Semiconductor Device N-type Cathode Buffer Layer Leakage Current
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Solution Overview
Problem
Semiconductor devices fabricated by grinding the substrate thickness and subsequent ion implantation often exhibit high reverse leakage current due to defects such as scratches or particles on the ground surface, which hinder uniform impurity implantation and lead to low production yield.
Innovation Solution
Incorporating a high-concentration N-type cathode buffer layer between the N-type drift layer and the N+ cathode layer, with a thickness that stops the depletion layer expansion under reverse bias, preventing it from reaching the cathode electrode and thus reducing leakage current. This is achieved by forming the semiconductor device structure with specific impurity concentration and thickness profiles and using ion implantation and laser activation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the substrate thickness is decreased by grinding and ion implantation is performed, then the device structure is improved and electrode formation is enabled, but reverse leakage current increases due to surface defects
Solution Approach 1:
A buffer layer is formed in advance on the ground surface before ion implantation. This buffer layer serves as a preliminary protective structure that prevents impurity penetration into defective regions, thereby reducing reverse leakage current while still allowing the ion implantation process to proceed for forming the cathode layer
Solution Approach 2:
The buffer layer acts as an intermediary between the ground surface and the ion implantation process. It mediates the interaction by absorbing or blocking impurities that would otherwise penetrate into the substrate through surface defects, thus protecting the underlying structure from harmful effects
2Length of stationary object
If grinding is performed to decrease substrate thickness, then the final device thickness is achieved, but surface defects such as scratches and particles are generated
Solution Approach 1:
The harmful effect of surface defects is extracted and isolated by introducing a buffer layer that specifically targets and addresses the defective regions. The buffer layer is applied selectively to the ground surface, extracting the problem of surface quality issues from the overall device structure
Solution Approach 2:
The buffer layer provides local quality improvement by being formed specifically on the ground surface where defects exist. It creates a localized protective region that addresses surface quality issues without affecting the overall device structure or requiring global process changes
3Ease of manufacture
If ion implantation is performed on the ground surface, then the cathode layer is formed, but uniform impurity distribution is hindered by surface defects
Solution Approach 1:
The buffer layer is formed as a preliminary step before ion implantation, preparing the surface to receive ions uniformly. This preliminary structure ensures that subsequent ion implantation proceeds evenly across the surface, overcoming the hindrance caused by surface defects
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
The semiconductor device exhibits significantly reduced reverse leakage current and improved production yield by ensuring uniform impurity distribution and preventing depletion layer expansion to the cathode electrode, enhancing the device's electrical characteristics.
Implementation Method 1
such an ion-implanted surface is irradiated with YAG 2ω laser light by a double pulse method setting an energy density of 4 J/cm2 and a delay time of 300 nanoseconds, so that the phosphorous is electrically activated
Implementation Method 2
the impurity can be activated without adversely affecting the previously formed electrode
Implementation Method 3
the wafer is subjected to grinding from a back face, so that the thickness of the wafer is made to be 140 μm
Implementation Method 4
phosphorous is ion-implanted into the polished surface
Data Source
AI summary
A method of manufacturing a semiconductor device by thinning a substrate by grinding, and performing ion implantation. In a diode in which a P anode layer and an anode electrode are formed at a side of a right face of an N− drift layer, and an N+ cathode layer and a cathode electrode are formed at a side of a back face of the N− drift layer, an N cathode buffer layer is formed thick compared with the N+-type cathode layer between the N−-type drift layer and the N+ cathode layer, the buffer layer being high in concentration compared with the N− drift layer, and low compared with the N+ cathode layer. When a reverse bias voltage is applied, a depletion layer is stopped in the middle of the N cathode buffer layer, and thus prevented from reaching the N+ cathode layer, so that the leakage current is suppressed.