JP4014700B2 - Crystal thin film manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a crystalline thin film. More specifically, the present invention relates to a new crystal thin film manufacturing method capable of growing an arbitrary number of crystal thin films in units of one atomic layer.
[0002]
[Prior art and its problems]
In recent developments in electronic devices, particularly semiconductor devices, devices with controlled composition ratios and atomic species in atomic layer units such as superphoton devices or quantum well devices have been developed in order to improve performance and develop new functions. It is thriving.
To realize such a device, it is necessary to control the crystal growth at an atomic layer unit, as a method for enabling such growth, the proposed atomic layer Epitaki sheet over the Suntra (ALE: Atomic Layer Epitaxy) method. Since this ALE method can logically grow an arbitrary number of layers in units of one atomic layer, it has attracted attention as an ideal method for crystal growth on an atomic scale, and various related technologies are actively developed. It has been broken.
[0003]
In recent years, the ALE method has been applied as a growth method for binary compound semiconductors such as III-V semiconductors, for example, GaAs.
Specifically, two kinds of molecules each containing one of two kinds of atoms of a binary compound semiconductor, for example, Ga and As of GaAs are used, and each molecule is irradiated onto the substrate alternately. The bond strength between atoms is stronger between different species than between the same species, and the irradiated molecules are likely to react with different types of molecules adsorbed on the substrate, and hardly react with the same type of molecules. For this reason, when one raw material molecule is irradiated, the molecule or its decomposition species reacts with a different kind of underlying molecule and is further adsorbed and saturated. Unnecessary molecules contained in the raw material molecules are detached in the adsorption process. This saturated adsorption is called a self-stop function, and crystals can be grown in units of one atomic layer by this self-stop function.
[0004]
Such an ALE method is suitable for a method of manufacturing a compound semiconductor composed of two or more kinds of atoms.
On the other hand, in recent years, group IV semiconductors such as Si / Ge are expected to be applied to high-speed transistors such as heterojunction bipolar transistors and modulation-doped field effect transistors, and strained superlattice optical devices, and crystal growth in units of atomic layers is necessary. It has been said that. However, in the case of single element materials, the principle of alternating adsorption found in the ALE method of compound semiconductors described above cannot be used, so there is no general principle for obtaining a monomolecular layer, and it is difficult to obtain a saturated adsorption amount of a monomolecular layer. is there.
[0005]
Therefore, in the ALE method for a single element material, there is no choice but to expect that the raw material molecules or their decomposition species are saturated with the adsorption amount of the monomolecular layer in the adsorption process of irradiating the raw material molecules. After that, unnecessary molecules contained in the monolayer adsorbed by saturation are removed by thermal excitation by heating or photoexcitation by light irradiation, or by irradiating other reactive molecules and releasing them together with the molecules. Can be considered. After the unnecessary molecules are detached, the desired atoms are further grown. Therefore, the general procedure of the ALE method of a single element material is to repeat a cycle of (1) irradiation of raw material molecules and (2) removal of unnecessary molecules, and grow a monoatomic layer for each cycle.
[0006]
Up to now, a group IV semiconductor Ge or Si single element using molecules containing C or Cl such as Ge (C ₂ H ₅ ) ₂ H ₂ , Ge (CH ₃ ) ₂ H ₂ , GeCl ₄ , SiH ₂ Cl _2, etc. With regard to the material ALE method, the self-stopping function that the saturated adsorption amount is about a monomolecular layer, that is, the ALE growth about a monoatomic layer is realized.
[0007]
However, such an ALE method has a problem that a small amount of impurities such as C and Cl remain and the purity of the crystal is lowered.
Therefore, Si ₂ H ₆ , Si ₃ H ₈ , SiH ₄ , and GeH ₄ , which are hydrogen compound molecules that do not cause the problem of impurities, have attracted attention as raw material molecules in the ALE method of Si and Ge, and have been actively researched and developed. Yes.
[0008]
However, research and development revealed that Si ₂ H ₆ and Si ₃ H ₈ have a saturated adsorption amount of less than a monomolecular layer at room temperature and are difficult to use as raw material molecules in the ALE method as they are. It was. In addition, although it has been found that SiH ₄ and GeH ₄ tend to be saturated with a single molecule, the irradiation pressure of molecules at the time of saturation is as high as several Torr (1 atm = 760 Torr), and the substrate is annealed at the time of irradiation. There is a problem that the utilization efficiency of the raw material molecules becomes very low due to the high irradiation pressure. This problem is caused by the fact that the saturated adsorption amount of SiH ₄ and GeH ₄ is less than a monolayer at room temperature.
[0009]
Thus, the hydrogen compound molecule has the advantage that there is no problem of impurities as a raw material molecule for the ALE method of Si or Ge, and exhibits a saturated adsorption phenomenon, but its saturated adsorption amount is less than a monomolecular layer. However, it was difficult to actually use the ALE method.
The present invention has been made in view of the circumstances as described above, and can increase the saturated adsorption amount of a hydrogen compound molecule to a monomolecular layer and realize ALE growth of a group IV semiconductor, that is, a monoatomic layer unit. An object of the present invention is to provide a new crystal thin film manufacturing method capable of manufacturing a crystal thin film.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention thermally decomposes at least a part of the hydride molecule before the hydride molecule consisting of the group IV atom (X) for crystal growth reaches the substrate surface. By irradiating a gas containing a decomposed species (XH ₂ ) or decomposed species (XH ₂ ) obtained by thermal decomposition, the adsorbed species (XH ₂ ) composed of group IV atoms (X) that grow crystals are further adsorbed on the substrate surface. A plurality of steps including: a first step of evacuating; a second step of exhausting residual gas that has not been adsorbed; and a third step of exciting the substrate surface using surface excitation means to release unnecessary hydrogen from the substrate surface. There is provided a crystal thin film manufacturing method (claim 1) characterized in that one cycle is formed for each cycle and one atomic layer is formed for each cycle.
[0011]
Further, the present invention provides a substrate surface for at least one kind of hydrogen compound molecule when simultaneously or sequentially irradiating two or more kinds of hydrogen compound molecules each containing two or more kinds of group IV atoms (X) for crystal growth. Two or more kinds of crystals that are grown by irradiating at least a part of them with a gas containing a decomposed species (XH ₂ ) or a decomposed species (XH ₂ ) obtained by this thermal decomposition. Using a first step of further adsorbing two or more adsorbed species (XH ₂ ) containing each of group IV atoms (X) , a second step of exhausting residual gas that has not been adsorbed, and surface excitation means A crystal thin film manufacturing method (contract) characterized in that a plurality of steps including a third step of exciting the substrate surface and releasing unnecessary hydrogen from the substrate surface are defined as one cycle, and one atomic layer is formed for each cycle. Section 2) also provides a.
[0012]
And in said manufacturing method, the surface excitation means in a 3rd process is thermal excitation (Claim 3 ), the surface excitation means in a 3rd process is optical excitation (Claim 4 ), or a 3rd process The aspect is that the surface excitation means is electron beam excitation (Claim 5 ) and that one cycle includes a step of lowering the substrate temperature (Claim 6) .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the crystal thin film manufacturing method of the present invention thermally decomposes at least a part of the hydrogen compound molecules before the hydrogen compound molecules consisting of group IV atoms (X) that grow crystals reach the substrate surface, By irradiating a gas containing the decomposed species (XH ₂ ) or decomposed species (XH ₂ ) obtained by this thermal decomposition, the adsorbed species (XH ₂ ) composed of group IV atoms (X) that grow crystals are further deposited on the substrate surface. In the first step of adsorbing, or when irradiating two or more types of hydrogen compound molecules each containing two or more group IV atoms (X) that grow crystals simultaneously or sequentially, at least one type of hydrogen compound molecule, Before arriving at the substrate surface, at least a part of the substrate is thermally decomposed and irradiated with a gas containing decomposed species (XH ₂ ) or decomposed species (XH ₂ ) obtained by the thermal decomposition. A first step in which two or more adsorbed species (XH ₂ ) each containing two or more types of group IV atoms (X) for crystal growth are combined and further adsorbed, and a second step in which residual gas that has not been adsorbed is exhausted A single atomic layer for each cycle, with a plurality of steps including three steps including a third step of exciting the substrate surface using surface excitation means and releasing unnecessary hydrogen from the substrate surface. It is characterized by forming.
[0014]
When using hydrogen compound molecules as raw material molecules, the inventor of the present invention irradiates the pyrolysis species or a gas containing the pyrolysis species at room temperature, even if the saturated adsorption amount is less than a monomolecular layer. It was found that saturated adsorption occurs in a monolayer.
For example, when SiH ₄ and Si ₂ H ₆ are used as raw material molecules, SiH ₂ mainly generated by pyrolyzing them is adsorbed on a monolayer on the surface. Therefore, since SiH ₂ is saturated and adsorbed as a single molecule, the reactivity of the substrate with Si is high, but it is less likely to be further adsorbed onto H of SiH ₂ adsorbed on the substrate.
[0015]
In addition to SiH ₄ and Si ₂ H ₆ , the same effect can be obtained when Si ₃ H ₈ , GeH ₄ , Ge ₂ H ₆ , CH ₄ , C ₂ H ₆ , and C ₃ H ₈ are used as raw material molecules. Obtainable.
Therefore, these hydride molecules are effective for monolayer adsorption of Si, Ge, and C, respectively. That is, these hydrogen compound molecules are thermally decomposed before arriving at the substrate surface, and by using the resulting decomposed species, the adsorbed species consisting of the growing atoms are saturated and adsorbed. The amount can be a single molecule. Such decomposition species effective for single molecule adsorption are those obtained when the hydrogen compound molecules are thermally decomposed.
[0016]
Next, unnecessary hydrogen contained in the adsorbed species can be removed from the substrate surface by annealing at, for example, about 500 ° C. and removed. The removal and removal of unnecessary hydrogen from the substrate surface can be performed by using light or an electron beam and exciting the substrate surface by photoexcitation or electron beam excitation. In addition to photoexcitation and electron beam excitation with little heat generation, thermal excitation can also be used as an excitation means for the substrate surface by increasing the light intensity and electron beam intensity. When utilizing thermal effects on withdrawal removal of hydrogen may be added a step of lowering the board temperature.
[0017]
Further, for example, a Si ₂ H ₆ and GeH ₄ by irradiating simultaneously thermally decomposed, for example, when the adsorption of SiH ₂ and GeH ₂ on the substrate surface, it is hard to adsorb to both the hydrogen, SiH ₂ and GeH ₂ is distributed in a certain proportion and can be saturated and adsorbed in a monolayer. The ratio of SiH ₂ and GeH ₂ to be adsorbed can be adjusted by, for example, the dose ratio of Si ₂ H ₆ and GeH ₄ . This means that, for example, a mixed crystal of Si / Ge can be grown in units of a monoatomic layer and the composition ratio is changed in each layer.
[0018]
In each cycle of the crystal thin film manufacturing method of the present invention, the first step described above does not have to be performed first, but the first step, the second step, and the third step in the cycle. These steps may be included in this order, and some other processing step other than the second step and the third step is performed before the first step before the hydrogen compound reaches the substrate surface. It does not prevent it.
[0019]
Hereinafter, embodiments will be described with reference to the accompanying drawings, and embodiments of the present invention will be described in more detail.
[0020]
【Example】
FIG. 1 is a schematic view illustrating a manufacturing apparatus using a crystal thin film manufacturing method according to an embodiment of the present invention.
In the manufacturing apparatus illustrated in FIG. 1, for example, a sample (3) having a Ge (100) surface on the surface thereof is attached to the approximate center of the vacuum vessel ( 1 ), and the vacuum vessel ( 1 ) is always an exhaust device ( 2 ) exhausted. In the vacuum vessel ( 1 ), a heater (4) as a surface excitation means used in the second step is installed in the vicinity of the sample (3). In the present embodiment, disilane (Si ₂ H ₆ ), which is a hydrogen compound molecule, is used as a raw material molecule, and this disilane is released by the raw material cylinder (6), and the pressure regulating pressure reducing valve (7) and the flow rate regulator ( 8) The pressure and flow rate of each are adjusted and flowed through the on / off valve (9) to the pyrolysis cell (5) provided in the vacuum vessel ( 1 ). And it is thermally decomposed by the thermal decomposition cell (5), and the thermal decomposition gas is irradiated to the sample (3) surface. The pyrolysis cell (5) is controlled by controlling the temperature of the tungsten wire wound spirally in the alumina tube , and whether or not disilane is irradiated is controlled by an on / off valve (9).
[0021]
Crystal growth in units of Si monoatomic layers was performed by the crystal thin film manufacturing method of the present invention using the manufacturing apparatus of FIG.
The atomic layer crystal growth procedure is as follows: (1) Pyrolysis gas irradiation for 1 minute (first step), (2) Unnecessary gas exhaustion for 1 minute (second step), (3) Thermal excitation of substrate by heater for 1 minute (3rd process), (4) Cooling is 3 minutes (4th process), These 4 processes are made into 1 cycle.
[0022]
FIG. 2 illustrates the dependence of the Si film thickness grown in one cycle on the dose of Si ₂ H ₆ . In this embodiment, the temperature of the tungsten fine wire of the pyrolysis cell (5) in the first step is set to 400 ° C., and the thermal excitation temperature of the substrate in the third step is set to 500 ° C.
Saturated adsorption amount when irradiated with Si ₂ H ₆ is not thermally decomposed but was 0.6, as apparent from FIG. 2, the method of the invention ^{1.0 × 10 4 L (1L =} 1 × 10 - A saturated adsorption amount of a single atom per cycle could be obtained at an irradiation dose of ⁶ Tol · sec or more. Therefore, it can be seen that Si is saturatedly adsorbed by a single atom by thermally decomposing Si ₂ H ₆ .
[0023]
FIG. 3 exemplifies a change in the grown film thickness of Si when the cycle is repeated. As is apparent from FIG. 3, it can be seen that Si is increased by a monoatomic layer for each cycle, and growth of a monoatomic layer unit is realized.
Of course, the present invention is not limited to the above examples, and it goes without saying that various aspects are possible in detail.
[0024]
【The invention's effect】
As described above in detail, according to the crystal thin film manufacturing method of the present invention, a group IV semiconductor of Si, Ge, C, in particular, can be grown in a monoatomic layer unit using hydrogen compound molecules that are not affected by impurities. At the same time, the hydrogen compound molecules are adsorbed during the adsorption process, so that the movement of atoms is suppressed by hydrogen, and the phenomenon that the same kind of atoms aggregate together and the phenomenon that the dissimilar atoms diffuse can be prevented. For example, the Si layer and the Ge layer can be grown in any number of layers and in any order.
[0025]
Also, even if a plurality of hydrogen compound molecules with different growth atoms, such as Si ₂ H ₆ and GeH ₄ , are used, the mechanism of saturation of adsorption is the same as a single molecule. Can grow in monolayer units. For example, mixed crystal layers of Si _0.6 Ge _0.4 and Si _0.9 Ge _0.1 can be alternately stacked in units of monomolecular layers. Furthermore, since a fine beam laser or electron beam can be used as a method for desorbing hydrogen, it is possible to draw these beams in the hydrogen removal step, thereby realizing fine selective growth and pattern formation.
[0026]
Furthermore, any hydrogen compound molecule can be used in the method of the present invention, so that it can be applied to various material systems.
[Brief description of the drawings]
FIG. 1 is a schematic view illustrating a manufacturing apparatus using a crystal thin film manufacturing method according to an embodiment of the present invention.
FIG. 2 is a diagram exemplifying the dependency of Si film thickness grown in one cycle on the irradiation amount of Si ₂ H ₆ .
FIG. 3 is a diagram illustrating a change in the growth thickness of Si when a cycle is repeated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Exhaust apparatus 3 Sample 4 Heater 5 Pyrolysis cell 6 Raw material cylinder 7 Pressure reducing valve 8 Flow controller 9 On / off valve

Claims (6)

Before the hydrogen compound molecule comprising the group IV atom (X) for crystal growth arrives at the substrate surface, at least a part of the hydrogen compound molecule is thermally decomposed, and the decomposition species (XH ₂ ) or decomposition obtained by this thermal decomposition by irradiating a gas containing seeds (XH _2), a first step of adsorbing species consisting of group IV atoms crystal growth (X) and (XH ₂₎ further adsorbed on the surface of the substrate, the residual gas not adsorbed A plurality of steps including a second step of exhausting and a third step of exciting the substrate surface using surface excitation means and releasing unnecessary hydrogen from the substrate surface are defined as one cycle, and one atomic layer is formed for each cycle. A method for producing a crystalline thin film, comprising: When simultaneously or sequentially irradiating two or more hydride molecules containing each of two or more group IV atoms (X) for crystal growth, at least one hydride molecule, before reaching the substrate surface, Two or more Group IV atoms (X) that grow crystals by irradiating at least a part of them and irradiating a decomposition species (XH ₂ ) or a gas containing the decomposition species (XH ₂ ) obtained by this thermal decomposition. A first step of further adsorbing two or more adsorbing species (XH ₂ ) including each of the above, a second step of exhausting residual gas that has not been adsorbed, and exciting the substrate surface using surface excitation means. A method for producing a crystalline thin film, wherein a plurality of steps including a third step of releasing unnecessary hydrogen from the substrate surface is defined as one cycle, and one atomic layer is formed for each cycle.   The crystal thin film manufacturing method according to claim 1 or 2, wherein the surface excitation means in the third step is thermal excitation.   3. The crystal thin film manufacturing method according to claim 1, wherein the surface excitation means in the third step is photoexcitation.   3. The method for producing a crystal thin film according to claim 1, wherein the surface excitation means in the third step is electron beam excitation.   6. The method for producing a crystal thin film according to claim 1, wherein one cycle also includes a step of lowering the substrate temperature.

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