JPH03222327A - Surface processing - Google Patents

Abstract

PURPOSE:To lessen the damage caused by ion irradiation by a method wherein an oxide film whose coupled state is changed by irradiating the oxide film with ions in heavier mass than those in lighter mass irradiating an underneath layer of the oxide film is sublimated. CONSTITUTION:The surface of an underneath layer 2 whereon an oxide film 1 is formed is irradiated with ions 4 in light mass (e.g. helium). These ions in light mass do not etch away the oxide film 1. The acceleration voltage of the ions 4 in light mass is selected to be able to change the coupled state 5 of atoms or molecules in the oxide film 1. For example, the acceleration voltage is selected to change from the crystal state to the amorphous state in the oxide film 1. Finally, the oxide film 1a whose coupled state 5 is changed during the light ion irradiation process (A) is further irradiated with the other ions 7 in heavy mass (e.g. argon ions) to be sublimated.

Description

[Detailed Description of the Invention] This overview relates to a surface treatment method for treating a base surface having an oxide film and sublimating the oxide film.Providing a dry treatment method for a surface having an oxide film that can reduce damage caused by ion irradiation. For the purpose of and a step of irradiating with ions to sublimate the oxide film in which the bond 8: state has changed.

E. Industrial Application Field] The present invention relates to a surface treatment method, and particularly to a surface treatment method for treating a base surface having an oxide film and sublimating the oxide film.

Materials that are easily oxidized, such as silicon and aluminum, immediately form a natural oxide film when left in the air. When bringing a conductive film into direct contact with these underlying materials,
It is often preferable to remove the oxide film on the surface.

Prior Art 3 A silicon substrate usually has a natural oxide film on its surface having a thickness of about 10 to 100 mm. In the conventional manufacturing process of semiconductor devices, in order to wet-remove the oxide film on the surface before forming a conductive thin film on the silicon substrate,
The silicon substrate is immersed in an etching solution containing dilute hydrofluoric acid to etch the oxide film, followed by washing with water and drying.

According to such wet etching, the natural oxide film on the surface is removed by etching, but water washing, drying, and subsequent W etching are necessary.
When inserting into the i-film forming apparatus, a thin natural oxide film is again formed on the surface.

Furthermore, when attempting to manufacture semiconductor devices in an environment isolated from the atmosphere by completely drying the process, the wet etching process becomes an obstacle.

As a dry removal method for a surface oxide film, a method has been proposed in which argon ions accelerated in an electric field are irradiated onto the surface of a silicon substrate heated to a high temperature of 600° C. or higher. When the oxide film on the silicon substrate is irradiated with argon ions accelerated by an acceleration electric field equal to or higher than a threshold value and the substrate is heated to 600° C. or higher, the oxide film on the surface sublimates.

According to such dry etching, the process can be made dry and the number of steps can be reduced. However, damage occurs in the silicon crystal due to the bombardment of argon ions. Also,
Re-oxidation occurs when oxides or oxygen released by argon ion irradiation adhere to the surface again.

[Problems to be Solved by the Invention] According to the conventional techniques described above, when a wet treatment method is used as a surface treatment method for a base surface having an oxide film, it is difficult to obtain a surface without an oxide film. However, it is difficult to reduce the number of steps, and the dry processing method causes damage to the silicon due to ion irradiation, and there are also problems of surface reoxidation.

An object of the present invention is to provide a dry treatment method for a surface having an oxide film that can reduce damage caused by ion irradiation.

Another object of the present invention is to provide a dry processing method for a surface having an oxide film, which can prevent damage to a semiconductor substrate and also prevent surface re-oxidation.

Measures to solve E-problems] FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 1 (A>) shows a light ion irradiation process.The surface of a base 2 having an oxide film 1 is irradiated with ions 4 having a light mass (for example, helium ions) 4 These light ions 4 etch the oxide film 1. The accelerating voltage of the light ions 4 with low mass is selected so that the bonding state 5 of atoms or molecules in the oxide film 1 can be changed, for example, the oxide film 1 changes from a crystalline state to an amorphous state. Choose as you like.

FIG. 1(B) shows the heavy ion irradiation process. Figure 1<A
> In the light ion irradiation step, heavy ions 7 having a heavier mass are
The oxide film 1a is sublimed by irradiation with (for example, argon ions).

1 Effect] In conventional dry etching, heavy ions such as argon (Ar) were accelerated and irradiated with an accelerating voltage higher than a threshold value, which resulted in damage to the underlying layer 2. - First, the oxide film 1 is irradiated with light ions 4 to change its bonding state 5 and become easily sublimed, and then the heavy ions 7 are accelerated and irradiated at a low accelerating voltage equivalent to or lower than the opening of the chain. Oxide film 1 with a changed bonding state
It becomes possible to sublimate a.

[Example 2] FIG. 2 shows a dry enching apparatus for carrying out the surface treatment method according to the embodiment of the present invention. Mechanical booster pon bu 12,
It is equipped with a first evacuation system consisting of a rotary pump 13 and a second evacuation system consisting of a rotary pump 14, and is configured to perform evacuation. Also, vacuum container 1
5 is connected to an oxygen gas source 22, a helium gas source 23, and an argon gas source 24 via a leak valve 21 so that the atmosphere can be adjusted. In addition, ion source 1
6 are provided, and the ion source 16 includes a helium gas source 23,
An argon gas source 24 is connected to generate helium ions and argon ions. A sample stage 17 made of T i N or A1 is arranged inside the vacuum container 15 .

One halogen lamp is provided directly below the sample stage 17, and can heat the sample stage 17. Also, near the top of the sample stage, there is another halogen lamp 20 for ozone generation.
is provided to excite the oxygen atmosphere and generate ozone.

Dry etching is performed as shown below using the apparatus shown in FIG. do. Subsequently, the vacuum container 15 is preliminarily evacuated using the second evacuation system and the first evacuation system. Next, the leak valve 11 is controlled to introduce oxygen into the vacuum container 15, and the pressure is adjusted to about 100 torr. A halogen lamp 20 is turned on in this oxygen atmosphere to generate ozone by thermal excitation. Note that the pressure of the atmosphere here can be selected from a range of about 1 torr to atmospheric pressure depending on the desired oxidation conditions. In addition, the surface of the silicon substrate 18 is oxidized for about 5 minutes in an oxygen atmosphere containing ozone, preferably at a temperature of 200° C. or lower, to grow a surface oxide film to an appropriate thickness.4 This oxide film growth step This is done to grow the oxide film to an appropriate thickness because it is easier to perform subsequent processing if the oxide film to be etched has a certain thickness than if it is too thin. After surface oxidation for about 5 minutes, the inside of the vacuum container 15 is transferred to the first vacuum system 11.12, 3
The sample was evacuated to 2 x 10' torr using the halogen lamp 19 directly below the sample stage 17.
One substrate 18 was heated in stages. Introducing helium gas from the helium gas a23 and operating the ion source 16,
The 81 substrate 18 is irradiated with helium ions. For example, the pressure inside the vacuum container 15 is approximately '3 x 10-5 to
The sample was heated in 100°C steps and held at each heating temperature for about 10 minutes. The 81 substrate 18 held at a constant temperature for 10 minutes was irradiated with helium ions, and the results were examined. Here, the helium ion acceleration voltage was approximately IKV. The irradiation with helium ions, which are light ions, is the SO2 on the surface of the 31 substrate.
Although it does not etch the film, it weakens the bonds between atoms or molecules within the film, making the SiO2 film amorphous. Furthermore, this light ion radiation can be made to have virtually no effect on the S substrate 18.

Thereafter, while controlling the pressure, argon gas was introduced into the ion source 16 from the argon gas source 24 to generate argon ions, and the substrate 81 was irradiated with the argon ions.

The accelerating voltage of the argon ions was selected to be about 20 V, which is equivalent to or slightly lower than the open chain for the silicon oxide film. Note that the pressure during argon ion irradiation is approximately 5 x 10
It was 'torr.

In the above process, even at a heating temperature of about 400° C. or lower, the silicon oxide film on the surface sublimated, and the surface made only of Si element was exposed. Increasing the temperature above 600° C. clearly caused surface reoxidation. In order to prevent surface reoxidation, the heating temperature is preferably 400° C. or lower. Previously, the oxide film did not sublimate unless it was heated to 600°C or higher, but due to changes in the bonding state of atoms and molecules due to light ion irradiation, sublimation can now occur even at lower temperatures of 400°C or lower. Conceivable.

The argon ion irradiation is preferably carried out at an acceleration voltage of about 50 V or less. By selecting the argon ion acceleration voltage sufficiently low, selective etching of only the silicon oxide film without etching silicon can be realized.

Furthermore, the argon ion irradiation step was effective in preventing surface reoxidation if it was performed under heating at about 400° C. or lower.

By selecting a sufficiently low heating temperature during argon ion irradiation to prevent surface re-oxidation, an electrode layer made of, for example, A1 or W is formed on the substrate 31 with the clean surface exposed. A good ohmic contact can be formed.

Note that the initial oxide film growth step can be performed simultaneously with helium ion irradiation. That is, by forming ozone and
While oxidizing the surface of one substrate, helium ions heated to, for example, about 50V are irradiated.

Porous amorphous oxide films can be formed under helium ion irradiation. In this case, since the helium ion energy can be lowered, damage to the S substrate can be further reduced. After forming the porous oxide film, the process of selectively etching the oxide film by irradiating with argon ions can be performed in the same manner as in the previous embodiment.

In this way, dry etching for selectively removing the SiO2 film on the 81 substrate is achieved. When such a process is used, the entire dry process of the semiconductor device manufacturing process is promoted. By eliminating high-temperature heating, surface re-oxidation can be prevented and the thermal age imparted to the 6Si substrate can be reduced.

Also, when using the A1 base layer instead of the 31 substrate,
The above-mentioned processing method can be applied. That is, selective dry etching can be performed on the alumina on the surface of the A1 layer, and another layer such as the electrode 8ii layer (AI or W) can be formed thereon while sufficiently suppressing the contact resistance.

Although the present invention has been described above along with examples, the present invention is not limited to these. It will be obvious to those skilled in the art that various changes, improvements, combinations, etc. can be made to the examples.

E. Effects of the Invention As explained above, according to the present invention, the surface oxide film can be selectively dry etched while preventing damage to the underlying layer.

Moreover, by selecting conditions, it is possible to selectively remove the surface oxide film while preventing surface re-oxidation.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention. FIG. 1(A) is a cross-sectional view showing the light ion irradiation process, FIG. 1(B) is a cross-sectional view showing the heavy ion irradiation process, and FIG. 1 is a schematic diagram illustrating a dry etching apparatus for performing dry etching according to an embodiment of the present invention; FIG. In the figure: 1 Oxide film 2 Base 1 2 3 4 5 6 7 8 9 0 1 2 3 4 Light ion bond state Heavy ion turbo molecular pump mechanical booster pump rotary bomb. Rotary Bonf. Vacuum container ion source Sample stage Single crystal 81 Halogen lamp for substrate heating Halogen lamp for ozone generation Leak valve Oxygen gas source Helium gas source Argon gas source (A) Light ion irradiation process (B) Heavy ion irradiation process Figure 1 Dry etching equipment Figure 2

Claims (4)

[Claims] (1) Light ion irradiation that changes the bonding state (5) of atoms or molecules within the oxide film (1) by irradiating the surface of the base (2) with the oxide film (1) with ions (4) of low mass. step, the substrate surface is covered with ions heavier than the lighter ions (
Oxide film (1a) whose bonding state has changed by irradiation with step 7)
A surface treatment method comprising a heavy ion irradiation step to sublimate. (2) The surface treatment method according to claim 1, further comprising the step of exposing the base (2) to an oxidizing atmosphere to grow the oxide film (1) to a desired thickness. (3) The surface treatment method according to claim 2, wherein the oxide film growth step is performed in parallel with the light ion irradiation step according to claim 1. (4) Any one of claims 1 to 3, wherein the heavy ion irradiation step includes irradiating the heavy ions at an acceleration energy equal to or lower than a sputtering threshold for the oxide film under heating at about 400° C. or lower. The surface treatment method described in .