SADP Patterned Test Wafers: 25 nm L&S

SADP Patterned Test Wafers

SADP 25nm L&S PATTERNED TEST WAFERS

Self-aligned double patterning (SADP) is a fine-patterning technique in which a spacer film is formed on the sidewalls of a pattern called a core, or mandrel. After the core is removed, the remaining spacers serve as lines. Because it uses sidewall spacers, the technique is also called spacer patterning.

Forming spacer lines on both sides of a single core can double the line density relative to the original core pattern.

Philtech has used SADP to fabricate SiO line-and-space (L&S) patterns with a line width of 25 nm, a space width of 25 nm, and a pitch of 50 nm on 300 mm Si wafers.

We can also review your specifications to determine whether custom SADP is feasible for your evaluation objectives and requested structures and dimensions.

Evaluation Applications by Process Stage

Test wafers at intermediate SADP process stages can be used for the following evaluations, depending on the stage.

Film Coverage EvaluationWafers at the stage after SiN core formation can be used to evaluate coverage of the film deposited on the core tops, sidewalls, and bottoms of the openings.

Core Film Removal EvaluationWafers at the stage after etch-back and before SiN core removal can be used to evaluate selective removal of the SiN cores and the condition of the SiO spacers remaining after removal.

Etch-Back Performance EvaluationWafers at the stage after SiO deposition and before etch-back can be used to evaluate removal from horizontal surfaces after anisotropic etch-back and the formation of SiO spacers remaining on the sidewalls.

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25 nm L&S Fabrication Example

Fabrication Example Specifications

Item	Details
Substrate	300 mm Si wafer
Patterning Method	SADP
Core Film	SiN (LP-SiN), film thickness 80 nm
Spacer Film	SiO (LP-TEOS)
Fabricated Structure	SiO, line width 25 nm / space width 25 nm / pitch 50 nm

Fabrication Process

SiN Core Formation

Schematic cross section of SiN cores formed on a Si substrate — SiN is patterned into periodic raised features that serve as the template for spacer formation.

SiO Deposition

Schematic cross section of SiO deposited on the SiN core tops, sidewalls, and bottoms of the openings — A 20 nm film of SiO (LP-TEOS) is deposited along the core tops, sidewalls, and bottoms of the openings.

SiO Etch-Back

Schematic cross section with SiO removed from horizontal surfaces and retained on the SiN core sidewalls — Anisotropic etch-back removes SiO from horizontal surfaces, leaving SiO on the SiN core sidewalls.

SiN Removal and SiO L&S Formation

Idealized schematic cross section of 25 nm lines and spaces formed by vertical SiO spacers after SiN core removal — The SiN cores are selectively removed, leaving SiO spacers that form 25 nm L&S.The diagram shows an idealized cross-sectional shape.

SEM Observation Results

The periodic L&S pattern is observed using a critical-dimension SEM (a scanning electron microscope used to measure pattern dimensions).

SADP Patterned Test Wafers: 25nm L&S