JPH10256404A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the variation in the diameter of crystal particles by allowing halogen to be absorbed by the surface of an insulating film using halogen gas. SOLUTION: Fluorine radicals 103b are generated using, for example, fluorine gas 103a. Then, the fluorine radicals are supplied to a silicon substrate in a vacuum equipment to allow fluorine atoms to be absorbed by the surface of a gate oxide film. Nextly, amorphous silicon 106a is deposited using, for example, disilane gas. Then, a heat treatment is conducted to crystallize the amorphous silicon. After that, amorphous silicon 107 is deposited again. This time, most of the fluorine atoms absorbed by the surface of the oxide film are desorbed through crystallization and heat treatment of the first amorphous silicon and therefore the second amorphous silicon deposited this time is evenly deposited on the entire surface of the semiconductor substrate. Then, the second amorphous silicon is heat-treated and then is crystallized with the first silicon particles as growth nuclei. Therefore, the silicon can be grown into polycrystalline silicon 108 of well-controlled grain diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for controlling a crystal grain size of polycrystalline silicon.
The present invention relates to a method for manufacturing a MOS semiconductor device having a gate electrode with improved reliability.

[0002]

2. Description of the Related Art In recent years, as the integration of semiconductor devices and the miniaturization of elements have progressed, MOS transistors and MOS transistors have been developed.
The thickness of the gate oxide film used for the capacitor is becoming thinner, and accordingly, its reliability has become an issue. It is known that the reliability is affected not only by the oxide film forming method but also by post-processes such as film formation, post-oxidation, patterning, and heat treatment of a polycrystalline silicon electrode.

Among them, the material of the gate electrode is C
VD (Chemical Vapor Deposit)
A polycrystalline silicon thin film formed by the (ion) method is generally used. When the silane degrades, silane (SiH ₄ ) gas diluted with a hydrogen gas is used to decompose the silane with energy such as heat to deposit on the semiconductor substrate.

FIG. 11 is a sectional view showing a process in the case where a gate electrode is formed by a conventional method. First, as shown in FIG. 11A, a gate oxide film 202 is formed on the surface of a silicon substrate 201 by a thermal oxidation method using an oxygen gas or a mixed gas of oxygen and hydrogen. Subsequently, as shown in FIG. 11B, the silicon thin film 203 is deposited on the substrate surface by thermally decomposing silane using a mixed gas of hydrogen and silane in a CVD apparatus. Subsequently, as shown in FIG. 11C, using POCl ₃ using nitrogen gas or the like as a carrier gas,
A phosphorus diffusion treatment is performed at 850 ° C. for 30 minutes to cause the silicon thin film 203 to contain phosphorus as a dopant. At this time, the silicon thin film to be deposited is usually a polycrystalline silicon film, and a problem caused by the thin film is becoming apparent. For example, at the time of phosphorus diffusion, phosphorus diffuses along the crystal grain boundary of polycrystalline silicon, and at this time, phosphorus that has reached the interface between the polycrystalline silicon and the oxide film directly enters the oxide film.
At this time, if the thickness of the gate oxide film is small, phosphorus easily penetrates to the silicon substrate, the phosphorus concentration of the channel increases, and the threshold voltage varies between elements.

[0005] In addition, NAND type EEPROMs, which have attracted attention as alternatives to magnetic memories and are characterized by low cost, high reliability, and high-speed writing characteristics, also have problems caused by polycrystalline silicon. NAND type EEPROM
Has two electrodes, an electrode (floating gate) for storing electric charges and an electrode (control gate) for forming an electric field for taking electric charges in and out of the floating gate. In a general device structure, a high voltage is applied to the control gate,
Electrical writing and erasing are performed by taking electrons in and out of the floating gate from the substrate via the insulating film. FIG. 12 is a process sectional view of a NAND type EEPROM. In FIG. 12, the same parts as in FIG.
The same reference numerals are given. First, as shown in FIG. 12A, an oxide film 202 is formed on a silicon substrate 201 by a thermal oxidation method using an oxygen gas or a mixed gas of oxygen and hydrogen.
Is formed, and then, as shown in FIG.
In the apparatus, for example, silane gas diluted with hydrogen gas is thermally decomposed, and polycrystalline silicon 203 serving as a floating gate is deposited. Next, phosphorus oxychloride (POCl ₃ ) is used, for example, at 850 ° C. using nitrogen gas as a carrier gas.
Is supplied to the substrate to perform a phosphorus diffusion process, so that the polycrystalline silicon 203 contains phosphorus as a dopant. next,
As shown in FIG. 12C, an oxide film 204 is formed on the surface of the polycrystalline silicon 203 by a thermal oxidation method using an oxygen gas or a mixed gas of oxygen and hydrogen. Subsequently, FIG.
As shown in FIG. 2D, a silane gas diluted with, for example, hydrogen gas is thermally decomposed in a CVD apparatus to deposit polycrystalline silicon 205 serving as a control gate, and phosphorus is added to the polycrystalline silicon in the same manner. Spread. At this time, as described with reference to FIG. 11A, since the floating gate and the control gate are polycrystalline silicon thin films, phosphorus penetrates the oxide film and the silicon substrate through the crystal grain boundaries, and the device characteristics vary. Is generated. Also,
When phosphorus is diffused in a polycrystalline silicon thin film serving as a floating gate, crystal grains of polycrystalline silicon grow and the surface roughness of the polycrystalline silicon increases. Further, when the polycrystalline silicon surface is thermally oxidized to form an oxide film 202,
Since the oxidation rate varies depending on the plane orientation of each crystal grain, the oxide film thickness varies. Variations in the surface roughness and oxide film thickness of the polycrystalline silicon cause a reduction in reliability due to electric field concentration and variations in characteristics such as threshold voltage between elements.

On the other hand, a method of forming polycrystalline silicon by crystallization of amorphous silicon has been studied. This is because, for example, a silane gas diluted with hydrogen is decomposed at a temperature lower than the temperature at which polycrystalline silicon is deposited and deposited on an oxide film, and this is crystallized by heat treatment at, for example, 600 ° C. in a nitrogen atmosphere. . According to this,
Since the deposition is in an amorphous state, the surface roughness of the silicon thin film is small, and the grain size of the polycrystalline silicon after crystallization can be increased, so that phosphorus seeps into the oxide film and the silicon substrate. The amount can also be reduced.

[0007]

However, in the case of a polycrystalline silicon thin film formed by crystallization of amorphous silicon, the crystal grain size varies, and an element having a large crystal grain and an element having a small crystal grain are mixed. However, variations in device characteristics cannot be fundamentally solved, and the crystal grain size varies depending on amorphous silicon film formation conditions and crystallization heat treatment conditions. However, it is necessary to intentionally control uniform crystal grains. It is difficult. In order to solve this, a method of forming the gate electrode with single crystal silicon has been considered. In this case, a method of exposing the silicon substrate by partially removing the frame film and growing single-crystal silicon using the silicon substrate as a seed can be considered, but the single-crystal silicon is uniformly deposited on the insulating film over a wide area. It is extremely difficult to form a silicon thin film. The present invention has been made in view of the above circumstances, and has as its object to provide a method for forming a highly reliable polycrystalline silicon gate electrode having a uniform crystal grain size.

[0008]

According to the present invention, the following means have been taken in order to solve the above-mentioned problems. The gist of the present invention is to make it possible to uniformly deposit granular silicon by adsorbing halogen on an insulating film using a halogen-based gas, deposit amorphous silicon from above, and perform crystallization heat treatment. Accordingly, it is an object of the present invention to provide a method for forming a highly reliable polycrystalline silicon gate electrode having a uniform crystal grain size by using granular silicon as a seed for crystal growth and controlling the crystal grain size of the polycrystalline silicon. .

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention comprises a step of forming an insulating film on a main surface of a semiconductor substrate; A step of adsorbing atoms or molecules on the insulating film; a step of depositing granular first silicon on the insulating film; and a step of depositing a second silicon thin film on the insulating film. It is characterized by.

A preferred embodiment of the present invention is as follows. (1) The step of growing the uniform crystal grains is performed in the second step.
Further comprising a step of smoothing the surface of the silicon by chemical mechanical polishing or dry etching. (2) An oxide film formed by heat treatment is used as the insulating film. (3) The step of exposing the insulating film to the halogen-based gas and the step of forming the first granular silicon on the insulating film are continuously performed in a non-oxidizing gas atmosphere or vacuum. (4) The granular first silicon to be deposited is amorphous silicon. (5) In the step of depositing the first granular silicon, at least one of a film formation temperature, a film formation gas composition, a film formation gas partial pressure, a film formation time, and a temperature rising atmosphere up to the film formation temperature is changed. Controlling the density of the silicon particles deposited on the insulating film. (6) Before the step of depositing the second silicon thin film,
Crystallizing the deposited granular first silicon by heat treatment. (7) In the step of depositing the second silicon thin film, the amount of the natural oxide film formed on the surface of the first silicon grain is 4 ×
It should be 10 ¹⁴ / cm ² or less. (8) The silicon thin film to be deposited is amorphous silicon. (9) The first granular silicon and the second silicon thin film contain a group III or group V element. (10) The second silicon thin film is crystallized by heat treatment. (11) The crystallized silicon thin film is used as a gate electrode of a MOS semiconductor device.

According to the method of the present invention as described above, a polycrystalline silicon film having a smooth surface and a controlled crystal grain size can be formed on an insulating film. By using the floating gate or the control gate of a type EEPROM, variation in characteristics between elements can be suppressed and high reliability can be realized.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process cross-sectional view showing a method for manufacturing polycrystalline silicon with a controlled crystal grain size according to the first embodiment.

First, as shown in FIG. 1A, a mirror-polished semiconductor substrate 101 is dropped on a semiconductor substrate 101 in a pure oxygen atmosphere or a mixed gas of oxygen and hydrogen at 850 ° C.
To form oxide film 102 to a desired thickness.
Subsequently, as shown in FIG. 1B, for example, a fluorine (F ₂ ) gas 103a is microwave-discharged in a cavity 105 in an alumina tube 104 to generate fluorine radicals 103b, which are generated in a vacuum device. It is supplied to the silicon substrate. As a result, fluorine atoms are adsorbed on the surface of the gate oxide film. Next, amorphous silicon 106a is deposited at 400 ° C. using disilane (Si ₂ H ₆ ) gas. At this time, the deposited amorphous silicon 1
06a accumulates granularly as shown in FIG. 1 (c). This is because the silicon film hardly deposits on the surface of the oxide film on which the fluorine atoms are adsorbed, and silane is adsorbed and desorbed in the portion where the fluorine atoms are desorbed locally, and silicon is deposited. Subsequently, the silicon substrate is heated in a vacuum or in a non-oxidizing atmosphere at 600 ° C.
For 2 hours. Thereby, the amorphous silicon grains on the oxide film surface are crystallized. At this time, since the size of the silicon grain 106b is sufficiently small, the silicon grain 106b is single-crystallized. Further, as shown in FIG. 1D, disilane gas is again supplied to the substrate, and amorphous silicon 107 is deposited at 400 ° C. At this time, the fluorine atoms adsorbed on the oxide film surface are removed by the crystallization heat treatment (6).
(00 ° C., 30 minutes), the second amorphous silicon, which is mostly desorbed and deposited, as shown in FIG.
It is uniformly deposited on the entire surface of the semiconductor substrate. Subsequently, the semiconductor substrate is heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere. At this time, the second amorphous silicon crystallizes,
At that time, generation of crystal nuclei from other regions such as on the oxide film has a latent time, and thus crystallization proceeds with the first silicon grains as growth nuclei. Therefore, as shown in FIG. 1E, it is possible to grow the polysilicon 108 having a controlled grain size.

FIG. 2 is a process sectional view showing a second embodiment of a method for producing polycrystalline silicon having a controlled crystal grain size. As in the first embodiment shown in FIG.
(A) As shown in FIG.
The oxide film 3 is thermally oxidized at 850 ° C., for example, in a pure oxygen atmosphere or using a mixed gas of oxygen and hydrogen.
02 to a desired thickness. Subsequently, as shown in FIG. 2B, for example, a fluorine (F ₂ ) gas 303 a is microwave-discharged by a cavity 305 in an alumina tube 304 to generate a fluorine radical 303 b, which is generated in a vacuum device. It is supplied to the silicon substrate. As a result, fluorine atoms are adsorbed on the surface of the gate oxide film. Next, amorphous silicon 306a is deposited at 400 ° C. using disilane gas. At this time, the deposited amorphous silicon 307 is deposited in a granular form as shown in FIG. Subsequently, the silicon substrate is heated in a vacuum or in a non-oxidizing atmosphere and subjected to a heat treatment at 600 ° C. for 2 hours. Thereby, the amorphous silicon grains on the oxide film surface are crystallized. Further, as shown in FIG. 2D, disilane gas is again supplied to the substrate, and amorphous silicon 307 is uniformly deposited on the entire surface of the semiconductor substrate at 400 ° C. Subsequently, the semiconductor substrate is heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere. At this time, the second amorphous silicon is crystallized, but at this time, generation of crystal nuclei from other regions such as on an oxide film has a latent time, so crystallization is performed using the first silicon grains as growth nuclei. move on. Therefore,
As shown in FIG. 2E, it can be grown on polycrystalline silicon 308 having a controlled grain size. In the second embodiment, since the size of the amorphous silicon grains serving as the crystal growth nucleus is larger than that of the embodiment of FIG. 1, irregularities are formed on the surface of the amorphous silicon as shown in FIG. It is formed. This unevenness on the surface is shown in FIG.
As shown in FIG. For example, NAND
In the case of a type EEPROM, this polycrystalline silicon is used as a floating gate, and an insulating thin film and polycrystalline silicon serving as a control gate are formed thereon. However, unevenness of the surface of the floating gate causes variations in characteristics between elements.

To avoid this, as shown in FIG. 2F, the surface of the polycrystalline silicon is subjected to chemical mechanical polishing (Chemic polishing).
al Mechanical polish) method to flatten the surface. At this time, a similar effect can be obtained even if the surface is flattened by a dry etching method other than the chemical mechanical polishing method.

FIG. 3 shows the substrate temperature dependence of the amount of fluorine adsorbed on the oxide film after the fluorine radicals are supplied to the silicon substrate surface at room temperature. Thus, the surface of the oxide film exposed to fluorine radicals at room temperature is about 2 × 10 ¹⁵ / cm 2
A large amount of fluorine atoms are adsorbed, and the amount of adsorption tends to decrease gradually as the substrate temperature rises. Even at a film forming temperature of about 520 ° C., about 1 × 10 ¹⁵ / cm ² of fluorine is oxide film. It can be seen that it remains on the surface. The adsorbed fluorine suppresses the adsorption / decomposition of silane as a film forming species. Then, the silane adsorption / decomposition reaction occurs only in the portion where the fluorine film is not locally adsorbed and the oxide film surface is exposed, and the deposited amorphous silicon grows in a granular form. However, this tendency is shown in a vacuum or in a non-oxidizing atmosphere. In an oxidizing atmosphere, particularly in the presence of moisture, fluorine adsorbed on the oxide film reacts with moisture and is desorbed. As a result, the effect of suppressing the adsorption / decomposition reaction of silane by the fluorine atoms on the surface of the oxide film is lost, and the deposited amorphous silicon does not become granular but is uniformly deposited on the entire surface. Therefore,
It is necessary to continuously deposit amorphous silicon on a silicon substrate treated with fluorine radicals while keeping it in a vacuum or in a non-oxidizing atmosphere.

On the other hand, amorphous silicon is deposited on the underlying crystalline silicon by changing the amount of oxygen at the interface, and when the crystal is grown at 600 ° C. for 2 hours, the amount of oxygen at the interface is 3 × 10 ¹⁵ / cm 3. ^In the case of ² , the amorphous silicon deposited on the upper part cannot take over the crystallinity of the underlying silicon and grow epitaxially, and crystal growth nuclei are formed in the amorphous silicon and polycrystallized.
On the other hand, by controlling the amount of oxygen at the interface to about 4 × 10 ¹⁴ / cm ² or less, epitaxial growth can be performed while inheriting the crystallinity of the underlying silicon. Therefore, in the case of the present invention, since the granular silicon is used as a crystal growth nucleus, the residual oxygen amount on the surface of the granular silicon is 4 × 10 4
^It is necessary to deposit amorphous silicon in a state where it is suppressed to ¹⁴ / cm ² or less. As described above, as a method of suppressing the amount of residual oxygen on the surface of the granular silicon, before forming the second amorphous silicon, for example, a treatment with dilute hydrofluoric acid is performed to terminate the silicon particle surface with hydrogen and prevent oxidation. Is formed. However, this method cannot be applied to a gate oxide film. If the gate electrode is to be formed of polycrystalline silicon according to the present invention,
If dilute hydrofluoric acid treatment is performed before depositing the second amorphous silicon, the gate oxide film is etched and the oxide film thickness is reduced, and the oxide film thickness immediately below the granular silicon and the etched oxide film are reduced. There is a difference between the thickness and the film thickness, and irregularities are formed on the surface of the gate oxide film, resulting in deterioration of device characteristics. Therefore, when the present invention is applied to a gate electrode, after forming the first granular amorphous silicon, a crystallization heat treatment is performed in a vacuum or an oxidizing atmosphere to prevent the surface of the granular amorphous silicon from being oxidized. The second amorphous silicon film is formed while maintaining this atmosphere. Thereby, crystallization of the second amorphous silicon can be advanced using the granular silicon as a crystal growth nucleus.

FIGS. 4 and 5 are process sectional views showing a method for producing polycrystalline silicon having a controlled crystal grain size according to the third and fourth embodiments. Similar to the embodiment of FIGS. 1 and 2, first, as shown in FIGS. 4 (a) and 5 (a),
On the mirror-polished semiconductor substrate 601 (701),
The oxide film 602 (70) is thermally oxidized in a pure oxygen atmosphere or using a mixed gas of oxygen and hydrogen at, for example, 850 ° C.
2) is formed to a desired thickness. Subsequently, as shown in FIGS. 4B and 5B, for example, a fluorine (F ₂ ) gas 6
03a (703a) is microwave-discharged by a cavity 605 (705) in an alumina tube 604 (704) to generate fluorine radicals 603b (703b), which are supplied to the silicon substrate in a vacuum apparatus. As a result, fluorine atoms are adsorbed on the surface of the gate oxide film. Next, amorphous silicon 606a (706a) is deposited at 400 ° C. using disilane gas. At this time, the deposited amorphous silicon is deposited granularly as shown in FIGS. 4C and 5C, and the generation density of the granular silicon can be controlled by the deposition conditions. Subsequently, the silicon substrate is heated in a vacuum or kept in a non-oxidizing atmosphere and subjected to a heat treatment at 600 ° C. for 2 hours to crystallize amorphous silicon grains on the surface of the oxide film. Further, as shown in FIGS. 4D and 5D, disilane gas is again supplied to the substrate, and amorphous silicon 607 (707) is continuously deposited uniformly at 400 ° C. over the entire surface of the semiconductor substrate. Subsequently, the semiconductor substrate is heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere. At this time, the second amorphous silicon is crystallized. At this time, since the crystallization proceeds with the first silicon grains as growth nuclei, the first amorphous silicon is crystallized as shown in FIGS. Reflecting the density of the granular silicon of polycrystalline silicon 608
The particle size of (708) can be controlled.

As described above, a method for controlling the production density of granular amorphous silicon includes at least one of a film forming temperature, a film forming gas composition, a film forming gas partial pressure, a film forming time, and a temperature rising atmosphere up to the film forming temperature. Change one. As an example, first, as shown in FIG. 3, the substrate temperature after the treatment with the fluorine radical is given. The amount of adsorbed fluorine remaining on the oxide film varies depending on the substrate temperature. As the substrate temperature increases, the amount of adsorbed fluorine desorbs and decreases, and the portion where the oxide film is exposed increases. Therefore, when it is desired to increase the formation density of the first granular amorphous silicon in order to obtain a small crystal grain size, the substrate temperature is increased before film formation, and the adsorbed fluorine is desorbed from the oxide film surface. On the contrary, in order to obtain a large crystal grain size, without increasing the temperature before film formation,
What is necessary is just to keep the state in which fluorine is left on the oxide film and suppress the generation density of granular amorphous silicon.

FIG. 6 shows an example of the film forming pressure and the density of the granular amorphous silicon produced. As shown therein, the formation density of granular amorphous silicon can be increased by setting the film formation pressure from 0.1 Torr to 0.2 Torr. Further, as shown in FIG. 7, the same applies to the partial pressure (dilution concentration) of the film forming gas. By increasing the partial pressure, the generation density of granular amorphous silicon increases.

Further, the production density of the granular amorphous silicon on the oxide film can be controlled also by the film forming temperature of the amorphous silicon. An example of this is shown in FIG. According to this, the generation density of granular amorphous silicon is 4
The lowest value is around 00 ° C (1000 / K 1.49),
At a temperature higher than this, the fluorine adsorbed on the oxide film is desorbed, and the number of sites where disilane molecules can be adsorbed and decomposed increases, so that the generation density of granular amorphous silicon increases. Further, with respect to the film formation temperature of 400 ° C. or less, fluorine adsorbed on the oxide film is not easily desorbed,
When the disilane molecules are adsorbed on the surface, the distance to move on the plane is small due to the low temperature, making it difficult to reach the oxidized armpit surface part where fluorine has been desorbed, and desorbed again in the gas phase Energy cannot be obtained, and as a result, a decomposition reaction occurs between the disilane molecules adsorbed on the surface and between the disilane molecules in the gas phase and the granular amorphous silicon on the oxide film surface The production density increases. Therefore, in order to suppress the generation density of granular amorphous silicon and increase the grain size of polycrystalline silicon, the film forming temperature is set to around 400 ° C., and conversely, if the grain size is to be reduced, a temperature of 300 ° C. or 500 ° C. May be formed.

As described above, the generation density of granular amorphous silicon can be controlled by appropriately selecting the pressure and temperature during film formation. In the present invention, granular silicon is formed by crystallization of amorphous silicon. However, granular silicon can also be formed by directly forming crystallized silicon from a gas phase. In this case, for example, the film is formed under ordinary epitaxial growth conditions in which the film forming temperature is 750 ° C. and the pressure is 1 × 10 ⁻⁴ Torr or less. Also in this case, silicon is formed in a granular form on the oxide film, but the surface of the oxide film is etched by silane simultaneously with the deposition due to the high deposition temperature and low pressure. In this case, the device characteristics may be degraded, for example, the oxide film thickness may change or the surface may be uneven. Therefore, in the present invention, the first granular silicon is amorphous silicon.

FIG. 9 is a process sectional view of a MOS type semiconductor device manufactured by using the present invention. First, for example, a silicon substrate 1201 that has been subjected to mirror polishing is prepared, and an element isolation oxide film 1202 is formed on the silicon substrate 1201 by using a selective oxidation method. If necessary, ion implantation such as formation of a well is performed on the silicon substrate. For example, 1 × 1 phosphorus ion
0 ¹³ / cm ² , 1 × 10 ¹³ boron ions in the p-well
/ Cm ² ions are implanted. Thereafter, thermal oxidation is performed at 850 ° C. for 40 minutes in a pure oxygen atmosphere to form a MOS gate oxide film 1203 having a thickness of 7 nm. Subsequently, FIG.
As shown in (b), for example, fluorine (F ₂ ) gas 120
4a is microwave-discharged through a cavity 1206 in an alumina tube 1205 to produce fluorine radicals 1204b.
Is supplied to the silicon substrate in a vacuum apparatus. As a result, fluorine atoms are adsorbed on the surface of the gate oxide film. Next, as shown in FIG. 9C, the granular amorphous silicon 1 was formed at 400 ° C. using disilane gas.
Deposit 208a. Subsequently, the silicon substrate is heated in a vacuum or in a non-oxidizing atmosphere,
Heat treatment at ℃ for 2 hours. Thereby, the amorphous silicon grains on the oxide film surface are crystallized. Further, FIG.
As shown in (d), disilane gas is again supplied to the substrate, and amorphous silicon is uniformly deposited on the entire surface of the semiconductor substrate at 520 ° C. Subsequently, the semiconductor substrate is
By performing heat treatment in a nitrogen atmosphere at a temperature of 2 ° C. for 2 hours, the second amorphous silicon was crystallized using the first granular silicon as a growth nucleus, and the grain size was controlled as shown in FIG. Grow on polycrystalline silicon 1208b. Subsequently, for example, phosphorus oxychloride (POCl ₃ ) is supplied to the substrate using nitrogen gas as a carrier gas, and a phosphorus diffusion treatment is performed at 850 ° C. for 30 minutes, so that phosphorus as a dopant is contained in the polycrystalline silicon 1208b. Next, FIG.
As shown in (1), a resist pattern 1209 is formed using a normal photolithography technique. Using this resist pattern as a mask, as shown in FIG. 9G, the polycrystalline silicon is etched by, for example, a reactive ion etching (RIE) method. Next, as shown in FIG. 9H, after the gate electrode is oxidized to cover the gate electrode polycrystalline silicon with an oxide film 1210, an element serving as a dopant is formed to form the source / drain diffusion layer 1211. Is ion-implanted. Phosphorus or arsenic ions are implanted into the n-type diffusion layer at a high concentration, and B or BF ²⁺ ions are implanted into the p-type diffusion layer at a high concentration.
These dopants, which have been ion-implanted at a high temperature for a short time, such as 30 seconds, are activated. Subsequently, as shown in FIG. 9I, after a silicon oxide film 1212 is deposited on the entire surface by a CVD method, a contact hole is opened in the silicon oxide film by anisotropic dry etching.

Next, silicon and steel, for example, are each added to a thickness of 0.1 mm.
After forming an aluminum film containing 5% each, this is patterned to form source / drain electrodes 1213. Thereafter, heat treatment was performed at 450 ° C. for 15 minutes in a nitrogen atmosphere containing 10% of hydrogen. As a result, a MOS semiconductor device in which the crystal grain size of the polysilicon gate electrode was controlled could be formed.

FIG. 10 is a process sectional view of an embodiment applied to a floating gate and a control gate of a NAND type EEPROM. In the same manner as in FIG. 9, for example, as shown in FIG. 10A, a mirror-polished silicon substrate 1301 is prepared, and ion implantation such as formation of a well is performed on the silicon substrate as necessary. Thereafter, thermal oxidation is performed at 850 ° C. for 40 minutes in a pure oxygen atmosphere, and M
A gate oxide film 302 of OS is formed to a thickness of 7 nm. Subsequently, as shown in FIG. 10B, for example, a fluorine (F ₂ ) gas 1303 a is microwave-discharged by a cavity 1305 in an alumina tube 1304 to generate a fluorine radical 1303 b, which is generated in a vacuum device. It is supplied to the silicon substrate. As a result, fluorine atoms are adsorbed on the surface of the gate oxide film. Next, as shown in FIG. 10C, granular amorphous silicon 1306a is deposited at 400 ° C. using disilane gas. Subsequently, the silicon substrate is heated in a vacuum or in a non-oxidizing atmosphere, and subjected to a heat treatment at 600 ° C. for 2 hours. Thereby, the amorphous silicon grains on the oxide film surface are crystallized. Further, as shown in FIG. 10D, disilane gas is supplied to the substrate again, and amorphous silicon 1306a is uniformly deposited at 400 ° C. on the entire surface of the semiconductor substrate. Subsequently, the semiconductor substrate is subjected to a heat treatment at 600 ° C. for 2 hours in a nitrogen atmosphere to crystallize the second amorphous silicon using the first granular silicon as a growth nucleus.
As shown in FIG. 3E, a polycrystalline silicon 1307b having a controlled grain size is grown. Subsequently, for example, phosphorus oxychloride (POCl ₃ ) is supplied to the substrate by using nitrogen gas as a carrier gas, and a phosphorus diffusion treatment is performed at 850 ° C. for 30 minutes so that phosphorus as a dopant is contained in the polycrystalline silicon.
Next, as shown in FIG. 10F, the surface of the polycrystalline silicon is thermally oxidized by, for example, about 15 nm in a pure oxygen atmosphere to form an oxide film 1308 serving as an interpoly insulating film. At this time, the interpoly insulating film 1308 is not limited to a thermal oxide film, but may be any reliable insulating film functioning as a transistor. For example, an oxide film formed by a CVD method, an oxynitride film, Similar effects can be obtained by using an ONO film. Subsequently, in the same manner as the formation of the floating gate, for example, fluorine (F ₂ ) gas is subjected to microwave discharge through a cavity in an alumina tube to generate fluorine radicals. To the silicon substrate. As a result, fluorine atoms are adsorbed on the surface of the interpoly insulating film 1308.

Next, as shown in FIG. 10 (g), granular amorphous silicon 1309a is deposited at 400 ° C. using disilane gas. Subsequently, the silicon substrate is heated in a vacuum or in a non-oxidizing atmosphere, and
Heat treatment is performed at 00 ° C. for 2 hours. Thereby, the amorphous silicon grains on the oxide film surface are crystallized. Further, as shown in FIG. 10H, disilane gas is again supplied to the substrate, and amorphous silicon 13a is uniformly deposited on the entire surface of the semiconductor substrate at 400.degree. Subsequently, FIG.
As shown in (1), the semiconductor substrate is subjected to a heat treatment in a nitrogen atmosphere at 600 ° C. for 2 hours to crystallize the amorphous silicon deposited on the entire surface using the granular silicon on the surface of the interpoly insulating film as a growth nucleus. Subsequently, for example, phosphorus oxychloride (POC) is used with nitrogen gas as a carrier gas.
l ₃ ) is supplied to the substrate, and a phosphorus diffusion treatment is performed at 850 ° C. for 30 minutes so that phosphorus as a dopant is contained in the polycrystalline silicon. As described above, a floating gate 1307b and a control gate 1310b made of polycrystalline silicon having a controlled grain size were formed.

In this embodiment, disilane (Si ₂ H ₆ ) gas is used as the amorphous silicon deposition gas. However, the gas type is not limited, and any gas that can form a silicon layer may be used. For example, silane (Si
H ₄ ), SiH ₂ Cl ₂ , SiCl ₄ , SiF ₄ ,
Si ₂ H ₄ Cl ₂ , SiH ₂ F ₂ , Si ₂ H ₂ Cl ₄ , Si ₂ C
l _6, a Si ₂ H ₄ F _2, Si even _{2 H 2 F 4, Si 2} F 6 can be applied. In addition, in the present invention, phosphorus diffusion treatment using phosphorus oxychloride (POCl ₃ ) was performed as a method for introducing a dopant, but a method of introducing a dopant by ion implantation may be employed, and an impurity-doped amorphous silicon layer may be deposited. May be. At this time, phosphine (PH ₃ ), arsine (AsH ₃ ), or a halide containing phosphorus or arsenic may be mixed with a silicon film formation gas such as disilane. In the case of a P-type gate electrode, diborane (B ₂ H ₆ ), boron trichloride (BCl ₃ ),
Boron trifluoride (BF ₃ ) or a halide containing B may be mixed. Further, as a pretreatment for selectively depositing an amorphous silicon film only on the silicon surface, fluorine radicals were generated by microwave discharge using F _2. However, this method uses another halogen-based material such as CF _4. , Cl ₂ , SF ₆ , HF, ClF ₃ or the like.
However, since some gases etch an oxide film, it is preferable that the oxide film is not etched when the present invention is used for a gate electrode. The present invention is not limited to the above embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

[0028]

According to the present invention, the following effects can be obtained. According to the present invention, a polycrystalline silicon film having a smooth surface and a controlled crystal grain size can be formed on an insulating film, and this can be formed on a gate electrode or a NAN of a MOS semiconductor device.
By using the semiconductor device as a floating gate or a control gate of a D-type EEPROM, a highly reliable semiconductor device with less variation in characteristics between elements can be formed.

[Brief description of the drawings]

FIG. 1 is a process cross-sectional view showing an example of a method for producing polycrystalline silicon having a controlled grain size formed according to the present invention.

FIG. 2 is a process cross-sectional view showing an example of a method for producing polycrystalline silicon having a controlled grain size formed according to the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the substrate temperature and the amount of fluorine adsorbed on an oxide film for explaining the effect of the present invention.

FIG. 4 is a process cross-sectional view showing an example of a method for producing polycrystalline silicon having a controlled grain size formed according to the present invention.

FIG. 5 is a process cross-sectional view showing an example of a method for producing polycrystalline silicon having a controlled grain size formed according to the present invention.

FIG. 6 is a characteristic diagram showing a relationship between a film forming pressure and a generation density of granular amorphous silicon on the surface of an oxide film for explaining an effect of the present invention.

FIG. 7 is a characteristic diagram showing the relationship between the partial pressure of disilane and the generation density of granular amorphous silicon on the surface of an oxide film for explaining the effect of the present invention.

FIG. 8 is a characteristic diagram showing a relationship between a film forming temperature and a generation density of granular amorphous silicon on the surface of an oxide film for explaining an effect of the present invention.

FIG. 9 is a process sectional view showing an example of a MOS transistor formed according to the present invention.

FIG. 10 shows a NAND type EEPR formed according to the present invention.
Sectional drawing which shows an example of OM.

FIG. 11 is a process sectional view showing an example of a method for manufacturing polycrystalline silicon according to a conventional technique.

FIG. 12 is a process cross-sectional view showing another example of a method for manufacturing polycrystalline silicon according to a conventional technique.

[Explanation of symbols]

 Reference Signs List 101: silicon substrate, 102: thermal oxide film, 103a: fluorine gas, 103b: fluorine radical, 104: alumina tube, 105: cavity 106a: granular amorphous silicon, 106a: granular single crystal silicon, 107: amorphous silicon, 108: many Crystal silicon, 201: silicon substrate, 202: thermal oxide film, 203: floating gate electrode, 204: interpoly insulating film, 204: control gate electrode, 301: silicon substrate, 302: thermal oxide film, 303a: fluorine gas, 303b: fluorine radical, 304: alumina tube, 305: cavity, 306a: granular amorphous silicon, 306a: granular single crystal silicon, 307: amorphous silicon, 308: polycrystalline silicon, 601: silicon substrate, 602: thermal oxide film, 603a: fluorine gas, 603b: fluorine radical, 604: alumina tube, 605: cavity, 606a: granular amorphous silicon, 606a: granular single crystal silicon, 607: amorphous silicon, 608: polycrystalline silicon, 701 ... Silicon substrate, 702 ... thermal oxide film, 703a ... fluorine gas, 703b ... fluorine radical, 704 ... alumina tube, 705 ... cavity, 706a ... granular amorphous silicon, 706a ... granular single crystal silicon, 707 ... amorphous silicon, 708 ... multiple Crystal silicon, 1201 silicon substrate, 1202 element isolation insulating film, 1203 thermal oxide film, 1204a fluorine gas, 1204b fluorine radical, 1205 alumina tube, 1206 cavity, 1207 ... granular amorphous silicon, 1207b ... granular single crystal silicon, 1208a ... amorphous silicon, 1208b ... polycrystalline silicon, 1209 ... resist, 1210 ... oxide film, 1211 ... source / drain diffusion layer, 1212 ... CVD oxide film, 1213 ... source Drain electrode 1301 silicon substrate 1302 thermal oxide film 1303a fluorine gas 1303b fluorine radical 1304 alumina tube 1305 cavity 1306a granular amorphous silicon 1306b granular single crystal silicon 1307a amorphous silicon 1307b: polycrystalline silicon (floating gate) 1308: interpoly insulating film, 1309a: granular amorphous silicon, 1309b: granular single crystal silicon, 1310 ... amorphous silicon, 1310b ... polycrystalline silicon (control gate).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/304 321 H01L 29/78 301P 27/115 301G 29/78 21/336

Claims (2)

[Claims] A step of forming an insulating film on a main surface of the semiconductor substrate; and supplying a halogen-based gas to the main surface of the semiconductor substrate.
A step of adsorbing halogen atoms or molecules on the insulating film, a step of depositing granular first silicon on the insulating film, and a step of depositing a second silicon thin film on the insulating film;
A method for manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 2, wherein the step of growing the uniform crystal grains includes the step of smoothing the surface of the second silicon by a chemical mechanical polishing method or dry etching. A method for manufacturing a semiconductor device, further comprising: