Deposition of insulating thin film by plurality of ion beams

Abstract: A method of depositing insulating thin films on a substrate (50) employs a target (40) that is formed of material which includes a constituent element of the insulating thin film. An ion beam (35) preferably of inert gas is then directed toward the target (40) to disperse the target material. Simultaneously, a second ion beam (37) which includes another constituent element of the insulating thin film is also directed toward the substrate (50). The material from the target (40) and the element of the second ion beam (37) react in proper stoichiometry and is deposited onto the substrate (50) as the insulating thin film.

Description: Field of the Invention This invention relates to magnetic recording head fabrication and in particular to methods of depositing insulating thin films on magnetic recording heads. Background of the Invention Present day processing technology enables the fabrication of magnetic heads at a miniaturized scale. To achieve this end, circuit components are scaled down both in areal dimension and in height dimension with thinner interposing layers. However, there are certain thickness limits the interposing layers need to maintain. Beyond such limits, various reliability problems may arise. For example, in a magnetic head, the read-write gap is formed of an insulating layer spacing two magnetic layers. A thinner gap offers the benefit of allowing the magnetic head to process high density data signals. However, the thinner insulating layer forming the gap is more prone to pinholes, which may bridge the magnetic layers and render the magnetic head inoperable. For example, where an insulating layer separates two conducting layers, a thin insulating layer may be incapable of withstanding the electric fields emanating from the two conducting layers. Consequently, the insulating layer may experience a dielectric breakdown, which results in a disastrous failure. Accordingly, there is a need to provide high quality insulating films to meet the demands of the magnetic recording head industry. Materials most commonly used as insulating layers in magnetic recording heads are alumina (Al 2 O 3 ) and silicon dioxide (SiO 2 ). The quality of these insulating layers can be gauged by a number of parameters. A good insulating film is uniform in thickness over a large surface area, thereby allowing the overlying layers to assume good step coverage. In addition, the film should be free of pinholes, thereby preventing any magnetic or electrical shorts of the overlying and underlying layers. Furthermore, a good insulating film is capable of withstanding high electric breakdown voltage, and is resistant to certain chemical etchants. Insulating films can either be thermally grown by oxidation or by deposition. For instance, SiO 2 can be grown out of a silicon substrate via the process of oxidation. However, when the substrate material is different from the insulating material, deposition methods are preferred. U.S. Patent 5,256,266 to Blanchette et al. discloses a process for sputtering and depositing alumina that is crypto-crystalline and is useful as the insulating layer which forms the transducing gap of the head. Thin film deposition may be accomplished by sputtering, chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD). One example of depositing insulating thin films by sputtering is described herein with reference to Fig. 1. A typical arrangement for depositing insulating thin films during magnetic head fabrication employs a sputterer 2 encased within a chamber 4. Fixed inside the chamber 4 are a target plate 6 and a substrate fixture 8. Secured atop the substrate fixture 8 are substrates 10 of the magnetic recording heads to be processed. The target plate 6 is normally formed of material to be deposited onto the substrate 10. For example, as shown in Fig. 1, the target plate 6 is made of alumina. Prior to the deposition process, air is first pumped out of the chamber 4 in a direction signified by arrow 12 via outlet 14. After a satisfactory vacuum level inside chamber 4 is reached, an inert gas, such as argon (Ar), is then admitted into the chamber 4 in a direction designated by arrow 16 via an inlet 18. When the inert gas inside the chamber 4 reaches a sufficiently high pressure level, the sputterer 2 is then ready for operation. The target 6 and the substrate fixture 8 are normally biased through a steep electric potential by the voltage source 20 in the range of 500 Volts to 1000 Volts. The inert gas atoms between the target 6 and the substrate fixture 8 are thereby ionized. In essence, the electrons of the inert gas atoms are attracted toward the substrate fixture 8 while the positively charged ions 22 move toward the target 6. In the process, target molecules 24 are dislodged and dispersed from the target 6 and deposited onto the substrate 10 as the insulating thin film. It should be noted that the above description is depicted at the molecular level. Actually, the gas ions 22 form a plasma 26 bombarding the target 6 constantly. The sputtering method, as described above, has been widely used in the processing of electronic circuits. However, there are several drawbacks associated with this method. First, inert gas inside the chamber 4 must be at a relatively high pressure in order to sustain a plasma. Very often, at such high pressure level, impurities inside the inert gas can easily be deposited onto the substrate surfaces, resulting in deposited films with high pinhole counts. Equally as undesirable, both the target plate 6 and the substrate fixture 8 of the sputtering apparatus 2 are tied to high voltage potentials. As arranged, the target plate 6 especially and the substrate fixture 8 are practically incapable of any mechanical motions. The main reason is that any relative motions between the target plate 6 and the substrate fixture 8 would disturb the sustained plasma 26 and negatively affect the sputtering process. However, with the substrate 10 stationary relative to the target 6, the target molecules 24 may not be uniformly deposited onto the surfaces of the substrate 10. Consequently, the insulating films may be deposited with uneven thickness. For electronic circuits having large geometrical sizes, insulating thin films fabricated from the sputtering method may be capable of fulfilling their intended functions. However, as circuits scale down in physical dimensions, conventionally deposited insulating films with the aforementioned shortfalls could affect the final production yield and reliability. In the US 4,793,908 there is disclosed a method of fabricating multiple layer, solid, thin films on a substrate having a surface to be coated, the method providing control over the thickness, stoichiometry, and morphology of each separate layer formed by a method comprising the steps of: A. forming a first ion beam from an inert gas; B. bombarding a target surface with said first ion beam in a vacuum chamber to generate a vapor cloud composed of the target material atoms by the process of sputtering; C. adjusting the respective positions of the substrate surface for coating and the target surface to promote the condensation of the vapor upon the substrate surface for coating; D. forming a second ion beam, the second ion beam's ions being formed from a mixture of inert and reactive gases; E. bombarding the substrate surface simultaneously with the second ion beam to promote a chemical reaction between the target vapor atoms and the chemically reactive gas ions as the target atoms and the chemically reactive gas ions impinge upon the substrate surface for coating, the resulting chemical compound building up in thickness as a homogeneous thin solid film layer; F. positioning an alternative target material in the place occupied by the previous one; G. repeating the above method steps to produce each successive thin solid film layer of different material formed upon each previous layer. The US 4,992,298 discloses a dual ion beam ballistic alloying process for forming a film such as diamond onto a substrate, which comprises the steps of: (a) cleaning the surface of the substrate with a first energy beam of inert atoms; (b) depositing a layer of a desired non-hydrocarbon substance on the substrate with a low energy, sputtered atomic beam; (c) simultaneously exposing the substrate to said first energy beam of inert atoms with a high energy to grow a ballistically alloyed layer having a thickness of about 10-2000 Å; and (d) reducing the energy level of the first, high energy beam to cause the growth of the layer of said substance on said substrate to a final desired thickness. Summary of the Invention An object of the invention to provide a method of depositing insulating films with uniformity in thickness over a large surface area, that are less susceptible to pinholes, and are capable of withstanding high electric fields and are more resistant to certain chemical etchants. Another object is to provide thin films with more uniform physical and chemical properties. The invention is defined in the independent claim. Further developments are set forth in the dependent claims. These and other advantages, features, and objects of the present invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanyihg drawings, in which like reference numerals refer to like parts. Brief Description of the Drawings Fig. 1 is a schematic drawing of a prior art sputtering system for depositing insulating films; and Fig. 2 is a schematic drawing of a sputtering system, which is employed to implement the method of the present invention. Detailed Description of the Invention With reference to Fig. 2, a deposition apparatus 28 which comprises a chamber 30 that houses a primary ion beam gun 32, a secondary ion beam gun 34, a target holder 36 and a substrate support 38. The primary and the secondary ion beam guns 32 and 34 are directed toward the target holder 36 and the substrate support 38, respectively. The substrate support 38 includes a turntable 38A revolvable around a shaft 38B. There are a plurality of substrate mounts 38C disposed atop the turntable 38A. The substrate mounts 38C are also implemented to be rotatable about axes 46 on the top of turntable 38A. The mechanical motions of the turntable 38A and the mounts 38B are controlled by an control circuit board 48 external to the chamber 30. An air outlet 44 is also built in as part of the chamber 30. Ion guns 32 and 34 are substantially similar in structure. Only the primary ion gun 32 is described herein. The ion gun 32 includes a ground shroud 32A which in turn encompasses a quartz discharge chamber 32B. Wound around the quartz discharge chamber 32B is a RF (Radio Frequency) coil 32C. A screen grid 32D and an accelerator grid 32E, which are spaced from each other, are disposed in front of the opening of the ground shroud 32A. A pair of neutralizers 57 and 58 are also positioned adjacent to and in front of the ions guns 32 and 34, respectively. The target holder 36 comprises a target mount 36B upon which a target 40 is releasably attached to. An oscillating drive 36C is engaged with the target mount 36B through a pivotal shaft 36D. The drive 36C is capable of oscillating the target mount 36B as shown by the bidirectional arrows 42. Prior to the deposition process, a target 40 with the target material for deposition is first mounted onto the target mount 36B. Substrates 50 to be deposited with the target material are then positioned onto the rotatable mounts 38C. Thereafter, the chamber 30 is pumped to a vacuum level through the outlet 44. At a sufficiently low pressure level, the deposition process is ready to be initiated. There are two basic processes within the scope of the invention whereby insulating films can be deposited onto the substrates 50. They are, namely, the nonreactive process and the reactive process. In the nonreactive process, the chosen target 40 comprises material substantially the same as the films to be deposited. For example, in the deposition of alumina films, the target 40 can be an alumina block. On the other hand, in the reactive process, the selected target 40 includes material content substantially different from the material content of films to be deposited. In the deposition of alumina films, the chosen target 40 can be an aluminum (Al) metal block. In any event, the target 40 comprises a constituent element of the insulating film to be deposited. In the two examples described above, the film to be deposited includes Al 2 O 3 , and Al in either target is a constituent element of Al 2 O 3 . To start the nonreactive process, argon (Ar) gas of ultra high purity is first admitted into the inlet 32F of the discharge chamber 32B. In a similar manner, a mixture of Ar and O 2 gases are released into chamber 34B. The coils 32C and 34C are then energized with the required RF power. Electrons emitted from neutralizers 57 and 58 ignite the Ar atoms inside chambers 32B, and the Ar atoms and O 2 molecules inside the chamber 34B, respectively. As a consequence, plasmas of the respective ions are formed in each of the chambers 32B and 34B. Screen and accelerator grids 32D and 32E in primary gun 32, and grids 34D and 34E in secondary gun 34 are then adjusted to define the proper beam energy levels. Essentially, the positively powered grids 32D and 34D, form with the negatively powered grids 32E and 34E, steep potential fields within the narrowly confined grid spaces 32S and 34S, respectively. The ions inside the discharge chamber are attracted to and accelerated toward the steep potential fields, and emit beyond the grids 32E and 34E as ion beams 35 and 37, respectively. In should be noted that by generating plasmas in separate discharge chambers 32B and 34B, gaseous pressure inside the overall chamber 30 can be set at a level much lower than that required by the sputtering method. The consequential benefit is that with the cleaner surrounding environment, the chance of contamination is accordingly reduced resulting in deposited films with less physical defects. As shown in Fig. 2, the primary gun 32 directs the ion beam 35 toward the target 40. The ion beam 35 in turn disperses the material from the target 40. In this specification and in the appended claims, the phrase "disperse material" and its equivalent thereof, when used in conjunction with a target, is construed as to dislodge and to disassociate the material from the target at the atomic or molecular level. For example, in this case, the Ar ions disperse the material from the target 40 in the form of molecular alumina particles 52 traveling in somewhat random directions 54. The target particles 52, carrying the transferred momentums of the ions from the ion beam 35, travel and accumulate onto the surfaces of the substrate 50 as the deposited insulating film. The secondary gun 34 also aims another ion beam 37 toward the substrates 50 during the deposition process. As mentioned before, the ion beam 37 is composed of O 2 and Ar ions. The purpose of bombarding the substrate 50 with the ion beam 37 is twofold. The moderate bombardment of the assist beam helps to improve film adhesion and thereby forms a thin film with better density than without the assist beam. Also, the oxygen in the beam helps to maintain proper stoichiometry in the nonreactive mode. In the reactive mode, oxygen becomes the major ingredient of the film to be formed at the substrate 50. The higher powered assist beam containing oxygen ions reacts with aluminum from the target 40 directly at the surface of the substrate 50. This greatly enhances the formation of crystalline alumina. It also should be noted that in contrast to the prior art sputtering mechanism illustrated in Fig. 1, there are no high voltage wirings or contacts affixed to either the target 36 or the substrate support 38. In a preferred embodiment the target holder 36 is designed with an oscillating motion signified by bidirectional arrow 42. In addition, the turntable 38A is operated with rotating motions signified by arrow 59. Likewise, the substrate mounts 38C is designed with rotatable motion signified by arrow 56 atop the turntable 38A. Optionally, the entire substrate support 38 is operated in an oscillating motion as represented by bidirectional arrow 60. The motions 42, 56, 59 and 60 are all designed to achieve uniform film thickness on the substrate 50. In the nonreactive process, the deposition rate is about 90 Å/minute. During deposition, the primary gun 32 may be operated at a power level substantially higher than that of the secondary gun 34. A typical set of operating parameters is with the beam current of the primary ion beam 35 set at approximately 650 mA (milliamperes) and the current of the secondary beam 37 at about 200 mA. The grid voltages applied at primary accelerating grid 32E and the secondary accelerating grid 34E can be fixed at respectively 1500 Volts and 300 Volts. The atmospheric pressure inside the chamber 30 can be maintained between 266,6448 x 10 -4 Pa to 399,9672 x 10 -4 Pa (2 x 10 -4 Torrs to 3 x 10 -4 Torrs). As a demonstration, insulating Al 2 O 3 films of approximately 2000 Å are deposited via the nonreactive process under the above stated conditions and via the sputtering method. During sputtering, the target-to-substrate bias voltage is set from a few hundred to 1000 Volts under a gas pressure in the order of 10 -2 Torr. The resultant films from both methods are compared and analyzed. The measured parameters are tabulated as follows: Nonreactive Deposition Process Sputtering Mechanical Stress (x 10 10 dyne/cm 2 ) 0.15 to 0.25 1 Breakdown Voltage (x 10 6 V/cm) 2 to 3 1.4 to 2 Etch Rate (in positive resist developer) 40 Å/min. 70 Å/min. From the above table, the mechanical stress is defined as the tension force existent between the substrate and the deposited film at room temperature. As shown, films deposited with the deposition method of the present invention are significantly less stressed in comparison. The breakdown voltage is defined as the voltage applied to the major surfaces of the film just prior to dielectric breakdown. The result shows that films fabricated from the preferred method of the invention are approximately 50% better in performance. The films deposited from the method of the invention also show more resistance to positive photoresist developers, such as AZ400K manufactured by Hoechst Celanese Corp., Sunnyvale, California. Photoresist developers are etchants used to define patterns of other layers during processing. With this inventive process, the deposited films are more uniformly distributed over a larger surface area. Also better step coverage of the overlying layers is achieved. The operational details of the reactive and nonreactive process are substantially similar. For the sake of brevity, only the differences are herein highlighted. In the reactive process, as mentioned before, the selected target 40 comprises material content substantially different from that of films to be deposited. During deposition, the material dispersed from the target 40 by the primary ion beam 35 reacts with the material from the secondary ion beam 37, in which oxygen ions are a majority, to be deposited onto the substrates 50 as the insulating thin film. There is a higher degree of activity of chemical reaction during deposition in the reactive deposition process than with the nonreactive process. During deposition, using the reactive process, the secondary gun 34 is operated at a power level comparable to that of the primary gun 32. For example, the primary beam 35 can be set at 400 mA (milliamperes) and the secondary ion beam 37 can be set at approximately 300 mA. The grid voltages applied at primary accelerating grid 32E and the secondary accelerating grid 34E can be fixed respectively at 650 Volts and 550 Volts. Moreover, the discharge chamber is proportionally mixed with gas higher in oxygen content. The gaseous pressure inside the chamber 30 can be maintained at between 266,6448 · 10 -4 Pa to 399,9672·10 -4 Pa (2 x 10 -4 Torrs to 3 x 10 -4 Torrs). The deposition rate under the above operating conditions is approximately 15 Å/min. As the assist ion beam energy and current density in reactive mode are significantly higher than in the nonreactive mode, the localized reaction at the substrate surface and the mobility of the impinging atoms are greatly enhanced. Insulating films thus deposited are crystalline, as demonstrated by transmission electronmicroscopy (TEM) in both plane view and cross-section view. The refractive index is 1.75 measured at 623.8 nanometers. Such films have very high resistance to etching. It etches less than 30 Angstroms (Å) only in a 10% hydrogen fluoride (HF) solution. Other variations are possible within the scope of the invention. The materials used need not be restricted to these described above. For example, films to be deposited can be SiO 2 and the target 40 can be a silicon (Si) block. As a further alternative, the film deposited can be silicon nitride (Si 3 N 4 ) and the selected target 40 can be Si or Si 3 N 4 depending on whether the reactive or nonreactive process is chosen.

Claims: A method of forming within a vacuum chamber a single insulating thin film of alumina on a substrate (50) of a magnetic recording head, wherein said thin film of alumina is disposed between conductive magnetic layers, providing a substrate support (38), said substrate support (38) including a turntable (38A); providing a plurality of substrate mounts (38c) supported on said turntable; providing a target (40) formed of a material which includes a first component of the insulating thin film; providing a target holder for supporting said target (40); directing a first ion beam (35) toward said target (40) for dispersing material from said target (40); directing a second assist ion beam (37) toward said substrate, said second assist ion beam including a second component of the insulating thin film, wherein the material dispersed form said target (40) reacts with said second component of said second assist ion beam (37) and desposits onto the substrate (50) as the single insulating thin film; while directing said first ion beam (35) and said second assist ion beam (37), simultaneously rotating said substrate mounts (38c) continuously about substantially parallel spaced axes and rotating said turntable (38A) continuously about a shaft and oscillating said target holder continuously and bidirectionally between two points and oscillating said substrate support (38) continuously and bidirectionally between two points such that an oscillatory tilt-motion of said turntable (38A) results; whereby said single insulating thin film of said alumina is deposited uniformly on said substrate of said magnetic recording head with minimal pinholes. The method of forming an insulating thin film as set forth in claim 1, wherein the substrate (50) is positioned adjacent to said target (40); and wherein the material dispersed from said target (40) by said first ion beam (35) substantially deposits on the substrate (50). The method of forming an insulated thin film as set forth in any one of the preceding claims, wherein said first ion beam (35) comprises argon. The method of forming an insulating thin film as set forth in any one of the preceding claims, wherein said second ion beam (37) comprises oxygen.

Inventors: TAN MINSHEN, TAN SWIE-IN, TAN, MINSHEN, TAN, SWIE-IN
Applicants: READ RITE CORP, READ-RITE CORPORATION
Application year: 1996
Main classification: G11B5
IPC codes: C23C14, G11B5