3D NAND Channel Poly Recess Etch

Channel poly recess is the middle depth in a three-step sequence that carves room for the drain plug at the very top of a finished channel hole, cutting the conducting poly back further than the core-oxide fill beside it but not as far as the drain etch-back that follows it.

Upper-deck channel hole etched
poly/oxide fill deposited
Core-oxide recess
shallowest cut, center fill
Channel poly recess
deeper cut, conducting ring
Drain poly etch-back
deepest cut, plug cavity
Drain plug deposited
bit-line contact lands here next

Getting that relative depth order right is the entire point — this is not one etch repeated three times, it is three different target depths on three different materials in the same small space.

Channel Poly Recess — Carving Room for the Plug at the Top of the Hole one of three recess steps that finish the channel hole's top before bit-line contact can land top of the channel hole, cutaway view ONO memory film (outer ring) channel poly (conducts current) core oxide ("macaroni") — fills the hollow center 1. shallow: core-oxide recess (cut back first, least) 2. deeper: channel poly recess — removed further than core oxide, less than drain etch-back 3. deepest: drain-poly etch-back — the plug's own cavity, cut furthest Three recesses, three different depths, one shared target: room for the plug core-oxide, channel-poly, and drain etch-back each remove a different ring at a different depth — channel poly recess sits in the middle of that sequence, carving space without exposing the ONO film beside it.

The top of a finished channel hole is not a single material — it is concentric rings. Working outward from the center: core oxide (sometimes called "macaroni" fill) occupies the hollow middle, channel poly wraps around it as the conducting path the transistor actually uses, and the ONO memory film sits as the outermost ring, already protected by earlier steps and not meant to be touched again here.

Core-oxide recess goes first and cuts the shallowest. It pulls the center fill back just enough to open working room at the top of the hole without disturbing the channel poly ring around it.

Channel poly recess goes second and cuts deeper than the core-oxide step, by design. Because the poly is what will later connect to the drain plug and, through it, to the bit-line contact, this recess needs to clear enough depth for that plug to form properly — deeper than the oxide recess beside it, but still shallow enough to leave the ONO ring at the edge of the hole untouched.

Drain-poly etch-back finishes the sequence at the deepest point, carving the actual cavity the drain plug will fill. By the time this step runs, the recess depths of core oxide and channel poly have already set the boundaries this final etch has to respect — too shallow here and the plug has no room to seat; too deep and it risks cutting into material the channel-poly recess was supposed to protect.

Each ring recessed by the wrong depth produces a different downstream failure. A shallow channel-poly recess can starve the eventual drain plug of a clean contact surface; a channel-poly recess cut too deep risks exposing the ONO film it sits beside, the same film the earlier bottom-punch and ONO-punch etches worked carefully to protect at the other end of the hole.

Channel poly recess is a small step with an outsized dependency: Samsung's V-NAND, SK hynix's 4D NAND, Kioxia/WD's BiCS, Micron, and YMTC's Xtacking all rely on this exact middle-depth cut to hand the drain-plug and bit-line-contact modules a clean, correctly sized conducting surface — the last thing the channel-hole module does before the top of the hole is considered finished.

Take 3d nand channel poly recess etch further

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