JP2000150504A - Method and device for forming thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To successively laminate thin films of low substrate temperature, high throughput, and excellent in constant film-thickness by evaporating a solid material by laser ablation method, plasma-exciting a gas material, supplying the material to a substrate surface, and depositing a thin film on the substrate surface. SOLUTION: A GaAs substrate 2 is attached to a susceptor 1 set in a chamber. The substrate 2 is heated and a valve 4 is opened for introducing an oxygen gas. The introduced oxygen gas causes helicon plasma 8 for ionization at a helicon antenna 5 by an electric power applied from an RF power source 6 and the magnetic field generated from a magnetic coil 7. An ArF excimer laser is projected to an Si target 10 through a synthetic quartz optical window 9. Then, Si evaporates from the Si target 10 to generate a plume 11. The plume 11 together with the helicon plasma 8 comes to be a plasma flow 12, which is supplied to the surface of substrate 2 for an SiO2 film to be deposited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for depositing a thin film using a laser ablation method and a plasma excitation method, and more particularly to a method and apparatus for forming a thin film having a high throughput and a uniform film thickness at a low substrate temperature. About.

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor device such as a semiconductor laser or a field effect transistor, a process of forming a dielectric thin film (silicon nitride, silicon dioxide, etc.) has conventionally been mainly performed by a chemical vapor deposition (CVD) method or a reaction method. The reactive sputtering method has been used. In the CVD method, gas molecules supplied as a raw material are decomposed or excited by heat or plasma and used for thin film deposition. When a dielectric thin film is formed by thermal decomposition, the film is formed at a substrate temperature of 400 ° C. or higher. In the method using plasma excitation, the film is formed at a substrate temperature of 250 ° C. or higher.

In the reactive sputtering method, a high-quality film can be formed at around room temperature. However, when different kinds of thin films are stacked, a sample is transferred between a plurality of chambers having different kinds of solid targets.

Recently, as an alternative to the CVD or reactive sputtering method, a plasma deposition apparatus has been proposed (see the product catalog of Enya System Co., Ltd.). In this method, since the solid raw material is evaporated by the electron beam, different kinds of targets can be stored compactly in one chamber. Thus, for example, a silicon oxide film and an aluminum oxide film can be continuously formed in one chamber.

[0005]

Among the above-mentioned prior arts, the CVD method using thermal decomposition requires a high substrate temperature of 400 ° C. or more. Therefore, when a dielectric thin film is formed after an electrode metal forming step of a semiconductor device. In addition, electrical characteristics are significantly deteriorated due to a thermal reaction between the electrode metal and the semiconductor substrate. In the case of the plasma-excited CVD method, it can be formed at a lower temperature than the CVD method by thermal decomposition, but the film quality also decreases as the substrate temperature decreases. In addition, when the semiconductor surface is irradiated with ions in the plasma, defects are likely to occur in the surface layer, and the characteristics of the element are degraded. In the reactive sputtering method, a film can be formed at room temperature. However, when laminating different kinds of thin films, a sample is transferred between a plurality of chambers provided with different kinds of solid targets, so that the throughput is extremely poor.

[0006] In the plasma deposition method, different types of targets are used.
Since it can be housed compactly in one chamber, it is possible to form a stacked film with higher throughput than the reactive sputtering method, but the structure becomes complicated due to the use of electron beams, and the stability when the target is replaced is reduced. There's a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film forming method and a thin film which have a low ion bombardment, can be formed at a low temperature, and have a high throughput in forming a continuous laminated film required in a surface protection step of a semiconductor device. An object of the present invention is to realize a forming apparatus.

[0008]

In the method of forming a thin film of the present invention, a solid and a gas are used as a raw material of the thin film. Laser ablation is used as a means for evaporating the solid raw material. In the laser ablation method, a laser beam focused from the outside of a vacuum chamber is introduced through an optical window and irradiated on a surface of a solid raw material installed in the vacuum chamber, whereby the raw material is released into a gas phase. Since no electron beam filament is used, contamination of the vacuum chamber can be suppressed.
Further, the evaporation amount of the raw material can be controlled stably from outside the vacuum chamber by the intensity and frequency of the laser. Further, a plurality of solid raw materials to be subjected to laser ablation can be loaded in the apparatus, and the change of the solid raw materials is extremely easy, and there is no mutual contamination.

A plume generated by laser ablation and gas molecules introduced from the outside are plasma-excited and irradiated on the surface of a substrate loaded in a vacuum chamber to form a compound thin film on the surface of the substrate.

In this system, different kinds of thin films can be continuously stacked at a high speed by loading a plurality of solid materials to be subjected to laser ablation into the same chamber.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> A first embodiment will be described with reference to FIG. In this embodiment, silicon (Si) and aluminum (Al) are used
A formation method and a formation apparatus for continuously forming a silicon oxide film and an aluminum nitride film on an aAs (001) substrate will be described.

First, the susceptor 1 installed in the chamber
Is loaded with a GaAs (001) substrate 2. The susceptor 2 is provided with a substrate heating heater. The substrate 2 was rotated 10 times per minute by a rotation mechanism. The reactor is evacuated to a vacuum of 3 × 10 ⁻⁸ Torr by a turbo molecular pump (TMP). Next, the substrate 2 is heated by a heater and
Hold at 50 ° C. Subsequently, the valve 4 is opened, and O ₂ gas (flow rate 50 sccm) is introduced. At this time, the degree of vacuum in the chamber is maintained at 1 mTorr. The introduced O ₂ gas is supplied to the helicon antenna 5 with an electric power of 500 W applied from an RF power source (13.56 MHz) 6 and a magnetic field 5 generated from a magnetic coil 7.
Helicon plasma 8 is generated by 0 Gauss and is ionized. At this time, the degree of vacuum was 5 × 10 ⁻⁴ Torr. Subsequently, an ArF excimer laser (wavelength 193 nm, intensity 1 J
/ Cm ^{2 at} a frequency of 100 Hz) is applied to the Si target 10 through the optical window 9 made of synthetic quartz. At this time, Si evaporates from the Si target 10 and a plume 11 is generated. The plume 11 becomes a plasma flow 12 together with the helicon plasma 8 and is supplied to the surface of the substrate 2 to deposit an SiO ₂ film. At this time, nitrogen gas was introduced through the bulb 13 for the purpose of preventing the deposition of the thin film on the synthetic quartz optical window 9.

The deposition rate under the above film formation conditions is 40 nm
/ Min. Further, when the composition of the film was analyzed by the RBS method, it was found that the SiO ₂ film had a substantially stoichiometric composition. When a film is formed by a normal sputtering method, argon of% order is mixed as an impurity,
Since the SiO ₂ film formed in this example did not use argon for the reaction system, the content of argon was below the detection limit.

After the SiO ₂ film is formed by the above method, the target is changed from Si to the Al target 14, and the gas supplied to the helicon plasma is changed from oxygen to nitrogen to easily form the SiO ₂ film on the SiO ₂ film. Continuously Al
An N film can be formed. The etching rate of this AlN film with hydrofluoric acid was almost zero. The refractive index is 2.05, and the single crystal A formed by MOCVD
It was almost equivalent to the 1N film. The absorption edge wavelength was 250 nm or less. That is, the laser light of the red laser (650 nm) and the blue-violet laser (410 nm) is not absorbed. The film composition was examined using Rutherford backscattering. The ratio of Al to N was approximately 1 to 1, and the concentration of other impurities was 1% or less.

In an experiment in which two types of films continuously formed by the above method were respectively deposited on an InP substrate, a GaAs substrate, a sapphire substrate, and a Si substrate, a film thickness of 800
No cracks or the like were observed up to nm.

Further, a SiO ₂ film (thickness: 300 nm) / A
When a sample on which a two-layered 1N film (500 nm thick) was deposited was subjected to a humidification test at 85 ° C. and a humidity of 100 ° C. for 200 hours, no crack or peeling occurred on any of the substrates. Was.

In this embodiment, the method of forming the SiO ₂ film and the AlN film has been described. However, it is possible to continuously deposit various oxide films and nitride films by changing the kind of gas supplied to the helicon plasma. SiN / AlN or SiO
_No peeling occurred in the above test in the laminated structure of any of the films of ₂ / SiN and Al ₂ O ₃ / AlN: H.

<Embodiment 2> A second embodiment will be described with reference to FIG. In the present embodiment, silicon (Si) and aluminum nitride (AlN) are used
a silicon oxide film and hydrogenated Al on an As (001) substrate
A forming method and a forming apparatus for continuously forming an N film will be described. As in the first embodiment, first, a GaAs (001) substrate 2 was loaded on a susceptor 1 installed in a chamber, and the substrate 2 was rotated 10 times per minute by a rotating mechanism. The reactor is evacuated to a vacuum of 3 × 10 ⁻⁸ Torr by a turbo molecular pump (TMP). Next, the substrate 2 is heated by a heater and kept at 150 ° C. Subsequently, the valve 4 is opened, and O ₂ gas (flow rate 50 sccm) is introduced. At this time, the degree of vacuum in the chamber is maintained at 1 mTorr. Next, the helicon plasma 8 of oxygen is generated and ionized by the electric power 500 W applied from the RF power source (13.56 MHz) 6 to the helicon antenna 5 and the magnetic field 50 gauss generated from the magnetic coil 7. At this time, the degree of vacuum was 5 × 10 ⁻⁴ Torr. Subsequently, an ArF excimer laser (wavelength 193n)
m, intensity 1 J / cm ² , frequency 100 Hz) is applied to the Si target 10 through the synthetic quartz optical window 9. At this time, Si evaporates from the Si target 10 and the plume 1
1 is generated. The plume 11 is supplied to the surface of the substrate 2 as a plasma flow 12 together with the helicon plasma 8,
An SiO ₂ film is deposited.

Next, a method for continuously forming a hydrogenated AlN film will be described. After the formation of the SiO ₂ film, the target is changed from Si to the AlN target 15, and the gas supplied to the helicon plasma is changed from oxygen to hydrogen.
The AlN is evaporated by excimer laser irradiation and supplied to the surface of the substrate 2 together with the helicon plasma of hydrogen to form a hydrogenated AlN film. The deposition rate of this hydrogenated AlN film was 30 nm / min. Hydrogen content is 10%
And it was found from the result of X-ray diffraction that it was in an amorphous state. The refractive index is 2.03 and Al
It was almost equivalent to the N film. The absorption edge wavelength was 250 nm or less. That is, the laser light of the red laser (650 nm) and the blue-violet laser (410 nm) is not absorbed.

The hydrogenated AlN formed by the above method (AlN
H) In an experiment in which a film was deposited on an InP substrate, a GaAs substrate, a sapphire substrate, and a Si substrate,
No crack or the like was observed up to 000 nm.

A sample on which a two-layer film of a SiO ₂ film (thickness: 300 nm) / a hydrogenated AlN film (thickness: 700 nm) was deposited was subjected to a humidification test at 100 ° C. for 200 hours under a condition of 85% humidity. As a result, on any substrate,
No cracking or peeling occurred.

<Embodiment 3> FIG. 2 shows a third embodiment of the present invention.
This will be described with reference to FIG. In this embodiment, the present invention is applied to a 0.98 μm-band high-power semiconductor laser for exciting a rare-earth-doped optical fiber amplifier used for a repeater or a receiver in an optical transmission system. FIG. 2 shows a planar structure of a semiconductor laser having a Fabry-Perot resonator, and FIG.
3A shows a sectional structure, and FIG. 3B shows an enlarged view of the active layer.

Next, a method of manufacturing the device will be described. n
A GaAs buffer layer 406 on a GaAs substrate 405,
N-InGaP cladding layer 40 lattice-matched to GaAs
_{7, In 1-x Ga x} As y P 1-y barrier layers (x = 0.82, y =
0.63, barrier layer thickness 35 nm) 417 and In _z Ga _{1 -z} As
A strained quantum well active layer 408 composed of a strained quantum well layer (z = 0.16, well layer thickness 7 nm) 418, a p-InGaP cladding layer 409 lattice-matched to a GaAs substrate, p-G
aAs optical waveguide layer 410, p- lattice matched to GaAs
The InGaP cladding layer 411 and the p-GaAs cap layer 412 are sequentially formed by the MOVPE method, the gas source MBE method, or the CBE method.

Next, a ridge as shown in FIG. 3A is formed by a photoetching process using the oxide film as a mask.
Etching at this time is wet, RIE, RIBE,
Any method such as ion milling can be used. Etching is P-
The GaAs optical waveguide layer 410 is completely removed, and stops in the middle of the p-InGaP cladding layer 409 so as not to reach the strained quantum well active layer 408.

Next, as shown in FIG. 3A, the n-InGaP current confinement layer 413 is selectively grown by MOVPE using the oxide film used as an etching mask as a mask for selective growth. Thereafter, the wafer is taken out of the growth furnace, and the oxide film used as the selective growth mask is removed by etching. After that, the p-GaAs contact layer 414 is
It is formed by the OVPE method or the MBE method. After forming the p-side ohmic electrode 415 and the n-side ohmic electrode 416, a laser device having a cavity length of about 900 μm is obtained by a cleavage method.

Then, the second embodiment is applied to the front surface (z = L) of the element.
10 nm thick AlNH film 3 formed by the method shown in FIG.
01 and a silicon oxide (SiO 2) having a thickness of λ / 4 (λ: oscillation wavelength)
₂ ) Low reflection (AR) by a two-layer film composed of the thin film 302
A film 303 is formed by forming a SiO ₂ thin film and A on the rear surface (z = 0) of the device.
High-reflection (HR) film 30 of an eight-layer film composed of an 1NH film
4 was formed. Thereafter, the device was bonded on a heat sink with the bonding surface facing down.

The prototype device has a threshold current of about 10 mA.
At room temperature, and the oscillation wavelength was about 0.98 μm. The element oscillated in transverse single mode stably up to 600 mW. Further, even when the light output was increased, the end face did not deteriorate, and the maximum light output 950 mW was limited by the thermal saturation. When 50 devices were continuously driven at a constant light output of 200 mW under an environment temperature of 80 ° C., the initial drive current was about 280 mA, and all the devices stably operated for 100,000 hours or more.

[0028]

According to the present invention, an oxide film and a nitride film can be continuously grown in the same chamber. By using laser ablation and reactive plasma at the same time, it is possible to continuously laminate thin films without cross-contamination,
A longer life of the device can be achieved as compared with a conventional surface protection film of a semiconductor device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a thin film forming apparatus used in first and second embodiments.

FIG. 2 is a plan view of a semiconductor laser used in a third embodiment.

FIG. 3 is a sectional view of a semiconductor laser used in a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Susceptor, 2 ... Substrate, 3 ... Heater, 4 ... Gas inlet valve, 5 ... Helicon antenna, 6 ... RF power supply, 7 ... Magnetic coil, 8 ... Helicon plasma, 9 ... Synthetic quartz window, 1
0: Si target, 11: plume, 12: plasma flow, 13: purge gas inlet valve, 14: Al target, 301: AlNH layer, 302: SiO ₂ layer, 30
3 AR film, 304 HR film, 405 substrate, 406
Buffer layer, 407: cladding layer, 408: active layer, 4
09: clad layer, 410: optical waveguide layer, 411: clad layer, 412: cap layer, 413: current confinement layer, 4
14 contact layer, 415 p-type ohmic layer, 41
6 ... n-type ohmic layer, 417 ... barrier layer, 418 ... strained quantum well layer.

Continued on front page F term (reference) 4K029 AA04 BA46 BA58 BB02 BD01 CA04 DB20 DD02 5F045 AA12 AA16 AB10 AB32 AB40 AC11 AC15 AD05 AE13 AF04 AF09 BB13 CA12 DC64 DP05 EH16 GB12 HA22 5F058 BA04 BB02 BC02 BC09 BF07 BF07 B09

Claims (8)

[Claims] 1. A method for forming a thin film in which a first constituent element raw material of a thin film composed of at least two elements is a solid and a second constituent element raw material is a gas molecule is provided. Forming a thin film by evaporating a solid material by a laser ablation method, exciting a gas material of the second constituent element by plasma, supplying the above two kinds of materials to a substrate surface, and depositing a thin film on the substrate surface; Method. 2. A thin film comprising at least three elements, wherein the first and second constituent element raw materials are solid compounds made of the first and second elements, and the third constituent element raw material is gas molecules. In a method of forming a thin film, a solid compound raw material of the first and second constituent elements is evaporated by a laser ablation method, a gas raw material of a third constituent element is plasma-excited, and the above three kinds of raw materials are supplied to a substrate surface. And depositing a thin film on the surface of the substrate. 3. A thin film composed of at least three elements, wherein the first constituent element raw material is a solid, and the second and third elements are solid.
In the method of forming a thin film in which the constituent element material is a gas molecule, the solid source material of the first and second constituent elements is evaporated by a laser ablation method, and the gas material of the second and third constituent elements is plasma-excited, The above 3 on the substrate surface
A method for forming a thin film, comprising supplying seed materials and depositing a thin film on a substrate surface. 4. A thin film according to claim 1, wherein a plume generated by laser ablation is supplied to a substrate surface after plasma excitation, and a thin film is deposited on the substrate surface. Formation method. 5. A thin film forming apparatus comprising a solid raw material evaporating apparatus, a gas raw material introducing section, a plasma exciting apparatus and a substrate susceptor, wherein a solid raw material evaporating apparatus comprising an optical window for introducing laser light, an optical system for converging laser light, and a solid target. A thin film forming apparatus equipped with the apparatus. 6. A thin film forming apparatus according to claim 5, wherein a plasma excitation device is arranged between the solid material evaporator and the substrate susceptor. 7. The thin-film forming apparatus according to claim 5, wherein a plasma excitation device is arranged between at least two targets and the substrate susceptor in the target holding section of the solid raw material evaporating device. 8. A semiconductor light emitting device wherein a thin film formed by the method according to claim 1 is provided on an end face of an optical resonator.