JPH10340898A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon insulating film wherein charge density in a film is low and permittivity is reduced, by performing formation by applying an electronic cyclotron resonance plasma CVD method using silicon fluoride based gas and silane based gas, and installing a silicon insulating film wherein fluorine containing ratio and hydrogen group containing ratio are specified values. SOLUTION: Mixture gas of silicon tetrafluoride gas (SiF4 ) and monosilane gas (SiH4 ) whose amounts are 32.5 sccm respectively is supplied from a second gas introducing system 7 to a reaction chamber 2. After that, microwave whose output power is 2.5 kW is introduced in a plasma forming chamber 1, and a magnetic field is generated in the plasma forming chamber 1 with an exciting coil 4. Ar gas and oxygen gas which are supplied to the plasma forming chamber 1 are decomposed, and plasma is formed. The formed plasma is introduced in the reaction chamber 2 by the magnetic field in the plasma forming chamber 1, and activates SiF4 and SiH4 . An SiOF film is formed on a specimen S by reaction with oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electron cyclotron resonance (ECR) plasma CVD (chemical vapor deposition).
The present invention relates to a semiconductor device including a fluorine-containing silicon insulating film formed by por deposition and a method for manufacturing the same.

[0002]

2. Description of the Related Art An insulating film used for an LSI includes a gate capacitance insulating film, an interlayer insulating film, a passivation film and the like. The interlayer insulating film and the passivation film are required to have low dielectric properties for the purpose of increasing the speed of LSI. Conventionally, when forming such an insulating film, monosilane and oxygen gas or nitrous oxide gas or TEOS (Tetra Ethyl Ortho Silicate) are used as various plasma generating sources.
And oxygen gas. However, since the silicon oxide film formed by plasma supply using these gases contains several percent of hydroxyl groups, it is 3.8 to 4.5.
, Which is significantly higher than that of the thermal oxide film. When an insulating film having a high relative dielectric constant is used, for example, as an insulating film between wirings, the capacitance between wirings increases and the operating frequency of the semiconductor device decreases.

In order to prevent this, attempts have been made to reduce the relative dielectric constant by incorporating fluorine into a silicon oxide film. The insulating film containing fluorine is generally called an SiOF film, and is formed by a plasma CVD method using a reactive gas containing fluorine. As a combination of reaction gases, an organic silane-based gas and oxygen (JP-A-7-74245), an organic silane-based gas and oxygen or nitrous oxide and a fluorocarbon-based gas (JP-A-7-307293) are proposed. Have been. By these methods, a silicon oxide film containing several% to 10% of fluorine is formed,
Its relative dielectric constant is 3.3 to 3.6, which is much lower than that of a silicon oxide film containing no fluorine.

[0004]

As described above, a silicon oxide film having a low relative dielectric constant can be formed by using a fluorine-containing reaction gas. However,
During the formation of the SiOF film by the plasma CVD method, there is a problem that carbon, which is a constituent element of the reaction gas, is mixed into the SiOF film and deteriorates the electrical characteristics of the semiconductor device. The SiOF film formed by the plasma CVD method is
It is also known that reliability as an insulating film is low due to high hygroscopicity.

Accordingly, the applicant of the present application has proposed an ECR plasma CV
In forming a silicon oxide film by a high-density plasma method such as the method D, a method using silicon tetrafluoride gas and oxygen or nitrous oxide as a reaction gas is disclosed in Japanese Patent Laid-Open No. 6-333919.
No. in the publication. In this proposal, since the reaction gas does not contain carbon, the electrical characteristics of the semiconductor device are not degraded, and since high-density plasma is used, an insulating film is formed densely and a SiOF film having low hygroscopicity can be formed. Has been demonstrated.

However, it has been found from the measurement results that the SiOF film formed by this method has a high charge density. Table 1 shows that SiO formed on a P-type silicon substrate
MIS (Metal In) with aluminum metal laminated on F film
It shows the value of the flat band voltage obtained by the CV characteristic analysis of the (sulator semiconductor) structure, and also shows the flat band voltage of the insulating film obtained by another forming method. In each case, an insulating film with a thickness of approximately 200 nm was
It is a value obtained by measuring the flat band voltage after heat treatment for one minute. As can be seen from the table, the absolute value of the flat band voltage is the largest in the SiOF film, and a flat band voltage shift of about 1 V to 4 V is seen when compared with the thermal oxide film. This indicates that the charge density in the SiOF film is high.

[0007]

[Table 1]

Since the charge density in the SiOF film is high, when this SiOF film is used as an interlayer insulating film or a passivation film, a voltage of several volts is constantly applied to the underlying element. For this reason, the electrical characteristics of the underlying element may deteriorate,
There has been a problem that reliability is reduced. Further, since silicon tetrafluoride gas is a relatively stable gas, there is a possibility that the decomposition reaction is insufficient even when a high-density plasma CVD method is used.

The present invention has been made in view of such circumstances, and uses a silicon fluoride-based gas and a silane-based gas as reaction gases in an ECR plasma CVD method. Is set to a predetermined ratio, the charge density in the film is low,
It is another object of the present invention to provide a semiconductor device including a silicon insulating film having a reduced dielectric constant and a method for manufacturing the same.

[0010]

The semiconductor device according to the first invention is formed by an electron cyclotron resonance plasma CVD method using a silicon fluoride-based gas and a silane-based gas, and has a fluorine content of 6.7 atomic%. ~ 8.0 atomic
%, And the hydroxyl group content is 1.3 atomic% to 1.4 atom.
It is characterized by having a silicon insulating film of ic%.

In the first invention, the fluorine content is 6.
The silicon insulating film having a content of 7 atomic% to 8.0 atomic% and a hydroxyl group content of 1.3 atomic% to 1.4 atomic% is made of silicon tetrafluoride gas (SiF ₄ ) and monosilane as shown in FIG. This is a case where the flow ratio of monosilane to the sum of the flow rates of (SiH ₄ ) is 40% to 70%. Silane-based gases such as monosilane and disilane have high reactivity and can form a silicon oxide film only by mixing with oxygen without forming a plasma state. For this reason,
The reaction is promoted by simultaneously supplying a silicon fluoride-based gas and a silane-based gas during the formation of the silicon insulating film,
The plasma is stabilized. When the flow rate ratio of the silane-based gas is increased, the flat band voltage of the silicon insulating film decreases, and the charge density in the film decreases. This is because the addition of a highly reactive silane-based gas compensates for structural defects in the SiOF film by Si—O bonds, and reduces unbonded ends. On the other hand, if the flow rate ratio of the silane gas is too high, the hydroxyl group content increases and the relative dielectric constant increases.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device.
A fluorine-containing silicon insulating film is formed using a silicon fluoride-based gas and a silane-based gas by an electron cyclotron resonance plasma CVD method.

In the second invention, a silicon fluoride-based gas and a silane-based gas are supplied by an electron cyclotron resonance (ECR) plasma CVD method. The silane-based gas has high reactivity, and stabilizes plasma. This allows
In a high-density plasma method such as the ECR plasma CVD method, the film formation rate is further improved, and a silicon insulating film having good moisture absorption is obtained.

According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device.
In the second invention, the silicon fluoride-based gas contains SiF_Four
To the silane-based gas_FourUsing SiF_FourAnd S
iH _FourTo the sum of the flow rates_FourFlow rate of 4
It is characterized by being 0% to 70%.

In the third invention, as shown in FIG. 2 described later, when the flow rate of SiH ₄ is lower than 40%, the charge in the film is not sufficiently compensated for structural defects in the SiOF film. Density increases. On the other hand, if it is higher than 70%, the hydroxyl groups become excessive and the relative dielectric constant becomes high.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic longitudinal sectional view showing the structure of an ECR plasma CVD apparatus used for carrying out the present invention. In the figure, reference numeral 1 denotes a plasma generation chamber, which is formed in a hollow cylindrical shape. A circular microwave inlet 1b is provided at the upper center, and a cylindrical microwave waveguide 3 has one end connected to a microwave oscillator (not shown), and a flange 3a provided at the other end and connected to the microwave inlet 1b. Have been. The microwave inlet 1b is provided with a microwave inlet window 1 made of a quartz glass plate.
a is provided so as to close the microwave introduction port 1b. An excitation coil 4 is arranged around the plasma generation chamber 1 concentrically with one end of the microwave waveguide 3 connected to the plasma generation chamber 1 so as to surround the one end, and the excitation coil 4 is not shown. Connected to DC power supply. Further, a first gas introduction system 6 is provided on the upper wall of the plasma generation chamber 1.
Is established, and an Ar gas and an oxygen gas or a nitrous oxide gas can be introduced into the plasma generation chamber 1.

At the center of the lower wall of the plasma generation chamber 1, a plasma extraction window 1c is provided at a position facing the microwave introduction port 1b, and a reaction chamber 2 is formed so as to face the plasma extraction window 1c. A sample table 5 is disposed in the reaction chamber 2 at a position facing the plasma extraction window 1c, and a sample S such as a Si wafer is mounted thereon. A high-frequency power supply 9 is connected to the sample stage 5 so that a bias voltage is applied to the sample S. In addition, a second gas introduction system 7 is provided on a side wall of the reaction chamber 2 so that a reaction gas can be introduced into the reaction chamber 2. An exhaust system 8 connected to an exhaust device (not shown) is provided on the lower wall.

Embodiment 1 Using the above device,
When an SiOF film is formed on the sample S, the sample S is placed on the sample stage 5 and 93 sccm from the first gas introduction system 6.
And an oxygen gas of 104 sccm are supplied into the plasma generation chamber 1. This Ar gas is not involved in the composition of the insulating film, but is a sputtering gas used for planarizing the formed insulating film. Next, a silicon tetrafluoride gas (SiF ₄ ) and a monosilane gas (S
A mixed gas with iH ₄ ) is supplied into the reaction chamber 2. At this time, the volume ratio between SiF ₄ and SiH ₄ is 1: 1. The pressure inside the plasma generation chamber 1 and the reaction chamber 2 is a predetermined pressure, for example, 2
Vacuum exhaust is performed by the exhaust system 8 so that the pressure becomes mTorr.
Note that the supply of SiF ₄ and SiH ₄ is not limited to the mixed gas, and each separate SiF ₄ and SiH ₄ may be supplied, for example, for 32.5 seconds.
It may be supplied at a flow rate of ccm.

Thereafter, a microwave having an output of 2.5 kW was applied to the microwave.
Through the microwave introduction tube 3 and the microwave introduction window 1a,
While being introduced into the zuma generation chamber 1, the excitation coil 4
A magnetic field is generated in the plasma generation chamber 1. This allows
Electron cyclotron resonance occurs in the plasma generation chamber 1.
Condition is satisfied, and Ar supplied into the plasma generation chamber 1
The gas and oxygen gas are decomposed to generate plasma.
The generated plasma is generated by the magnetic field in the plasma generation chamber 1.
Introduced into the reaction chamber 2_FourAnd SiH _FourActivate
And a SiOF film is formed on the sample S by a reaction with oxygen.
Form. At this time, the sample S is negative by the high frequency power supply 9.
Bias voltage is applied, and the surface of the SiOF film
Planarized by sputtering on.

According to the ECR plasma CVD method as described above,
A SiOF film having a thickness of 200 nm
Formed on a substrate, and the deposition rate, relative permittivity,
Voltage, charge density in the film and hygroscopicity were measured. Table of results
It is shown in FIG. At the same time, the same measurement is performed for the comparative example and the conventional example.
And the results are shown in Table 2. Comparative Example 1 was made of SiH
_FourComparison by ECR plasma CVD method without using
Example 2 is SiF_FourECR plasma CVD method without using
Things. Conventional example 1 uses a plasma CVD method.
Conventional example 2 is a plasma CVD method.
Conventional example 3 is a thermal oxide film.
The charge density in the film shown in Table 2 is the SiOF film having the MIS structure.
Based on the flat band voltage obtained by the CV characteristic analysis of
It is a value calculated based on the above.

[0021]

[Table 2]

From Table 2, the SiOF film of the first embodiment is
It can be seen that the flat band voltage and the charge density in the film are reduced while having substantially the same relative dielectric constant as Comparative Example 1 in which SiH ₄ is not used. Further, it is clear that the film forming rate of the first embodiment is improved as compared with Comparative Example 1 and Conventional Example 1. Furthermore, it can be seen that the first embodiment has a smaller change in the relative dielectric constant due to moisture absorption as compared with the conventional example 2, and is excellent in moisture absorption.

As described above, in the first embodiment, 32.5
sccm SiF ₄ , 32.5 sccm SiH ₄ (S
Using iH ₄ / (SiF ₄ + SiH ₄ ) = 0.5),
SiOF film is formed by ECR plasma CVD method,
A dense, low-hygroscopic SiOF film with few structural defects can be formed. This has characteristics suitable as an interlayer insulating film or a passivation film of an LSI. In addition, since the ECR plasma CVD method uses plasma having high activity,
Even when the volume ratio of the silane-based gas is low, the silicon fluoride-based gas is sufficiently decomposed.

Embodiment 2 FIG. Next, the relationship between the ratio of the flow rate of SiH _{4 to} the sum of the flow rates of the reaction gas, the charge density in the film, and the relative dielectric constant was examined. E similar to that of the first embodiment described above.
Using a CR plasma CVD apparatus, SiH ₄ and SiF ₄
Were formed at different flow rates, and the charge density and relative permittivity in the film were measured. Conditions other than the flow rates of SiH ₄ and SiF ₄ are the same as those of the first embodiment, and a description thereof will be omitted. FIG. 2 is a graph showing the measurement results.
The ratio of iH ₄ / (SiF ₄ + SiH ₄ ) is shown, and the vertical axis shows the charge density in the film and the relative dielectric constant. From the graph,
It can be seen that the charge density in the film sharply drops at about 40% of the ratio of SiH _{4 in} the gas flow. Further, it can be seen that the relative dielectric constant sharply increases at about 70% of the gas flow rate of SiH ₄ . Further, the flow rate ratio of SiH ₄ is 4
In the range of 0% to 70%, the relative dielectric constant is 3.8 or less, which is almost the same as that of the thermal oxide film, and the charge density in the film is ECR plasma CV.
It can be seen that the thickness is 5.9 × 10 ¹⁶ cm ⁻³ or less, which is almost the same as that of the SiO ₂ film formed by D.

From these results, it can be seen that SiF ₄ and SiH ₄
Ratio of the flow rate of SiH _{4 to} the sum of the flow rates of
When it is 0%, it can be said that an SiOF film having a small relative dielectric constant and a small charge density in the film is formed. SiH
_When the flow rate ratio of ₄ is lower than 40%, the charge density in the film becomes high due to insufficient compensation of the structural defects in the SiOF film, and when it is higher than 70%, the hydroxyl group becomes excessive and the relative dielectric constant increases. Will be higher. The ratio of the flow rate of SiH _{4 to} the sum of the flow rates of SiF ₄ and SiH ₄ is preferably 40% to 70%.

Embodiment 3 FIG. Next, the relationship between the ratio of the flow rate of SiH _{4 to} the sum of the flow rates of the reaction gas, and the OH group concentration and the fluorine concentration was examined. Using the same ECR plasma CVD apparatus as in the first embodiment, SiH ₄ and SiF
_The SiOF film was formed by changing the flow rate of Step ₄
The OH group concentration and the fluorine concentration of the OF film were measured.
The conditions other than the flow rates of SiH ₄ and SiF ₄ are the same as those in the first embodiment.
The description is omitted. FIG. 3 is a graph showing the measurement results, and the horizontal axis represents the flow rate SiH ₄ / (SiF ₄ + Si).
H ₄ ), and the vertical axis indicates the OH group concentration and the fluorine concentration. From the graph, it can be seen that the flow rate of SiH ₄ is 4
In the case of 0% to 70%, the OH group concentration is 1.3% or more and 1.4% or more.
% And the fluorine concentration is 6.7% or more and 8.0% or less. The SiOF films having these concentrations are described in Embodiment 2.
As described above, it can be said that the relative dielectric constant is small and the charge density in the film is small.

In the above embodiment, silicon tetrafluoride gas (SiF ₄ ) and monosilane gas (SiH ₄ )
Is described, but the present invention is not limited to this, and SiHF ₃ , SiH ₂ F ₂ , SiH ₃ F, and Si
By using the silicon fluoride-based gas and a silane derivative gases such as disilane, such as ₂ F _6, the same effect.

The flow rates of SiF ₄ and SiH ₄ are not limited to the values in the above-described embodiment, and flow rates SiH ₄ / (SiF _4
4 + SiH ₄ ) may be in the range of 40% to 70%.

[0029]

As described above, in the present invention, by supplying a silane-based gas during the supply of a silicon fluoride-based gas, an increase in hydroxyl groups is suppressed, the relative dielectric constant is reduced, and the film charge density is reduced. Therefore, the electrical characteristics of the underlying layer of the insulating film do not deteriorate. Further, the present invention has excellent effects such as an improved film forming rate and good moisture absorption.

[Brief description of the drawings]

FIG. 1 shows an ECR plasma CVD used in practicing the present invention.
FIG. 2 is a schematic longitudinal sectional view showing the structure of the device.

FIG. 2 is a graph showing the relationship between the ratio of the flow rate of SiH _{4 to} the sum of the flow rates of reaction gases, the charge density in the film, and the relative dielectric constant.

FIG. 3 is a graph showing the relationship between the ratio of the flow rate of SiH _{4 to} the sum of the flow rates of the reaction gas, and the OH group concentration and the fluorine concentration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma generation chamber 1b Microwave introduction port 2 Reaction chamber 3 Microwave waveguide 5 Sample stand 6 First gas introduction system 7 Second gas introduction system

Claims (3)

[Claims] An electron cyclotron resonance plasma CVD method using a silicon fluoride-based gas and a silane-based gas has a fluorine content of 6.7 atomic% to 8.8 atomic%.
0 atomic%, and the hydroxyl group content is 1.3 atomic% or more.
A semiconductor device comprising a 1.4 atomic% silicon insulating film. 2. Electron cyclotron resonance plasma CVD
A method for manufacturing a semiconductor device, comprising forming a fluorine-containing silicon insulating film using a silicon fluoride-based gas and a silane-based gas by a method. 3. SiF ₄ is added to the silicon fluoride-based gas.
SiH ₄ is used as the silane-based gas, and SiF ₄ and SiH ₄ are used.
₄ the flow rate ratio of SiH ₄ to the sum of the flow rate of 40%
3. The method for manufacturing a semiconductor device according to claim 2, wherein the ratio is set to 70%.