Semiconductor Electrode Thermal Stress Balancing
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Solution Overview
Problem
Semiconductor substrates used in vertical MOS transistors warp due to differing stress from front and back surface electrodes with different coefficients of linear expansion, leading to peeling issues and reduced current drive ability, especially during temperature changes.
Innovation Solution
Forming front and back surface electrodes using metals with substantially the same coefficient of linear expansion, such as copper and silver, to equalize thermal stress and prevent warping, while enhancing current drive ability by increasing electrode thickness through plating methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If front surface electrodes and back surface electrode have different coefficients of linear expansion, then the semiconductor device can be manufactured with conventional materials, but the semiconductor substrate warps during temperature changes causing peeling of protection film and electrodes
Solution Approach 1:
The patent changes the material parameter (coefficient of linear expansion) of the electrodes to match between front and back surfaces. Specifically, it uses aluminum or aluminum alloy for both front surface electrodes (source electrode 101, gate electrode 104) and back surface electrode (drain electrode 106), ensuring their coefficients of linear expansion are substantially equal, thereby preventing differential thermal expansion stress and substrate warping during temperature changes
Solution Approach 2:
The patent applies homogeneous material selection by using the same material type (aluminum or aluminum alloy) for all electrodes on both front and back surfaces of the semiconductor substrate. This homogeneity in material composition ensures uniform thermal expansion characteristics across the entire device structure, eliminating the warping problem caused by heterogeneous material properties
2Power
If the thicknesses of front surface electrodes are increased to enhance current drive ability, then the current carrying capacity improves, but the manufacturing complexity increases due to plating process requirements
Solution Approach 1:
The patent replaces conventional thin-film deposition methods with electroplating or electroless plating processes to form the electrode layers. This substitution enables the formation of thick electrode layers (5 μm to 20 μm or more) that provide enhanced current drive ability, as plating methods can deposit much thicker metal layers compared to sputtering or evaporation techniques
Solution Approach 2:
The patent changes the thickness parameter of the electrode layers from conventional thin films to thick layers ranging from 5 μm to 20 μm or more. This parameter change is achieved through plating processes that can controllably deposit thick metal layers, thereby increasing the cross-sectional area for current flow and enhancing the current drive ability of the power transistor
3Length of moving object
If the semiconductor substrate is thinned during manufacturing, then the device size is reduced, but the substrate warps due to back surface electrode formation or heat treatment causing resist layer defects
Solution Approach 1:
The patent applies preliminary anti-action by forming the front surface electrodes (source electrode 101, gate electrode 104) with thick plating layers before thinning the semiconductor substrate. This preliminary formation of stress-balanced electrode structures prevents warping during subsequent substrate thinning and heat treatment processes, thereby avoiding resist layer peeling and formation defects that would otherwise occur
Solution Approach 2:
The patent performs preliminary electrode formation and stress balancing operations before the substrate thinning step. By establishing the electrode structure with matched thermal expansion coefficients prior to thinning, the patent preemptively prevents warping issues that would compromise subsequent resist layer processing and pattern formation accuracy
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
Prevents substrate warping and peeling, enhances current drive ability by ensuring equal thermal expansion across electrodes, thereby improving the reliability and performance of semiconductor devices.
Implementation Method 1
The first and second metals have substantially the same coefficient of linear expansion
Implementation Method 2
an effective approach is to increase the thicknesses of the front surface electrodes in the vertical direction. This is because the bump electrodes 102, 105 are formed on part of the front surface electrodes extending over the front surface of the semiconductor substrate 100 as shown in FIG. 13A and the amount of electric current components that flow in the front surface electrodes in the horizontal direction relative to the semiconductor substrate 100 is large. Increasing the thickness of the back surface electrode in the vertical direction is also an effective approach. For this reason, a plating method is suitable as a method of manufacturing the front surface electrodes and the back surface electrode in order to increase the thicknesses of the front surface electrodes and the back surface electrode in the vertical direction.
Data Source
AI summary
The invention prevents a semiconductor device from warping due to heat when it is used. The invention also prevents a formation defect such as peeling of a resist layer used as a plating mask and a formation defect of a front surface electrode. A source pad electrode connected to a source region is formed on a front surface of a semiconductor substrate forming a vertical MOS transistor. A front surface electrode is formed on the source pad electrode by a plating method using a resist layer having openings as a mask. The semiconductor substrate formed with the front surface electrode is thinned by back-grinding. A back surface electrode connected to a drain region is formed on the back surface of the semiconductor substrate. The front surface electrode and the back surface electrode are made of metals having the same coefficients of linear expansion, preferably copper. The front surface electrode and the back surface electrode preferably have the same thicknesses or almost the same thicknesses.