JPH0983075A - Method for producing silicon-based light emitting material - Google Patents

Abstract

(57) An object of the present invention is to provide a method capable of controlling the particle size distribution of silicon nanocrystals in a gas phase and producing a silicon-based light emitting material suitable as a material for a light emitting device. SOLUTION: A silicon oxide film containing silicon nanocrystals is irradiated with laser light having a predetermined wavelength of 500 nm or less in an oxygen-containing atmosphere to oxidize the surface of the silicon nanocrystals that absorbs the laser light. The particle size is 5n
Reduce to m or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon-based light emitting material used in a light emitting device such as a light emitting diode and a semiconductor laser.

[0002]

2. Description of the Related Art At present, most of materials for semiconductor very large scale integrated circuits are occupied by silicon. The reason for this is that silicon is a very excellent material which has the advantages that silicon is easily available and inexpensive, large single crystals can be produced, and integrated circuits can be produced with a high yield. However, since the silicon single crystal has an indirect transition type electronic band structure, it is difficult to observe light emission, and it is difficult to use it as a light emitting element.

Therefore, conventionally, a semiconductor laser (hereinafter,
LD) and light emitting diode (hereinafter referred to as LED)
III-V such as GaAs or ZnSe as the material of
Group-based or II-VI group-based compound semiconductor materials are used. However, there are many difficulties in manufacturing a device using a compound semiconductor. Further, in order to expand the use of the device, it is possible to emit light of short wavelength such as blue, violet and ultraviolet light.
D and LED are desired.

Under these circumstances, research and development of light emitting silicon such as porous silicon have recently become active. Silicon-based materials for which luminescence has been observed so far include porous silicon, polysilane, silicon nanocrystals, siloxene and Si.
_1-x Ge _x / Si superlattices are known. That is, light emission is observed when the size of the silicon crystal is reduced to reduce the dimension of the atomic arrangement. For example, silicon microcrystals having a grain size on the order of nm (silicon nanocrystals)
Emits light at a wavelength of 370 nm to 900 nm based on a band structure different from that of a silicon single crystal and a surface level effect. There is also a theory that the light emission observed in porous silicon is actually caused by silicon nanocrystals.

There are some reports on the above-mentioned silicon nanocrystals (for example, Hiroshi Takagi, Masanori Sandome, Yoji Yano, Takashi Nakagiri, Solid State Physics, Vol. 27, No. 11,
1992, p. 874-879; Y. Kanemit
su, T .; Ogawa, K .; Shirai, K .;
Takeda, J .; Lumin. 60-61, 337-
339 (1994)). The former discloses a method of producing silicon nanocrystals by the plasma CVD method. That is, the substrate is placed in the CVD chamber and
After evacuating to ^-6 Pa, monosilane gas is supplied together with a carrier gas (H ₂ or Ar or a mixed gas thereof) and decomposed by microwave (2.45 GHz) plasma to generate silicon nanocrystals. In this case, the silicon nanocrystals in the gas are carried and deposited on the substrate by the carrier gas, and the silicon nanocrystals are obtained in a form in which the silicon nanocrystals are dispersed in the amorphous silicon layer.

On the other hand, here, monosilane and Si (OC ₂ H
_By supplying ₅ ) ₄ (hereinafter referred to as TEOS) alternately or simultaneously, silicon nanocrystals can be dispersed in SiO ₂ . The silicon nanocrystals obtained by such a method are dispersed in the silicon oxide film at intervals of about 2 to 5 nm, and the conditions suitable for the light emitting material are provided.

However, it is known that the particle size of the silicon nanocrystals in the silicon oxide film thus obtained varies, and a distribution containing a large number of particles having a large particle size is shown (Y. Kanemitsu, T. Ogawa, K .;
Shirai, and K. Takeda, Phy
s. Rev. B48, 4883 (1993)). Since the conduction band level of such a silicon nanocrystal having a large grain size is low, when carriers are injected, the carriers are accumulated in the levels and it is difficult to contribute to light emission. Further, in forming the LD, the luminous efficiency is increased by concentrating the density of states of excited electrons. Therefore, as can be easily understood from the above, it is desirable to realize a particle size distribution containing less silicon nanocrystals having a large particle size in application to a light emitting device. However, conventionally, no method has been known for controlling the particle size distribution of silicon nanocrystals.

[0008]

As described above, a silicon-based light emitting material containing silicon nanocrystals is promising as a constituent material of a light emitting device, but conventionally, the particle size distribution cannot be controlled and the particle size is controlled. Good emission cannot be obtained when a silicon nanocrystal having a large size is included. Further, considering the manufacturing process of the light emitting device, it is desirable to realize such control of the particle size distribution in the gas phase.

An object of the present invention is to provide a method capable of controlling the particle size distribution of silicon nanocrystals in a gas phase and producing a silicon-based light emitting material suitable as a material for a light emitting device.

[0010]

The method for producing a silicon-based light-emitting material of the present invention comprises irradiating a silicon oxide film containing silicon nanocrystals with a laser beam having a predetermined wavelength of 500 nm or less in an oxygen-containing atmosphere, It is characterized in that the surface of silicon nanocrystals of a size that absorbs laser light is oxidized to control the particle size thereof.

In the present invention, the oxygen-containing atmosphere has only to contain oxygen in an amount of 3% or more, and may be an inert gas atmosphere such as nitrogen containing oxygen, helium, or argon, an air atmosphere, or a 100% oxygen atmosphere.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The principle of the present invention will be described below.
First, when a fused state of a silicon oxide film and silicon is formed on a substrate such as a silicon wafer by CVD or sputtering and annealed in vacuum or in an inert gas, silicon atoms are aggregated and silicon nanocrystals are deposited. When laser annealing is performed in this state, electrons in the outermost shell of silicon are excited in the silicon nanocrystals that absorb the laser light of the wavelength (ν) used, and when they are relaxed, they are heated by the interaction with phonons. As a result, melting or activation of silicon occurs. FIG. 1A shows this phenomenon based on the band structure.
On the other hand, in the silicon nanocrystal that does not absorb the laser light, the state of silicon does not change.

In the present invention, laser annealing is performed in an oxygen-containing atmosphere. In this case, the silicon nanocrystals that absorb the laser light are melted or activated and the surface is oxidized, so that the substantial particle size becomes smaller. Further, as the laser beam, a laser beam having a wavelength ν having an energy hν corresponding to the band-to-band excitation energy of the silicon nanocrystal having the particle size to be controlled is used (however, the momentum does not change with the band-to-band excitation energy). Means the minimum transition energy of, and is a little different from the band gap because silicon is an indirect transition type). Therefore, in the present invention, among silicon nanocrystals, those having an interband excitation energy smaller than the energy hν of the laser beam, that is, those having a relatively large particle size are oxidized and the substantial particle size is reduced. Further, as the particle size becomes smaller, the band-to-band excitation energy of silicon nanocrystals gradually increases, and when it becomes larger than hν, the laser light is not absorbed and the oxidation does not proceed. FIG. 1B shows this phenomenon based on the band structure. In this way, the grain size of the silicon nanocrystals can be controlled to be equal to or smaller than the target grain size. In the present invention, by using a laser beam having a wavelength of 500 nm or less, it is possible to make the particle diameter of the silicon nanocrystals 5 nm or less, and it is possible to satisfy a preferable condition as a light emitting material.

In the present invention, in order to form a silicon nanocrystal by annealing a mixed substance of a silicon oxide film produced by plasma CVD or the like and a silicon atom, laser light having a wavelength used in a vacuum chamber is 30% or more. A transparent window made of transparent glass or the like may be provided, a laser may be installed outside the window, and annealing may be performed with the laser light. In particular, when 80% or more of the light having a wavelength of 200 nm or more is used, it is desirable to use quartz glass as the material of the transparent window. Further, laser annealing in an oxygen-containing atmosphere to control the particle size of silicon nanocrystals does not need to be hermetically sealed as long as an environment in which unnecessary gas is not mixed in from the outside, for example, glass The sample chamber and laser can be combined.

In the present invention, conditions such as plasma CVD are adjusted so that the distance between the silicon nanocrystals dispersed in the silicon oxide film is a distance at which current can be injected by tunneling of electrons and holes. Preferably. Further, if polysilane is arranged between the silicon nanocrystals, the current easily flows and the emission wavelength can be changed. In order to disperse silicon nanocrystals and polysilane in the silicon oxide film, TEOS is supplied in plasma CVD so that SiO _x (0 <X <
In the process of forming 2), silane, simultaneously or alternately,
Disilane, trisilane, tetrasilane, or a mixed gas thereof may be supplied.

By using the silicon-based light emitting material manufactured by the method of the present invention, a silicon-based light emitting device can be manufactured by applying a semiconductor manufacturing process. In addition, such a silicon-based light emitting device is used as an LSI such as a transistor.
When combined with a circuit, a low-cost opto-electronic integrated circuit can be realized. Further, a multicolor silicon light emitting integrated circuit display using such a silicon-based light emitting material is promising as a substitute product for a liquid crystal panel currently used for a display panel. That is, since the current liquid crystal panel has two polarizing plates in front of the lamp, at least 1/2 of the light is not used. However, the multicolor silicon light emitting integrated circuit display does not have such a problem and consumes light. It is possible to reduce power consumption and improve screen brightness.

[0017]

Embodiments of the present invention will be described below. Example 1 A silicon wafer was placed in an LPCVD reaction furnace and evacuated. The temperature of the silicon wafer is set to 700 ° C., TEOS (tetraethoxysilane), silane and tetrachlorosilane are supplied together with a carrier gas,
A mixed substance of SiO ₂ and silicon atoms was deposited to a film thickness of 500 nm on a silicon substrate. Next, this silicon wafer is transferred into a vacuum chamber, and at room temperature,
The film on the silicon wafer was annealed by irradiating THG (wavelength 355 nm) of a pulse Q-switch YAG laser of 10 Hz. At this time, 10 pulses were irradiated with the energy per pulse being 3 J / cm ² . When observed with a transmission electron microscope, it was confirmed that silicon nanocrystals having a particle size of 2 to 7 nm were present. The particle size distribution of the silicon nanocrystals at this time is shown in FIG. The distance between the silicon nanocrystals, that is, the thickness of the silicon oxide film between the silicon nanocrystals was about 1 nm on average.

Next, in order to reduce the particle size by oxidizing the surface of the silicon nanocrystal having a large particle size, O ₂ : H
In the oxygen-containing atmosphere of e = 1: 1, the second harmonic of Q-switched Ti: sapphire laser (wavelength 380 nm) was repeatedly applied to the film on the silicon wafer at 1 kHz, peak power density 300 kW / cm ² , pulse width 300 nsec.
It was irradiated under the conditions of. Observe this with a transmission electron microscope,
Fig. 2 (b) shows the results of examining the particle size distribution of silicon nanocrystals.
Shown in

As is clear from the comparison between FIGS. 2 (a) and 2 (b), the proportion of silicon nanocrystals having a grain size of 4 nm or more was about 50% before the oxidation treatment. On the other hand, it decreased to 10% or less after the oxidation treatment.

The obtained silicon-based light-emitting material was added to the third harmonic (wavelength: 300) of a Q-switched Ti: sapphire laser.
nm) repeatedly at 1 kHz, peak power density 30 W
When irradiation was performed under the conditions of / cm ² and a pulse width of 300 nsec, emission at a wavelength of 390 nm was confirmed.

Example 2 An example of manufacturing an integrated circuit of a light emitting element and a MOS transistor having the structure shown in FIG. 3 will be described. This device has a structure in which a diffusion layer of a MOS transistor, which serves as an electrode, is connected to both ends of a silicon oxide film in which silicon nanocrystals which are a light emitting material are dispersed.

First, a region which becomes a light emitting portion of the p-type silicon substrate 1 is selectively etched to form a trench. An Al layer 2 functioning as a mirror is formed on the bottom of this trench by sputtering. An oxide film 3 is deposited on this Al layer 2.

Next, in the same manner as in Example 1, after the inside of the LPCVD reaction furnace was evacuated, the temperature of the silicon substrate 1 was adjusted to 70.
The temperature is set to 0 ° C., TEOS, silane and tetrachlorosilane are supplied together with a carrier gas to deposit a mixed substance of SiO ₂ and silicon atoms on the oxide film 3 to a film thickness of 500 nm. This silicon substrate 1 is transferred into a vacuum chamber, and a 10 Hz film is formed on the oxide film 3 at room temperature.
Pulse Q-switch YAG laser THG (wavelength 35
5 nm) and anneal. Furthermore, O ₂ : Ar
The second harmonic of the Q-switched Ti: sapphire laser (wavelength 3
80 nm) to oxidize the surface of silicon nanocrystals having a large grain size. In this way, the light emitting layer 4 containing silicon nanocrystals with uniform grain size is formed.

Next, a region where one of the electrodes is formed is selectively etched to form a trench, and an oxide film 3 is deposited on the bottom of the trench. After depositing polysilicon in the trench, it is annealed to form a single crystal. Arsenic is ion-implanted into this polysilicon and annealed to further promote single crystallization to form an n ⁺ type diffusion layer 5. Similarly, a region in which the other electrode is formed is selectively etched to form a trench, and the oxide film 3 is deposited on the bottom of the trench. After depositing polysilicon in the trench, it is annealed to form a single crystal.
Boron is ion-implanted into this polysilicon and annealed to further promote single crystallization to form the p ⁺ -type diffusion layer 6.
These two electrodes are formed non-parallel so as not to form a resonator.

Further, the n-type well region 7, the n ⁺ type diffusion layer 8, the p ⁺ type diffusion layer 9, the gate insulating film 10 and the gate electrode 1 are formed.
1 and 12 are sequentially formed to fabricate a device. In this element, when two MOS transistors are turned on and a voltage of, for example, +12 V is applied to the n ⁺ type diffusion layer 5 and a voltage of, for example, −12 V is applied to the p ⁺ type diffusion layer 6, the light emitting layers 4 to 390 are emitted.
Emission of nm is produced.

[0026]

As described above, by using the method of the present invention, the particle size distribution of silicon nanocrystals can be controlled in the gas phase, and a silicon-based light emitting material suitable as a material for a light emitting device can be manufactured. be able to.

[Brief description of drawings]

1A is a diagram showing a band structure of a silicon nanocrystal, and FIG. 1B is a diagram showing a change in a band structure of a silicon nanocrystal due to oxidation.

FIG. 2A is a particle size distribution diagram of silicon nanocrystals before oxidation, and FIG. 2B is a particle size distribution diagram of silicon nanocrystals after oxidation.

FIG. 3 is a sectional view showing an integrated circuit of a light emitting element and a MOS transistor according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... p-type silicon substrate, 2 ... Al layer, 3 ... oxide film, 4 ...
Light-emitting layer, 5 ... n ⁺ type diffusion layer, 6 ... p ⁺ type diffusion layer, 7 ... n
Type well region, 8 ... N ⁺ type diffusion layer, 9 ... P ⁺ type diffusion layer,
10 ... Gate insulating film, 11, 12 ... Gate electrode.

Claims (1)

[Claims] 1. A silicon oxide film containing silicon nanocrystals is irradiated with laser light of a predetermined wavelength of 500 nm or less in an oxygen-containing atmosphere to oxidize the surface of the silicon nanocrystals of a size that absorbs the laser light. A method for producing a silicon-based light-emitting material, which comprises controlling the particle size of the material.