JP2966157B2 - Method of forming gate electrode structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a gate electrode structure, and more particularly, to a method for forming a thin film having a very small thickness and an insulating layer provided between a Si underlayer and a gate electrode. And a method for forming a gate electrode structure.

[0002]

2. Description of the Related Art A silicon integrated circuit formed by a state-of-the-art technology uses an oxide film having a very small thickness, particularly a silicon oxide film (for example, an SiO ₂ film). Especially 1.
Non-volatile semiconductor memory having a design rule of 0 μm or less, particularly 1 MEEPROM (Electrically
rasable and programmable
In the read-only memory, an SiO ₂ film having a thickness of, for example, 100 Å or less (hereinafter, Angstroms is indicated by a symbol of A °) is used as a tunnel oxide film. The characteristics of such a thin oxide film depend on the number of rewrites in the operation of the EEPROM,
It is a very important factor in determining the data storage time.

[0003] The formation of such an oxide film is described, for example, in the literature:
As disclosed in "VLSI Manufacturing Technology, edited by Wei Tokuyama and Tetsuichi Hashimoto, Nikkei BP, P. 83 (1989)", the following procedure is performed.

In the method disclosed in this document, a cleaned substrate is first placed in a quartz tube heated to 800 to 1200 ° C. by an electric furnace. Thereafter, an oxidizing gas for forming an oxide film is introduced into the quartz tube. As the oxidizing gas, for example, dry oxygen gas, a mixed gas of oxygen and hydrogen, or a gas obtained by atomizing hydrochloric acid and mixing with oxygen gas is used. In a quartz tube into which an oxidizing gas has been introduced, the substrate is left at a constant temperature for a certain period of time corresponding to the film thickness to be formed, and the oxide film is continuously grown, so that an oxide film having a uniform film thickness is formed on the substrate surface. Has formed.

Next, referring to FIGS. 6A and 6B, the EEPR is applied by applying such a method of forming an oxide film.
A conventional example of manufacturing an OM will be briefly described. FIG. 6A is a schematic diagram for explaining a step of forming a conductive polySi layer (a layer serving as a gate electrode layer) on a Si (silicon) substrate with an SiO ₂ film interposed therebetween. FIG. 6B is a schematic diagram for explaining the state of the conductive polysilicon (polySi) layer after the heat treatment (annealing) is performed after the layer is formed.
This is shown in a state of a cross section of a gate electrode structure having a structure.

According to this conventional method, an SiO ₂ film 102 is formed as a tunnel oxide film on a Si substrate 100, and a conductive poly-Si layer 104 is formed on the SiO ₂ film 102. Usually, the conductive poly-Si layer 104 is formed as an n-conductive type by introducing phosphorus (P) as an impurity at a high concentration. The structure thus formed is shown in FIG. Normally, no grain boundaries are generated in the poly-Si layer in a state where the poly-Si layer 104 is formed. Therefore, not only the thickness of the SiO ₂ film but also the interface between the poly Si layer and the SiO ₂ film maintains flatness.

[0007]

However, after this poly-Si layer 104 is formed as a gate electrode, usually, during the step of providing an intermediate insulating layer (not shown) between the gate electrodes, it is performed at a high temperature of 1000 ° C. or more. Since the heat treatment is performed, phosphorus introduced into the poly-Si layer 104 is segregated to generate a grain boundary 106 (FIG. 6B). The grain boundaries grow while growing the poly-Si layer 104 and the
It reaches the interface with the O ₂ film 12, and at this interface, the grain boundary 106
Reacts with the phosphorus (P) segregated to the SiO ₂ film 104,
Therefore, the SiO ₂ film 102 grows abnormally in the region near the grain boundary, and a so-called oxide ridge 108 is generated (for example, reference: “1990 Symposi”).
umon VLSI Technology, Dige
st of technical papers, p
p. 121 (1990) ".

Due to the generation of the oxide ridge 108, for example, when the EEPROM operates, particularly when data is erased, a variation in tunnel current occurs.

In order to avoid this variation, a method of performing a heat treatment at a lower temperature after the formation of the poly-Si layer and a method of lowering the phosphorus concentration have been tried (for example, literature: "Nikkei Microdevice, No. 64"). (199
0), pp. 85-86 ").

However, using these methods,
There is a new problem that the activation of the impurity cannot be sufficiently achieved, and the resistance value of the poly-Si itself does not decrease.

The present invention has been made in view of the above-mentioned various problems of the related art, and accordingly, an object of the present invention is to provide a thin film having a very small thickness provided between a Si base and a gate electrode. It is another object of the present invention to provide a method for forming a gate electrode structure for forming a thin film including a Si oxide film with high quality.

[0012]

According to the present invention, there is provided a method for forming a gate electrode structure, comprising the steps of: forming a conductive film by interposing a Si oxide film on a lower surface of Si in the same reactor; In forming the gate electrode of the poly-Si layer,
(A) a step of performing a heat treatment of a Si underlayer in an oxidizing gas atmosphere to form a thin Si oxide film on the surface of the Si underlayer; Heat treatment is performed in a first mixed gas atmosphere of a reactive gas to form a thin Si-Ge film on the Si oxide film.
A step of forming a film; and (c) a heat treatment is then performed in a second mixed gas atmosphere of the Si-containing reactive gas and the impurity-containing reactive gas for determining conductivity, thereby forming the Si-Ge film described above. Forming a conductive poly-Si layer thereon.

[0013] In implementing the present invention, preferably, each of the Si-containing reactive gas silane (Si _m H
_n : wherein m and n are integers of 1 or more) gas, and the Ge-containing reactive gas is a germane-based (Ge
_m H _n: where, m and n is good an integer of 1 or more) gas.

According to a preferred embodiment of the present invention, the reactive gas containing impurities is preferably a phosphine (PH ₃ ) gas or an arsine (AsH ₃ ) gas.

In practicing the present invention, preferably, the conductive poly-Si layer is an n-conductive type layer.

In practicing the present invention, preferably, the Si oxide film is a SiO ₂ film.

According to a preferred embodiment of the present invention, S
It is preferable that the i-Ge film be a non-doped film that does not contain an impurity imparting conductivity.

In practicing the present invention, the composition of the Si-Ge film is preferably set to Si _1-x Ge _x (where x is any value in the range of 0 <x <1). .

In practicing the present invention, preferably, the heat treatment is performed by infrared irradiation.

Here, the silicon underlayer means not only a silicon substrate, but also an epitaxial layer formed on this silicon substrate, and not limited thereto, and at least the surface region of the underlayer is formed of silicon. Widely means groundwork.

[0021]

SUMMARY OF According to the method for forming the gate electrode structure of the invention described above, after forming the temporarily Si-Ge film on the SiO ₂ film, a conductive poly-Si for the gate electrode formed on the Si-Ge film Layers are provided. Therefore, even if a grain boundary is generated in the poly-Si layer when a required heat treatment is performed in a subsequent step, the growth of the grain boundary can be suppressed at the Si-Ge film. Therefore, this grain boundary is formed by the lower Si
It does not reach the O ₂ film, and therefore, the SiO ₂ film / Si-Ge
Oxide ridge generation at the film interface and in the vicinity thereof can be suppressed. Therefore, the SiO ₂ film / S
The interface between the i-Ge film becomes extremely flat and SiO 2
The thicknesses of the _two films themselves are also substantially constant.

As a result, when an element using such a gate electrode structure is formed, the tunnel current under a certain electric field can maintain a constant state without variation among the elements.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings only schematically show the dimensions, shapes, and arrangement positions of the components so that the invention can be understood. In the following description, specific materials and specific numerical conditions will be described. However, these materials and conditions are merely preferable examples, and are not limited thereto.

First, before describing the method of the present invention,
An apparatus for carrying out the present invention will be described.

<Description of Embodiment of Structure of Film Forming Apparatus Suitable for Use in Carrying Out the Present Invention> FIG. 3 shows main parts (mainly a reaction furnace and a reactor) of a film forming apparatus for carrying out the method of the present invention. FIG. 3 is a cross-sectional view schematically showing a configuration of a heating unit.
FIG. 3 shows a state where the substrate is installed in the reaction furnace.

FIG. 4 is a view for explaining an embodiment of the present invention, and is a view schematically showing an entire configuration of a film forming apparatus.

As shown in FIG. 3, the main parts of the film forming apparatus include a reaction furnace 10 in which a substrate is installed, an exhaust unit 12 for evacuating the reaction furnace 10, and a gas supply unit 14.
And a heating unit 16 for performing a heat treatment.
Hereinafter, an embodiment of the structure of the main part will be described.

As shown in FIG. 3, in this embodiment, the reaction furnace (chamber) 10 includes, for example, a main body 10a, a lid member 10
b and the elevating member 10c. For example, stainless steel may be used as a material for forming the main body 10a and the elevating member 10c, and quartz may be used as a material for forming the lid member 10b and a support 20 to be described later, or a combination of the opposite may be used.

The main body 10a and the elevating member 10c are integrally formed so as to be separable and form a concave portion a. A support 20 for mounting the substrate 18 on the concave portion a side of the elevating member 10c is provided. The support 20 is moved up and down
The substrate 18 placed in the reactor 10 or the reactor 1
So that it can be taken out of zero. In the illustrated example, the lifting member 10
For example, an elevating member 10 c for mechanically elevating and lowering c is connected to the elevating device 22.

The cover member 10b is detachably attached to the main body 10a.
Attach to An airtight holding member 24, for example, viton packing, is provided between the main body 10a, the lid member 10b, and the elevating member 10c. Therefore, when the inside of the reaction furnace 10 is evacuated, the airtight state is established via the airtight holding member 24. It can be formed.

Further, a temperature measuring means 26 for measuring the surface temperature of the substrate 18, for example, an optical pyrometer, is provided at a position near the substrate in the concave portion a.

Further, in this embodiment, the heating section 16 is provided with infrared irradiation means of any suitable configuration, for example, an infrared lamp 16a.
And a support member 16b for supporting the means 16a. The substrate 18 is used as the infrared lamp 16a.
Is preferably a lamp that emits light in a wavelength range in which the substrate can be efficiently heated. In this embodiment, a tungsten halogen lamp or any other suitable lamp is used. Preferably, a plurality of infrared lamps 16a are arranged so that the inside of the reaction furnace 10 can be uniformly heated.

Normally, the infrared lamp 16a is
Place outside. At this time, a part of the reactor 10 is made of a material that transmits infrared rays, and the infrared rays are transmitted from outside the reactor 10 into the reactor 10. As described above, in this embodiment, since the lid member 10b is made of quartz, infrared light can be transmitted.

The configuration and location of the heating section 16 may be any suitable configuration and location where heating processing to be described later can be performed. For example, the heating section 16 is configured with a heater, and this heater is installed in the reactor 10. May be provided.

Although the arrangement position of the support member 16b is not limited to this, in the illustrated example, the support member 16b is arranged so that the contact portion of the cover member 10b and the main body 10a is closed between the support member 16b and the main body 10a. In addition, an airtight holding member 24 is provided between the support member 16b and the main body 10 so as to be detachably attached to the main body 10a. Thus, the support member 1
By providing 6b, the vacuum tightness in the reactor 10 can be improved.

In FIG. 3, reference numeral 28 denotes a gas supply pipe provided between the reaction furnace 10 and the gas supply unit 14 via a valve 44, and reference numeral 30 denotes an exhaust pipe provided between the reaction furnace 10 and the exhaust means 12. Is shown.

Next, the evacuation system and gas supply system of this embodiment will be described with reference to FIG. The evacuation system and the gas supply system are not limited to the examples described in the following embodiments.

First, the evacuation system will be described. In this embodiment, the exhaust means 12 is constituted by, for example, a turbo molecular pump 12a and a dry pump 12b connected to the pump 12a. The exhaust means 12 is connected to and connected to the reaction furnace 10 via, for example, an exhaust pipe 30 and valves provided as shown. In FIG. 4, reference numerals 32 a to 32 d denote vacuum gauges (or pressure gauges) provided in communication with the exhaust pipe 30.
A Baratron vacuum gauge (or Pirani vacuum gauge) used for pressure measurement in the range of 0 ^-3 (10 to the third power) Torr is used, and the vacuum gauges 32b and 32c are, for example, 10 ^-4 (1
0 minus 4th power) ^{-10 -10} (10 minus 10)
Squared) An ion gauge used for pressure measurement in the range of Torr. A vacuum gauge 32 is provided between the vacuum gauge 32b and the exhaust pipe 30.
An automatic opening / closing valve 34 for protecting the valve b is provided, and the valve 34 is automatically opened and closed so that a pressure of 10 ^-3 (10 to the third power) Torr or more is not applied to the vacuum gauge 32b when the vacuum gauge 32b operates. Control. 36a to 36f are automatic opening / closing valves provided between the exhaust means 12 and the reaction furnace 10, and control the pressure in the reaction furnace 10 to any suitable pressure by opening and closing these valves 36a to 36f, respectively, as appropriate. Then, a low vacuum evacuation state and a high vacuum evacuation state are formed in the reaction furnace 10.

Further, reference numeral 38 denotes a needle valve for adjusting pressure and reference numeral 40 denotes a relief valve. The valve 40 automatically opens when the pressure in the reactor 10 exceeds atmospheric pressure, for example, 760 Torr. The gas supplied from the gas supply unit 14 into the reaction furnace 10 is exhausted.

Next, the gas supply system will be described. In this embodiment, the gas supply unit 14 includes an oxidizing gas source 14a and reactive gas sources 14b, 14c, and 14d. A supply pipe 28 in which the gas supply unit 14 is disposed, for example, as illustrated.
And a valve connected to the reaction furnace 10 via a valve.

In FIG. 4, 42 is a gas supply system, 44 is a valve, 46a to 46d, 48a and 48b are automatic opening / closing valves, and 50a and 50b are automatic gas flow controllers for gas introduced from the gas supply unit 14 into the reactor gas. It is.

Valves 44, 48a, 48b, 46a-4
A desired gas can be supplied from the gas supply unit 14 to the reaction furnace 10 by appropriately opening and closing the respective 6d.

<Description of Embodiment of Method for Forming Gate Electrode Structure of the Present Invention> FIGS. 1A to 1D are process diagrams for explaining an embodiment of a method of forming a gate electrode structure of the present invention. Each figure schematically shows a cross-section of the structure obtained in the main process step. FIG. 2 is a view for explaining a reheating cycle of film formation, which is used for describing the present invention. The horizontal axis of the figure is plotted with time (unit is seconds) and the vertical axis is plotted with temperature (unit is ° C). In the following description, FIG. 3 and FIG.

In the present invention, the support 20 in the reactor 10
After installing the substrate 18 on the substrate, the substrate is cleaned,
The formation of the SiO ₂ film as the insulating film, the formation of the Si—Ge film, and the formation of the poly-Si film are continuously performed. Hereinafter, this will be described sequentially.

[Pretreatment] In the embodiment of the present invention, for example, a silicon substrate is prepared as a base, and the substrate 18 is precleaned by using a chemical agent, pure water or the like as a conventional pretreatment. The portion of the pre-processed Si substrate on which the gate electrode is to be formed is indicated by 110 here (FIG. 1A). In the following description, the Si substrate will be represented by 110.

Next, the substrate 110 is set in the reaction furnace 10. The substrate 110 is fixed on the support 20 of the elevating member 10c. At this time, since the substrate 110 is once exposed to air, a natural oxide film is formed on the surface of the substrate.
0 may be cleaned in the reaction furnace 10 as usual. Here, regarding the substrate cleaning process,
Description is omitted.

[0047] To form an SiO ₂ film as one of the insulating films on the main surface of [SiO ₂ film of the film-forming] substrate 110, first, the exhaust means 12 is operated, 1 × reaction furnace 10 e.g. The inside of the reaction furnace 10 is cleaned by evacuating to a high vacuum of about 10 ⁻⁸ (10 ⁻⁸ ) Torr.

To perform this evacuation, a valve 38,
With the valves 36a, 36b, 36f and 34 closed, the valves 36b, 36c and 36d are opened, and the dry pump 12b is operated. The degree of vacuum is monitored while measuring the pressure with a vacuum gauge 32a provided in the reaction furnace 10. And
After the pressure in the reactor 10 reaches, for example, 1 × 10 ⁻³ Torr, the valves 36 c and 36 d are closed and the valves 36 e and 3
Open 4. This evacuation is performed when the pressure in the reactor 10 is 1 ×
Repeat until the pressure reaches 10 ^-8 Torr.

Next, a heat treatment is performed in an oxidizing gas atmosphere to form an oxide film on the substrate 110.
b, 36e are closed and valves 38, 36a, 48a, 46
a is opened, and an oxidizing gas, for example, oxygen (O ₂ ) gas is supplied into the reaction furnace 10 (O ₂ flow in a time region indicated by I in FIG. 2). The flow rate of the oxygen gas at this time is, for example, 1 liter / minute. This oxide film can be formed under atmospheric pressure. However, since the reaction products during the formation of the oxide film are exhausted to the outside of the reaction furnace 10, the inside of the reaction furnace 10 is, for example, 100 to 10 ^-2.
Maintain a suitable low vacuum pressure in the range of (10 minus the square) Torr.

Next, the substrate 110 is heated by a heating process performed by the heating unit 16 to form a silicon oxide film (SiO ₂ film) 1.
12 (FIG. 1B). The heating of the substrate 110 is performed by the infrared lamp 16 a of the heating unit 16. At this time, for example, while measuring the substrate surface temperature by the temperature measuring means 26, the substrate is heated at an appropriate rate of, for example, 50 ° C./sec to 200 ° C./sec, preferably at a heating rate of about 100 ° C./sec. The temperature is raised to a temperature T1 of about 1000 ° C., preferably for about 60 seconds (the time period indicated by H1 in FIG. 2) for about 10 seconds.
It is performed so as to keep it at 00 ° C. In this case, it is preferable to increase the temperature at a constant rate, in order to form a high-quality film with a constant growth rate of an insulating film such as an oxide film. The reason why the heating rate is set in the above-mentioned range is to form a film with good controllability and / or quality of the film thickness. The heating temperature T1 is set to about 1000 ° C. because it is a preferable minimum temperature required for forming an insulating film. The reason why the time period H1 is set to about 60 seconds is from the viewpoint of controllability of the film thickness and / or film quality. Under such conditions, by heating the substrate, a thin, high-quality SiO ₂ film 112 having a thickness of about 100 A ° can be formed.

The thickness of the oxide film (SiO ₂ film) can be controlled, for example, by adjusting the oxidation temperature, the oxidation time and the flow rate of the oxidation gas.

After the SiO ₂ film 112 having a desired thickness is formed, the heating of the substrate 110 is stopped, and the room temperature, for example, 25 ° C.
Cool down to Next, the valves 38, 36a, 48a, 46
a is closed, the valves 36b and 36e are opened, and the inside of the reaction furnace 10 is evacuated to a high vacuum of, for example, 1 × 10 ⁻⁸ (10 ⁻⁸ ) Torr.

[Formation of Si-Ge Film] Next, a heat treatment is performed in a first mixed gas atmosphere of a Si-containing reactive gas and a Ge-containing reactive gas to form a Si oxide film on the Si oxide film. A Si-Ge film thinner than the film is formed. Less than,
This point will be described.

For this purpose, first, the gas supply source is switched from the oxidizing gas supply source 14a to the reactive gas supply sources 14b and 14c. In the case of this embodiment, a silane-based (Si _m H _n : m and n) gas is used as the first mixed gas necessary for forming a Si—Ge (silicon-germanium) thin film.
Is an integer of 1 or more) gas, and a germane-based (Ge
_m H _n: where, m and n are a mixed gas of an integer of 1 or more) gas. Hereinafter, this point will be described.

With the valves 36a and 38 opened, the valves 48a and 46b are opened, and the mass controller 50a is set so that the flow rate of hydrogen (H ₂ ) diluted 10% silane (SiH ₄ ) gas is 1 liter / minute. Is introduced into the reaction furnace 10 while controlling the temperature. At this time, the inside of the reactor 10
It is preferable to maintain a reduced pressure at an appropriate degree of vacuum within the range of 10 ^-2 Torr.

Next, the valves 48b and 46c are opened, and hydrogen-diluted 1% germane (GeH ₄ ) gas is introduced into the reaction furnace 10 while controlling the mass controller 50b so that the flow rate becomes 1 liter / minute. (Period of (SiH ₄ + GeH ₄ ) flow in the time domain indicated by II in FIG. 2)).

This silicon (Si) -germane (Ge)
In forming a thin film, the reaction product during the film formation is quickly exhausted to the outside of the reaction furnace 10.
Maintain a suitable low vacuum pressure in the range of -10 ^-2 (10 minus the square) Torr.

Next, 10% SiH ₄ / H ₂ gas and 1%
When the mixing ratio of the% GeH ₄ gas becomes constant, the heating unit 16 heats the substrate 110 by heating. This substrate 110 is heated by the infrared lamp 16a of the heating unit 16.
Done by At this time, for example, while measuring the substrate surface temperature by the temperature measuring means 26, for example, 50 ° C./sec.
C./s, preferably at a rate of about 1
The temperature is increased at a rate of 00 ° C./sec to a heating temperature T1 of about 1000 ° C., and is preferably maintained at about 1000 ° C. for about 100 seconds (a time period indicated by H2 in FIG. 2). In this case, it is preferable to perform the heating at a constant rate,
This is because a high-quality film is formed while keeping the growth rate of the Si-Ge film constant. The reason why the heating rate is set to the above range is to decompose Si from silane gas and Ge from germane gas to form a film having good controllability and / or quality. The reason why the heating temperature T1 is set to about 1000 ° C. is that it is a preferable minimum temperature required for forming the Si—Ge film. The reason why the time period H2 is set to about 100 seconds is from the viewpoint of controllability of the film thickness and / or film quality. Under these conditions,
By heating the substrate, a thin, high-quality Si _0.8 Ge _0.2 film 114 having a thickness of about 1000 A ° (the content in this case: Si: Ge = 4: 1) can be formed (FIG. 1).
(C)). Preferably, the Si-Ge film is a non-doped film that does not contain an impurity imparting conductivity.

The thickness of the Si—Ge film can be controlled, for example, by adjusting the heating temperature, the heating time, and the flow rate of the mixed gas. The Si and Ge contents of this film can also be set to any suitable ratio as required. That is, the composition of the Si—Ge film is changed to Si _1-x Ge
_X (where x is any value within the range of 0 <x <1).

After the formation of the Si-Ge film 114 having a desired thickness, the heating of the substrate 110 is stopped, and the room temperature, for example, 25 ° C.
Cool to ° C.

[Deposition of Poly-Si Film] Next, a heat treatment is performed in a second mixed gas atmosphere of a Si-containing reactive gas and an impurity-containing reactive gas for determining conductivity.
A conductive poly-Si layer is formed on the i-Ge film. In this embodiment, silane Si-containing reactive gases (Si _m H _n:
However, m and n are integers of 1 or more) gas, and
The reactive gas containing impurities is a phosphine (PH ₃ ) gas or an arsine (AsH ₃ ) gas.

In this embodiment, a phosphine gas is used,
An example in which an n-type poly-Si film, that is, a phosphorus-doped polysilicon film is formed on a Si-Ge film surface by performing a heat treatment in a reactive gas atmosphere will be described.

For this reason, the valve 46b is closed and 1% Ge
The supply of the H ₄ / H ₂ gas is stopped. And valve 4
6d, open the above-mentioned reactive gas such as 10% SiH ₄
/ H ₂ gas dilution while maintaining hydrogen (H ₂ )
% Phosphine (PH ₃ ) gas is simultaneously supplied into the reaction furnace 10 ((SiH ₄ + P in the time domain indicated by III in FIG. 1).
H ₃₎ flow). The gas flow rate at this time is 1 liter / minute.

Next, a heating process is performed by the heating unit 16 to form a poly-Si film 116 on the surface of the Si-Ge film 114 (FIG. 1D).

This heating is performed by the infrared lamp 16 of the heating section 16.
a. At this time, for example, while measuring the substrate surface temperature by the temperature measuring means 26, for example, 50 ° C./sec.
At an appropriate rate between 0 ° C./sec, preferably at a rate of about 100 ° C./sec, the temperature is raised to a heating temperature T1 of about 1000 ° C., preferably for about 250 seconds (shown as H3 in FIG. 2). (Period of time) to maintain the temperature at about 1000 ° C. Under such conditions, the phosphorus-doped poly-Si film 116 having a thickness of about 3500 A ° (phosphorus concentration of about 4 × 10 ²⁰ (10
Squared)) can be formed.

In this case, it is preferable to increase the temperature at a constant rate, in order to form a high-quality film with a constant growth rate of the poly-Si film. The reason why the heating rate is set in the above-mentioned range is to form a film with good controllability and / or quality of the film thickness. The reason why the heating temperature T1 is set to about 1000 ° C. is that it is a preferable minimum temperature required for forming the poly-Si film. The time period H3 was set to about 250 seconds because the poly-S
i can be used as an electrode.
° from the time period required for growth. By heating the substrate under such conditions, an electrically activated, high-quality poly-Si film can be formed.

The thickness of the poly-Si film can be controlled, for example, by adjusting the heating temperature, the heating time, and the gas flow rate.

After the formation of the poly-Si film 116 having a desired film thickness, the heating is stopped, and the film is cooled to room temperature, for example, 25 ° C.

Next, the valves 38, 36a and 48a, 4a
The valves 8b, 46b, 46d are closed, the valves 36b, 36e are opened, and the inside of the reaction furnace 10 is evacuated to a high vacuum of, for example, 1 × 10 ⁻⁸ (10 ⁻⁸ ) Torr.

Thereafter, 36b and 36e are closed, and a nitrogen gas, for example, is purged from the inert gas source (not shown) into the reaction furnace 10 until the pressure reaches the atmospheric pressure.
6 is prevented from being oxidized.

Through a series of steps as described above, a thin SiO ₂ film 112 as an insulating film is formed on the Si substrate 110.
A gate electrode structure composed of the Si-Ge thin film 114 and the n-type poly Si film 116 is obtained.

Next, the effect of the grain boundary on the gate electrode structure will be described with reference to FIG. With such a structure, when a heat treatment is performed in a later step, the poly-Si film 116 is formed.
The grain boundaries 120 formed therein reach the lower Si—Ge film 114, but the grain boundaries 120 are formed by the poly Si film 116.
And stop at the interface between Si and the Si-Ge film 114. For this reason,
There is no possibility that the grain boundary reaches the SiO ₂ film 112, and therefore, there is no possibility that an oxide ridge is generated in a region near the interface between the Si—Ge film and the SiO ₂ film. In this state, the interface between the Si—Ge film and the SiO ₂ film becomes an extremely flat surface, and the film thickness of the SiO ₂ film itself remains substantially constant without changing.

The present invention is not limited to the above-described embodiment, but can be modified or modified in various ways as described below.

In the above-described embodiment, the Si-containing gas is
Although described as H ₄ , the present invention is not limited to this, and SiH ₂ Cl ₂ gas or Si (CH ₃ ) ₂ H ₃ gas may be used, or SiH ₄ , SiH ₂ Cl
Any two or more mixed gases selected from the group consisting of ₂ and Si (CH ₃ ) ₂ H ₃ may be used.

Although the Ge-containing gas is GeH ₄ gas, the present invention is not limited to this. GeF ₄ , GeF ₄
Gases such as ₂ , GeF, and GeH ₃ F can also be used.

In the above-described embodiment, the thickness of the Si—Ge film is set to about 1000 A °. However, even if the thickness is less than 1000 A °, a film in which the grain boundary generated by the heat treatment in the subsequent process is not removed. Any thickness is acceptable.

Although phosphine is used as the impurity-containing reactive gas, a similar effect can be obtained by using arsine instead.

Although oxygen (O ₂ ) gas is used as the oxidizing gas in the above-described embodiment, a gas containing oxygen such as dinitrogen monoxide (N ₂ O) gas may be used instead of the oxygen gas. Even when used, a sufficient oxidation effect can be similarly increased.

In the above embodiment, each heat treatment is performed by an infrared lamp, in order to heat and cool the substrate with good responsiveness. However, in the present invention,
In this heat treatment, infrared irradiation may be performed using an arc lamp, a laser beam, a heater, or the like.

In the above-described embodiment, the substrate serving as the base is cleaned by heating in a reducing gas atmosphere before the formation of the insulating film. However, this process may be omitted if necessary. Of course it is good.

[0081]

As is apparent from the above description, according to the method for forming a gate electrode structure of the present invention, a thin silicon oxide film is provided on the lower surface of silicon, and silicon-germanium (Si- Ge) After providing the thin film,
Since a conductive poly-Si film to be the gate electrode was formed,
Even if, for example, an intermediate insulating film or other necessary heat treatment is performed thereafter, the grain boundaries generated in the poly-Si film during the heat treatment stop at the Si-Ge thin film. Therefore, there is no possibility that the grain boundary will reach the silicon oxide film.
Therefore, there is no possibility that an oxide ridge is generated in a region near the interface between the Si—Ge film and the silicon oxide film. In this state, the interface between the Si—Ge film and the silicon oxide film becomes an extremely flat surface, and the thickness of the silicon oxide film itself remains substantially constant without changing.

As a result, using this gate electrode structure,
When an element such as an FET constituting an EPROM or the like is configured, a tunnel current under a certain electric field has no variation among the elements, and a constant state can be maintained in each element.

Further, since the heat treatment after the formation of the poly-Si film can be performed at a high temperature, the impurities of the poly-Si film can be sufficiently activated, and the resistance of the poly-Si film itself can be reduced. Therefore, a good gate electrode, for example, a floating gate can be formed.

[Brief description of the drawings]

FIGS. 1A to 1D are process diagrams for explaining one embodiment of a method for forming a gate electrode structure according to the present invention.

FIG. 2 is a thermal cycle diagram for explaining one embodiment of a method for forming a gate electrode structure according to the present invention.

FIG. 3 is a cross-sectional view schematically showing a main part of an apparatus for carrying out one embodiment of a method for forming a gate electrode structure according to the present invention.

FIG. 4 is a diagram schematically showing an overall configuration of an apparatus for carrying out an embodiment of a method of forming a gate electrode structure according to the present invention.

FIG. 5 is a diagram provided for describing an effect of the present invention.

FIGS. 6A and 6B are diagrams for explaining a conventional technique.

[Explanation of symbols]

10: reaction furnace 10a: body 10b: lid member 10c: elevating member 12: exhaust means 12a: turbo molecular pump 12b: dry pump 14: gas supply unit 14a: oxidizing gas source (for example, O ₂ gas source) 14b: reaction Reactive gas source (for example, SiH ₄ gas source) 14c: Reactive gas source (for example, GeH ₄ gas source) 14d: Reactive gas source (for example, PH ₃ or AsH ₃₎
Gas source) 16: Heating section 16a: Infrared lamp 16b: Support member 18: Substrate 20: Support body 22: Lifting device 24: Airtight holding member 26: Temperature measuring means 28: Gas supply pipe 30: Exhaust pipe 32a to 32d: Vacuum Total 34, 36a to 36f, 38, 40, 44, 46a to 4
6d, 48a, 48b: valve 50a, 50b: gas flow controller 100: Si substrate 112: SiO ₂ film 114: Si-Ge film 116: poly Si film 120: a grain boundary.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/8247 H01L 27/115 H01L 29/788 H01L 29/792 H01L 29/88

Claims (8)

(57) [Claims] 1. A method for forming a gate electrode of a conductive poly-Si layer by interposing a Si oxide film on a lower surface of Si in the same reaction furnace, comprising the steps of: (a) setting an Si base in an oxidizing gas atmosphere; (B) forming a thin Si oxide film on the underlying surface of the Si by performing a heat treatment of (b), and subsequently heating in a first mixed gas atmosphere of a Si-containing reactive gas and a Ge-containing reactive gas. Performing a process to form a thin Si-Ge film on the Si oxide film; and (c) thereafter, a second mixed gas atmosphere of a Si-containing reactive gas and an impurity-containing reactive gas for determining conductivity. Forming a conductive poly-Si layer on the Si-Ge film by performing a heat treatment therein. 2. A method according to claim silane each of the Si-containing reactive gas according to 1 (Si _m H _n: where, m and n is an integer of 1 or more) as a gas, and the Ge-containing reactive gas In a Germanic system (Ge _m H _n : m and n
Is an integer of 1 or more) gas. 3. The method of claim 1, wherein the reactive gas containing impurities is phosphine (PH ₃ ) gas or arsine (As).
A method for forming a gate electrode structure, comprising using H ₃ ) gas. 4. A method for forming a gate electrode structure, wherein the conductive poly-Si layer according to claim 1 is an n-conductivity type layer. 5. The method according to claim 1, wherein said Si oxide film is formed of Si.
A method for forming a gate electrode structure, comprising an O ₂ film. 6. The Si—Ge film according to claim 1,
A method for forming a gate electrode structure, comprising forming a film in a non-doped state without an impurity imparting conductivity. 7. The Si-Ge film according to claim 1, wherein the composition is Si _1-x Ge _x (where x is an arbitrary value within a range of 0 <x <1). A method for forming a gate electrode structure. 8. The method for forming a gate electrode structure according to claim 1, wherein each of the heat treatments is performed by infrared irradiation.