Hard Disk Concentration
Depth Profile

Figure 1: Schematic diagram showing the multilayers
of a magnetic hard disk.

Overview

The application of complex multilayer thin film materials in devices, such as computer hard disk media, is steadily increasing so that the production of these materials must increase without compromising quality. The technique of X-ray photoelectron spectroscopy (XPS) is ideally suited to provide critical information on film thickness and chemical composition, although the technique is little used in a quality control environment. The AMICUS X-ray photoelectron spectrometer with its compact size and eose of operation is designed with quality control applications in mind. Here, the chemical state characterization and film thickness monitoring of computer hard disk media are demonstrated using AMICUS.

Figure 2: X-Ray photoelectron survey scans
as a function of depth from the "as introduced" surface.

Sample Preparation

3mm diameter samples were punched from a computer hard disk and mounted with conductive tape onto a sample stub. Rapid sample introduction into the analysis chamber of up to 10 samples is possible by utilizing the optional carousel system of the AMICUS allowing high throughput of samples. Photoelectron spectra were recorded with the Mg K

source. Depth profiling was performed using the integral Ar⁺ ion gun coupled with automatic sample rotation to ensure both rapid etch rates and excellent interface resolution.

Figure 3: Elemental concentration profile
of a computer hard disk.

Hard Disk Media - Depth Profile

The initial investigation of the hard disk samples involved recording survey scans as a function of sputter time, to determine the elemental composition of the revealed surface material after each sputter. Survey scans as a function of depth from the "as introduced" surface are shown in Figure 2. The identification of each layer is highlighted by the accompanying schematic cross section of the hard disk in Figure 1.

From these survey scans, the composition of each layer could be determined and a complete concentration profile calculated through the hard.disk. Figure 3 shows the concentration of the component hard disk layers as a function of depth from the surface. This figure demonstrates the well-defined interface boundaries between each layer, with no obvious degradation in the interface resolution as a function of depth. Also noted is the persistence of carbon contamination, through the magnetic media layers.

Figure 4:C 1s X-ray photoelectron spectra of hard disk media
(a) prior to sputtering, and
(b) after a 30s sputter.

Hard Disk Media - Lubrication Layer Thickness

The thickness of the uppermost lubrication layer is critical to avoid wear and crashes of the recording head. Too much lubrication may cause stiction, too little can cause premature head wear.

The technique of XPS is ideally suited for the measurement of lube thickness; both the protective DLC layer and the fluoropolymer lubrication layer are predominantly made from carbon although the carbon exists in quite different chemical environments. XPS has the ability to differentiate these two species of carbon. The C signal from the protective layer is attenuated by the lubrication layer therefore a quantitative measure of overlayer thickness can be made. The ability to routinely determine lube thickness is demonstrated by the carbon spectrum of the thin lubrication and protective layer The XPS spectrum indicates the uppermost lubrication layer is composed of a graphitic type carbon as would be expected in DLC as well as hydrocarbon (probably environmental contamination), with the spectra showing a C 1s peak at 285eV binding energy as well as the fluorocarbon overlayer, with a well resolved peak at 293eV. The asymmetry at the high binding energy of the 285eV C 1s peak implies that the surface polymer also contains oxygen. The delicate nature of the fluorocarbon overlayer is demonstrated by the second C 1s spectra. After a short argon ion sputter the fluorocarbon lubrication layer has been removed, exposing the diamond like carbon layer.

Summary

A high quality elemental concentration profile for a computer hard disk has been recorded using the AMICUS X-ray photoelectron spectrometer.
The features demonstrated for AMICUS include:

Good interface depth resolution with no decrease in resolution as a function of sputter depth.
Chemical state information from thin surface layer enabling determination of lube thickness.

Applications Index

	Copyright © Kratos 1999 Last Update: 99/02/22 Kratos Analytical is a wholly owned subsidiary of the Shimadzu Corporation.

For comments, suggestions, contributions or an Instrument Demonstration e-mail to: dsurman@kratos.com