High aspect ratio structures are the backbone of advanced chips, from deep vias in interconnect stacks to vertical transistors and 3D memory. Achieving straight walls with clean bottoms requires the right plasma chemistry, precise pressure control, and a balance between chemical and physical etching. This guide explains the Top 10 Dry Etch Chemistries for High Aspect Ratio Semiconductor Features in simple language with practical process insights. You will learn what each chemistry excels at, how passivation works, and which knobs matter as aspect ratio dependent etching grows. The aim is to support beginners and practitioners with guidance you can apply in development and production.
#1 C4F8 Ar O2 for SiO2 vias
C4F8 Ar O2 for SiO2 vias: For deep oxide trenches, a fluorocarbon plasma forms a protective polymer on sidewalls while ions clear the trench bottom. Keeping low pressure and moderate bias encourages ion directionality and prevents bowing. A small O2 flow adjusts polymer thickness so that the etch remains vertical without closing at the neck. Adding argon raises ion density and helps sputter the passivation locally at the bottom. Control microloading with uniform pattern density, wafer temperature, and seasoning cycles to stabilize chamber walls and reduce etch rate drift. Use endpoint traces and post etch measurements to tune overetch without wasting selectivity or causing notches.
#2 CHF3 rich fluorocarbon for contact holes
CHF3 rich fluorocarbon for contact holes: CHF3 dissociation creates CFx fragments and hydrogen that tune polymer formation. It is popular for oxide contact etch where selectivity to photoresist and nitride matters. Higher CHF3 raises passivation and mitigates notch formation near etch stop layers, while a small O2 fraction keeps residue manageable. Operate at low pressure to reduce aspect ratio dependent etching and maintain ion energy. A post etch O2 ash followed by solvent clean removes polymer, protecting downstream metallization from carbon residues and improving electrical yield. Use chamber pre conditioning wafers to stabilize wall chemistry and keep first wafer effects under control.
#3 SF6 C4F8 time multiplex for deep silicon
SF6 C4F8 time multiplex for deep silicon: The Bosch style sequence alternates deposition and etch steps. SF6 rich steps supply fluorine radicals for high silicon etch rate, while short C4F8 steps deposit a polymer that shields sidewalls. Adjust duty cycle to reduce scallop amplitude, then apply a finishing cycle with shorter periods for smoother walls. Lower platen temperature increases polymer stability and improves verticality. For smoothness, combine with brief isotropic SF6 steps, and use helium backside cooling control to avoid footing near buried oxide stops. Endpoint using pressure or optical methods, and validate with cross section to ensure corner rounding stays within design limits.
#4 HBr O2 for polysilicon gates
HBr O2 for polysilicon gates: HBr creates a silicon bromide layer that passivates sidewalls, while O2 scavenges polymer and tunes selectivity. Operating at mid pressure with controlled bias yields straight profiles with low microtrenching. Nitrogen can be added to stabilize the plasma and reduce notching over oxide or nitride underlayers. Careful endpoint detection prevents overetch damage to hardmask and gate oxide. A brief oxygen lean clean within the same chamber can remove residue without roughening, supporting tight line edge roughness targets for advanced logic and memory. Follow with diluted wet cleans to protect high k dielectrics and prevent roughness driven variability.
#5 Cl2 BCl3 for metal hardmasks and Al lines
Cl2 BCl3 for metal hardmasks and Al lines: Chlorine provides volatile metal chlorides, while BCl3 moderates ion energy through polymer formation and improves selectivity to oxide. Use low pressure and high source power to maximize radical production, with modest bias to limit sidewall roughness. A small addition of nitrogen or argon can improve profile control and minimize faceting. Pre soak surfaces with a brief BCl3 exposure to condition native oxides, then start the main etch. Follow with a neutralizing downstream O2 or H2 plasma clean to remove chlorinated residues and reduce corrosion risk. Dry storage with humidity control prevents post process pitting and discoloration.
#6 CF4 H2 or CHF3 H2 for nitride spacer etch
CF4 H2 or CHF3 H2 for nitride spacer etch: Adding hydrogen shifts the chemistry toward polymer rich conditions that protect oxide while etching nitride. Operate at pressures that sustain ion directionality without excessive scattering. Balance hydrogen carefully because too much can choke the trench with polymer and slow clearing at the bottom. A temperature controlled chuck keeps deposition predictable across the wafer. Endpoint on optical emission or time mode with conservative overetch to preserve spacer width while clearing footings, which is important for subsequent epitaxy and silicide steps. A short post etch O2 treatment removes residual polymer while keeping line edge roughness within specification.
#7 CH3F CO Ar for high selectivity oxide etch
CH3F CO Ar for high selectivity oxide etch: This recipe favors controlled polymer creation and reduced ion damage. CO assists by forming volatile COF2, which moderates free fluorine and increases selectivity to silicon nitride and resist. Ar sustains ion bombardment that opens the bottom while sidewalls remain protected. Run at low pressure with steady bias and moderate source power to limit charging and notching. After etch, apply a short in situ O2 clean followed by wet solvent to remove organics, which prevents defects during copper electroplating or dielectric deposition. Use periodic chamber audits for metallic contamination because trace copper can suppress selectivity and drive defects.
#8 Cl2 O2 for TiN and barrier stacks
Cl2 O2 for TiN and barrier stacks: Mixed chlorine and oxygen plasmas convert TiN to volatile chlorides while oxygen helps break carbon containing layers. Keep oxygen modest to avoid nonvolatile TiOx formation that slows etch and increases roughness. Bias should be tuned to overcome native oxide caps without causing trench sidewall attack. A brief pre clean with Ar can remove contaminants and reduce microtrenching. Finish with a hydrogen containing downstream clean to neutralize chlorine and suppress post etch corrosion during subsequent wet cleans or dielectric depositions. Inline surface analysis helps catch residual halogens early, which preserves adhesion of the next film.
#9 C4F6 rich fluorocarbon for narrow oxide features
C4F6 rich fluorocarbon for narrow oxide features: C4F6 produces heavier fragments that form robust sidewall films at very high aspect ratios. This helps prevent bowing and necking in ultra narrow trenches and vias. Oxygen is kept very low to maintain protection, while bias and pressure are tuned to maintain bottom opening. Care must be taken to manage microloading through dummy fill and density equalization. Season chambers with dedicated wafers so that wall conditions are stable, which improves within wafer and wafer to wafer uniformity at tight design rules. Use careful post etch cleans to remove tenacious polymer without eroding critical dimensions.
#10 Cl2 HBr O2 for fin and line etch on silicon
Cl2 HBr O2 for fin and line etch on silicon: Combining chlorine and bromine offers balanced volatility and passivation. Chlorine drives main etch while bromine builds a thin passivation film that resists lateral attack. A small oxygen flow limits polymer and reduces line edge roughness. Operate at controlled temperature to prevent footing and taper in dense arrays. Careful bias pulsing or low frequency bias can reduce charging and microtrenching, which protects critical dimensions across dense to isolated pattern environments and enhances yield for advanced nodes. Use selective hardmasks and staged overetch recipes to clear trenches without losing height in narrow fins.