Nitride Semiconductor Device with Chlorine Plasma Surface Treatment
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Solution Overview
Problem
Existing processes for forming nitride semiconductor devices face challenges in achieving stable and non-rectified metal contacts, particularly due to the formation of aluminum silicide (AlSix) and poor adhesion of metals on dense silicon nitride (SiN) films, which can lead to peeling off of electrodes during high-temperature alloying.
Innovation Solution
The process involves epitaxially growing nitride semiconductor layers, depositing a silicon nitride film using LPCVD, forming openings and exposing peripheral areas to chlorine plasma to create recesses, and alloying metals at a lower temperature than the deposition temperature to form non-rectified electrodes, ensuring secure contact and preventing AlSix formation by using a dense SiN film deposited at a higher temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride film is deposited at a high temperature (higher than 550°C, preferably higher than 700°C) by LPCVD to achieve dense film structure and prevent AlSix formation, then the film density and ability to prevent aluminum silicide formation are improved, but the adhesion of metals on the film deteriorates, causing electrodes to peel off during high-temperature alloying
Solution Approach 1:
The patent applies preliminary action by exposing the silicon nitride film to chlorine plasma before metal deposition. This pre-treatment creates a modified surface layer that will subsequently provide good adhesion for metals during the alloying process, while the bulk film structure remains dense to prevent AlSix formation. The plasma exposure is performed in advance to prepare the surface without compromising the film's barrier properties.
Solution Approach 2:
The patent applies local quality by creating a differentiated surface structure through chlorine plasma exposure. The surface layer acquires different properties (enhanced adhesion) compared to the bulk film (maintained density and barrier function). This local modification allows the same film to simultaneously provide both adhesion and protection against aluminum silicide formation.
2Reliability
If metals are alloyed at a high temperature to form non-rectified contacts, then the electrical contact properties are improved, but the risk of electrode peeling from the silicon nitride film increases
Solution Approach 1:
The patent applies preliminary action by modifying the silicon nitride film surface with chlorine plasma before metal deposition and subsequent high-temperature alloying. This pre-treatment creates a surface that can withstand high-temperature processing while maintaining strong adhesion, enabling the alloying step to proceed at temperatures sufficient for forming stable non-rectified contacts without causing electrode peeling.
3Reliability
If the silicon nitride film is made dense by high-temperature deposition to prevent aluminum silicide formation, then the barrier function against AlSix is improved, but the metal adhesion deteriorates leading to electrode peeling
Solution Approach 1:
The patent applies local quality by creating a differentiated structure where the bulk silicon nitride film maintains high density for barrier function, while the surface layer is modified by chlorine plasma exposure to provide enhanced metal adhesion. This local differentiation allows simultaneous achievement of both barrier protection and strong electrode attachment.
Solution Approach 2:
The patent applies preliminary action by performing chlorine plasma exposure on the silicon nitride film before metal deposition. This pre-treatment modifies the surface properties to enhance adhesion while preserving the bulk film's dense structure and barrier function, solving the contradiction between film density and metal adhesion.
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 results in stable and secure metal contacts for nitride semiconductor devices, preventing the formation of aluminum silicide and ensuring the electrodes remain firmly attached to the SiN film even during high-temperature alloying, thereby enhancing the reliability and performance of the semiconductor device.
Implementation Method 1
depositing a silicon nitride (SiN) film on the semiconductor stack by a low pressure chemical vapor deposition (LPCVD) technique
Implementation Method 2
exposing a surface of the semiconductor stack appearing within the opening in the SiN film and a peripheral area of a surface of the SiN film around the opening to plasma that contains chlorine (Cl) ions and partially etches the semiconductor stack
Data Source
AI summary
A nitride semiconductor device is disclosed. The semiconductor device is formed by a process that first deposits a silicon nitride (SiN) film on a semiconductor layer by the lower pressure chemical vapor deposition (LPCVD) technique at a temperature, then, forming an opening in the SiN film for an ohmic electrode. Preparing a photoresist on the SiN film, where the photoresist provides an opening that fully covers the opening in the SiN film, the process exposes a peripheral area around the opening of the SiN film to chlorine (Cl) plasma that may etch the semiconductor layer to form a recess therein. Metals for the ohmic electrode are filled within the recess in the semiconductor layer and the peripheral area of the SiN film. Finally, the metals are alloyed at a temperature lower than the deposition temperature of the SiN film.