LDMOS Drift Region Edge Protection via Sacrificial Oxidation
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Solution Overview
Problem
The silicon on the edge of the oxide layer in an LDMOS drift region is easily exposed during the sacrificial oxidation process, leading to leakage and breakdown of the LDMOS device, and increasing the drift region length to improve breakdown voltage increases on-resistance and chip area, reducing the device's drive capability.
Innovation Solution
A semiconductor device manufacturing method that involves forming a sacrificial oxide layer, removing it, and then using a thinner masking layer comprising silicon nitride and oxide to protect the LDMOS drift region during the formation of the drift region oxide layer, ensuring the sacrificial oxidation step is performed before forming the LDMOS drift region to prevent edge damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drift region length is increased to improve breakdown voltage, then the breakdown voltage is improved, but the on-resistance increases and chip area increases, reducing drive capability
Solution Approach 1:
The patent performs sacrificial oxidation before forming the drift region oxide layer, creating a protective oxide layer in advance that prevents silicon exposure at the drift region edges during subsequent processing. This preliminary protective action eliminates the need to increase drift region length for reliability, thereby maintaining drive capability.
Solution Approach 2:
The patent introduces a sacrificial oxide layer as an intermediary protective layer between the silicon substrate and the drift region oxide layer. This intermediary layer prevents direct exposure and damage of the drift region edges, allowing the drift region to maintain its original dimensions while achieving both high breakdown voltage and drive capability.
2Ease of manufacture
If the sacrificial oxide layer etching loss is increased to ensure complete removal, then the sacrificial oxide layer is completely removed, but the drift region oxide layer is also etched, causing edge damage
Solution Approach 1:
The patent forms the drift region oxide layer before removing the sacrificial oxide layer. This preliminary formation creates a protective barrier that prevents etching damage to the drift region oxide layer edges during the sacrificial oxide removal process, ensuring complete removal without edge damage.
Solution Approach 2:
The patent creates the drift region oxide layer in advance as a protective cushion layer that shields the drift region oxide layer edges from etching damage during sacrificial oxide removal. This beforehand cushioning allows aggressive etching conditions to be used without compromising the integrity of the drift region structure.
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 method enhances the breakdown voltage of the LDMOS device while maintaining its drive capability and reduces production costs by using a thinner masking layer to form a thinner drift region oxide layer, preventing edge damage and leakage.
Implementation Method 1
Before growing the gate oxide, the substrate surface must be oxidized, and the oxide layer is removed via etching, thus exposing a high quality gate oxide. This process is also known as the sacrificial oxidation process.
Implementation Method 2
using a thinner masking layer comprising silicon nitride and oxide to protect the LDMOS drift region during the formation of the drift region oxide layer
Data Source
AI summary
A method for manufacturing a semiconductor device according to this specification solves the problem in the prior art that the silicon on the edge of an oxide layer in an LDMOS drift region is easily exposed and causes breakdown of an LDMOS device. The method includes: providing a semiconductor substrate comprising an LDMOS region and a CMOS region; forming a sacrificial oxide layer on the semiconductor substrate; removing the sacrificial oxide layer; forming a masking layer on the semiconductor substrate after the sacrificial oxidation treatment; using the masking layer as a mask to form an LDMOS drift region, and forming a drift region oxide layer above the drift region; and removing the masking layer. The method is applicable to a BCD process and the like.