JPH069197B2 - Gate insulating film fabrication method - Google Patents

Description

The present invention is to activate or decompose a reactive gas containing a fluorine-based reactive gas and oxygen or other oxidizing gas by inductive energy in a reaction system depressurized to 1 atm or less. According to the temperature of 1050 ℃ or less, preferably 500 ~ 1050 ℃
The present invention relates to a method of oxidizing a silicon semiconductor in an atmosphere maintained at the temperature of 1 to produce an oxide film containing a fluorine element.

The present invention chemically activates or decomposes a reactive gas by this high frequency or microwave energy, so that chlorine in a silicon oxide film formed on a substrate semiconductor surface at a temperature lower by 50 to 500 ° C. than ever before. The present invention relates to a method for producing an oxide film to which a halogen element is added.

Conventionally, in a semiconductor device, in particular, an insulating gate type field effect semiconductor device (hereinafter referred to as MOS.FET) or IC, LSI, VLSI in which they are integrated on the same substrate, the gate insulating film is 100 to 1000 Å thinner than before. The thickness is required to be 100-500Å. In addition, the most important silicon oxide film among the gate insulating films is expected to have very little interface charge at the interface with the substrate semiconductor, especially silicon. Therefore, in the past, this interface charge was
In order to make it 10 ¹⁰ cm ⁻² or less, especially 5 × 10 ⁹ cm ⁻² or less, this silicon oxide film is heated and oxidized in oxygen and hydrogen chloride (HCI) at a temperature of 1100 ° C. or higher, particularly 1200 ° C. It is known to be extremely good at making.

However, when the MOS.IC is VLSI (VeryLargeScaleIn
As a result of heat treatment of the silicon wafer used at high temperature, warpage occurs due to thermal strain associated with the loading and unloading of 50 to 200 slices into and out of the reaction furnace, and so-called photo-chip formation is inevitable. It has become.

Therefore, it is required to form the insulating film such as the gate oxide film at a low temperature of 600 to 800 ° C. But especially the temperature it takes
It was found that below 1100 ° C, the halide was not chemically activated, and as a result, even if such a halide was added in the oxidation step, it was not diffused into the film and had no effect.

The present invention, in such a conventional method, even at a low temperature oxidation of 1050 or less, or even a gate film having a gate film thickness of 100 to 1000Å or a thin film for nonvolatile memory having a film thickness of 10 to 100Å , Which contains a fluorine element which is homogeneous and chemically active, that is, which can neutralize the dangling bonds of silicon, which is the interfacial charge, and neutralize mobile ions such as sodium, was prepared. It is a thing.

Further, in order to carry out such a method, the present invention provides chemical activation of a fluoride by applying high-frequency energy or microwave energy to the fluoride, and further converting the reaction product into plasma to chemically activate it. Therefore, set the reaction system to 1
Reduced pressure below 1 atm, especially 0.1 to 100
Torr Typically, in the range of 5 to 50 torr, the partial pressure of oxygen, which is an oxidizing gas, is smaller than that of 760 torr, and the oxidation rate can be relatively slowed down to form a predetermined film thickness on the silicon substrate. It is a feature of the present invention that the time required for the operation can be adjusted to 1 to 5 minutes in terms of operation of the apparatus so that it is not too short, and the time can be set to 15 to 60 minutes.

The features of the present invention will be described below with reference to examples.

Embodiment 1 FIG. 1 shows one of the embodiments of the present invention.

In the drawing, the substrate (1) is loaded on the quartz boat (2) and installed in the reaction furnace (oxidation furnace) (3). To improve the mixing of reactive gas in this reactor, a homogenizer (4) is provided on the gas inlet (5) side, and the substrate (1) boat (2) is taken in and out from the outlet (8) side. Is done. Substrate (Although it is called a substrate here, it is a generic name for a semiconductor substrate that has undergone several steps, especially a silicon single crystal semiconductor substrate or a substrate in which a semiconductor film is formed on a part of the surface of the substrate such as SOS) (1) In the present invention in which a solid phase-gas phase reaction is carried out, at least a part of its surface must be a silicon semiconductor.

As shown in FIG. 1, the fluorine-based reactive gas is introduced from (11) from the oxidizing gas or (12) at a position away from the substrate. In addition, an inert gas from (13) for purging and diluting, and for high frequency induction annealing, hydrogen,
He is introduced from (18). High frequency induction furnace for chemically activating or decomposing these with high frequency energy
(6) is provided. Further, a resistance heating furnace (7) is provided to heat the substrate, and the reacted fluorine element and oxidizing gas are discharged from the reduced pressure exhaust system by the vacuum pump through the valves (16) and (9). The valve (9) is a needle valve for adjusting the pressure in the reaction furnace. The reactive gas containing the fluorine element is introduced from (11) through the needle valve. A typical example of this reactive gas is hydrogen fluoride (HF).

Oxidizing gas includes oxygen (O ₂ ), ozone (O ₃ ), water (H
₂ O), nitrous oxide (NO ₂ ) and the like are typical, but O ₂ was used in this example.

For the reaction, 50 to 200 sufficiently cleaned substrates were loaded into a reaction furnace at a temperature of 500 to 700 ° C., and the whole system was evacuated to 0.01 to 0.001 torr. After this, HF was mixed in oxygen to a concentration of 1-10%, especially 4%. This mixed gas was replaced with the reaction system by closing the valve (15) and opening the valve (16) through the purge line (17). Prior to this, the high frequency energy (6) is 1 to 20MHz
For example, RF of 13.5 MHz was applied. In particular, this induced energy causes 100 to 300w of power so as to cause voltage excitation. Then the pressure in the reactor is 0.001 to 1 torr
Experimentally, a glow discharge in the plasma state was confirmed.

Furthermore, when the pressure in the reaction furnace is set to 1 to 100 torr, for example, 30 torr, based on the oxygen partial pressure recognized by this pressure,
The substrate surface was oxidized. The oxidation temperature at this time is 800-1000
℃, especially 900 ℃. Film thickness 100-1000Å Especially 100-300
Å Oxidation temperature is 100 for film thickness of 500-1000Å
The temperature is preferably 0 to 1050 ° C.

However, conversely, it was preferable to set the temperature to 600-800 ° C to obtain a film thickness of 10-100Å.

If you want to stop the oxidation, set the oxygen pressure of the reaction system to 0.
It suffices to immediately vacuum the inside of the reactor so that the pressure becomes 1 Torr or less. After the oxidation for a predetermined time is completed, the reaction system is forcibly decompressed to 0.01 torr by the decompression exhaust system to stop the oxidation reaction, and then the reaction system is filled with an inert gas and the reaction system is exhausted. After lowering the temperature of 100 to 300 from the oxidation temperature, the system in which the silicon oxide film was formed was set to normal pressure, and the substrate (1) was taken out.

In order to evaluate the silicon oxide film, an aluminum or silicon semiconductor (phosphorus-doped) electrode was provided on this film, and the CV characteristic (gate capacitance-gate voltage characteristic) was determined. As a result, a silicon oxide film formed at a temperature of 1050 ° C or lower, for example, 800 ° C, has a temperature of 200 ° C for 30 minutes (electric field strength 1 × 10 ⁶ V /
cm) ± BT (bias-temperature treatment) was performed. As a result, the V _th drift was 0.1 V or less in the hydrochloric acid oxidation method of the present invention in which high frequency excitation was performed. However, in the case of the conventional method without high frequency excitation, there was a drift of 0.3 to 0.8V. Further, this is approximately the same as the drift amount of the oxide film when oxidized without adding a halogen element, and not only the halogen element is simply added but also the chemically activated or decomposed halogen element is present in the silicon oxide. Has been found to be important to be added to. It has been found that the method according to the invention, in which hydrogen chloride decomposes to generate chemically active chlorine and hydrogen, especially at temperatures below 900 ° C., for example 700 to 800 ° C., is of great importance in semiconductor electronics.

Also, the initial (initial) interface charge is 5 × 10 ⁹ to 10 ¹⁰ cm ^-2
Was obtained in the method of the present invention which was chemically activated and decomposed by high frequency energy.

In this example, high frequency induction energy was applied after mixing oxygen and hydrogen chloride. However, for the halogen element only, the high frequency induction energy is applied to the valve (18) at the inlet (12)
May be added near the. At this time, hydrogen chloride is chemically activated or decomposed, but an oxidizing gas such as oxygen is not chemically activated or decomposed. As a result, the oxidation rate was not particularly high at the same temperature, but the effect of activated chlorine and hydrogen was remarkable in reducing the interfacial charge and stabilizing it by BT treatment. In addition, even after the oxide film is produced, if an active halogen element such as chlorine is also added to this film together with hydrogen,
The effect of reducing the interfacial charge was observed.

The presence or absence of high-frequency induction energy increases the oxidation rate by 1.5 to 4 times, which not only chemically activates the halide but also activates oxygen, which is an oxidizing gas, and oxidizes nascent oxygen or ozonized oxygen. It turned out to be speeding.

Embodiment 2 FIG. 2 shows another embodiment of the present invention.

In FIG. 2, the same substrate (1) as in Example 1 is installed in the reaction furnace (3) loaded in the quartz boat (2). This loading was performed in an atmosphere in which the reaction system was continuously purged with an inert gas or oxygen.

The reactor is provided with a homogenizer (4) on the inlet (5) side to promote mixing. The boat (2) is placed on the substrate (1) and is taken in and out through the exhaust port (8).

In FIG. 2, an exciter (20) for chemically activating or decomposing the reactive gas by electric energy, particularly microwave energy, is provided at a position apart from the substrate. In addition, an induction excitation system (23), which is an oscillation source of high-frequency energy, is provided on the core (3) side inside the resistance heating furnace (7).
The microwave has a frequency of 1 to 4 GHz, and chemically activates or decomposes a halogen element such as hydrogen fluoride (HF) and an oxidizing gas such as oxygen (O ₂ ) as in Example 1, so-called physical properties. It had an excited state or a chemically active state or a nascent state.

The reaction is 50 to 20 for a sufficiently clean substrate (3 to 5 inches).
O ₂ and HF (mixing ratio of gas is 4%), which was previously introduced to the 0-sheet reactor and adjusted to a concentration of 1 to 10%, for example 4%, was introduced from the purge line (17) through valves (15) (16). Was opened and closed and introduced into the reaction furnace.

The other procedures for handling the reactor were the same as in Example 1.
The opening and closing of the valves (11) to (16) were controlled by a microcomputer that was temporally sequential. FIG. 3 shows the relationship between the growth rate and the temperature of the halogen-added silicon oxide film.

FIG. 3 (A) shows the relationship between the temperature of the substrate in the reaction furnace and the growth rate of the film. As is clear from the figure, the higher the reaction temperature, the faster the film growth rate. Also microwave energy (20) or high frequency energy (23)
The curve (30) and the growth rate are low when is not used. However, when HF and oxygen were installed at a position apart from the inside of the reactor loaded with the substrate by the microwave energy (20), the growth rate increased to the curve (31). When the energy power was increased, the growth rate increased to some extent, but at 30 W or higher, there was a saturation tendency.

Further, the high-frequency induction furnace (23) provided inside the resistance heating furnace was so arranged that its electric field was positioned in a direction perpendicular to the heating furnace (7) so that high-frequency energy was not absorbed by the resistance heating furnace. This inductive energy was not current excitation in which energy is used to heat the substrate, but chemical activation or decomposition of the reactive gas was performed as voltage excitation on or near the substrate. Of course, not only HF and O _2, but also the atmosphere at that time, He and H _2, are simultaneously activated or decomposed. As a result, the excited or nascent reactive gas immediately reacts with the substrate and oxidizes without moving to a stable state,
And bonded to the dangling bond of silicon. In this case the pressure is 10
Even at 0 to 760 torr, it had an effect of activating it, that is, lowering Qss.

As is clear from Fig. 3 (A), the oxidation rate also increases,
Also, in this case, high-frequency induction energy is used, so the power is
It can easily generate high output of 100-300W or more.

FIG. 3 (B) shows the relationship between the pressure in the reactor and the film growth rate when high frequency induction energy is used.

When microwave and high frequency energy were added, it became a curve (31 '). The substrate temperature in this case was 800 ° C.

Of course, it is possible to change the substrate temperature and to use these two energies together.

When the silicon oxide film to which the halogen element was added obtained in this example was used as a gate insulator of a MOS.FET having a gate electrode, Nss was 10 ⁹ to 10 ¹⁰ cm ^-2 and B
The effect of adding the halogen element to the −T treatment was as remarkable as in Example 1. In addition, the gm (mutual conductance) of MOS.FET is high, and the breakdown strength of the gate insulation film is 8-10 because of the uniform film quality with very few pinholes.
× 10 ⁶ V / cm was obtained at a gate film thickness of 200 to 300 Å, which was a very preferable characteristic.

As described above, according to the present invention, in order to obtain a uniform film quality without pinholes at a low substrate temperature, it has hitherto been 1100 ° C
Fluorine element, which is an active halogen element that was possible only at the above high temperature, can now be made at a temperature of 600 to 1000 ° C, and a thin gate insulator, which is important for the development of VLSI, can be formed on a wafer. It is extremely important industrially that the heat treatment makes it possible without warping the potato chips.

The present invention is characterized in that the pressure is 1 atm or less, but the effect is slightly observed even when the pressure is 1 atm, and particularly when high-frequency energy is applied near the substrate in FIG. Therefore, the induced energy (23) shown in FIG. 2 was effective in increasing the oxidation rate under normal pressure or pressure. Therefore, it was effective to apply the method of the present invention to the case where the feed insulator is made 1 to 2 .mu.

Further, the present invention can be applied to a MIS.FET having an NMOS structure in which a barrier layer such as a silicon nitride film is provided on the upper side of a gate insulating film, or can be applied to a nonvolatile memory provided with a floating gate.

It goes without saying that the method of the present invention does not deny that a gate electrode made of silicon doped with impurities, a silicide metal such as WSi, or a metal-semiconductor multi-layer electrode of Mo-Si is formed on the upper side.

[Brief description of drawings]

1 and 2 show an example of a semiconductor device manufacturing apparatus of the present invention for carrying out the method of the present invention. Figure 3 is second
It is a characteristic view of the film growth rate obtained by the apparatus of the figure.

Claims (2)

[Claims] 1. A silicon oxide film containing fluorine is formed on the semiconductor by leaving the silicon semiconductor in an atmosphere in which a reactive gas containing fluorine and an oxidizing gas are mixed and having a temperature of 1050 ° C. or lower to oxidize the silicon semiconductor. A method of manufacturing a gate insulating film, which comprises manufacturing a gate insulating film of an insulating gate type semiconductor device by performing the method. 2. A reactive gas containing a fluorine element and an oxidizing gas are mixed by applying inductive energy to a mixed gas in which the reactive gas is mixed with the oxidizing gas at a mixing ratio of 10% or less. A gate insulating film of an insulating gate type field effect semiconductor device is manufactured by oxidizing a surface of a silicon semiconductor left in a gas and forming a silicon oxide film containing fluorine on the semiconductor. Membrane fabrication method.