{"id":"plasma-wet-etch-transfer","level":"matter","name":"Plasma and wet etch: selectivity and profile","shortName":"Plasma and wet etch: selectivity and profile","role":"Removes selected material while preserving the feature and surrounding stack.","description":"Etching converts temporary masking geometry into a material feature. Wet etching relies on reactions in a liquid and can depend strongly on crystal orientation and chemistry. Plasma etching combines reactive species with energetic particle effects that can help control directionality. Neither is simply “cutting downward”: sidewall reactions, transport, charging and mask erosion influence the result. Selectivity compares removal of the target material with loss of another exposed material. A successful transfer must satisfy depth, profile, roughness, residue and damage requirements together. This explains why an acceptable resist image does not automatically become an acceptable transistor or via.","specs":[{"label":"Selectivity","value":"Target removal rate / protected-material removal rate","context":"Dimensionless ratio measured under the same process conditions."},{"label":"Profile","value":"Depth, sidewall angle and bottom shape","context":"Name the material boundary and measurement stage."}],"interfaces":[{"name":"Patterned mask and stack","direction":"in","signal":"Exposed materials, feature geometry and initial surface state"},{"name":"Transferred structure","direction":"out","signal":"Etched profile, residues and possible surface damage"}],"tradeoff":"More directional or faster removal can trade against selectivity, damage and uniformity; the best compromise depends on the complete stack.","whyAI":"Fin shapes, contacts, vias and TSVs rely on accurate material removal that leaves neighboring structures electrically and mechanically usable.","related":["resist-track-development","nanosheet-gate-last-integration","hbm-tsv-reveal"],"sources":[{"title":"Lam Research — Our Processes","url":"https://www.lamresearch.com/products/our-processes/"},{"title":"MIT 6.152J — Micro/Nano Processing Technology lecture notes","url":"https://ocw.mit.edu/courses/6-152j-micro-nano-processing-technology-fall-2005/pages/lecture-notes/"},{"title":"Applied Materials — New Ways to Shrink","url":"https://ir.appliedmaterials.com/static-files/f2fbf48d-a761-4c4f-ab4c-73f312ab1ebc"}],"scale":"Optical field to nanometer pattern; material states distinguished","kind":"process","branch":"Fabrication / Repeated operations","subbranch":"From resist image to etched feature","mechanism":["Identify the exposed target, mask and stop/protected materials before choosing the route.","Deliver reactive species and, for a plasma route, control the relevant energetic interactions.","Remove reaction products while transport changes along a deepening feature.","Monitor endpoint or timing while allowing for wafer and pattern-density variation.","Measure depth, sidewall profile, residues and damage after transfer and cleaning."],"misconception":"High selectivity is not the same as vertical sidewalls or low defectivity.","check":{"question":"A process preserves the mask well but leaves tapered holes. Which property is still inadequate?","options":["Atomic number of silicon","Only the test software","Profile control, despite acceptable mask selectivity"],"answer":2,"explanation":"Selectivity compares material removal; it does not uniquely determine the spatial removal profile."},"science":[{"title":"Mask-consumption estimate","equation":"Δh_mask ≈ h_target / S","explanation":"h_target is etched target depth and S target-to-mask selectivity; lengths use matching units.","assumptions":"Constant-rate approximation without loading, faceting, endpoint overetch or spatial variation; use it only as an initial material-budget check."}],"prerequisites":["resist-track-development","process-chamber-control"],"learningObjective":"Separate etch selectivity, directionality, endpoint and damage.","workstream":"W02","visualFamily":"process-wafer","engineeringExample":"Synthetic budget: etching 200 nm with target-to-mask selectivity 10 consumes about 20 nm of mask in the simple model. A 20 nm starting mask has no allowance for nonuniformity or overetch.","evidenceNotes":"No plasma settings or wet-chemical composition is given. Schematic etch routes are not production recipes or proof of a defect cause.","labId":"library","scope":"Use the manufacturing investigation to trace compatible inputs, assembly and operating constraints; no current standalone calculator models this lesson’s full mechanism.","investigationId":"manufacturing","labScope":"Use the manufacturing investigation to trace compatible inputs, assembly and operating constraints; no current standalone calculator models this lesson’s full mechanism."}