JPH0682643B2 - Surface treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for a semiconductor device, and particularly to cleaning a surface of a semiconductor or a metal substrate having a film such as a natural oxide film on the surface. The present invention relates to a surface treatment method suitable for.

[Conventional technology]

Deposition of semiconductor material on crystalline semiconductor substrate in ultra high vacuum,
The molecular beam vapor deposition method for forming an epitaxial crystal thin film is one of the important techniques in semiconductor device manufacturing because crystal growth can be performed at a relatively low substrate temperature.

However, since a layer of a natural oxide film having a thickness of 1 to 3 nm exists on the surface of a crystal semiconductor substrate that is usually used as an epitaxial crystal growth substrate, the oxide film layer is removed to expose a clean crystal semiconductor surface. If it is not vapor-deposited after that, a crystalline thin film having good interface characteristics cannot be obtained.

Therefore, in the conventional method, S.M.
L, S, I Technology "published by McGraw-Hill Bookstore, 1983 (" VLSI Technology ", ed. By SMSze, Mc Graw-Hill I
nternational Book Company, 1983), page 76, the following two methods have been implemented when the substrate is a Si single crystal. The first method is to raise the temperature of the Si single crystal substrate having a SiO ₂ -like natural oxide film on the surface to 1000 ° C. or higher.
By keeping the temperature below 1250 ° C for several tens of minutes, the natural oxide film is thermally decomposed and removed. The second method is to irradiate the treated substrate surface with a low-energy rare gas ion beam, remove the natural oxide film existing on the substrate surface by the sputter etching method, and then irradiate the Si substrate surface with ions. The crystal damage that occurred is
The substrate is heated for a short time and removed.

[Problems to be solved by the invention]

In the above conventional technology, the substrate temperature during crystal growth is 400 ° C to 800 ° C.
Although relatively low, the removal of the native oxide film, which is a pretreatment for crystal growth, requires a high substrate temperature of 800 ° C. or higher. That is, in the related art, when the above-mentioned substrate pretreatment is considered to be part of the crystal growth technique, high temperature treatment of 800 ° C. or higher is included, so that consideration is not given to lowering the temperature of all processes. Therefore, there has been a problem in applying the conventional technique to the production of a semiconductor device including an organic substance or a low-melting point metal as a constituent material to which high temperature treatment cannot be applied, or a semiconductor device including an impurity having a large diffusion coefficient.

An object of the present invention is to remove a coating layer such as a natural oxide film existing on the substrate surface in a temperature range equal to or lower than the substrate temperature during crystal growth without contaminating the substrate, It is to obtain a method for obtaining a crystal substrate surface necessary for crystal growth.

[Means for solving problems]

The above object is achieved by irradiating the natural oxide film with atomic hydrogen having a property of reducing the natural oxide film and hydrogen plasma.

In the present invention, as a means for generating atomic hydrogen and hydrogen plasma having a reducing action, as shown in FIG. 6, a laser beam 2 generated from a high power laser device 1 is condensed by a condensing optical system 3, It is introduced into the vacuum container 4 through the window 5. This is a method in which the reducing gas 6 containing hydrogen or a halogen element introduced into the vacuum container 4 is ionized by the laser light 2 and turned into plasma. The reducing gas plasma 7 generated by the above method is applied to the processing substrate 9 heated by the heater 8 and has a function of reducing a film such as a natural oxide film existing on the surface of the substrate 9.

[Action]

The plasma generation method using laser light whose electric field intensity reaches 10 ⁶ to 10 ⁷ V / cm is a method that has been known for a long time and has been widely studied in the field of fusion. The major feature is that high-density plasma can be spatially localized and generated.

In the case of laser fusion, plasma generated by laser light is used as an energy source for causing a fusion reaction, whereas in the present invention, laser generated plasma is used to form a film such as a natural oxide film existing on the substrate surface. It is used for reduction, and differs in that it utilizes the chemical action of laser-produced plasma. The laser-produced plasma in the present invention is produced by condensing laser light by a condensing optical system and ionizing the reducing gas only in a local space where the electric field strength of the laser light exceeds a certain value. It is a thing. The above constant value is in the range of 10 ⁶ to 10 ⁷ V / cm, although it depends on the type of gas used. As described above, since the plasma generation method using laser light does not use any electrodes, DC discharge plasma or high frequency discharge plasma produced by ionizing gas using the electrodes contains a sputtered electrode material as impurities. There is almost no such phenomenon. Therefore, the laser-generated plasma of the present invention is a plasma that is less contaminated by electrodes and the like.

In addition, even when compared with electrode-less high-frequency discharge plasma and microwave discharge plasma, in the laser-produced plasma, the position where the laser electric field intensity is 10 ⁷ to 10 ⁸ V / cm is located at a place sufficiently separated from the vacuum vessel wall. If you adjust the focusing optics so that
Plasma can be generated in a local space away from the vacuum vessel wall. On the other hand, even with high-frequency discharge plasma, plasma is generated in the internal region of the discharge tube made of silicon dioxide, alumina porcelain, etc., and due to the contact between the plasma and the discharge tube wall, the constituent material of the discharge tube wall Often oxygen and the like are mixed in the plasma. In that case, the reduction reaction of the surface coating of the semiconductor / metal substrate by the reducing plasma composed of hydrogen or a halogen element is greatly suppressed. Further, there is a defect that impurities such as oxygen generated from the wall of the discharge tube are trapped in the substrate surface layer as contamination.

In contrast to the above drawbacks, the method of the present invention for producing a reducing plasma containing hydrogen or a halogen element by the action of the electric field of the focused laser light does not require any electrode or discharge tube that is likely to become a pollution source. . Therefore, it can be said that the laser-generated plasma of the present invention, which is formed by focusing the laser light at a position sufficiently distant from the inner wall of the vacuum container, is a plasma that is less contaminated by oxygen and metal atoms forming the electrodes.

Next, in the laser-produced plasma produced by ionizing the gas containing one or both of hydrogen and halogen elements by the above method, dissociated hydrogen atoms, hydrogen ions, and dissociated halogen having a chemical reducing action are generated. There are atoms and halogen ions. When this reducing plasma is applied to the surface of a semiconductor / metal substrate having a film of natural oxide, for example, in the case of a Si single crystal substrate having a film of silicon dioxide, the reaction of SiO ₂ + 4H → Si + 2H ₂ O ↑ Occurs, the silicon dioxide film is reduced, and the surface of the Si single crystal substrate having no film is obtained. H ₂ O generated as a result of the reduction reaction is desorbed and removed in a vacuum by heating the substrate. Halogen atoms also react with silicon dioxide to form silicon halides and oxygen, which are etched away.

As described above, hydrogen, at least one of the halogen elements,
Alternatively, when a laser-produced plasma of a gas containing both is created and irradiated on the surface of the semiconductor / metal substrate, silicon dioxide, etc. is generated by the reducing action of dissociated hydrogen atoms, hydrogen ions and halogen atoms present in the laser-produced plasma. It is possible to reduce surface coatings such as oxides and nitrides.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of a surface treatment method according to the present invention, FIG. 2 is a diagram showing a relation between an oxide film thickness of a Si surface and treatment time in the above-mentioned embodiment, and FIG. FIG. 4 is a configuration diagram showing a second embodiment of a surface treatment method according to the invention, FIG. 4 is an explanatory view of the principle of improving the surface treatment speed by a magnetic field, and FIG. 5 is an explanatory diagram of the principle of improving the surface treatment speed by an electric field.

First Embodiment Referring to FIG. 1 showing a first embodiment of the present invention, a laser beam 22 having a wavelength of 248 nm generated by a pulse oscillation KrF excimer laser 21 is passed through a convex lens 23 and a window 24 made of fused silica and having a focal length of 50 cm. , Is introduced into the vacuum container 25. Above vacuum container
25 is evacuated by the vacuum exhaust pump 26, and the hydrogen gas 27 is caused to flow through the gas leak valve, so that the vacuum container 25
Si (100) single crystal substrate 28 having a natural oxide film (silicon dioxide) with a thickness of 1 to ² nm on the surface that keeps the degree of vacuum at 1 × 10 ^-2 Torr, and a substrate holder 30 with a heater 29. Installed on top,
Keep the temperature at 600 ° C.

A KrF pulse laser beam 22 having a pulse width of 10 nsec, a pulse energy of 300 mJ, and a cross-sectional beam size of 10 mm × 40 mm is 0.1 mm at a position 10 mm above the substrate 28 by the convex lens optical system 23.
It was confirmed by light emission from the red hydrogen plasma that the hydrogen gas was ionized and the local hydrogen plasma 31 was generated when the light was focused at × 0.4 mm. The repetition frequency of the laser pulse was set to 10 Hz, and the Si substrate 28 was exposed to the hydrogen plasma for about 10 seconds. During that time, the thickness of the natural oxide film was measured by the ellipsometer device 32 attached to the vacuum container 25.
As shown in the figure, the initial film thickness was 2.5 nm, but after 8 minutes of hydrogen plasma irradiation, the film thickness became 0 nm, and after 8 minutes, it was saturated at 0 nm. As described above, it is understood that the natural oxide film on the surface of the Si substrate 28 was removed by the plasma irradiation for about 10 minutes.

After that, the irradiation of laser light and the supply of hydrogen gas are stopped,
The degree of vacuum in the vacuum container 25 is set to 1 × 10 by the vacuum exhaust pump 26.
After exhausting up to ^-10 Torr, Si vaporization source 33
Then, it was evaporated and deposited on the Si substrate 28. Si substrate 28 at this time
The temperature was 700 ° C. The Si substrate 28 was taken out of the vacuum container 25, and the film thickness of the vapor deposition portion was measured and found to be 100 nm. In addition, when the crystallinity of the deposited film was evaluated by a reflection electron beam diffraction method, it showed the same crystal plane Si (100) as the substrate 28. However, the hydrogen plasma irradiation of the present invention was not performed in the vacuum container 25, and Si (10
0) The Si film formed by performing Si vapor deposition on a single crystal plate under the same vapor deposition conditions as described above had an amorphous structure in terms of crystallography.

From the above, irradiating laser-produced hydrogen plasma is
It can be seen that this is an effective surface treatment method for obtaining a clean semiconductor surface by reducing and removing the natural oxide film on the semiconductor surface.

Further, it is more effective to remove the organic substances attached to the surface before the main treatment. For example, a laser-induced oxygen plasma treatment is performed in advance, and then the above-mentioned surface treatment is performed to obtain a clean semiconductor or metal surface.

Second Embodiment A second embodiment shown in FIG. 3 is an embodiment in which the surface treatment of a plurality of substrates is performed by using one laser, and a Q switch having an output of 20 J / pulse, an oscillation frequency of 1 Hz and a pulse width of 30 nsec. Using the pulsed ruby laser 42, the wavelengths 692.9 nm and 69
A 4.3 nm laser beam 43 was condensed to a diameter of 0.05 mmφ by a convex lens 44 having a focal length of 500 mm and introduced into a vacuum container 45. The vacuum container 45 contains chlorine gas (5%) and hydrogen gas (95%).
A mixed gas 46 of and was introduced and the pressure was set to 1 Torr. The position where the laser beam 43 is focused by the lens 44 is located on the two Si substrates 41.
The hydrogen plasma 47 was generated at the above-mentioned condensing position, and the hydrogen plasma 47 was uniformly applied to the two Si substrates 41. At this time, the two Si substrates 41 are respectively heated by the heater 48.
Is heated to 600 ° C. as in the first embodiment.
It was confirmed that the natural oxide film on the Si substrate 41 can be reduced by repeating the irradiation of the hydrogen plasma at a repetition frequency of 1 Hz for 30 minutes, as in the first embodiment.

Third Embodiment In a third embodiment shown in FIG. 4, a magnetic field 53 is applied to a position where a plasma 51 generated by laser light and a substrate 52 are placed, and a natural state is formed on the surface of the substrate 52. This is a method of accelerating the reduction and removal of an oxide film, and shows one application example of the present invention.

A permanent magnet 54 for generating a magnetic field 53 was installed behind the substrate 52, and a magnetic field of 0.1 Tesla was generated near the substrate 52.
When this embodiment was applied to the second embodiment, when no magnetic field was applied, it took 30 minutes of laser irradiation to reduce and remove the 25Å-thick SiO ₂ natural oxide film. When this example was applied, the laser irradiation time was shortened to 20 minutes. In this embodiment, the permanent magnet 54 is used to generate the magnetic field 53, but other magnetic field generation sources such as coils may be used.

Fourth Embodiment In a fourth embodiment shown in FIG. 5, an electric field 64 is applied between a plasma 62 generated by laser light and a substrate 63 by using an electrode 61 to remove ions or electrons in the plasma 62. This is a method of accelerating and irradiating the substrate 63 to reduce and remove the natural oxide film on the surface of the substrate 63, and shows one application example of the present invention.

When an electric potential 64 of 100 V is applied between the electrode 61 and the substrate 63 by using the electrode 61 made of Si as a material, the present embodiment is applied to the first embodiment. , 10 Å for reducing and removing SiO ₂ natural oxide film with a thickness of 25Å
While the laser irradiation for one minute was required, the laser irradiation time could be shortened to 5 minutes by applying this embodiment.

In each of the above-mentioned examples, the case of using the KrF excimer laser or the ruby laser was shown, but as the laser to be used, the electric field intensity 10 ⁶ to 10 ⁷ V / only for converting reducing gas such as hydrogen gas into plasma. Any cm can be used as long as it can generate cm at the focal position.

Further, as the gas for generating the reducing plasma for reducing and removing the natural oxide film, hydrogen gas was used in each of the above-mentioned examples, but other than this, a gas containing halogen as a constituent element, HCl or HF, Cl ₂ , SF _6, etc., or mixtures thereof can also be used.

The substrate to be surface-treated may be any one as long as it has an oxide film on its surface, and is not particularly limited to Si.
The present invention is also effective for cleaning compound semiconductors such as InP and GaAs, and metal surfaces such as Al and W.

〔The invention's effect〕

As described above, the surface treatment method according to the present invention is a method of treating a surface of a treated substrate whose surface is covered with a film such as an oxide film, in which a gas containing at least one of hydrogen and / or a halogen element as a constituent element is laser light. Is irradiated to ionize and generate plasma having a chemical reducing action,
By irradiating the treated substrate with the plasma to reduce the coating layer on the treated substrate surface, in a clean reducing atmosphere, chemically active hydrogen atoms and hydrogen ions are generated, and Irradiation is possible, so a natural oxide film
There is an effect that the substrate can be reduced and removed at a low temperature of 800 ° C. or lower in a short time of 30 minutes to 30 minutes. Further, by applying a magnetic field or an electric field to the space between the generated plasma and the processing substrate, the time for removing the oxide film can be further shortened, and the processing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a surface treatment method according to the present invention, FIG. 2 is a diagram showing a relation between an oxide film thickness of a Si surface and treatment time in the above-mentioned embodiment, and FIG. FIG. 6 is a configuration diagram showing a second embodiment of the surface treatment method according to the invention, FIG. 4 is an explanatory view of the principle of improving the surface treatment speed by a magnetic field, and FIG. 5 is an explanatory diagram of the principle of improving the surface treatment speed by an electric field.
The figure is a basic configuration diagram showing the principle of the present invention. 22, 43 …… Laser light, 27,46 …… Hydrogen gas 28,41,52,63 …… Processed substrate 31,47,51,62 …… Plasma 53 …… Magnetic field, 54 …… Permanent magnet 61 …… Electrode , 64 …… electric field

Claims (4)

[Claims] 1. A method of treating a surface of a treated substrate whose surface is covered with an oxide film, wherein a gas containing at least one of hydrogen and / or a halogen element as a constituent element is used.
A surface treatment method comprising irradiating a laser beam to ionize it to generate plasma having a chemical reducing action, and irradiating the treated substrate with the plasma to reduce the coating layer on the surface of the treated substrate. 2. The surface treatment method according to claim 1, wherein the treated substrates are a plurality of treated substrates arranged around the laser-generated plasma. 3. The surface treatment method according to claim 1, wherein a magnetic field is applied to the generated plasma in a space between the plasma and the treated substrate. 4. The surface treatment method according to claim 1, wherein an electric field is applied to the generated plasma in a space between the plasma and the treated substrate.