JPH04308095A - Dry etching method - Google Patents

Abstract

PURPOSE:To selectively etch the silicon in a silicon oxide film without any damage by irradiating a substrate to be treated in a vacuum vessel with a fluorine radical and simultaneously with vacuum UV ray. CONSTITUTION:A substrate 3 to be treated is set in a vacuum vessel 1. The substrate 3 is irradiated with a fluorine radical and simultaneously with UV, and the silicon in a silicon oxide film is selectively etched. The wave length of the vacuum UV ray is controlled to <=150nm or preferably to <=149.4nm. The fluorine radical and vacuum UV are generated by the electron cyclotron resonance plasma using a microwave and a magnetic field. The fluorine radical is supplied by a fluorine atom-contg. gas such as NF3 and SF6. Consequently, the silicon in the silicon oxide film is selectively etched without spoiling vacuum treatment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel dry etching method for selectively etching a silicon oxide film with respect to silicon.

0002

2. Description of the Related Art At present, plasma processing apparatuses for plasma processing a substrate to be processed (hereinafter simply referred to as a substrate) using high frequency glow discharge are widely used in the manufacture of semiconductor integrated circuits. Among these, reactive ion etching (RIE) equipment, which etches a substrate by placing it on a high-frequency application electrode, is widely used in each process of semiconductor device manufacturing because it is capable of anisotropic etching and has excellent mass productivity. It's starting to happen. Particularly, selective etching of silicon oxide films with respect to silicon mostly relies on this RIE at present.

[0003] In order to realize selective etching for silicon, gases such as CF4, CHF3, and C2 are used.
This is done by mixing H2, O2, etc. with a fluorinated hydrocarbon gas such as F6. This reaction mechanism is thought to be because silicon oxide film is etched by CF3 + ion bombardment, whereas silicon is etched by fluorine radicals. Therefore, in order to perform highly selective etching, it is necessary to suppress the generation of fluorine radicals as much as possible. For this reason, for example, methods have been adopted in which H2 is mixed with CF4 or a trace amount of O2 is mixed with CHF3. Furthermore, high-speed etching is difficult unless the energy of ion bombardment, ie, the self-bias voltage of RIE, is increased.

0004

[Problems to be Solved by the Invention] However, in the etching method as described above, fluorocarbon polymers are likely to be generated, and especially after the oxide film is etched, a carbonized layer of silicon may remain on the silicon surface. Due to the high bias voltage applied to the substrate, lattice defects could occur in silicon due to ion bombardment. For this reason,
Frequently, damage occurred to the semiconductor devices being manufactured. In particular, there has been a limit to the production of ultra-super LSI devices with high density patterns and thin diffusion layers. Furthermore, the fluorocarbon polymer adhered badly to the vacuum chamber to be etched and to the electrode surface, requiring a large amount of time for cleaning.

[0005] The present invention has been made to solve these problems, and it is possible to reduce the amount of silicon in a silicon oxide film to silicon without generating any fluorocarbon polymer and hardly applying ion bombardment to the substrate. The purpose of this invention is to provide a dry etching method that achieves selective etching.

[0006]

[Means for solving the problem] Solving the above problems,
The present invention is characterized in that a substrate to be processed is placed in a vacuum container, and the substrate to be processed is irradiated with fluorine radicals and simultaneously irradiated with vacuum ultraviolet light, thereby performing selective etching of silicon in a silicon oxide film. . The wavelength of the vacuum ultraviolet light is 150 nm or less, preferably 149 nm or less.
The thickness shall be 4 nm or less. In addition, the means for generating fluorine radicals and vacuum ultraviolet light may be composed of electron cyclotron resonance (hereinafter referred to as ECR) plasma using microwaves and a magnetic field, or a vacuum ultraviolet light generation lamp and a radical source provided separately. It consists of a means for transporting more radicals. Supply of fluorine radicals by NF3, SF6, F2, CF
4, ClF3 and other gases containing fluorine atoms, and furthermore, vacuum ultraviolet light is generated by adding He to these gases.
, Ne, or other gas capable of emitting vacuum ultraviolet light with a short wavelength may be mixed.

[0007]

[Operation] According to the present invention, there is no need to use a fluorinated hydrocarbon gas that often generates fluorocarbons, and the substrate can be etched without applying a bias voltage to the substrate, resulting in etching with extremely little damage. Not only can this be achieved, but since no fluorocarbon polymer is generated, there is less contamination of the vacuum container, and selective etching of the silicon oxide film with respect to silicon can be achieved with almost no cleaning required.

[0008]

[Embodiment] FIG. 1 shows an ECR apparatus embodying the present invention, in which a substrate 3 is mounted on a substrate support stand 2 inside a vacuum processing chamber 1.
is placed insulated from ground potential. An ECR ion source 4 is attached to the top of the vacuum processing container 1 . The ECR ion source 4 has a structure in which the surrounding area can be cooled with a water cooling jacket 5. Microwaves of 2.45 GHz are introduced into the ECR ion source 4 from a waveguide 7 through a quartz window 6. An electromagnetic coil 8 is installed around the ECR ion source 4 so that a magnetic field of 875 Gauss, which satisfies the ECR conditions, is generated in the ECR ion source 4. An electromagnetic coil 9 is also installed around the substrate support stand 2, and serves to irradiate the obtained ECR plasma perpendicularly to the substrate surface.

To operate this, a silicon wafer to which a silicon oxide film patterned with photoresist is attached is placed on a substrate support 2 as a substrate 3, and after the vacuum processing chamber 1 is evacuated to a high vacuum in advance, NF3 gas is introduced into the ECR ion source 4 through the gas introduction pipe 10, and the pressure inside the vacuum processing container 1 is maintained at 5×10 −4 torr or less. Next, an optimum direct current is applied to the electromagnetic coils 8 and 9, and microwaves are introduced into the ECR ion source 4 through the waveguide 7. As a result, F radicals are generated by the NF3 ECR plasma, and at the same time, 149.
Vacuum ultraviolet light of 2 nm and 120.1 nm is generated, and the substrate is irradiated with F radicals and vacuum ultraviolet light. The energy of this vacuum ultraviolet light is the bond energy of Si and O, 8.3 eV (
(equivalent to the wavelength of light of 149.4 nm),
The bond between Si and O becomes weaker, and due to the incidence of F radicals,
The silicon oxide film can be easily etched even without the effect of ion bombardment. Silicon is also etched at the same time by F radicals, but S
The etching rate of i tends to decrease rapidly, and 1×
At a pressure of 10-4 torr or less, the etching rate of the silicon oxide film becomes faster than the etching rate of silicon, and selective etching of the silicon oxide film can be realized. At this time, since no bias voltage is applied to the substrate and it is at a floating potential, the substrate is not bombarded by ions generated by the ECR plasma.

Furthermore, the gas is carbon-free NF3.
Since a gas is used, and even if the gas contains carbon, selective etching can be achieved under conditions in which fluorocarbon polymers are not generated, so the substrate and the vacuum processing chamber 1 are not contaminated with fluorocarbon polymers. Therefore, no damage is caused, and the vacuum processing container 1 and EC
It is possible to realize selective etching of the silicon oxide film with respect to silicon without requiring cleaning of the R ion source 4.

FIG. 2 shows the example of FIG. 1, and shows how the selectivity ratio of silicon to the silicon oxide film changes when a rare gas is added to the NF3 gas. In the figure, a curve 21 shows the case when He gas is added, and a curve 22 shows the case when Ne gas is added. In both cases, the selectivity ratio tends to increase as the concentration of rare gas increases. In particular, when He gas is added, the selectivity is significantly improved. This is because the vacuum ultraviolet light of He emitted from the ECR plasma has a wavelength of 58.4 nm, which is high in energy. Since Ne also emits vacuum ultraviolet light at 73.6 nm, the selectivity improves as more Ne is added. As in this embodiment, by adding a gas that generates high-energy vacuum ultraviolet light, the selectivity can be further improved. In this case as well, this added gas does not generate fluorocarbon polymers and there is no ion bombardment on the substrate, so there is no damage and the silicon oxide film is highly selective to silicon without the need for cleaning. Etching can be achieved.

FIG. 3 shows another apparatus in which the present invention is implemented, in which a hydrogen discharge tube or a rare gas discharge tube lamp such as He is used as the vacuum ultraviolet light generation source, and a lamp separated from the vacuum processing vessel is used as the F radical source. This is an example using another radical source placed at the same location. In the figure, 11 is a hydrogen discharge tube for generating vacuum ultraviolet light, and the vacuum ultraviolet light is introduced into the vacuum processing container 1 through a lithium fluoride window 12 and irradiated onto the substrate 3. A raw material gas for generating fluorine radicals such as NF3 is introduced into the radical source 13 via the gas introduction pipe 10. The radical source 13 is coupled to the waveguide 7 and absorbs microwaves generated by the magnetron 14 to generate NF3 plasma inside the radical source 13.

[0013] The F radicals generated in the radical source 13 are transported to the vacuum processing vessel 1 through the transport pipe 15 and irradiated onto the substrate 3, and at the same time, the vacuum ultraviolet light generated in the hydrogen discharge tube 11 is irradiated onto the substrate 3 through the window 12. . As a result, selective etching of the silicon oxide film relative to the silicon of the substrate 3 can be performed in a clean atmosphere without damaging the substrate 3 due to the interaction between the vacuum ultraviolet light and the F radicals.

[0014] In this example, N is used as a supply source of F radicals.
Although F3 gas is used, the gas is not limited to this, and it goes without saying that any gas that can supply fluorine, such as F2, SF6, ClF3, and HF, may be used. Of course, it is also possible to use a fluorocarbon-based gas such as CF4, but in this case, it is preferable to use an oxidizing atmosphere that does not generate fluorocarbon polymers, such as an atmosphere mixed with oxygen gas.

[0015] Although ECR plasma, a hydrogen discharge tube, a microwave plasma generator, etc. were used as the generation source of vacuum ultraviolet light and F radicals, these generation methods are not limited to these. The structure of the plasma source may be changed to a method using a multi-pole magnet, or the strength of the magnetic field may be increased to 875.
Needless to say, the intensity may be twice that of Gauss, or even magnetron discharge or discharge using ordinary parallel plate electrodes may be used instead of ECR discharge. In short, any structure is sufficient as long as it can efficiently generate vacuum ultraviolet light and F radicals and irradiate the substrate.

In this example, the wavelength of vacuum ultraviolet light is set to NF
3, He, Ne, H2, etc. We selected a specific wavelength generated from plasma such as He, Ne, H2, etc., but this wavelength should be 150 nm or less, preferably with the bond energy of Si and O (149.4 nm in wavelength).
It goes without saying that any wavelength of light may be used as long as it has an energy of more than ).

In addition, in this example, a bias voltage was not applied to the substrate to attract ions, but if the damage to the substrate is not a problem, the substrate may be actively biased. It goes without saying that the etching rate of the silicon oxide film may be further improved.

Furthermore, in this example, the substrate was not actively heated or cooled, but it goes without saying that it is also possible to perform etching while cooling or heating the substrate. .

In particular, by performing etching while cooling the substrate and suppressing the reactivity between silicon and F radicals, it becomes possible to achieve higher selective etching of the silicon oxide film with respect to silicon.

[0020]

[Effects of the Invention] As explained above, according to the present invention,
Selective etching of silicon oxide film to silicon
The effect can be achieved without causing damage and without contaminating the vacuum processing container.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of essential parts of an ECR etching apparatus embodying the present invention.

FIG. 2 is a graph of changes in the selectivity of silicon oxide film to silicon when the mixing ratio of rare gas to NF3 is changed.

FIG. 3 is a cross-sectional schematic diagram of another device implementing the invention.

[Explanation of symbols]

1 Vacuum processing container 2　Board support stand 3 Board 4 ECR ion source 5 Water cooling jacket 6 Quartz window 7 Waveguide 8, 9 Electromagnetic coil 10 Gas introduction pipe 11 Hydrogen discharge tube 12 Lithium fluoride window 13 Radical source 14 Magnetron

Claims (1)

[Scope of Claims] [Claim 1] Selective etching of silicon in a silicon oxide film by placing a substrate to be processed in a vacuum container and irradiating the substrate with fluorine radicals and vacuum ultraviolet light at the same time. [Claim 2] A dry etching method characterized in that the wavelength of the vacuum ultraviolet light is 150 nm or less,
The dry etching method according to claim 1, wherein the wavelength is preferably 149.4 nm or less.Claim 3: The means for generating fluorine radicals and vacuum ultraviolet light is an electron cyclotron resonance plasma using microwaves and a magnetic field. 4. The dry etching method according to claim 1, wherein the means for generating vacuum ultraviolet light is a vacuum ultraviolet light generating lamp, and fluorine radicals are introduced into the vacuum container from a radical generation source other than the vacuum container in which the substrate is placed. 5. The dry etching method according to claim 1, characterized in that the fluorine radicals are supplied by NF3, SF6.
The dry etching method according to claim 1, characterized in that the dry etching method is carried out using a gas containing fluorine atoms such as , F2, CF4, ClF3.
The dry etching according to claim 3, characterized in that the dry etching is carried out by mixing a gas containing fluorine atoms such as , F2, CF4, ClF3, etc. with a gas capable of emitting short wavelength vacuum ultraviolet light, such as He, Ne, etc. Method