Plasma Dicing Secondary Etch for Backside Metal Tearing
Solution Overview
Problem
Plasma dicing methods face challenges with backside metal (BSM) tearing due to the incompatibility of plasma chemistry with BSM layers, leading to irregular die edges and potential metal residues during silicon wafer singulation.
Innovation Solution
A multi-step plasma etching process is employed, where a main etch with high etch rates is followed by a secondary etch that removes less silicon, forming smaller and shallower scallops near the BSM interface, thereby increasing the angle between the BSM plane and the die sidewall, reducing Aspect Ratio Dependent Etching effects, and minimizing BSM tearing. The secondary etch process reduces silicon removal to maintain throughput while ensuring clean separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional anisotropic Bosch etch process is used for plasma dicing, then high etch rates and excellent anisotropic profiles can be obtained, but the sidewalls develop inherent roughness (scallops) that increase the risk of backside metal tearing
Solution Approach 1:
The patent applies periodic action by implementing a multi-stage Bosch process where the etch cycle parameters are dynamically adjusted. The process alternates between high-rate etching phases and low-rate finishing phases, with each phase having specific deposition and etch step configurations. This periodic variation in etch rate and deposition rate controls scallop formation, reducing sidewall roughness while maintaining overall productivity.
2Ease of manufacture
If larger and more pronounced scallops are formed to improve die separation, then the BSM layer can be removed more effectively, but the angle between the BSM plane and the local die sidewall plane decreases, increasing the risk of BSM tearing
Solution Approach 1:
The patent applies parameter changes by systematically varying critical process parameters including RF power, pressure, gas flow rates, and temperature throughout the etch cycle. Specifically, the deposition step uses different gas compositions and flow rates compared to the etch step, and these parameters are adjusted between different stages of the Bosch process to control scallop dimensions and sidewall angle, optimizing both BSM removal and separation quality.
3Productivity
If the etch rate is increased to improve throughput, then productivity increases, but the Aspect Ratio Dependent Etching effects become more pronounced, creating irregular die base edges
Solution Approach 1:
The patent applies preliminary action by performing a controlled deposition step before the main etch step in each Bosch cycle. This preliminary deposition creates a uniform protective layer on the sidewalls that prevents excessive etching at lane intersections and centers, compensating for ARDE effects before they occur. The deposition step establishes a baseline that ensures more uniform etching rates across different lane positions.
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 achieves clean separation of BSM layers with reduced irregularities, minimizing metal residues and enhancing die yield by forming high-angle, shallow scallops at the BSM interface, thus preventing BSM tearing and improving die strength and density.
Implementation Method 1
a first plasma etching process is performed to partially form dicing lanes through the silicon substrate
Implementation Method 2
The plasma chemistry for etching the bulk silicon
Implementation Method 3
a second plasma etching process is performed to remove less silicon than the first plasma etching process to continue forming the dicing lanes through the silicon substrate
Implementation Method 4
The first plasma etching process is a Bosch plasma etch in which a deposition step and a plasma etch step are alternately repeated
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
According to the invention there is provided a method of plasma etching one or more dicing lanes in a silicon substrate having a backside metal layer attached thereto, the method comprising the steps of: performing a main etch using a cyclical plasma etch process in which a deposition step and an etch step are alternately repeated to produce dicing lanes having scalloped sidewalls; and switching to performing a secondary etch using a cyclical plasma etch process in which a deposition step and an etch step are alternately repeated until the backside metal layer is reached; wherein the amount of silicon removed in one etch step during the secondary etch is half or less than half of the amount of silicon removed in one etch step during the main etch.