JPS6313341B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a treatment method for stabilizing the state of the interface between the silicon dioxide (SiO ₂ ) film and Si when forming a thermal oxide film on the surface of a silicon (Si) substrate. be.

Stabilizing the interface between SiO ₂ and Si is an important issue in the formation of semiconductor devices, but if the interface between the gate oxide film and the substrate of a MOS transistor is unstable, Vth will fluctuate and its operation will be affected. Becomes unstable.

The main cause of such interface instability is Na ⁺
It is thought that there are ions such as ions and K ⁺ ions that move freely around the SiO ₂ film. These ions change Vth by moving through SiO ₂ . What is simply expressed as Vth here is the channel formation threshold voltage when a gate electrode is provided on an oxide film to form a MOS structure, and the same applies in the following text.

It is considered that these mobile ions are captured by chlorine (Cl) ions to prevent fluctuations in Vth. The typical technology is to distribute Cl - ions in SiO 2 by forming a thermal oxide film in an atmosphere containing vapors such as hydrogen chloride (HCl) and trichloride (CHCl ₃ ), thereby distributing Cl ^- ions in SiO ₂ ^. It captures mobile ions such as ions and immobilizes them.

Although this method is effective, there is a problem in that it is difficult to handle because it uses a harmful gas such as HCl.

The aim of the invention is to use more harmless raw materials
The purpose of the present invention is to provide a method for containing Cl ^- ions in SiO ₂ , and to achieve this purpose, the treatment method of the present invention involves exposing the substrate surface to a plasma of a chlorine-containing compound and then performing thermal oxidation. It is characterized by

The inventor has discovered that chlorine-containing gases (e.g. CCl ₂ F ₂ )
As a result of analyzing the surface of a Si substrate exposed to plasma using an ion microanalyzer, it was found that the surface of the Si substrate subjected to the above treatment adsorbed a large amount of Cl ^- ions. The present invention is based on this new knowledge, and basically involves exposing the Si substrate surface to a chlorine-containing gas plasma and then thermally oxidizing it to incorporate the Cl ^- ions adsorbed on the surface into SiO ₂ . This forms a SiO ₂ film with a stable Vth.

FIG. 1 shows an embodiment of the present invention. Parallel plate electrodes 1 and 2 are connected to a high frequency power source, and a Si substrate 4 is placed on electrode 1. These electrodes and Si substrates were installed inside a reduced pressure reaction chamber (not shown), and the chamber atmosphere was 1 Torr of oxygen (O ₂ ) and 0.01 Torr.
It is a mixed gas of freon chloride (CCl ₂ F ₂ ).
13.56MHz to electrodes 1 and 2 by high frequency power supply 3.
When 500 W of high-frequency power is applied, the gas is turned into plasma, and Cl ^- ions are adsorbed onto the surface of the Si substrate.

After being exposed to radiation for about 1 minute under the above conditions, thermal oxidation is performed in the usual manner, and the resulting SiO ₂ film contains
Cl ^- ions are contained and Na ⁺ ions are immobilized.

FIG. 2 shows another embodiment of the invention. In this embodiment, the plasma generating section 5 is provided separately from the exposure processing section. The raw material gas is the same as in the previous example.
_O2 + _{CCl2F2 .} The gas is turned into plasma by high-frequency power applied to electrodes 1 and 2 provided outside the room, and then introduced into the reaction tube 6, where Cl ^- ions are adsorbed onto the surface of the Si substrate placed inside the tube. .

In the apparatus shown in FIG. 2, thermal oxidation can be carried out immediately by stopping the high frequency power supply and switching the gas supplied to the reactor to a normal thermal oxidation gas. In this case, even if the plasma exposure treatment is performed at an oxidizing temperature, Cl ^- ions are sufficiently adsorbed.

In these embodiments, a mixed gas of CCl ₂ F ₂ and O ₂ is used to prevent carbon from adhering to the Si substrate. In other words, a large amount of carbon is deposited on the Si substrate when exposed to plasma containing only CCl ₂ F ₂ ;
When a mixed gas with O ₂ is used, the carbon plasma generated combines with oxygen plasma to become CO ₂ or CO.
It does not adhere to the Si substrate.

The SiO ₂ film formed by the above method
Vth is very stable because Cl ^- ions adsorbed on the substrate surface are incorporated into SiO ₂ , resulting in
This is thought to be due to immobilization of Na ⁺ ions, etc.

By implementing the processing method of the present invention, it is possible to realize a MOS structure with stable Vth,
Improvements in device characteristics and manufacturing yields can be seen.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of the present invention, in which 1 and 2 are electrodes, 3 is a high frequency power source, 4 is a Si substrate, 5 is a plasma generation region, and 6 is a reaction tube. It is.

Claims (1)

[Scope of Claims] 1. A method for surface treatment of a semiconductor substrate, which comprises exposing the main surface of the semiconductor substrate to plasma of a compound containing chlorine, and then performing thermal oxidation. 2. The method of surface treatment of a semiconductor substrate according to claim 1, wherein the plasma of the compound containing chlorine is a plasma of a mixed gas of a carbon chloride compound and oxygen.