JPS6144183A - Optical cvd method - Google Patents

Abstract

PURPOSE:To obtain a deposited film almost free from inpurities at a high rate of deposition by feeding two or more kinds of gaseous starting materials in the form of molecular beams, irradiating light for excitation on each of the beams, and carrying out CVD on a substrate placed in a region where the excited molecular beams intersect each other. CONSTITUTION:Gaseous SiH4 22 and gaseous N2O 23 as gaseous starting materials for CVD are introduced into the preliminary chambers 24, 25 of molecular beam generators under about 1Torr pressure. Since a reaction cell 26 for CVD has been evacuated to about 10<-8>Torr pressure, the gases 22, 23 are fed into the cell 26 through pinholes 27, 28 in the form of molecular beams 29, 30. Laser light 31 is irradiated on the beam 29 to dissociate SiH4 into Si and H2, and at the same time, laser light 32 is irradiated on the beam 30 to dissociate N2O into N2 and excited O. Si reacts with O in a region 34 where the beams 29, 30 intersect each other, and SiO2 is deposited on a substrate 1 placed in the region 34.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photo-CVD method, and in particular to a photo-CVD method that improves the utilization efficiency of CVD raw materials.

(Prior art and its problems) Conventionally, compounds are processed by photo-CVD using multiple CVD raw material gases.
In the case of deposition, a method has been adopted in which CVD raw material gas 14 mixed as shown in the if diagram is introduced into reaction cell 11 and light is irradiated through window 12 to perform CVD. For example, Kim (H,M.

Kim) et al.
Asu International e-Conference on
Chemical Paper Deposition (Proceedi)
ngsof the 8th 1n(ernajion
alcon(erence on chemical
In the paper described on pages 258 to 266 of ``vapor deposition'', the cause that determines the deposition rate of 5iOz is that SiH+ and N of the source gas, N! It is stated that the reason is that excited oxygen atoms generated by photodecomposition of O are adsorbed to the wall 15 of the reaction cell 11, resulting in a shortage of necessary excited oxygen atoms. On the other hand, Boyer (P, ni, Bo
yer) et al. Applied Fixtures Letters (Ap
pliedPhysics Letters) Magazine 40
In the paper published on pages 716 to 719 of Vol. 1, Siol was created by irradiating ArF laser light on a mixed gas containing much more N and O than iC and SiH, in order to avoid a shortage of excited oxygen atoms. A method for depositing on substrate 13 is described. However, in this case, excited state oxygen atoms generated by photolysis of N and O are deexcited and N,
recombination to 0, formation of active nitrogen and oxygen compounds, and 8
5i such as the formation of compounds such as iHO=8iH10
A problem occurred in that it was consumed in the process of not forming O1 and was not effectively used for forming 5iO1. Furthermore, NtO is
S10°K deposited 1 to mix more than iH4
There was also the problem that M element was easily mixed in as an impurity.

(Object of the Invention) The object of the present invention is to eliminate the drawbacks of the conventional methods as described above, to efficiently utilize the products necessary to obtain a desired deposited film by irradiation with light, and to eliminate impurities in the deposited film. It is an object of the present invention to provide a novel photo-CVD method that can reduce the

(Structure of the Invention) The present invention supplies at least two source gases among a plurality of CVD source gases used in photo-CVD as independent molecular beams, and irradiates each of the molecular beams with excitation light. This photo-CVD method is characterized in that the excited molecular beams intersect and CVD is performed on a substrate placed in the area where the molecular beams intersect.

(Operation/Principle of the Invention) The present invention solves the problems of the prior art by employing the method described above. When the CVD raw material gas to be used is ejected through a pinhole into a CVD reaction cell evacuated to a high vacuum, a molecular beam is produced in which there is no collision between gas molecules and intermolecular interactions can be ignored.

Therefore, by irradiating the excitation light before each molecular beam intersects, it is possible to eliminate the deexcitation of the excited state necessary for forming a deposited film, the adhesion to the walls of the reaction cell, and the generation of unnecessary substances. Therefore, the products necessary to obtain a desired deposited film can be efficiently utilized, and as a result, a deposited film with few impurities can be obtained at a high deposition rate. Furthermore, since each raw material gas is supplied independently, the optimal wavelength of excitation light can be selected for each raw material gas, so the range of raw material gas selection can be expanded.

In addition, when high-pressure CVD raw material gas is ejected through a pinhole and orifice into a CVD reaction cell that is evacuated to a high vacuum, the raw material gas becomes a hydrodynamic jet and spreads out, causing supersonic molecules to propagate. It becomes a line. Therefore, not only can intermolecular interactions be ignored, but also extremely low temperature raw material gas can be obtained without liquefying or solidifying, making it possible to equalize the energy level of the raw material gas before excitation. Since there is little interaction between the energy levels of the source gas, the laser can easily bring the source gas into the excited state necessary for forming the deposited film.

Therefore, the above-mentioned advantages obtained by using a molecular beam can be further enhanced by using a supersonic molecular beam.

(Example) Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 is a schematic cross-sectional view showing an example of an apparatus implementing the method of the present invention. For example, S10. When depositing on the substrate 21, SiH* gas and N, O gases of about I Torr are introduced into the front chambers 24 and 25 of the molecular beam generator as CvD source gases 22 and 23, respectively.

The CVD reaction cell 26 is evacuated to about 10-' Torr, and the CVD reaction cell 26 is evacuated through pinholes 27 and 28 with diameters of 0.75 made in the front chambers 24 and 25.
The raw material gas exits into molecular beam 26 as molecular beam 29.30. The molecular beams 29 of SiH, and the molecular beams 30 of N and O are irradiated with ArF laser beams 31 and 32 on the way, and SiH4 dissociates into Si and hydrogen, and N20 dissociates into nitrogen molecules and excited oxygen atoms. Then, Si and O react in the molecular beam intersection region 34 to form 5i02, which is deposited on the substrate 21.

The substrate 21 can also be heated with a heater 33.

When KSIH4, N, and O are made into molecular beams as in this example,
The products produced by irradiation with ArF laser light 31.32, especially the excited oxygen atoms that play an important role in the formation of 8i01, collide and de-excite on the way as in the conventional method, and other products. The molecular beam is supplied to the intersection region 34 of the molecular beam without being lost by recombination with the molecular beam.

Furthermore, since molecular beams tend to have directivity, and the CVD reaction cell 26 is always exhausted from the exhaust port 37, photodissociation products may adhere to the walls, and the ArF laser beam 31ν32 may be
The light transmittance does not decrease due to adhesion to the windows 35 and 36 for introducing the light into the reaction cell 26.

Therefore, the excited state oxygen atoms created by ArF laser light irradiation can be used more efficiently than before, and as a result, the amount of N and O used can be reduced compared to before, so the deposited film In this example, 5i01 could be deposited at a rate of about 10 nm/min, and the nitrogen content in the deposited film could be reduced by about 50% compared to the conventional method.

Figure 2 shows an example of using molecular beams.
It is possible to increase the deposition rate by using a supersonic molecular beam. In this case, the front chamber 24 in FIG.
Two supersonic molecular beam generators are used for the CvD raw materials 5jH4, N, and O gases in place of the molecular beam generators consisting of 25 and pinholes 27 and 28. Approximately 500
Torr of SiH4 and about 600 Torr of N and O were passed through a nozzle with a diameter of Q, l nut at about 10”Torr.
It is ejected into the front chamber 24.25 which is exhausted to rr. Next, in order to take out the supersonic molecular flow out of the ejected molecular flow, a skimmer with an inverted horn-shaped opening with a diameter Q and 55 m is attached to the pinhole 27.28, and the entire skimmer is passed through the CVD reaction cell 26. By spouting it into the inside of
Supersonic molecular beams of H4, N, and O are obtained. Since the supersonic molecular beam is generated by introducing a gas of several hundred Torr into the front chamber 24125, the number density is thicker than that of a molecular beam. In addition, supersonic molecular beams are generated by adiabatic expansion, so the molecules are approximately 4
Since it is cooled down to K and the internal energy state is well aligned, the energy states of the products formed by laser irradiation are also well aligned, and the products can contribute to the reaction more efficiently than when using molecular beams. can. In this case, approximately 60 nm of SiOx could be deposited in 7 minutes.

It is clear that other methods combining molecular beams and supersonic molecular beams are possible.

Further, according to the present invention, the degree of freedom in selecting the raw material gas is increased, and S
iH+ and O2 can also be used. Conventionally, it has been difficult to maintain stable pressure, temperature, and flow rate of a mixed gas of SiH+ and 01. However, in the method of the present invention, SiH
Since 4 and 01 are supplied separately, the above-mentioned difficulty can be avoided.

Also, SiH, F! Irradiate the laser beam and apply Ar to N and O.
As with irradiation with F laser light, the optimum imaging light can be irradiated for each source gas, so the deposition rate of 5iO1 can be further increased.

Note that although this example describes the deposition of 8i0z,
It is clear that the method of the present invention can be widely applied to compounds for which photoCVD is possible. For example, when depositing Si3N4, SiH4 and NH are used as CVD source gases, and each gas is converted into a supersonic molecular beam. The supersonic molecular beam of SiH, is irradiated with F2 laser light, and the supersonic molecular beam of NH, is irradiated with ArF laser light to deposit Si3N4 on the substrate to a thickness of approximately 70 nm. It could be deposited in minutes. Furthermore, the hydrogen content in the deposited film could be reduced to approximately half that of the conventional method.

(Effects of the Invention) As described above, the optical CVD method using crossed molecular beams of the present invention makes it possible to align the internal energy states of molecules necessary for forming a deposited film, and moreover, it is possible to align the internal energy states of molecules necessary for forming a deposited film. As a result, a deposited film with few impurities can be obtained at a high deposition rate. Furthermore, since the optimum wavelength of light can be selected for each raw material gas, the degree of freedom in selecting the raw material gas can be expanded.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional example, and FIG. 2 is a plan sectional view showing an embodiment according to the method of the present invention.

Claims (1)

[Claims] At least two of a plurality of CVD source gases used in photo-CVD are supplied as independent molecular beams, and each of the molecular beams is irradiated with excitation light to excite the excited molecules. A photo-CVD method characterized by intersecting lines and depositing a product on a substrate placed in the area where the molecular beams intersect.