Bonded Wafer Etching Using Mixed Acid
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for manufacturing bonded wafers, such as alkaline etching, cause metallic contamination and damage to semiconductor devices due to the delamination of unbonded portions during the thinning process, leading to reduced device yield and electric characteristics deterioration.
Innovation Solution
A method using a mixed acid etchant comprising hydrofluoric acid, nitric acid, and acetic acid at 30°C or less is employed for etching the unbonded portions of the bond wafer, providing a high selectivity ratio that stops etching upon reaching the buried oxide film, preventing damage to the base wafer and avoiding metallic contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If alkaline etching is used to remove unbonded portions, then the unbonded portions are effectively removed, but metallic contamination occurs and device electric characteristics deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the etching process by using a mixed acid solution (hydrofluoric acid, nitric acid, and acetic acid) instead of alkaline etchants, and controls the temperature at 30°C or lower. This parameter change achieves high selectivity (Rs/Rsio2 ≥ 10) while avoiding metallic contamination, thereby resolving the contradiction between effective unbonded portion removal and contamination prevention
2Manufacturing precision
If the bond wafer is thinned by grinding or polishing, then the desired thickness is achieved, but unbonded portions delaminate and generate particles
Solution Approach 1:
The patent applies preliminary etching to remove unbonded portions before the thinning process. By performing this action in advance, the unbonded portions that would otherwise delaminate during grinding or polishing are eliminated, preventing particle generation while still achieving the desired wafer thickness
3Productivity
If etching is performed at higher temperature, then the etching rate increases, but the selectivity ratio between Si and SiO2 decreases
Solution Approach 1:
The patent identifies that the selectivity ratio Rs/Rsio2 decreases as temperature increases. By changing the temperature parameter to 30°C or lower, the patent maintains a high selectivity ratio (≥10) while achieving sufficient etching rate through the optimized mixed acid composition, thereby resolving the contradiction between productivity and manufacturing precision
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 method effectively removes unbonded portions without causing metallic contamination, ensuring the buried oxide film protects the base wafer and maintains the integrity of semiconductor devices, while being cost-effective and reducing equipment size and operational costs through spin etching.
Implementation Method 1
etching the unbonded portion of the outer periphery of the bond wafer by using a mixed acid at 30°C or less
Data Source
Figure 1(a)~1(g)
Figure 2(a)~2(b)
Figure 3
AI summary
The present invention provides a method for manufacturing a bonded wafer comprising steps of forming an oxide film on at least a surface of a base wafer or a surface of a bond wafer; bringing the base wafer and the bond wafer into close contact via the oxide film; subjecting these wafers to a heat treatment under an oxidizing atmosphere to bond the wafers together; grinding and removing the outer periphery of the bond wafer so that the outer periphery has a predetermined thickness; subsequently removing an unbonded portion of the outer periphery of the bond wafer by etching; and then thinning the bond wafer so that the bond wafer has a desired thickness, wherein the etching is conducted by using a mixed acid at 30°C or less at least comprising hydrofluoric acid, nitric acid, and acetic acid. Thus there is provided a method for manufacturing a bonded wafer by which unbonded portions of the outer periphery of the bond wafer are removed with a high selectivity ratio (RSi/RSiO2) without causing metallic contamination.