SiC Substrate Flatness Control for Photolithography

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Solution Overview

Problem

In the photolithography process for silicon carbide semiconductor devices, position deviation of mask patterns occurs due to variations in substrate thickness, leading to reduced flatness and accuracy.

Innovation Solution

A silicon carbide single crystal substrate with specific geometric and flatness parameters, including central and outer square regions, is designed to maintain precise flatness by controlling the ratios of Local Total Indicated Reading (LTIR) and Local Thickness Variation (LTV), ensuring the substrate's flatness is consistent across its surface, thereby minimizing position deviation during photolithography.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional polishing methods are used on silicon carbide substrates, then manufacturing process is simple, but position deviation of mask patterns occurs due to thickness variations

Engineering Contradiction:

ImproveflatnessVSAvoidsubstrate structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The substrate surface is divided into a central square region and an outer square region with specific dimensional relationships. This segmentation allows different flatness control strategies for different areas, enabling precise mask pattern positioning in the central region while managing overall substrate flatness through the structured outer region.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different flatness requirements are applied to different regions of the substrate. The central square region maintains a specific LTIR/LTV ratio (0.8-1.2) to ensure precise photolithography, while the outer square region has a controlled LTV ratio (1.0-3.0) relative to the central region. This local quality differentiation resolves the contradiction by optimizing the critical central area without requiring complete uniformity across the entire substrate.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If substrate thickness is not controlled, then manufacturing is easier, but mask pattern position deviation occurs reducing photolithography accuracy

Engineering Contradiction:

Improvemask pattern positionVSAvoidthickness variation

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

Specific parameter ranges are established for flatness control: LTIR/LTV ratio in central region (0.8-1.2), LTV ratio between outer and central regions (1.0-3.0), and overall TTV (≤5μm). These parameter changes transform the manufacturing approach from uncontrolled thickness to precisely controlled flatness characteristics, enabling accurate mask pattern positioning while maintaining manufacturability through clear specification ranges.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9978651B2Silicon carbide single crystal substrate, silicon carbide semiconductor device, and method for manufacturing silicon carbide semiconductor device

Publication Date: 2018.05.22 SUMITOMO ELECTRIC INDUSTRIES LTD

AI summary

A silicon carbide single crystal substrate includes a first main surface and a second main surface opposite to the first main surface. The first main surface includes a central square region and an outer square region. When viewed in a thickness direction, each of the central square region and the outer square region has a side having a length of 15 mm. The first main surface has a maximum diameter of not less than 100 mm. The silicon carbide single crystal substrate has a TTV of not more than 5 μm. A value obtained by dividing a LTIR in the central square region by a LTV in the central square region is not less than 0.8 and not more than 1.2. A value obtained by dividing a LTV in the outer square region by the LTV in the central square region is not less than 1 and not more than 3.