜質原子的濃 度受固態溶解度的限制且會發生橫向 擴散和晶圓熱形變等缺點，嚴重影響 了元件功能。離子佈植 技術解決上述 擴散製程的困難，而且還能進行一些 傳統技術難以製作的元件結構。 http//www.ndl.gov.tw/ICFAB_CLASSROOM/MULTI_MEDIA/index.htm 摻雜原子是以帶電離子的形式，被 加速至某一能量並直接撞擊晶片而 進入晶格內部之適當的位置。因此 分佈之深度可藉由能量大小來控制， 而其劑量可由佈植過程之時間及離 子束電流來控制，至於原子種類則 由佈植機中的磁場來做精確選擇。 9 2005/3/6吳志偉吳志偉17 NTOU Aquatic NEMS Research Center 離子佈植原理離子佈植原理 當具有一定初始能量的入射離子射入固體靶 （target）時，會與靶中的原子核或電子發生碰撞， 在碰撞過程中將部份能量傳給靶材內的原子核或電子， 入射離子的能量因而減小，運動方向發生偏折。爾後， 此入射離子又與另外的靶材原子核或電子發生碰撞。 這個過程一直不斷地發生 ，直到入射離子停下來為 止，因此，具有一定初始 能量的入射離子射入靶材 後，會有一個〸分曲折的 運動路徑，同時持續地損 失能量，最後在靶材內的 某一位置停止下來。 2005/3/6吳志偉吳志偉18 NTOU Aquatic NEMS Research Center 離子分佈離子分佈 電子制止 入射離子與電子碰撞後，電 子被激發或撞離其軌道，電子 需藉釋放能量以回到基態，這 種入射離子激發電子，並損失 能量之機制即為電子制止。 摻雜原子為何會停下來 Ref 張俊彥, 積體電路製程及設備技術手冊 原子核制止 M2V224M1M2/M1M22 10 2005/3/6吳志偉吳志偉19 NTOU Aquatic NEMS Research Center 離子通道效應離子通道效應 若入射離子沿方向的晶格植入軌跡，離子不 會太靠近靶原子，離子宛若在一個無阻礙的通道內運 動，因而不易與原子碰撞減少能量損失。這種入射離 子，因晶片之方向性，而較深入晶片內部的情形，通 稱為離子通道效應 Ref 張俊彥, 積體電路製程及設備技術手冊, p. 233 2005/3/6吳志偉吳志偉20 NTOU Aquatic NEMS Research Center 離子束產生方法離子束產生方法 氣體通入離子源頭，同時在離子源頭加上電壓，以 造成氣體解離，拉出解離後的正離子。 離子束經加速及聚焦後再送往磁場，因原子量的不 同產生不同的偏轉角度，因此可取出植入所需的雜 質種類 Ref 張俊彥, 積體電路製程及設備技術手冊, p. 220 11 2005/3/6吳志偉吳志偉21 NTOU Aquatic NEMS Research Center 退火退火 離子佈植之後會嚴重地破壞晶圓內矽晶格的完整性。所以離 子佈植之後的晶圓必須經過適度的退火處理。退火就是利用 熱能來消除晶圓內晶格缺陷和內應力，恢復矽晶格的完整性， 同時使摻雜原子擴散到矽晶格上的替代位置。適當的退火溫 度、時間及環境必須是在最佳化之組合下，才能有效地消除 因植入所造成之損壞。最常用的退火方式是熱退火的方式， 可利用傳統爐管或RTA來退火。爐管回火所需的時間大約為 數分鐘至數小時，RTA則需數秒鐘至100秒左右。 2005/3/6吳志偉吳志偉22 NTOU Aquatic NEMS Research Center 退火設備退火設備 退火爐管為一個通入特定 氣體的加熱石英管， 將 需退火的晶圓經表面處理 後推入爐管中，待一定時 間後再將晶圓取出。 http//www.ndl.gov.tw/ICFAB_CLASSROOM/MULTI_MEDIA/index.htm 快速退火爐利用燈管快 速照光來加熱晶圓表面， 使擴散源得以擴散到晶 圓內部，或使佈植之離 子有足夠能量來達到電 性活化。 12 2005/3/6吳志偉吳志偉23 NTOU Aquatic NEMS Research Center DopingDoping 2005/3/6吳志偉吳志偉24 NTOU Aquatic NEMS Research Center ElectrochemistryElectrochemistry Electrochemistry, which is the study of chemical reactions caused by the passage of an electric current, is an important subject in MEMS design and fabrication. In the electroplating of polymer molds with thin metal layers by electrolysis in the LIGA process. In electrohydrodynamic pumping, which includes both electrophoresis and electro-osmosis; for driving capillary flow of fluids in microfluidic systems. Electrolysis An electrolysis process involves the production of chemical changes in a chemical compound in solution by oppositely ions moving in opposite directions under an electric potential difference. A solution that conducts electric current is called an electrolyte and the vessel that holds the electrolyte is called an electrolytic cell. 13 2005/3/6吳志偉吳志偉25 NTOU Aquatic NEMS Research Center ElectroplatingElectroplating Power supply Cathode Anode e-e- Ni →→ Ni2 →→ Ni 2e-2e- 2H2O 2e-→→ H2 2OH- ↑ H2 ↑ H2 ↑ H2 ↑ H2 Ni deposition H2evolution Ni dissolution 2005/3/6吳志偉吳志偉26 NTOU Aquatic NEMS Research Center Electrolysis ProcessElectrolysis Process A pair of submerged electrodes is required in order to provide an electric potential in an electrolysis process. The electrodes are connected to a DC source. This source acts as an electron pump that pushes electrons into one electrode, making it a cathode, and pulling electrons from the other electrode to make it an anode. The motion of ions in electrolytes under an electric field leads to the very important effect know as electrohydrodynamics of microfluid flow. 14 2005/3/6吳志偉吳志偉27 NTOU Aquatic NEMS Research Center ElectrohydrodynamicsElectrohydrodynamics ElectrohydrodynamicsEHD deals with the motion of fluids driven by an electric field applied to the fluids. Electro-osmotic pumping Electrophoretic pumping These techniques are used to move chemical and biological fluids in channels. Microfluidics are widely used in the pharmaceutical industry and in biochemistry analyses using extremely small sample quantities in the order of a few hundred nanoliters. Electrohydrodynamic pumping involves no moving mechanical parts. It is the only effective way to move fluids in extremely small channels because of the capillary effect. 2005/3/6吳志偉吳志偉28 NTOU Aquatic NEMS Research Center ElectrohydrodynamicsElectrohydrodynamics Electro-osmotic Pumping is used to move electrically neutral fluids through channels of extremely small cross sections. The condition is that the walls of the conduit in channel must have attached, immobile charges. The charges can be moved with the applied electric charges along the longitudinal direction. Electrophoretic Pumping is often used to separate minute foreign particles or species. The movement of ions of the particles in a medium is prompted by an high-voltage electric field. When the flow is fully developed, the ions in the stream can automatically separate themselves