JPS605531A - Formation of insulating film - Google Patents

Abstract

PURPOSE:To enable to form a dielectric film, through which leakage current little flows and whose insulating withstand voltage is high, by a method wherein at least a part of the surface of a metal film, which has been turned a part of the surface into an amorphous substance by irradiating ions, is oxidized. CONSTITUTION:A Ta film 2 is formed on the surface of a silicon substrate 1 by such a technique as a vacuum evaporation one, etc. This film 2 is oxidized afterwards and converted into a Ta2O5. A thin one is desirable as the film for obtaining a large capacity. The film has been usually made into a polycrystalline structure. Then, such substances as Ar, O2, Ta, etc., are ionized and an amorphous Ta film 21, whose surface has an amorphous structure, is formed by performing an ion-implantation in the Ta film 2. After that, the amorphous tantalum film 21 is converted into t Ta2O5 film 25 by being performed an oxidation in the atmosphere of oxidation or by being performed an anodic oxidation in the solution of oxalic acid. As the Ta2O5 film 25 formed in such a way is formed due to the oxidation of an amorphous tantalum, the film structure is amorphous. After this, an electrode is formed on the surface of the Ta2O5 film 25 and an MOS structure is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a dielectric film such as Ta2O, Tio, etc., and in particular, the present invention relates to a method for forming a dielectric film such as Ta2O, Tio, etc.
The present invention also relates to a method of forming an insulating dielectric film having a single voltage.

In recent years, MOS type semiconductor devices have been widely used, and their density is increasing year by year. Hitherto, higher density has been achieved by making patterns finer. However, dynamic random access memo 1, 1 (L
)1 (AM), the use of a slight oil in the pattern causes a decrease in the amount of accumulated charge relative to the signal, which can lead to memory malfunctions (not-en-) caused by radiation such as alpha rays. arise. For this reason, patterning $
Even if it becomes +1 ntl, it is an accumulation army.

Is it necessary to find a way to prevent the load from decreasing? Conventionally,
The solution was to protect the insulating film in the capacitive part that stores charge and not reduce the capacitance value.

However, as the film becomes thinner, the number of pin poles increases, making it impossible to obtain sufficient withstand pressure and lowering the yield.Therefore, there are limits to thinning the film.

Normally, 5IO2 with a dielectric constant of 3.9 is used as the dielectric material for the capacitor part, but if an I material with a high dielectric constant is used, the capacitance can be reduced even with the same electrode surface. Therefore, further %B conversion becomes ir]-function. For this reason, high dielectric materials such as Ta2O, Ti02, etc. have already been considered. The means for forming these films is, for example, by depositing metal particles such as fil a and Ill i in vacuum and then oxidizing them by heat treatment in an oxygen atmosphere or by anodic oxidation. Yes, it is being formed. However, films produced using these methods have not yet reached a stage where they can be put to practical use because a large amount of leakage current flows when a low voltage is applied.

The cause of this is thought to be that the sensitized metal layer has a crystal grain structure, and the contact layer formed by oxidation also has a polycrystalline structure, causing the crystal grains to rise. As the leakage current continues to flow, J1. Jl, Ru.

Therefore, 1 barge is 44! The inventor thought that it would be possible to reduce the leakage current by finding a way to avoid making the structure a polycrystalline structure.

Based on this consideration, the present invention aims to eliminate the disadvantages of low insulation 110j voltage and large leakage current of films formed by conventional methods, and to provide a means for realizing films of higher quality. The goal is to turn the metal film into a beast that has the means to make it amorphous4). Hereinafter, the present invention will be explained in detail using one example of Practical/1Ii.

FIG. 1 is a cross-sectional structural diagram for explaining the process, taking as an example the case where the present invention is applied to form an MO8 type capacitor. In the figure, 1 is a semiconductor substrate, 2 is a metal film,
J is an amorphous gold 14% layer, 25 is an insulating film, 3 is an ion flying direction 71. Show it.

A silicon flexible plate is used as the semiconductor substrate l, and T is used as the metal film 2.
We decided to create an MO8 capacity using a film, and invented the manufacturing process step by step.

First, a Ta film 2 is formed on the surface of a silicon substrate 10 by a method such as vacuum evaporation (FIG. 1a). The film can be oxidized and converted into Ta, O, etc., and in order to obtain a large capacity, the thinner the film, the better, and a film thickness of about 200 to soo X is preferable. The formed film 2 is usually a polycrystalline structure.

Next, a substance such as Ar102 or Ta is ionized and ion-implanted into the Ta film 2, thereby forming an amorphous 'J' a film 21 having an amorphous structure on the film surface. Figure 1 b). Since the Ta film 2 is of high quality, the ion implantation is performed, for example, at an acceleration voltage of 10 to 30 KeV.
If ions of 14 to 1016 cm' are implanted, an amorphous film of sufficient quality is formed. In this ion implantation, Ta film 2
Ion implantation may be performed by changing the accelerating voltage so that the entire thickness direction becomes sufficiently amorphous. At this time, the surface of the silicon substrate 1 is also made amorphous, but this is not a practical problem since the crystallinity is restored by heat treatment in a later step. If a mask film pattern is provided to serve as a mask for W ion implantation into the surface of the uncut Ta film 2, ions may be implanted only into a portion of the tantalum film.

In the ion implantation, it is possible to make the tantalum film 2 amorphous by implanting impurity ions such as arsenic, phosphorus, and boron. An impurity region will be formed. Formation of the impurity region according to the above method has a wide range of application when the present invention is applied to semiconductor devices of other structures.9 Preferably 1.
b0 After the amorphous tantalum film 21 is formed, the amorphous tantalum film 21 is oxidized at a temperature of 400 to 500 C in an oxidizing atmosphere, or by anodic oxidation in an acid bath. Ta, 0. can be changed to membrane 25 (
Figure 1C). Since the Ta205 film 25 formed here is formed by oxidation of amorphous tantalum, the film structure is amorphous. Thereafter, an electrode is formed on the surface of the Ta2O film 25 to form an MO8 structure. In addition, only a part of the surface of the amorphous 'ra film 21 is coated with Ta2.
05 May be changed to a membrane.

Note that the Ta film 2 and the silicon substrate 1 react to some extent during the heat treatment in this step, and a tantalum silicide layer is formed on the surface of the silicon substrate 1, but this poses no problem for the purpose of forming a capacitor. However, the electrical characteristics (especially Ta
2O, and silicon) will deteriorate, so in order to improve this, it is necessary to
It is desirable to form the Ta film 2 after forming the 5i02 film with a thickness of 50 to 150 angstroms.

When we investigated the flow rate of MO8 capacity leakage formed using the present invention, we found that the leakage flow rate was reduced by about two orders of magnitude compared to the conventional method.
It was found that a sufficiently good film was formed.

FIG. 2 shows another embodiment in which a capacitor is formed using the present invention, and shows a cross-sectional structure for explaining the manufacturing process. In the figure, the same symbols as in FIG. 1 indicate substances having the same functions, 4 is an insulating film, 5 is an impurity region, and 6 is an electrode. The process f:1@ of creating a capacitor using silicon for the semiconductor substrate 1 and tantalum for the metal film 2 will be explained in detail.
An insulating film 4 such as O2 is provided, and then a portion of the insulating film 4 is selectively removed to form a window 45 (FIG. 2a).

Next, impurities are introduced into the surface of the silicon substrate 10 through the window 45 using the insulating film 4 as a mask, and an impurity region 5 having a conductivity type opposite to that of the substrate 1 is formed. 7L is formed using the means of (Fig. 2 &
)). The impurity may be introduced by thermal expansion method or ion implantation method, and the choice is free. Since the impurity region 5 is used as an electrode, it needs to be formed at a high concentration. There are two tantalum films, part of which is used as an electrode, so it needs to be thick.
Its preferred thickness is 0.3-1 micron.

Next, A r X (1) 2 , 'J
, 'A material 3 is ion-implanted, and an amorphous tantalum film 21 having an amorphous structure is formed on the second surface of the film (Fig. 2c) 1. Preferred ion implantation method The conditions are: voltage 10-20 KeV, implantation amount 10-10
cm, and 100 to 300 squares on the surface of the tantalum film 20.
The angstrom region becomes an amorphous mental film 21. In addition, an amorphous tantalum film can be formed on the surface of the Ta film 2 by removing a part of the Ta film 2 from all stages of the mask film pattern that serves as a mask for ion implantation, or by anodic oxidation in an oxalic acid solution. 21 is changed to a Ta2U3 film 25, and then an electrode pattern 6 is formed to form a pTa film,'
l'a; Ua membrane 25.111M 6 with jUj I/
C capacity is configured (Fig. 2 d). In this process, the surface C of the amorphous tantalum film 21 is reduced by 17L of lead oxide.
Drita-1' a 20. Even if it is changed to a film, in addition to the film 21, the surface of the tantalum film 2 is also lT a 2+
, ), B! Changing the AK will not cause any problems in terms of characteristics.

However, '1' a 205 below the film 25: (T is a must 15 where the tantalum film 2 remains.

In this embodiment, since the l1la film 2 and the high-temperature impurity region 5 are in ohmic contact with each other, the capacitance can be operated by t It has an 'ib length that can be used.

In the above (, 7) two embodiments, the i'a crotch is used to
2O, . However, even if other metals, such as AA', Mg, T1, Nb, etc., are used, it is also possible to form The present invention can also be applied if a polycrystalline silicon material is used.

Also, metal film 2X? The step of making the gold PA film 2 amorphous was carried out using the image implantation method 7.
If it is possible to make it amorphous (t!, lv month - using the second stage, it is a) / - 0 - as an example, Ar, 02
The speed of the metal film 20 is accelerated by several hundreds of seconds, and the metal film 20
A similar effect can be obtained by employing a so-called sputtering method in which the material is bombarded with a surface. In this case, the surface of the polymetal film may be removed to some extent by sputtering, but there is no problem if the metal S+ is formed thickly in advance.

[Brief explanation of drawings]

Figure 2 is a diagram for explaining one embodiment of the present invention.
The figure is a diagram for explaining another embodiment, and shows a cross section of the Hikentai device in each process drawing. In the figure, l is a semiconductor substrate, 2 is a metal film, 21 is an amorphous metal layer, and 25 is an insulator)
In the figure, 3 indicates the direction in which ions fly, 4 indicates an insulating film, 5 indicates an impurity region, and 6 indicates an electrode. ``Representative Liton Attorney'': Jiha Shin Figure 1 j i = Figure 2 1d)

Claims (1)

[Claims] A metal film is provided on a semiconductor substrate or a semiconductor substrate with an insulating film provided on the optical surface, and then at least a part of the metal film surface is irradiated with accelerated ions to the surface of the metal film. 1. A method for forming an insulating film, comprising forming an amorphous metal film and then oxidizing at least a part of the surface of the amorphous metal film to form an insulating film.