IC工艺技术3-刻蚀.ppt

IC工艺技术系列讲座 第三讲,ETCHING 刻蚀,讲座提要,1. General 1.1 Isotropic/Anisotropic etch (无定向/定向刻蚀) 1.2 Facility(动力环境) 2. Wet etch 2.1 Wet etch mechanism （湿化刻蚀机理） 2.2 BOE etch （氧化硅刻蚀) 2.3 Aluminum etch (铝刻蚀) 2.4 Nitride etch (氮化硅刻蚀) 2.5 Poly/silicon etch (多晶硅/单晶硅刻蚀) 2.6 DI water rinse and dry 3. Dry etch 3.1 Plasma Theory and application (等离子理论和应用) 3.2 Type of plasma etch (等离子刻蚀种类) 3.3 Etching gases and pressure (刻蚀气体和低压） 3.4 Etch process highlight (刻蚀工艺简介) 3.5 Etch process parameter (刻蚀工艺参数) 3.6 Ion milling (离子铣) 3.7 BCD plasma etching equipment and application 5. Next etch process 未来的刻蚀工艺,1.1 General,Isotropic etch (无定向刻蚀) Etching has no direction. Wet etch or a plasma etch without side wall passivation process. It causes undercut during the etching and change critical dimension. Anisotropic etch (定向刻蚀) Etch with direction or side wall protection Ion milling, RIE or the plasma etch with enough side wall passivation process. After etch, critical dimension has no change or very slightly difference.,Isotropic etch (无定向刻蚀),Anisotropic etch (定向刻蚀),Resist,1.2 Facility,DI water (去离子水) 17mhom Drain(排水) Special chemical dispose system Exhaust(排风) Compress air and Nitrogen (加压空气,氮气) In house vacuum(真空管道) Cooling water(冷却水) Gas cabinet / Gas line (气柜,气体管道) Gas bottle(气瓶),2.0 Wet etch,Advantage and disadvantage Chemical etch (化学刻蚀）- isotropy CD loss （线宽变小） High particle contamination （高颗粒） Unable for small geometry (不能用于小尺寸工艺) Higher process cost （工艺费用高） Most of wet etch process have high selectivity to the under layer （高选择比） Fast throughput （产量高） Low equipment (investment) cost （投资少）,2.1.1 Wet etch mechanism （湿化刻蚀机理）,Wafer surface wetting and contact with etch chemical Chemical reaction takes place, soluble byproduct formation. Remove by product from wafer surface The etch rate (and uniformity) affects by Temperature The slowest step of one of above step,2.1.2 Wet etch byproduct (副产物),Part of byproduct will be converted to water soluble material. (水溶性) Part of byproduct will converted to gas form. If the gas can not be removed from the wafer surface soon enough, the problem will occur * Block etch - snow (雪花) * Hiding at edge of resist - lifting (浮胶),2.1.3 Wet etch improvement,Improvement method Pre-wet - wetting agent （湿润剂） Agitation （搅动） Circulation （循环） Temperature control （温度控制） Filtration （过滤） In a vacuum （真空） Spray etch （喷洒） Vapor etch （蒸发） Selection of high purity of chemical （选择高纯度化学药品）,2.2.1 BOE etch,BOE (Buffer oxide etch) mixed with HF and NH4F Chemical reaction SiO2 + 6HF H2 SiF6 + 2H2O NH4F NH3 + HF NH4F (buffer agent 缓冲剂) keep a constant HF concentration during reaction NH3 -control PH value,CD lost in BOE etch（氧化硅刻蚀),BOE etch sink （氧化层刻蚀水槽),2.3 Nitride etch （氮化硅腐蚀）,Phosphoric acid (磷酸）- H3PO4 Heat up to 140 to 200oC Constant water contain （稳定水含量） Etch rate 50A/min at 165oC Selectivity to oxide 10:1 Selectivity to undoped silicon 30:1 Selectivity to N-silicon is much poorer (higher doping faster etch rate),2.4 Aluminum Etch(铝刻蚀),Chemical Phosphoric acid 77% Acetic acid 20% Nitric acid 3% Etch Temperature 30 to 70oC (keep etch time from 3 to 5 min) Etch time Manual/auto endpoint Etch rate affect Temperature Amount of Nitric acid By product Aluminum Acid-ate Hydrogen Equipment Manual etch bath Automatic etch sink Water flow etch (Watanabe) Vacuum etcher Spray etcher (Dinippon),Few special issues in Aluminum Etch,Snow - There are a lot of H2 are released during etching. In the high viscosity acid, the H2 bubble is easily to attach on the wafer surface but can not float to the surface. It blocks the etching. * Agitation - mechanical * Water flow - mechanical * Spray - mechanical * Vacuum - reduce surface tension Residue - When etch aluminum alloy film, the silicon is unable to be etched in the acid . It will leave on wafer. * Defeckle etch - may attack aluminum * Plasma etch - residue is difficult to be etch in dense area,2.5 Poly/silicon etch (硅刻蚀）,Chemical 1. HNO3 + HF (8:1) 2. KOH solution (for signal crystal silicon) Poly etch Poly need oxide mask Dilute the HF/ HNO3 with acetic acid or DI H2O Silicon etch HF/ HNO3 etch with no direction KOH etch with direction - along crystal line,Wet etch table,DI water rinse equipment Cascade - Slow, initial bath contain weak chemical QDR (Quick Dump Rinser) Fast, Create ESD (particle), Cycle time, number of cycle Spray rinse - Run with dryer * Hot DI water is increasing the rinse efficiency,2.5 DI water rinse and dry,Wafer dry,Mechanical dry - (particle, residue) Multiple cassettes spin dry FSI Single cassette spin dry Semitool Chemical Dry Freon vapor Hot water/air dry Alcohol vapor dry Alcohol dry,3.0 Dry etch （干化刻蚀）,Advantage and disadvantage Anisotropy etch (定向刻蚀) CD loss under control （线宽可控制） Etch small geometry （小尺寸刻蚀） Simple process (dry in dry out) （简单程序） Low process cost （低成本工艺） Plasma damage （刻蚀损害) Low selectivity （低选择比） Lower throughput （产量低） High equipment cost （投资高）,3.1 Plasma Theory and application (等离子理论和应用),Definition of a plasma is a partially ionized gas that is electrically conductive. Plasma energy can be used to activate chemical reactions and to etch or deposit upon surfaces exposed to the plasma,Often, electrical power is coupled into a plasma by means of parallel metal electrodes The acceleration of electrons is the principal means by which energy is coupled into the plasma. The amount of energy gained by a electron is equal to the force on it times the distance,Plasma density In a plasma, we have seen that new free electrons are generated by electron-impact ionization gas atoms and molecules. At the same time, many of electron lost to the electrode and other surrounding surface. So the plasma stabilize at a density of electrons for which the generation rate is balanced by the loss rate. This stabilized electron level is called the plasma density.,For a given reactor, plasma density is determined by four principle inputs: 1. The voltage applied to the electrode Higher applied voltage leads to more electron energy gain between collisions 2. The gas composition The molecule that has weaker molecule bond is easier ignite plasma 3. The gas pressure Gas pressure affects plasma density through the collision rate. In higher pressure shorter mean free path. At low voltage, too much energy lost in non-ionizing collision and plasma dies out. At high voltage, one electron initials so many ionizing collisions that an excessively conduct path is create through the plasma, it cause arcing. Too low pressure, gas cross the electrode gap before they generate enough ionizing collisions. 4. The application of a magnetic field A magnetic field can be set up across a plasma reactor using external magnets. Electron attempting to cross the magnetized plasma will have a much longer path length in which to encounter collision with gas molecule s before they are lost to the electrode. This means that the pressure can be much lower before the collision rate becomes insufficient to sustain the plasma.,In high pressure plasma,Added a magnetic field,Etch theory - ion bombardment The electron are much less massive than the ions, so they move much more rapidly. The result in a depletion of electrode of electrons from the space above the cathode. The ions left here constitute a positive space charge. The region of positive space charge is cal cathode sheath . Constricting the voltage drop in this way increase the force on the ions in the sheath and cause them to be accelerated into cathode where they arrive with considerable energy 500 electron-volts,Etch theory - ion bombardment effect Electron emission - emission the secondary electrons that help sustain the direct-current plasma. Chemical activation- Chemical reactive and physical bombardment Momentum transfer - No chemical reaction, move surface atom to remove of impurity atoms by evaporation,AC plasma,The above DC plasma theory is to be used to illustrate a basic of plasma. The AC plasma is used in real time. The cathode and the anode is alternating in a AC power source. The frequency of the AC power is selected to be used in this industry. The lowest frequency to maintain a plasma is 100KHz 13.56MHz RF (radio frequency) is mainly used in semiconductor field Wafer that sits on power plate receives more bombardment Wafer that sits on ground plate has less plasma damage,Plasma etch mechanism (等离子刻蚀机理),The positive ion are drawn to the cathode, and the negative ions to anode. In a medium pressure diode reactor, only 1 in 50,000 of the gas molecules are ionized. Therefore, ions are not the main drivers in the etch process, although they play a major role. Because free radicals are neutral, they behave much like standard gas molecules. When a gas molecule fragments in the plasma, each free radical formed takes up as much space as the original molecule. (This is why the pressure jumps when a plasma ignites) They are more reactive than they were in their original form, and are important etch rate drivers. Free radicals are very long-lived in a vacuum environment.,Plasma etch mechanism (等离子刻蚀机理),Plasma etch mechanism,CF4 etch Chemical reaction (CF4刻蚀化学反应),Plasma etch mechanism (等离子刻蚀机理),),Plasma etch mechanism (等离子刻蚀机理),Few notes in CF4 plasma etch The plasma contains energetic ions which bombard the wafer surface, as well as other surface in the reactor chamber. They are accelerated across the voltage drop region at the surface, and collide with it at high speed This ion bombardment is also causes anodization wear. During the silicon etch, the most prevalent chemical reaction proceeds as follows: 4F* + Si - SiF4 As the SiF4 gas forms, it is pumped away. The bi-product (CF polymer) deposits on the wafer as well as in the chamber. Only the polymer on wafer surface that receive bombardment will be removed. The etch process continues as long as the deposition rate of the polymer dose not exceed its etch rate due to ion bombardment and gas reaction. When etch hits the under layer, SiF4 formation decrease. The light emission from the Si in plasma decrease. The etching can be signed to reach endpoint,3.2 Type of plasma etch (等离子刻蚀种类),Operating Frequency Pressure Equipment Barrel 13.56MHz 500mt IPC Downstream 2.45GHz 2torr Gasonic A1000 Parallel plate 13.56MHz 300mt Lam autoetch, Rainbow 4400,4600,4700 Tegal 700,800,900 Triode 13.56MHz (T) 300mt Tegal 1500,1600 100KHz (B) Drytek 384T SPRP 400KHz 200mt Lam Rainbow 4500 MERIE 13.65MHz 100mt Precision 5000 RIE 13.56MH 20mt AME 8000 TCP 13.56MHz (P) 1-5mt Lam 13.56MHz(B) DPS 13.56MHz (P) 1-5mt Centrura 13.56MHz(B MRE 13.56MHz (T) 3mt Tegal 6000 800KHz (B) ECR 2.45GHz(T) 0.5-5mt Hitachi 13.56MHz(B) Helicon 0.5-5mt,IPC barrel etcher,13.56MHz Use oxygen only for resist ashing at 1 torr/500w Use CF4/O2 for etching at 0.5 torr/250w,Tegal 900 series,Parallel plate etcher,Lam autoetch 490/590,Parallel plate etcher,Tegal 1500/1600 series,Triode- dual frequency etcher,AME 8300 Series,AME 8100 series is the manually wafer loading system AME 8300 series is the automatically wafer loading system AME 8310 - Oxide etcher AME 8330 - metal etcher AME 8340 - poly etcher,Lam Rainbow etcher,Rainbow is the name of Lam etch platform 4400 is a poly etcher used RF power, wafer sits on ground. 4500 is an oxide etcher used SPRP power source 4600 is a metal etcher, wafer sits on power electrode.,ECR,Gasonic 1000,Use microwave power for disassociate Gas,Trends in plasma etch chemistry 1,3.3 Etching gases and pressure (腐蚀气体和低压）,Trends in plasma etch chemistry 2,3.3 Etching gases and pressure (腐蚀气体和低压）,3.3 Etching gases and pressure (腐蚀气体和低压）,Pumps used in semiconductor process Applied Pressure Vacuum Range Mechanic pump 10-2 760 - 10-3 机械泵 Mechanic pump/blower 10-2 760 - 10-3 机械泵+罗茨泵 Diffusion pump 10-5 10-3 - 10-7 扩散泵 Turbo molecule pump 10-5 10-2 - 10-10 分子泵 (50000 rpm) Cryo pump 10-7 10-6 - 10-12 冷泵,3.3 Etching gases and pressure (腐蚀气体和低压）,Pumps used in etch process,Dry pump stack,Turbo pump,Oil pump,Oil pump Stack,3.4 Etch process highlight (腐蚀工艺简介),Poly silicon etch Nitride etch Oxide etch Aluminum/aluminum alloy etch Polycides etch SOG etch W/TiW/TiN etch Resist etch (ash),Type of etch process,Polysilicon & salicides Etch,Polysilicon can be etched by CF4, SF6 or Cl2 chemistry in a parallel plate etcher, but only the Cl2 process is an anisotropic process. Here are some more advance polysilicon etch recipes and salicide recipes: 1. CL2 with ECR uwave plasma, 875 gauss, etch rate increases with CL2 flow, etching by neutrals, lowers the flow rate, increases ions and increases anisotropic profile; 2. MERIE of silicide over polysilicon (salicide) on gate oxide; CL2 at -80V d.c.bias for silicide, reduce d.c. bias and power density for poly etch to endpoint, switch to HBr to clear windows of stringers, etc.,Silicon dioxide and doped glasses-sidewall spacer etching,Use a single wafer system, the typical etch chemistry is CHF3/C2F6(CF4)/He. It removes bulk of oxide in timed cycle, reduce C2F6(CF4) flow power, increase selectivity to poly to 11:1 to endpoint. Reduce temperature on wafer electrode will increase selectivity. TCP, NF3+He, improved selectivity oxide to poly of 60:1 to 100:1, -600nm/min for BPSG.,Aluminum alloys and sandwich metal systems,Chlorine based compounds etch Al and Al+Si readily. The addition of copper is a problem, because the volatility of CuClx is very low. Most metal etching is done by ion-enhanced protective with BCL3+CL2+CHF3, followed by post etch treatment in a fluorine-rich plasma to exchange the adsorb Cl with non-corrosive F. The addition of N2 and Al increases the etch rate of Cu.,Photoresist,Oxygen plasma are a standard method for stripping photoresist by ashing. Damage can occur during this relatively uncontrolled operation. Widely accepted are the metal atoms and ionic contamination present in the resist, which are not removed in the plasma. A combination of dry and wet stripping is preferred.,3.4 Etch process highlight (腐蚀工艺简介),Break through Remove nave oxide - lower selectivity Bulk etch (Main etch) High etch rate, maximized selectivity, optimum selectivity Over etch Good endpoint signal, high selectivity to under-layer material * Resist removal Partially or completely remove resist,The major etch steps,3.5 Etch process parameter (刻蚀工艺参数),Etch rate (every steps) (刻蚀率） etch uniformity (every steps) (刻蚀均匀度） Selectivity (to bottom layer material/ resist/impurity in film) (选择比） Endpoint detection (终点检测） Loading effect （负载效应） Residue （残余） Damage （损伤） Throughput （产量）,Forward /reflective power Base pressure Leak rate Partial pressure (gas flow and pump speed) MFC calibration Wafer transfer reliability Wafer transfer cycle time Pump maintenance,* The useful parameter data is taken from an equipment that has been proved its performances are in specification,Preventive Maintenance,Etch Rate Uniformity Selectivity,Type of Endpoint detection,Type of endpoint detection Equipment Laser Dryteck, AME 8110 Emission spectroscopy Most of dry ether Infra-red Vacuum etcher Bright light reflection Spray aluminum wet etch,Emission spectroscopy Endpoint detection,In a plasma, excited atoms and molecules emit light spectrum when their electrons change energy states. The strength of the emitted light spectrum indicate the progression and characterization of the chemical and atomic reaction. Emission spectroscopy study the specific light spectrum and detection the end of a special reaction,Lam 590 Endpoint trace,Typical wavelengths in EP application,Oxide CO: 482.5 nm or 520 nm SiF: 440 nm Poly SiCl2 405 nm F 704 nm Nitride SiN 405 nm Aluminum AlCl 261.4 nm, 527nm Al 396 nm Resist CO 297.7 nm, 483.5 nm 520 nm Silicon SiCl2 405 nm,Loading effect,The loading effect is the phenomenon that etching uneven locally. This phenomenon is new and special to the plasma etch processes. The etch rate can be best stated by this equation: Plasma etch rate = 1_ exposed surface area Loading effect is more severe to be happened * on the chemical behave etching plasma process. * on the etch process that relies on sidewall passivation. * Wafer with uneven resist pattern density. * Wafer with various size of opening,Poly Residue,1. Cause by under etch 2. Impurity in the film - POCL3 contamination in poly 3. Contamination in under layer film 4. Polymer left over,Poly film etched to endpoint in Lam 490,Damage,Some of the problems associated with anisotropic RIE are listed as follow: Metallic Contamination-Deep level traps; Degraded lifetimes; High contact resistance; Leakage current Polymer Formation-High contact resistance UV Radiation-Trap generation Electro Static Discharge (ESD)-Gate oxide breakdown Physical Damage-Due to energetic ion bombardment The etching process is directional; therefore, foreign material on the surface can also act as a mask, changing the desired etched pattern. Heavy metals (for example, knocked off chamber walls or the electrode by ion bombardment) may contaminate the wafers. Radiation damage can occur in the silicon dioxide by the build up of trapped charge in the oxide layer,3.6 Ion milling (离子铣),Ion beam milling uses the energy imparted to a beam of ions. The ion beam usually consists of an ionized inert gas such as argon to perform etching. The ions with energies in the 300-1500eV range strike the bonds that hold them to adjacent atoms. This process depends on impact and energy transfer, not on the charge of the incoming ion. The charge on each ion in the incident beam makes the formation of a collimated, single energy beam possible. The schematic of a typical ion milling system is shown in Figure 6.,3.7 BCD plasma etching equipment and application,Lam 490 Diode Poly, Nitride Lam 590 Diode Oxide AME 8330 RIE Metal, Metal alloy AME 8310 RIE Oxide Tegal 1611 Triode Poly, Nitride Tegal 1612 Triode Metal, Metal alloy Tegal 903 Diod