JPS634275B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a magnetic bubble memory chip in which dry etching is performed while preventing damage to the conductor when opening a window in the conductor pattern. Magnetic bubble memory chips are made by epitaxially growing a garnet crystal thin film with the required magnetism on gadolinium gallium garnet (Gd ₃ Ga ₅ O ₁₂ ), which is a non-magnetic garnet, and then depositing polyimide resin or SiO on this. Memory chips are manufactured by forming a conductor pattern and a driving pattern using a spacer such as ₂ layers, and then forming a protective layer such as an SiO ₂ layer on top of this, making a window in the electrode area and cutting the chips individually. The present invention relates to a method of opening a window in an electrode portion necessary for an externally extending electrode in such a memory chip while preventing damage to the conductor pattern, and will be explained below with reference to the drawings in comparison with a conventional method. FIG. 1 shows a cross-sectional structure of an embodiment of a magnetic bubble memory chip which has been opened using a conventional method. On top of a magnetic garnet crystal film 1, a first insulating layer of SiO ₂ (silicon oxide) with a thickness of approximately 1000 Å is deposited. ) layer 2, on which a pattern is formed with a conductor layer 3 made of Au (gold) about 3500 Å thick and TaMo (tantalum molybdenum) alloy layers 4 about 200 Å thick above and below this. ing. Here, the TaMo alloy layer is used to improve adhesion between the substrate and the Au conductor and to prevent the diffusion of conductor metal atoms, and it is not necessary to limit it to this metal.
It may be used alone or in combination with Ti (titanium) and Pt (platinum). Next, a layer of about 3500 Å thick is placed on top of this as interlayer insulation.
A drive pattern 6 made of permalloy with a thickness of about 4000 Å is provided via the SiO ₂ insulating layer 5, and a protective layer 7 is further applied thereon to complete the layer structure of the chip, after which the electrode portion 8 is opened. Here, dry etching technology is used to form fine patterns such as magnetic bubble memory chips and semiconductor ICs because it has high pattern accuracy and does not involve the side etching phenomenon. The feature of this technology is that a gas containing halogen elements introduced under low pressure is used to generate a glow discharge at high frequencies such as 13.56 MHz, and the radicals generated by the low-temperature plasma react with surface materials. Etching proceeds by producing volatile products and exhausting them. Depending on the discharge mode and reaction mode, etching is divided into plasma etching, chemical dry etching, reactive ion etching, etc., and each method is used depending on the substrate material to be etched. However, plasma etching is generally used for this purpose to etch the SiO ₂ layer. Figure 3 is a configuration diagram of a barrel-type plasma etching apparatus, where A is _a cross-sectional view and _B is a side view. The degree of vacuum in the reaction tube 11 is maintained at 3 torr by supplying from 9 and exhausting from the exhaust hole 10.
A sample wafer to be etched is placed on a holder 14 and held in the center of the reaction tube 11 by applying a high frequency of 13.56 MHz to the high frequency electrode 12 to cause glow discharge. In such a case, CF ₄ and O ₂ are generated by plasma discharge as follows: CF ₄ →F ^* +CF ₃ ^* O ₂ +e→O ₂ ^* +e Here, the * mark represents a radical. However, in this case, the effective radical for etching is F ^* , and the reaction of SiO ₂ +4F ^* →SiF ₄ +O ₂ produces SiF ₄ , which is exhausted as a gas, thereby promoting etching. Additionally, the TaMo alloy layer provided on the Au conductor layer is also etched at the same time.
This is because Ta and Mo react with F ^* to produce Ta+5F ^* → TaF ₅ Mo+6F ^* → MoF ₆ . The reason why TaMo alloy is easily etched is that the melting point and boiling point of the produced fluoride are low as shown in Table 1.

[Table] Therefore, the _SiO2 layers 5 and 7 that constitute the insulating film are
Not only is this removed, but the Ta/Mo alloy layer 4 formed on the Au conductor pattern 3 is also removed, resulting in the Au conductor pattern being directly exposed to F ^* and O ^* , resulting in damage. become. The reason for this is thought to be that F ^* acts as a catalyst and causes Au and O ^* to react. Therefore, as a method to prevent such damage to the Au conductor pattern 3, a thin layer of Cr ₂ O ₃ (chromium oxide) has been provided on the conductor pattern, but this method is ineffective as long as a barrel type device is used. That's enough. The purpose of the present invention is to perform etching without damaging the Au conductor pattern when drilling holes in the insulating layer by barrel _- type plasma etching. ) layer is provided in advance, and after drilling, the MgF ₂ remaining in the hole is removed to expose the electrode section. The reason why MgF ₂ was chosen as the protective layer for the Au conductor pattern is that MgF ₂ has an extremely high melting point of 1260°C and boiling point of 2260°C, so it is obvious that it is difficult to be etched. Figure 2 shows a cross-sectional structure of an example in which the same pattern formation and hole drilling as in Figure 1 were performed using the present invention.
The _MgF2 layer 15 was formed on the TaMo protective layer 4 on the Au conductor layer 3 to a thickness of about 300 Å using a resistance heating method. Next, as for the drilling method, 5% O ₂ was used as before.
Plasma etching was performed using a barrel type device using CF ₄ gas containing gas at a vacuum level of 3 torr. In this case, the etching rate of the SiO ₂ layer is approximately 2000
In contrast, the MgF ₂ layer is etched at a rate of 5 Å/min or less, and is hardly etched, so that the electrode portion 8 of the perforated conductor pattern is not damaged. Next, the MgF ₂ layer 15 remaining in this part is
It can be easily removed by immersion in an aqueous HNO ₃ (nitric acid) solution. Note that the MgF ₂ layer is not only suitable as a protective film during plasma etching as described above, but also effective as an antireflection film during conductor pattern formation. That is, when metal vapor deposition is performed to form a conductor pattern on the magnetic garnet crystal film 1 based on the first insulating layer 2, and the required resist pattern is formed by irradiation with light after coating a photoresist film, a highly accurate pattern is formed. It is desirable for the substrate to have a low reflectance.When MgF ₂ is used in the present invention, the reflectance is low because it is a non-metallic compound, so if the thickness is selected appropriately, it will serve as a protective layer for plasma etching. It is also effective as an antireflection film when forming conductor patterns. The present invention uses a barrel type plasma etching device to drill holes in the SiO ₂ protective layer without damaging the underlying conductor, and by carrying out the present invention, the purpose can be achieved without changing the conventional method. was completed. Note that although this example deals with the case of an Au conductor, it can also be applied to Cu. Furthermore, although MgF ₂ was deposited over the entire surface of the conductive metal film, it may also be deposited only in the vicinity of the electrode parts where openings are required, and chemical etching can also be used to remove MgF ₂ that remains after drilling. The present invention is not limited to the above, and may be modified and implemented as appropriate within the scope of the claims.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional structural diagram of a magnetic bubble memory chip in which electrode holes are formed using the conventional method.
FIG. 2 is a cross-sectional structural view of the hole-drilling device according to the present invention, and FIG. 3 is a diagram of a barrel-shaped plasma etching device used for the hole-drilling, with A being a sectional view and B being a side view. In the figure, 1 is a magnetic garnet film, 2, 5,
7 is a SiO ₂ insulating layer, 3 is an Au layer, 4 is a Ta/Mo layer,
8 is an electrode part, and 15 is a MgF ₂ protective layer.

Claims (1)

[Claims] 1 In the conductor window opening process of a magnetic bubble memory chip, when opening the window by dry etching, a protective layer made of magnesium fluoride is provided in advance on the metal layer forming the conductor pattern, and the protective layer that remains in this part after the window opening process is A method for manufacturing a magnetic bubble memory chip, characterized by removing magnesium fluoride.