IGBT Back Face Polysilicon Removal via Thermal Oxidation
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Solution Overview
Problem
Conventional methods for removing polysilicon protection layers from IGBT structures risk metal contamination and can corrode the field stop layer due to inadequate control during wet etching, especially in backend processes where a front face metal layer is already formed.
Innovation Solution
The method involves thermally oxidizing the polysilicon protection layer to form a SiO2 layer, which is then removed using dry etching, preventing metal contamination and corrosion of the field stop layer by terminating oxidation at the gate oxide layer barrier, allowing for safe formation of metal layers without affecting device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching of silicon (SEZ) is used to remove the polysilicon protection layer and SiO2 layer on the back face, then the removal process can be completed, but metal contamination risk increases and the field stop layer may be corroded
Solution Approach 1:
The patent extracts and removes the polysilicon protection layer and SiO2 layer separately through selective etching processes. The first etching step removes the SiO2 layer, and the second etching step removes the polysilicon layer, preventing the need for aggressive wet etching that would contaminate metal layers or corrode the field stop layer.
Solution Approach 2:
The patent performs preliminary removal of the SiO2 layer before forming metal layers on the front face. This preliminary action eliminates the source of potential metal contamination and prevents corrosion of the field stop layer before critical manufacturing steps occur.
2Reliability
If thermal oxidation is used to form SiO2 layer from polysilicon protection layer, then metal contamination is avoided, but additional process steps are required
Solution Approach 1:
The patent changes the chemical state of the polysilicon protection layer by converting it to SiO2 through thermal oxidation. This parameter change (from polysilicon to oxide) enables selective removal through etching processes that do not affect metal layers or the field stop layer, thereby preventing contamination while adding controlled process steps.
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 effectively avoids metal contamination and ensures the integrity of the field stop layer, maintaining device performance parameters by using thermal oxidation and dry etching processes compatible with conventional IGBT manufacturing, reducing the risk of etching errors.
Implementation Method 1
thermally oxidizing the polysilicon protection layer to form a SiO2 layer
Implementation Method 2
removed by means of dry etching
Data Source
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AI summary
Disclosed is a method for removing a polysilicon protection layer (12) on a back face of an IGBT having a field stop structure (10). The method comprises thermally oxidizing the polysilicon protection layer (12) on the back face of the IGBT until the oxidation is terminated on a gate oxide layer (11) located above the polysilicon protection layer (12) to form a silicon dioxide layer (13), and removing the formed silicon dioxide layer (13) and the gate oxide layer (11) by a dry etching process. The method for removing the protection layer is easier to control.