The present invention generally relates to thin film magnetic devices such as transducers, sensors, recording heads, and random access memory, and methods of making the same.
Thin film deposition techniques are used to form thin films on underlying substrates. Several types of thin film deposition techniques exist, including physical vapor deposition, chemical vapor deposition, atomic layer deposition, and others.
Thin film deposition techniques are used in the manufacture of magnetic devices, by the deposition of thin films of magnetic material on a substrate. These thin films can then be used to make a wide variety of devices, including magnetic transducers/sensors (AMR), magnetic recording (GMR) and magnetic random access memory (MRAM). To achieve good device sensitivity with negligible hysteresis, the magnetic domains within the NiFe film have to be aligned in the same direction. This alignment is achieved by depositing the film in a strong magnetic field that aligns the deposited particles to a so-called “Easy Axis” or preferred orientation of the magnetization (M), which is typically in the plane of the film, as seen in
Permalloy (Ni81Fe19) is a ferromagnetic Ni—Fe alloy with high magnetic permeability, high magnetic saturation and low coercivity that has been used often for thin films. However, films of permalloy are susceptible to circulating induced currents or eddy currents, particularly at greater film thickness. These currents lead to undesirable losses, and their incidence is proportional to the square of the core thickness. High frequency sensors, which are increasingly in demand, require a thicker conducting core, which has proven difficult to accomplish using Permalloy due to the increasing induction of eddy currents. The result has been degraded magnetic properties, illustrated in
One known approach to reducing eddy currents in magnetic material, is to laminate the magnetic material with insulating layers. This technique has been used in high power transformers as well as in micromachined magnetic cores and inductors.
In on aspect, the present invention addresses the limitations of the prior art by providing a PVD chamber for growing a magnetic film of NiFe alloy at a growth rate of greater than 200 nm/minute, which produces a film exhibiting magnetic skew of less than plus or minus 2 degrees, magnetic dispersion of less than plus or minus 2 degrees, DR/R of greater than 2 percent and film stress of less than 50 MPa. The chamber enables a method of sputtering NiFe alloy from a target at a distance of 2 to 4 inches, at a DC power in the range of 50 Watts to 9 kiloWats and pressure in the range of 3 to 8 milliTorr.
In another aspect, the chamber features a unique field shaping magnetron having magnets arranged in outer and inner rings, the outer ring magnets having North poles facing the electrode and sputtering target assembly and the inner ring having South poles facing the electrode and sputtering target assembly, wherein the inner and outer rings extend about a periphery of the magnetron except in two radially opposed regions in which the radially opposed regions the inner and outer rings diverge substantially toward a central axis of the magnetron. The magnetron develops a field uniformity sufficient for rapid growth of high uniformity, low stress films by the appropriate adjustment of process conditions as described herein.
Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
Referring first to
Referring to
A magnetron 26 provides electrical energy and regulates erosion of the target 24 during sputtering operations. The magnetron source 26 may be a DC magnetron or RF magnetron PVD energy source. Moreover, a non-magnetron energy source, such as RD diode, may also be used. The backing plate 22 receives the electrical power for target sputtering and is electrically isolated from a vacuum lid 27 using an insulating ring 25. An access valve 28 provides a resealable opening for moving a substrate 30 into and out of the chamber 16 (e.g., using a central water handler in a cluster tool).
The substrate 30 is supported on a mounting surface 32 of the chuck assembly 12. The mounting surface 32 is part of a mounting table 34 that can be arranged to regulate substrate temperature. For example, the table 34 can incorporate a heating unit, a cooling unit, or both. Heat exchanges between the table 34 and the substrate 30 can be facilitated by a heat-transfer gas. More detailed examples of chuck assemblies for regulating substrate temperature are found in U.S. Pat. No. 6,138,745, which is hereby incorporated by reference. The chuck assembly 12 may also provide a capability for electrical biasing such as RF biasing of the substrate.
A drive mechanism 36 translates the chuck assembly 12 along an axis 38 toward or away from the target 24 in order to control the substrate-to-target spacing. Bellows 39 seal the chuck assembly 12 to the processing chamber 16 to accommodate a range of chuck assembly translation heights and to atmospherically isolate the components of the chuck assembly 12, including electromagnet 14, from the evacuated space of the processing chamber 16. Power supplies 46 and 48 operated by a controller 96 implement the desired positioning of the substrate and magnetic drive.
Sputtering and annealing operations lay down and treating thin-film magnetic materials 98 on the substrate surface 94. Processes for laying down films on substrates are well known. U.S. Pat. No. 5,630,916 describes a plate-shaped electromagnet incorporated into a chuck assembly for magnetically orienting such thin magnetic films. The relevant descriptions of this patent are also incorporated by reference.
With this configuration, magnetically aligned NiFe is deposited at rates >500 nm/min without a prior target conditioning step, leading to a process times of less than 40 sec/laminate for a 335 nm thick film. Wafer temperature is controlled under 150 C for the entire process to preserve the magnetic film properties. Stress is maintained under 100 MPa (tensile).
With an appropriate tool configuration, throughputs of less than 25 min/wafer can be achieved for a 333 nm NiFe/10 nm alternating insulating film (like AlN) for a total stack of ˜10000 nm.
The parameters of tool configuration and the range, nominal, low rate and high rate settings for each parameter are set forth in the following table:
The performance of the chamber in the growth of Permalloy films, Permalloy laminates, AlN insulating layers, and TaN insulating layers, has been measured as follows:
The chamber shown in
Up to a total 15000 nm of NiFe has been deposited by alternating between the NiFe layer between 300-750 nm and an insulating layer between 5-10 nm to form a laminate structure, as shown in the second and third columns of the above table.
Thicker Permalloy films may also be deposited, subject to possible reduction of magnetic properties. As one example,
The insulating layer may be formed of AlN or alternatively of TaN, with similar results, as shown in the last column of the above table.
Thicker NiFe films require a high deposition rate for throughput optimization. This high rate generates high temperatures at the substrate and therefore good substrate cooling is critical to minimize degradation of magnetic properties. In addition, the magnetron must be of an optimum design to enable, high rate sputtering with uniform deposition without disrupting the magnetic orientation of the film.
The laminated process described herein permits control of film stress, which is critical, particularly for thicker films for adhesion reasons and to minimize substrate bow which could interfere with the device performance, as well as to reduce magnetrorestrictive effects.
The SEM micrograph of a NiFe laminate film in
While the present invention has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept. What is claimed is:
The present invention is a divisional application that claims priority to U.S. Ser. No. 14/324,937 filed Jul. 7, 2014, which is a non-provisional application of U.S. Ser. No. 61/843,571, filed Jul. 8, 2013, all of which are incorporated herein in their entirety.
Number | Date | Country | |
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61843571 | Jul 2013 | US |
Number | Date | Country | |
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Parent | 14324937 | Jul 2014 | US |
Child | 15289725 | US |