JPH0515308B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for vapor phase growth of a thin film constituting a capacitive element used in a semiconductor device.

[Conventional technology]

Integrated circuits formed on semiconductor substrates, particularly silicon semiconductor substrates, are becoming increasingly highly integrated and have a large capacity, and the degree of integration of integrated circuits such as memory devices is increasing to 1M bits or more. An IC that consists of one transistor and one capacitive element as a basic cell, like dynamic RAM.
Reducing the area of the capacitive element is the most effective means for achieving high integration of memories.

However, if the area of the capacitor element is reduced and the capacitance value decreases, reliability against soft errors (memory malfunctions) due to alpha rays etc. will deteriorate, so the capacitance value needs to be 50PF or more. Conventionally, therefore, the decrease in capacitance value due to area reduction has been compensated for by making the capacitor insulating film thinner. However, when the silicon oxide film conventionally used has a thickness of less than 100 Å, its dielectric strength cannot withstand a power supply voltage of 5V, making it unusable.

Therefore, by forming a groove in the substrate and forming a capacitive element on the inner wall of the groove, or by forming the capacitive element into a stacked structure (stack structure), it is possible to maintain the same capacitance value as before, while maintaining a planar structure. Consideration has been given to reducing the area of the capacitive element portion and achieving higher integration. Also, Ta ₂ is used instead of silicon oxide film.
The use of high dielectric constant materials such as metal oxides such as O ₅ , TiO ₂ and HfO ₂ for the capacitive film is also being considered.

Large-capacity dynamic RAM of 16 Mbit or more requires electrode materials with low layer resistance, and high-melting point metal materials such as W, Ti, Mo, and Pt are used in place of the current polysilicon electrodes and polycide electrodes. It is expected that For this reason, capacitive films currently formed on Si substrates and polysilicon electrodes also need to be formed on high-melting point metals.

Methods for forming high dielectric constant films include Ta, Ti, Hf
A method in which metals such as metals are vacuum evaporated and oxidized, or a so-called reactive sputter evaporation method in which a small amount of oxygen is introduced during vacuum evaporation of these metals to deposit a film as an oxide, or a method in which metals such as Ta ₂ O ₅ , TiO ₂ , HfO ₂ , etc. are deposited as oxides. A method of vacuum deposition (sputter deposition) of the oxide of
Furthermore, methods of depositing films using chemical vapor deposition are being considered. However, in order to form a capacitive film on the inner wall of a groove formed on the substrate surface, among the conventional methods described above, when forming a high dielectric constant film by chemical vapor deposition, Ta, Ti, Hf
It is necessary to first form a metal electrode film by transporting the gas of a compound containing , etc. to a reactor, but alcoholate, an organic material, can be used because it can be grown at low temperatures and the gas to be transported can be easily controlled. It is introduced into a reactor together with oxygen gas to deposit a film. Oxygen gas is used to promote thermal decomposition of alcoholate and improve film quality.

[Problem that the invention seeks to solve]

However, when a capacitive film is formed by vapor phase growth on an electrode using a high-melting point metal, a problem arises in that the high-melting point metal is oxidized because oxygen is included in the atmosphere. That is, a temperature of 400 to 600° C. is usually used as the vapor phase growth temperature, and when a high melting point metal is exposed to oxygen at such a temperature, the surface of the metal film is oxidized and an oxide film of several hundred Å or more is formed in a very short time. Therefore, for the purpose of forming a thin film with a high dielectric constant and obtaining a large capacitance value, oxidation of the electrode surface brings extremely bad results.

An object of the present invention is to provide a high dielectric constant film vapor phase growth method that suppresses oxidation of the surface of a high melting point metal electrode.

[Means for solving problems]

In order to prevent alignment on the surface of a high melting point metal film such as W, Ti, Mo, Pt, etc., a high dielectric constant film may be deposited without introducing O ₂ as an oxidizing agent. However, without the introduction of O ₂ , high-quality film formation cannot be expected.

Therefore, according to the present invention, Ta _X O _Y or _Ta
Deposit a thin film of _HfO
A vapor phase growth method is obtained in which O ₂ is introduced and a film is deposited to a desired thickness.

〔Example〕

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows an example of the order of gas introduction into a reactor and the order of reactor temperature when a metal oxide film is deposited on a high melting point metal using a vapor phase growth method according to an embodiment of the present invention. It is. In the figure, the horizontal axis represents time with the deposition start time being zero, and the vertical axis represents the type of gas. The solid line represents the state in which gas is introduced into the reactor, and the broken line represents the state in which gas is not introduced into the reactor.
The circle indicates the starting point at which gas is introduced into the reactor.

In this example, a film deposition procedure will be described assuming that a Ta ₂ O ₅ film is formed on a tungsten electrode using the present invention. The gas used is liquid raw material.
Ar gas bubbled with Ta (OC ₂ H ₅ ) ₅ (hereinafter referred to as raw material gas), Ar gas as a base gas for adjusting the pressure inside the reactor during film deposition,
And O ₂ gas is used to improve the deposition rate and quality of the Ta ₂ O ₅ film. First, there are 300 substrates in the reactor.
The base gas and raw material gas are introduced into the reactor while being heated to ~500°C. Thermal decomposition of Ta(OC ₂ H ₅ ) ₅ forms a Ta ₂ O ₅ film on the tungsten electrode. Next, after the Ta ₂ O ₅ film is formed to a thickness of 20 to 50 Å, O ₂ gas is introduced in addition to the above gases, and the Ta ₂ O ₅ film is subsequently formed to a predetermined thickness. Note that the temperature of the reactor is kept constant from the beginning to the end of Ta ₂ O ₅ film formation.

FIG. 2a shows the depth profile of the film composition of a Ta ₂ O ₅ film formed on a tungsten electrode using the above-mentioned vapor phase growth method. FIG. 2b shows the compositional depth profile of a Ta ₂ O ₅ film formed by a conventional vapor phase growth method. In the conventional method shown in FIG. 2b, a tungsten oxide film is formed between the Ta ₂ O ₅ film and the tungsten electrode, but in the method according to the present invention shown in FIG. It can be seen that almost no film is formed. This shows that a capacitive film can be formed using only the Ta ₂ O ₅ film, which is a high dielectric constant material, and it is clear that a capacitive film with a high dielectric constant can be formed according to the present invention.

FIG. 3 shows the order of gases introduced into the reactor and the order of reactor temperatures when forming a metal oxide film on a high-melting point metal using a vapor phase growth method according to another embodiment of the present invention. There is. Here, we will explain the film deposition method, taking as an example a method for forming HfO ₂ on a titanium electrode. The gas used is a liquid raw material.
Ar gas (raw material gas) bubbled with Hf(OC ₂ H ₅ ) ₄ , Ar gas as a base gas to adjust the pressure inside the reactor during film deposition, and O ₂ to improve the HfO ₂ deposition rate and film quality. Use gas. Base gas and raw material gas are introduced into the reactor while the substrate temperature in the reactor is heated to 100 to 300°C. Hf
Thermal decomposition of (OC ₂ H ₅ ) ₅ produces _HfO
is formed. After the HfO film was formed at about 20 to 50 A, the substrate temperature was raised to 400 to 500°C, and in addition to the above gases, O ₂ gas was introduced into the reactor to continue forming the HfO ₂ film. Repeat until the desired film thickness is reached. The reason why the substrate temperature is set low at the beginning of film deposition is to further suppress oxidation of the titanium metal electrode surface by oxygen atoms contained in the raw material Hf(OC ₂ H ₅ ) ₄ . According to this example, similar to the example _shown in _{FIG .}
Films can be formed with good reproducibility.

In the above example, tungsten and titanium were used as the refractory metal electrode, but molybdenum, platinum,
It is also free to use tantalum or the like. In addition, although Ta ₂ O ₅ and HfO ₂ were used as the metal oxide film, ZrO ₂ ,
It is also free to use TiO ₂ or the like. In addition, a combination of the above-mentioned embodiment (tungsten and Ta ₂ O ₅ )
Even if formed by the method of other embodiments, the effect is the same,
The opposite effect also exists.

〔Effect of the invention〕

As explained above, the present invention is a method of growing a metal oxide film as a capacitive film on the surface of a high-melting point metal electrode in a vapor phase. By additionally introducing and subsequently growing films in an atmosphere mixed with the source gas, oxidation of the electrode surface can be prevented, which has the effect of vapor phase growth of a capacitive film with a high dielectric constant.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the order of gas introduction into a reactor and the temperature order of the reactor when a metal oxide film is grown in vapor phase on a high melting point metal electrode according to an embodiment of the present invention. In the figure, the horizontal axis shows the time when the deposition start time is 0, the vertical axis shows the temperature of the substrate and the type of gas, the solid line shows the state in which gas is introduced into the reactor, and the broken line shows the state in which gas is introduced into the reactor. The state where gas is not introduced is indicated by the circle mark, which indicates the starting point at which gas is introduced into the reactor. Figure 2a shows the composition depth profile of a Ta ₂ O ₅ film formed on a high melting point metal electrode (W electrode) according to an embodiment of the present invention, and Figure 2b shows the composition depth profile of a Ta 2 O 5 film formed on a high melting point metal electrode (W electrode) according to an embodiment of the present invention. FIG. 3 is a diagram showing the depth profile of Ta ₂ O ₅ film composition. In the figure, the horizontal axis represents the depth from the surface of the Ta ₂ O ₅ film, and the vertical axis represents the composition. FIG. 3 is a diagram showing the order of gas introduction into the reactor and the temperature order of the reactor when a metal oxide film is vapor-phase grown on a high-melting point metal electrode according to another embodiment of the present invention. Each part of the figure is the same as in FIG.

Claims (1)

[Claims] 1. A metal oxide film containing any one of Ta, Ti, Zr, Hf, etc. and oxygen atoms in its composition is grown in a vapor phase on an electrode of a high melting point metal such as W, Ti, Mo, Pt, etc. The method is characterized in that oxygen is not introduced at the initial stage of deposition of the metal oxide film, and then oxygen gas is introduced to continuously grow the metal oxide film in a vapor phase in an atmosphere mixed with the source gas. A method for vapor phase growth of capacitive element films.