wet-and-dry-etching2.ppt

1、Plasma Etching,By Student : EE576 (VLSI Processing) Minh Anh Thi Nguyen 11/8/01,Outline,What is plasma Etching Parameters in plasma Isotropic and Anisotropic Types of plasma etching system Reactive plasma etching and equipment Processes of plasma etching Advantages and disadvantages of plasma etchin

2、g How plasma etching works Why use plasma etching,When Plasma Etching applies in Microelectronic,By the early 1970s, plasma etching was first widely adapted to device manufacturing, which was mainly oxygen plasma. At this time, it was primarily used for photo resist ashing. By the late 1970s, it was

3、 widely recognized that plasma etching can offer the possibility of anisotropy etching, then rapidly increasing microelectronic industry drives the transition from wet etching to plasma etching and continuously promotes its development.,What is Plasma Etching,Also known as dry etching One of the mos

4、t important processes in IC manufacturing A key process for removing material from surface has a number of advantage over chemical etching uses a gas that is subjected to an intense electric field the only commercially usable technology for anisotropy removal of material from surface,Types of plasma

5、 etching system,None plasma based uses spontaneous reaction to appropriate reactive gas mixture 2. Plasma based uses radio frequency (RF) power to drive chemical reaction,None plasma based,Isotropic etching of silicon Typically fluorine-containing gases (interhalogens) that is readily to etch si Hig

6、hly selectivity making layers No need processing plasma equipment,Plasma based,RF power is used to drive chemical reactive Plasma takes place of elevated temperature or very reactive chemicals,Isotropic etching,A process that etches at the same rate in all direction Very good pattern transfer Poor s

7、electivity Can etch anything High etch rate,Anisotropic etching,A process that etches only in one direction. Preferable for smaller feature dimension,Isotropic Vs. Anisotropic,Isotropic: vertical and horizontal Anisotropy: much higher vertical rate than horizontal Isotropic Anisotropic,Isotropic vs.

8、 Anisotropic,hf = thickness of the thin film l= lateral distance etched underneath Af = degree of anisotropic Af = 1- l/hf Anisotropic Af = degree of isotropic hf = l Af = 0 isotropic,Plasma etching,There are five classes of plasma etching mechanisms Sputter etching Chemical etching Accelerated ion-

9、assisted etching Sidewall-protected ion-assisted etching Reactive ion etching (RIE),Sputter etching,Highly anisotropic A purely physical process Very similar to ion implantation but low energy ions are used to avoid implantation damage,Chemical etching,isotropic Plasma is used to produce chemically

10、reactive species (atoms radical and ions) from inert molecular gas. Production of gas by products is extremely important,Accelerated ion assisted etching,Like the sputter etching ions are accelerated by the sheath potential,Sidewall-protected ion-assisted etching,Can be anisotropic Involves addition

11、al species to create a protective sidewall barrier.,Reactive ion etching,Process in which chemical etching is accompanied by no undercutting since side-wall are not exposed (ie. Ion assisted etching) Bombardment opens areas for reactions Low selectivity,Parameters in plasma,Temperatures: etching rat

12、e and directivity Pressure: ion density and ion directivity Densities :charged and neutral particles Power: ion density and ion kinetic energy Other variable: gas flow rate, loading, reactor material and masking material,Plasma etch process temperature control,Process temperature is the single most

13、important parameter in the plasma process. Process temperature has primary control over etch rate and has a secondary effect on etch uniformity the temperature at which the process operates has a major influence on processing rates.,Plasma temperature control (cont.),The higher the process temperatu

14、re, the faster the processing rate. Process temperature control is mandatory when processing temperature sensitive devices. Uncontrolled process temperature can cause distortion.,Low pressure,-To help etching by product diffuse out the via - The mean free path lengths of gas molecules and ion are lo

15、nger and this reduces scattering collision that can cause a loss in profile control,How Plasma etching works,Chamber is evacuated Chamber is filled with gases RF energy is applied to pair of electrodes,How Plasma etching works,Applied energy accelerates electron increasing kinetic energy Electron co

16、llide with neutral gas molecules forming ions and more electrons Plasma discharge is bulk region and dark or sheath region near electrodes Bulk region is semi-neutral or nearly equal to number of electrons and ions Sheath region is nearly all of the potential drop; accelerates “+” ions from bulk reg

17、ion which bombard the substrate Maintained at 1 Pa(75mtorr) to 750 Pa (56torr) with gas density of 27x1014 to 2x 1017 molecules / cm3,Reactive plasma etching and equipment,Barrel reactor Reactive Ion Etcher (RIE) Magnetic-Enhanced RIE (MRIE) electron cyclotron resonance plasma etcher (ECR) inductive

18、ly coupled plasma (ICP) Clustered plasma processing,Barrel Reactor,The main components of the barrel reactor is the cylindrical vacuum chamber with a pair of RF electrodes concentrically inside,RIE system,Asymmetrical parallel plate system Plasma, sheath and boundary layer Combination physical and c

19、hemical etching Advantage: Anisotropy etching Disadvantage: low etch rate low selectivity Surface damage,MRIE system,Advantage: large anisotropic high etch rate reduced surface damage etching relative independent of loading,ERC system,Higher plasma density at low pressure Control the density of reac

20、tive ion and their kinetic energy separated,ICP system,Simple system Almost same process result as that from ERC system Two RF power generators to control ion energy and ion density separately,Clustered plasma system,Use a wafer handle to pass wafers from one process chamber to another in a vacuum e

21、nvironment can also increase throughput, and provide an advantage of high chip yield, since wafer is exposed to less contamination. minimize particulate contamination,Processes of plasma etching,Advantages of Plasma etching,Easy to control and reproduce Operated in low pressure chamber No liquid waste Uses small amounts of chemicals Eliminates handling of dangerous acids can be highly selective to underlying layers causes little damage to the photo re