Slant Sub-Resolution Mask Features for Lens Heating

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Solution Overview

Problem

During photolithography, non-uniform lens heating in wafer steppers or scanners can cause variations in the critical dimension of semiconductor device features, leading to failed devices, especially as feature sizes decrease and tolerance ranges narrow, due to off-axis illumination from light sources.

Innovation Solution

Implementing a slant sub-resolution fill pattern in the mask that redirects light intensity to both X- and Y-poles, reducing localized heating by redistributing light intensity across the projection lens, using a light source with a shorter wavelength than the primary source to project through the mask, thereby suppressing lens-heating-induced critical dimension variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If off-axis illumination is used in photolithography, then the light source can effectively expose the mask pattern, but non-uniform lens heating occurs causing critical dimension variations

Engineering Contradiction:

Improvecritical dimension controlVSAvoidlens heating uniformity

Core Design Contradiction:

Manufacturing precisionVSTemperature

Solution Approach 1:

The illumination aperture is divided into multiple segments (first and second portions) that direct light through different paths. This segmentation allows the light to be distributed in a manner that reduces localized heating while maintaining effective exposure, thereby resolving the contradiction between achieving good pattern exposure and preventing non-uniform lens heating.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the illumination system are given different functions: one portion directs light through the optical axis while another directs light off-axis. This local differentiation allows simultaneous optimization of both uniform heating (through on-axis components) and effective pattern exposure (through off-axis components), resolving the critical dimension control versus lens heating uniformity contradiction.

Inventive Principle:

Principle #3Local quality

2Productivity

If feature sizes are reduced to increase device capacity, then more devices fit on the wafer, but tolerance ranges narrow making them more sensitive to lens heating variations

Engineering Contradiction:

Improvedevice capacity per waferVSAvoidfeature dimension tolerance

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

By segmenting the illumination aperture into multiple portions that direct light through different paths, the system achieves more uniform energy distribution across the lens. This reduces heating-induced dimensional variations, which is critical when manufacturing smaller features with tighter tolerances to maintain high device capacity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The illumination parameters are changed by using multiple wavelengths or adjusting the angular distribution of light through different aperture portions. This parameter optimization allows effective exposure of smaller features while maintaining uniform lens heating, thereby preserving tight dimensional tolerances needed for high-density device fabrication.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a single light source wavelength is used, then the exposure process is simple, but lens heating cannot be effectively redistributed

Engineering Contradiction:

Improveillumination system simplicityVSAvoidlight intensity distribution

Core Design Contradiction:

Device complexityVSTemperature

Solution Approach 1:

The illumination system is segmented into multiple aperture portions, each directing light at different angles. This segmentation enables effective redistribution of light intensity across the lens without requiring multiple light sources, maintaining relative system simplicity while achieving uniform heating and reduced critical dimension variations.

Inventive Principle:

Principle #1Segmentation

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

The redistribution of light intensity across the lens reduces non-uniform heating, maintaining feature dimension tolerance and preventing device failures by balancing light concentration, thus enhancing the precision and reliability of semiconductor manufacturing.

Implementation Method 1

a slant sub-resolution fill pattern in the mask that redirects light intensity to both X- and Y-poles, reducing localized heating by redistributing light intensity across the projection lens

Methodology Applied

Scientific EffectLight redirection and redistribution: Reflection

Implementation Method 2

using a light source with a shorter wavelength than the primary source to project through the mask, thereby suppressing lens-heating-induced critical dimension variations

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS8916314B2Reduced lens heating methods, apparatus, and systems

Publication Date: 2014.12.23 MICRON TECHNOLOGY INC

AI summary

In one embodiment, a system is disclosed that includes an illuminator having a source that produces light waves having a first wavelength, and a mask. The mask includes at least one partly opaque area and at least one opening within the opaque area includes a slanted, sub-resolution feature that redistributes a portion of the light passing through the open area to an off-axis location. A method of forming a device by way of photolithography might include forming unresolvable features on a mask and projecting light through the mask. Other systems, methods, and apparatus are disclosed.