JPS6329584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a deposition method mainly used in the manufacture of semiconductor devices, and in particular to a method of deflecting a flow of raw material gas turned into plasma by a magnetic field and depositing it on a substrate. It is.

In the manufacture of semiconductor devices, chemical vapor deposition (hereinafter referred to as chemical vapor deposition) is one of the methods for depositing new materials on a substrate.
There is a method called CVD method (abbreviated as CVD method). This involves supplying a gas phase raw material and depositing the resulting material on the substrate through a chemical reaction that involves thermal decomposition. High temperatures in the area were unavoidable. On the other hand, as a means to avoid high temperatures and accelerate the reaction, it has been considered to supply the raw material gas in the form of plasma, but there are problems such as difficulty in controlling the reaction and insufficient reproducibility. Therefore, many problems remain to be resolved.

The present invention converts raw material gas into plasma, but unlike these prior art techniques, it presents a new chemical deposition method that utilizes the principle of MHD power generation to supply raw materials. .

Simply put, the principle of MHD power generation is to flow plasma gas into a magnetic field and separate negative and positive ions using the Lorentz force to generate an electromotive force. The present invention also utilizes this principle. It's hot,
After converting the raw material gas into a plasma state, the plasma is moved in a magnetic field in a substantially constant direction at a substantially constant speed, and the plasma ions are caused to reach the substrate surface by the Lorentz force, and the ions are The method is characterized in that atoms or atomic groups generated by neutralizing the charges of are deposited on the substrate.

The drawings schematically represent an embodiment of the present invention. Taking the case of forming a silicon layer as a deposited layer as an example, first, monosilane (hereinafter referred to as SiH ₄ ) as a raw material gas is supplied into the reaction tube 1 from the right side of the figure. The pressure at this time is set to a pressure that allows plasma formation, that is, within a range of 0.0001 to 10 Torr. SiH ₄ introduced into the reaction tube moves to the left in the figure at a nearly constant rate and is first turned into plasma in the plasma generation region. All commonly used plasma generation methods can be used, but
The one shown in the figure is of a type in which a high frequency current is passed through a coil 2 wound around a reaction tube to excite plasma.

When SiH ₄ becomes plasma, it becomes SiH ₄ ⁺ , SiH ₃ ⁺ ,
This plasma, which now contains positive ions such as SiH ₂ ⁺ and electrons corresponding to negative ions, moves further to the left at a velocity V and enters the magnetic field region 3. In this region, charged particles move in a magnetic field perpendicular to the direction of plasma movement, so the Lorentz force acts on the ions, and as shown in the figure, under the magnetic field moving from the front to the back of the paper, the charged particles move positively. Ions flow downward, and anions flow upward.

As a result, the lower electrode 4 is placed in the magnetic field region.
Cations reach the upper electrode 5, anions reach the upper electrode 5, and an electromotive force (hereinafter referred to as this) is generated between the two electrodes.
(expressed as MHD electromotive force) is generated. When both electrodes are connected with a conductor in this state, a current flows, and through the process of neutralizing the charges, the ions become atoms or atomic groups and are deposited on the electrode surface. At this time, if a conductive substrate (not shown) is placed on the electrode, deposition will occur on the surface of the substrate.

Continuing with the above example, for example, a SiH ₄ ⁺ ion whose course has been changed by the Lorentz force loses its charge when it gently collides with the substrate, and
It decomposes into Si and _H2 gas, and Si is deposited on the substrate.
This reaction is similar to thermal decomposition, but raw material ions with a certain kinetic energy greater than thermal energy are forcibly supplied, and active ions are involved in the reaction on the solid surface. For this reason, deposition can be performed at lower substrate temperatures than with conventional CVD methods.

Considering that ionization in the form of Si ⁺ due to plasma formation becomes Si and deposits only by neutralization of charge, in the method of the present invention, when the raw material is supplied in the form of cations, It can be seen that the substance oxidized by plasma formation is reduced on the electrode and the deposition progresses.

Considering only charge neutralization, deposition can occur simply by short-circuiting the electrodes 4 and 5 in the device shown in the figure, but since it is difficult to strictly control the deposition rate with just that, one of the embodiments of the present invention The constant current device 6 controls the neutralization rate, that is, the deposition rate of ions to be kept constant. Since only ions whose charges have been neutralized are deposited on the substrate, the deposition rate can be controlled by controlling the neutralization current. In this case, the current value is, for example,
If you want to obtain a deposition rate of about 1 nm, the current density should be set to 1 mA/cm ² , although it varies slightly depending on the type of deposited material.
It should be controlled to a certain extent.

If the present invention is considered as MHD power generation, the electromotive force V is proportional to the product of the velocity v of the charged particles and the strength B of the magnetic field.
That is, V∝B·v, and if the velocity v is disturbed for some reason, the deposition rate will fluctuate, so keeping the neutralization current constant is also effective in solving this problem. Furthermore, constant current control can also deal with changes in the condition of the substrate surface as the deposition progresses.

In addition to the above-mentioned control using current, control using voltage may be effective. When it is necessary to maintain a constant gas flow rate while reducing the pressure to a predetermined pressure, as in the device used in the present invention, the range of flow rates that can be realized is limited depending on the capacity of the exhaust device.
The desired flow rate may not be obtained. As mentioned above, while the MHD electromotive force appearing at the electrode is proportional to the flow velocity, the characteristics of the deposited film are affected by the collision energy during deposition, so a voltage that reduces or enhances the MHD electromotive force is applied. The purpose of the voltage control is to control the quality of the membrane.

The above current range is used not only to control the neutralization current when controlling the deposition rate by voltage, but also to control the neutralization current.
There are cases where the neutralization current is increased by applying an external voltage, but in that case, the externally applied voltage accelerates the ions, which weakens the non-impact feature as described below. become.

When the deposition proceeds with a neutralizing current as described above, selective growth is possible because no deposition occurs on the portion of the substrate surface covered with the insulating layer. On the other hand, deposition on an insulating layer is possible by setting the magnetic field to an alternating magnetic field of about 0.1 to 1 Hz. That is,
Cations are first deposited on the substrate, and then the magnetic field is reversed to deposit anions, which neutralizes the charge and progresses the deposition. In the above example, first SiH ₄ ⁺ and then electrons reach the substrate and a Si layer grows. Even when the substance to be deposited is an insulator, the deposition can be progressed by applying an alternating magnetic field.

The plasma deposition method of the present invention has been explained above, but
Next, the features of the present invention will be described.

First, since the deposition rate can be electrically controlled, the accuracy of the film thickness is good. Furthermore, since the raw material is actively transferred onto the substrate using Lorentz force,
Although the deposition rate can be increased compared to relying solely on diffusion, the Lorentz force does not impart kinetic energy to the particles, so they collide with the substrate at a low speed and are less likely to damage the substrate. Moreover, this non-impact characteristic has the effect of reducing contamination of the deposited layer in that unnecessary substances are not knocked out from the electrode.

Further, when the deposition rate can be controlled by an element independent of the flow rate as in the present invention, it is possible to form a better film by setting the flow rate large. This is based on the fact that in this type of chemical growth method, the higher the flow rate, the less the amount of impurities entering the growth layer tends to be.

[Brief explanation of the drawing]

The drawing schematically shows an example of an apparatus for carrying out the present invention, in which 1 is a reaction tube, 2 is a plasma excitation coil, 3 is a magnetic field region, 4 and 5 are electrodes, and 6 is a constant current device. It is.

Claims (1)

[Claims] 1. After converting the raw material gas into a plasma state, the plasma is moved in a magnetic field in a substantially constant direction at a substantially constant speed, and the plasma ions are caused to reach the substrate surface by the Lorentz force. A plasma deposition method characterized in that atoms or atomic groups generated by neutralizing the charge of the ions on the substrate surface are deposited on the substrate. 2. The plasma deposition method according to claim 1, wherein the charge of the ions is neutralized by passing a current through an electrode electrically connected to the substrate. 3 Claims characterized in that by making the magnetic field an alternating magnetic field, negative ions including positive ions and electrons are made to reach the surface of the substrate alternately, thereby neutralizing the charges. The plasma deposition method according to item 1.