JP2793441B2 - Insulating film formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating film, and more particularly to a method for forming an insulating film having a small thickness and excellent characteristics.

[0002]

2. Description of the Related Art The development of VLSIs, particularly miniaturization of devices, largely depends on whether or not a thin and thermally stable insulating film can be formed. Device reliability and operating characteristics are greatly affected by the characteristics of the insulating film. As this insulating film, a silicon thermal oxide film (SiO ₂ film) is still the main material due to its stability, and its properties are expected to be improved in the future.

The method of forming the oxide film is described in the literature:
"Tokushi Tokuyama and Tetsuichi Hashimoto Compiler MOS LSI
Manufacturing technology, Nippon McGraw-Hill, 1985 p. 65 "
Is disclosed. Prior to the description of the present invention, the conventional oxide film forming technique will be briefly described.

First, a cleaned silicon substrate (Si) is placed in a quartz tube in a resistance heating furnace (also called a film forming furnace or a reaction furnace).
Substrate). The quartz tube is heated to a suitable temperature in the range of 800-1200C. Under this heating,
An oxidizing gas, for example, an oxygen gas (O ₂ gas) or a mixed gas of oxygen and hydrogen flows into the quartz tube to form an oxide film on the substrate.

According to this conventional method, the substrate is 800-1
Since the oxide film is formed by thermal oxidation using an oxidizing gas at a high temperature of 200 ° C., the growth rate of the film is high. For this reason, especially when it is desired to grow a semiconductor thin film having a thickness of 10 nm or less, it is difficult to precisely control the thickness, and it is difficult to form an oxide film with good reproducibility.

Therefore, in order to form such a thin film with good reproducibility, the oxidation temperature must be lowered to 800 ° C. or less;
It is conceivable to reduce the oxidation rate by taking measures such as diluting oxygen with an inert gas such as an argon (Ar) gas or a nitrogen (N) gas.

[0007]

However, in the oxidation method at such a low temperature, the flatness of the interface between the Si substrate and the oxide film is impaired due to the stress generated in the oxide film.
As a result, the film quality is not good.

Further, when oxidation is carried out by the dilution method, impurities in the substrate are taken into the oxide film due to the oxidation process at a high temperature for a long time, and the film quality is not good. There is a risk that the impurities may serve as nuclei to cause dielectric breakdown.

In addition, the oxide film formed by any of the low-temperature oxidation method and the dilution oxidation method described above also has many unpaired bonds of Si atoms near the interface between the oxide film and the Si substrate. There are distorted Si-O bonds. If a large number of such unpaired bonds or weak bonds of Si atoms and O atoms are contained, these bonds are broken by the stress of electron injection, or holes generated by impact ionization due to electron injection are trapped. For example, there is a problem in that dielectric breakdown occurs, thereby increasing leakage current and / or lowering resistance to high electric field stress.

Accordingly, it is an object of the present invention to provide a method for easily controlling the film thickness and forming the insulating film in a shorter time.

Another object of the present invention is to provide a method for forming an insulating film having excellent film quality and excellent insulation resistance.

[0012]

In order to achieve this object, according to the method of forming an insulating film of the present invention, an oxide film is formed on a lower surface of silicon, and the oxide film is oxynitrided. In forming an insulating film as a film, the oxynitriding treatment is divided into first and second oxynitriding treatments, and the first oxynitriding treatment is performed in a nitrogen-containing oxidizing gas atmosphere and when an oxide film is formed. carried out at a heating temperature and the same temperature of the first base, and a second oxynitride process, oxidizing gas atmosphere of a nitrogen-containing
Medium and at a second temperature of 800 ° C. to 950 ° C., and
The first temperature is higher than the second temperature .

In practicing the present invention, preferably, the above-described oxide film is formed to a thickness of about several tens of angstroms in an oxidizing gas atmosphere containing no nitrogen, and the first oxynitriding treatment is performed with nitrogen. It is preferable that the above-mentioned oxide film is replaced with an oxynitride film having a film thickness of any value within a range of 50 to 100 Å by carrying out in an atmosphere containing oxidizing gas.

According to a preferred embodiment of the present invention, the nitrogen-free oxidizing gas is preferably oxygen (O ₂ ) gas or ozone (O ₃ ) gas.

In practicing the present invention, preferably, the above-mentioned nitrogen-containing oxidizing gas is replaced with nitrogen monoxide (N
It is preferable to use one kind of gas selected from the group consisting of O) gas, dinitrogen monoxide (N ₂ O) and nitrogen dioxide (NO ₂ ) gas, or a mixed gas of two or more kinds.

[0016]

As described above, according to the insulating film forming method of the present invention, after the oxide film is formed, the first oxynitriding is performed at the same first temperature as the processing temperature for forming the oxide film. Is changed to an oxynitride film. Therefore, the processing temperature does not increase or decrease between the formation of the oxide film and the formation of the oxynitride film, so that the number of unpaired and weak bonds in the insulating film can be more effectively reduced. The amount of moisture entering the oxynitride film being formed during the process can be suppressed. Further, the entire processing time can be reduced.

Further, according to the present invention, following the first oxynitriding process, the second oxynitriding process is performed at a second temperature lower than the first temperature. This second temperature is a temperature at which the film thickness of the oxynitride film does not increase from the film thickness when formed by the first oxynitriding process, and furthermore, the nitrogen atoms in the oxynitride film being formed. It is performed at a temperature at which the capture is performed without stopping. Therefore, by the second oxynitriding treatment, the amount of nitrogen in the oxynitride film can be increased as a whole without increasing the thickness of the oxynitride film being formed. Resistance can be improved.

Further, the above-mentioned oxide film is formed to a thickness of about several tens angstroms, and
By substituting an oxynitride film having a film thickness of any value within the range of 0 Å, the oxynitride film can be applied to a device.

By using an oxygen (O ₂ ) gas or an ozone (O ₃ ) gas as the nitrogen-free oxidizing gas, it is possible to oxidize the silicon base efficiently and without deteriorating the film quality.

The nitrogen-containing oxidizing gas may be one type of gas selected from the group consisting of nitrogen monoxide (NO) gas, dinitrogen monoxide (N ₂ O) and nitrogen dioxide (NO ₂ ) gas. By using a mixed gas of more than two kinds, the oxide film can be changed to an oxynitride film efficiently and without deteriorating the film quality, and nitrogen can be efficiently introduced into the oxynitride film.

[0021]

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 shapes, arrangements, and dimensions of the components so that the present invention can be understood. It should also be understood that the embodiments described below are merely preferred examples, and thus the present invention is not limited to the embodiments described below.

First, an insulating film forming apparatus used to carry out the insulating film forming method of the present invention will be briefly described with reference to FIGS.

The reactor 10 of this apparatus comprises a main body 10a made of stainless steel, a lifting member 10c, and a lid member 1 made of quartz.
0b and an underlayer (here, by way of example, of the substrate 18) support 20.

The loading and unloading of the substrate 18 into and from the reactor 10
The lifting and lowering of the lifting member 10c by the lifting device 22 is performed. Main body 10a, lid member 10b, and elevating member 10c
A security member 24, for example, Viton packing, is provided between them. Therefore, when the inside of the reaction furnace 10 is evacuated, the confidential state in the furnace can be maintained via the confidentiality maintaining member 24.

A temperature measuring device 26, for example, an optical pyrometer, is mounted at a position near the substrate in the concave portion 10a, and is used to measure the surface temperature 18 of the substrate 18. The heating section 16 is provided with an infrared lamp 16a as an infrared irradiation means, which is supported by a support member 16b. As the infrared lamp 16a, for example, a tungsten halogen lamp is used. Since the lid member 10b of the reaction furnace 10 is formed of an infrared transmitting material, the infrared light penetrates into the reaction furnace 10.

It is assumed that a control unit (not shown) of the power supply device for the lamp forms a closed loop with the temperature measurement device. That is, the temperature of the substrate 18 measured by the temperature measuring device is fed back to the lamp power control unit, and the lamp power is controlled so that the substrate temperature is kept constant at a target value. I have.

The gas supply pipe 28 is provided between the reactor 10 and the gas supply unit 14 (FIG. 3). Further, a vacuum exhaust device is connected to the exhaust pipe 30.

Next, the gas supply system of this embodiment will be described with reference to FIG. In this embodiment, the gas supply unit 14 includes a nitrogen-free oxidizing gas source 14a, a nitrogen-containing oxidizing gas source 14b, and an inert gas source 14c. 3, reference numeral 42 denotes a gas supply system, 44 denotes a valve, 46a to 46c denote an automatic opening / closing valve, and 50 denotes a monitor of a gas flow introduced from the gas supply unit 14 into the reaction furnace. A desired flow rate of gas can be introduced into the reactor by opening and closing the valves 44 and 46a to 46c by an appropriate amount.

Next, a specific embodiment of the method for forming an insulating film according to the present invention will be described.

According to the present invention, an oxide film is formed on a lower surface of silicon. Thereafter, the oxide film is subjected to an oxynitriding process to form an insulating film as an oxynitride film.

For this purpose, first, a Si substrate, preferably a Si single crystal substrate, serving as a base for film formation is introduced into the reaction furnace 10. It is assumed that this substrate has been subjected to a surface cleaning treatment as required.

Next, a first insulating film is formed. FIG.
FIG. 4 is a diagram for explaining a heat treatment and a gas control cycle for forming an insulating film, in which the left vertical axis represents a processing temperature in units of ° C., and the right vertical axis represents pressure To.
It is shown in units of rr. The solid line indicates the temperature profile, and the dashed line indicates the pressure of various gases in the reactor.

First, before forming the insulating film as the oxynitride film, an oxide film, that is, a silicon oxide film (SiO ₂ film) 60 in this case is formed on the Si substrate 18 (FIG. 4).
(A)). Therefore, first, the inside of the reaction furnace 10 is, for example,
Evacuation is performed so that the degree of vacuum becomes appropriate within the range of 10 ⁻³ −10 ⁻⁵ Torr (period indicated by VI in FIG. 1).

Next, the valves 44 and 46a are opened, and an oxidizing gas containing no nitrogen, for example, an oxygen (O ₂ ) gas is introduced into the reaction furnace 10 (a period indicated by O ₂ in FIG. 1). In this embodiment, the pressure in the furnace is set to the atmospheric pressure (760 Torr).
The pressure may be maintained at a reduced pressure at an appropriate pressure up to about 100 Torr.

Next, the substrate 18 is heated by the heating unit 16 to form a Si oxide film on the surface of the Si substrate 18. In this case, the heating of the substrate 18 is performed at an appropriate heating rate within the range of 100 to 200 ° C./sec, preferably 100 ° C./sec, while measuring the temperature of the substrate surface by the temperature measuring means 26. The reason for setting the temperature rising rate within such a range is to improve the film quality while keeping the growth rate of the oxynitride film constant.
The first heating temperature, that is, the peak temperature T1 of the heating is preferably set to an appropriate temperature in the range of 1000 to 1200 ° C. By appropriately controlling the heating temperature and the time for maintaining the atmosphere of the reactive gas (the period indicated by O1 in FIG. 1), an oxide film 60 having an arbitrary thickness of the order of several tens angstroms (A °) or more is formed. You can do it.

Next, an oxynitriding process is performed to convert the oxide film 60 to a nitride film. Therefore, first, in the present invention, the oxynitriding treatment is divided into first and second oxynitriding treatments,
The oxynitriding process is performed at the first temperature T1 which is the same as the heating temperature of the base when forming the oxide film.
This is performed at the second temperature T2 where the thickness of the oxynitride film does not increase and the introduction of nitrogen atoms into the oxynitride film during the formation is maintained.

First, in performing the first oxynitriding treatment,
Once was evacuated O ₂ gas (the period indicated by V2 in Fig. 1)
Thereafter, the valves 44 and 46b are opened to introduce an oxidizing gas containing nitrogen, for example, N ₂ O gas into the reaction furnace 10 (a part of the time period indicated by N ₂ O in FIG. 1). At this time, the heating temperature of the substrate, that is, the processing temperature is maintained at the first temperature T1 which is the temperature at which the oxide film 60 was formed. Thus, the heat treatment temperature is maintained (O in FIG. 1).
Due to the time period indicated by N1, the oxynitridation process starts immediately after the gas is introduced, and as a result, the Si oxide film 60 becomes a Si oxynitride film (oxynitride).
e) is replaced by membrane) 62; Here, assuming that the Si oxynitride film has a composition ratio of Si-ON (x, y, SiOx
Although it can be expressed as Ny, the values of x and y are not certain. ) Represented as membrane. Also in this case, similarly to the case of forming the oxide film, the pressure in the reaction furnace 10 may be set to an appropriate reduced pressure of 700 to 100 Torr. By appropriately setting the atmosphere maintaining time (the time period indicated by ON1 in FIG. 1), the increase in the thickness of the insulating film can be several to several tens of angstroms. If the thickness of the oxynitride film is determined in advance in the design stage, an atmosphere maintaining time suitable for the thickness may be set according to the thickness of the oxide film formed first.

Next, following this first oxynitriding treatment,
An oxynitriding process is performed. For this reason, N
_While continuing the inflow of the ₂ O gas, the heat treatment temperature, that is, the heating temperature of the substrate 18 is lowered to the second temperature T2 and maintained at that temperature. As the second heating temperature T2, without increasing the thickness of the oxynitride film 60 being formed,
A temperature is set such that the introduction of nitrogen atoms to zero does not stop. This second heating temperature T2 is preferably set to 800 to 9
An appropriate temperature in the range of 50 ° C. is preferable. In this case, the temperature is maintained at this temperature for an appropriate time period in order to ensure that nitrogen is sufficiently introduced (or called intrusion) into the Si oxynitride film being formed. FIG. 1 shows this time period as ON2. After the elapse of this time period, a final oxynitride film 64 into which a sufficient amount of nitrogen atoms have been introduced is obtained (FIG. 4C).

Finally, the inside of the furnace is evacuated (a time period indicated by V3 in FIG. 1), and then the valves 44 and 46c
Is opened and an inert gas, for example, a nitrogen gas is introduced into the reaction furnace 10 (a time period indicated by N ₂ in FIG. 1).
Is cooled to room temperature. Thus, the step of forming the oxynitride film as the insulating film to be obtained in the embodiment of the present invention is completed.

The insulating film formed by the above-described method of the present invention is a Si oxynitride film. In this oxynitride film, nitrogen atoms (N) penetrate or replace these bonding portions. The insulation resistance is improved by the stability of the bond between Si (silicon) and N (nitrogen). The oxynitride film has a denser structure than the oxide film, and therefore has an effect of suppressing impurity diffusion. Furthermore, the introduction of nitrogen can be expected to improve the dielectric constant,
It can also be expected that the barrier height at the interface between the -ON film and the Si substrate is reduced.

Further, in the method of forming an insulating film according to the present invention, since the introduction / replacement of the reactive gas is repeated without lowering the heat treatment temperature to the reaction stop temperature, the gas introduction into the reaction furnace as in the prior art is performed. The number of unpaired and weak bonds in the insulating film can be reduced more effectively than the case where the processing temperature is increased or decreased in each cycle, and the number of uncoupled or weak bonds in the insulating film can be reduced. The resulting moisture is not taken into the film. Further, the entire processing time required for forming the oxynitride film can be reduced.

Next, the distribution of nitrogen in the oxynitride film formed according to the method of the present invention was measured.

FIG. 5 is a diagram showing a nitrogen distribution curve in the oxynitride film. This distribution is measured by secondary ion mass spectrometry (SIMS).
It is a result measured in. The vertical axis of this figure is the concentration distribution of nitrogen (N) (unit: atoms / cm ² ), and the horizontal axis is the depth (unit: nm) from the surface of the oxynitride film toward the substrate surface. is there. The oxynitride film is formed to a thickness of 10 by the first oxynitriding process.
In the case of the present invention in which the two oxynitride films are formed under the same conditions up to the point of forming the oxynitride film and thereafter the second oxynitridation process of the present invention is performed to obtain an oxynitride film (curve I ) And a case different from that of the present invention in which an oxynitride film was obtained without performing the second oxynitriding treatment (indicated by curve II). Note that the second heating temperature T2 is 9
The temperature was set to 50 ° C., and the ON2 time period was set to 60 seconds. This O
Although the time period of N2 varies depending on various conditions, in the case of this embodiment, it is preferable that the time period be about 200 seconds at the maximum.

As can be understood from the measurement results, in the case of the oxynitride film not subjected to the second oxynitriding treatment (curve II), nitrogen segregates quickly near the interface with Si, and this interface structure is changed. Have strengthened. Therefore, it can be understood that the insulation resistance on the Si side can be sufficiently ensured by the first oxynitriding treatment, but the nitrogen concentration on the surface side is on the order of 10 ¹⁸ atoms / cm ² , which is insufficient.

FIG. 6 is a diagram for explaining an example in which a MOS capacitor is formed using an oxynitride film formed according to the present invention. This structure has a structure in which a Si oxynitride film 72 is formed on a Si substrate 70, and a gate electrode 74 is provided thereon by patterning. In this case, after the second oxynitriding process, the nitrogen concentration at the interface between the gate electrode 74 and the oxynitride film 72 increases, so that the interface on the gate electrode side is strengthened. Therefore, the resistance to a high electric field stress (electron injection from the gate) in which the gate electrode 74 has a negative polarity is also improved.

When the electrical characteristics of the actually formed MOS capacitor were measured, the results shown in FIGS. 7 and 8 were obtained. In this case, the capacitor is:
It was set to 2 × 10 ⁻⁴ cm ² .

FIG. 7 shows the leakage current characteristics, in which the vertical axis represents the Si
The leak current (unit: amperes) flowing between the substrate and the gate electrode is taken, and the electric field strength (unit: MV / cm) between the Si substrate and the gate electrode is shown on the horizontal axis. In this measurement, a Si oxide film (dashed curve I1), a Si oxynitride film obtained by performing the first oxynitriding process (curve I2), and a Si oxynitride film obtained by performing the second oxynitriding process for 30 seconds (curve I2) The measurement was performed for each of the curve I3) and the Si oxynitride film (curve I4) obtained by performing the second oxynitriding treatment for 60 seconds.
In this measurement, the thickness of the film to be measured was 6 nm, and n
^The result of electron injection of 5 C / cm ² at a current density of −100 mA / cm ² from the −− poly Si gate 74 is shown in FIG.
The oxynitriding time is shown as a parameter.
The second temperature T2 at this time was set to 950 ° C. As can be understood from the results, the second oxynitriding time was set to 6 hours.
The occurrence of leakage current at 0 seconds (curve I4) is significantly suppressed as compared with the case of the oxide film (curve I1) and the processing time of 0 seconds (curve I2). I understand. In addition, from the viewpoint of device fabrication, the electric field strength is preferably set to a value in the range of 8 to 10 MV / cm ^2. This is advantageous because the current is suppressed.

FIG. 8 shows a MOS transistor having the structure shown in FIG.
FIG. 4 is a characteristic curve diagram showing a result of measuring a dielectric breakdown charge (Qbd) of a capacitor. In this measurement, the thickness of the film to be measured was 6 nm, and the current injection density was -100 mA / c.
It was measured as m ^2. The vertical axis of FIG. 8 shows the amount of dielectric breakdown charge (Qbd) (unit: C / cm ² ), and the horizontal axis shows the oxynitriding time (ON2) (unit: second). In the drawing, the Si oxide film is denoted by II1, the oxynitride film with the second oxynitriding time being 0 second is denoted by II2, the oxynitride film with the second oxynitriding time being 30 seconds is denoted by II3, and the second oxynitriding is denoted by II3. The results are shown with the oxynitride film having a processing time of 60 seconds as II4. As can be understood from this result, Qbd has an increasing function according to the second oxynitriding treatment time (ON2). That is, it is understood that the second oxynitriding treatment improves the insulation resistance of the oxynitride film against electron injection from the gate electrode.

Further, although no experimental results are shown here, it has been found that the amount of charges trapped in the oxynitride film is reduced by the second oxynitriding treatment.

As can be understood from the above experimental results, when an oxynitride film as an insulating film formed according to the present invention is used as a tunnel oxide film of, for example, an EEPROM, the endurance characteristic and the retention ( It is expected that both the retention characteristics will be improved.

It is clear that the invention is not limited to the embodiments described above, but that many variations or modifications can be made. For example, in the above-described embodiment, oxygen (O ₂ ) gas is used as the nitrogen-free oxidizing gas, but ozone (O ₃ ) gas may be used. Further, although an example in which dinitrogen monoxide (N ₂ O) is used as the nitrogen-containing oxidizing gas has been described, a nitrogen monoxide (NO) gas or a nitrogen dioxide (NO ₂ ) gas may be used. Alternatively, a mixed gas of two or more types selected from the group consisting of nitrous oxide (N ₂ O), nitric oxide (NO) gas, and nitrogen dioxide (NO ₂ ) gas may be used.

In the above-described embodiment, a silicon single crystal substrate is preferably used as a silicon underlayer. However, in some cases, a polycrystalline silicon substrate may be used.

[0053]

According to the insulating film forming method of the present invention described above, the first oxynitriding process is performed at the same temperature as that of the oxide film formed first to change this oxide film into an oxynitride film.
For this reason, the insulating film formed according to the present invention is more effective than the insulating film formed according to the present invention, in which the processing temperature is increased or decreased for each gas introduction cycle into the reaction furnace. The number of bonds and weak bonds can be reduced, and the amount of water entering the film being formed can be suppressed. Further, the entire processing time for forming the insulating film can be reduced as compared with the conventional case.

Further, at a temperature which does not change the film thickness of the film obtained by the first oxynitriding treatment, and at a temperature at which the amount of nitrogen taken into the film as a whole is increased,
Since the second oxynitriding treatment is performed, an insulating film having a thickness designed beforehand can be formed, but an insulating film containing a large amount of nitrogen can be formed. Resistance can be improved.

[Brief description of the drawings]

FIG. 1 is a cycle diagram of processing temperature and pressure for explaining an insulating film forming method of the present invention.

FIG. 2 is a diagram mainly showing a schematic configuration of a reaction furnace of an apparatus for performing the insulating film forming method of the present invention.

FIG. 3 is a diagram mainly showing a schematic configuration of a gas supply system of an apparatus for performing an insulating film forming method of the present invention.

FIGS. 4A to 4C are formation process diagrams for explaining an insulating film formation method of the present invention.

FIG. 5 is a curve diagram showing a nitrogen distribution in an oxynitride film for describing an insulating film forming method of the present invention.

FIG. 6 is a diagram showing a structure of a MOS capacitor formed using an insulating film formed according to the insulating film forming method of the present invention.

FIG. 7 is a measurement diagram for explaining leakage current characteristics according to various insulating films incorporated in the MOS capacitor having the structure of FIG. 6;

8 is a measurement diagram for explaining the amount of dielectric breakdown charge corresponding to various insulating films incorporated in the MOS capacitor having the structure of FIG. 6;

[Explanation of symbols]

18, 70: Si substrate, 60, 72: S
i-oxide film 62: Si oxynitride film, 64, 74: final Si oxynitride film

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/318 H01L 21/8247 H01L 29/788 H01L 29/792

Claims (4)

(57) [Claims] An oxide film is formed on a lower surface of silicon, and the oxide film is oxynitrided to form an insulating film as an oxynitride film. The first oxynitriding is performed in a nitrogen-containing oxidizing gas atmosphere.
In addition , the first temperature which is the same as the heating temperature of the base when forming the oxide film is used.
Performed at a temperature, and the second oxynitriding is performed at a nitrogen-containing temperature.
The second temperature of 800 ° C. to 950 ° C. in an oxidizing gas atmosphere
Degrees, and the first temperature is higher than the second temperature.
A method for forming an insulating film, which is performed at a temperature . 2. The method according to claim 1, wherein the oxide film is formed to a thickness of about several tens of angstroms in a nitrogen-free oxidizing gas atmosphere, and
The oxynitriding is performed in a nitrogen-containing oxidizing gas atmosphere,
A method for forming an insulating film, characterized in that said oxide film is replaced with an oxynitride film having a film thickness of any value within a range of 50-100 Å. 3. The method of claim 2, wherein the nitrogen-free oxidizing gas is an oxygen (O ₂ ) gas or an ozone (O ₃ ) gas. Method. 4. The method according to claim 2, wherein the nitrogen-containing oxidizing gas is nitrogen monoxide (NO) gas, nitrous oxide (N ₂ O), and nitrogen dioxide (N
O ₂₎ insulating film forming method characterized in that a single type of gas or two or more mixed gas selected from the group of gases.