3d nand inter deck plug etch

Inter-deck plug, or joint etch, is the step that exists purely to let a channel hole be cut in two separate passes and still come out looking like one continuous hole — a seam that has to disappear electrically even though it is never erased physically.

Lower-deck CH etch done
50-80:1 aspect ratio reached
Sacrificial plug fill
seals the open lower-deck hole
Upper-deck mask alignment
must register to the buried hole
Sac-poly recess
reopens the lower-deck hole
Upper-deck CH etch
continues the same channel

The problem it solves is simple to state and hard to avoid: a deep, open hole cannot sit underneath a second mask and deposition step without something going wrong.

Inter-Deck Plug (Joint) — the Seam Between Two Channel-Hole Passes a sacrificial fill and recess that gives the upper-deck mask a flat surface to align to lower deck (etched first) upper deck (etched second, after the plug) lower-deck CH etch sacrificial plug fill — seals the hole upper-deck CH etch mask aligned to buried lower hole any misalignment here = a kinked channel Why a plug, not a direct join the lower-deck hole can't stay open under the upper- deck mask and deposition a sacrificial fill seals it, giving a flat, stable surface to pattern on later removed by sac-poly recess, opening the hole back up for the upper deck A seam, not a second etch of the same kind the inter-deck plug is a fill-and-recess step, not a high-aspect-ratio etch — but the alignment it sets up for the upper-deck mask is just as critical as either deck's own aspect-ratio control. triple- and quad-deck channel holes multiply this exact seam — one more plug, one more alignment risk, per extra deck

A fully etched lower-deck channel hole cannot just sit open while the upper-deck mask gets patterned on top of it. Photoresist, hard-mask material, and deposited films would all fall unevenly into an open 50-to-80-to-1 hole, so a sacrificial fill plugs the hole first, turning an open trench into a flat, stable surface the upper-deck lithography can actually pattern on top of.

Alignment, not depth, is this step's real risk. The upper-deck mask has no direct view of the buried lower-deck hole underneath the plug — it has to register to it using overlay marks and process control alone, and any registration error here becomes a kinked or offset channel where the two decks meet, a defect that a perfectly etched lower deck and a perfectly etched upper deck can still produce together if the joint between them drifts.

Sac-poly recess is what turns the seal back into an opening. Once the upper-deck mask and etch are ready to continue the channel, this recess removes the sacrificial fill from the lower-deck hole, reopening it so the upper-deck etch can continue straight down into the same channel the lower deck already carved — the two passes meeting, ideally, as if they had never been separated at all.

This same seam multiplies with every additional deck. Triple- and quad-deck channel holes, now appearing as layer counts climb past what two decks can comfortably reach, don't just add more etch depth — they add one more inter-deck plug, one more sacrificial fill-and-recess cycle, and one more alignment seam per additional deck, each one carrying the same kink risk as the first.

Inter-deck plug etch is the clearest proof that channel-hole etch is not really one problem but two, joined: Samsung's V-NAND, SK hynix's 4D NAND, Kioxia/WD's BiCS, Micron, and YMTC's Xtacking all depend on this plug-and-recess seam to make a two-pass channel hole read, electrically, as a single continuous one — and as decks keep getting added, it is this joint, not either etch on its own, that increasingly decides whether the channel survives intact.

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