JP2001176870A - Method for forming nitride film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a nitride film at a low temperature. SOLUTION: A nitride gas is dissociated by means of electron beam pumped plasma, a voltage (a) is applied across electrodes 16, 18 with a power source 11 to obtain a beam by accelerating electrons irradiated to a nitride gas for generating a plasma. A substrate 22 is disposed in parallel to an electron beam and heated by a heater 20. Degree of dissociation higher than 20% can be expected by the electron beam, resulting in the formation of a nitride film at a low temperature below 400 deg.C. A silicon can be oxidized by using the substrate 22, and a silicon nitride film can be obtained directly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a nitride film, and more particularly to a method for dissociating nitrogen with a high degree of dissociation.

[0002]

2. Description of the Related Art Conventionally, nitrides such as silicon nitride films have attracted attention in the field of semiconductor devices and device processing. In particular, in a FET, it has been proposed to use a silicon nitride film having a relative dielectric constant about twice that of an oxide film as a gate insulating film in order to suppress a tunnel current due to an insufficient thickness of the gate oxide film.

In order to form a nitride film, for example, NH ₃ gas or N ₂ gas is introduced, and a nitride film is formed on a substrate by a CVD method such as an LPCVD method or a plasma CVD method.

Japanese Patent Application Laid-Open No. H11-8384 describes that a silicon nitride film is formed on a silicon substrate by LP (low pressure) CVD using SiH ₂ Cl ₂ / NH ₃ / N ₂ as a source gas. ing.

[0005]

However, in this prior art, the substrate temperature is heated to 760 ° C. to form the nitride film, and the device characteristics may be degraded by heating, and the substrate material is limited. Problem. That is,
For example, in the case of a TFT liquid crystal, a gate insulating film needs to be formed on a glass substrate.
The temperature is as low as about 400 ° C., so that there is a problem that the heating cannot be performed to 400 ° C. or more.

[0006] In general, performs the dissociation and ionization of the gas by RF discharge or microwave plasma CVD method, dissociation energy of N ₂ is higher than that of O _2, in the conventional method N ₂
The number of high-energy electrons that can contribute to the dissociation of
N ₂ cannot be sufficiently dissociated (dissociation degree is 2% or less). For this reason, at a low substrate temperature, a high film formation rate cannot be obtained and a sufficient film thickness cannot be obtained, and high-temperature heating of the substrate is required to obtain a practical film formation rate.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to improve the degree of dissociation of nitrogen more than before, thereby forming a nitride film on a substrate at a low temperature. It is to provide a method that can be performed.

[0008]

In order to achieve the above object, a method of the present invention comprises disposing a N-containing gas by irradiating the N-containing gas with an electron beam to form a nitride film on a substrate. It is characterized by the following. As the N-containing gas, for example, N ₂ gas or a mixed gas of N ₂ and another gas can be used.

As described above, in the present invention, the N-containing gas is turned into plasma by irradiating an electron beam, instead of turning the N-containing gas into plasma by supplying energy by RF, high frequency, microwave, or the like as in the prior art. . By using an electron beam excited plasma apparatus, the electron beam energy (80 eV to 10 e) with respect to the maximum value of the ionization cross section of the N-containing gas is obtained.
The supply energy can be set to 0 eV), and the N-containing gas can be efficiently turned into plasma to improve the degree of dissociation. When the degree of dissociation is as low as 2% or less, it is necessary to promote the reaction between Si and N by heating the substrate. However, by sufficiently forming chemically active dissociated nitrogen (2% or more), it is possible to achieve the conventional method. The substrate heating is not required, and the nitride film can be formed at a low temperature (a temperature lower than 400 degrees).

Further, the present invention is characterized in that a mixed gas of a Si-containing gas and a N-containing gas is irradiated with an electron beam to dissociate the mixed gas to form a silicon nitride film SiN on the substrate. Also in this case, sufficient dissociated nitrogen can be efficiently formed, and SiN can be formed efficiently by reacting with nitrogen.

After the nitride film is formed on the substrate,
By irradiating the mixed gas of the i-containing gas and the N-containing gas with an electron beam to dissociate the mixed gas and form SiN on the nitride film, the crystal interface of the substrate is reduced as compared with the case where SiN is formed directly on the substrate. The condition can be kept excellent. This is because a nitride film exists at the interface with SiN, and this nitride film functions as a buffer layer.

The electron beam is preferably supplied using an electron beam excited plasma apparatus. Further, it is preferable that the substrate is arranged in parallel with the flow of the electron beam. This is because, when the substrate is arranged perpendicular to the electron beam, the potential of the substrate is kept more negative than the plasma potential by direct irradiation of the electron beam, and the substrate is damaged by ion bombardment from the plasma.

Preferably, the temperature at which the nitride film is formed on the substrate is lower than 400 degrees. By making the substrate temperature lower than 400 ° C., glass can be used as a material of the substrate, and it can be used for a wide range of uses, for example, for manufacturing a TFT.

Preferably, the substrate is a Si substrate, and the nitride film is formed by nitriding the Si substrate. This eliminates the need to separately introduce a gas containing Si, and simplifies the SiN formation process. In addition, since Si is directly nitrided, the interface state can be improved and the electrical characteristics can be improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a nitride film forming apparatus according to this embodiment. The basic configuration is the same as that of a known electron beam excited plasma apparatus. This device is divided into a discharge region, an acceleration region, and a plasma generation region.

In the discharge region, the gas flow controller 24
Ar gas is introduced from a discharge power source 10 and a discharge voltage Vd
Is applied to generate plasma with electrons from the cathode 12. Electrons extracted from the plasma are supplied to an acceleration region. The electron current (electron beam current) increases in proportion to the discharge current Id.

In the acceleration region, a voltage Va is applied between the electrodes 16 and 18 by the acceleration power supply 11 to accelerate electrons generated in the discharge region. Further, a coil 14 is wound in the acceleration region, thereby generating a magnetic field indicated by B0 in the drawing to control the spread of the electron current due to radial diffusion, thereby forming an electron beam. The electron beam accelerated in the acceleration region is supplied to a plasma generation region.

N ₂ gas is introduced into the plasma generation region via the gas flow controller 24, and the N ₂ gas is dissociated by the energy of the electron beam to be in a plasma state.
A heater 20 and a silicon substrate 22 are arranged in a direction parallel to the electron beam flow in the reaction chamber in the plasma generation region. The silicon substrate 22 is heated by the heater 20 and exposed to plasma. By arranging the silicon substrate 22 in parallel with the electron beam flow, the electron beam is directly transmitted to the silicon substrate 2.
2 can be prevented from being damaged.

Further, the apparatus according to the present embodiment can independently control the electron beam current Ib and the electron beam energy, that is, the acceleration voltage Va, so that the electron beam having various energy levels and current values can be controlled in the reaction chamber. N ₂
Can be irradiated.

FIG. 2 shows the relationship between the plasma generation by the conventional RF discharge and the distribution of electron energy and the ionization cross section of nitrogen in the electron beam excited plasma of the present embodiment. In the figure, the dashed line is the ionization cross section of nitrogen, and in the conventional RF discharge, only an electron energy lower than the electron energy at which the ionization cross section reaches a peak is obtained (the number of high energy electrons that can contribute to ionization is small). Although the plasma generation efficiency is low, the ionization cross section of nitrogen is maximized by using an electron beam as in this embodiment.
electron energy near the energy of eV can be obtained,
Thereby, the N ₂ gas can be efficiently turned into plasma. Also, the dissociation cross section of nitrogen by electron collision is 50 ~
It is the largest in the energy range of 130 eV. By setting the electron beam at about 100 eV, the dissociation degree of nitrogen gas, that is, the ratio of dissociation of nitrogen molecules into single nitrogen atoms is also improved.

FIG. 3 shows the relationship between the acceleration voltage Va and the dissociation degree D of N ₂ obtained by conducting an experiment using a mixed gas of N ₂ and Ar. The degree of dissociation D was determined by measuring the mass spectrum of nitrogen molecule ion N ₂ ⁺ when plasma was turned on and off using a quadrupole mass spectrometer, and measured its intensity (I
on, Ioff) by the following equation.

[0023]

D = 1− (Ion / Aon) (Aoff / Ioff) where Aon and Aoff are the mass spectral intensities of the argon ions Ar ⁺ when the plasma is on and off, and the neutral particle temperature accompanying the plasma on In order to consider the change, Ar gas is introduced at a mixing ratio (partial pressure ratio) (N ₂ : Ar = 5: 1) under the condition that the total gas pressure is constant, and normalized by its mass spectrum intensity. In the flow rate, Ar
₂ ccm, N ₂ 10 ccm, pressure 0.9 mTo
rr and the electron beam current Ib are 3.4 amps.

As can be seen from the figure, the acceleration voltage Va is 80
As the acceleration voltage Va increases in the range of V ≦ Va ≦ 140 V, the dissociation degree D of nitrogen increases exponentially, and the acceleration voltage Va =
At 140 V, the degree of dissociation D = about 16% is obtained.

FIG. 4 shows the relationship between the electron beam current Ib and the dissociation degree D of nitrogen gas. Note that Ar
And the flow rate of N ₂ are the same as in FIG.
30V. The dissociation degree D is 1.4 amps ≦ Ib ≦
The electron beam current Ib increases proportionally as the electron beam current Ib increases in the range of 3.1 amps, and the degree of dissociation D = about 12% is obtained when the electron beam current Ib = 3.1 amps.

As described above, in the present embodiment, the dissociation degree exceeding 2% can be obtained by converting N ₂ into plasma using the electron beam. Therefore, in order to form a nitride film on the Si substrate 22,
2 is not heated at a high temperature as in the prior art,
The nitride film can be formed at a temperature lower than 0 degrees.

FIG. 5 shows that N is added to the reaction chamber in the plasma generation region.
₂ was introduced at a flow rate of 25 sccm, and the pressure in the reaction chamber was increased to 1
3 mTorr, 350 ° C. lower than 400 ° C., acceleration voltage Va of 100 V, electron beam current I
FT-IR measurement results of the Si substrate 22 when b is set to 3 amps are shown. In the figure, the vertical axis represents transmittance, and absorption is present at 1070 (cm ⁻¹ ). SiN F formed by conventional LPCVD
Since T-IR has absorption near 1065 (cm ^-1 ), this absorption is due to SiN. In the present embodiment, not only a nitride film can be obtained at a low temperature by obtaining a sufficient degree of dissociation, but also the Si substrate 22 can be nitrided by using the Si substrate 22 to directly form SiN.

[0028] Note that although an SiN in direct nitrided at low temperature of the Si substrate 22 by using N ₂ in this embodiment is not limited to N _2, to form the SiN using N-containing gas be able to. N-containing gases include N ₂ and N ₂
+ H ₂ mixed gas, N ₂ + H ₂ + inert gas (such as Ar gas) mixed gas, and NH ₃ . By diluting with H ₂ or an inert gas, operating conditions such as a nitride film deposition rate can be easily controlled.

In this embodiment, the Si substrate 22
Forming SiN directly by using (direct nitridation of Si substrate)
After that, it is also possible to deposit and form further SiN on this SiN. That is, after nitriding the Si substrate 22, a Si-containing gas is further introduced into the atmosphere and reacted with nitrogen having a high degree of dissociation to deposit SiN at a low temperature. Since SiN obtained by directly nitriding the Si substrate 22 can be used as a base layer, SiN having an excellent interface state can be obtained.

Specifically, the flow ratio of the Si-containing gas to the N-containing gas is set in the range of 1:20 to 5: 1, the total flow is in the range of 1 sccm to 500 sccm, and the total pressure is 0.2 mTorr. An electron beam is irradiated in the range of 100 mTorr to further deposit a SiN film on the SiN. The SiN deposition rate was 0.01 nm.
/ Sec to 1 nm / sec.

As an example, after the Si substrate 22 is directly nitrided under the conditions described above, the flow rate of N ₂ is changed from 25 sccm to 5 s.
The temperature is changed to ccm, and a silane gas is introduced as a Si-containing gas at a flow rate of 2 sccm to form a mixed gas. The pressure of the reaction chamber is maintained at 3 mTorr, and an electron beam is again incident on the reaction chamber to generate plasma for 20 minutes. This allows
A SiN film is deposited on the Si substrate 22. And Si
After depositing an N film, aluminum is deposited using a deposition apparatus, and a front electrode and a back electrode are formed.
(Metal Insulator Semiconductor
(actor) diode, and an element for evaluating the characteristics of the gate insulating film of the MIS transistor. The thus formed device was annealed, and the refractive index, the nitride film thickness, the interface charge density, and the relative dielectric constant were measured with an ellipsometer.
8. A relative dielectric constant of 7.2 and an interface charge density of 6.0 to 20 × 10 ¹⁰ cm ^{−2 at} the Si—SiN interface were obtained. These characteristic values indicate that the nitride film forming method according to the present embodiment has a wiring width of 0.1 mm.
This shows that the method can be applied to the formation of a 1-micron generation gate insulating film.

After nitriding the Si substrate 22 directly,
Instead of introducing the i-containing gas and the N-containing gas to deposit SiN, immediately after the Si substrate 22 is placed in the reaction chamber, the Si-containing gas (silane gas or the like) and the N-containing gas (N ₂ or N ₂ and H _{2 (} A mixed gas of ₂ or the like) and irradiating an electron beam to directly deposit SiN on the Si substrate 22.

In this embodiment, the Si substrate 22 is used, but as described above, in this embodiment, a sufficiently high dissociation degree (2
%), The N-containing gas can be dissociated at a low temperature (4%).
(Less than 00 degrees), and the selection of the substrate material is expanded, and a glass substrate can be used.

[0034]

As described above, according to the present invention,
The degree of dissociation of the N-containing gas can be made higher than conventional (2% or more), whereby a nitride film can be formed at a low temperature (400 degrees or less).

By obtaining a sufficient degree of dissociation, when Si is used for the substrate, the Si substrate is directly nitrided at a low temperature,
An SiN film can be formed.

Furthermore, by directly nitriding the Si substrate at a low temperature and then depositing a SiN film, a SiN film having excellent interface charge density and dielectric constant can be obtained, and is also used, for example, as a gate insulating film of a MIS transistor. be able to.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram of an embodiment.

FIG. 2 is a graph showing a relationship between an electron energy distribution and an ionization cross section of nitrogen according to the embodiment.

FIG. 3 is a graph illustrating a relationship between an acceleration voltage and a dissociation degree according to the embodiment.

FIG. 4 is a graph showing a relationship between an electron beam current and a dissociation degree according to the embodiment.

FIG. 5 is a graph showing an FT-IR result of the silicon substrate of the embodiment.

[Description of Signs] 11 Acceleration power supply, 14 coils, 16, 18 electrodes, 2
0 heater, 22 silicon substrate.

Continuation of the front page (72) Inventor Shingo Masuko 2-12-1 Kugata, Tempaku-ku, Nagoya City, Aichi Prefecture Inside the Toyota Gakuen (72) Inventor Kazunari Taniguchi 2-12-1, Kugata, Tempaku-ku, Nagoya City, Aichi Prefecture Inside the Toyota Gakuen School (72) Inventor Masatoshi Udaka 2-12-12 Hisakata, Tempaku-ku, Nagoya City, Aichi Prefecture Inside the Toyota Gakuen School (72) Inventor Toshio Sada 2--12 Kukata, Tenpaku-ku, Nagoya City, Aichi Prefecture 1 F-term in the school corporation Toyota Gakuen (reference) 4M104 AA01 CC05 EE03 EE17 GG09 GG10 GG14 HH20 5F040 DA19 ED04 5F058 BA20 BB04 BB07 BC08 BF30 BF37 BF39 BF60 BF72 BF74 BF75 BJ10

Claims (8)

[Claims] 1. A method for forming a nitride film, comprising irradiating an N-containing gas with an electron beam to dissociate the N-containing gas and form a nitride film on a substrate. 2. The method according to claim 1, wherein the N-containing gas contains N ₂ . 3. A method for forming a nitride film, comprising: irradiating a mixed gas of a Si-containing gas and a N-containing gas with an electron beam to dissociate the mixed gas to form SiN on a substrate. 4. The method according to claim 1, wherein, after forming the nitride film on the substrate, the mixed gas is irradiated with an electron beam to a mixed gas of a Si-containing gas and a N-containing gas. A method for forming a nitride film, comprising: dissociating a gas to form SiN on the nitride film. 5. The method according to claim 1, wherein the electron beam is supplied using an electron beam excited plasma apparatus. 6. The method according to claim 1, wherein the substrate is disposed in parallel with the flow of the electron beam. 7. The method according to claim 1, wherein a temperature at which the nitride film is formed on the substrate is lower than 400 degrees. 8. The method according to claim 1, wherein the substrate is a Si substrate, and the nitride film is formed by nitriding the Si substrate. Method.