ON spacer

# ON / ONO Spacer

ON and ONO describe oxide/nitride layer sequences when used as spacer-stack shorthand.

## Read the retained sidewall

A conformal coating covers both horizontal and vertical surfaces before etchback. The intended final feature is the retained sidewall material, not a uniformly thinned blanket film.

## Integration context

ONO conventionally expands to oxide/nitride/oxide. For a sidewall stack, the document must state whether the sequence is listed from the gate outward or in deposition order. Multiple layers can provide liner protection, etch contrast or other integration functions. This is not automatically a flash-memory charge-storage stack.

## What to verify

Draw each layer and identify its removal or retention target; avoid treating the composite as one uniform film.

Before selecting removal conditions, identify all exposed neighboring materials and the amount of loss each can tolerate. Verify the result using the measurements appropriate to the structure, then check that the surface is suitable for the next deposition, contact or clean step.

## Related terminology

ON spacer, ONO spacer, oxide nitride spacer. Short abbreviations are local process vocabulary and can have other meanings; use the full module name when searching.

## Source and scope

[Selective nitride spacer etching](https://plasma.oxinst.com/assets/uploads/documents/3182_PT_Process_News_Mar2015_Low_res_Spreads.pdf). The diagram is an original teaching schematic. Layer choices and process families describe an example rather than a universal manufacturing recipe.