JPS60209931A - Formation of thin film - Google Patents

Abstract

PURPOSE:To enable suppression of curling in the stage of forming successively the 1st and 2nd thin film layers with time intervals on both surfaces of a high polymer film substrate by specifying the relation between the thickness of the 1st thin film layer and the thickness of the 2nd thin film layer. CONSTITUTION:The 1st thin film layer is formed on one surface of a high polymer film base body then the 2nd thin film layer is formed on the other surface of the above-described high polymer film base body. The relation alphaF<alphaT and delta1>delta2 is satisfied where the coefft. of thermal expansion of the high polymer film base body is designated as alphaF, the coefft. of the 1st and 2nd thin film layer as alphaT, the thickness of the 1st thin film layer as delta1 and the thickness of the 2nd thin film layer as delta2. Formation of the thin films is continuously executed in a vacuum vessel 1. The high polymer film base body 10 consisting of PET, etc. wound on a supply roller 2 is continuously delivered from the roller 2 and is wound on a main roller 4a via an auxiliary roller 3a according to need. The body 10 is taken up on a take-up roller 6 via an auxiliary roller 3c by which a series of thin film forming stages is completed.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for forming thin film layers on both sides of a polymer film substrate, and in particular, a method for forming a thin film suitable for forming a recording layer in a disk-shaped perpendicular magnetic recording medium. Regarding the method.

[Technical Background of the Invention and Problems thereof] In recent years, perpendicular magnetization recording methods that perform high-density recording using magnetization in a direction perpendicular to the medium surface of a magnetic recording medium have attracted attention. A typical magnetic recording medium for this perpendicular magnetization recording (referred to as a perpendicular magnetic recording medium) is one in which the recording layer is a co-Cr sputtered thin film having an axis of easy magnetization perpendicular to the film surface. Such perpendicular magnetic recording media are based on a polymer film such as polyethylene terephthalate film (PET film), which has inferior heat resistance compared to polyimide, and has the above co-coated film on one or both sides.
It is manufactured by forming a Cr-based sputtered thin film, and is used for magnetic tapes, disk-shaped magnetic recording media,
In particular, application to floppy disks is being considered.

Incidentally, among perpendicular magnetic recording media, especially disk-shaped media such as floppy disks, it is strongly required that the medium has good magnetic properties and good flatness, that is, has almost no curl. However, what is currently being considered as a disk-shaped perpendicular magnetic recording medium is a recording layer consisting of a CO-based alloy film such as co-Cr formed on a polymer film substrate by a physical method such as sputtering or vacuum evaporation. That is. In such a medium, not only when a thin film layer is formed on only one side of a polymer film substrate, but also when a thin film layer is formed on both sides of the substrate under almost the same conditions, the first Thin WAl! When a second thin film layer is formed on the other side after forming the li, that is, when the front and back thin film layers are formed after a period of time, curling is observed.

Furthermore, if the coercive force HC in the direction perpendicular to the film surface of the thin film layer is increased by increasing the actual temperature of the polymer film substrate in order to increase the reproduction output, curling tends to increase significantly. .

The existence of such curls is a thin film! Since it is a metal film, it has low flexibility, which makes it extremely difficult to keep the spacing between the magnetic recording medium and the magnetic head as small and stable as possible. Therefore, in order to achieve high-density recording, which is an advantage of the perpendicular magnetization recording method, it is essential to make the curl sufficiently small so that the surface of the thin film layer is almost flat.

[Objective of the Invention] The object of the present invention is to reduce the occurrence of curling in the thin film layer and to make the thin film layer almost flat when forming the thin film layer on both sides of a polymer film substrate over time. One objective is to provide a method for forming WIm that can be covered.

[Summary of the Invention] A thin film forming method according to the present invention includes forming a first thin film layer on one surface of a polymer film substrate, and then forming a second thin film layer on the other surface of the polymer film substrate. In this case, the coefficient of thermal expansion of the polymer film substrate is αF, the coefficient of thermal expansion of the first and second thin film layers is αT, and the thickness of the first thin film layer is 6.
1. It is characterized in that when the thickness of the second thin film layer is 62 mm, the following relationship is satisfied: αF <α th, and δ1> δ2.

[Effects of the Invention] According to the present invention, as described above, the coefficient of thermal expansion αF of the polymer film substrate is determined by the coefficient of thermal expansion αT of the first and second thin film layers.
By making the thickness δ1 of the first thin film layer larger than the thickness δ2 of the second thin film layer, curling of the thin film layer can be extremely reduced.

The reason why curling decreases in this way is not well understood at present, as well as the mechanism by which curling occurs even though the first and second thin film layers are conventionally formed under almost the same conditions. do not have. Although it is necessary to fully consider the thermal change (for example, heat shrinkage) of the polymer film substrate during formation of the WJ1 layer as a cause of curl, it is important to note that the same tendency for curl to occur regardless of the magnitude of heat shrinkage. Therefore, other factors need to be considered as well.

Considering qualitatively, when the first thin film layer is formed, the substrate is just a polymer film, whereas when the second thin film layer is formed, the substrate is already substantially on the opposite side. It can be thought of as a laminated film of the first thin film layer and a polymer film, and curl occurs because its effective coefficient of thermal expansion and Young's modulus have changed since the first thin film layer was formed. This is considered to be the main cause. In particular, when forming thin film layers on the front and back sides with a continuous thin film forming apparatus having a main roller, the flexibility of the polymer film base is small when forming the second thin film layer, and therefore the flexibility of the polymer film base and the main It is thought that this is also due to the fact that the heat conduction of the roller becomes smaller and the effective temperature of the molecular film substrate becomes higher. For this reason, the second thin film layer needs to be made thinner than the first thin film layer by the amount of the higher effective temperature.

Therefore, if the relationship between the difference in thermal expansion coefficient between the polymer film substrate and the first and second thin film layers and the difference in thickness between the first and second thin film layers is appropriately selected, the first thin film Curls caused by thermal changes in the substrate during layer formation are
When the second thin film layer is formed, the same degree of thermal change is applied to the substrate from the opposite direction, so that it is exactly offset, and as a result, a thin film layer with very little curl is obtained. . In reality, other effects are expected to contribute, but unfortunately they are not well understood.

[Embodiment of the Invention] The present invention will be explained in detail by way of an embodiment. FIG. 1 shows the configuration of a continuous thin film forming apparatus as an example of an apparatus for carrying out the WJIllI forming method of the present invention.

In FIG. 1, reference numeral 1 denotes a vacuum chamber, and thin film formation is continuously performed within this vacuum chamber 1. That is, supply roller 2
From there, the polymer film base 10 made of PET or the like wound around this roller 2 is continuously sent out, and is wound around the main roller 4a via an auxiliary roller 3a as necessary. When the polymer film substrate 10 runs on this main roller 54a, a film forming material is supplied from a sputter target 5a (for example, a Co-Cr alloy target containing 22% by weight of Cr) placed opposite the main roller 4a. As a result, as shown in FIG. 2(a), the first thin film layer 11 is continuously formed over one surface of the substrate 10 to a thickness δ.

Next, the main roller 4b passes through the auxiliary roller 3b.
The polymer film base 10 is guided above the main roller 4.
When the polymer film substrate 1o runs on b, the sputter target 5a is placed facing the main row 54b.
By supplying a film forming material from the sputtering target 5b having approximately the same composition as , the second thin film layer 12 is formed on the other surface of the substrate 10 to a thickness of δ2 (as shown in FIG. 2(b)).
δl>δ2) are continuously formed. Thereafter, the polymer film substrate 10 is wound up on the take-up and rewind roller 6 via the auxiliary roller 3C, thereby completing the series of thin film forming steps.

Figure 3 shows two types of heat-resistant polymer film substrates with thermal i-layer weights smaller than Co-Cr, the thickness δ of the first thin film layer being constant at about 0.6 μm, and the second RIM ! It shows the change in curl amount when the thickness δ2 of the I layer is changed. Figure 4 shows the two types of polymer film substrates used: ■■ and Thin 1! These are the results of measuring the coefficient of thermal expansion of the co-Qr alloy film, which is a layer, and the measurement was performed using a thermal dilatometer manufactured by Rigaku Mti.

The measurement conditions are shown in the table below.

L Note that if the polymer film substrate contains water in each member, the water will be released during heating, and the accompanying dimensional change will also occur, so the dimensional change when the substrate is almost completely dehydrated. The coefficient of thermal expansion was determined by . During sputtering,
Most of the water in the polymer film substrate is released by the gas release process. In addition, the coefficient of thermal expansion of the thin film layer (Co-Cr film) is determined by melting the polymer film base and forming a single C0-Cr film.
A film was made and measured under almost the same conditions, and this value almost matched the value in the polycrystalline bulk state. Note that the curl amount was defined based on the dimensions shown in FIG. 5 for a punched floppy disk with a diameter of 85 am.

As can be seen from the measurement results in Fig. 3, when the first and second thin m layers of appropriate thickness satisfying δl>δ2 are formed using a polymer film substrate of αF , a nearly flat floppy disk with little curl was obtained. When actual recording and playback was performed using the floppy disk thus obtained, a playback output with a uniform envelope was obtained.

In other words, the coefficient of thermal expansion of the polymer film substrate is made smaller than that of the first and second thin film layers, and
When the thicknesses of the thin film layers are made equal, when the first thin film layer is formed, the first thin film layer side becomes concave (curl).
Conversely, when the second my layer is formed, a curl (positive curl) occurs in which the first thin film layer side is convex and the second thin film layer side is concave. This is because the Young's modulus of the polymer film base is effectively high in the state in which the first thin film layer is formed as described above, so the contact between the polymer film base and the main roller, etc. As a result of the difference in heat conduction with the system, if the thickness of the second thin film layer is comparable to the thickness of the first thin film layer, the thermal stress applied to the substrate during formation of the second thin film layer will be too large. It is thought that. In this regard, if the thickness of the second thin film layer is made appropriately smaller than the thickness of the first thin film layer as in the present invention, the thermal stress applied to the substrate during formation of the second thin film layer will be at an appropriate value. As explained above, according to the present invention, the negative curl that occurred during the formation of the first thin film layer is just cancelled, and according to the present invention, the first and second thin film layers are sequentially formed on both sides of the polymer film substrate over time. When forming by placing, it is possible to effectively suppress the occurrence of curls. Therefore, when applied to the production of disk-shaped magnetic recording media such as floppy disks, it is advantageous that media with good flatness can be obtained.

In addition, this invention is not a batch method, and there are restrictions on how to apply tension to the polymer film substrate, and tension can only be applied mainly in the longitudinal direction of the substrate, and furthermore, the friction between the substrate and the main roller is limited. In the continuous 81M forming process using a roller that is difficult to perform 1tlIWJ, a flat III with little curl! It is effective when forming

[Brief explanation of the drawing]

FIG. 1 shows Il! of this invention. FIG. 2 is a cross-sectional view for explaining the thin film forming process of an embodiment of the present invention, and FIG. 3 is a diagram showing the schematic configuration of a continuous SM forming apparatus used in the forming method. A diagram showing the change in curl amount when the thickness of the first thin film layer that is formed is constant and the thickness of the second thin film layer that is formed later is changed. Figure 4 shows the polymer used in the example. Film substrate and thin film layer (Go-O
FIG. 5 is a diagram showing the measurement results of the thermal expansion coefficient of the r-alloy film) and is a diagram for explaining the evaluation method of the amount of curl. 1... Vacuum chamber, 2... Supply roller, 3a to 3C...
・Auxiliary rollers, 4a, 4b...Main rollers, 5a, 5b
... Sputter target, 6... Winding roller, 1
0... Polymer film base, 11... First thin film layer, 12... Second thin film layer. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Scope of Claims] (1) After forming a first thin film layer on one side of the polymer film base, a second thin film layer is formed on the other side of the polymer film base.
In the method for forming a thin film layer, the coefficient of thermal expansion of the polymer film substrate is αF, the coefficients of thermal expansion of the first and second thin film layers are αT, and the thickness of the first thin film layer is 61.
A method for forming a thin film, characterized in that, when the thickness of the second thin film layer is 62, the relationships αF>α and δ1<δ2 are satisfied. (2) The formation of the first and second thin film layers on the polymer film base is performed at different positions in the running direction of the polymer film base while the polymer film base is continuously running. A thin film forming method according to claim 1. (a The first and second thin film layers are made of cobalt alloy or
The method for forming a single film according to item 1 or 2. (4) Thin film formation according to claim 1, 2 or 3, wherein at least one of the first and second thin film layers is a recording layer of a disk-shaped perpendicular magnetic recording medium. Method.