JP2835891B2 - Thin film making method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention performs selective epitaxial growth on a substrate patterned with a material having a low adhesion coefficient to the molecules of a reaction gas, and grows a desired thin film only in the openings formed by the patterning. The present invention relates to a method for forming a thin film.

[0002]

2. Description of the Related Art Conventionally, a method of forming a thin film by selective growth using a reaction gas includes (1) a film formed by patterning (an oxidation process, a diffusion process, a resist process, an etching process, a thin film forming process, etc. In the process of manufacturing a semiconductor device, a thin film attached to a substrate is selectively etched simultaneously, and as a result, a desired thin film is grown only in an opening formed by patterning. And (2) a method in which the supply rate of the reaction gas is reduced, and (3) a method in which the temperature of the substrate is lowered.

[0003]

However, in the above-mentioned conventional method, when the selective etching of (1) is performed simultaneously, it is necessary to raise the substrate temperature.

For example, when a Si film is selectively grown on a Si substrate, a gas for etching Si (for example, SiCl ₂ H _{2) is used.}
With or HCl + SiH _4, etc.) and the combined reaction gas was done. This is to grow a Si film on a Si substrate while etching a polysilicon film formed on an oxide film. However, in this method, it is considered necessary to increase the substrate temperature in order to etch the polysilicon film. In addition, since the growth of Si on the Si substrate is inhibited simultaneously with the etching of the polysilicon, it is considered that the substrate temperature needs to be high in order to obtain a sufficient growth rate of the Si film.

According to a study by Yew et al. (J. Appl.
s. 65 (6), 15 march 1989, P2500-2507, "Selective s
ilicon epitaxial growth at 800 oC by ultralow-pres
surechemical vapor deposition using SiH ₄ and SiH ₄
/ H ₂ "), the temperature of the substrate is reported to require about 800 ° C..

Therefore, a structure formed in a substrate by a thermal diffusion method or the like may be broken at a high temperature.

The method of (3) for lowering the temperature of the substrate is reported by Hirayama et al. (Appl. Phys.
Lett. 52 (26), 27 June 1988, P2242-P2243, "Selecti
ve growth condition in disilane gas source silicon
melecular beam epitaxy "). According to this study,
It has been reported that it is necessary to suppress the supply rate of the reaction gas when performing selective growth by lowering the substrate temperature.
However, in this case, it has been considered that high-speed selective growth is not possible and is not suitable for manufacturing a semiconductor device.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is directed to a method of forming a thin film capable of setting a substrate temperature low (for example, 800 ° C. or less) and performing high-speed selective growth. It is intended to provide.

In order to achieve the above object, the present invention provides the following conditions on a substrate in which a material having a lower adhesion coefficient to a reaction gas than the material of the substrate is formed on a substrate surface (hereinafter referred to as "patterning"). It is characterized by protecting and forming a thin film. The conditions are as follows: (1) The pressure in the vacuum vessel is set to a low pressure region where the reaction gas substantially does not cause a gas phase reaction,
And (2) the surface molecular concentration of the reaction gas on the material having a low adhesion coefficient is equal to or less than the surface molecular concentration at which nucleation occurs,
Create a thin film.

In practice, it is not easy to know the concentration of molecules on the substrate surface. However, as described below, the present inventors have found that whether or not nucleation occurs is determined by the total amount of the supplied reaction gas. Therefore, in the present invention, the condition that “the surface molecular concentration of the reaction gas on a material having a low adhesion coefficient is equal to or less than the surface molecular concentration at which nucleation occurs” is set as “the total amount of the supplied reaction gas is The total amount of the reaction gas at which nucleation occurs is not more than ".

[0011] Controlling the total amount of reactant gas supply is effective under certain conditions. If conditions such as the shape of the ejection port of the gas nozzle of the thin film growth apparatus, the distance from the ejection port to the substrate, and the size of the vacuum vessel change, the total supply amount until nucleation occurs and selective growth is disrupted changes.

Therefore, the condition that “the surface molecular concentration of the reaction gas on a material having a low adhesion coefficient is equal to or less than the surface molecular concentration at which nucleation occurs” is defined as “the total amount of the reaction gas molecules flying to the substrate is low. By setting the number to be equal to or less than the number of molecules at which nucleation occurs on the material (that is, the number of molecules colliding on the substrate), a universal condition can be obtained. If the number of reactive gas molecules flying to the substrate satisfies the above conditions,
Even if the physical conditions of the thin film growth apparatus change, selective growth can be performed.

The pressure region in which the gas phase reaction does not substantially occur means that the molecules of the reactive gas collide with the inner wall (exposed wall on the vacuum side) or the substrate before colliding with each other in the vacuum vessel. It means a pressure region where the probability becomes extremely large. In such a pressure region, the probability of collision of the reactant gas with the substrate or the inner wall is larger than the probability of collision between the molecules, so that the probability of transferring heat between the molecules is small, and the molecules are exclusively between the substrate and the inner wall. Will give and receive heat. The low probability of transferring heat between molecules means that
It means that heat conduction in the gas phase is very small. Under these conditions, even if molecules receive thermal energy from the substrate or the inner wall to such an extent as to cause a thermal decomposition reaction, the thermal conduction in the gas phase is so small that the thermal decomposition reaction occurs in the entire gas phase. Never get up. That is, the gas phase reaction does not substantially occur in the space inside the vacuum vessel. Here, if the temperature of the inner wall of the vacuum vessel is set to a temperature at which the molecules of the reaction gas do not cause a thermal decomposition reaction, the thermal decomposition reaction of the reaction gas occurs only on the substrate surface. As a result,
A film can be formed only on the substrate surface by a thermal decomposition reaction of the reaction gas. In order to achieve a pressure range in which the gas phase reaction does not substantially occur, the mean free path (me
Optimally, the pressure of the vacuum vessel is set so that the free path is longer than the shortest distance between the substrate and the inner wall. That is, the mean free path of the molecules of the reaction gas is set to d, and the shortest distance between the substrate and the inner wall is set to L so as to satisfy the equation (4).

[0014]

(Equation 4)

By setting the conditions in this manner, the reaction gas does not cause a thermal decomposition reaction in the gas phase. In other words, even if a molecule that receives heat by colliding with the substrate jumps out of the substrate, the average free path of the molecule is longer than the shortest distance between the substrate and the inner wall, so the probability that the molecules collide with each other is small, This is because molecules have a high probability of colliding with the inner wall.

In order to prevent the molecules of the reaction gas from colliding with each other in the vacuum vessel, the distance between the gas nozzle and the substrate may be set shorter than the mean free path of the molecules of the reaction gas. When the distance between the gas nozzle and the substrate is set in this manner, the probability that the molecules (primary molecules) of the reaction gas supplied from the gas nozzle reach the substrate directly without colliding between the molecules can be increased.

Here, since it is sufficient to consider the probability of collision with molecules given thermal energy capable of thermal decomposition reaction, the molecular energy supplied from the gas nozzle to the molecular energy to which thermal energy of thermal decomposition reaction has not yet been given has been given. There is no need to consider collisions. Therefore, it is sufficient if the condition of d> L is satisfied.

[0018]

When a reaction gas is supplied at the same supply rate to a substrate and a material having a lower adhesion coefficient of the reaction gas than the substrate, the time for nucleation to start on the material having a lower adhesion coefficient than the substrate is as follows. Many are needed. This is because the total amount of molecules to be supplied before reaching the surface molecular concentration at which nucleation starts is required to be larger than that of the substrate. The condition on which nucleation starts on a material having a low adhesion coefficient is only the surface molecular concentration. Therefore, according to the present invention, since the growth is terminated at a critical supply amount or less at which nucleation starts, selective crystal growth on the substrate can be performed at a low substrate temperature and at a high growth rate.

Generally, the surface molecular concentration is defined as the number of aggregates (or critical nuclei) in which one or two atoms are associated as a nuclear precursor (precursor) on a unit area of a substrate.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to disilane (Si ₂
An example in which the present invention is applied to silicon gas source epitaxy using H ₆ ) gas will be described.

FIG. 1 shows a schematic configuration of an apparatus used in the embodiment. It should be noted that this diagram merely schematically shows the size, shape, and positional relationship of each component so that the present invention can be understood. A gas nozzle 2 is provided in the vacuum vessel 1, a liquid nitrogen shroud 3 is provided along the inside of the vacuum vessel 1, and a substrate holder 4 is provided above a space surrounded by the liquid nitrogen shroud 3. A heating device 5 is provided so as to face the substrate holder 4.

The vacuum vessel 1 can be evacuated to a vacuum by a turbo-molecular pump (1000 l / sec) 6 and an auxiliary rotary pump 7 provided at the lower part, and the pressure in the vacuum vessel 1 is set on the side wall. The measurement can be performed via the nude ion gauge 8. The nude ion gauge 8 is not turned on during film formation. Further, the substrate holder 4
A RHEED device (reflection high-speed electron beam diffraction) composed of an electron gun 10 and a screen 11 is installed for observing the surface of the substrate 9 held in the device.

On the other hand, a gas introduction system 13 provided with a three-way valve 12 is connected to the gas nozzle 2. Gas introduction system 1
3 is a mass flow controller 14, valves 15, 16,
The line is constituted by a regulator 17, and the regulator 17 is connected to a gas cylinder (disilane gas cylinder) 18. An exhaust system constituted by a turbo molecular pump 19 and an auxiliary rotary pump 20 is connected to one of the three-way valves 12 so that the inside of a pipe of the gas introduction system 13 can be exhausted.

The ultimate pressure of the vacuum vessel 1 having the above configuration was 1.0 × 10 ⁻⁹ Torr or less. In this embodiment, the scattered molecules are adsorbed by using the liquid nitrogen shroud 3, and the molecules reaching the substrate are only the molecules directly flying from the gas nozzle 2. Further, the total amount of molecules reaching the substrate was determined by the total amount of supplied gas. Furthermore, even when the coolant of the liquid nitrogen shroud 3 is water and used as a water-cooled shroud (Japanese Patent Application No. 2-253).
002), even if molecules scattered by the water-cooled shroud fly to the substrate, the total amount of molecules flying to the substrate can be grasped by the total amount of supplied gas.

The flow rate of the Si ₂ H ₆ gas is controlled by a mass flow controller 14 installed in a gas line 13.
The gas is supplied to the substrate 9 through the gas nozzle 2. The gas is switched by the three-way valve 12, and when the gas is not irradiated to the substrate, the gas is exhausted by the turbo-molecular pump 19 for exhausting piping.

Here, when Si ₂ H ₆ gas is introduced and the pressure in the vacuum vessel 1 is set to 1.5 × 10 ⁻³ Torr, the d> L
Consider whether or not the condition is satisfied. The shortest distance L between the substrate 9 of the apparatus and the liquid nitrogen shroud 3 was 40 mm.

The mean free path d (m) of the numerator is obtained by the equation (5).

[0028]

(Equation 5)

T is the gas temperature (K), P is the pressure (Pa),
D is the diameter (m) of the molecule.

Therefore, the mean free path of the Si ₂ H ₆ gas molecule will be obtained by using equation (6). In determining the diameter D of the Si ₂ H ₆ gas molecule, the molecular structure model of FIG. 2 was used. In this model, the distance between Si atoms is 2.34 Å, and the distance between Si and H atoms is 1.480 Å. The apex angle (θ in the figure) of a triangular pyramid composed of Si atoms and three H atoms is 110.2 °. Therefore, when calculating the height of the triangular pyramid, 0.475
Angstrom.

The diameter D of the Si ₂ H ₆ molecule is obtained by (distance between Si atoms) +2 (height of the triangular pyramid), and D = 3.29 angstroms, that is, 3.29 × 10 ⁻¹⁰ m.

The value of the diameter D and T = 298 K (normal temperature is 25
° C), P = 1.5 × 10 ^-3 Torr = 0.1995 Pa
Substitute into the formula. As a result, the mean free path of the Si ₂ H ₆ gas molecule is d = 42.9 × 10 ⁻³ m = 42.9 mm.

Since L = 40 mm, it can be said that the condition of d> L is satisfied. Therefore, the pressure in the vacuum vessel 1 becomes
If the pressure is 1.5 × 10 ⁻³ Torr or less, the pressure is set to a pressure range in which the gas phase reaction does not substantially occur.

Usually, the size (diameter D) of the molecule of the reaction gas
Is generally several angstroms, and the shortest distance between the substrate and the exposed wall on the vacuum side of the vacuum vessel is generally set to about several centimeters. Therefore, the pressure inside the vacuum vessel 1 is 1 × 10
^By setting the pressure to ^-3 Torr or less, it is possible to achieve a condition in which a gas phase reaction does not occur.

Even if the reaction gas is a mixed gas, the total
If it is × 10 ⁻³ Torr or less, the mean free path of the molecules of each gas will be several cm or more.

The above considerations take into account the collision probability between the molecules of the reaction gas and the substrate, the inner wall, and between the molecules. However, from a macroscopic point of view, if the heat conduction in the gas phase is very small, heat will not be uniformly transmitted to the entire gas phase. That is, it means that no substantial gas phase reaction occurs.

[0037] Indeed, the inventors have found that by the above apparatus, Si ₂ H
_{Even when} the pressure of the vacuum vessel into which the _six gases were introduced was set to about 1.5 × 10 ^-2 Torr, the phenomenon described below, which is considered to be caused by the gas phase reaction, in which the selectivity was lowered was not observed.

This is presumably because the thermal conductivity of the molecules of the Si ₂ H ₆ gas as the reaction gas was sufficiently small even at about 1.5 × 10 ⁻² Torr. In other words, even if the probability of collision with molecules given thermal energy is increased to some extent, substantial heat-dissipation will not occur unless heat is uniformly distributed throughout the gas-phase reaction gas due to heat conduction. It is not expected to occur.

It is important to make the pressure in the vacuum vessel 1 a pressure region where the gas phase reaction of the reaction gas does not substantially occur, in performing selective growth on the substrate.

Using Si ₂ H ₆ gas as a source gas,
When selective growth is performed between SiO ₂ and SiO ₂ , a reaction gas that has sufficiently decomposed before reaching the substrate (pre-cracked
In source-gas), selective growth is unlikely to occur. This can be inferred from the following facts. a. In the deposition of solid Si, complete Si does not grow selectively so that selective growth does not occur on the substrate. b. When a device whose exposed wall on the vacuum side of the vacuum container is at a high temperature is used, the selectively grown film becomes thin. For example, the report of Recannelli et al. (Appl. Phys.
Lett. 58 (19), 13 May 1991, P2096-P2098, "Low-temp
erature selective epitaxyby ultrahighvacuum chemic
alvapor deposition from SiH ₄ and GeH ₄ / H ₂ "). It is considered that the selectivity was lowered because the reactant gas was decomposed to some extent on the high-temperature exposed wall on the vacuum side. Is thought to be because the decomposition reaction produces products in the gas phase, which are deposited on the substrate, that is, the decomposition reaction of Si ₂ H ₆ results in Si atoms or more selective Bad molecule (Si _x H
It is believed that _y ) is formed and this is deposited.

In performing selective growth, an SiO 2 film is formed on a 4-inch (001) substrate by a CVD method.
Use an iO ₂ film patterned and use an aqueous ammonia solution (H ₂ O: H ₂ O ₂ : NH ₃ OH = 2) before setting.
The substrate was washed by boiling at 0: 6: 1) and then set on the substrate holder 4. 850 ° C. using the heating device 5 in the vacuum vessel 1,
After cleaning by heating for 10 minutes to remove the natural oxide film, selective epitaxial growth was performed at various substrate temperatures. SiO
It is considered that the SiO ₂ film has a low adhesion coefficient to Si between the _two films and the Si film (substrate). Various literature on selective growth is well known to those skilled in the art. RHEED for selective growth
Determined by the image on the screen 11 of the device. When no nucleation of polysilicon is observed on the oxide film formed by patterning, the RHEED image is 2 × 1 + in FIG.
In the halo state, a scanning electron microscope (SEM) image of the surface of the substrate 9 at this time was as shown in FIG. On the other hand, when polysilicon nucleation is observed on the oxide film, a 2 × 1 + ring of the RHEED image of FIG. 4A is observed, and an SEM image of the surface of the substrate 9 at this time is shown in FIG. b). RHEED observation was performed periodically because the pressure when the reaction gas (disilane gas) was introduced into the vacuum vessel 1 deteriorated the filament of the electron gun 10. The growth rate was calculated by removing the oxide film by patterning with a hydrofluoric acid (HF) solution after selective growth and measuring the thickness of the epitaxial film at the center of the substrate by the step method.

The RHEED image is observed at regular intervals,
The time during which selective growth collapsed due to changes in the image was examined. As a result, nucleation of polysilicon on the oxide film occurs after a certain incubation period, and when the substrate temperature is 600 ° C., the product of the incubation time and the reaction gas supply rate, that is, the supply gas amount during the incubation time is reduced. It was constant regardless of the gas supply speed. In other words, it has been found that the total supply gas amount until the nucleation of polysilicon occurs, that is, the critical supply amount at which the nucleation of polysilicon starts, is constant irrespective of the gas supply speed if the substrate temperature is constant. did.

FIG. 5 shows the substrate temperature dependence of the critical supply amount at which selective nucleation occurs due to the formation of polysilicon nuclei. As shown in the substrate temperature dependence of this critical supply, the substrate temperature
At 650 ° C. or lower, it is found that the critical supply amount changes only depending on the substrate temperature and does not depend on the supply rate of the reaction gas, and further, the critical supply amount decreases as the substrate temperature increases. On the other hand, it was found that at a substrate temperature of 750 ° C or more, the critical supply amount changes depending on the substrate temperature and the gas supply rate, and increases with the substrate temperature, respectively, and decreases with an increase in the supply rate.

The existence of the critical supply amount of the reaction gas in the low-temperature region (650 ° C. or lower) indicates that the nucleation mechanism of the polysilicon on the oxide film is such that the molecular density on the surface of the oxide film exceeds a certain amount. The mechanism is considered to be the same as that of the three-dimensional island-shaped growth in the conventional MBE (Molecular Beam Epitaxy) method.

This can be easily known from the following modeled selective growth mechanism.

First, it is assumed that the polysilicon film on the oxide film (SiO ₂ ) and the epitaxial silicon film on silicon do not affect each other. That is, the formation of the polysilicon film on SiO ₂ is achieved by the mechanism of polysilicon formation when the entire surface of the substrate is an oxide film, and the silicon film on silicon is grown by the mechanism of epitaxial growth. Think that it has caused.

More specifically, a polysilicon film on an oxide film (SiO ₂ ) is generated and grown through the steps shown in FIG. That is, (1) Si ₂ H ₆ molecules fly over the oxide film.

(2) Most of the Si ₂ H ₆ molecules are reflected, but a part adheres to the oxide film and is thermally decomposed.

(3) The precursor of the nucleus generated by the thermal decomposition stays on the oxide film, and the amount of the precursor gradually increases.

(4) When the amount of the precursor exceeds a critical amount at which nucleation of the polysilicon film starts, a polysilicon film is generated and grows on the oxide film. At this point, selective growth collapses.

It is considered that a complicated process actually exists from the decomposition of the Si ₂ H ₆ molecule to the formation of Si. However, in the end, it is thought that the number of precursors (presumed to be Si atoms or Si with some H 2) exceeds a certain amount (about several atoms) and forms polysilicon.

During the progress of steps (1) to (4), epitaxial growth of Si proceeds on the patterned Si substrate independently of the reaction on the oxide film. This difference appears as selective growth.

This phenomenon can be easily understood by formulating as follows.

In formulating, the following premise or definition is made.

Substrate temperature: constant Decomposition efficiency of Si ₂ H ₆ on SiO ₂ (reflecting molecules are not decomposed here): P Si ₂ H ₆ Flux amount: F (pieces /
Time) Amount of precursor formed on SiO ₂ per unit time: n (pieces) Here, the precursor is used in the meaning of atoms in the final form of forming polysilicon, and is assumed to be Si atoms. The amount of precursor is Si ₂
Increases as long as supplying H _6, is not reduced. This can be estimated from the fact that the critical supply amount (total supply amount) does not change even when the supply of the reaction gas is stopped and the intermittent supply of the gas is performed, such as when an experiment is performed by observing RHEED.

Critical amount of precursor before formation of polysilicon film starts: Qc (pieces) Critical amount of precursor actually observed until formation of polysilicon film starts: qc (pieces) Unit time Amount of molecules evaporating as SiO ₂ : E (pieces / hour) When the amount n of the precursor formed on SiO ₂ per unit time is increased, the amount E of the molecules evaporating as SiO ₂ increases in proportion to n I do. However, when n exceeds a certain amount, E becomes the reaction rate-limiting. In other words, E is very small compared to the increasing speed of n, and the reaction is rate-limiting, and has a constant value.

The amount n of the precursor formed on SiO ₂ per unit time can be obtained by the equation (8).

[0058]

(Equation 8)

This can be understood from the equation (9).

[0060]

(Equation 9)

However, the Si in this reaction formula is the Si constituting the film.
It is assumed that the precursor is not an atom but a Si atom (step in FIG. 6).

Further, the critical amount q of the precursor actually observed
c is represented by the following equation (10).

[0063]

(Equation 10)

Therefore, when the SiO 2 is not evaporated (low temperature region), the time t until the critical amount is reached is represented by the equation (11) since the precursor formed on the SiO ₂ does not decrease. .

[0065]

[Equation 11]

That is, it is represented by the equation (12).

[0067]

(Equation 12)

Therefore, the critical quantity qc actually observed by the equation (13) is represented by the equation (14).

[0069]

[Equation 14]

As a result, it is found that the critical amount qc does not depend on the flux amount F of Si ₂ H ₆ . However, for the precursor on SiO ₂ , the migration length (the distance that molecules can move around) increases with the substrate temperature, and the decomposition rate (decomposition efficiency) of Si ₂ H 6 increases, so that more precursor is formed. For this reason, the probability of encountering other decomposed molecules increases. As a result, since the probability of forming polysilicon increases, it is considered that the critical amount Qc of the precursor decreases as the substrate temperature increases.

Next, when SiO 2 is evaporated (high temperature region), the amount n of the precursor generated per unit time is expressed by the following equation (15).
SiO 2 is evaporated by the reaction represented by the following formula:
−E (pieces).

[0072]

(Equation 15)

The time required to reach the critical amount is expressed by Expression 17 from Expression 16:

[0074]

[Equation 17]

Therefore, the critical amount qc of the precursor actually observed in this case is expressed by the equation (18).

[0076]

(Equation 18)

In this case, it can be seen that it depends on the supply speed of the reaction gas. Further, from the equation (19), (1) The observed critical amount qc is larger than the theoretical critical amount Qc. In other words, the critical amount increases as the temperature of the substrate increases.

(2) The flux F of Si ₂ H ₆ is small,
When 2F × P becomes equivalent to the evaporated molecular weight E, the right side of the equation becomes infinite. Conversely, when F increases and 2F × P increases, the right side of the equation approaches Qc without limit. That is, the flow rate dependence of the reaction gas is shown.

FIG. 7 shows the temperature dependence of the growth rate of the epitaxial silicon film selectively grown on the substrate. The thickness of the obtained selectively grown film was measured by the step method, and the growth rate was determined. It was confirmed that a growth rate of several angstroms to 100 angstroms / min can be obtained even in a low temperature range (650 ° C. or lower). Further, by performing growth at a critical supply amount of the reaction gas obtained in FIG. 5 or less, selective growth was possible in all temperature regions. Substrate temperature 700 ℃, gas flow 30 sc
At a growth rate of 640 angstroms / min in cm and a film thickness of 1280
An Angstrom silicon high-speed selective growth epitaxial film was obtained.

It should be noted that a water-cooled shroud using water as the shroud medium instead of the liquid nitrogen shroud 3 can satisfy the condition that a gas phase reaction does not occur. This is as proved in another application of the same inventor (Japanese Patent Application No. 2-253002). If a water-cooled shroud is used, the growth rate can be further increased, and the thickness of the epitaxial film can be increased.

Although the embodiment has been described in connection with the case where the selective epitaxial growth is performed on the silicon substrate,
It goes without saying that the present invention can be applied to other substrates such as an As substrate. The reaction gas is determined according to the material of the substrate, and a patterning material having a low adhesion coefficient to the reaction gas is also determined.

FIG. 8 shows a pattern patterned with a Si ₃ N ₄ film.
It is the result of the Example which performed selective growth on the Si substrate. Also in this case, Si ₂ H ₆ gas was used as a reaction gas, and Si was epitaxially grown on a Si substrate. In this case, Si ₃ N
₄ film on the Si is changed to SiO, it never becomes evaporated. Therefore, even at a high substrate temperature of 700 ° C or higher,
The critical supply amount that breaks the selective growth does not depend on the supply rate of the Si ₂ H ₆ gas. From FIG. 8, another important result can be known. In other words, the higher the substrate temperature, the lower the critical supply amount that breaks the selective growth. This is because if the decomposition rate (decomposition efficiency) of Si ₂ H ₆ increases, many precursors are formed, and the aggregates (or critical nuclei) in which the atoms as precursors are associated with each other become hot when the substrate temperature becomes high. ,
It is considered that it is easy to move (migrate) on the substrate. If the aggregate (critical nucleus) moves easily,
It encounters other aggregates (critical nuclei) and increases the probability of coalescence. As soon as the aggregates (critical nuclei) begin to coalesce, film formation occurs. For this reason, when the substrate temperature increases, the film formation sufficiently starts even if the surface molecule concentration is low. Therefore, even if the critical supply amount is small, if the temperature of the substrate is high, the selective growth is broken. Also, the critical supply amount at the same temperature is about 1/10 of that of SiO _{2 in} Si ₃ N _4.
It is. This is considered to be because the density of the adsorption points (Site) of Si2H6 molecules on Si3N4 is nearly 10 times higher than that of SiO2.

FIGS. 9A and 9B are SEM photographs comparing the actually formed poly-Si films. In the figure, (a) is SiO
_In the case of _two films, (b) is the case of a Si ₃ N ₄ film. The substrate temperature was 580 ° C. The nuclear densities of (a) and (b) are clearly different.

Further, using Si ₂ H ₆ and GeH ₄ gas,
Also in the case of forming a mixed crystal of / Ge, selective growth was possible in the same manner.

It was also found that there is a critical supply amount in selective W-CVD as well. Further, it was also found that when Si ₂ H ₆ was irradiated on amorphous Si, a poly-Si film was formed. From this result, it was found that a selective poly-Si film can be formed between the oxide film and the amorphous Si by the same method. Further, a selective poly-Si film can be formed on Si ₃ N ₄ and SiO ₂ .

In the above description, the thin film growth apparatus for selectively growing a thin film has a fixed structure, that is, a structure as shown in FIG. 1, the distance between the gas nozzle 2 and the substrate 9, the size of the vacuum vessel 1, With the physical conditions such as the size of the liquid nitrogen shroud 3 kept constant, the critical supply amount of the reaction gas until the selective growth collapsed was determined. Therefore, when an apparatus different from the thin film growth apparatus used in the embodiment is used, the critical supply amount has a different value.

If this method is further extended to the total amount of reaction gas molecules flying on the surface of the substrate 9, it is possible to provide universality which is not affected by the physical conditions of the thin film growth apparatus.

Hereinafter, a method for controlling the selective growth of the thin film by the total amount of the reaction gas molecules flying on the surface of the substrate 9 will be described.

The amount of reaction gas molecules colliding with the substrate surface Γm
(G / cm ² · sec) can be expressed by Expression 20.

[0090]

(Equation 20)

Where P (Torr) is the pressure of the reaction gas, T
(K) is the temperature of the reaction gas, and M is the molecular weight of the reaction gas.

The amount of the reaction gas molecules Γm (g / cm ² · sec) determined by the equation (21) is converted into the number of the reaction gas molecules Γn (pieces /
When expressed in cm ² · sec), the following equation is obtained.

[0093]

(Equation 22)

Where NA is the Avogadro number of the molecule (6.02
× 10 ²³ ).

Assuming that the time required for the critical nuclei on the SiO ₂ film to reach the critical amount and for the selective growth to collapse is t cri (sec), the total amount of reaction gas molecules flying over the substrate surface before the nucleation starts, Δcri (Pieces / cm ² ) can be expressed by the equation (24) from the equation (23).

[0096]

(Equation 24)

This is the total critical molecular weight.

FIG. 10 and FIG. 11 show data when selective growth was performed using shroud medium as water. FIG. 10 is a graph showing the relationship between the substrate temperature and the critical supply amount of the Si ₂ H ₆ gas, and FIG. 11 is a graph showing the relationship between the flow rate of the Si ₂ H ₆ gas and the pressure of the vacuum vessel 1.

By applying the equation of Equation 25 to this data,
Let's find the total critical molecular weight cri cri that causes the selective growth to collapse. When the substrate temperature T _{S was} 680 ° C., the critical supply was about 20 cc. The pressure when Si ₂ H ₆ gas was supplied to the vacuum vessel at a supply rate (v) of 10 sccm was about 1.2 × 10 ⁻³ Torr.

In this case, time t until the selective growth collapses
cri is represented by Expression 26.

[0101]

(Equation 26)

V is the supply speed of the reaction gas. That is, t = 20/10 = 2 min = 120 sec. The molecular weight M of the Si ₂ H ₆ gas is 62.22. The temperature T is set to 25 ° C. = 298 K. By substituting into the equation of Equation 27, Equation 28 is obtained.

[0103]

[Equation 28]

The critical molecular total amount cricri is constant irrespective of the supply speed of the reaction gas. For example, assuming that the supply rate of the reaction gas is 5 sccm, the pressure in the vacuum vessel is about 6 × 10 ⁻⁴ Torr and t cri is 240 sec from FIG. 11, so the total critical molecular weight cri cri is From the expression, Expression 29 is obtained, which is the same value.

[0105]

(Equation 29)

Similarly, the supply rate of the reaction gas is increased from 1 sccm to 10 sccm.
Even if it changes to sccm, the total critical molecular weight cri cri is about
The value was 3.7 × 10 ¹⁹ to about 6 × 10 ¹⁹ (pieces / cm ² ). Such a certain range is considered to be caused by a flow rate control error of the mass flow controller and a pressure measurement error.

The critical molecular total amount cricri up to the point at which the selective growth collapses is a value completely unrelated to the physical conditions of the thin film growth apparatus. For example, physical conditions such as the shape of the outlet of the gas nozzle 2, the distance to the substrate, the temperature of the shroud, the shape and size of the vacuum vessel, and the like can be mentioned. Even when these conditions are changed, the total critical molecular weight Γcri does not change. Of course, it is not related to the supply speed of the reaction gas. The critical molecular total amount cricri is determined by the physical properties such as the pressure, temperature and molecular weight of the reaction gas, and the material and temperature of the substrate for determining the adhesion coefficient.

The total critical collision molecule amount cricri for each substrate temperature shown in FIG. 10 was determined and is shown in Table 2.

[0109]

[Table 2]

The critical molecular total amount shows a unique value when the reaction gas is Si ₂ H ₆ gas and the substrate temperature is 680 ° C., 630 ° C., 580 ° C., and 530 ° C. Therefore, no matter how the other conditions change, the selective growth collapses when the critical molecular total amount is reached.

This has a different meaning from the critical supply amount described above. That is, in the case of the critical supply amount, the value is the same under a certain condition. The certain conditions include, for example, the shape of the gas nozzle orifice, the distance and relative positional relationship between the substrate and the gas nozzle, the temperature of the shroud, and the size of the vacuum vessel. Therefore, even if the critical supply amount can be known by one device, another device has a different critical supply amount.

The case where the temperature of the shroud is changed will be described. One device circulated liquid nitrogen through the shroud, and the other circulated water. The critical feed rate in the apparatus circulating water was about 1/10 of the critical feed rate in the apparatus circulating liquid nitrogen. FIG. 5 shows a case where liquid nitrogen is circulated through the shroud, and FIG. 10 shows a case where water is circulated. On the surface of the shroud in which the water is circulated, the colliding reactant gas molecules are scattered, so that most of the supplied reactant gas molecules fly over the substrate. On the other hand, the reaction gas molecules are adsorbed on the surface of the shroud in which the liquid nitrogen is circulated. Therefore, the number of molecules of the reaction gas flying on the substrate is smaller in the liquid nitrogen shroud. Therefore, more reactant gas must be supplied until the nucleation starts, that is, the critical supply amount is reached.

As described above, the critical supply amount of the reaction gas changes according to the change in the temperature of the shroud, but the critical supply amount also changes according to changes in other conditions. However, if the critical condition for breaking the selective growth is determined by the number of molecules flying to the substrate, it has nothing to do with the state or internal structure of the thin film growth apparatus. This means that if one device can know the total critical molecular weight of a certain reaction gas for a certain substrate,
This means that selective growth can be controlled by the critical molecular total amount.

[0114]

As described above, according to the present invention, nucleation of molecules of a reaction gas starts on a material having a low adhesion coefficient to the molecules of the reaction gas, which is used as a material for patterning. Before the selective epitaxial growth is completed, there is an effect that the selective growth can be surely performed. Further, since the growth rate can be increased without increasing the temperature of the substrate, it can be applied to the manufacture of a semiconductor device, and has an effect of contributing to the manufacture of an ultra-high integration device.

Conventionally, it has been considered that selective growth is possible only when the gas flow rate is low or the substrate temperature is low (for example, Hirayama et al., Appln. Phys. Lett.
52 (26), 27 June 1988, P2242-2243). As long as this is followed, it is necessary to keep the growth rate low in a system where the growth rate depends on the gas flow rate and the substrate temperature.

On the other hand, the present invention has found that the selective growth is determined not by the gas flow rate nor the substrate temperature but by the total amount of the supplied gas (the presence of a critical supply amount that degrades the selectivity). We decided to end growth. For this reason, as long as the critical supply amount is kept, the gas flow rate and the substrate temperature that affect the growth rate can be changed, and the growth rate can be increased by increasing the gas flow rate and the substrate temperature. (In the selective growth of Si using Si ₂ H ₆ gas, there is a growth rate controlled by the hydrogen elimination reaction from the surface, so the rate cannot be increased any more.) In other words, if the substrate temperature is constant, selection The condition under which the growth collapses is determined by the total amount of the supplied result regardless of the gas supply method. For example,
As shown in FIG. 8, the critical amount at which the selective growth collapses at a substrate temperature of 600 ° C. is about 20 cc. If the supply rate of the reaction gas is 30 sccm, the selective growth is disrupted when the reaction gas flows for 40 seconds. Similarly, 15 s
If the flow is ccm for 80 seconds, and if the flow is 10 sccm for 120 seconds, the selective growth is broken. If the flow is continued at a supply speed of 10 sccm at intervals of 10 seconds for 10 seconds, the selective growth is broken. Even if the gas is intermittently supplied in this manner, the condition for breaking the selective growth is determined by the total amount of the supplied gas.

As described above, the most significant feature of the present invention is that the condition under which the selective growth is broken can be determined by the total amount of the reaction gas. Therefore, if the supply of the reaction gas is stopped before reaching the total amount, selective growth can always be performed. That is, the selective growth can be controlled by the total amount of the reaction gas. From this point of view, controlling the selective growth as the incubation period before the start of film formation (for example, Murota et al., Applln. Phys.
Lett 54 (11), 13 March 1989, P1007-1009, "Low-tem
perature siliconselective deposition and epitaxy o
n silicon using the thermal decomposition of silan
e under ultraclean environment ") is a completely different technical idea because the present invention uses" the total amount of gas supply "as a means of controlling selective growth and" the incubation period "in Murata et al. .

Therefore, it can be said that there are several methods for specifically performing selective growth. For example, if the critical supply amount is known in advance from the film forming conditions (for example, substrate material, temperature, type of reaction gas, etc.), the supply of the reaction gas is stopped until the critical supply amount is reached. Thus, selective growth is performed. Secondly, if the critical supply amount is not known at all, film formation is performed in advance under appropriate film formation conditions, and the total supply amount of the reaction gas when the selective growth is lost is obtained. From the next film formation, the obtained total supply amount of the reaction gas is set as a critical supply amount, which is used as a selective growth condition.
Thereby, selective growth is performed.

When the total critical molecular weight Γcri is known from the relationship between the material of a certain substrate and a certain reaction gas,
The critical supply amount Qc in a certain apparatus can be obtained by the equation (32) from the equations (0) and (31).

[0120]

(Equation 32)

M and N _A are constants, and T is considered to be room temperature. Therefore, the critical supply amount Qc can be obtained by obtaining the pressure P at an arbitrary supply speed of v in a certain device.
That is, it is not necessary to previously determine the total supply amount of the reaction gas when the selective growth is broken by actually forming the film.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus used in an embodiment of the present invention.

FIG. 2 is a molecular structure model of Si ₂ H ₆ gas.

FIGS. 3A and 3B are photographs of a case where polysilicon nucleation is not formed on an oxide film in an embodiment of the present invention, wherein FIG.
(B) is a photograph of the SEM image of the surface.

FIGS. 4A and 4B are photographs of a case where nucleation of polysilicon has occurred on an oxide film in the same embodiment, where FIG. 4A is a photograph of an RHEED image and FIG. 4B is a photograph of an SEM image of the surface.

FIG. 5 is a graph showing a substrate temperature dependency of a critical amount for breaking selective growth in an example of the present invention.

FIG. 6 is a diagram showing a model of a growth mechanism of polysilicon grown on an oxide film.

FIG. 7 is a graph showing the substrate temperature dependence of the growth rate of an epitaxial silicon film.

FIG. 8 is a graph showing the substrate temperature dependence of a critical amount in an example in which selective growth was performed on a Si substrate patterned with a Si ₃ N ₄ film.

FIG. 9: Poly S formed on the surface of SiO ₂ film and Si ₃ N ₄ film
i layer is an SEM photograph of, (a) shows the SiO _2, (b) is Si ₃ N ₄
Is for

FIG. 10 is a graph showing the substrate temperature dependence of a critical amount that disrupts selective growth according to another embodiment of the present invention.

FIG. 11 is a graph showing the relationship between the flow rate of Si ₂ H ₆ gas and the pressure in another example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Gas nozzle 3 Liquid nitrogen shroud 4 Substrate holder 5 Heating device 6 Turbo molecular pump 7 Auxiliary rotary pump 8 Nude ion gauge 9 Substrate 13 Gas introduction system 14 Mass flow controller

(Equation 6)

(Equation 7)

(Equation 13)

(Equation 16)

[Equation 19]

(Equation 21)

(Equation 23)

(Equation 25)

[Equation 27]

[Equation 30]

(Equation 31)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tohru Tatsumi 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (56) References JP-A-1-227991 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) C30B 1/00-35/00 H01L 21/203-21/205

Claims (8)

(57) [Claims] 1. A method of forming a thin film on only a surface of at least one kind of material on a substrate having a surface made of at least two kinds of materials, comprising: (1) placing the substrate in a vacuum vessel; After the inside of the container is evacuated to a predetermined pressure, a reaction gas is introduced into the vacuum container. Are set in a pressure region that is longer than the shortest distance (L) between the substrate in the vacuum vessel and the vacuum-side exposed wall of the vacuum vessel (d>L); A thin film is grown only on one of the materials, and the reaction gas vacuum container is used until the total supply amount of the reaction gas introduced into the vacuum container reaches an amount sufficient to generate a thin film on the other material. A method for producing a thin film, characterized by stopping the introduction into the inside. 2. A method for forming a thin film only on a surface of at least one kind of material on a substrate having a surface made of at least two kinds of materials, comprising: (1) placing the substrate in a vacuum vessel; After the inside of the container is evacuated to a predetermined pressure, a reaction gas is introduced into the vacuum container. Are set in a pressure region that is longer than the shortest distance (L) between the substrate in the vacuum vessel and the vacuum-side exposed wall of the vacuum vessel (d>L); A thin film is grown on only one of the above materials, and the reactant gas is introduced into the vacuum vessel until the total amount of the reactant gas molecules flying on the substrate reaches an amount that generates a thin film on the other material. Stopping the film formation. 3. The method according to claim 1, wherein the pressure in the vacuum vessel to which the reaction gas is supplied is set to 1.5 × 10 ⁻² Torr or less. 4. The thin film forming method according to claim 1, wherein the at least two materials constituting the surface of the substrate have different adhesion coefficients with respect to the reaction gas. 5. The total amount of reaction gas molecules flying on the substrate Γ c
3. The ri is obtained by the equation (1).
Thin film preparation method described: Here, T is the temperature of the reaction gas, M is the molecular weight of the reaction gas molecule, N _A is the Avogadro number, and P is the pressure of the reaction gas.
Further, t cri is the supply speed v of the reaction gas when the pressure P is set, and is obtained by dividing the total supply amount Qc of the reaction gas when the thin film is formed on the other material by the equation (2). Value. (Equation 2) 6. The surface of the substrate is composed of SiO ₂ and Si, the reaction gas is Si ₂ H ₆ gas, and the conditions of Table 1 are set between the temperature of the substrate and the total critical molecular weight of the reaction gas. The method for preparing a thin film as described above. [Table 1] 7. When a reaction gas is supplied to a certain apparatus,
After obtaining the supply speed (v) of the reaction gas and the pressure (P) in the vacuum vessel, the critical supply amount Qc is calculated by using these values and the following equation 3 is used to calculate the critical supply amount. 3. The method for producing a thin film according to claim 2, wherein the introduction of the reaction gas into the vacuum vessel is stopped. (Equation 3) T is the temperature of the reaction gas, M is the molecular weight of the reaction gas N _A is Avogadro's number, cri cri is the total critical molecular weight 8. A method of forming a thin film on only a surface of at least one kind of material on a substrate having a surface made of at least two kinds of materials, comprising: (1) placing the substrate in a vacuum vessel; After the inside of the container is evacuated to a predetermined pressure, a reaction gas is introduced into the vacuum container. Are set in a pressure region that is longer than the shortest distance (L) between the substrate in the vacuum vessel and the vacuum-side exposed wall of the vacuum vessel (d>L); A thin film is grown on only one of the above materials, and the total amount of reactant gas supplied when the total amount of reactant gas introduced into the vacuum vessel reaches an amount sufficient to generate a thin film on the other material Measure
A method for forming a thin film, wherein the introduction of the reaction gas into the vacuum vessel is stopped until the measured total supply amount of the reaction gas is reached.