JP2640828B2 - Method for removing native oxide film on semiconductor substrate surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for removing a native oxide film on the surface of a semiconductor substrate, which aims at removing the native oxide film without damaging the semiconductor or deteriorating its characteristics. , Carbon monoxide, nitrogen monoxide gas was added to chlorine gas, the semiconductor substrate was placed in a reduced pressure atmosphere for a certain period of time and etched by ultraviolet light irradiation, and the natural oxide film formed on the semiconductor substrate was removed. The method comprises a method of removing a natural oxide film on the surface of a semiconductor substrate, which is characterized by being removed.

[Industrial applications]

The present invention relates to processing of a semiconductor substrate, and more particularly, to a method of removing a native oxide film on the surface of a semiconductor substrate.

[Conventional technology]

As a method of removing a natural oxide film formed on a semiconductor surface, particularly a silicon surface by dry (dry etching),
Conventionally, it has been performed in each atmosphere of hydrogen gas, fluorine-based gas and chlorine gas.

In the method using hydrogen gas, in a reducing atmosphere of H ₂ to about 10
The native oxide film is removed by exposing the wafer to a high temperature of 00 ° C. However, in this method, the wafer is directly exposed to the high temperature, and the sharpness of the impurity concentration distribution in the wafer is blurred by thermal diffusion, and the semiconductor is exposed to the high temperature. The problem is that the circuit structure is stressed or damaged.

On the other hand, a method using a fluorine-based gas can remove a natural oxide film at a low temperature. However, in this method, not only a natural oxide film on the surface to be removed but also a gate material and a heat for element isolation are removed. The oxide film is also etched. Furthermore, when the reaction chamber is made of quartz, there is a disadvantage that the quartz is also etched and dust is generated.

In addition, even with the method using chlorine gas, the natural oxide film can be removed at a low temperature and the quartz etching is not performed by this method. However, according to this method, the natural oxide film is not completely removed and the semiconductor is not removed. A phenomenon occurs in which only the silicon substrate remains on the substrate surface and only the silicon substrate is gradually etched from the surface. Although the principle of the natural oxide film remaining is not clear, as shown in FIG. 5, the natural oxide film is instantaneously desorbed to the gas phase, but adheres to the substrate surface again due to electronegativity, and is bonded. While chlorine (Cl) and silicon (S
It is considered that i) is bonded to form SiCl ₄ and escape from the substrate.

[Problems to be solved by the invention]

As described above, in the related art, there is a problem that the semiconductor is damaged, the characteristics are deteriorated, and the natural oxide film cannot be sufficiently removed with the removal of the natural oxide film formed on the surface of the semiconductor substrate.

The present invention has been made in view of such a problem, and has as its object to remove a natural oxide film without damaging a semiconductor or deteriorating characteristics.

[Means for solving the problem]

The above-described problem is that in photoetching a semiconductor substrate, the semiconductor substrate is etched by ultraviolet light irradiation by placing the semiconductor substrate in a reduced-pressure atmosphere obtained by adding any one of carbon monoxide and nitrogen monoxide to chlorine gas for a predetermined time, The problem is solved by a method for removing a native oxide film on the surface of a semiconductor substrate, which comprises removing a native oxide film formed on the semiconductor substrate.

[Action]

Since the present invention uses such a method, oxygen radicals O ^* on the surface of the semiconductor substrate are desorbed from the substrate surface by chlorine gas Cl ^* activated by receiving light energy in a reduced pressure atmosphere. The reaction of the oxidized radical O ^* with CO, NO, etc. in the inside is performed, and CO + O ^* → CO ₂ , NO + O ^* → N
By changing to O ₂ or the like, it becomes possible to completely remove oxygen radicals O ^* released from the substrate without remaining on the surface.

〔Example〕

(A) First Embodiment FIG. 1 is a schematic view of an apparatus used in an embodiment of the present invention, in which a silicon substrate 4 is placed on a mounting table 3 provided in a quartz chamber 2 of a reaction apparatus 1. While the inside of the chamber 2 is depressurized by the vacuum pump P, the mounting table 3 is heated by the heater 5, while chlorine gas (Cl ₂ ) and carbon monoxide gas (CO) are flowed into the chamber 2 and emitted from the light source 6. UV light in chamber 2
It is configured to transmit light to the upper part and irradiate the silicon substrate 4.

In the reactor 1, chlorine (Cl ₂ ) becomes a radical Cl ^* under ultraviolet light, and releases oxygen from the SiO ₂ film 4a on the substrate 4. Also, carbon monoxide gas (CO) in the chamber 2
Is an oxygen radical O liberated from the substrate surface by Cl ^{* *}
And become carbon dioxide (CO ₂ ). In this case, the silicon of the substrate 4 is slightly separated.

More specifically, the above-described embodiment will be described. The pressure in the chamber 2 is reduced to 10 to 20 Torr, the mounting table 3 is heated to 100 to 500 ° C., and high-purity chlorine gas is supplied in the chamber 2 to 10 to 100 cc / cm 2.
min, and simultaneously add carbon monoxide gas at 0.1-20cc / 2
Flow at min flow rate. In this state, the substrate is irradiated vertically with ultraviolet light having a wavelength of 200 to 400 nm at an intensity of 10 to 100 mW / cm ² . This state is maintained for 1-2 minutes.

2 (a) to 2 (c) are cross-sectional views showing changes in the state of the silicon substrate surface under the above conditions. According to the above-described method, chlorine gas is converted into chlorine radical Cl under ultraviolet light. ^* (FIG. 2 (a)), which forms a native oxide film (SiO ₂ film) 4a on the surface of the silicon substrate 4.
It was allowed to leave from the surface to an oxygen radical O ^*, then in order to become CO ₂ reacts with carbon monoxide (CO) (FIG. 2 (b)), desorbed oxygen radicals O ^* again silicon substrate 4 No return to the surface. After the oxygen O ^* is desorbed from the surface of the substrate 4, the silicon (Si) of the silicon substrate 4
Reacts with Cl ^* to vaporize into SiCl ₄ and be etched.

FIG. 3 is a characteristic diagram showing a spectrum of the silicon substrate surface with respect to Auger electron energy. In the case where etching is performed by performing the treatment of the present invention (FIG. 3A), the case of the conventional chlorine only (FIG. compared to FIG. (b)), SiO ₂
It was experimentally confirmed that the waveform derived from the film 4a completely disappeared.

FIG. 4 shows the etching depth with respect to light and time. The depth of etching is constant at a certain rate when only chlorine gas (Cl ₂ ) is used. It is considered that this is because the oxygen radical O ^* once released again bonds with Si on the surface due to electronegativity as shown in FIG.

On the other hand, when CO is added to Cl ₂ , T _L on the optical time axis
The etching progresses at a low speed up to the point, and then progresses rapidly (solid line I in FIG. 4). This is the substrate 4 up to the point _TL
The natural oxide film on the surface is etched, and thereafter the substrate 4
Possible for Si to be etched.

(B) Second Embodiment The second embodiment of the present invention is based on the natural condition on the surface of the silicon substrate 4 in a reduced pressure atmosphere containing chlorine gas and carbon monoxide gas under the same conditions as the first embodiment. Although the oxide film 4a is removed, the difference from the first embodiment is that chlorine gas and carbon monoxide gas (CO) are added simultaneously, and after 1 to 5 minutes have elapsed, the supply of carbon monoxide gas is stopped. While stopping first, the chlorine gas is continuously sent for a while.

The supply and stop of the carbon monoxide gas and the chlorine gas are individually adjusted for the following reasons. That is, if the supply of carbon monoxide and chlorine is stopped at the same time after the photoetching treatment is performed in the same manner as in the first embodiment by simultaneously introducing carbon monoxide and chlorine into the reduced-pressure atmosphere, carbon contamination due to carbon monoxide adsorption will occur. This is because it causes the occurrence of. If the chlorine gas continues to flow for a while after the supply of the carbon monoxide gas is stopped, the surface of the silicon substrate 4 is etched by chlorine, and the carbon monoxide adsorbed on the surface of the silicon substrate 4 is also discharged to the outside together with the chlorine gas. Will be removed. As described above, by preventing the adsorption of carbon monoxide on the surface of the silicon substrate 4, carbon contamination such as carbon monoxide becoming a carbide and contaminating the surface of the silicon substrate 4 is prevented.

(C) Other Examples Although only carbon monoxide has been described above, nitric oxide (N
Similar results can be obtained by using O) or an unsaturated oxygen compound gas.

In this case, nitric oxide (NO) combines with O on the surface of the substrate 4 to become nitrogen dioxide (NO ₂ ), and the SiO ₂ film 4a can be removed.

〔The invention's effect〕

As described above, in the present invention, in the photoetching of a semiconductor substrate, carbon monoxide, an unsaturated oxygen compound gas such as nitric oxide is added to a reduced pressure atmosphere of chlorine gas, and the gas is separated by chlorine radicals. Oxygen radicals on the surface of the semiconductor substrate are captured and become carbon dioxide and the like, and a natural oxide film on the surface of the substrate can be completely removed, and further, there is no damage or deterioration of characteristics of the semiconductor.

Further, if photoetching is performed in a reduced pressure atmosphere containing only chlorine at the end of such a process, the substrate surface will be in a better state.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an apparatus used in the present invention, FIG. 2 is a cross-sectional view showing a change in the surface of a semiconductor substrate according to the present invention, and FIG. FIG. 4 is a characteristic diagram of the etching depth with respect to light and time, and FIG. 5 is a cross-sectional view showing the state of the substrate surface according to the conventional method. (Description of symbols) 1 ...... reactor, 2 ...... chamber, 4 ...... substrate, 4a ...... SiO ₂ film, 5 ...... heater, 6 ...... source.

Claims (2)

(57) [Claims] A semiconductor substrate is placed in a reduced-pressure atmosphere in which either carbon monoxide or nitric oxide is added to chlorine gas for a certain period of time to perform etching by irradiation with ultraviolet light, and the natural oxidation formed on the semiconductor substrate is performed. A method for removing a native oxide film on a surface of a semiconductor substrate, comprising removing the film. 2. A semiconductor substrate is placed in a reduced-pressure atmosphere in which one of carbon monoxide and nitric oxide is added to chlorine gas for a predetermined period of time to perform etching by irradiation with ultraviolet light. Removing the natural oxide film formed on the semiconductor substrate by stopping the addition of nitrogen oxide and setting the reduced pressure atmosphere to a chlorine gas atmosphere. .