JP2600243B2 - High purity metal deposition method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for depositing a high-purity metal on a substrate such as a semiconductor wafer. A substrate having the metal is placed in a gas space of a metal compound containing the metal as a component, an electric field crossing the surface is applied, and ions of the metal are generated from the metal compound by a multiphoton resonance ionization process. And irradiating the gas space of the metal compound with light having a predetermined wavelength.

[Industrial applications]

The present invention relates to a method for depositing a high-purity metal on a substrate such as a semiconductor wafer.

[Conventional technology]

There has been proposed a method in which a gaseous metal compound is decomposed by irradiating a strong laser beam, and a metal as a decomposition product is deposited on a substrate placed in an atmosphere of the metal compound gas.

This method has an advantage that a technique similar to a normal CVD (chemical vapor deposition) method can be used, and that a thin metal layer can be formed at a low temperature. Further, when the laser beam is irradiated so as to be focused at a point near a predetermined area on the substrate,
Since metal is mainly deposited in this region, when the focal point of the laser beam is moved relative to the substrate, a thin metal layer is formed according to the locus of the focal point. Therefore, a thin metal wire having a predetermined pattern can be formed on a substrate without using a normal photolithography technique.

[Problems to be solved by the invention]

Examples of the gaseous metal compound that can be used in the above method include organometallic compounds such as Ga (CH ₃ ) ₃ (trimethylgallium) and Al ₂ (CH ₃ ) ₆ (trimethylaluminum), and W (CO) ₆ And carbonyls such as Ni (CO) ₆ and fluorides such as WF ₆ and MoF ₆ .

When the above gaseous metal compound is irradiated with a powerful laser beam, the metal compound is not always completely decomposed until an atomic metal is generated.

Taking Ga (CH ₃ ) ₃ as an example, some CH ₃ groups remain, such as Ga (CH ₃ ) ₃ → Ga, GaCH ₃ , Ga (CH ₃ ) ₂ ... (1) Ga atoms are generated.
When such Ga atoms having a CH ₃ group are deposited, carbon atoms and the like are taken into the deposited metal, and the purity of the metal is reduced.

As described above, the present invention provides a method of depositing a metal on a substrate at a low temperature by decomposing a gaseous metal compound by irradiating a laser beam or the like. Is to be deposited.

[Means for solving the problem]

Disposing a substrate having one surface on which a metal is deposited in a gas space of a metal compound containing the metal consisting of atoms in a ground state; On the other hand, a step of irradiating light having a wavelength such that the metal in the metal compound is ionized by a multiphoton resonance ionization process, and the electric field crossing toward the substrate surface causes the metal ion to be applied to the substrate surface. Inducing said metal to deposit on said substrate surface.

(Operation)

With reference to the principle diagram of the present invention shown in FIG. 1, when a gaseous metal compound atmosphere space 2 is irradiated with a powerful laser beam 1 having a predetermined wavelength in a visible region or an ultraviolet region, the metal compound is decomposed, Ionization can occur in a process called photon resonance. Since this process is a resonance reaction, the ion species generated differs depending on the wavelength of the irradiation light. When the wavelength of the laser beam 1 is appropriately selected, the metal in the metal compound is decomposed so as to generate only ions M ⁺ . By applying an electric field having a positive potential to the counter electrode 3 to the space 2, the metal ions M ⁺ are aligned in the direction of the substrate 4 and deposited on the surface of the substrate 4. Since the metal ion M ⁺ does not have a group composed of a different element, a high-purity metal is deposited.

The above multiphoton resonance ionization process in a metal compound gas has been investigated for Ga (CH ₃ ) ₃ by SAMitchell et al. (SAMitchell, et al., J. Chem. Phys., Vol. 8
3, p.5083 (1985)] According to this report, Ga produced by the decomposition reaction of the wavelength of the laser beam and _{Ga (CH 3) 3, GaCH} 3, Ga (CH 3) Relative content such as ion species of ₂ The relationship with the rates is shown in the following table.

As described above, ionization is performed by laser light having a wavelength in a range from ultraviolet light to visible light, and the ratio of generated ionic species changes depending on the wavelength. Noteworthy is wavelength 40
At 8 nm, only Ga ⁺ ions are generated. This is because Ga (CH ₃ )
₃ is completely dissociated into atoms and this Ga
This is because atoms are ionized by a multiphoton resonance process.

 The multiphoton resonance ionization process will be briefly described.

Generally, energy of 6 eV or more is required to ionize atoms. In order to perform this ionization with one photon, ultraviolet rays of 200 nm or less must be irradiated. However, when a strong laser beam is used, an ion beam can be generated even with visible light having a longer wavelength than the above.

That is, as shown in FIG. 3, the photons (hν) in the visible light region having a smaller energy cause the atoms M in the ground state to transition to the excited state M ^*, and the photons in the hν state cause the atoms M in the excited state. There is a process of ionizing M ^* .

Here, when the value of hν is selected as the energy difference ΔE ₁ between the ground state M and the excited state M ^* , the concentration of the excited atoms M ^* increases resonantly, and as a result, the number of generated ions M ⁺ also increases. Increase. Needless to say, the value of hν needs to be larger than the ionization energy ΔE ₂ from the excited state M ^* .

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the following drawings, the same parts as those in the already described drawings are denoted by the same reference numerals.

FIG. 2 is a schematic perspective view showing a schematic configuration of an apparatus for carrying out the present invention.

A parallel plate type counter electrode 3 is provided inside a reaction vessel 11 made of, for example, stainless steel. Similarly, a counter electrode 3 is provided on a susceptor 12 provided inside the reaction vessel 11.
A substrate 4 made of, for example, gallium arsenide (GaAs) single crystal is placed so as to face the substrate. The inside of the reaction vessel 11 is evacuated to a high vacuum through an exhaust pipe 13 by an exhaust system (not shown).

A voltage is applied between the counter electrode 3 and the substrate 4 with the counter electrode 3 being positive,
An electric field of about 300 V / cm is formed toward the substrate 4. Then, Ga (CH ₃ ) ₃ gas is introduced into the inside of the reaction vessel 11 through a gas introduction pipe (not shown), and the pressure becomes, for example, about 1T.
Control so that it is kept at orr. In this case, the reaction vessel 11
And it is not necessary to heat the susceptor 12 in particular.

In the above state, the inside of the reaction vessel 11 is irradiated with the laser light 1 having a wavelength of 408 ° from the light-transmitting window 14 provided at one end of the reaction vessel 11. The laser light 1 is focused by the lens 15 so as to focus on a central portion P between the counter electrode 3 and the substrate 4. As a result, the counter electrode 3 and the substrate 4
Ga (CH ₃ ) existing in the minute space at the focal point P between
_{The three} gases are irradiated with a strong laser beam, and as described above, Ga is completely dissociated into atoms and ionized into Ga ⁺ by a multiphoton resonance process.

The Ga ⁺ ions generated in the minute space are aligned in the direction of the substrate 4 by the electric field between the counter electrode 3 and the substrate 4 and collide with the substrate 4 to lose charge. In this way, the metal Ga is formed in a minute area near the convergence point on the surface of the substrate 4.
Accumulates. Therefore, the susceptor 12 is moved in the X direction or Y direction.
By moving in the direction or in both directions, a thin metal Ga layer having a linear, planar, or predetermined pattern can be formed.

In the present invention, since a multiphoton resonance ionization process is used, a laser light source emitting a selected predetermined wavelength is required. A wavelength-variable dye laser may be used as such a laser light source. Specifically, a known excimer laser or a pulsed dye laser excited by a Nd: YAG laser (for example, FL3001 manufactured by Lambda Physics) can be used. Thereby, the output light wavelength can be selected in the range of about 200 nm to 950 nm.

The energy of the laser beam is controlled to about 3 _× 10 ⁸ W / cm ² ± 50% at the focal point P between the counter electrode 3 and the substrate 4. This energy density can be achieved by focusing the output light of the pulsed dye laser by the lens 15. An energy density higher than the above is not preferable because it causes a discharge in Ga (CH ₃ ) ₃ gas, generates ionic species other than Ga ⁺ , and lowers the purity of Ga due to the inclusion of carbon as described above. .

When the substrate 4 is insulative, a predetermined conductor pattern is formed on the back surface of the substrate 4 in advance, and the counter electrode 3 is formed.
And a voltage is applied. As a result, since the electric field is focused on the conductor pattern, Ga ⁺ is selectively deposited on the conductor pattern.

When utilizing the focusing of the electric field, it is not essential that the laser beam 1 be focused by the lens 15 if a laser light source having a required energy density can be obtained.

Further, the susceptor 12 is controlled to move in the X and Y directions, so that the focal point P of the laser light 1 is relatively moved along the conductor pattern. As a result, this conductor pattern
Ga ⁺ ions are collected, and a high-precision metal Ga pattern is formed.

According to the principle of the present invention, silicon (S
It goes without saying that a thin layer of high-purity Si, Ge or the like can be selectively deposited on the substrate by using i) or a compound gas such as germanium (Ge). And
If the conditions such as the type of substrate, temperature, and deposition rate are appropriately selected, S
There is also a possibility that a thin layer of i, Ge or the like can be epitaxially grown.

〔The invention's effect〕

According to the present invention, a high-purity metal can be deposited on a conductor, a semiconductor, or an insulating substrate at a low temperature of about room temperature in a fine pattern in a planar or linear shape. Therefore, it is possible to selectively form a fine pattern made of a metal or a semiconductor in a predetermined region of a substrate without using a normal lithographic technique, and there is an effect of providing a new method of manufacturing a semiconductor device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part for explaining the principle of the present invention, FIG. 2 is a schematic perspective view showing a schematic configuration of an apparatus for carrying out the present invention, and FIG. 3 is a diagram showing a multiphoton resonance ionization process. It is an energy phase diagram for explanation. In the figure, 1 is a laser beam, 2 is a metal compound atmosphere space, 3 is a counter electrode, 4 is a substrate, 11 is a reaction vessel, 12 is a susceptor, 13 is an exhaust pipe, 14 is a window, and 15 is a lens.

Claims (5)

(57) [Claims] A substrate having a surface on which a metal is deposited is provided.
Installing the metal compound containing the metal in the ground state in the gas space of the metal compound containing the metal, and applying the multi-photon resonance ionization process to the gas space of the metal compound containing the metal in the ground state atom in the gas space. Irradiating light having a wavelength to ionize the metal therein; and an electric field crossing toward the substrate surface to guide the metal ions to the substrate surface and deposit the metal on the substrate surface. A method of depositing a high-purity metal. 2. The method according to claim 1, further comprising the step of focusing the light at a predetermined position in the gas space, thereby selectively depositing the high-purity metal on one region of the substrate surface near the predetermined position. The method for depositing a high-purity metal according to claim 1, wherein 3. The method according to claim 1, further comprising the step of: moving the substrate surface relative to the predetermined position in the gas space, thereby depositing the high-purity metal in the region moving on the surface. 3. The method for depositing a high-purity metal according to claim 2, wherein: 4. The method according to claim 1, further comprising the steps of: focusing the electric field on a region on the substrate surface; and moving the region relative to the predetermined position in the gas space. 3. The method for depositing a high-purity metal according to claim 2. 5. The method according to claim 1, further comprising the step of focusing the electric field on one or more regions on the substrate surface to selectively deposit the high purity metal on each of the regions. 2. The method for depositing a high-purity metal according to claim 1.