Lithography Test Pattern Asymmetric Diffraction Focus Offset

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Solution Overview

Problem

The semiconductor industry faces challenges in accurately monitoring and controlling lithography process parameters, particularly focus and dose, which affect the precision and reliability of feature formation on shrinking IC chip sizes, leading to increased complexity and costs.

Innovation Solution

A method involving the use of a test pattern with asymmetric and symmetric diffraction properties to determine lithography parameter offsets, allowing for precise adjustments in focus and dose during the exposure process, utilizing a control system to modify exposure parameters based on measurements from a scanning electron microscope.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If photolithographic exposure is performed with radiation passing through masks to form patterns on photoresist, then IC features can be defined and formed with increasing functional density, but manufacturing precision deteriorates due to optical effects and processing imperfections near lithography limits

Engineering Contradiction:

Improvefunctional densityVSAvoidfeature formation precision

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by performing focus and dose measurements using test patterns before producing the actual IC features. The exposure apparatus measures focus and dose parameters on a test substrate, then uses these measurements to adjust exposure conditions for subsequent IC feature production, preventing defects before they occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using measurements from test patterns to determine focus and dose parameters, then adjusting the exposure apparatus settings based on these measurements. The control system continuously monitors and adjusts exposure conditions to maintain manufacturing precision as functional density increases

Inventive Principle:

Principle #23Feedback

2Manufacturing precision

If exposure parameters are adjusted to compensate for optical effects and processing imperfections, then manufacturing precision improves, but device complexity increases

Engineering Contradiction:

Improvefeature formation precisionVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts the measurement and adjustment process from the main IC production flow by using separate test patterns and test substrates. The focus and dose measurements are performed independently on test structures, and only the essential adjustment parameters are applied to IC feature production, simplifying the overall process

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes physical parameters (focus position and dose) based on measurements from test patterns. The control system adjusts exposure parameters within a defined range to optimize feature formation while maintaining process simplicity through automated parameter optimization

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If focus position and dose parameters are precisely controlled, then manufacturing precision improves, but loss of time increases due to costly and timely expenditure on parameter verification

Engineering Contradiction:

Improvelithography parameter accuracyVSAvoidparameter verification time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent performs focus and dose measurements in advance using test patterns before IC feature production. By establishing exposure parameters upfront through test pattern analysis, the system avoids time-consuming parameter verification during actual IC manufacturing

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The exposure apparatus performs self-verification by automatically measuring focus and dose parameters using test patterns and adjusting its own settings without external intervention. This automated self-calibration reduces both time and cost of parameter verification

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables accurate monitoring and adjustment of lithography parameters to within nanometer scales, improving the precision and reliability of feature formation on ICs, reducing production costs and complexity by correlating test pattern shifts with exposure parameters.

Implementation Method 1

irradiating a second region of the test pattern providing for an asymmetrical diffraction

Methodology Applied

Scientific EffectAsymmetric diffraction: Diffraction

Data Source

PatentUS11467509B2Lithography process monitoring method

Publication Date: 2022.10.11 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of performing a lithography process includes providing a test pattern. The test pattern includes a first set of lines arranged at a first pitch, a second set of lines arranged at the first pitch, and further includes at least one reference line between the first set of lines and the second set of lines. The test pattern is exposed with a radiation source providing an asymmetric, monopole illumination profile to form a test pattern structure on a substrate. The test pattern structure is then measured and a measured distance correlated to an offset of a lithography parameter. A lithography process is adjusted based on the offset of the lithography parameter.