Nitrogen Purging for Alumina Etch in PMR Head Fabrication
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Solution Overview
Problem
Perpendicular magnetic recording (PMR) head fabrication faces challenges with main pole corrosion and alumina residue issues during the alumina etching process, leading to reduced production yields and degraded product quality due to oxidation-reduction reactions and unstable etch rates.
Innovation Solution
The implementation of a nitrogen (N2) purging process during alumina etch steps to remove oxygen from the solution, using a purge board with circular holes connected to a N2 gas line, and maintaining a stable pH with aqueous solutions of NaHCO3 and Na2CO3 or EDTA and NaOH, which reduces corrosion and residue formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alumina etching process is used to remove alumina around the main pole, then the alumina layer can be removed to allow conformal side gap formation, but main pole corrosion occurs due to oxidation-reduction reactions during de-ionized water soaking
Solution Approach 1:
The patent applies inert atmosphere by purging the aqueous etching solution with nitrogen gas to remove dissolved oxygen. This creates an oxygen-depleted environment that prevents oxidation-reduction reactions during the etching process, thereby eliminating main pole corrosion while maintaining effective alumina removal. The nitrogen purge establishes an inert environment throughout the etching bath, protecting the main pole from corrosive attacks.
2Productivity
If conventional alumina etching process is used, then alumina can be removed, but etch rate becomes unstable and drifts lower due to CO2 absorption from air
Solution Approach 1:
The patent uses nitrogen purging to create an inert atmosphere over the etching solution, preventing CO2 from air from dissolving into the solution. This stabilizes the pH and chemical composition of the etching bath, maintaining consistent etch rate throughout the process without the drift to lower rates observed in conventional open-air etching processes.
3Manufacturing precision
If conventional alumina etching process is used, then alumina removal can proceed, but alumina residues build up around the main pole due to insufficient buffer capacity
Solution Approach 1:
The patent modifies the chemical parameters of the etching solution by using buffered aqueous solutions with controlled pH and buffer capacity. The nitrogen purging maintains stable pH conditions, allowing the etching process to proceed completely without residue formation. The stabilized chemical environment ensures consistent reactivity with alumina, enabling complete removal without the buildup of residual material.
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
Significantly reduces main pole corrosion and alumina residue, stabilizes the etch rate, and improves etch uniformity, resulting in higher product yields and quality by preventing oxidation-reduction reactions and CO2 absorption.
Implementation Method 1
purging with inert gas such as N2 during each of the alumina etch steps... the continuous N2 flow essentially drives all O2 from the solution
Implementation Method 2
the injection of N2 bubbles into the alumina etch bath reduces CO2 absorption from the air and thus stabilizes the pH and improves buffering capability
Implementation Method 3
an alumina etch bath that is N2 purged and heated to essentially the same temperature... comprised of an aqueous solution of NaHCO3 and Na2CO3 with a pH between 9.5 and 11
Data Source
AI summary
A method of removing an alumina layer around a main pole layer during perpendicular magnetic recording head fabrication is disclosed. The alumina etch sequence includes immersing a substrate in a series of aqueous solutions purged with an inert gas to remove oxygen thereby avoiding corrosion of the main pole. Initially, the substrate is soaked and heated in deionized (DI) water. Once heated, the substrate is immersed in an etching bath at about 80° C. and pH 10.5. Bath chemistry is preferably based on Na2CO3 and NaHCO3, and N2 purging improves etch uniformity and reduces residue. Thereafter, the substrate is rinsed in a second DI water bath between room temperature and 80° C., and finally subjected to a quick dump rinse before drying. Inert gas, preferably N2, may be introduced into the aqueous solutions through a purge board having a plurality of openings and positioned proximate to the bottom of a bath container.