Etch Feature Tilt Budget

# Etch Feature Tilt Budget

An etch feature tilt budget defines the allowed change in feature-center position with depth and the measurements needed to verify it. It connects the etched path to the landing, spacing or alignment requirements of the integration.

Tilt is not the same as taper. A feature can preserve its width while its center moves laterally, or change width while its center remains fixed. Both properties may need separate acceptance rules.

## Define the geometric reference

In this guide, endpoint tilt is the angle between the surface normal and the chord joining specified top and bottom centers. The normal is defined relative to a stated wafer surface reference. Depth is the separation along that normal, not the length of the slanted path.

Define how each center is determined. For an irregular opening, different center-fitting conventions can give different values. Record the top and bottom reference planes and the local surface orientation.

An endpoint chord does not describe the complete centerline. A curved, bowed or twisting feature can have a small endpoint offset but a larger intermediate excursion. If the requirement governs the entire path, measure that path rather than only its endpoints.

## Preserve both lateral components

The invented example uses a vertical depth of 1000 nm and orthogonal endpoint offsets of 20 nm in x and 15 nm in y. The lateral magnitude is sqrt(20^2 + 15^2) = 25 nm. The chord angle from the surface normal is atan(25/1000), approximately 1.43 degrees.

A section aligned only with x would show a 20 nm projected displacement and an angle of about 1.15 degrees. That projection does not establish the full three-dimensional value. Likewise, an unfavorable section orientation can make a tilted feature appear closer to vertical.

The dimensions are teaching values, not a qualified tilt limit. Retain signs, coordinate orientation and uncertainty as well as a magnitude when direction matters.

## Keep tilt, width and registration distinct

A shift of the entire feature at every depth is a placement change; a difference between its top and bottom centers is an endpoint-path change under this definition. Separating those terms requires a common coordinate reference and suitable registration.

Feature width, sidewall angles and center displacement answer different questions. For example, symmetric taper can change width without moving the center. Asymmetric erosion can affect both. Do not infer centerline tilt from one wall angle alone.

Bottom landing and spacing requirements can involve top placement error, path displacement, bottom width and the target geometry together. Combine them with an explicit coordinate and uncertainty model rather than adding unrelated scalar magnitudes automatically.

## Connect acceptance to the actual integration

Derive allowed displacement and path limits from the intended device and subsequent process. A feature that clears to the required depth can still land outside the acceptable region. A passing endpoint offset does not establish minimum spacing or the full buried shape.

Specify whether the rule applies to angle, lateral displacement, intermediate excursion or a defined statistic across sampled features. A fixed angle produces a larger endpoint displacement at greater depth, so angle and displacement limits are not interchangeable without the depth definition.

There is no universal acceptable tilt angle for all materials, depths, pitches and landing structures.

## Measure with representative spatial coverage

Record section orientation, dimensional calibration, surface-reference alignment and center-extraction method. Preparation or imaging tilt can create apparent feature tilt; distinguish those artifacts from the etched geometry.

Use suitable evidence for the required three-dimensional scope. A single two-dimensional section is generally a projection, not a complete vector measurement. Include relevant feature layouts, wafer radii and azimuths, and retain individual directions rather than averaging opposite offsets into zero.

Keep the process checkpoint visible, including any strip or clean before measurement. Changes to the visible boundary can affect the extracted center.

## Investigate without assigning a cause from shape alone

Plasma conditions near a wafer edge, incoming mask geometry, transport and other process conditions can influence etched paths in particular integrations. Manufacturer discussions identify tilt control as an application-specific requirement and describe edge-profile challenges.

Those observations do not identify the cause of every tilted feature. Use controlled comparisons and suitable equipment and incoming-state evidence. Qualify any corrective change together with width, clearing, selectivity and integrity requirements.

A useful tilt budget records where the feature goes, relative to which surface and coordinate system. Endpoint width and one favorable section cannot replace that directional evidence.

## Sources and scope

• [Lam Research — DSiE product family](https://www.lamresearch.com/product/dsie-product-family/): application-specific requirements for tilt, asymmetry and profile control.
• [Lam Research — Uniformity control at the edge, August 2017](https://newsroom.lamresearch.com/New-Corvus-Technology-Takes-Uniformity-Control-to-the-Edge): process-specific discussion of edge conditions and tilted etch profiles.

Original diagrams and vector-geometry example. No universal tilt limit, root cause or qualified recipe is implied.