3D NAND Slit Spacer Etch

Slit-spacer etch has one very specific job: remove an insulating film from the floor of the slit while leaving it fully intact on the walls, so the trench can be filled without the fill shorting to the word-line metal right next to it.

Replacement gate done
word-line metal fills the slit walls
Conformal spacer film deposited
coats walls and floor alike
Anisotropic spacer etch
directional, floor-clearing
Walls stay insulated, floor opens
source-line plate reachable again
CSL contact fill next
fills the now-clear trench

That split outcome — clear here, keep there — is only possible because the etch is deliberately anisotropic rather than a simple blanket removal.

Slit-Spacer Etch — Lining the Trench Before Anything Fills It an anisotropic etch that leaves insulation on the walls but clears the floor of the slit array stack — word-line metal already in place from replacement gate before: conformal liner coats every surface floor liner — must be removed after: anisotropic etch clears the floor, keeps the walls floor open for CSL fill Anisotropic by requirement, not by convenience a spacer that also stayed on the floor would block the CSL fill from ever reaching the source-line plate below; a spacer removed from the walls too would leave the word-line metal exposed to the fill — this etch has to do both jobs, floor-clear and wall-keep, in a single directional pass. runs after replacement gate, right before CSL contact fill — the slit's second-to-last step before it is sealed

The spacer film goes down conformally, covering everything equally. After replacement gate has already filled the slit's cavities with word-line metal, an insulating film is deposited across the entire open trench — walls and floor alike — exactly the way a liner deposition normally behaves, with no preference yet for where it should ultimately stay.

The etch itself is what creates the asymmetry a conformal deposition cannot. Run directionally, straight down the trench, this etch clears the insulating film off the horizontal floor far faster than it clears the vertical walls, leaving the walls lined and the floor open — the same anisotropic principle that makes a directional plasma etch behave differently on horizontal versus vertical surfaces anywhere else in the flow.

Leaving the walls insulated is what prevents the next step from shorting the array. Without that wall liner intact, the CSL contact fill that follows would deposit tungsten or doped poly directly against the word-line metal exposed in the slit — a direct short between the common source line and every word line layer the fill touches.

Clearing the floor is what lets that same fill actually reach its target. If the spacer were left in place at the bottom of the trench, it would block CSL from ever contacting the source-line plate below, leaving the source connection open no matter how well the fill itself goes.

One film, one etch, two opposite requirements satisfied at once. Slit-spacer etch is a small, late step in the flow, but Samsung's V-NAND, SK hynix's 4D NAND, Kioxia/WD's BiCS, Micron, and YMTC's Xtacking all depend on this single anisotropic pass getting both outcomes right simultaneously — because neither replacement gate's metal fill nor CSL's contact fill can be trusted to coexist safely in the same trench without it.

Take 3d nand slit spacer etch further

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