JPH0414498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for forming a nitride film in which silicon or the like is directly nitrided to form a nitride film.

(Technical background of the invention and its problems) LSI devices are becoming more and more highly integrated year by year. For example, as a typical example of MOS memory,
Looking at DRAM (dynamic random access memory), it goes from 16k bits to 64k to 256k.
It is rapidly expanding to 1M bits.
DRAM is also expected to develop in the next few years.
In this way, the size of the chip remains approximately the same and the density becomes higher, so the area of the DRAM memory cell section has to become smaller and smaller, but the storage capacity will not decrease proportionally. This must be avoided due to problems with the S/N ratio during on and off states, and as a result, the SiO ₂ film of the MOS capacitor that forms the storage capacitor section must be made thinner. For example, taking DRAM as an example, the SiO ₂ film thickness is currently 400 Å for 64 k bits, 250 Å for 256 k bits, and 70 Å for 1 M bits. However, as the SiO ₂ film becomes thinner, not only the controllability of the film formation but also the defect density increases significantly, and the withstand voltage characteristics of the SiO ₂ film deteriorates rapidly. To solve this problem, a _silicon nitride film (here:
It is conceivable to use a Si ₃ N ₄ film). on the other hand,
Conventionally, Si ₃ N ₄ has been deposited by thermally decomposing monosulfuric acid (SiH ₄ ) and ammonia (NH ₃ ) at a temperature of about 850°C, followed by vapor phase growth (CVD). However, with this method, even if a thin Si ₃ N ₄ film is formed on a Si substrate, (1) it is difficult to control the film thickness, and (2) the Si film originally has a thickness of 30 Å.
There is a certain amount of natural oxide film, forming an MNOS structure,
Hysteresis occurs in the C-V characteristics, (3) Si ₃ N ₄ −
The surface state density of the Si interface becomes more than 10 ¹² /cm ² eV,
The fundamental drawback was that a good MOS structure could not be created. Therefore, attempts have recently been made to directly react N ₂ and Si at high temperatures of 1200° C. or higher to form a Si ₃ N ₄ film on Si. However, in the case of SiO ₂ film, a film of about 1000 Å is formed in a short time by oxygen or steam at 900 to 1100°C, whereas in the case of Si ₃ N ₄ film, it is formed by N ₂ gas at 1100°C. 1
Even if Si is nitrided for a long time, a thickness of only 50 Å can be obtained.
Even at a high temperature of 1200°C, nitriding hardly progresses after 100 Å. Furthermore, the film quality is not uniform and is likely to be formed into islands. (For example, J.Electrochem・
Soc: SOLID−STATE SCIENCE AND
TECHNOLOGY (March 1978) paper “Very
Jhin Silicon Nitride Films Grown by Direct
(See “Jhermal Reactive with Nitrogen”).

In response to the problem of mainly low growth rate of direct nitriding of silicon, a method of direct nitriding of silicon using glow discharge was recently reported at the 28th Spring Meeting of the Japan Society of Applied Physics in 1981 ( Takashi Ito: 29P-C-5). The outline of this method will be explained using FIG. 1. One end of the quartz tube 1 is connected to a lid 2, and the other end is connected to an exhaust system. Si wafers 4 supported by a susceptor 3 coated with SiC are vertically arranged in a quartz tube 1. On the other hand, a coil 5 is wound around the outside (atmosphere) of the quartz tube 1, and an RF power source 6 is connected thereto. 7 is a gas introduction part, from which gases such as NH ₃ , N ₂ +H ₂ , N ₂ are supplied. Now, set the pressure in the quartz tube 1 so that the NH ₃ gas is around 0.1 to 10 Torr, and set the pressure in the quartz tube 1 to 400kHz from the RF power supply 6.
When high frequency is applied, a glow discharge 8 occurs in the quartz tube 1.
is generated, NH ₃ gas and the like are dissociated, and the Si wafer 4 is heated by induction heating. As a result, a reaction occurs between the nitrogen-containing gas plasma and the high-temperature Si wafer 4, and direct nitridation of Si is performed. According to reports, the flow rate of NH ₃ is 1/min, and the high frequency power is
At 10kW and Si wafer temperature of 1050℃, approx.
A Si ₃ N ₄ film of about 100 Å was formed in 150 minutes.

It has been confirmed that by using glow discharge in this manner, nitridation is promoted more quickly at a relatively low temperature. However, since this method uses a 400 kHz discharge, the ionization energy in the plasma is high, and therefore the ion bombardment on the sample is large, and there is a concern that semiconductor elements may be damaged by irradiation. In addition, this method uses the clever means of simultaneously heating the Si and glow-discharging the introduced gas, but this makes the nitriding parameters dependent only on the introduced RF power, which limits the nitriding rate and There is a risk that the gas plasma, such as , NH ₃ , reduces the SiO ₂ in the quartz tube to produce oxygen, which will be mixed into the membrane, and this is also shown in the data in the above report. On the other hand, since this method places the sample in plasma, it is difficult to determine whether the nitridation mechanism is carried out by neutral radical species in the plasma or by the assist by the high-energy bombardment of the ions. It was done in , but it was not clear.

Recently, in order to solve the problems that occur when performing direct nitridation of Si in the above plasma, the present inventors have developed a method to dissociate nitrogen-containing gas by microwave discharge in a discharge chamber, thereby producing long-life activated nitrogen. generate,
We devised an apparatus that can produce a high-quality nitride film by transporting this activated nitrogen into a reaction chamber that is separated from the discharge chamber and causing the heated sample to react with the activated nitrogen in the reaction chamber. Patent Application No. 56-139340 (Japanese Patent Application No. 58-40833)]. And in this device
A film thickness of 100 Å was obtained by nitriding at 950°C for 2 hours. However, even with such a device,
Obtaining a nitride film thickness of 100 Å or more at a temperature of 900° C. or less requires a nitriding time of 5 hours or more, which is not practical in terms of mass production. Furthermore, in today's world where LSI manufacturing processes are required to be performed at lower temperatures, it is desired to develop an apparatus and method that can generate nitride films at even lower temperatures.

On the other hand, RPHChang et al. have recently reported on the study of Si nitridation in plasma, which is different from the method of Ito et al. mentioned above (RPHChang.et al.
al; Appl, Phys, Leeft, 36, 999 (1980)). They nitrided Si by placing a sample on one side of a parallel plate electrode, concentrating plasma using a magnetic field, and applying a DC voltage to the sample. At a low temperature of 600℃, a film thickness of only 50 Å can be obtained with N ₂ alone, but by adding a small amount of nitrogen tetrafluoride (1-2%) to N ₂ , a film thickness of about 1000 Å can be obtained with nitriding for several hours. reported that it was obtained. According to AES analysis, a large amount of oxygen atoms are mixed into the film, indicating that it is an oxynitride film, and that there are numerous holes of approximately 1000 Å in diameter due to the influence of fluorine ions or radicals. In this way, a gas containing fluorine atoms is added to _N2 to form a plasma, and Si is formed in the plasma.
An increase in the nitriding rate was observed by nitriding. However, when halogen atoms such as fluorine are present in the plasma, the halogen ions spatter the sample, and some of them are etched by being implanted, and the manner in which the etching occurs depends on the effect of the implant. Not uniform. Furthermore, it goes without saying that the element is damaged not only by etching but also by the influence of charged particles. The nitriding rate multiplication effect of fluorine is RP
Although H. Chang et al. did not make it clear, the result was that Si−
It plays the role of effectively lowering the formation energy of N.

(Objective of the Invention) An object of the present invention is to provide a nitride film production method capable of producing a high-quality nitride film at a high growth rate by direct nitridation without damaging a sample.

(Summary of the invention) The present invention directly nitrides the silicon substrate surface to form a nitride film by heating the silicon substrate at high temperature in a mixed atmosphere of at least nitrogen (N ₂ ) gas and nitrogen trifluoride (NF ₃ ) gas. It is something to do.

That is, in the present invention, the formation of Si--N is enhanced by fluorine (F) atoms generated by thermal decomposition of nitrogen trifluoride gas.

(Effects of the Invention) According to the present invention, it is possible to produce a high-quality nitride film at a high growth rate without damaging a sample such as a nitride film.

(Embodiment of the Invention) FIG. 2 is a schematic diagram showing a nitride film production apparatus used in an embodiment of the present invention. In the figure, reference numeral 11 denotes a nitriding gas inlet, which is continuous with a quartz nitriding chamber 12 heated by a resistance heating furnace 16 whose temperature can be controlled. The reactant gas is exhausted from the sample inlet/outlet 13. In such a reactor system, for example, nitrogen (N ₂ ) is supplied from the gas inlet 11.
Nitrogen trifluoride _NF3 gas diluted to approximately 0.1% with gas
Argon (Ar) gas is introduced into the reactor at 200c.c./min using 4/min as a carrier gas. At this time, the sample heated by the heater was controlled at 1000±1°C. As a result of nitriding the silicon substrate for 60 minutes under these nitriding conditions, a silicon direct nitride film of 400 Å was formed.

Figure 3 shows the silicon nitride film when the nitrogen trifluoride (NF ₃ ) concentration was varied from 0.1 ppm to 10,000 ppm in the nitriding apparatus according to Example 1, and the sample concentration was kept at 1,000°C and the nitriding time was constant at 60 minutes. As shown in the change in thickness, an effective silicon nitride film was obtained at an NF ₃ /N ₂ concentration of 10 ^-7 (0.1 ppm) to 10 ^-2 (1.0%), and 5×16 ^-4
It can be seen that the maximum value is reached at (500ppm). In the obtained nitride film, Si--N bonds were also confirmed by Auger analysis. It was also confirmed that the film thickness of the silicon nitride film decreases on the high concentration side of NF ₃ because etching of Si by F from NF ₃ begins.

Next, in the nitriding system used in Example 1,
NF ₃ /N ₂ concentration 0.1% (200c.c.), substrate temperature 600℃ with argon (Ar) 4/min as carrier gas
From 1300℃ (a) 600℃, (b) 800℃, (c) 1000℃, (d)
Figure 4 shows the thickness of the silicon nitride film when the nitriding time was varied between 1100°C and (e) 1300°C. As shown in the figure, a silicon nitride film was formed which tended to increase as the substrate temperature increased, and it was confirmed by ellipsometry and Augier analysis that the formed film was a silicon nitride film.

(Other Embodiments of the Invention) The present invention can be carried out under reduced pressure, and examples thereof will be described in detail with reference to the drawings.

FIG. 5 is a schematic configuration diagram showing a nitride film production apparatus used in an embodiment of the present invention. 21 in the figure is a microwave power supply, which supplies 245 GHz microwave power to the isolator 22 and the directional integrator 2.
The signal is supplied to a waveguide 25 equipped with a sleeve through a three-post tuner 24 and the like. A discharge tube 26 made of quartz passes through the waveguide 25 . discharge tube 2
A quartz reaction tube 28 is connected to the tip of 6 via a transport tube 27 also made of quartz. The reaction tube 28 is exhausted from an exhaust port 29 by a rotary pump (not shown) through a liquid nitrogen trap 30 for preventing backflow of pump oil. A gas inlet 11 is provided on one side of the discharge tube 26, and a mixed gas of, for example, nitrogen trifluoride ( _NF3 ) diluted with nitrogen ( _N2 ) with a concentration of 0.1 to 10,000 ppm is introduced from the gas inlet 11 to about 0.1 to 10 torr. When the microwave power introduced into the waveguide 25 is matched and supplied by the three-pillar tuner 24 and the shot plunger tuner 32 at both ends of the waveguide 25, a glow discharge is generated in the discharge tube 26. 33 is a water cooling jacket for cooling the sleeve of the waveguide 25. When activated nitrogen is generated in the discharge tube 26 by glow discharge of N ₂ in this way, it is introduced into the reaction tube 28 via the transport tube 27 . A heat source 34 such as a halogen lamp (or heater) whose temperature can be controlled is disposed outside the reaction tube 28.
A sample 36 supported on a support stand 35 made of quartz is placed inside. 27 is a lid of the reaction tube 28, and 33 is a vacuum gauge.

In this embodiment under reduced pressure, the discharge tube 26, the transport tube 27, and the reaction tube 28 collectively constitute one vacuum vessel, but the discharge tube 26 dissociates the introduced gas by discharge. A portion of the reaction tube 28 located apart from the discharge chamber serves as a reaction chamber in which the sample is nitrided by activated nitrogen and F atoms generated and transported in the discharge chamber.

Figure 6 shows that using this device, a silicon substrate was used as a sample 36, and NF ₃ was diluted with N ₂ at 0.05% (500 ppm).
The mixed gas amount is fixed at 500c.c./min, and the pressure is
The figure shows the nitride film thickness when the substrate temperature is varied while the microwave power is fixed at 1.0 torr and 100 W. The nitriding time was 60 minutes. As is clear from FIG. 6, it can be seen that the growth rate increases as the substrate temperature increases. At the same time, the concentration of NF ₃ was increased from (a) 0.1 ppm.
(b) 1ppm, (c) 10ppm, (d) 100ppm, (e) 1000ppm, (f)
The figure shows the growth rate when the NF _{3 concentration changes to 10,000 ppm.As is clear from the figure, the growth rate increases as the NF 3} concentration increases and reaches its maximum at 1,000 ppm.This is due to the same reason as in Example 1. It turns out that there is something.

Figure 7 shows the Si ₃ N ₄ film produced in the above example.
Create MIS diode using 100Å (within 1mm area)
FIG. 3 is a diagram showing the breakdown voltage distribution.

In FIG. 7, A is a nitride film formed with an NF ₃ concentration of 1 ppm, and B is a nitride film formed with a NF 3 concentration of 100 ppm. As is clear from FIG. 7, even when NF ₃ was changed, the withstand voltage characteristics did not change and excellent results were obtained. Also, when determining the surface state density using the C-V characteristic, it is 2 for any NF ₃ concentration.
A good result of ~3×10 ⁻² /cm ² eV was obtained.
When the composition of the film was analyzed by XPS, F atoms were observed at an atomic concentration of 1% or less.

As a result, it is thought that the growth rate of Si nitride increased due to the incorporation of a small amount of F atoms into the film. Furthermore, when the surface was observed using SEM, it was confirmed that the surface had no irregularities.

In this way, nitrogen (N ₂ ) gas mixed with nitrogen trifluoride (NF ₃ ) is dissociated by discharge in the discharge chamber to generate active nitrogen and F atoms, which are then placed at a location away from the discharge chamber. transported to a reaction chamber provided,
It was found that when the sample surface is directly nitrided by reacting with a heated sample in a reaction chamber, the growth rate increases significantly depending on the NF ₃ concentration, and a film of good quality can be obtained.

It should be noted that the present invention is not limited to the embodiments described above, and can be implemented with various changes without departing from the gist of the invention. Alternatively, F atoms may be generated by thermal decomposition of NF ₃ as described in Example 1. Furthermore, N ₂ and NF ₃ are mainly used as reaction gases, but argon (Ar) and helium (He) are used as means of transporting these gases.
Gas or the like may also be used. In addition, the mixing ratio of nitrogen (N ₂ ) gas and nitrogen trifluoride (NF ₃ ) gas may be determined as appropriate depending on the specifications such as the carrier gas flow rate.
A range of 0.1 ppm to 10,000 ppm is more preferable.

Although the above examples have been described under normal pressure or lower, similar results were obtained under high pressure.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a conventional nitride film generation apparatus by direct nitriding, FIG. 2 is a schematic configuration diagram showing a nitride film generation apparatus used in an embodiment of the present invention, and FIG.
Figure 4 and Figure 4 are for explaining the effects of the above embodiment, respectively, and Figure 3 shows the NF ₃ /N ₂ concentration and
A characteristic diagram showing the relationship between SiN ₄ film, Figure 4 is a characteristic diagram showing the relationship between Si ₃ N ₄ film thickness and reaction temperature, and Figure 5 explains another embodiment of the present invention (under reduced pressure). 6 and 7 are for explaining the operation of the embodiment shown in FIG. 5, and FIG. 6 is a characteristic diagram showing changes in silicon nitride film thickness, substrate temperature, and NF ₃ concentration. FIG. 7 is a characteristic diagram showing the breakdown voltage distribution of the Si ₃ N ₄ film. In the figure, 1...quartz reaction vessel, 2...lid, 3
...susceptor, 4...Si wafer, 5...coil, 6...
RF power supply, 7... Gas introduction part, 8... Plasma, 11
...Gas inlet, 12...Reaction tube, 13...Lid, 14
...Susceptor, 15...Si wafer, 16...Heater, 21...Microwave power source, 22...Irerator, 23...Directionality integrator, 24...3-pillar tuner, 25...Waveguide, 26...Quartz discharge tube, 27 …
Quartz transport tube, 28... Quartz reaction tube, 29... Exhaust port, 30... Liquid nitrogen trap, 31... Gas inlet, 32... Sheet plunger tuner, 33...
Water cooling jacket, 34...Halogen lamp, 35
...susceptor, 36...Si wafer, 37...lid, 3
8...Vacuum gauge.

Claims (1)

[Claims] 1. A method of directly nitriding a silicon substrate to form a silicon nitride film, in which at least nitrogen (N ₂ ) gas and nitrogen trifluoride (NF ₃ ) are heated in a resistance heating furnace.
The silicon substrate is placed in a mixed gas atmosphere with
A method for forming a nitride film, characterized by forming a silicon nitride film through heat treatment at 600 to 1300°C. 2 Nitrogen trifluoride (NF ₃ ) concentration from 0.1 ppm
The method for forming a nitride film according to claim 1, wherein the amount of the nitride film is 10,000 ppm. 3 In a method of directly nitriding a silicon substrate to form a silicon nitride film, activated nitrogen is transported by microwave discharging a mixed gas of at least nitrogen (N ₂ ) gas and nitrogen trifluoride (NF ₃ ) gas. A method for forming a nitride film, characterized in that the silicon substrate is introduced into a reaction chamber through a tube, and the silicon substrate is heat-treated at 600 to 1300° C. in the reaction chamber to form a silicon nitride film. 4 Nitrogen trifluoride (NF ₃ ) concentration from 0.1 ppm
The method for forming a nitride film according to claim 3, characterized in that the concentration is 10,000 ppm.