GB2353293A

GB2353293A - FeXN deposition process based on helicon sputtering

Info

Publication number: GB2353293A
Application number: GB9919407A
Authority: GB
Inventors: Michael Thwaites
Original assignee: RTC Systems Ltd; Plasma Quest Ltd
Current assignee: RTC Systems Ltd; Plasma Quest Ltd
Priority date: 1999-08-18
Filing date: 1999-08-18
Publication date: 2001-02-21
Also published as: GB9919407D0

Abstract

A process for the deposition of FeXN (where X could be Ta, Mo, Zr, Al or some other unspecified material) with high saturation magnetic moment, as applied to magnetic storage media, is achieved using Helicon sputter deposition technology. This is achievable using either an iron or ceramic FeXN target material, yielding optimal control of deposited thin film properties.

Description

2353293 FeXN Deposition Process Based on Helicon Nputtering Thin film

compounds based on FeXN (where X could be Ta, Mo, Zr, A] or some other unspecified material) have potentially the highest saturation magnetic moment of any material. This is particularly important in the development of the soft pole and shields on the write head of a read/write head assembly as used in the media industry. Currently, the material is grown by conventional magnetron sputtering from a ceramic FeXN target or by reactive sputtering from a metallic FeX target.

The substrate to be deposited on is positioned in a uniform magnetic field (the biasing field typically 30 Oe) during the growth process in order that the easy axis of magnetisation is aligned in the surface plane of the substrate. Unfortunately it is apparent that the magnetic field associated with the magnetron sputter source perturbs the magnetic biasing field and alters the orientation of the easy axis of magnetisation, resulting in inferior material properties.

Furthermore, as the material to be sputtered is ferromagnetic it is necessary to use thin sputter targets in order that the magnetic field strength from the magnetron source is high enough in front of the target itself to facilitate sputtering at a reasonable deposition rate. This leads to reduced up time of the process tool as the Fe target needs to be replaced often.

According to the present invention there is provided a process for FeXN deposition that enhances both the material properties and the "up time" of the process tool The deposition method employed in the present FeXN process invention is Helicon assisted sputtering, as described in patent application GB9825324. 8 but is described here, in general terms, for completeness.

Referring to figure I which shows a stainless steel vacuum chamber with electromagnets positioned on either side of the main chamber. On the left of the chamber (as viewed from the front) is a quartz tube surrounded by an RF antenna, which is connected via a matching unit to an RF power supply.

Due to this configuration there is an interaction between the electric field profile generated by the antenna and the magnetic field generated by the electromagnets which produces a plasma wave travelling from left to right (in this configuration).

Plasma electrons from the high energy region of the Boltzman energy distribution are accelerated by the plasma wave via the well known energy transfer mechanism, Landau damping. This results in a high density plasma, commonly called a helicon plasma or whistler wave. A further electromagnet is positioned at the top side of the chamber surrounding the magnetron (now called a tron). This allows the plasma from the helicon source to be directed towards the sputter target, generating an intense plasma directly in front of the sputter target surface. The target is then biased in the conventional way (with dc or rf power) to initiate the deposition process.

Uniformity of the coating can be controlled by the position of the plasma with respect the target, which is controlled by the top electromagnet coil current The operating pressure (during sputtering) is in the range IxI04mb to >IxIO-1 mb, making the process at the low end of the pressure regime, a long throw process, i.e. a small number of scattering events between the target and the substrate.

As can be seen from the above discussion it is clear that the plasma generation is by way of the plasma launch tube rather than from the magnetron magnetic flux. Consequently, the magnets can be removed from the magnetron (hence the name tron) with the resultant effect of no racetrack and the ability to sputter from thick ferromagnetic targets. Further, as the plasma is generated remote from the sputter target, the properties of the film are controlled mainly by the voltage across the target sheath. This voltage controls the energy of fast secondary electrons and energetic neutrals emitted from the target and impinging on the substrate, this in turn controls the energy transferred into the growing film which is the primary property controlling parameter.

This deposition technology provides the following advantages over conventional sputtering processes:- The ability to sputter without the formation of a racetrack in the target surface.

The ability to sputter from thick (>6mm) targets, including ferromagnetic materials.

Near independent control of deposited thin film properties Long throw process.

A specific embodiment of the invention will now be described by way of example:

Deposition of thin rdm FeN (reactive sputtering) Many thin film compounds can be produced using a modification of conventional sputtering called reactive sputtering. Here, material being deposited is sputtered in an argon/reactive gas atmosphere such as (but not limited to)02and N2. With this type of process'the deposition rate (and the material properties) exhibit a dependence on the partial pressure of the reactive gas as shown in figure 2, i.e. the well known hysterisis curve.

-1 Unfortunately, in many cases the optimum properties of the deposited thin film are to found with a reactive gas partial pressure on the steepest part of the hysterises curve, making process control difficult. Information relating to the partial pressure of the reactive gas can be obtained from an optical emission or chromaticity analysis of the plasma. This information is then used in a real time closed loop system, controlling the quantity of reactive gas admitted to the process chamber such that the operatingg position on the hysterises curve remains constant.

For the case of the deposition of FeXN the target can be Fe or FeX (where X is a second element) and the process gas is an Ar/N2rrixture with the percentage of N2 between 0% and 100%, but typically closer to 8%. Substrate temperature can be between ambient and 400'C.

Clearly, as there are no magnets associated with the sputter source (tron) the magnetic bias field should not suffer any localised perturbations influencing the material properties, sputtering is conducted with no racetrack and from thick ferromagnetic targets, leading to high uptime of the deposition tool.

Deposition of FeXN from a ceramic FeXN target.

As above but using an FeXN sputter target and with simple control of the Ar/N2 ratio.

i

Claims

Claims

A technology has been developed that enables the growth of thin film FeXN:- To be undertaken in a uniform magnetic field not perturbed by the magnetic associated with a conventional magnetron target.

0 To be deposited with a high (>70%) target utilisation.

To be deposited from thick Fe, FeX and FeXN targets.

To be deposited with near independent control of material properties.

To be deposited reactively under plasma emission or plasma chromaticity control.

To be deposited by a conventional pressure or long throw process 4+