JPH07263359A - Method of forming thin film - Google Patents

Abstract

(57) [Summary] [Structure] A gas containing TiCl ₄ , H ₂ , N ₂ and O ₂ is used as a raw material, and TiO is produced by a CVD method using plasma generated by electron cyclotron resonance (ECR) excitation.
The thin film forming method of forming an _x N _y films. [Effect] In the formed TiO _x N _y thin film, the content of columnar crystal grains is remarkably reduced as compared with the TiN thin film containing no oxygen, and the number of grain boundaries formed almost vertically on the surface of the semiconductor substrate is small. to significantly reduced, also flows into a metal such as Al on TiO _x N _y film, it is possible to prevent the penetration of metal into the TiO _x N _y thin film. In addition, TiO _x
Since the N _y thin film has a good wettability with a metal such as Al, when the TiO _x N _y thin film is formed as a barrier layer such as a contact hole formed in a semiconductor substrate, the N _y thin film sufficiently exhibits its function as a barrier layer. Can be made.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a thin film,
More specifically, the present invention relates to a method of forming a thin film of TiO _x N _y composition that can be used as a barrier metal of a semiconductor device.

[0002]

2. Description of the Related Art Usually, the contact portion of an LSI has a diffusion layer on the surface of the substrate as a base, and an Al layer is formed through a contact hole.
It is connected with wiring. However, with today's miniaturization and high integration of LSI, the aspect ratio of this contact hole is increased and the depth is deeper than the diameter of the contact hole, so that the metal such as Al is completely contacted. It's getting harder to embed in the hole.

Therefore, in order to completely embed the metal in the contact hole, Al is formed near the contact hole.
A method (reflow process) in which a metal film such as the above is subjected to heat treatment at high temperature and then the metal is poured into the contact hole is promising from the viewpoint that the number of steps in the semiconductor manufacturing process can be reduced.

However, since the diffusion layer is becoming shallower with the miniaturization and higher integration of the LSI, if Al metal is directly poured onto this shallow diffusion layer, an Al spike will occur and the junction will be destroyed, or a contact hole will be formed. There is a problem that Si is deposited on the bottom and contact resistance increases.

Conventionally, in order to prevent the above-mentioned problems such as Al spikes, a method of forming a diffusion preventing thin film (barrier layer) using a metal called a barrier metal or a compound thereof between an Al metal and a semiconductor substrate. Has been adopted. The TiN thin film has characteristics that it has a small specific resistance and is chemically stable, and satisfies the required characteristics as a barrier layer, and is therefore widely used as a compound for forming a barrier layer.

As a method of forming the TiN thin film, for example, a reactive sputtering method or a plasma CVD method can be cited. The thin film formed by the reactive sputtering method has poor step coverage and is formed at the bottom of the contact hole. There is a problem that it is difficult. On the other hand, plasma CVD method, especially electron cyclotron resonance (ECR: Electron C
ycrotron resonance (CVD) method utilizing plasma generation by excitation (hereinafter referred to as ECR plasma CVD
Method), which has excellent directivity and can form a uniform thin film inside a contact hole having a small diameter, and is therefore attracting attention as a method of forming a barrier layer for the next-generation ULSI.

Therefore, a method of forming a TiN thin film using this ECR plasma CVD method will be described below. FIG. 5 is a sectional view schematically showing an apparatus used in this ECR plasma CVD method.

The apparatus comprises a plasma generation chamber 11 and a reaction chamber 1
2, an excitation coil 14 connected to a DC power supply (not shown) around the plasma generation chamber 11, and a microwave oscillated from a microwave oscillator (not shown). Is introduced into the plasma generation chamber 11 and the like. Reference numeral 16 is a microwave introduction window, 17 is a high-frequency generation source for applying a high-frequency (RF) power source to the microwave introduction window, and 18 is a sample table on which a sample 19 is placed.

The plasma generation chamber 11 is formed in a substantially cylindrical shape, and a first hole 20 for introducing a microwave is formed in a substantially central portion of an upper wall of the plasma generation chamber 11, and the plasma generation chamber 11 is formed. A reaction chamber 12 having a larger diameter than the plasma generation chamber 11 is integrally formed below the plasma generation chamber 11. Further, the reaction chamber 12 and the plasma generation chamber 1
1 is partitioned by a partition plate 21, and a second hole (plasma lead-out window) 22 is provided at a substantially central portion of the partition plate 21.
Are formed.

Further, a first introducing pipe 23 is connected to the side wall of the reaction chamber 12, and an exhaust pipe 24 communicating with an exhaust system (not shown) is connected to the bottom of the reaction chamber 12. A second introduction pipe 25 is connected to the upper wall of the plasma generation chamber 11.

The high frequency source 17 is the microwave introduction window 1
It is connected to a flat plate electrode (not shown) sandwiched between 6 and the waveguide 15, and a high frequency is applied to the microwave introduction window 16 via this parallel electrode.

Although not shown, a high-frequency oscillator for applying a high frequency to the sample 19 is connected to the sample table 18, and a predetermined high frequency is applied to the sample 19 by this high-frequency oscillator to form a thin film. The bias voltage applied to the sample 19 causes the sample (semiconductor device) to
Even if a contact hole having a small diameter is formed in 19, it is possible to form a thin film having good step coverage.

In order to form a TiN thin film using the above apparatus, first the exhaust system is operated to reduce the pressure inside the apparatus main body 13, and then TiCl ₄ is introduced from the first introduction pipe 23 into the reaction chamber 12.
Supply in. On the other hand, Ar, H ₂ , and N ₂ are supplied into the plasma generation chamber 11 through the introduction pipe 25. Then, the inside of the apparatus main body 13 is set to a predetermined pressure.

Further, the high frequency generation source 17 is energized to apply a high frequency to the microwave introduction window 16, and the microwave introduction window 1
The TiN thin film is prevented from adhering to the microwave introducing window 16 by the sputtering effect of Ar ions due to the bias voltage generated at 6. On the other hand, a microwave is introduced into the plasma generation chamber 11 from the microwave oscillator through the waveguide 15, and a direct current is passed through the exciting coil 14 to generate a magnetic field in the plasma generation chamber 11. Then, high-energy electrons collide with the raw material gas in the plasma generation chamber 11, and the raw material gas is decomposed and ionized to generate plasma.

The generated plasma passes through the plasma extraction window 22 and is accelerated toward the sample stage 18 by the divergent magnetic field, and the sample 1 such as the semiconductor device mounted on the sample stage 18 is accelerated.
A TiN thin film is formed on the surface of 9.

[0016]

FIG. 6 is a cross-sectional view schematically showing the cross-sectional structure of a TiN thin film formed by the above method, in which 31 is a TiN thin film and 32 is a semiconductor substrate. is there.

As can be seen from the figure, the TiN thin film 31 formed by the above method is an aggregate of columnar crystal grains,
There are many crystal grain boundaries 33 formed substantially vertically along the surface of the semiconductor substrate 32.

Therefore, when the TiN thin film is formed inside the contact hole by the above method, the TiN thin film having the columnar crystal structure as described above is formed inside the contact hole, and the Al reflow is formed on the TiN thin film. When Al flows in by the process, Al may penetrate into the crystal grain boundaries 33 of the columnar crystal grains and reach the diffusion layer on the surface of the underlying semiconductor substrate. In such a case, TiN is used.
There is a problem that the thin film cannot sufficiently function as a barrier layer.

The present invention has been made in view of the above problems, and even when a metal such as Al covers the upper portion thereof, there is no fear that the metal will permeate to the surface of an underlying semiconductor substrate and a contact hole or the like may be formed. It is an object of the present invention to provide a method for forming a thin film capable of sufficiently fulfilling the function as a barrier layer.

[0020]

In order to achieve the above object, a method of forming a thin film according to the present invention comprises a TiCl ₄ , H ₂ ,
Using a gas containing N ₂ and O ₂ as a raw material, ECR plasma C
It is characterized in that a TiO _x N _y thin film is formed by the VD method (1).

The method for forming a thin film according to the present invention may also, O ₂
It is characterized in that the flow rate ratio of gas to N ₂ gas is 0.05 to 0.5 (2).

[0022]

FIG. 1 is a sectional view schematically showing the structure of a section of a TiO _x N _y thin film formed by the method of forming a thin film according to the present invention. In the figure, 10 is a TiO _x N _y thin film. is there.

The TiN thin film shown in FIG. 6 and the T shown in FIG.
As can be seen from the comparison with the iO _x N _y thin film, the TiO _x N _y thin film containing oxygen relaxes the clear columnar crystal structure as shown in FIG. 6 and is almost perpendicular to the surface of the semiconductor substrate 32. The number of the crystal grain boundaries 33 formed in 1 is significantly reduced. It is considered that this is because the crystallinity of TiO _x N _y is lowered and is close to an amorphous state, and the size of the crystal grains themselves is large.
Since the TiO _x N _y thin film has such a structure,
Even when a metal such as Al flows into the TiO _x N _y thin film, the metal does not penetrate to the underlying semiconductor substrate 32 and can sufficiently function as a barrier layer such as a contact hole.

That is, according to the method of forming a thin film described in (1) above, a gas containing TiCl ₄ , H ₂ , N ₂ and O ₂ is used as a raw material, and TiO _x N is formed by an ECR plasma CVD method.
_{Since the y} thin film is formed, a TiO _x N _y thin film having good step coverage is formed even if unevenness exists on the sample surface.
The iO _x N _y thin film has a significantly lower content of columnar crystal grains than the TiN thin film containing no oxygen, and the number of crystal grain boundaries formed substantially perpendicular to the semiconductor substrate surface is significantly reduced. the TiO _x N is not possible to penetrate the TiO _x N _y thin film flows the metal on _{the y} thin film such as Al. Further, since the TiO _x N _y film also a good wettability with the metal such as Al, the case of forming the TiO _x N _y film as the barrier layer, such as a contact hole formed in a semiconductor substrate, as the barrier layer The function of is fully exerted.

According to the method of forming a thin film described in (2) above, the flow rate ratio of O ₂ gas to N ₂ gas is 0.05 to.
Since it is 0.5, the TiO _x formed by the above method is
The N _y thin film is particularly excellent in the function of preventing the permeation of metals such as Al, and has a small specific resistance, so that the function as a barrier layer is more effectively exhibited.

If the flow ratio of the O ₂ gas to the N ₂ gas is less than 0.05, the crystal characteristic of the TiN thin film remains, so that the leakage current tends to increase when the barrier layer is formed in the contact hole. On the other hand, when the flow rate ratio of the O ₂ gas to the N ₂ gas exceeds 0.5, the specific resistance increases. Therefore, when the barrier layer is formed in the contact hole, the function as the barrier layer is not sufficiently exhibited. There is.

[0027]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the method for forming a thin film according to the present invention will be described below with reference to the drawings. Since the apparatus used for the ECR plasma CVD method according to the embodiment is the same as that described in "Prior Art", detailed description will be omitted here.

Next, a method of forming a thin film (TiO _x N _y thin film) according to the embodiment using the above apparatus will be described. First, a carbon substrate was used as the sample 19 and placed on the sample table 18, the temperature of the sample 19 was set to 500 ° C., and a TiO _x N _y thin film was formed on the surface of the carbon substrate by the following method.

First, the inside of the apparatus main body 13 was decompressed by operating the exhaust system, and then TiCl ₄ was supplied from the first introducing pipe 23 into the reaction chamber 12 at a flow rate of 10 sccm. On the other hand, from the introduction pipe 25, 75 sccm of Ar, the H ₂ 2
6 sccm, N ₂ was set to 8 sccm, and oxygen was supplied to the plasma generation chamber 11 at a flow rate to be described later, and then the inside of the apparatus main body 13 was set to a pressure of 3.0 mTorr.

Next, the high-frequency generation source 17 is energized to supply the microwave introduction window 16 with a high frequency of 13.56 MHz of 150 W.
The TiN thin film is applied with the power of
On the sample table 18 while preventing it from adhering to
A high frequency of 6 MHz was applied with a power of 500 W to improve the directivity. In addition, a microwave of 2.45 GHz is 2.8 kW from the microwave oscillator through the waveguide 15.
While being introduced into the plasma generation chamber 11 with a power of 1, a DC current was passed through the exciting coil 14 to generate a magnetic field in the plasma generation chamber 11, and a TiO _x N _y thin film was formed on the surface of the sample 19.

Regarding the introduced O ₂ gas, the flow rate was first set to 0 sccm, a TiN thin film having a thickness of 800 Å was formed by the above method, and the sample 19 was replaced with a new sample 19 to replace the O ₂ gas. The flow rate was set to 0.2 sccm, and the other conditions were the same, and 800 Å thickness of TiO _x N.
_y thin film. Then, similarly, the flow rate of O ₂ gas is set to 0.4 s.
ccm, 0.5 sccm, 1 sccm, 2 sccm, 3
sccm, 4sccm, 5sccm, 6sccm, 7s
The thickness was changed to 8 cm and 8 cm, and a TiO _x N _y thin film having a thickness of 800 Å was similarly formed on each sample 19.

Next, TiO _x formed by the above method
The elemental analysis of the N _y film was measured by RBS (Rutherford back scattering method). FIG. 2 is a graph showing the measurement results, in which the vertical axis represents the atomic ratio of O and N with respect to Ti, and the horizontal axis represents the flow rate of O ₂ gas.

As the flow rate of O ₂ gas increased, the oxygen content in the thin film increased almost linearly, while N ₂
It can be seen that the gas content decreases as the O ₂ gas content increases. As you can see from this result,
The oxygen content in the formed TiO _x N _y thin film can be controlled by changing the flow rate of the introduced O ₂ gas.

Then, a silicon substrate is used as the sample 19, and 10 is formed on the silicon substrate in the same manner as the above method.
A TiO _x N _y thin film having a thickness of 00Å was formed, and the specific resistance of the formed thin film was measured by a four-terminal measuring method. FIG. 3 is a graph showing the measurement results, where the vertical axis represents the formed T
The specific resistance of the iO _x N _y thin film, and the horizontal axis represents the flow rate of O ₂ gas.

As can be seen from the figure, the specific resistance of the TiO _x N _y thin film is about 250 μΩc when the flow rate of O ₂ gas is 4 sccm.
m is 5 sccm, it is about 400 μΩcm, and when used as a barrier layer, its specific resistance is 250 μΩ.
In cm, there is little influence on the contact resistance at the time of forming the contact hole, so there is no problem as the contact resistance, but in 400 μΩcm, the resistance cannot be ignored, which causes a problem.

Next, a semiconductor device was used as the sample 19, and a TiO _x N _y thin film was formed as a barrier layer on the contact portion of the semiconductor device.

First, as a semiconductor device, an n-channel diffusion layer having a diffusion length of 0.2 μm, a contact hole diameter of 0.4 μm, a depth of 2 μm, and an aspect ratio (depth / diameter) of 5 is used. Using the above-mentioned TiO _x
Respectively in the same manner as in the formation of N _y film in the contact hole to form a TiO _x N _y film at a thickness of 1000 Å. Thereafter, this semiconductor device was transferred to a sputtering apparatus, an Al film was formed to a thickness of 8000 Å, followed by heat treatment at 500 ° C. for 30 minutes to reflow Al, and then a Kelvin pattern was formed. And
The leak current in the contact hole portion was measured for each sample 19 manufactured by changing the flow rate of O ₂ gas. The leak current was measured by measuring the leak current when a reverse bias of 10 V was applied.
FIG. 4 is a graph showing the measurement results, where the vertical axis is the logarithmic value of the leak current and the horizontal axis is the flow rate of O ₂ gas.

When the flow rate of O ₂ gas is 0 sccm (10
^-9 A), by increasing the flow rate of O ₂ gas to 0.4 sccm, the leakage current value is about 10
^It can be seen that it has decreased by about an order of magnitude of ^-10 A. If the leak current value itself is 10 ^-9 A, there is no particular problem,
From the viewpoint of reliability when a large number of semiconductor devices are manufactured by mass production, the leak current value is more preferably 10 ⁻¹⁰ A.

The above, TiO _x N _y film formed is preferably from the viewpoint of the leakage current O ₂ gas flow rate is greater than or equal to 0.4 sccm, the flow rate of O ₂ gas from the viewpoint of specific resistance while the It is preferably 4 sccm or less. Therefore, considering both characteristics, the preferable flow rate is 0.4 to 4 sccm.

The content of oxygen in the TiO _x N _y thin film to be formed, other associated with the flow rate of O ₂ gas flow rate from the considered correlation with the flow rate of N _2, and N ₂ gas Taking the ratio, the ratio (flow rate of O ₂ gas / flow rate of N ₂ ) in the above example is 0.05 to 0.5, and the above range is considered to be a range in which the characteristics as the barrier layer are more excellent. .

[0041]

As described above in detail, in the method of forming a thin film according to the present invention, TiCl ₄ , H ₂ , N ₂ and O _{2 are used.}
Since a TiO _x N _y thin film is formed by an ECR plasma CVD method using a gas containing a gas as a raw material, it is possible to form a TiO _x N _y thin film having good step coverage even if unevenness exists on the sample surface. The TiO _x N _y thin film has a significantly lower content of columnar crystal grains than the TiN thin film containing no oxygen, and the number of grain boundaries formed almost vertically on the semiconductor substrate surface is significantly reduced. Even _if a metal such as Al flows into the TiO _x N _y thin film, the Ti
It is possible to prevent the penetration into the O _x N _y thin film. Moreover, the order TiO _x N _y films good wettability with a metal such as Al, etc. in a contact hole formed in the semiconductor substrate when forming said TiO _x N _y film as the barrier layer, as a barrier metal The function can be fully exerted.

According to the method of forming a thin film described in (2) above, the flow rate ratio of O ₂ gas to N ₂ gas is 0.05 to.
Since it is 0.5, the TiO _x formed by the above method is
The N _y thin film is particularly excellent in the function of preventing the permeation of metals such as Al, has a small specific resistance, and can exhibit the function as a barrier layer more favorably.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a cross-sectional structure of a TiO _x N _y thin film formed by a thin film forming method according to the present invention.

FIG. 2 is a graph showing the relationship between the atomic ratio of O and N to Ti in the TiO _x N _y thin film formed by the thin film forming method according to the example and the O ₂ gas flow rate.

FIG. 3 is a graph showing the relationship between the specific resistance of a TiO _x N _y thin film formed by the thin film forming method according to the example and the O ₂ gas flow rate.

FIG. 4 is a graph showing the relationship between the logarithmic value of the leakage current and the O ₂ gas flow rate of the TiO _x N _y thin film formed in the contact hole portion of the semiconductor device by the thin film forming method according to the example.

FIG. 5 is a cross-sectional view schematically showing an apparatus used for ECR plasma CVD method.

FIG. 6 is a TiN formed by a conventional thin film forming method.
FIG. 3 is a cross-sectional view schematically showing the structure of a cross section of a thin film.

[Explanation of symbols]

10 TiO _x N _y thin film

Claims (2)

[Claims] 1. A TiO _x N _y thin film is formed by a CVD method using a gas containing TiCl ₄ , H ₂ , N ₂ and O ₂ as a raw material and using plasma generated by electron cyclotron resonance (ECR) excitation. And a method for forming a thin film. 2. The method for forming a thin film according to claim 1, wherein the flow rate ratio of O ₂ gas to N ₂ gas is 0.05 to 0.5.