JPH077760B2 - Semiconductor oxidation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for oxidizing a semiconductor, and more particularly to a method for forming an oxide film on a surface layer of a semiconductor.

[Conventional technology]

In recent semiconductor device manufacturing processes, oxide film formation has become an indispensable technique.

Conventionally, as a method for forming an oxide film on a semiconductor substrate such as a silicon substrate in the manufacturing process of a semiconductor device, for example, a method using thermal oxidation such as dry oxidation or steam oxidation, or a vapor phase growth method is known. There is.

However, demand for improved yields due to technological advances,
There is a demand not only for planarization but also for three-dimensional miniaturization, and as a technology to meet these demands, a method of forming an oxide film at low temperature quickly and with high precision is required, and as an example of responding to this, semiconductors such as excimer laser A short-wavelength pulse laser that is absorbed by the surface layer of the substrate and instantly heats this surface portion is irradiated to the semiconductor substrate in an oxygen atmosphere while keeping the inside of the semiconductor substrate at a low temperature, and an oxide film is rapidly formed on the surface portion. In addition, there is known a method of forming an oxide film so as to prevent the occurrence of such distortion on the inner side.

[Problems to be solved by the invention]

As described above, the short-wavelength pulse laser has an advantage that an oxide film can be formed at high speed and that oxidation can be performed at low temperature without damaging the inside of the substrate.
However, if the atmosphere is oxygen O ₂ , the surface oxidation reaction rate is slow, and not only the performance of the short-wavelength laser cannot be sufficiently drawn out, but also because the oxidation reaction is carried out instantaneously and at a low temperature, SiO and SiO ₂ There is also a possibility that a non-uniform oxide film that coexists with is formed.

In view of such problems, it is an object of the present invention to provide a method for forming an oxide film uniformly and at high speed on the surface layer of a semiconductor.

[Means for solving problems]

The present invention relates to a semiconductor substrate disposed in a strong oxidizing gas, an energy beam having a first wavelength for heating the substrate, and a second wavelength having energy capable of photolyzing the strong oxidizing gas. The surface of the semiconductor substrate is oxidized by the oxygen atoms in the photolyzed excited state by irradiating the above energy beam, and the above-mentioned problems are solved by this.

At this time, the energy beam of the first wavelength and the energy beam of the second wavelength are preferably irradiated from a direction substantially perpendicular to the substrate surface of the semiconductor substrate, and the energy beam of the first wavelength is 1130 nm. The following energy beam and the energy beam having the second wavelength are preferably energy beams having a wavelength of 260 nm or less.

[Action]

The semiconductor substrate is irradiated with the energy beam of the first wavelength to be preheated, and the strongly oxidizing gas absorbs the energy beam of the second wavelength to dissociate or further electronic system of constituent atoms of the strongly oxidizing gas. In the photoexcited state, the constituent atoms of the strongly oxidizing gas in the excited state and the constituent atoms of the semiconductor substrate easily oxidize, so that an oxide film is uniformly and rapidly formed.

〔Example〕

 A preferred embodiment of the present invention will be described with reference to the drawings.

In the first embodiment, as shown in FIG. 1, a mixture gas of ozone and oxygen is used as a strong oxidizing gas (O ₂ gas with a partial pressure of 0.5 atm and 1%).
Mixed gas containing O ₃ gas and O ₂ gas having a partial pressure of 0.5 atm) is used, and a KrF excimer laser (wavelength 249 nm) is used as a light source for photodecomposing the gas.

First, in this example, a laser beam a of a XeF excimer laser (wavelength 350 nm) for heating the substrate in advance is applied to the silicon substrate 2 arranged in the reaction chamber 3 of the oxide film forming apparatus 1 through the quartz window 4. This XeF excimer laser is a pulse laser, and the laser beam a of the XeF excimer laser is irradiated from above in the figure to heat the surface layer portion of the silicon substrate 2. This preheating is carried out below about 900 ° C., so that no thermal distortion occurs inside the substrate.
Furthermore, before and after heating the surface layer of the silicon substrate 2,
A mixed gas of ozone and oxygen, which is a strong oxidizing gas that photolyzes and rapidly oxidizes the surface layer of the silicon substrate 2, is sent to the reaction chamber 3. By sending this mixed gas, the atmosphere in the reaction chamber 3 becomes the mixed gas, and the mixed gas in the reaction chamber 3 of the oxide film forming apparatus 1 is provided as a separate beam.
The laser beam b of the KrF excimer laser is irradiated.

The laser beam b of the KrF excimer laser photolyzes or photoexcites oxygen atoms which are the constituent atoms of the mixed gas in the atmosphere of the reaction chamber 3. Then, the oxygen atoms of this mixed gas become the laser beam a of the XeF excimer laser.
By easily combining with the Si atoms that are the constituent atoms of the silicon substrate 2 preheated by, an oxide film is rapidly formed on the surface layer portion of the silicon substrate 2.

Explaining this reaction, as shown in FIG. 2, there is a relationship between the strong oxidizing gas and the wavelength of the energy beam irradiated and the relationship between the silicon substrate and the wavelength of the energy beam irradiated. Regarding the relationship between the gas and the wavelength of the energy beam to be irradiated, when O ₃ gas is contained as the strongly oxidizing gas as in this first embodiment, By the photolysis, the excited oxygen atom O ^* is generated, and the generated excited oxygen atom O ^* has a strong oxidizing power, so that a rapid oxidation reaction can be realized.

Next, regarding the wavelength dependence of the absorption spectrum of ozone contained in the mixed gas, it has been shown that light absorption occurs efficiently at 249 nm which is the wavelength of the KrF excimer laser, as shown in FIG. It can be seen that the quantum efficiency of photolyzing ozone at the wavelength to generate excited oxygen atoms is also excellent as shown in FIG. Therefore, irradiating ozone with the laser beam b of the KrF excimer laser efficiently supplies oxygen atoms that have been photodecomposed and activated by excitation, which is a factor for high-speed formation of an oxide film.

Regarding the relationship between the wavelength of the energy beam irradiated to the silicon substrate and the wavelength of the energy beam used to heat the silicon substrate 2, the energy beam having a wavelength of about 1130 nm or less means that only the surface layer of the silicon substrate can be efficiently used. Necessary for heating. The preheating described in the first embodiment is performed by the laser beam a of the XeF excimer laser which directly irradiates the silicon substrate 2 as described above.
The wavelength of this laser beam a is
350 nm. Therefore, only the surface layer of the silicon substrate 2 can be efficiently heated by the laser beam a of the XeF excimer laser used in the first embodiment, and since the photolysis and the heating are different light sources, the oxide film The thickness control is also accurate. In addition, depending on the direction of the light beam to be irradiated, a region where photolysis or photolysis occurs can be wide in the vicinity of the surface layer portion, and an oxide film can be efficiently formed. Furthermore, by controlling the amount of energy, thermal strain does not occur inside the substrate,
On the contrary, when the amount of energy is increased, only the surface layer portion can be melted and rapidly oxidized.

The laser beam for photolysis used in the first embodiment is not limited to the KrF excimer laser as long as it is an energy beam having a wavelength of 320 nm or less in an ozone mixed gas atmosphere, and any energy beam may be used. Good. Further, the XeF excimer laser for heating is not limited to this, and any pulsed laser having a wavelength of 1130 nm or less may be used. It may be an energy beam.

In the first embodiment, the silicon substrate 2 is not directly irradiated with the laser beam a having photolytic energy. However, when the energy beam having photodecomposable energy is applied to not only the strongly oxidizing gas but also the substrate, heating is performed as in the relationship between the silicon substrate and the wavelength of the energy beam shown in FIG. A phenomenon such as a break in the bonding between the constituent atoms of the substrate or the substrate occurs. Then, the bonding film between the constituent atoms of the substrate can be used to more rapidly form the oxide film. That is, when the substrate is a silicon substrate, the second
As shown in the figure, these phenomena occur at a wavelength of 1130 nm or less for heating and at a wavelength of 260 nm or less for the breaking of bonding between constituent atoms of the substrate, respectively, and combine these with the above photolytic action. This can cause a more rapid oxidation reaction.

The second embodiment of the present invention uses a mixed gas of ozone as the strong oxidizing gas as in the first embodiment, and when the energy beam wavelength is 260 nm or less, the bond cutting between Si atoms which are the constituent atoms of the substrate is performed. The wavelength of 26
This is an example in which a KrF excimer laser (wavelength 249 nm) is used as an energy beam of 0 nm or less, and bonding cutting between atoms and photolysis of the above mixed gas are combined.

First, in the example shown in FIG. 5, the laser beam c of the KrF excimer laser irradiates the silicon substrate 12 arranged inside the reaction chamber 13 of the oxide film forming apparatus 11 through the quartz window 14. The above mixed gas, which is a photodecomposable strong oxidizing gas, is sent to the reaction chamber 13 as an atmospheric gas. Kr
The laser beam c of the F excimer laser is applied to the silicon substrate 12, and the surface layer of the silicon substrate 12 is heated to 900 ° C.
Simultaneously with preheating below, at the surface layer portion of the silicon substrate 12, bonding atoms of Si atoms which are constituent atoms of the silicon substrate 12 are cut. Further, the laser beam c of the KrF excimer laser is also absorbed by the mixed gas of ozone and oxygen, which is a strongly oxidizing gas, as in the first embodiment, and the photodecomposition occurs due to this light absorption. Generates an excited oxygen atom O ^* . Then, the oxygen atoms O ^{* in the} excited state and the bonding-cut Si atoms are easily bonded to form an oxide film at a higher speed than general SiO ₂ film formation.

In the second embodiment, not only the action of mere photolysis as in the above-described first embodiment, but also the bonding cut Si atom and the excited oxygen atom generated by the photolysis are easily bonded. The oxide film formation mechanism can be quickly formed by extracting the performance of the energy beam due to the combined action of, and further, preheating, bonding cutting and photolysis are performed using a single light source. Is simple and has an advantage on the device.
Further, since the energy is supplied only to the surface layer portion, no strain is generated inside the substrate, and only the surface layer portion of the substrate can be melted to form the oxygen film at a higher speed.

The KrF excimer laser that causes the above-mentioned preheating, bonding cutting, and photolysis is not limited to this.
Any energy beam having a wavelength of 60 nm or less may be used, and another energy beam for heating only the surface layer portion for preheating may be used.

Next, a third embodiment of the present invention will be described. The third embodiment is a method of forming an oxide film by the same method as the second embodiment, but is an example in which a low pressure mercury lamp is used as a light source.

As shown in Fig. 6, a low-pressure mercury lamp (wavelength: 235 nm) is used as an energy beam that uses a mixed gas of ozone as a strong oxidizing gas and causes photolysis and cuts the bonding of Si atoms that are the constituent atoms of the substrate. The beam d of the low-pressure mercury lamp irradiates the silicon substrate 22 and ozone, which is a strong oxidizing gas. When using this low pressure mercury lamp,
Since the low-pressure mercury lamp itself lacks the amount of energy for preheating the surface layer of the silicon substrate 22, a separate beam for preheating is required. ) Is used.
The other beam for preheating is not limited to this, and Xe
The wavelength of Cl excimer laser or Ar laser is 1130nm
The following energy beams can be used for preheating.

The method of forming an oxide film according to the third embodiment is performed according to the second embodiment, and the generation of excited oxygen atoms by photolysis by irradiating the ozone mixed gas with the beam d of the low-pressure mercury lamp, Silicon substrate 22 of beam d of low-pressure mercury lamp
Bonding cutting of Si atoms in the surface layer portion of the silicon substrate 22 by irradiating the surface of the silicon substrate 22 and the oxygen atoms in the excited state and Si atoms are easily bonded, whereby an oxide film can be formed at high speed.

Next, as a fourth embodiment, a YAG laser beam (wavelength 106
An example using a second or higher harmonic wave of 5 nm) will be described.

Since the fourth harmonic of the YAG laser beam has a wavelength of about 266 nm, photolysis of ozone gas can be caused when a mixed gas of ozone is used as the strong oxidizing gas. As shown in FIG. 7, the fourth harmonic wave e of the YAG laser beam is applied to the mixed gas of ozone, which is the atmospheric gas of the silicon substrate 32, to generate excited oxygen atoms from the optical absorption of this ozone gas. . Then, the oxygen atoms in the excited state are easily combined with Si atoms, which are the constituent atoms of the silicon substrate 32, to quickly form an oxide film. Also in the case of this embodiment, another energy beam can be used for preheating the substrate, and an energy beam for cutting the bonding of Si atoms in the surface layer portion of the silicon substrate 32 having a wavelength of 260 nm or less, or , Energy beams that melt the surface layer of the silicon substrate 32 can be combined.

Finally, as a fifth embodiment, an example using a laser beam f of an XeCl excimer laser (wavelength 308 nm) will be described.

Similar to the above example, using the above mixed gas of ozone and oxygen as a strong oxidizing gas photodecomposable into the gas of the atmosphere,
The laser beam f of the XeCl excimer laser is used as an energy beam for photodecomposing this mixed gas and heating the silicon substrate 42, with an energy amount of 500 mJ / cm ² , a pulse width of 35 ns, and a total of 800 pulses with 10 pulses per second. In the case of irradiating with, the oxide film could be formed at about twice the oxidation rate as compared with the case of using only oxygen gas as the atmosphere gas.

Although the strong oxidizing gas used in each of the first to fifth embodiments is a mixed gas of ozone, the strong oxidizing gas is not limited to this, and for example, NO gas may be used. , N ₂ O gas, NO ₂ gas and halogen Cl ₂
Gas such as CCl ₄ or SF ₆ , or a combination thereof, and any gas that can photolyze and easily bond with the constituent atoms of the substrate when irradiated with an energy beam. Good. Also, the energy beam can be selected according to the strongly oxidizing gas,
These relationships can be selected or combined depending on the wavelength, that is, in terms of the functions of heating, photolysis and bond cutting. As an example, as shown in FIG.
NO ₂ gas, when using the N ₂ O gas and O ₂ gas, NO ₂
Is 244 nm or less, N ₂ O is 230 nm or less, and O ₂ is photolytically decomposed with an energy beam having a wavelength of 175 nm or less, so for example, for O ₂ , use a Xe resonance lamp, F ₂ excimer laser, ArF excimer laser, etc. It is possible,
For N ₂ O, ArF excimer laser, deuterium lamp, low pressure mercury lamp, etc. can be used, and for O ₃ mentioned above, KrF excimer laser, low pressure mercury lamp, deuterium lamp, XeCl excimer laser, etc. can be used. It is possible to perform photolysis with these energy beams and easily bond with constituent atoms of the substrate.
Furthermore, as the energy beam, higher harmonics of various laser beams can be used, and an electron beam or an ion beam may be used.

Further, the substrate is not limited to the above-mentioned silicon substrate, a germanium substrate or a substrate of a compound semiconductor such as GaAs, InP, GaP, a substrate of a metal such as Ta, Mo, Al, GaAs,
In the case of a substrate such as InP or GaP, the oxide film can be formed quickly without generating arsenic or phosphorus inside the substrate.

〔The invention's effect〕

According to the method for forming an oxide film of the present invention, an oxide film is formed without giving thermal strain to the inside of the substrate, and the activated oxygen atoms are removed from the silicon substrate by photolysis of the strong oxidizing gas. Since it can be bonded to Si atoms and the like, a high-speed and high-quality oxide film can be formed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method of photodecomposing with a KrF excimer laser of the first embodiment of the present invention to form an oxide film, and FIG. 2 is a relationship between the wavelength of an energy beam and its function with respect to a silicon substrate. FIG. 3 is a diagram showing the relationship between the wavelength of the energy beam and the photolysis of the strongly oxidizing gas, and FIG. 3 is a characteristic diagram showing the light absorption spectrum of ozone,
FIG. 4 is a characteristic diagram showing the wavelength dependence of the quantum efficiency of photodecomposing ozone to produce excited oxygen, and FIG. 5 is a graph showing the silicon atoms of the KrF excimer laser of the second embodiment of the present invention. It is a schematic diagram explaining the oxide film forming method by the method of performing bonding cutting and photolysis of ozone mixed gas of strong oxidizing gas, and FIGS. 6 to 8 are the third embodiment and the fourth embodiment, respectively. 9A and 9B are schematic diagrams when another light source for explaining the fifth embodiment is used. 2, 12, 22, 32, 42 ... Silicon substrate a ... XeF excimer laser laser beam b, c ... KrF excimer laser laser beam d ... Low-pressure mercury lamp beam e ... YAG laser beam fourth order Harmonics f …… Laser beam of XeCl energy beam

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-51-25967 (JP, A) JP-A-51-147177 (JP, A) JP-A-59-75636 (JP, A) JP-B-37- 10258 (JP, B1) JP-B 42-19029 (JP, B1) JP-B 44-15737 (JP, B1)

Claims (3)

[Claims] 1. A semiconductor substrate disposed in a strong oxidizing gas, an energy beam of a first wavelength for heating the substrate, and a second beam having energy capable of photolyzing the strong oxidizing gas. A method of oxidizing a semiconductor by irradiating an energy beam of a wavelength and oxidizing the surface of a semiconductor substrate with oxygen atoms in a photolyzed excited state. 2. The energy beam of the first wavelength and the energy beam of the second wavelength are irradiated from a direction substantially perpendicular to the substrate surface of the semiconductor substrate. Semiconductor oxidation method. 3. The energy beam of the first wavelength has a wavelength of 1130.
2. The method for oxidizing a semiconductor according to claim 1, wherein the energy beam having a wavelength of nm or less and the energy beam having the second wavelength is an energy beam having a wavelength of 260 nm or less.