JPS5843322B2 - Titsukakei Sohaku Makuno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicon nitride thin film, and its purpose is to obtain a silicon nitride thin film of several microns or smaller by utilizing the high energy state within the plasma region of glow discharge. We aim to provide the following.

Recently, research on silicon nitride thin films has been actively conducted, and their superiority as thin films has been recognized.

Conventionally, silicon oxide thin films have been used as diffusion masks and surface protection films for thin film integrated circuits, but they have many drawbacks, and silicon nitride is extremely promising as a replacement for silicon oxide. is beginning to be recognized at the academic level.

It has been found that silicon nitride is stable as a dielectric up to high temperatures, has strong resistance to oxidation in the air, has a high withstand voltage, and can also be used as a good diffusion mask for boron and phosphorous. It's here.

Conventionally, a method for obtaining a thin film of nitride and arsenic has been to grow silane and ammonia in a vapor phase.
This method requires a high temperature close to 00° C., and there is a risk that undecomposed ammonia may be contained in the formed film, which is not preferable due to the alkalinity of the ammonia.

Furthermore, the silane used in this method is very expensive and is completely unsuitable for industrial use.

Another method using sputtering has been announced, in which nitrogen plasma is created, nitrogen ions are applied to a silicon target, and silicon is ejected, and the ejected silicon reacts with active nitrogen while flying to the opposing substrate, but the reaction time is There are many problems before it can be industrialized, such as the long period of time required.

The inventor has conducted various studies keeping in mind the above points, and as a result,
A thin film with a relatively large thickness can be obtained at a relatively low temperature and in a fairly short time, and it is very inexpensive compared to conventional methods.
He invented a method for manufacturing silicon nitride thin films that can also be used as insulating films such as capacitor insulating layers.

That is, it is characterized in that alkylsilane and nitrogen are used as raw materials by glow discharge, and the raw materials are directly reacted and grown on a substrate placed in an electrically floating state within the plasma region of the glow discharge. This led to the invention of a method for manufacturing silicon nitride thin films.

To briefly explain the glow discharge in the present invention,
This is a so-called polarized glow discharge, and the inside of the airtight container 1 is heated to about 10 Torr using a device like the one shown in the figure.
After creating a vacuum state of
When a high frequency current with a voltage of 300 to 1000 volts is applied to the electrodes, an electric discharge occurs between the two electrodes.

The state in which this discharge reaches a steady state of continuation is called glow discharge.

In this Gouraud discharge, the part 8 in the figure is a light emitting region commonly called solar light, which is in a plasma state.

In the present invention, this plasma state is macroscopically low energy but microscopically very high energy state, and it activates nitrogen, which is normally known as an inert gas, to produce alkylsilane. They discovered that silicon nitride can be produced by reacting with silicon nitride, and this was utilized.

The present invention will be explained in detail with reference to the drawings. The substrates 7 on which the silicon nitride thin film is to be attached are arranged in an electrically floating state as shown in the drawings in a portion 8 in the airtight container 1 that can become a plasma state. The air inside the container 1 is removed using a vacuum pump 6 to create a vacuum of about 1 O-5 Torr.

Then, alkylsilane and nitrogen are sucked into the container 1 through the raw material suction port 4, and the pressure is adjusted to 0.1 to 3 Torr.

Next, apply 300 to 100
When a high frequency current of 0 volts is applied, a glow discharge state occurs.

The temperature inside the container 1 is adjusted to 200 to 400°C, and the electron energy in the plasma is set to 1 to 10 eV.

The raw material gas is activated and deposited on the floating substrate, where silicon and nitrogen react, forming a thin film on the substrate surface.

The silicon nitride thin film grows with the reaction time, and when a thin film of a suitable thickness (usually several microns or less) is obtained, the power supply 3 is turned off to stop the reaction, and the substrate processed with the silicon nitride thin film is taken out.

Note that the high frequency tributary current in the present invention is an alternating current having a frequency of 1 to 100 K cycles/sec.

Alkylsilane, which is one of the raw materials in the present invention, refers to compounds in which a total of four of the same or different alkyl groups are bonded to a silicon atom, such as tetramethylsilane, tetraethylsilane, tetrapropylsilane, dimethyldiethylsilane, and monomethyltriethylsilane. say.

The number of carbon atoms in this alkyl group does not need to be particularly limited, but at least the number of carbon atoms in the alkyl group is 0.1 to 0.
It must be able to gasify at 400°C or less under a pressure of 3 Torr. In the present invention, the alkylsilane ions, nitrogen ions, or their neutral gases occupying the plasma may cause a chemical reaction by any mechanism. Although it is not clear whether a thin film of nitriding is generated, the surface of the floating substrate immersed in the plasma is constantly irradiated with ultraviolet rays or soft X-rays with an energy of several eV to several tens of eV emitted from the plasma. It is assumed that the source gas molecules on the substrate are easily activated because of the reaction, and that the activation energy can be excited to a state that sufficiently contributes to the progress of this reaction.

The mechanism by which source gas molecules are deposited on the floating substrate 7 is due to the so-called plasma ion sheath phenomenon.

That is, in plasma, the temperature of electrons is two to three orders of magnitude higher than the temperature of ions, so the speed of electron flight is high, and the floating substrate is negatively charged by the collision and has a more negative potential than the plasma.

The vicinity of the substrate will then be surrounded by ions.

These surrounding ions reach the substrate surface, combine with electrons, and are deposited.

As described above, the present invention allows a thin film of several microns or less of silicon nitride to be formed extremely uniformly on a substrate at a relatively low temperature of around 300° C. and in a fairly short time.

The silicon nitride thin film thus obtained can be used as an extremely well-balanced insulating film.

For example, silicon dioxide, silicon monoxide, tantalum pentoxide (T
a20. ), etc., the silicon nitride thin film produced by the method of the present invention has an extremely high dielectric strength voltage, a very small dielectric loss (Tan δ) of 115 to 1/10, and a dielectric constant of about 10 , and silicon dioxide is 2
~3, which is high compared to about 8 for tantalum pentoxide.

As described above, the silicon nitride thin film produced by the method of the present invention has important physical properties as an insulating film, that is, high dielectric strength voltage,
It exhibits extremely well-balanced physical properties of low dielectric loss and high dielectric constant, making it an extremely suitable material for capacitor insulating layers.

Furthermore, the method of the present invention is much cheaper than the conventional method, and since nitrogen gas is neutral, even if it is included in the membrane strength, it has no bearing on the life of the membrane, so it is extremely durable. It is.

A substrate for forming a silicon nitride thin film was suspended in a glow discharge device as shown in the figure having the capacity of Example 456, and the inside of the container 1 was evacuated to -5 to 10 Torr using a vacuum pump. .

Then 0.15 Torr of tetramethylsilane and 1 Torr of nitrogen
．． A gas mixture with a partial pressure of 0 Torr was drawn into the vessel 1 and the total pressure was adjusted to a pressure of 1.15 Torr.

Immediately after inhaling this raw material gas, glow discharge was generated.

The conditions were a high frequency current with a frequency of 5 and a cycle of 7 seconds, a discharge voltage of 600 V, and a discharge current amount of 1.5 mA/- in a cross section within the plasma region.

Further, the reaction temperature was adjusted to the substrate temperature of 300°C.

As a result of reaction growth for 1 hour in this manner, 1.
A 2 micron silicon nitride thin film was formed.

As a result of measuring the infrared absorption spectrum of this thin film, the wavelength was 12.
．． The maximum absorption was found at 1 micron, confirming that this was a thin film made of silicon nitride.

The dielectric constant of the obtained thin film was approximately 10, and the dielectric loss tangent was Q, 000.
1. The dielectric strength was 5 x 1015V 7cm, and it had extremely excellent physical properties as an insulating film.

Next, the results of measuring the thickness of the silicon nitride thin film obtained by the present invention will be shown.

FIG. 2 shows the arrangement diagram 1 of the substrates in the reaction apparatus and the thickness measurement position diagram i[ of each substrate.

In other words, the number of substrates was 6, numbered 1 to 6, and the film thickness was measured at 9 locations numbered 1 to 9 on each substrate.

The reaction conditions at this time are as follows.

Tetramethylsilane partial pressure...0.15Torr
Partial pressure ratio> Nitrogen partial pressure...1.0OTorrO・1
5 Reaction rate...300'0°Current density...-1.5m A/cv¥, 5 K C
Time: 60 minutes As a result, the average film thickness of the six substrates was 1.199 μ, standard deviation: 0.0556, standard deviation %: 4.64%, and the film thickness was very uniform. This was recognized.

Further, FIG. 3 shows the relationship between film thickness and electrical properties, and FIG. 4 shows the relationship between raw material composition and electrical properties.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of one example for implementing the invention. 1 is an airtight container, 2 is an electrode, 3 is a high frequency power source, 4 is a raw material inlet, 5 is an exhaust outlet, and 6 is a vacuum pump. 7 indicates an electrically floating substrate, and 8 indicates a plasma region. FIG. 2 shows a substrate arrangement diagram 1 in the reaction apparatus in a film thickness measurement experiment and a thickness measurement position diagram 11 of each substrate. FIG. 3 is a graph showing the relationship between the film thickness and electrical characteristics of the silicon nitride film obtained by the present invention. FIG. 4 is a graph showing the relationship between the raw material composition and the electrical characteristics of a silicon nitride film in the present invention.

Claims (1)

[Claims] 1. Using alkylsilane and nitrogen as raw materials by glow discharge, the raw materials are directly reacted and grown on a substrate placed in an electrically suspended state within the plasma region of the glow discharge. Method for manufacturing silicon nitride thin film.