METHOD OF FORMING AN ASSEMBLY OF STACKED LAYERS

Abstract: Method of forming an assembly of layers, making use of a first layer (105) having a recess (107) and a second layer (117) which is deposited on the first layer, whereby the recess is filled. After forming the second layer, a polishing treatment is carried out so as to create a flat and smooth surface (119). An intermediate layer (109) is formed prior to forming the second layer, which intermediate layer is formed by deposition of a material which is more resistant than the material of the second layer in order to have a restraining influence on the polishing treatment. Said treatment may be stopped after reaching the intermediate layer.

Description: Method of forming an assembly of stacked layers The invention relates to a method of forming an assembly of stacked layers, in which method use is made of a recessed first layer on which a second layer filling up the recess is formed by depositing a material, and a polishing treatment is performed for forming a plane surface. Such a method is known from EP-A 0 617 409 (PHN 14.428). In the known method, which is used in the manufacture of thin-film magnetic heads, a first layer is formed by depositing zirconium or quartz on a support, whereafter a recess is provided in this layer by removing material. Subsequently, a second layer filling up the recess is formed by depositing a soft-magnetic material. After the formation of the second layer, a mechanochemical polishing treatment is carried out until the first layer is reached, resulting in a plane surface formed by the first layer and the remaining part of the second layer present in the recess. It has been found that in the known method, in which the second layer is more wear-resistant than the first layer, it is difficult to control the polishing process in such a way that a smooth and plane surface is or has been obtained after reaching the first layer. It is an object of the invention to improve the method described in the opening paragraph in such a way that a plane surface can be obtained in a simple manner during the polishing treatment. To achieve the object the method according to the invention is characterized in that, prior to forming the second layer, an intermediate layer restraining the polishing treatment is formed on the first layer by depositing a material which is more wear-resistant than the material of the second layer, and in that the polishing treatment is terminated after the intermediate layer has been reached. When the polishing treatment, for example, a mechanochemical polishing treatment is being carried out, only the second layer, at least opposite and proximate to the recess, is polished initially. Since this layer has a homogeneous composition, the polishing treatment proceeds regularly in this phase and a smooth and plane polishing surface is obtained. The polishing rate changes at the instant when the plane in which the polishing treatment takes place reaches the intermediate layer. In fact, due to the larger wear resistance of the intermediate layer, the resistance against polishing increases. This means that a plane and smooth surface is ensured if the polishing treatment is terminated at that instant. The method according to the invention is particularly important if the second layer has a larger wear resistance than the first layer. This is the case, for example, if the first layer is or has been formed from SiO 2 , Al O 3 or Si and the second layer is or has been formed from an FeNbSi, CoZrNb or FeSiAl alloy. If the first and the second layer have the same wear resistance, it is favorable to use the intermediate layer as an indicator for terminating the polishing treatment. Also if the layers have mutually different wear resistances, it is favorable to use the intermediate layer as a visual indicator for terminating the polishing treatment. When using an indicator, the polishing treatment does not need to be temporarily interrupted for repeatedly measuring the quantity of material which is still to be polished off before a desired thickness of the second layer is reached and polishing should be terminated. An embodiment of the method according to the invention is characterized in that at least substantially chromium and/or a chromium compound is used as a material of the intermediate layer. Although various materials may be used, it has been found that chromium and chromium compounds are particularly suitable as materials for forming the intermediate layer. Chromium and chromium compounds may be sputtered, which has the advantage that the composition and hence the wear resistance of the intermediate layer can be adjusted by adding nitrogen and/or oxygen during sputtering. If it is desirable to remove, prior to the formation of the second layer, parts of the intermediate layer in the recess or remainders of the intermediate layer outside the recess after polishing, this may be done by selectively non- chemical etching when chromium and chromium compounds are used. A further advantage of chromium and chromium compounds is that very thin layers, of the order of 20 to 50 nm, are sufficient to obtain a desired wear resistance. The intermediate layer provided on the first layer may successfully serve as a protective layer during manufacture so as to prevent scratches which might be caused, for example, during polishing, and similar damages in the first layer. This is particularly important if the first layer has an insulating function such as, for example, in semiconductor structures. A damaged first layer may then easily give rise to short circuit in a conductor pattern provided on or in this layer. An embodiment of the method according to the invention is characterized in that a chromium nitride and/or a chromium oxide and/or a chromium oxynitride is used as a chromium compound. A specific advantage of such compounds is that the quantity of nitride and/or oxide which is present determines the extent of wear resistance of the intermediate layer. In other words, the wear resistance is dependent on the quantity of oxide and/or nitπde. By varying the quantity of oxide and/or nitπde, a desired wear resistance, particularly determined by the mateπal of the second layer, can thus easily be adjusted. An embodiment of the method according to the invention is characteπzed as defined in claim 5. A further embodiment is characteπzed as defined in claim 6. In another embodiment, a mateπal corresponding to the mateπal from which the first layer is formed is used as a mateπal for the second layer In all cases, the first layer may be or have been provided on a substrate or support. The first layer itself may also function as a support. The invention also relates to an assembly manufactured by means of the method according to the invention. The invention also relates to a magnetic head as defined in claim 9 Dependent on the transducing element used, such a magnetic head may be an inductive or a magnetoresistive magnetic head and may be used in a device for magnetically wπting and/or reading information. Such a device is, for example, a magnetic tape apparatus or a hard disk dπve The invention also relates to a magnetic head unit as defined in claim 10. Such a magnetic head unit may be used, for example, for wπting information into and/or reading information from a magnetic optical storage medium. It should be noted with respect to the claims that vaπous combinations of characteπstic features defined in the dependent claims are possible. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments descπbed hereinafter. In the drawings: Figs. 1 to 7 show diagrammatically vaπous stages of a first embodiment of the method according to the invention, Fig. 8 shows diagrammatically a thm-film magnetic head according to the invention, manufactured by means of the first embodiment of the method according to the invention, Figs. 9 to 13 show diagrammatically vaπous stages of a second embodiment of the method according to the invention, and Fig. 14 shows diagrammatically a magnetic head unit according to the invention, manufactured by means of the second embodiment of the method according to the invention. A first embodiment of the method according to the invention will now be described with reference to Figs. 1 to 8. This embodiment starts from a plate-shaped support 1 of ferrite, in this example an NiZn ferrite. A first layer 5 of an insulating material, in this example quartz, is formed on a surface la of the support 1 by means of, for example, sputtering deposition. Two recesses 7a and 7b are formed in the first layer 5, for example, by chemically etching or reactive ion etching while using a mask. A layer, further referred to as intermediate layer 9, is formed on the first layer 5 thus structured by means of deposition, for example, sputtering deposition of a wear-resistant material, in this example a chromium oxide. Subsequently, a second layer 17 of a soft-magnetic material is formed, while the recesses 7a and 7b are filled up completely for forming two flux guides 17a and 17b. In this example, the layer 17 is formed by sputtering deposition of a CoZrNb alloy. Instead of a CoZrNb alloy, it is alternatively possible to use a different suitable alloy such as an FeNbSi alloy or an FeSiAl alloy. After formation of the second layer 17, a polishing treatment, for example, a mechanochemical polishing treatment is performed. Initially, the polishing treatment is carried out exclusively on the second layer 17 so that a plane polishing surface is obtained. However, at a given instant, the intermediate layer 9 is reached. From that instant, the intermediate layer 9 has a polishing-restraining effect on the performed polishing process due to the applied choice of material. The increased polishing resistance which then occurs is an indication that the intermediate layer 9 has actually been reached and that the polishing process can be terminated. After termination, a substantially completely smooth and plane surface 19 is obtained, a part of which is formed by the material of the intermediate layer 9 and another part of which is formed by the soft-magnetic material of flux guides 17a and 17b. If a mechanochemical polishing treatment is used, for example, a colloidal suspension of SiO 2 particles in an alkali solution may be used. A thin insulation layer 21 of a non-magnetic, insulating material is provided on the plane surface 19 obtained in the manner as described hereinbefore. In this example, quartz is deposited for that purpose. A layer 23a of a magnetoresistive material is provided on the layer 21, for which purpose an alloy of NiFe is sputtered in this example. The layer 23a is subsequently structured by means of known lithographic techniques so as to form an MR element 23. An electrically conducting material, for example Au, may be deposited on the MR element 23 so as to form equipotential strips 25a. Subsequently, an insulation layer 27 of, for example, quartz is provided, whereafter a protective counter block 31 of, for example BaTiO 3 or CaTiO 3 is secured, for example, by means of an adhesive. The intermediate product now obtained is provided with a head face 33 for co-operation with a magnetic recording medium, particularly a magnetic tape, by means of treatments such as, for example, grinding and/or lapping. If the soft-magnetic material of the flux guides 17a and 17b in the thin-film magnetic head according to the invention, shown in Fig. 8, is replaced by a soft-magnetic material which is electrically non-conducting or electrically poorly conducting, particularly an MnZn ferrite, an NiZn ferrite or Fe O 3 ferrite, the MR element 23 may be directly provided on the plane surface 19. Consequently, the insulation layer 21 may be dispensed with and the MR element 23 may be in direct magnetic contact with the flux guides 17a and 17b. A second embodiment of the method according to the invention will now be described with reference to Figs. 9 to 14. This method for forming an assembly of stacked layers starts from a first layer 105 in the form of a plate-shaped substrate of, for example an oxidic material such as quartz. A layer, further referred to as intermediate layer 109, is formed on this layer by depositing a wear-resistant material such as a chromium oxide. Subsequently, a photoresist layer 110 of, for example a customary photoresist is formed, which serves as a mask for an etching treatment in which a part of the photoresist layer 110 is first removed and subsequently a recess 107 is formed in the first layer 105. After removal of the photoresist layer 110 and parts of the intermediate layer 109 possibly overhanging the recess 107, the combination of layers diagrammatically shown in Fig. 12 is obtained, with the first layer 105 being provided with the recess 107 and, outside the recess 107, coated with the intermediate layer 109. An element 123, in this example an inductive transducing element in the form of a coil, is provided in the recess 107, whereafter a second layer 117 is formed by means of deposition of, for example, an oxidic material such as quartz. With regard to the materials used, this is chosen to be such that the material of the intermediate layer 109 is more wear- resistant than the material of the second layer 117. After formation of the second layer 117, a polishing treatment is performed so as to form a smooth and plane surface 119. When the intermediate layer 109 is reached during polishing, its wear resistance has a restraining effect on the polishing treatment so that the intermediate layer 109 can be considered as a polish- stopper layer. The use of such a layer has the advantages that a predefined level is indicated for terminating the polishing treatment and that the polishing treatment results in a plane and smooth surface. After termination of the polishing treatment, the intermediate layer 109 is completely removed in this example. This may be done, for example by means of sputter etching. The magnetic head unit according to the invention thus obtained may be used for writing video and/or audio and/or data information in a magnetic optical recording medium, for example a disc. It is to be noted that the invention is not limited to the embodiments shown. For example, the method according to the invention may be alternatively used in methods of manufacturing semiconductor elements.

Claims: CLAIMS 1. A method of forming an assembly of stacked layers, in which method use is made of a recessed first layer on which a second layer filling up the recess is formed by depositing a material, and a polishing treatment is performed for forming a plane surface, characterized in that, prior to forming the second layer, an intermediate layer restraining the polishing treatment is formed on the first layer by depositing a material which is more wear- resistant than the material of the second layer, and in that the polishing treatment is terminated after the intermediate layer has been reached. 2. A method as claimed in claim 1, characterized in that the intermediate layer is also used as an indicator for terminating the polishing treatment. 3. A method as claimed in claim 1, characterized in that at least substantially chromium and/or a chromium compound is used as a material of the intermediate layer. 4. A method as claimed in claim 3, characterized in that a chromium nitride and/or a chromium oxide and/or a chromium oxynitride is used as a chromium compound. 5. A method as claimed in claim 1, characterized in that a non-magnetic, non- electrically conducting layer is used as the first layer. 6. A method as claimed in claim 5, characterized in that a magnetic and/or electrically conducting material is used as a material for the second layer. 7. A method as claimed in claim 1, characterized in that a material corresponding to the material from which the first layer is formed is used as a material for the second layer. 8. An assembly manufactured by means of the method as defined in any one of the preceding claims. 9. A magnetic head comprising an assembly manufactured by means of the method as defined in any one of claims 1 to 6, the second layer constituting a flux-guiding element extending in the recess of the first layer. 10. A magnetic head unit comprising the assembly manufactured by means of the method as defined in any one of claim 1, 2, 3, 4, 5 or 7, in which a transducing element embedded in the second layer extends in the recess.

Inventors: THEUNISSEN GERARDUS S A M, VAN ZON JOANNES B A D, THEUNISSEN, GERARDUS, S., A., M., VAN ZON, JOANNES, B., A., D.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1999
Main classification: H01L21
IPC codes: G11B5, G11B11