WET工艺介绍

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1、WET Process Introduction,Purpose of Wet Cleaning Process,Through to a series of processes to make the wafers free from particles, organic contaminations, metal contamination, surface microroughness and native oxide using some kinds of chemicals including DIW.,Purpose of Wet Cleaning Process,For Etch

2、ing process Oxide remove. Nitride remove. Photoresist & polymer remove. For Cleaning process Free of particles. Free of metal ion. Free of organic. Free of micro-roughness. Free of native oxide.,Wet Cleaning (Pre-treatment),Wet Cleaning (Post-treatment),Resist Removal,Diffusion,CVD,PVD,Lithography,E

3、tching,Doping,Wafer In,Wafer Out,IC Processing,Wet Process,1. FEOL post-ash clean 35% - typical SPM. - trend is to integrate resist striping and cleaning. 2. Pre-diffusion clean 30% - RCA clean - trend is to use dilute chemistries to reduce cost, improve equipment reliability and process performance

4、. 3. BEOL post-etch clean 20% - issues with technical, cost, environment - trend is to use single wafer dry clean 4. Others (Post CMP and special cleaning) 15% - SC1 based cleaning,Chemicals Involved,Wet bench,Purpose of Pre-clean is to remove the last unwanted oxide layer and prepare surface free o

5、f metallic contaminants and good PC for next oxidation.,Pre-diffusion clean - RCA clean,SiO2( s ) + 6HF( l ) H2SiF6( l ) + 2H2O( l ) The etch rate (or reaction rate of HF with oxide) can be slowed by adding more water and lowers the concentration of HF. HF will etch BPSG Oxide Nit Si,H2O:HF 100:1 (5

6、0: 1, 49%) Function : Remove Oxide(SiO2) Mechanism: Reacts with Oxide and form a solvable byproduct.,Oxide Etch HF,Etching off native oxide leaving hydrophobic Si surface, repels H2O, that is prone to H2O mark As a method to passivate surface, H2O2/SC1/SC2 last is used.,After cleaning HF on Si, the

7、Si wafer has H2SiF6= it is charged up with SiF6 2- ions = this has high affinity to attract defects, due to strong polarity.,What is H2O mark?,It is some H2O stain which oxidises the Si surface. It can also be a concentration of H2O contaminants.,H2O attracted area easy to create H2O mark,ox,ox,Si w

8、afer,What is the impact of water mark?,Water mark can cause problems with adhesion of films, contact resistance, non-uniformity between conducting layers, block etch, gate oxide defects.,How to prevent it?,Treat the wafer surface with eg.H2O2, SC1,SC2 (some oxidation effects) to ensure hydrophilic s

9、urface throughout. Ensure dryers performance Vapor Jet dryer Low pressure Dryer Spin Dryer Micro Mist Dryer,DI water is De-ionized water.,Water Rinse: DI Water,DIW tank is for rinsing wafer as clean as possible before going into the next chemical tank to prevent cross-contamination or before leaving

10、 the hood. DIW can overflow or quick dump rinse (QDR). Overflow is very stable flow of DIW and gives good PC control. It makes use of diffusion and dilution. QDR, on the other hand makes use of extra drag force when DIW dump & it is fast at removing acid trace, but since there is more agitation in t

11、he tank, it may result in higher PC. Control of the DIW tank and surrounding cleanliness is important. DIW tank overflows at all times with by-pass flow to prevent bacteria. Bacteria will result in PC & metallic contamination.,DIW Tank,DIW can be hot or cold - depends on previous and next tanks. Hot

12、 Chemical will be followed by Hot DIW/Cold DIW; this is to prevent thermal shock. For high viscosity chemical, HDIW rinse will improve solubility of the chemical, thus improve the diffusion of chemical to bulk of DIW, this improves the rinse efficiency. There is also the DIW Megasonic Tank (overflow

13、 or with quick dump rinse). The extra Megasonic power helps particle reduction and improves rinsing efficiency especially for viscous chemical.,DIW Tank,DIW flow-rate. Process Time. Dump Cycle & Process Time for each sequence. Megasonic On Sequence.,Critical Parameters,30C, NH4OH: H2O2:H2O (1:2:50)

14、Function: Particle removal, Light polymer removal Mechanism: oxidation and electrical repulsion,Oxidation,Dissolution,Surface etching,Electrical repulsion,Oxidation mechanism,Electrical repulsion mechanism,Particle clean SC1 (Standard clean 1),SC1 with Megasonic,Transducer,Transducer,Transducer,Part

15、ial wetting,Solvent diffusing at interface,Total wetting,Floating free,Benefit: enhance the particle remove rate. Drawback: H2O2 will be reduced during operation, which cause surface roughness!,The mechanism producing the rough surface is the NH4OH acts as the etchant of the oxide while H2O2 acts as

16、 the oxidant:,Surface Micro-roughness,Si H2SiO42- (H3SiO4-, HSiO43- etc),V1,V2,HO2-,OH -,Path-1,Path-2,OH -,V3,V1 = k1HO2-3 k1=1.2x1014 (65C) V2 = k2OH- k2=5970 (65C) V3= k3OH-2 k3=2.0x109 (65C),Path-1,Path-2,Si Substrate,Methods of reducing the microroughness can be summarized as: Reduce the proportion of NH4OH ( the etchant) Reduce the temperature of the bath Reduce the cleaning time Co

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