JPH09148325A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacture method to obtain an oxynitride film which exhibits high uniformity of in-plane film thickness and excellent electric properties. SOLUTION: A wafer is transferred into a chamber in a lamp heating furnace. The interior pressure of the chamber is reduced to 1×10<-1> torr or lower, returned to atmospheric pressure by flowing O2 gas, heated at the rate of 50-200<=/second. The temperature of the wafer is kept at about 110 deg.C to form an oxide film of predetermined thickness and then the temperature is increased to less than 600 deg.C and the pressure is reduced to finish the oxidation step. The pressure is next increased to atmospheric pressure by flowing NH3 gas and the temperature is increased and kept at about 1000 deg.C to form an oxynitride film by nitriding the oxide film. The temperature and the pressure are decreased to finish the nitriding step. Then N2 O gas is flowed and the temperature is increased as the oxydation step, maintaining the vacuum at less than 25Torr. The temperature is increased as the oxidartion step. The temperature is kept at about 1100 deg.C for 30 seconds to dehydrogerate the oxynitride film and then decreased. The pressure is also decreased to finish the dehydrogenation step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a tunnel insulating film of an EEPROM and a DR.
The present invention relates to a method for manufacturing an oxynitride film suitable as an insulating film for an AM memory capacitor.

[0002]

2. Description of the Related Art EEPROM which is a semiconductor nonvolatile memory
In the cell transistor, the drain and source diffusion regions are provided in the silicon substrate, the tunnel insulating film is formed on the channel formed between the drain and the source, and the floating gate made of polysilicon is formed on the tunnel insulating film. In addition, a control gate is further laminated on this via an insulating film.

In the cell transistor having the above structure, a current is caused to flow between the drain and the source, a positive voltage is applied to the control gate, and hot electrons generated by impact ionization near the drain are injected into the floating gate through the tunnel insulating film. (Writing), the injected electrons are retained in the floating gate (data retention), and a positive voltage is applied to the source, and the electrons retained in the floating gate are extracted to the source through the tunnel insulating film (erasing). This is the operation.

Therefore, the tunnel insulating film functions as an insulating film that electrically insulates the floating gate during data retention and retains electric charges, and at the same time, it must penetrate the electric charges during writing and erasing. Film thickness 80-12
An ultra-thin 0 Å thin film with good film thickness uniformity and high insulation and insulation reliability against through current when data such as direct tunnel current is retained is required. In the flash EEPROM in which the operation is limited to the batch operation, the above points are emphasized as having a great influence on the device performance and reliability.

Conventionally, an oxide film has been used as a tunnel insulating film, but this tunnel oxide film has an insulating property and an insulating reliability (hereinafter, the insulating property and the insulating reliability are collectively referred to simply as electrical characteristics). However, the oxynitride film formed by nitriding the oxide film has been studied as a material for improving the electrical characteristics of the tunnel oxide film.

As a method for producing an oxynitride film, there are known a three-step treatment of oxidation / nitridation / dehydrogenation (reoxidation), a two-step treatment of oxidation / oxynitridation, and a one-step treatment of oxynitridation. These conventional oxynitride film manufacturing methods are described below.

FIG. 11 is a manufacturing process diagram of an EEPROM cell transistor for explaining a conventional method of manufacturing an oxynitride film by a three-step process, and FIGS. 11A to 11D are views obtained in the manufacturing stage. 1 is a schematic view of a cross section of a structure.

FIG. 11A shows an active region 102 formed by forming an isolation oxide film 101 on the surface of a silicon substrate 100 using the LOCOS technique.

FIG. 11B shows the structure shown in FIG. 11A, in which the active region 102 is oxidized to form an oxide film 103 by performing rapid thermal processing (RTO) in an O ₂ atmosphere. Yes (oxidation step).

In FIG. 11C, the oxide film 103 is subjected to rapid thermal processing (RTN) in an NH ₃ atmosphere to nitride the oxide film 103 to form an oxynitride film (nitriding step). Is subjected to a rapid thermal treatment (RTON) in an N ₂ O atmosphere to perform a dehydrogenation process for desorbing hydrogen contained in the oxynitride film and a reoxidation of the oxynitride film. To form the nitride film 104 (dehydrogenation step).

The reason for carrying out the above nitriding step in an NH ₃ atmosphere is that the concentration of nitrogen introduced into the oxide film can be controlled over a wide range.

The dehydrogenation step is intended to improve the reliability of the oxynitride film by the dehydrogenation treatment.

FIG. 11D shows a floating gate 105, an interlayer insulating film 106, and a control gate 107 on the oxynitride film 104.
Is formed, and further, the source region and the drain region of the active region 102 are exposed, and by ion implantation,
The source 108 and the drain 109 are formed in the silicon substrate below the source region and the drain region, respectively, and show the structure of the cell transistor of the EEPROM.

Next, in the method of two-step oxidation / oxynitridation, the oxide film 10 is formed by subjecting the structure shown in FIG. 11 (b) to rapid thermal processing (RTON) in an N ₂ O atmosphere.
An oxynitride film is formed by oxynitriding No. 3.

Further, in the method of one-step treatment of only oxynitriding, the active region 102 is directly oxynitrided by subjecting the structure shown in FIG. 11A to rapid thermal processing (RTON) in an N ₂ O atmosphere. By this, an oxynitride film is formed.

An oxide film has been conventionally used as an insulating film of a DRAM memory capacitor, but this memory capacitor also requires an insulating film having high insulation reliability, and an oxynitride film is preferably used. Is being considered.

[0017]

However, in any of the above-mentioned methods, the thickness of the oxynitride film in the peripheral portion of the wafer is thicker than that in the central portion, and an equal thickness line ( There is a problem that an oxynitride film having good in-plane uniformity of film thickness cannot be obtained because the lines connecting the points of the same film thickness) are concentric.

The above-mentioned in-plane variation of the film thickness is caused by rapid thermal processing (RTO, RTN) in an O ₂ atmosphere or an NH ₃ atmosphere.
It was a phenomenon not seen in the oxide film and the oxynitride film by the above, but was observed only when the rapid thermal processing (RTON) was performed in the N ₂ O atmosphere.

Further, since this film thickness variation depends on the RTON temperature and decreases as the RTON temperature lowers, it was studied to lower the RTON temperature in order to solve the above problems. This time, there was a problem that the electrical characteristics deteriorated.

The above problem of the film thickness will be described in more detail based on the experimental data by the inventor of the present application.

FIG. 12 shows the in-plane film thickness distribution of an oxynitride film formed by conventional RTON.

In FIG. 12, (a) shows that in the oxynitriding process of the one-step process, the silicon substrate 11
The in-wafer film thickness distribution of the oxynitride film formed by applying RTON at 00 ° C for 30 seconds is shown. The film thickness value is an oxide film equivalent value (refractive index of oxide film is fixed at 1.46. The average value X of the film thickness is 48Å, the standard deviation (hereinafter referred to as σ) is 5.83Å, and the variation value (σ
/ X) has reached 12%. FIG. 12 (b) shows R at 1100 ° C. for 30 seconds in the dehydrogenation process of three-step treatment.
The film thickness distribution within the wafer surface of the oxynitride film formed by applying TON is shown, and the average value X = 86Å, σ = 2.36.
Å, variation value = 2.8%.

When functioning as a tunnel insulating film, the tunnel current due to hot electrons is approximately proportional to the square of the electric field, and the electric field is inversely proportional to the film thickness. Therefore, the variation in film thickness varies the tunnel current in a quadratic relationship. In order to increase the thickness, it is better that the film thickness variation within the wafer surface is as small as possible, and it is generally said that the maximum is ± 5Å from the viewpoint of the erase margin. Also in FIG. 12 (b), three times σ is 7.08Å, The difference in film thickness between the peripheral portion and the peripheral portion was outside the erase margin.

Next, as shown in FIG. 12C, in the oxynitriding step of the one-step process, 900 ° C. × 60 ° C. is directly applied to the silicon substrate.
2 shows the in-wafer film thickness distribution of the oxynitride film formed by applying RTON for 2 seconds, and the average value X = 25Å, σ = 0.
76Å, variation value = 3.0%.

FIG. 12 (d) shows the film thickness distribution of the oxynitride film formed by applying RTON at 900 ° C. for 60 seconds in the dehydrogenation process of the three-step process, and shows the average value X.
= 88Å, σ = 1.52Å, and variation value = 1.7%.

FIG. 13 shows the RTON temperature dependence of the variation in the in-wafer film thickness of the oxynitride film by the conventional RTON. The curve a in the figure shows the case where the RTON is directly applied to the silicon substrate in the one-step process. Shows the curve b
Shows the case where RTON was applied in the dehydrogenation step of the 3-step process.

In FIG. 13, the variation in film thickness decreases with the decrease of the RTON temperature in any case, and the variation value in the one-step processing can be suppressed to 3% at 900 ° C.

However, in the one-step processing, 900
The film thickness of the oxynitride film that can be formed at a low temperature of ℃ is shown in FIG.
Is less than 30 Å, and the insulation property against the direct tunnel current is remarkably poor at this film thickness.

In the dehydrogenation process of the three-step process, dehydrogenation may be incomplete at a low temperature of 900 ° C., and the insulation reliability may be inferior to that of a normal oxide film.

Although not shown, even when RTON at 1100 ° C. for 30 seconds is performed in the two-step oxynitriding process, the oxynitride film formed is the same as that shown in FIG. 12B. Thickness variation is shown, and the variation value is 2 to 2.
5%.

Even in the two-step process, the film thickness variation can be improved by lowering the RTON temperature to 900 ° C., but the nitrogen concentration that can be introduced into the oxide film is low,
The electrical characteristics could not be improved.

As described above, in order to improve the electrical characteristics of the conventional tunnel oxide film, a high temperature RTO of about 1100 ° C.
In N, it is a current subject to develop a manufacturing method capable of obtaining an oxynitride film having good in-plane uniformity.

The present invention solves the above problems, and an object of the present invention is to provide a method of manufacturing a semiconductor device capable of obtaining an oxynitride film having excellent in-plane film thickness uniformity and electrical characteristics. An object of the present invention is to provide a method for manufacturing a semiconductor device, which can obtain an ultrathin oxynitride film excellent in in-plane film thickness uniformity and electrical characteristics.

[0034]

In order to achieve the above object, the manufacturing method of the present invention comprises an oxidation step of forming a thermal oxide film on a silicon substrate and a heat treatment of the oxide film in an NH ₃ atmosphere. Thus, by performing a nitriding step of nitriding the oxide film to form an oxynitride film, and performing a heat treatment on the oxynitride film in an N ₂ O atmosphere having a vacuum degree of less than 25 Torr, preferably about 10 Torr to 1 Torr, And a dehydrogenation step of performing a desorption process of hydrogen contained in the oxynitride film.

Each step of the above manufacturing method is carried out, for example, by using a lamp heating furnace, and, for example, the oxidation step is performed under atmospheric pressure at a rate of 50 to 200 ° C./sec for 100 times.
Rapid heat treatment is performed to raise the temperature to 0 to 1100 ° C., preferably about 1100 ° C., and the nitriding step is performed under atmospheric pressure at a rate of 50 to 200 ° C./sec.
Rapid heat treatment is performed to raise the temperature to about 0 ° C.
In the dehydrogenation step, a rapid thermal processing film is used in which the temperature is raised to about 1100 ° C. at a rate of 50 to 200 ° C./sec under a reduced pressure with a degree of vacuum of about 10 Torr to 1 Torr.

Another manufacturing method of the present invention comprises an oxidation step of forming a thermal oxide film on a silicon substrate, a vacuum degree of less than 25 Torr,
An oxynitriding step of nitriding the oxide film to form an oxynitride film by subjecting the oxide film to a heat treatment in an N ₂ O atmosphere of preferably about 10 Torr to 1 Torr is performed. .

In any one of the above manufacturing methods, in the oxidation step, the degree of vacuum is less than 25 Torr, preferably about 10 Torr.
An oxide film may be formed on the silicon substrate by heat-treating the silicon substrate in an O ₂ atmosphere of 1 Torr.

Still another manufacturing method of the present invention is a vacuum degree 2
It is characterized by including an oxynitriding step of forming an oxynitride film on the silicon substrate by subjecting the silicon substrate to a heat treatment in an N ₂ O atmosphere of less than 5 Torr, preferably about 10 Torr to 1 Torr.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a lamp heating furnace used in an embodiment of the present invention.

In FIG. 1, dozens or dozens of halogen lamps 202 equipped with a reflecting mirror 201 are attached to the outside of a quartz glass chamber 200 so as to face each other vertically. , Wafer 20
4 is provided with a wafer tray 203 for supporting 4,
By heating the lamp with the halogen lamp 202, the temperature of the wafer 204 can be raised at a rate of 50 to 200 ° C./second (rapid heat treatment specification), and the temperature can be raised to about 1200 ° C.

An automatic vacuum degree control device (APC) for automatically controlling the degree of vacuum by adjusting the exhaust pipe 205 and the vacuum valve.
A vacuuming mechanism (hereinafter, simply referred to as a vacuum pump) configured by 206, a turbo molecular pump 207, and a rotary pump 208 has a structure capable of adjusting the degree of vacuum in the chamber 200.

Further, the gas introducing valve 210, the N ₂ gas introducing valve 211, the O ₂ gas introducing valve 212, the NH ₃ gas introducing valve 213, and the N ₂ O gas introducing valve 214.
By opening and closing, various kinds of gas can be introduced into the chamber 200 from the gas inlet 209.

The front door 215 is normally closed,
Opened when loading and unloading wafers.

Next, a first embodiment of the present invention will be described.

In this embodiment, 1 in 3 step processing is used.
By carrying out the dehydrogenation process using a high temperature RTON of 100 ° C. under reduced pressure, it is possible to improve the in-plane film thickness variation of the oxynitride film.

FIG. 2 shows the sequence (temperature sequence, pressure sequence, and process gas sequence) in the first embodiment.

The temperature sequence of each step shown in FIG. 2 is 50.
It is a rapid thermal processing sequence with a heating rate of ~ 200 ° C / sec.

The oxynitride film forming procedure according to the first embodiment will be described below.

First, a wafer is loaded into the lamp heating furnace shown in FIG.

That is, the front door 2 of the chamber 200 is opened while the N ₂ gas introducing valve 211 and the gas introducing valve 210 are opened and the N ₂ gas is kept flowing in the chamber 200.
15 is opened, and the wafer tray 20 in the chamber 200 is opened.
The wafer is set to 3, and the front door 215 is closed.

Next, the N ₂ gas introducing valve 211 and the gas introducing valve 210 are closed to stop the N ₂ gas flowing in the chamber 200, and according to the sequence shown in FIG.
The inside of the chamber 200 is 1 × 10 ⁻¹ To by a vacuum pump.
Reduce the pressure to rr or less.

Next, the O ₂ gas introducing valve 212 and the gas introducing valve 210 are opened, the O ₂ gas is caused to flow into the chamber 200 to return to atmospheric pressure, and 50 to 2 by lamp heating.
The temperature is raised at a rate of 00 ° C./sec and the wafer temperature is maintained at about 1100 ° C. to form an oxide film having a predetermined film thickness.

The RTO temperature may be set to 1000 ° C. to 1100 ° C. depending on the oxide film thickness.

Next, the lamp is turned off, the temperature is lowered to 600 ° C. or lower, the O ₂ gas introducing valve 212 and the gas introducing valve 210 are closed, the pressure inside the chamber 200 is reduced to 1 × 10 ^-1 Torr or less by a vacuum pump, and O _{2 is} reduced. Remove the gas,
The oxidation process is completed.

Next, the NH ₃ gas introduction valve 213 and the gas introduction valve 210 are opened, NH ₃ gas is flowed to return to atmospheric pressure, and the temperature of the wafer is raised to about the same rate as the above-mentioned oxidation step by lamp heating. The temperature is maintained at 1000 ° C., and the oxide film formed by the oxidation process is nitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the NH ₃ gas introducing valve 213 and the gas introducing valve 210 are closed, and the NH ₃ gas is removed by reducing the pressure to 1 × 10 ^-1 Torr or less as in the above-mentioned oxidation step. The nitriding process is completed.

Next, the N ₂ O gas introduction valve 214 and the gas introduction valve 210 are opened to allow N ₂ O gas to flow, and while maintaining the degree of vacuum at about 10 Torr (vacuum is continued, A
Adjust the opening and closing degree of the vacuum valve by PC206),
The lamp is heated to raise the temperature at the same rate as in the above oxidation step, and the wafer temperature is maintained at about 1100 ° C. for 30 seconds to perform dehydrogenation treatment of the oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the N ₂ O gas introducing valve 214 and the gas introducing valve 210 are closed, and the pressure is reduced to 1 × 10 ^-1 Torr or less in the same manner as in the above-mentioned oxidation step, and N ₂ O gas is added. Remove and complete the dehydrogenation step.

[0059] N ₂ to the last open N ₂ gas introducing valve 211 and the gas inlet valve 210 the chamber 200
Gas is flowed to lower the wafer temperature sufficiently, and then N
₂ Front door 215 of chamber 200 with gas flowing
Open and unload the wafer.

With the above, the oxynitride film forming procedure according to the first embodiment is completed.

FIG. 3 shows a wafer in-plane film thickness distribution of the oxynitride film obtained by the first embodiment (three-step process).

The oxynitride film shown in FIG. 3 has a variation value of 1.
It is 45%, and it can be seen that the in-plane film thickness variation is improved as compared with the variation value of 2.8% (FIG. 12B) when the conventional dehydrogenation step was performed under atmospheric pressure.

Although the detailed mechanism for improving the in-plane film thickness variation is unknown, the present inventor estimates as follows.

The wafer temperature was set to 1 in an N ₂ O atmosphere.
When the temperature is raised to 100 ° C., the next reaction occurs in the vicinity of the wafer surface by about 30%.

N ₂ O → N ₂ + O (1) Then, the oxidizing agent generated by the reaction of (1) starts the oxidation of the wafer.

When the reaction (1) is started, the remaining N ₂ O starts the next reaction in a short time. N ₂ O + O → 2NO (2) Next, if the wafer temperature is kept at 1100 ° C., heat is radiated from the wafer to generate an ascending air current at the center of the wafer surface, which diminishes the gas density. Also receives a large amount of N ₂ O gas, the reaction of (2) is promoted, and the atmosphere at the center of the wafer becomes rich in the reactant NO.

As a result, it is said that in-plane film thickness variation occurs because oxidation is suppressed in the central portion of the wafer as compared with the peripheral portion.

However, when the temperature of the wafer is lowered to 900 ° C., the reaction of 2O → O ₂ (3) has a higher priority than the reaction of (2), and therefore the reaction of (2) is suppressed, and the central part of the wafer is suppressed. In addition, since the oxidizing agent can be supplied similarly to the peripheral portion, it is considered that there is little variation in the in-plane film thickness.

However, at a low temperature of 900 ° C., the oxynitride film cannot be sufficiently dehydrogenated.

Therefore, in this embodiment, 1100 ° C.
In order to supply the oxidizer to the center of the wafer at a high temperature of, the entire surface of the wafer is covered with an airflow at a much higher velocity than the ascending airflow generated in the center of the wafer, and the gas density is reduced to reduce the gas concentration in the center of the wafer. It is considered that the in-plane film thickness variation could be improved by increasing the reaction efficiency of the reaction of the reaction formula (1) by suppressing the ascending air current.

The air velocity at 10 Torr of this embodiment is 2.1 m / sec, which is 76 times that at atmospheric pressure, and since the atmospheric pressure of 10 Torr is equivalent to the atmospheric pressure in the stratosphere, it is small. Updraft due to buoyancy due to the difference in density can be suppressed.

Therefore, LPCVD (reduced pressure gas phase reaction production)
This is different from the improvement of the film thickness distribution of the wafers at the short distance loading intervals due to the extension of the mean free path, which is the effect of the pressure reduction in the above.

As described above, according to the first embodiment of the present invention, RTON at 1100 ° C. under a reduced pressure of 10 Torr.
By performing the (dehydrogenation step of the three-step process),
An oxynitride film having excellent in-plane film thickness distribution and electrical characteristics can be obtained.

Further, in the dehydrated oxygen step, it is not necessary to return the pressure of the N ₂ O atmosphere to the atmospheric pressure, so that the consumption amount of N ₂ O gas and the processing time can be shortened.

In the first embodiment, RT
The oxide film formed by O (oxidation step) has a variation value of about 1% in-plane film thickness variation, so there is little substantial improvement in the in-plane film thickness variation of the oxynitride film. It is considered that if an oxide film having a good film thickness distribution is obtained, the in-plane film thickness variation of the oxynitride film is further improved.

Next, a second embodiment of the present invention will be described.

In this embodiment, 1 in 2 step processing
By carrying out the oxynitriding step using a high temperature RTON of 100 ° C. under reduced pressure, it is possible to improve the in-plane film thickness variation of the oxynitride film.

FIG. 4 shows a sequence (temperature sequence, pressure sequence, and process gas sequence) in the second embodiment.

The temperature sequence of each step shown in FIG. 4 is 50.
It is a rapid thermal processing sequence with a heating rate of ~ 200 ° C / sec.

The sequence shown in FIG. 4 is assumed to be carried out in the lamp heating furnace shown in FIG.

An oxynitride film forming procedure according to the second embodiment will be described below.

First, the wafer is loaded into the chamber 200, the N ₂ gas flowing in the chamber 200 is stopped as shown in FIG. 4, and the pressure is reduced to 1 × 10 ^-1 Torr or less by a vacuum pump.

Next, O ₂ gas is flowed to return to atmospheric pressure, the temperature is raised at a rate of 50 to 200 ° C./sec by lamp heating, and the wafer temperature is maintained at about 1100 ° C. to form an oxide film of a predetermined thickness. To do.

The RTO temperature may be set to 1000 ° C. to 1100 ° C. depending on the oxide film thickness.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower by a vacuum pump to remove O ₂ gas, and the oxidation step is completed.

Next, N ₂ O gas is flown to bring the degree of vacuum to about 1.
While maintaining 0 Torr, the temperature of the wafer was raised to about 11 by heating the lamp at the same rate as in the above oxidation process.
The temperature is maintained at 00 ° C. for 30 seconds, and the oxide film formed by the oxidation process is nitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, and the pressure is reduced to 1 × 10 ⁻¹ Torr or lower in the same manner as in the above-mentioned oxidation step, and N ₂ O is added.
The gas is removed, and the oxynitriding process is completed.

With the above, the oxynitride film forming procedure according to the second embodiment is completed.

FIG. 5 shows the second embodiment (two-step processing).
3 shows a wafer in-plane film thickness distribution of the oxynitride film obtained by.

The oxynitride film shown in FIG. 5 has a variation value of 1.
It is 7%, and it can be seen that the in-plane film thickness variation is improved as compared with the variation value of 2.8% when the dehydrogenation step is performed under the conventional atmospheric pressure.

As described above, according to the second embodiment of the present invention, RTON of 1100 ° C. is obtained under a reduced pressure of 10 Torr.
By performing the oxynitriding process of the two-step processing,
An oxynitride film having a good in-plane film thickness distribution and good electrical characteristics can be obtained, and since it is a two-step process, the processing time can be shortened as compared with the first embodiment.

Next, a third embodiment of the present invention will be described.

In this embodiment, 1 in 1 step processing
By carrying out the oxynitriding step using a high temperature RTON of 100 ° C. under reduced pressure, it is possible to improve the in-plane film thickness variation of the oxynitride film.

An oxynitride film forming procedure according to the third embodiment will be described below.

This embodiment is assumed to be carried out in the lamp heating furnace shown in FIG.

First, the wafer is loaded into the chamber 200, and the N ₂ gas flowing in the chamber 200 is stopped,
The pressure is reduced to 1 × 10 ⁻¹ Torr or less by a vacuum pump.

Next, a N ₂ O gas is flown to bring the degree of vacuum to 10 Torr.
While the temperature is maintained at 50 ° C./sec, the temperature of the wafer is raised at a rate of 50 to 200 ° C./sec, the wafer temperature is kept at about 1100 ° C. for 30 sec, and the silicon substrate is directly oxynitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, and the pressure is reduced to 1 × 10 ⁻¹ Torr or lower in the same manner as in the above-mentioned oxidation step, and N ₂ O is added.
The gas is removed, and the oxynitriding process is completed.

As described above, the formation of the oxynitride film according to the third embodiment using the one-step process is completed.

FIG. 6 shows a third embodiment (one-step processing).
3 shows a wafer in-plane film thickness distribution of the oxynitride film obtained by.

In FIG. 6, FIG. 6A shows a vacuum degree of 25 To.
The in-plane film thickness distribution is shown when RTON is performed at 1100 ° C. for 30 seconds under a reduced pressure of rr, and the variation value reaches 17%.

FIG. 6B shows the in-plane film thickness distribution when RTON was performed at 1100 ° C. for 30 seconds under a reduced pressure of a vacuum degree of 10 Torr, and the variation value was improved to 2.5%.

FIG. 6C shows the in-plane film thickness distribution when RTON was performed at 1100 ° C. for 30 seconds under a reduced pressure of a vacuum degree of 6 Torr, the average value X = 33Å, and the variation value = 3.3.
%Met.

FIG. 6 (d) shows the in-plane film thickness distribution when RTON was performed at 1100 ° C. for 30 seconds under a reduced pressure of 1.2 Torr, the average value X = 18Å, and the variation value = 3. It was 0.8%.

FIG. 7 is a diagram showing the relationship between the vacuum degree of the RTON and the film thickness (curve c) of the formed oxynitride film and its variation value (d) according to the third embodiment (one step process). is there.

As shown in FIG. 6 and FIG.
In Torr (Fig. 6 (a)), the variation value = 17%,
Variation value = 1 under conventional atmospheric pressure (Fig. 3 (a))
Although it is worse than 2%, when the pressure is further reduced, the film thickness variation is sharply improved (FIGS. 6A to 6D), particularly 10
In Torr (FIG. 6B), the variation value = 2.5% is obtained.

One of the causes that the film thickness variation at the vacuum degree of 25 Torr becomes worse than the atmospheric pressure is that the reaction of (2) above is more than the reaction of (3) than under atmospheric pressure due to the extension of the mean free path. It is possible that it is happening preferentially.

As described above, according to the third embodiment of the present invention, a high temperature RTO of 1100 ° C. is obtained under a reduced pressure of 10 Torr.
By performing N (one-step oxynitriding step), an oxynitride film having a good in-plane film thickness distribution and electrical characteristics can be obtained, and since it is one-step processing, the processing time is longer than that in the second embodiment. Can be shortened.

Further, as described with reference to FIGS. 6 and 7, the vacuum degree of the high temperature RTN is less than 25 Torr, especially about 1 Torr.
The range of 10 Torr is preferable. It is estimated that the particularly preferable range of the degree of vacuum is about 1 to 10 Torr, which is also applicable to the above-described first and second embodiments.

Next, a fourth embodiment will be described.

In this embodiment, 11 in the three-step processing.
By performing the oxidation process by the high temperature RTO of 00 ° C. and the dehydrogenation process by the high temperature RTON of 1100 ° C. under reduced pressure, it is possible to improve the in-plane film thickness variation of the oxynitride film and obtain an extremely thin oxynitride film. It makes it possible.

That is, in the oxidation step under the atmospheric pressure shown in the first embodiment or the second embodiment, 110
Even at RTO of 0 ° C. for 10 seconds, an oxide film of about 60 Å is formed, and the film thickness of the oxynitride film formed through the nitriding process and the reoxidation process is necessarily about 75 Å.

Therefore, 60Å suitable as a tunnel insulating film
In order to obtain an oxynitride film having a film thickness of
It was necessary to lower the temperature to 1000-1050 ° C.

However, the RTO temperature is set to 1000 to 10
If the temperature is lowered to 50 ° C., the electrical characteristics of the obtained oxynitride film will be inferior to those formed by RTO and RTON at 1100 ° C.

Therefore, the present embodiment has a good electrical characteristic.
This makes it possible to obtain an oxynitride thin film of about 0Å.

FIG. 8 shows a sequence (temperature sequence, pressure sequence, and process gas sequence) in the fourth embodiment.

The temperature sequence of each step shown in FIG. 8 is 50.
It is a rapid thermal processing sequence with a heating rate of ~ 200 ° C / sec.

The sequence shown in FIG. 8 is performed in the lamp heating furnace shown in FIG.

An oxynitride film forming procedure according to the fourth embodiment will be described below.

First, the wafer is loaded into the chamber 200, the N ₂ gas flowing in the chamber 200 is stopped as shown in FIG. 8, and the pressure is reduced to 1 × 10 ^-1 Torr or less by a vacuum pump.

Next, an O ₂ gas is flown to bring the degree of vacuum to about 10 T.
While maintaining at orr, heating the lamp at 50-200 ℃ /
The wafer temperature is raised to about 1100 at a rate of 2 seconds.
The temperature is kept at 0 ° C. to form an oxide film having a predetermined thickness.

Next, the lamp is turned off, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower by a vacuum pump to remove O ₂ gas, and the oxidation step is completed.

Next, NH ₃ gas is caused to flow to return to atmospheric pressure,
By heating with a lamp, the temperature is raised at the same rate as in the oxidation step,
The wafer temperature is maintained at about 1000 ° C., and the oxide film formed by the oxidation process is nitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower to remove NH ₃ gas in the same manner as in the oxidation step, and the nitriding step is completed.

Next, N ₂ O gas is flown to bring the degree of vacuum to about 1
While maintaining 0 Torr, the temperature is raised at the same rate as in the oxidation step, and the wafer temperature is maintained at about 1100 ° C. for 30 seconds to perform dehydrogenation treatment of the oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower to remove the N ₂ O gas in the same manner as in the oxidation step, and the dehydrogenation step is completed.

As described above, the oxynitride film forming procedure according to the fourth embodiment is completed.

According to the above fourth embodiment of the present invention,
Oxidation process under high temperature RTO of 1100 ℃ under reduced pressure of 10 Torr
By lowering the oxygen partial pressure in the RTO to suppress the formation rate of the oxide film, it is possible to obtain an oxynitride thin film of about 60 Å with good in-plane film thickness distribution and electrical characteristics.

Next, a fifth embodiment of the present invention will be described.

In this embodiment, 1 in 3 step processing is used.
By performing the oxidation step by the high temperature RTO of 100 ° C. and the oxynitridation step by the high temperature RTON of 1100 ° C. under reduced pressure, the in-plane film thickness variation of the oxynitride film is improved and an ultrathin oxynitride film is obtained. It makes it possible.

An oxynitride film forming procedure according to the fifth embodiment will be described below.

This embodiment is assumed to be carried out in the lamp heating furnace shown in FIG.

First, the wafer is loaded into the chamber 200, and the N ₂ gas flowing in the chamber 200 is stopped,
The pressure is reduced to 1 × 10 ⁻¹ Torr or less by a vacuum pump.

Next, an O ₂ gas is flown to raise the temperature at a rate of 50 to 200 ° C./sec by lamp heating while maintaining the degree of vacuum at 10 Torr, and the wafer temperature is maintained at about 1100 ° C. to oxidize a predetermined film thickness. Form a film.

Next, the lamp is turned off, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to the following by a vacuum pump to remove O ₂ gas, and the oxidation step is completed.

Next, NH ₃ gas is flowed to return to atmospheric pressure,
By heating with a lamp, the temperature is raised at the same rate as in the oxidation step,
The wafer temperature is maintained at about 1000 ° C., and the oxide film formed by the oxidation process is nitrided to form an oxynitride film.

[0137] flushed with following N ₂ O gas, the degree of vacuum of approximately 10T
While maintaining at orr, the temperature is raised at the same rate as in the oxidation step, and the oxide film in the oxidation step is oxynitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower to remove the N ₂ O gas similarly to the oxidation step, and the oxynitriding step is completed.

As described above, the oxynitride film forming procedure according to the fifth embodiment is completed.

According to the fifth embodiment of the present invention described above, the oxidation step is carried out at a high temperature RTO of 1100 ° C. under a reduced pressure of 10 Torr, and the oxygen partial pressure in the RTO is reduced to suppress the oxide film formation rate. As a result, it is possible to obtain an oxynitride thin film having a good in-plane film thickness distribution and electrical characteristics of about 60 Å, and since it is a two-step process, the processing time can be shortened compared to the fourth embodiment.

As described above, the preferable vacuum degree range in the oxidation step in the fifth and sixth embodiments is also 25.
It is less than Torr, particularly in the range of about 1-10 Torr.

Next, a sixth embodiment of the present invention will be described.

The present embodiment uses a core tube of batch processing specification capable of forming a thermal oxide film having a smaller variation in in-plane film thickness than the case of using the lamp heating furnace shown in FIG. By performing the oxidation step of the embodiment and performing the nitriding step and the dehydrogenating step on the formed thermal oxide film using the lamp heating furnace shown in FIG. It is possible to make further improvement over the first embodiment.

FIG. 9 shows the sequence of the nitriding process and the dehydrogenation process (temperature sequence, pressure sequence, and process gas sequence) in the sixth embodiment.

The temperature sequence of each step shown in FIG. 9 is 50.
It is a rapid thermal processing sequence with a heating rate of ~ 200 ° C / sec.

An oxynitride film forming procedure according to the sixth embodiment will be described below.

First, a predetermined number of wafers are loaded into a FURNACE furnace and subjected to a thermal oxidation process to form an oxide film having a predetermined thickness on a silicon substrate (oxidation step).

Next, the wafer on which the thermal oxidation is formed is subjected to F
9 is carried out from the URNACE furnace and is carried into the chamber 200 of the lamp heating furnace shown in FIG.
As shown in, the N ₂ gas flowing in the chamber 200 is stopped, and the pressure is reduced to 1 × 10 ⁻¹ Torr or less.

Next, NH ₃ gas is flowed to return to atmospheric pressure,
The temperature of the wafer is raised at a rate of 50 to 200 ° C./sec by lamp heating, the wafer temperature is maintained at about 1000 ° C., and the oxide film formed by the oxidation process is nitrided to form an oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ⁻¹ Torr or lower by a vacuum pump to remove NH ₃ gas, and the nitriding step is completed.

Next, N ₂ O gas is flown to bring the degree of vacuum to 10 Torr.
The temperature is raised at the same rate as in the nitriding step, and the wafer temperature is kept at about 1100 ° C. for 30 seconds to perform dehydrogenation treatment of the oxynitride film.

Next, the temperature is lowered to 600 ° C. or lower, the pressure is reduced to 1 × 10 ^-1 Torr or lower to remove the N ₂ O gas in the same manner as in the nitriding step, and the dehydrogenation step is completed.

With the above, the oxynitride film forming procedure according to the sixth embodiment is completed.

FIG. 10 shows a wafer in-plane film thickness distribution of the oxynitride film obtained by the sixth embodiment (three-step process).

The oxynitride film shown in FIG. 10 has an average value X = 97.
Å, σ = 0.52Å, and film thickness variation value = 0.5
%, The uniformity of the in-plane film thickness was very excellent.

As described above, according to the sixth embodiment of the present invention, the oxidization process is performed in the FURNACE furnace to suppress the variation in the in-plane film thickness of the oxide film. Further, an oxynitride film having a good in-plane film thickness distribution can be obtained.

Also in the fourth to sixth embodiments, the preferable range of the vacuum degree of the high temperature RTN is less than 25 Torr, particularly about 1 to 10 Torr.

[0158]

As described above, according to the manufacturing method of the first aspect, the dehydrogenation step is performed in the N ₂ O atmosphere having the vacuum degree of less than 25 Torr in forming the oxynitride film by the three-step treatment. As a result, there is an effect that an oxynitride film having good in-plane film thickness distribution and electrical characteristics can be obtained.

According to the manufacturing method of claim 2, 2
When forming the oxynitride film by step processing, the degree of vacuum is 2
The oxynitride film having a good in-plane film thickness distribution and electrical characteristics can be obtained by carrying out the oxynitridation step in an N ₂ O atmosphere of less than 5 Torr, and since it is a two-step process, the production according to claim 1. This has the effect that the processing time can be shortened as compared with the method.

Further, according to the manufacturing method of claim 6, in the method of claim 1 or 2, the oxidation step is carried out in an O ₂ atmosphere having a vacuum degree of less than 25 Torr to reduce the oxygen partial pressure to reduce the oxide film. Suppressing the formation rate of Al has the effect that it is possible to obtain an oxynitride thin film of about 60 Å with good in-plane film thickness distribution and electrical characteristics.

According to the manufacturing method of claim 3, 1
When forming the oxynitride film by step processing, the degree of vacuum is 2
The oxynitride film having a good in-plane film thickness distribution and electrical characteristics can be obtained by carrying out the oxynitridation step in an N ₂ O atmosphere of less than 5 Torr, and since it is a one-step process, the production according to claim 2. This has the effect that the processing time can be further shortened as compared with the method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a lamp heating furnace used in an embodiment of the present invention.

FIG. 2 is a first embodiment (three-step process) of the present invention.
FIG. 7 is a diagram showing a sequence in FIG.

FIG. 3 is a first embodiment (three-step process) of the present invention.
FIG. 3 is a diagram showing a wafer in-plane film thickness distribution of an oxynitride film obtained by.

FIG. 4 is a second embodiment (two-step processing) of the present invention.
FIG. 7 is a diagram showing a sequence in FIG.

FIG. 5: Second embodiment of the present invention (two-step processing)
FIG. 3 is a diagram showing a wafer in-plane film thickness distribution of an oxynitride film obtained by.

FIG. 6 is a third embodiment of the present invention (1 step process).
FIG. 3 is a diagram showing a wafer in-plane film thickness distribution of an oxynitride film obtained by.

FIG. 7: Third embodiment of the present invention (1 step process)
FIG. 3 is a diagram showing the relationship between the degree of vacuum of the RTON, the film thickness of the formed oxynitride film, and the variation value thereof.

FIG. 8 is a fourth embodiment of the present invention (3 step process).
FIG. 7 is a diagram showing a sequence in FIG.

FIG. 9 is a sixth embodiment of the present invention (3 step process).
FIG. 3 is a diagram showing a sequence of a nitriding process and a dehydrogenation process in FIG.

FIG. 10 is a diagram showing a wafer in-plane film thickness distribution of an oxynitride film obtained by a sixth embodiment (three-step process) of the present invention.

FIG. 11 is a manufacturing process diagram of the cell transistor of the EEPROM for explaining the conventional method of manufacturing the oxynitride film by the three-step process.

FIG. 12 is a diagram showing a wafer in-plane film thickness distribution of an oxynitride film formed by conventional RTON.

FIG. 13 is a diagram showing RTON temperature dependence of variations in film thickness within the wafer surface of an oxynitride film by conventional RTON.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H01L 21/8247 29/788 29/792

Claims (8)

[Claims] 1. An oxidation step of forming a thermal oxide film on a silicon substrate, and a nitriding step of nitriding the oxide film to form an oxynitride film by subjecting the oxide film to a heat treatment in an NH ₃ atmosphere, A dehydrogenation step of removing hydrogen contained in the oxynitride film by heat-treating the oxynitride film in an N ₂ O atmosphere having a vacuum degree of less than 25 Torr. Production method. 2. An oxidation step of forming a thermal oxide film on a silicon substrate, and a thermal treatment of the oxide film in an N ₂ O atmosphere having a vacuum degree of less than 25 Torr to nitride the oxide film to form an oxynitride film. A method of manufacturing a semiconductor device, comprising: an oxynitriding step of forming. 3. A method of manufacturing a semiconductor device, comprising: an oxynitriding step of forming an oxynitride film on the silicon substrate by heat-treating the silicon substrate in an N ₂ O atmosphere having a vacuum degree of less than 25 Torr. . 4. The vacuum degree of the N ₂ O atmosphere is about 10 Torr.
The method for manufacturing a semiconductor device according to claim 1, wherein: 5. The method of manufacturing a semiconductor device according to claim 4, wherein the N ₂ O atmosphere has a vacuum degree of about 1 Torr or more. 6. A vacuum degree of 25 Torr in the oxidation step.
_{3. The} method for manufacturing a semiconductor device according to claim 1, wherein the oxide film is formed on the silicon substrate by heat-treating the silicon substrate in an O ₂ atmosphere of less than 0. 7. The method of manufacturing a semiconductor device according to claim 6, wherein the degree of vacuum of the O ₂ atmosphere in the oxidation step is about 10 Torr or less. 8. The method of manufacturing a semiconductor device according to claim 7, wherein the degree of vacuum of the O ₂ atmosphere in the oxidation step is about 1 Torr or more.