SiC Backside Ohmic Contact Formation Without Thin-Wafer Flipping

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Solution Overview

Problem

The handling and processing of thin SiC wafers for electronic devices are prone to cracking and warping due to the need for multiple flipping steps, which complicates the manufacturing process and affects the on-state resistance (RON) of the devices.

Innovation Solution

A method for manufacturing SiC electronic devices that involves forming an ohmic contact on the back of the wafer using a LASER to generate Titanium compounds, allowing for wafer thinning after front-side processing without further flipping, thus simplifying the process and reducing the risk of damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the SiC substrate thickness is reduced to decrease substrate resistance contribution, then the on-state resistance RON is improved, but the wafer becomes excessively thin and prone to cracking and warping during handling

Engineering Contradiction:

Improveon-state resistance RONVSAvoidwafer integrity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The ohmic contact is formed on the back surface of the wafer before the wafer is thinned to the final thickness. This preliminary action allows the formation of a reliable electrical contact while the wafer still has sufficient mechanical strength, avoiding the need to handle and flip extremely thin wafers. The back surface processing is completed in advance, and then the wafer is thinned without requiring further flipping operations.

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If multiple flipping steps are performed to form ohmic contact on the back of the wafer, then the ohmic contact can be formed, but the handling complexity increases and the risk of wafer damage increases

Engineering Contradiction:

Improveohmic contact formationVSAvoidhandling steps

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The thinning process and the back surface ohmic contact formation process are merged into a single sequential operation. The wafer is thinned to the final thickness, and the ohmic contact is formed on the back surface in the same handling sequence without requiring the wafer to be flipped back to the front side. This integration reduces the number of flipping steps and simplifies the overall manufacturing process.

Inventive Principle:

Principle #5Merging (Combining)

3Manufacturing precision

If the wafer is thinned before forming the ohmic contact on the back, then the substrate resistance is reduced, but the wafer becomes too thin for safe handling and processing

Engineering Contradiction:

Improvesubstrate resistanceVSAvoidwafer handling

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

The ohmic contact formation on the back surface is performed as a preliminary action before the wafer is thinned to its final thin specification. This ensures that the electrical contact is established while the wafer still has adequate mechanical strength for handling, eliminating the need to manipulate extremely thin wafers during contact formation.

Inventive Principle:

Principle #10Preliminary action

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 simplifies the process flow, improves ohmic contact quality, reduces the risk of wafer cracking, and significantly lowers the substrate's resistive contribution to the device's total RON, while maintaining the integrity of structures on the front side.

Implementation Method 1

said intermediate layer is heated by means of a LASER to temperatures in the range 1400-2600° C., in particular equal to or higher than the melting temperature of the material of said intermediate layer

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS11784049B2Method for manufacturing a sic electronic device with reduced handling steps, and sic electronic device

Publication Date: 2023.10.10 STMICROELECTRONICS SRL

AI summary

A method for manufacturing an electronic device based on SiC includes forming a structural layer of SiC on a front side of a substrate. The substrate has a back side that is opposite to the front side along a direction. Active regions of the electronic device are formed in the structure layer, and the active regions are configured to generate or conduct electric current during the use of the electronic device. A first electric terminal is formed on the structure layer, and an intermediate layer is formed at the back side of the substrate. The intermediate layer is heated by a LASER beam in order to generate local heating such as to favor the formation of an ohmic contact of Titanium compounds. A second electric terminal of the electronic device is formed on the intermediate layer.