JPH04110471A - Formation of thin film - Google Patents

Abstract

PURPOSE:To obtain a thin film which is low in interfacial level density and excellent in the electric characteristics by exciting gaseous halogen introduced into a reaction vessel and treating a base body and thereafter introducing a first prescribed gas and exciting it by plasma and then introducing a second gas and sticking a reaction product on the base body and irradiating this base body with light. CONSTITUTION:Base bodies 3 are provided in a reaction chamber 2 and the inside thereof is exhausted at high vacuum. Thereafter gaseous halogen 10a such as F2, diluted by He is introduced and regulated to the prescribed operation pressure. The base bodies 3 are irradiated with light emitted from light sources 6 such as an Xe lamp. The gaseous F2 is excited and pretreatment is performed. The inside of the vessel is reexhausted at high vacuum to remove gaseous F2. Thereafter a first gas 10b such as O2 is not independently deposited even when it is excited. The first gas 10b is introduced into the vessel 2 and regulated to the prescribed operation pressure. Thereafter high-frequency voltage is impressed between the electrode 1 and the vessel 2 to plasmaize and excite oxygen. Then a second gas 10c such as SiH4 is introduced into the vessel 2 and regulated to the prescribed operation pressure. The second gas 10c is allowed to react with the excited oxygen and a produced reaction product is stuck on the base bodies 3. A thin film is formed by irradiating the base bodies 3 stuck with this reaction product with light emitted from the light source 6.

Description

[Detailed description of the invention] [Industrial use! The present invention relates to a method for forming a thin film, and more particularly to a method for forming an insulating film for semiconductor devices, and particularly to a method for forming an insulating film that can be suitably used for field effect type transistors.

[Description of Prior Art] Conventionally, the gate insulating film of a MOSFET using single crystal silicon is generally made by heating single crystal silicon in an oxidizing atmosphere at 90°C.
It is formed by heat treatment at 0~]100°C.

Also, amorphous silicon (hereinafter referred to as a-Si)
, TPT or In with polycrystalline silicon as the semiconductor layer
Insulating films of MIS type FETs such as P GaA and S are generally formed by a sputtering method, a thermal CVD method, a plasma CVD method, or the like.

[Problem to be solved by the invention] However, when forming a semiconductor device three-dimensionally, such as when applying an SOI structure MOSFET to a three-dimensional structure semiconductor device, the semiconductor layer is Formed in multiple layers. For this reason, if thermal energy is used to form the upper layer device, there is a risk that the semiconductor layer of the lower layer device will be damaged by the heat.

Furthermore, even in devices using polycrystalline Sj or single-crystalline Sl on glass, it is difficult to use thermal oxidation as a method for producing a gaming insulating film because the glass substrate is thermally damaged.

Furthermore, when sputtering or plasma CVD is used to form a gate insulating film, the semiconductor layer is damaged by accelerated ions, which increases the interface states between the semiconductor layer and the insulating film, which reduces carrier mobility. This may lead to deterioration of device performance.

[Objective of the present invention 1] An object of the present invention is to significantly improve device performance over conventional L.
The purpose of the present invention is to propose a method for forming a thin film that can achieve the following effects.

Another object of the present invention is to propose a thin film forming method that can reduce the interface states between a semiconductor layer and an insulating film.

A further object of the present invention is to propose a method for forming a thin film that can reduce the interface states between a semiconductor layer and an insulating film by subjecting a substrate to pretreatment.

[Means for Solving the Problems] The present invention was completed as a result of intensive research to solve the problems of the prior art, and the thin film forming method of the present invention uses plasma and light. A film forming method for forming a film includes a step of introducing a halogen gas into a film forming chamber in which a substrate is arranged, a halogen treatment step of exciting the halogen gas and treating the substrate, and a step of exciting the halogen gas after the halogen treatment. a step of introducing into a reaction vessel in which a substrate is arranged a first gas which is not deposited alone even if is introduced into the reaction vessel and reacted with the excited first gas, and the generated reaction product is transferred to the substrate.
The method is characterized by comprising a step of applying light to the substrate to which the reaction product is attached. Alternatively, in a film forming method in which a film is formed using plasma and light, a step of introducing a halogen gas into a film forming chamber in which a substrate is arranged, and a halogen treatment step of exciting the halogen gas and treating the substrate; After the halogen treatment, a step of introducing a first gas that does not deposit on its own even when excited into a reaction container in which a substrate is arranged, and a step of plasma exciting the first gas introduced into the reaction container. a step of exposing the substrate after the halogen treatment to the excited first gas; and a step of introducing a second gas into the reaction vessel and reacting with the excited first gas, resulting in a reaction. The method is characterized by comprising the steps of depositing a product on a substrate and irradiating the substrate to which the reaction product is deposited with light.

[Function] According to the present invention, the interface state density between the substrate surface and the semiconductor is reduced by pre-treating the surface of the substrate on which a film is to be formed and performing halogen treatment, or by performing treatment with a first gas following the halogen treatment. can be significantly reduced. Further, by using a film formation method using light and plasma, processing can be performed at low temperatures, and moreover, by using the same light source and plasma source as used for film formation, pretreatment can be performed more effectively. In particular, the ability to perform the treatment at low temperatures is particularly preferred when performing halogen treatment.

In the present invention, the reason why the interface state density is reduced by the halogen gas or the first gas pretreatment performed subsequent to the halogen gas is thought to be due to the following mechanism.

Sj substrates, which are generally used when manufacturing semiconductor devices, are treated with hydrofluoric acid (H) as an etching solution to remove impurities.
F) After etching using a solution, cleaning with ultrapure water is performed. It is known that the Si dangling bonds on the surface of these substrates are terminated with hydrogen atoms and are difficult to oxidize. Therefore, for example, when a SiO2 film is formed on this surface by the CVD method, since Sj-1-1 bonds exist on the substrate surface, direct bonding between Sj and oxygen is difficult. Therefore, an incomplete reaction occurs on the substrate surface, and many S j-H
It is considered that the interface state density becomes high due to remaining bonds or formation of 5j-OH bonds. On the other hand, by treating the Si wafer with an excited species of halogen atoms such as F, one of the Si-1-1 bonds at the interface can be efficiently replaced with F, and hydrogen can be removed. Since the substitution of F and O in the 5j-F bond occurs more easily than the substitution of G] and 0, the excited species of oxygen (the plasma By exposing the substrate to (obtained by excitation and/or photoexcitation), F and O can be substituted, and an even better and more stable 5j-0 bond can be obtained. By efficiently bonding Si and O on the substrate surface in this way, the interface state density between Sj and the SiO□ film can be reduced.

[Example] In the present invention, when an insulating film is formed on a semiconductor substrate, pretreatment is performed before film formation using light or plasma-excited halogen gas. and/or the interface state density at the substrate interface is reduced by performing treatment with the excited first gas following this gas treatment.

Furthermore, by using a film forming method that relies on light and plasma, the substrate can be processed at a low temperature suitable for halogen gas processing. In addition, the film forming apparatus can be simplified by using either a plasma source that excites the first gas during film formation or light that irradiates the substrate as means for exciting the halogen gas.

Furthermore, by irradiating light during the treatment with halogen gas, desorption of hydrogen is promoted, suppressing the incorporation of hydrogen that causes fluctuations in the threshold electrode, and making it possible to form a dense film. Similarly, in the gas treatment using the first gas, the first gas species can be efficiently replaced with the halogen element by plasma excitation of the gas or by irradiation with light.

An example of a film forming apparatus that can be suitably used to carry out the thin film forming method of the present invention will be described below with reference to FIG.

In FIG. 1, 1 is an electrode, and 2 is a reaction vessel that also serves as the other electrode. As shown in FIG. 1, the reaction vessel 2 is grounded.

3 is a substrate, for example, a semiconductor such as silicon or G
On a compound semiconductor substrate such as aAs or on an insulating substrate (
Examples include a substrate in which a semiconductor layer such as single crystal Si, polycrystalline Si, or amorphous silicon is deposited on a substrate made of an insulating material or a substrate whose surface is in an insulating state.

4a, 4b, and 4c are gas inlets, respectively, and the gas inlets 4a, 4b are located in the upper part of the reaction vessel 2, and are provided near the electrode J. A gas 10a containing a halogen element is introduced into the film forming chamber from the gas introduction port 4a, and a first gas 10b is introduced from the gas introduction port 4b. The gas 10a containing a halogen element is F2. diluted with an inert gas such as He or Ar. Diluent gas of halogen such as Ca2, B T2 or HF, l-I Cff, HBr, N
Examples include gases containing halogen compounds such as F3 and SF6.

Examples of the first gas include a gas containing nitrogen atoms, a gas containing oxygen atoms, and the like. In the present invention, when the first pretreatment is performed using a gas, the hydrogen content in the formed film is significantly reduced compared to when the film is formed using the parallel plate plasma CVD method. can be done.

The gas introduction port 4c is located on the lower side facing the electrode], and the second gas lOc is introduced from this introduction port [14c]. Second
Examples of the gas include SiH+ containing Si, Si2H6, etc., or TE01 ((C2+-+50), Si)
Organic oxysilane materials such as

5 is a power source for applying a voltage between the reaction vessel 2 and the electrode 1 to generate plasma. Note that the plasma generation means can also be generated using high frequency waves, microwaves, magnets, or a combination thereof.

The pressure inside the reaction vessel (operating pressure) during film formation was 10
It is preferable to set the temperature to 500 mTorr.

On the other hand, in order to further prevent plasma damage and increase the area of the substrate according to the above-mentioned thin film forming method, it is necessary to make the electrode area of the plasma source less than or equal to 1/]○ of the inner wall area of the reaction vessel. desirable. It is preferably 0.02 to 0.06, more preferably 0.04 to 005. In this way, if the area of the electrode is made smaller than the inner wall area of the reaction vessel and a voltage is applied between the electrode and the reaction vessel, the plasma intensity will be strong near the electrode and weaker near the substrate. Damage to the substrate or film can be reduced.

6 is a light source, for example, a Tolg lamp, a Xe lamp,
Lamps such as Xe-to-Ig lamps, W lamps, halogen lamps, or N2 lasers, Ar lasers, YAG
Examples include lasers such as lasers, CO2 lasers, and egisimer lasers. Of course, any light other than these may be used as long as it is not easily absorbed by the introduced gas and is absorbed by the reaction intermediate j-3 and the halogen gas during film formation. By using at least one of the plasma source for excitation of the first gas during film formation or the light that irradiates the substrate as a plasma source, the apparatus is simple and the pretreatment of the substrate and the film formation process can be performed continuously. The procedure for forming a thin film using this apparatus will be explained below.

After placing the substrate in the vacuum container 2 and reducing the pressure inside the reaction container 2 to a desired pressure using a vacuum evacuation device, a pretreatment halogen gas 10a is introduced to maintain the operating pressure at a desired value. On the other hand, at this time, light is irradiated from the light source 6 onto the substrate or electrodes.
A voltage is applied between the reactor and the reaction vessel 2 to excite the plasma, or to excite the plasma or both. Note that when infrared light or light containing infrared light is used as the light for irradiation, the temperature of the substrate can be set to a desired value by the light irradiation.

Furthermore, when using light that cannot raise the temperature of the substrate, a heater may be provided on the substrate support to set the temperature to a desired value.

Halogen pretreatment was performed under the above conditions. Thereafter, halogen gas is removed by evacuating the inside of the reaction vessel to a high vacuum. When subsequently performing treatment with the first gas,
Oxygen or nitrogen as a first gas is introduced into the reaction vessel and the operating pressure is adjusted to a desired value. At this time, as in the case of halogen pretreatment, it is preferable to irradiate the substrate 1 with light from the light source 6, or to apply a voltage between the electrode and the reaction vessel 2 to excite the plasma, or to perform both. Under the above conditions, the first
Pretreatment with gas can be performed.

Next, the inside of the reaction vessel 2 is evacuated to a desired pressure again. After that, first, the first gas l 01:l is flowed into the reaction vessel 2 from the gas inlet 4b, and the first gas is excited into plasma. The second gas 10c is introduced into the reaction vessel 2 through the gas introduction port 4c, and is caused to react with the excited first gas by setting the gas pressure to a predetermined value. For example, plasma is 1
It can be generated by applying a high frequency voltage of 3.56 MHz between the capacitively coupled electrode 1 and the reaction vessel 2. At this time, the substrate 1 is irradiated with light from a light source to form a film. Note that as a light source for performing light irradiation, a light source different from the light source used during pretreatment may be used, but by using the same light source, the apparatus can be simplified.

(Example 1) Hereinafter, preferred embodiments of the present invention will be described in more detail.

An Sj single crystal wafer was placed as a substrate in the reaction vessel 2, and the inside of the reaction vessel 2 was evacuated to 1×]0 Torr using a vacuum evacuation device. After that, H is used as the halogen gas 10a for pretreatment.
F diluted to 5% with e.

was introduced for 5 seconds and the operating pressure was increased to 1. OOm Tor
I kept it at r. On the other hand, from light source 6, 0.6W/cITI
' Xe lamp light was irradiated onto the substrate]. Note that this irradiation keeps the substrate temperature at 300°C, and under the above conditions
Pretreatment was performed for minutes.

Next, the inside of the reaction vessel 2 was evacuated to 1×10 −T o'r r again, and oxygen gas was used as the first gas 101, and monosilane gas was used as the second gas 10C. First, the first gas [O]] is introduced from the gas inlet 41] to the 101
0.005e into the reaction vessel 2 to excite the first gas into plasma. The second gas 10c was introduced into the reaction vessel 2 from the gas inlet 4c at a rate of 5 seconds, and the operating pressure at this time was 100 mTorr. Plasma was generated by applying a high frequency voltage of 13.56 MHz at 100 W between the capacitively coupled electrode 1 and the reaction vessel 2. The electron density at this time was 8×10 7 /cr& for the substrate 3-H. At this time as well, the substrate 1 was irradiated with light of 0.6 V+l/crd from the light source 6 in the same manner as in the pretreatment.

After 3 minutes of deposition under the above conditions] 000±2
Five 5iO21] mos were formed. That is, the variation in film thickness was as small as about ±2.5%.

The silicon oxide film formed as described above was evaluated.

(2) Refractive index] was 44 to 1.46, which was comparable to that of a thermal oxide film.

(2) Infrared spectral characteristics No absorption due to the S j -1-1, S -OH bond was observed, and only J absorption due to the S]-〇 bond was observed.

■ Electrical properties Relative dielectric constant 4.1, dielectric strength 10 M
V/crn, interface state density between semiconductor and insulating film (hereinafter referred to as interface state density) 5 x 10"
e V-'cm In this way, a film with good properties could be formed.

[Example 2] After evacuating the inside of the reaction vessel 2 in the same manner as in Example], l-
1eF25% gas 10a was introduced into the vacuum reaction vessel from the inlet 4a at 5 sec, and the operating pressure was 1, OOm To
Pretreatment was performed for 5 minutes by irradiating with a Xe lamp at rr.

Next, the F2 in the reaction container is removed by applying high vacuum to the container 2 one by one, and the oxygen which is the first gas is
05e was introduced and the operating pressure was increased to 1.00 mTorr. At this time as well, 0.6 W/ci light was irradiated from the light TA6 and oxygen treatment was performed for 5 minutes.

Next, the second gas Sjl (45 sec) was introduced into the reaction vessel from the gas inlet 4c, and the operating pressure was set to 1, OOm.
The first gas, oxygen, was excited by plasma. The Sin film prepared under the following conditions showed good results similar to those in Example 1 in terms of deposition rate, film thickness distribution, refractive index, infrared spectral characteristics, dielectric constant, and dielectric strength.

Also, the interface state density is 2 x 1.0 "e V-', cm
−”, which confirmed the effect of oxygen treatment.

[Example 3] After evacuating the inside of the reaction vessel in the same manner as in Example], HeN
After introducing 5% Fs gas into the reaction vessel from the inlet 4a at a rate of 5 sec, the operating pressure was set to 100 mTorr,
Excited by plasma. Pretreatment was performed for 5 minutes under the above conditions.

After that, the NF in the reaction container was removed by evacuating the reaction container to a high vacuum again, and the first gas (02) was introduced from the inlet 4] and the operating pressure was set to ]00 mTorr.
Oxygen treatment was performed for 5 minutes by plasma exciting oxygen. Next, add S I H4 as the second gas to gas inlet 4.
was introduced into the reaction vessel at a rate of 5 sec from C, the operating pressure was set to 100 rnTorr, and the first gas, oxygen, was excited by plasma, and at the same time, light was irradiated onto the substrate from the light source 6 to form a film. .

The 5jO2 film produced under the above conditions showed good results in terms of deposition rate, film thickness distribution, refractive index, infrared spectral characteristics, dielectric constant, and dielectric strength voltage similar to those in Example]. In addition, the interface state density was 010 eV-'cm.

[Example 4] After evacuating the inside of the reaction vessel 2 in the same manner as in Example 1, He
After introducing 5% NFs gas into the reaction vessel from the inlet 4a at a rate of 5 sec, the operating pressure was set to 100 mTorr, and at the same time the light source 6 was excited at 06 W/
ci light was irradiated. Thereafter, the NF in the reaction container is removed by evacuating the reaction container to high vacuum again, and the first gas (0,) is introduced from the introduction port 4b, and the operating pressure is set to 100.
mTorr. Then, oxygen treatment was performed by exciting oxygen with plasma and simultaneously irradiating light onto the substrate from the light source 6.

Next, S I H< as the second gas was introduced into the reaction vessel from the gas inlet 4c at a rate of 5 sec, and the operating pressure was increased to 1.
The film was formed by exciting the first gas, oxygen, with plasma and simultaneously irradiating light onto the substrate from the light source 6 at a pressure of 00 mTorr.

The SiC2 produced under the above conditions showed good results as in Example 1 in terms of deposition rate, refractive index, infrared spectral properties, dielectric constant, and dielectric strength. Also, the interface state density is 5X 101
It was possible to reduce it to 1 eV-'cm-2.

[Advantageous Effects of the Invention 1] According to the present invention, (1) the substrate can be placed away from the strongest part of the plasma, so that plasma damage to the substrate can be reduced. Furthermore, by performing pretreatment with excited halogen gas and/or treatment with excited first gas (oxygen treatment or nitrogen treatment), it is possible to significantly reduce the interface state density, and the electrical A film with excellent properties can be formed.

■Excitement of the halogen gas can be achieved by using either a plasma source used to excite the first reaction gas during film formation or a light source that irradiates the substrate (using either one simplifies the equipment and Membrane process can be performed continuously.

■A film with a close stoichiometric composition can be formed.

■It is possible to form a film with low hydrogen content, and it is possible to suppress fluctuations in threshold voltage.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an apparatus according to an embodiment of the present invention. ]...Electrode, 2...Reaction container, 3...Substrate, 4a, 4b, 4cm...Gas inlet, 5...Plasma generation means, 6...Light source,

Claims (1)

[Scope of Claims] 1. In a film formation method using plasma and light, the steps include: introducing a halogen gas into a film formation chamber in which a substrate is arranged; and exciting the halogen gas to treat the substrate. a step of introducing a first gas that does not deposit on its own even when excited after the halogen treatment into a reaction vessel in which a substrate is arranged; a step of plasma-exciting a gas; introducing a second gas into the reaction vessel and reacting with the excited first gas, depositing a generated reaction product on a substrate; A method for forming a thin film, comprising the step of irradiating light onto a substrate to which it is attached. 2. In a film formation method using plasma and light, the steps include: introducing a halogen gas into a film formation chamber in which a substrate is arranged; a halogen treatment step of exciting the halogen gas and treating the substrate; After the halogen treatment, a step of introducing a first gas that does not deposit on its own even when excited into a reaction container in which a substrate is arranged; and a step of plasma exciting the first gas introduced into the reaction container. a step of exposing the substrate after the halogen treatment to the excited first gas; and introducing a second gas into the reaction vessel and reacting with the excited first gas, resulting in a reaction. A method for forming a thin film, comprising the steps of: depositing a product on a substrate; and irradiating the substrate to which the reaction product is deposited with light.