JPS59128206A - Apparatus for forming nitride film - Google Patents

Abstract

PURPOSE:To obtain a good nitride film in a titled apparatus for directly nitriding Si or the like by using a double tube for the reaction, generating plasma only in the gap between an inner tube and an outer tube, reacting the formed nitride seed with a sample in the inner tube, and avoiding the damage of the sample caused by the bombardment of ions. CONSTITUTION:A gaseous NH3 for example, removed from an etching gas is introduced through a gas inlet 22 into a reaction tube 21 which is evacuated through an exhaust port 26. When a high-frequency electric power is supplied to a capacitive coupling electrode 25, a glow discharge is caused only in the gap between an outer tube 29 and an inner tube 30, and a discharge space 28 is formed. An activated nitride seed hereby formed by the glow discharge of NH3 is sent to the surface of a sample 36 on a boat 37 situated in the inner tube 30 through a hole 31 on the side of the inner tube 30. Then the sample 36 is heated to a high temp. by a heating source 32, and an Si3N4 film is formed by nitridation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nitride film forming apparatus that generates a nitride film by directly nitriding silicon or the like.

[Technical background of the invention and highlights]

LSI devices are becoming more and more highly integrated year by year. For example, as a typical example of MO8 memory, i) RAM
(Dynamic random access memory) f:
If you look, you'll see bits at 16, bits at 64, and then bits at 25.
DR
AM is also about to be announced in a few years. In this way, the thickness of the chips is approximately the same and the areal density increases, so
1) Although the area of the memory cell portion of a RAM is becoming smaller and smaller, a proportional decrease in its storage capacity must be avoided due to the poor signal-to-noise ratio between on and off. As a result, 810 of the MOS capacitor forming the storage capacitor section
Two films are required to be made thinner.

For example, taking DRAM as an example, the film thickness of 8i0□ is 64
In Bit, there are 256 people compared to the current 400 people.
50 inputs, and 70k is required for 1 Mbit.

However, as the S102 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 8i0□ film deteriorate rapidly. Regarding this problem, 83
It is conceivable to use a silicon nitride film (in this case, an Sr 3 N 4 film) having a dielectric constant of about twice that of Sr 3 N 4 instead of 02. On the other hand, Si3N4 has conventionally been deposited by thermally decomposing monosilane (S x N4) and ammonia (NE) at a temperature of about 850°C and then depositing it by vapor phase deposition (CVD). Even if a thin 513N4# is completely formed on the Si, (1) it is difficult to control the film thickness, (2) there is originally a natural oxide film of about 30% on the Si, an MNOS structure is formed, and the C-V characteristics are poor. hysteresis occurs. (3)
813N4 S with an interface surface state density of 10/cr
! ev or more, and there was an essential drawback that a good MO8 structure could not be formed. Therefore, recently, we have developed a method of directly reacting N2 and 8i at high temperatures of 1200°C or higher to form Sulfur on Si.
Attempts have been made to form i3N4 films. However, 5
In the case of I02 film, a film of about 100% is formed in a short time using oxygen or steam at 900 to 1100C, whereas in the case of Si3N4 film, even if Si nitrided for 1 hour with N2 gas at 1100C, 50% Even at a high temperature of 1200°C, the thickness is less than 100°C, and nitriding hardly progresses after that. Moreover, the film thickness is not uniform and is likely to be formed in an island shape. (For example, j@Electr
chemical Soc:5OLID8TATE
5CIENC similar WDTECHNOL(X)Y (Mar
ch 1978) paper “Jerry Th1nSili
con N1tride Films by dir
ect ThermelReactive With
Nitrogen').

In order to solve the problem of mainly low growth rate of direct nitriding of silicon, a method of direct nitriding of silicon using glow discharge was reported at the 28th Spring Conference of the Japan Society of Applied Physics in 1932 (Takashi Ito: 29P-c-5). An outline of this method will be explained using FIG. 1.

One of the quartz tubes 1 is two, and the other is connected to the exhaust system. Si wafers 4 supported by a susceptor 3 coated with 5iCQ 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.
F power supply 6 is connected.

7 is a gas introduction part, from which Ni(, N2+H2,
A gas such as N2 is supplied. i-i, NH3 gas is 0,
When the pressure inside the quartz tube 1 is set to about 1 to 10 Torr and a high frequency of 4QQI (Hz) is applied from the RF power source 6, a glow discharge 8 is generated in the quartz tube 1, and the Si wafer 4 is heated. As a result, a reaction occurs between the nitrogen-containing gas plasma and the madder-temperature Si wafer 4, and direct nitridation of Sr is performed.
Using glow discharge in this way, a high-frequency IOJ package-Si wafer was produced at 1 t/min. It has been confirmed that nitriding is promoted more quickly at comparatively low temperatures. However, since this method uses a discharge of 400 KI (z), the ionization energy in the plasma is high, so the ion bombardment on the sample is large, and there is a concern that the lateral side of the semiconductor element may be irradiated. Although an ingenious means of simultaneously heating the Si and counting the glow of the introduced gas is used, the nitriding parameters depend only on the introduced ItFE force, which limits the nitriding rate. The gas plasma such as N1(a) is
There is a risk that L02 will be reduced and oxidized to produce oxygen, which will be mixed into the film, and this is also shown in the data reported above. On the other hand, since this method places the sample within the plasma, it is not clear whether the nitridation mechanism is carried out by neutral radical species within the plasma or whether it is assisted by the high-energy bombardment of the ions. On the other hand, R, P, 14. Chang et al. have recently investigated and reported on the emptying of 8i in plasma, which is different from the method of Ito et al. (R, P, N Chang, e.
tal: Appli, Phys, Leaf, 3
6.999 (1980)).

They nitrided Si by placing a sample on one end 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'C, a film thickness of only 50 mm can be obtained with N2 alone, but by adding a small amount of carbon tetrafluoride (1 to 2 T) to N2, a film thickness of about 100 A can be obtained in a few hours of nitriding. It is reported that the film thickness was obtained.

According to AE8 analysis, a large amount of oxygen atoms are mixed into the film, indicating that it is an oxynidride film, and that there are numerous holes of about 1000λ due to the influence of fluorine ions or radicals. In this way, by adding a gas containing fluorine atoms to N2 to form a plasma, and nitriding Si in the plasma, an increase in the nitriding rate was found. However, when halogen atoms such as fluorine are present in the plasma, the halogen ions sputter the sample, and some of them are imbued, resulting in etching. It is not uniform due to the effect of Furthermore, it goes without saying that damage fK is caused to the element not only by etching but also by the influence of charged particles.

Therefore, the present inventors studied the apparatus shown in FIG. 2 in order to solve the problems that occur when nitriding Si or Si (-12) in the plasma.

That is, in FIG. 2, 21 is a quartz reaction tube, one of which is provided with a gas inlet 22.

23 is a high frequency power supply, which generates 13.56MNz
The high frequency power is supplied to the capacitively coupled electrode 25 via the matching box 24. This electrode 25 is connected to the reaction tube 21
The device is installed near the gas inlet 22 on the outside of the gas inlet 22 . on the other hand,
A temperature-controllable heating source 32, such as a halogen lamp or a heater, is installed around the reaction tube 21 on the exhaust side of the electrode 25. Heating region 35 of heating source 32 in reaction tube 21
A boat 37 made of quartz and a sample 3 placed on it
6 is located. The reaction tube 21 is exhausted from the exhaust port 26 via a liquid nitrogen trap 27 for preventing pump oil backflow by a rotary pump (not shown). Here, gas inlet 2
From 2, for example, ammonia gas (N) (3) is 05-5
- TOrr is introduced, and when the high frequency power is matched and supplied by the matching box 24, a glow discharge occurs in the region sandwiched between the electrodes 25 in the reaction tube 21, and the discharge section 28
is formed. On the other hand, the sample 36 is heated by a heating source 32 provided outside thereof, and reacts with the active nitride film generated by the discharge to form a nitride film. In this device, the region 28 where glow discharge occurs and the region where reaction of the sample occurs are separated, so that no high frequency electric field is directly applied to the sample. However, even in this device, it was found that the electrical characteristics of the υ element deteriorated due to the influence of glow from the discharge section extending to the sample.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the fact that ≠

[Summary of the invention]

The present invention provides a reaction tube with a double structure in which a mixed gas containing at least ammonia is dissociated by discharge using high-frequency power and reacted with a sample heated to high temperature to form a nitride film, and the outer tube and the inner tube are separated from each other. Plasma is generated only in the gap, and the resulting active nitride film is guided into the inner tube through the hole on the side of the inner tube and reacts with the heated sample placed inside the inner tube to form a nitride film. It is. By configuring the reaction tube in this way, a high-quality nitride film can be obtained without the sample being bombarded with ions in the plasma.

[Embodiments of the invention]

The present invention will be described in detail below with reference to Examples.

FIG. 3 shows 4'i# of a nitride film forming apparatus according to an embodiment of the present invention.
It is a complete drawing. Here, 21 is a quartz reaction tube, one end of which has a gas inlet 22, and the other end a lid 33 that can be opened and closed.
It consists of an outer tube 29 which is sealed and has an exhaust port 26 near the outer tube 29, and an inner tube 30 which has a number of holes 31 on the side surface, is open at both ends, and is arranged concentrically with the outer tube 29. Karasuha Denei 2
3, high frequency power of 13.56 to 1z is supplied to the capacitively coupled electrode 25 via the matching box 24.

This electrode 25, like the temperature controllable heating source 32,
It is located around the sample 36 on a boat 37 located within the inner tube 30. The gas is exhausted from the exhaust port 26 via a liquid nitrogen trap 27 for preventing backflow of bottled oil by a rotary pump (not shown). Here, 34 is a vacuum gauge.

From the gas inlet 22, ammonia gas (NH3) from which etching gas, etc. has been removed is passed through a device made of N, for example, at a rate of 0.5~
When approximately 5 Torr is introduced and high frequency power is supplied to the capacitively coupled electrode 25, glow discharge occurs only in the gap between the outer tube 29 and the inner tube 30, forming a discharge portion 28'e. When an active nitride film is generated by glow discharge of ammonia in the discharge section 28, the nitride film reaches the surface of the sample 36 through the hole 31 on the side surface of the inner tube 30. Here, the sample is heated to a high temperature by a heating source 32, and a nitriding reaction occurs (Y) Si3N4
A film is formed.

FIG. 4 shows the apparatus of this embodiment using a silicon substrate as a sample 36, a gas flow rate of 100 ammonia (N) (3) of 220.8 cc+M, a pressure of 1.0 Torr, and a high frequency power of 100 W (reflected wave 13- ■) and nitriding time is 2
Nitride film thickness f when changing substrate temperature as time: 4
This is shown in 1. The thickness of the nitride film formed under the same conditions using the apparatus shown in FIG. 2 originally proposed by the present inventors is indicated by 42. As can be seen from this figure, there is no significant change in the nitriding rate due to Kinoe and Akira. On the other hand, in the apparatus of this embodiment, the sample 36 is located in the inner tube 30 of the reaction tube 21,
Since the discharge of the introduced gas forms a discharge part 28 in the gap between the inner tube 30 and the outer tube 29, a high-quality nitride film can be obtained with a high yield without the sample coming into direct contact with the gas plasma. can. In this embodiment, the reaction tube 21 is also short, so that the apparatus can be made compact, but there is a structural restriction in that heating must be carried out from outside the electrode 25 through the electrode 25.

FIG. 5 is a block diagram of a fertilized film forming apparatus according to a second embodiment of the present invention. Reference numeral 21 denotes a reaction tube with a double tube structure.In particular, the inner tube 30 has a large number of holes 31 on the 11th side, and is placed in alignment with the outer tube 29, but is close to the gas inlet 22. The ends are closed, and the gap between the outer tube 29 and the inner tube 30 is closed in front of the exhaust port 26.

The capacitively coupled electrode 25 is installed outside the reaction tube 21 and near the gas inlet 22 . A temperature controllable heating source 32 is installed around the reaction tube 21 on the exhaust side of the electrode 25.

A boat 37 made of quartz and a sample 36 placed thereon are located in the heating region 35 of the heat source 32 within the inner tube 30.

From the gas inlet 22, for example, ammonia gas NH3 from which etching gas, etc. has been removed is passed through the entire purification device.
'orr high frequency power is introduced into the capacitively coupled electrode 2.
5, a glow discharge occurs between the outer tube 29 and the inner tube 30 of the reaction tube 21, and a discharge section 28 is formed. When an active nitride film is generated by glow discharge of ammonia in the discharge section 28, the nitride film forms the holes 31f! on the side surface of the inner tube 30!
: The surface of the sample 36 is reached. Here the sample is heating source 3
2, an 813N4 film is formed on the sample surface by a nitriding reaction.

In this second embodiment, the reaction tube 21 is longer than the first embodiment, but there are fewer structural restrictions because the electrodes and the heating source are separated, and the gas inlet 2 of the inner tube 30 is
Since the second side is closed, gas does not directly enter the inner tube 30, so that discharge can be carried out safely.

Figures 6 and 6 show ammonia (N
f(3) 100% gas flow rate is 220SCC&J, total pressure is 10'J'orr, high frequency power is 100~V (reflected wave 13W), substrate temperature is 1000℃, and many samples are nitrided for 2 hours at the same time. 3 shows the relationship between the position of the sample 36 and the nitride film thickness. As can be seen from this figure, as the I row of the sample 36 moves away from the gas inlet 22, the electrification IIQ thickness becomes thinner rapidly. This is considered to be due to a decrease in the concentration of the active nitride film.

FIG. 7 is a block diagram of a nitriding 1/A forming apparatus according to a third embodiment of the present invention. The basic configuration is the same as the apparatus of the second embodiment, so a detailed explanation will be omitted. The inverse winding conductance of the gas in the vicinity of the gas inlet 22 becomes smaller than that in the vicinity of the exhaust port 26, and multiple samples The density of the nitride film around 36 becomes uniform, and uniform nitride film can be formed all over the area.

FIG. 8 id Sample 3 using the apparatus of the third embodiment of the present invention
A silicon substrate was used as 6, and ammonia (N[(3)
100'% gas flow rate 220SCCM, pressure? 1.
0'l'orr high frequency potential is 100W (reflected wave 13ν
V) The relationship between the position of the sample and the thickness of the nitrided 1j steel when a large number of samples were nitrided at the same time under conditions of two nitriding times is shown using temperature as a parameter. As can be seen from the figure, it was confirmed that the apparatus of the third embodiment could form a uniform nitrided Wk shadow at a sufficiently high nitriding rate.

FIG. 9 (5) shows a sample of ammonia (NH3) 1 using a silicon substrate as a sample 36 using the apparatus shown in the third embodiment.
00% gas flow rate is 220 SCCM, pressure is 1. QT
orr.

High frequency power 100W (reflected wave 13W) Reaction temperature 100
This figure shows the breakdown voltage distribution of a MIS diode with an area of 4wn2 using 100 layers of nitride film formed under conditions of 0°C. Figure 9 CB) shows an area 4 using a nitride film xooA formed under similar conditions using the apparatus 1 shown in Figure 2.
This is the breakdown voltage distribution of the ■S diode of wn2. As can be seen from this figure, by forming the reaction tube 21 into a double-tube structure, high-quality nitrided +IK with high breakdown voltage and few defects can be obtained with a high yield.

Figure N (5) shows sample 3 obtained by the apparatus shown in the third embodiment.
Ammonia (NH3) 100% gas flow was applied at 220 SCCM and pressure was set to 1. OTo r r High frequency power 'e 100W (reflected wave 13W) Reaction temperature 1000
This is the C-■ characteristic of a MIS diode (area: 0.1 mm2) formed by reaction at .degree. C. for 2 hours. Figure N (B
) is the C-■ characteristic of a MIS diode (surface sum, 1 yo') formed using the apparatus shown in FIG. 2 under the same conditions and time. As can be seen from this figure, the diode obtained by the apparatus shown in FIG. 2 has hysteresis H, indicating that there is a defective interface between the base material and the nitride film.

〔Effect of the invention〕

As detailed above, in the apparatus for forming a silicon nitride film, the reaction tube has a double structure as in the present invention, the discharge part is formed only by the gap between the outer tube and the inner tube, and the sample is placed in the inner tube. By doing so, the influence of ion bombardment on the sample to be nitrided can be effectively prevented, and a high quality and uniform nitride film can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional nitride film forming apparatus by direct nitriding. Figure 2 shows the glow discharge area studied by the inventors, and
FIG. 2 is a configuration diagram of a nitride film forming apparatus in which a region where a sample reaction occurs is separated. FIG. 3 is a configuration diagram of the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing the relationship with reaction temperature in the apparatus of the first example. FIG. 5 is a configuration diagram of a second embodiment of the present invention. FIG. 6 shows silicon nitridation +j[
y, a characteristic diagram showing the relationship between thickness and sample position. FIG. 7 is a configuration diagram of a third example of an actual sword of the present invention. Figure 8 (lower side) is a characteristic diagram showing the relationship between the silicon nitride film thickness and the sample equipment in the apparatus of the third embodiment using the reaction temperature as a parameter. Figure 9 is a characteristic diagram showing the breakdown voltage distribution of the silicon nitride film. C- of the membrane
■It is a characteristic diagram showing characteristics. Note that (5) in FIGS. 9 and 0 and N is based on the apparatus of the third embodiment of the present invention! (B) shows the characteristics of the obtained nitride film. This is a characteristic of a nitride film obtained by the apparatus shown in FIG. 21... Reaction tube, 22 - Gas inlet, 25... Capacitively coupled electrode, 26... Exhaust port, 28... Discharge section, 29... Outer tube, 30... Inner tube , 31... Hole on the side surface of the inner tube, 32... Temperature controllable heating source, 36...
Sample, 37...Boat agent and patent attorney Kensuke Norichika (
1 other person) Army 1 Figure 〒2 Figure wafer-Q strategy 7 Figure 1Qg 28 (J 3 attack fl 44
; dJ wafer a position Figure 7 M7 stitch town house i CMv/c next army lO diagram (WCrATE BIAS ri (V) TlO diagram (B
) c7ATE BIAS Vl(V)

Claims (2)

[Claims] (1) High frequency gas containing at least ammonia gas
In an apparatus that forms a silicon nitride film by discharge dissociation using an air force, etc., the reaction tube consists of an outer tube and an @
The inner tube has holes on the B side, and the discharge part is formed only in the gap between the outer tube and the inner tube, and the nitride film reaches into the inner tube through the hole on the side surface of the inner tube. , a nitride film forming apparatus patented for forming a nitride film on a sample placed in the inner tube without being exposed to glow lightning. (2) Nitriding according to claim 1, characterized in that the gas passage conductance near the gas inlet is made smaller than that near the exhaust port by changing the gas passage area of the hole in the inner 9 side. Film forming device.