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Corrosion characterization of high moment magnetic material coated with diamond-like carbon
(2013-11-04)
Supadee, Laddawan
;
Chatruprachewin, Santi
;
Suriya-Amaranont, Chaba
;
Titiroongruang, Wisut
In order to increase data storage density of hard drive, DLC overcoat thickness was decreased to allow read/write head to come closer to magnetic alloy of the disk, andwith maintaining the main purpose of the overcoat to provide good corrosion and mechanical protection for the underlying magnetic recording film under unfavorably environmental conditions and occasional reactions. Base on that the edges of topography will be weak point for deposition films cause of shadow effect during the process, it's hard that deposition atomic will stay at the concave and convex of topography. DLC coverage performance at the edge of 3D topography becomes high sensitive with limited DLC films thickness. Currently the 3D profile of magnetic material that needs to protect with DLC, is about 2 nanometers with subnanometres DLC thickness. The enormous of data shrew corrosion pattern was usually happened at the edge of topography. Thus, the accelerated test or indirect methodology was applied for DLC integrity. This investigation was explore the methodology to verify the weakness of DLC films especially at the topography edges which is difficult for any direct metrology tools can pursue. With pore resistance, which related to the film structure, the electrochemical impedance indicated that DLC/Si3N4 is a suitable choice to against corrosion. However topography surface influence to DLC coverage. Controllable surface for DLC deposition also needed well defined. Two types of step height was created as 1 nm and 2 nm on (100) silicon substrate. The 20Å DLC film thickness was deposited on the silicon substrate with promised technique, Filtered Cathodic Vacuum Arch (FCVA). After this process the aluminum (Al) was deposited on the surface of DLC film by using evaporation technique. The silicon substrate was driven to Al surface thro pin holes on the DLC film at 577OC. To detect the pin holes on the DLC film, the aluminum layer was removed by using wet etch chemical process. The SEM image indicates that the square pitting at the edge of DLC film obtained for 2nm step height was around 2nm depth. The latest experiment in this investigation to characterize 2.3 T magnetic moment material degradation with DLC/Si3N4 coating, was performed with electrochemical impedance spectroscopy and AFM. The material with DLC overcoat after exposed to H2SO4 for 30 min, polarization resistance was increased for 2 times from uncoated material. Alternative charge transfer capacitance was reduced as desirable charge current. © (2013) Trans Tech Publications, Switzerland.
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Environmental treatment for perfect spray photoresist morphology and analysis
(2013-10-29)
Supadee, Laddawan
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Chatruprachewin, Santi
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Titiroongruang, Wisut
A homogeneous photoresist for IC or read-write data storage head fabrication requires a certain flowing of the resist film on the topography surface for at least few micrometers, thus defining certain minimal resist viscosity for the remaining solvent concentration for spraying technique. The high photoresist solvent evaporates during flight (between spray nozzle and substrate) prevents the droplets from sticking to the substrate and causes a rough surface. The limitation of very low photoresist viscosity for micro droplets spraying is a drawback of the technique. Because of very low viscosity of spray coating resist, nitrogen in spray coating system will act as 2 functions. First is for spread photoresist to be micro droplets. In the same time nitrogen can dry the small droplet before locating to substrate and perform obstacle for UV exposure. The unsatisfied resist was protected UV light during exposure cause pattern deformation. The study was investigated the particles which always found on finished photoresist surface spraying, and aimed to find the solution to decrease or eliminate dry droplet. EDX identified element of the obstacle particles is photoresist. They are dry resist ball about 1 - 6 um size. The selected chemicals for the investigation to dilute or dissolve the resist ball, IPA, acetone and mixing solution between 70% IPA and 30% acetone. Acetone is most effective. The proper time for dissolve dry resist ball with slight photoresist degradation is 40 s, very short because of high vapor pressure of acetone at room temperature. There is a trade-off between resist surface smoothness and reflow characteristics. Final resist thickness with the acetone vaporization condition will be achieved 7.5 um as expectation with less corner coverage problem. SEM and AFM images were confirmed that morphology after acetone vapor exposure was improved. Surface roughness was reduced for 3 times to 8 nm with acetone vaporization environment. The end of this study was include on corrosion characterization for magnetic CoFe alloys underlying photoresist to explore the method to determine photoresist type in future manufacturing which necessary to run the process with sensitive material. With AZ4999 spray photoresist protection indicated corrosion rate of CoFe films was reduced for 100 times compare to bare films. © (2013) Trans Tech Publications, Switzerland.
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A simulation of air bearing surface materials with copper substrate for corrosion investigation
(2013-09-02)
Chatruprachewin, Santi
;
Nuthong, Chaiwat
Corrosion defect is one of the important defects found in hard disk drive manufacturing. Fail to detect this defect might lead to fatal hard disk drive failure. In general, corrosion defect was found after the end of process. The fundamental methodology used to measure corrosion defect in head magnetic process of hard disk drive manufacturing is Electrochemical impedance spectroscopy (EIS). This method applies a low frequency voltage to a chemical cell in order to measure corrosion rate which is defined as a reaction of material in aqueous solution. The data obtained from EIS measurement method are complex and thus hard to analyze. Furthermore, EIS method is destructive materials measurement and the obtained results cannot well predict corrosion behavior of the system. However, head magnetic materials/slider is a stack of three materials in layers i.e. soft magnetic layer, diamond like carbon (DLC) layer, and photoresist layer respectively. These three stack layer of slider can be replaced by R-C equivalent circuit. Nyquist plot and Bode plot are used to observe the frequency response of the equivalent circuit. This observation can help in prediction of corrosion behavior before starting of mass fabrication or transferring to new materials. This work shows that the results obtained from an equivalent R-C circuit model of copper substrate coated with photoresist and the one obtained from EIS method are comparable. It should be noted that the parameters of R-C equivalent circuits are modified for corrosion behavior studying according to two different types of photoresists. © 2013 IEEE.
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Polymer film selection for corrosion protection of data storage magnetic materials
(2011-12-01)
Chatruprachewin, Santi
;
Supadee, Laddawan
;
Titiroongruang, Wisut
Due to the current requirement of high recording density of hard disk drive, the thickness of DLC layer which is the protective layer is needed to be reduced. Therefore, the corrosion of read-write elements that are fabricated from soft magnetic materials is more critical. During the photolithography process, polymer photoresist is playing the major role on controlling the corrosion of soft magnetic materials. Two different types of polymer photoresists are selected to investigate, noted as wet photoresist and dry photoresist, respectively. Contact angle measurement, AFM and SEM are techniques using to determine the quality of polymer photoresists. Furthermore, the direct corrosion is also studied by using potentiostat/galvanostat-based measurements. The result suggested that the wet photoresist, AZ4999 Clariant, is better as compared to that of dry photoresist. No surface degradation as well as surface defects of the wet photoresist was found after lithography process. The corrosion rate of the specimen coated by this corresponding wet film is found to be only 1.44×10 <sup>-6</sup> mm/y. In addition, the wet photoresist surface is hydrophobic posed of more than 75 degree of contact angle. Copyright © 2011 American Scientific Publishers All rights reserved.
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Photoresist hardness study of high moment head magnetic recording fabrication
(2011-08-12)
Chatruprachewin, Santi
;
Supadee, Laddawan
;
Titiroongruang, Wisut
Due to the current requirement of high recording density of hard disk drive, the thickness of DLC layer which is the protective layer is needed to be reduced. Therefore, the corrosion of read-write elements that are fabricated from soft magnetic materials is more critical. During the photolithography process, polymer photoresist is playing the major role on controlling the corrosion of soft magnetic materials. Two different types of polymer photoresists are selected to investigate, noted as wet photoresist and dry photoresist, respectively. Contact angle measurement, AFM is techniques using to determine the quality of polymer photoresists. Furthermore, the direct investigation is also studied by using elastic modulus measurements. The result suggested that the positive wet photoresist is better as compared to that of dry negative photoresist. No surface degradation as well as surface defects of the wet photoresist was found after lithography process. In addition, the wet photoresist surface is hydrophobic posed of more than 90 degree of contact angle. © 2011 IEEE.
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Polymer film selection for corrosion protection of data storage magnetic material
(2010-05-05)
Chatruprachewin, Santi
;
Supadee, Laddawan
;
Titiroongruang, Wisut
The prevention of soft magnetic material from corrosion in hard disk drive is very concern due to high magnetic moment come with high corrosion sensitivity. Photoresist that is used for read/write head fabrication is important to protect magnetic element. Good photoresist should not found porosity and low water adsorption. This investigation was methodology to classify 5 conditions of photoresist which is used in fabrication at lithography process. Potentiostat/Galvanastat is selected technique by applying external voltage for current response. The result suggested proper photoresist was wet photoresist type, AZP4999. There is no degradation after lithography process had finished. Chemical wear resistance still maintain at same level of magnitude since first step (coating) till last step (developing). ©2010 IEEE.

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