JP3182584B2 - Compound thin film forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a compound thin film, and more particularly to a method of forming a compound thin film capable of controlling a film thickness in atomic layer units and obtaining a high-quality compound thin film by raising the substrate temperature in a short time. Things.

[0002]

2. Description of the Related Art Conventionally, in a method of growing a compound semiconductor thin film single crystal by a vapor phase method, usually, a method of simultaneously supplying two or more kinds of raw materials to a substrate and reacting them is used.
For example, a vapor phase growth method (M
In a method of growing a crystal of a GaAs thin film by OVPE), tolmethylgallium (TMG) as a raw material for gallium (Ga) and arsine (As) as a raw material for arsenic (As) are used.
H ₃ ) is simultaneously supplied onto a substrate to perform crystal growth. In this case, by precisely controlling the supply amount and supply time of the raw material, it has become possible to precisely control the thickness of the crystal grown on the substrate.

In particular, a growth method having a controllability of a film thickness on the order of an atomic layer has been studied in recent years, and there is a monoatomic layer controlled crystal growth method (ALE method) as the method. The ALE method is characterized in that a source gas containing atoms constituting a thin film is alternately supplied onto a substrate. For example, in a GaAs crystal growth method, TMG and arsine are supplied alternately. Under appropriate crystal growth conditions, TMG supply achieves monolayer adsorption such as monomethylgallium (MMG) on the substrate surface, followed by reaction with arsine to form a GaAs monolayer. You. In this case, a single molecular layer is formed in each cycle of the supply of the raw material gas, regardless of the supply amount of the raw material. Therefore, if the lattice constant of the crystal is known, the thickness of the thin film is precisely controlled by the number of growth cycles. it can.

[0004] The ALE method requires an automatic deposition stopping mechanism utilizing the property of saturated adsorption of a monolayer of a source molecule. This automatic deposition stop mechanism means that after the source molecules form an adsorbed layer consisting of a monolayer on the substrate, the subsequently supplied source molecules are automatically rejected by utilizing the property of being repelled by the adsorbed molecules. The deposition of molecules is stopped at a monolayer.

Therefore, in order to realize this automatic deposition stopping mechanism, it is important to set crystal growth conditions such as the substrate temperature. For example, the saturated adsorption of only the TMG monolayer is formed when the surface temperature of the substrate is about 500 ° C., and when the temperature is higher than that, the degree of formation of the polylayer increases. In the conventional ALE method using an organometallic compound as a raw material, a large amount of a carbon component generated by decomposition of the raw material is taken into a crystal as an impurity due to a low crystal growth temperature. Easy to be. For this reason, it is a major disadvantage that it is difficult to manufacture an N-type semiconductor and control the carrier concentration by introducing other impurities, which is an obstacle to the manufacture of a semiconductor element and the like.

As a method of reducing the amount of a carbon component incorporated as an impurity into a crystal, there is a method of constantly raising the temperature of the entire substrate to about 700 ° C. during crystal growth (Appl. Phys. Lett., Vol. 59, No.19, P2397 4 November 19
91). However, in this method, carbon in the crystal is easily desorbed, but since the substrate temperature is too high, a crystal composed of multi-layers is easily formed, and a very strict raw material is required for forming a thin film composed of one molecular layer. It is necessary to control the supply time.

[0007]

As described above, in the ALE method using an organometallic compound as a raw material, the raw material molecules are adsorbed on the substrate surface, and the reaction of the raw material molecules on the surface is used. The resulting carbon compounds are abundant on the crystal surface. In the ALE method, since the temperature for achieving monolayer saturated adsorption is lower than the normal crystal growth temperature, the desorption rate of the carbon compound is slow and the time for staying on the substrate surface is long. Therefore, since the crystal formed by the ALE method has a higher carbon concentration than the crystal formed by the normal MOVPE method, it is difficult to control the electron or hole concentration by introducing other impurities. .

Further, when the crystal growth temperature is increased to eliminate the above-mentioned disadvantage, there is a disadvantage that a polymolecular layer is easily formed. Accordingly, an object of the present invention is to improve the conventional monoatomic layer controlled crystal growth method to reduce the carbon component concentration in a compound thin film such as a crystal, and to provide a method of forming a compound thin film having improved quality without crystal defects. To provide.

[0009]

The above object of the present invention is achieved by the following constitution. That is, the following step (a)
And (e). (A) a step of supplying the first raw material compound in a pulse form onto the substrate heated to a steady temperature, and allowing the first raw material compound or a decomposition product thereof to be saturatedly adsorbed on the substrate surface in a monomolecular layer; At a predetermined time after the supply of the raw material compound is stopped
Step placing between the (c) the supply and the pulsed substrate different second starting compound from the first raw material compound simultaneously pulsed light
Irradiating and reacting with the molecules of the first raw material compound or its decomposed product that is saturated and adsorbed to form a monomolecular compound thin film; and (d) lowering the temperature of the substrate to an initial steady temperature. (E) a step of forming a compound thin film having a required thickness by repeating the steps (a), (b), (c) and (d) a plurality of times.

[0010]

The first raw material compound of the present invention includes, for example, TMG (trimethylgallium), TEG (triethylgallium), TMA (trimethylaluminum),
A raw material containing a Group 3 atom, such as MI (trichymel indium), can be used. As the second raw material compound, a raw material containing a Group 5 atom, such as AsH ₃ (arsine) or PH ₃ (phosphine), can be used. .

Further, the steady-state temperature at which the monomolecular layer of the first raw material compound is saturated and adsorbed by the method of forming a compound thin film of the present invention is slightly different depending on the first raw material compound, and is approximately the following temperature. . TMG: about 500 ° C, TEG: about 350 ° C, TMA: about 500 ° C, TMI: about 360 ° C

Further, about 100 ° C. to 200 DEG as illustrated in temperature rise of the substrate surface by heating due to the pulsed light beam
It is in the range of ° C. It is not limited to this example.
It is desirable that the temperature increase on the substrate surface be performed within a few seconds. This is because, when the method of the present invention is applied to a semiconductor device, for example, when a semiconductor layer is formed on a GaAs substrate, if the temperature rising period of the GaAs substrate surface is too long, the As component in the substrate may be desorbed. Because.

[0014] Simultaneously with the heating of the pulse-like surface of the substrate by the light beam, or a little later than the heating by supplying a second starting compound is reacted with the first raw material compound molecules adsorbed on the substrate surface. The second raw material compound is 10
In a temperature range of 0 to 200 ° C., since no more than one molecular layer is deposited, a monolayer thin film obtained from the first raw material compound and the second raw material compound, for example, a Group 3 material such as GaAs.
A monolayer thin film of the group V compound is formed.

[0015] with <br/> the pulsed light beam used in the present invention is not particularly limited, efficiently near infrared rays can heat the surface of the substrate, the visible light on the long wavelength side is preferable. The compound thin film forming method of the present invention can be used for controlling the thickness of a semiconductor device such as controlling the thickness of a quantum well active layer of a semiconductor laser. Further, the present invention can be applied to a case where a thin film is formed on a material which does not make crystallinity a problem, for example, an X-ray waveguide material in a unit of one molecular layer.

[0016]

According to the present invention, when the first raw material compound is supplied onto the substrate in a steady temperature region where monolayer saturation adsorption occurs on the substrate, monolayer saturation adsorption is formed. Thereafter, the temperature of the substrate surface is raised by a certain temperature, and simultaneously with or after the heating of the surface of the substrate, the second source compound is supplied to react with the first source compound molecules adsorbed on the substrate surface. The reaction between the first raw material compound and the second raw material compound is accelerated, and a carbon compound or the like that is unnecessary for forming a compound thin film derived from the first raw material compound or unnecessary for forming a compound thin film generated by the reaction. Desorption can be promoted.

In this way, it is possible to greatly reduce the concentration of the carbon component taken into the compound thin film. Further, when the compound thin film is a crystal, the movement of atoms on the crystal surface can be promoted by the temperature rise on the substrate surface, and the generation of crystal defects can be reduced.

Further, by reducing the pulse width of the pulsed light beam, the temperature rise is limited to only a very shallow region of the substrate surface. Therefore, the temperature of the substrate surface after stopping the irradiation of the light beam becomes The temperature rapidly decreases to a steady temperature due to thermal diffusion from the substrate surface to the inside of the substrate. Thereafter, the first raw material compound is supplied again. As described above, the temperature of the substrate surface was rapidly increased and rapidly cooled, and the compound thin film formation such as crystal growth was repeated while the temperature at the time of supplying the first raw material compound was kept constant, whereby the carbon concentration as an impurity and crystal defects were reduced. A high-quality compound thin film is formed.

[0019]

An embodiment of the present invention will be described with reference to the drawings. This embodiment using the apparatus of FIG. 2, a method for forming a compound thin film of GaAs. In the apparatus of FIG. 2 , hydrogen gas 1 as a carrier gas, trimethylgallium (TMG) 2 as a first raw material compound, and arsine (AsH ₃ ) 3 as a second raw material compound are each supplied to a reaction furnace 5 through a gas valve 4. And exhausted through the exhaust port 6. The reactor 5 has a window 9 made of flat and transparent quartz glass for irradiating the surface of the GaAs substrate 7 with a light beam (in this embodiment, near-infrared light having a wavelength of 500 to 2000 nm) 8 and GaAs. A heater 10 for heating the substrate 7 to a steady temperature (about 500 ° C.) for forming a monolayer is provided. A shutter 11 is provided outside the window 9 of the reaction furnace to control the irradiation time of the light beam 8 into a pulsed light beam.

In this manufacturing apparatus, first, a GaAs substrate 7 is placed on a heater 10 in a reaction
Heat to a temperature of The hydrogen gas 1 is flowed at a flow rate of 3 liter / min, and the inside of the reaction furnace 5 is maintained at a constant pressure of 100 mbal. 2 × 10 ⁻⁷ mol of TMG2 is supplied into the reactor 5 per cycle. After the supply of TMG2, a purge time (1 second) for removing TMG2 not adsorbed on the substrate 7 in the reaction furnace 5 with a hydrogen stream is set. Next, the shutter 11
Irradiates the surface of the GaAs substrate 7 with a pulsed light beam 8 to control the surface temperature of the substrate 7 to about 650 ° C. Simultaneously with the irradiation of the light beam 8, 3 × 10 ⁻⁵ mol of AsH ₃ per cycle is supplied into the reaction furnace in a pulse form by the gas valve 4. Then again excess As
A purge time (1 second) for removing H ₃ with a hydrogen stream is set.

As described above, TMG 2 and AsH ₃ are alternately supplied into the reactor 5. After the heating by the light beam 8 is stopped, after the substrate surface temperature decreases to the steady temperature, the TMG is again
Supply 2. By repeating this cycle, GaAs
Can be manufactured on the substrate 7. Incidentally, the supply amount of such heating temperature and TMG2, AsH 3 ₃ gas of the substrate 7 may be appropriately changed.

FIG. 1 shows the time series of the gas supply and the light pulse of these starting compounds 2 and 3. TMG
2 is supplied for one second to cause saturated adsorption on the surface of the substrate 7. Then, after a purge time of 1 second TMG2, the light pulse 8
For 1 second. At this time, the surface temperature of the substrate 7 is changed from the steady temperature (T ₀ : 500 ° C.) to (T ₀ + ΔT: 500 + 15).
0 ° C). At this time, the carbon component generated from the TMG 2 saturated and adsorbed on the surface of the substrate 7 is desorbed from the surface of the substrate 7.

[0023] This will be described in Figure 3. Crystal quality was evaluated by measuring the emission spectrum of the compound thin film. Figure
As shown in FIG. 3 , the peak of the emission spectrum from the thin film formed at 350 ° C. without irradiating a light pulse was 1.47.
Appeared at 8 eV. This corresponds to the emission peak due to carbon impurities, indicating that the carbon concentration is high. On the other hand, a peak of an emission spectrum from a thin film formed by irradiation with a light pulse appeared at 1.497 eV in a high energy region. This corresponds to light emission from a high-purity thin film having a low carbon impurity concentration. Therefore, it is shown that the concentration of the carbon component in the thin film was significantly reduced by the light pulse irradiation.

[0024] The irradiation at the same time as the start of AsH _{3 3} of the light beam 8
For 2 seconds. Next, a purge time of 1 second of AsH ₃ gas is set, during which time the temperature of the surface of the substrate 7 is lowered to a steady temperature (T ₀ : 500 ° C.). Thus, one cycle of GaAs monolayer crystal growth is completed. By repeating this operation n times, an n-type GaAs layer is formed.

[0025]

As described above, the substrate 7 is irradiated with the light beam.
Even when the temperature of the surface rises, GaAs is not supplied when TMG2 is supplied.
By maintaining the temperature of the substrate 7 at a steady temperature (T ₀ : about 500 ° C.), the condition of monolayer saturated adsorption is maintained, and monoatomic layer controlled crystal growth is possible. At this time, crystal defects are eliminated due to a short temperature rise after the supply of TMG2, and the quality is improved. In addition, the result that the emission intensity was increased about 50 times was obtained. This indicates that the crystal quality has been improved. In this embodiment, the steady temperature of the substrate is set to about 500 ° C., but the optimum temperature can be appropriately selected depending on the size of the reaction apparatus.

[0027]

As described above, according to the present invention, it is possible to form a compound thin film having excellent quality and a thickness controllability on the order of one molecular layer, and further has the following effects. (1) The film thickness can be precisely controlled in units of one molecular layer. (2) When the compound thin film is a crystal, the quality is greatly improved, for example, the thickness of the quantum well active layer can be easily controlled, and the manufacture of a high-performance semiconductor device such as a semiconductor laser can be facilitated. (3) The ALE method according to the present invention can be applied to the manufacture of the semiconductor device or the manufacture of the X-ray waveguide material.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a source gas supply, an optical pulse, and a substrate temperature in a time series according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a manufacturing apparatus used in the method of the present invention.

FIG. 3 is a diagram showing an emission spectrum peak position with respect to a light pulse irradiation ratio.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Carrier gas (hydrogen gas), 2 ... First raw material compound (trimethylgallium), 3 ... Second raw material compound (arsine), 4 ... Gas valve, 5 ... Reaction furnace, 6 ... Exhaust port, 7 ...
GaAs substrate, 8: light beam, 9: window, 10: heater, 11: shutter

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-264218 (JP, A) JP-A-62-182195 (JP, A) JP-A-4-212415 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 21/205

Claims (4)

(57) [Claims] 1. A method for forming a compound thin film, comprising the following steps. (A) a step of supplying the first raw material compound in a pulse form onto the substrate heated to a steady temperature, and allowing the first raw material compound or a decomposition product thereof to be saturatedly adsorbed on the substrate surface in a monomolecular layer; At a predetermined time after the supply of the raw material compound is stopped
Step placing between the (c) the supply and the pulsed substrate different second starting compound from the first raw material compound simultaneously pulsed light
Irradiating and reacting with the molecules of the first raw material compound or its decomposed product that is saturated and adsorbed to form a monomolecular compound thin film; and (d) lowering the temperature of the substrate to an initial steady temperature. (E) a step of forming a compound thin film having a required thickness by repeating the steps (a), (b), (c) and (d) a plurality of times. 2. A method according to claim 1, wherein after the monolayer saturated adsorption is formed by supplying the first raw material compound, desorption of molecules unnecessary for forming the compound thin film is promoted by increasing the temperature of the substrate surface. 2. The method for forming a compound thin film according to item 1. 3. The compound thin film forming method according to claim 1, wherein the reaction with the second atomic compound is promoted by increasing the temperature of the substrate surface, and desorption of molecules unnecessary for forming the compound thin film is promoted. 4. The compound thin film forming method according to claim 1, wherein the increase in the temperature of the substrate surface promotes the movement of atoms on the substrate surface to reduce crystal defects at the time of forming the compound thin film.