JPH06333853A - Thin film formation - Google Patents

Abstract

PURPOSE:To provide thin film formation method which suppresses particle generation and film quality deterioration due to composition nonuniformity of a compound thin film. CONSTITUTION:High-frequency power modulated to interrupt an original high-frequency signal is supplied between the holder/electrode 6 and the discharge electrode 8 of a plasma CVD device from a high-frequency power source 14. As the material gas 16 for the film formation, two types of gas whose inter- atomic binding energies are the same or almost the same are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film forming method for forming a compound thin film such as a silicon nitride film on the surface of a substrate by a plasma CVD method.

[0002]

2. Description of the Related Art FIG. 1 is a schematic diagram showing an example of a plasma CVD apparatus. This device is a so-called parallel plate type (also known as capacitive coupling type) that uses high frequency discharge,
In a vacuum container 4 which is evacuated by a vacuum exhaust device (not shown), a holder / electrode 6 for holding a substrate 2 on which a film is to be formed and a discharge electrode 8 are housed in opposition to each other. The substrate 2 on the holder / electrode 6 is heated by the heater 10, for example.

The holder / electrode 6 is grounded, and the high frequency power source 1 is connected to the discharge electrode 8 via a matching box 12.
4 is connected, and high frequency power is supplied from the high frequency power supply 14 between the electrodes 6 and 8. This high frequency power is conventionally a continuous sine wave, the frequency of which is usually 13.56 MHz.

In such an apparatus, a required raw material gas (for example, a mixed gas of silane (SiH ₄ ) gas and ammonia (NH ₃ ) gas) is introduced into the vacuum container 4 and the inside of the vacuum container 4 is, for example, several hundreds. When the high frequency power is supplied from the high frequency power supply 14 between the electrodes 6 and 8 while being set to about mTorr, a high frequency discharge occurs between the electrodes 6 and 8 and the source gas 16
Is turned into plasma (18 indicates the plasma), whereby a compound thin film (for example, a silicon nitride film) is formed on the surface of the substrate 2.

The gas species of the raw material gas 16 used in the film formation is conventionally selected only in consideration of whether or not the element contained in the gas molecule is the constituent element of the film to be formed.

According to the above-described film forming method, particles are generated in the vacuum container 4 as the film forming time elapses and adhere to the film formed on the substrate 2 to cause defects in the film. It was a factor. This is the plasma 1
8 contains a radical (active species) that contributes to the formation of a desired thin film and a radical that is unnecessary for film formation and causes particles to be generated. Then, there is no means for suppressing the generation of unnecessary radicals, and therefore the generation of particles cannot be suppressed.

In order to solve such a problem, for example, as shown in FIG. 2, the original high frequency signal (for example, 1
There has been proposed a method of supplying high-frequency electric power, which is obtained by modulating a sine wave signal of 3.56 MHz) which is intermittently applied with a period T, between the electrodes 6 and 8.

When the high frequency power subjected to such intermittent modulation is used, among the radicals generated during the ON period t ₁ of the high frequency power, a radical having a relatively long life (for example, SiH ₃
Radicals) persist during the off period t ₂ , but radicals having a relatively short life (for example, SiH ₂ radicals, SiH radicals) disappear in a short time at the off period t ₂ . This makes it possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals, and suppress generation of particles.

[0009]

However, when the high frequency power subjected to the intermittent modulation as described above is used, the intermittent modulation condition (modulation frequency 1 / T or duty ratio t ₁ / T) is changed every time. , Various properties of the plasma 18 (for example, plasma space potential, ion current, etc.) change intricately,
There is a problem that the composition of the film formed on the substrate 2 changes.

Therefore, it is a main object of the present invention to provide a thin film forming method capable of suppressing the generation of particles and suppressing the deterioration of the film quality due to the composition deviation of the compound thin film.

[0011]

In order to achieve the above object, the first thin film forming method of the present invention is to intermittently interrupt the original high frequency signal between the discharge electrode and the holder / electrode. In addition to supplying modulated high-frequency power, two or more kinds of gases having the same or substantially the same binding energy between atoms are used as a raw material gas for film formation.

The second thin film forming method of the present invention is
A pulsed DC voltage is applied between the discharge electrode and the holder-cum-electrode, and two or more gases having the same or almost the same binding energy between atoms are used as a raw material gas for film formation. It is characterized by using.

[0013]

According to the above method, it is possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals by using high-frequency power that is intermittently modulated.
Generation of particles can be suppressed. By using a DC voltage that is intermittently pulsed, it is possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals by the same effect as when using high-frequency power with intermittent modulation. It is possible to suppress the generation of particles.

Further, by using two or more kinds of gases having the same or substantially the same binding energy between atoms as the raw material gas for film formation, the condition of intermittent modulation of high frequency power or the condition of intermittent DC voltage is changed. By doing so, even if the properties of the plasma such as the space potential and the ion current change, the rate of decomposition and bonding of gas molecules in the plasma approaches a fixed value, and the composition of the compound thin film formed also approaches a fixed value. As a result, it is possible to suppress the deterioration of the film quality due to the composition shift of the compound thin film.

[0015]

EXAMPLE The structure of the plasma CVD apparatus used in this example is the same as that of the apparatus shown in FIG.

Then, the high frequency power source 14 supplies high frequency power, for example, intermittently modulated as shown in FIG. 2, between the holder / electrode 6 and the discharge electrode 8 via the matching box 12. . This makes it possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals by the above-described action, and suppress generation of particles. As a result, it is possible to suppress the occurrence of defects in the thin film formed on the substrate 2.

Further, in this embodiment, two or more kinds of gases to be mixed in the raw material gas 16 are not selected by simply focusing on forming the compound thin film as in the conventional case, but are constituted by the gases. Even if the condition of intermittent modulation of the high frequency power supplied from the high frequency power supply 14 to the electrodes 6 and 8 is changed by selecting in consideration of the bond energy between the existing atoms (dissociation energy if changing the viewpoint). The composition of the compound thin film formed on the substrate 2 is made to approach a constant value.

For example, when a composition of A _m B _n is required as _a film, the film is formed by a plasma CVD method using A _a C _b gas and B _c D _d gas (A to D are elements,
a to d, m and n are the number of atoms). In this case, if the binding energies between A and C and between B and D are the same or substantially equal to each other, various properties such as the spatial potential of the plasma 18 and the ion current are changed by changing the conditions of the intermittent modulation of the high frequency power. Even so, the rate of decomposition and bonding of gas molecules in the plasma 18 approaches a constant value, and thus the composition of the compound thin film formed on the substrate 2 also approaches a constant value. as a result,
It is possible to suppress the deterioration of the film quality due to the composition shift of the compound thin film. Further, even when various conditions of the intermittent modulation of the high frequency power are changed, it is not necessary to set complicated conditions for preventing the composition deviation of the compound thin film each time, so that the rapid film formation is possible.

Next, silicon nitride (Si
A more specific example of forming a ₃ N ₄ ) film will be described. The film forming conditions at this time are as shown in Table 1.

[0020]

[Table 1]

In Table 1, the film forming condition 1 is that the bond energies between atoms are equal to each other according to the present invention.
For the purpose of comparison, the film forming condition 2 uses two kinds of gases having different binding energies between atoms as the raw material gas, which is different from the conventional method. It is equivalent.

Under any of the film forming conditions, the high frequency power is a continuous wave of 13.56 MHz without intermittent modulation, the frequency (1 / T in FIG. 2) is 500 MHz, and the duty ratio (t _{1 in} FIG. 2). / T) was 75% and intermittent modulation was applied, and the experiment was performed under three modulation conditions: a frequency of 500 MHz and a duty ratio of 50%.

Table 2 shows the results of film formation under the above film formation conditions. In Table 2, the particles are the results of measuring the density of particles having a particle diameter of 0.5 μm or more existing on the substrate 2.

[0024]

[Table 2]

As can be seen from Table 2, when the modulation condition is continuous wave, the N / Si composition ratio is 1.2 (ideal value is about 1.3) in both film forming conditions 1 and 2, but it is good. The particle density is 20, which is a very large problem.

The modulation condition is 500 Hz duty ratio 75%
In the case of No. 2, the particle densities are 10 and improved to some extent under the film forming conditions 1 and 2, but in the case of the film forming condition 2, the N / Si composition ratio is 1.0 and compositional deviation occurs. On the other hand, under the film forming condition 1, the N / Si composition ratio is 1.2, and the composition deviation is well suppressed.

The modulation condition is 500 Hz duty ratio 50%
In the case of the film forming conditions 1 and 2, the particle density is 2 which is greatly improved, but in the case of the film forming condition 2, the N / Si composition ratio is 0.9 and a large composition deviation occurs. . On the other hand, under the film forming condition 1, the N / Si composition ratio is 1.2, and the composition deviation is well suppressed.

From the above results, according to the present invention, the generation of particles can be suppressed by intermittently modulating the high frequency power and using two or more kinds of gases having the same or almost the same binding energy between atoms.
It can be seen that the composition shift of the compound thin film can be suppressed.

The method of intermittently modulating the high frequency power is as follows.
Instead of the simple (in other words, single) intermittent modulation as shown in FIG. 2, for example, double modulation as shown in FIG. 3 or triple or more modulation based on the same idea may be applied. . FIG. 3 shows an original high-frequency signal (for example, 13.56M).
(A sine wave signal of Hz), a first modulation for interrupting it at a cycle T ₁ and a second modulation for interrupting it at a cycle T ₂ shorter than the first modulation.

Some plasma CVD methods generate plasma by direct current glow discharge. In this case, a direct current power source is prepared instead of the matching box 12 and the high frequency power source 14 in FIG. The discharge electrode 8 and the holder-cum-electrode 6 are connected, for example, with the former on the positive side. Also in the case of the plasma CVD method using such a DC glow discharge, similarly to the case of the plasma CVD method using the above-mentioned high frequency discharge, it is possible to suppress the generation of particles by intermittently applying the DC voltage, and By using two or more kinds of gases having the same or substantially the same binding energy between atoms, it is possible to suppress the deterioration of the film quality due to the composition deviation of the compound thin film.

That is, when a pulsed DC voltage as shown in FIG. 4 is applied between the electrodes 6 and 8, the lifetime of the radicals generated during the ON period t ₁ of the DC voltage is relatively long. Long-lived radicals persist during the off period t ₂ , but radicals with a relatively short lifetime disappear in a short time at the off-period t ₂ , so preferential generation of radicals contributing to film formation and unnecessary radicals It becomes possible to suppress the generation of particles.

In that case, the characteristics of the plasma 18 (for example, plasma space potential, ion current, etc.) are complicated each time the intermittent condition of the DC voltage (intermittent period T or duty ratio t ₁ / T) is changed. However, there is a problem that the composition of the film formed on the substrate 2 changes, but as the raw material gas 16 for film formation, two or more kinds of gases having the same or almost the same binding energy between atoms are used. Is used, the rate of decomposition and bonding of gas molecules in the plasma 18 approaches a constant value even if the properties of the plasma 18 change by changing the conditions of the intermittent DC voltage.
The composition of the compound thin film formed on the substrate 2 also approaches a constant value. As a result, it is possible to suppress the deterioration of the film quality due to the composition shift of the compound thin film.

[0033]

As described above, according to the present invention, since the high frequency power subjected to the intermittent modulation is used, it is possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals, and to generate particles. Can be suppressed. As a result, it is possible to suppress the occurrence of defects in the film formed on the substrate. By using a DC voltage that is intermittently pulsed, it is possible to preferentially generate radicals that contribute to film formation and suppress unnecessary radicals by the same effect as when using high-frequency power with intermittent modulation. It is possible to suppress the generation of particles.

Further, since two or more kinds of gases having the same or almost the same binding energy between atoms are used as the raw material gas for film formation, the condition of intermittent modulation of high frequency power or the condition of intermittent DC voltage is changed. As a result, the composition of the compound thin film formed on the substrate can be kept close to a constant value even if the properties of plasma change. As a result, it is possible to suppress the deterioration of the film quality due to the composition shift of the compound thin film.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a plasma CVD apparatus.

FIG. 2 is a diagram showing an example of an intermittent waveform of high frequency power.

FIG. 3 is a diagram showing another example of intermittent waveform of high frequency power.

FIG. 4 is a diagram showing an example of a waveform of a DC voltage intermittently pulsed.

[Explanation of symbols]

 2 substrate 4 vacuum container 6 holder and electrode 8 discharge electrode 14 high frequency power supply 16 source gas 18 plasma

Claims (2)

[Claims] 1. A thin film forming method for forming a compound thin film on a surface of a substrate by a plasma CVD method in which plasma is generated by high-frequency discharge between a holder-cum-electrode holding a substrate and a discharge electrode facing the electrode. Between the electrode and the holder / electrode, high-frequency electric power that is modulated to interrupt the original high-frequency signal is supplied, and whether the bond energies between the atoms are the same as the raw material gas for film formation. A method of forming a thin film, which comprises using two or more kinds of gases which are substantially equal to each other. 2. A thin film forming method for forming a compound thin film on the surface of a substrate by a plasma CVD method in which plasma is generated by direct current glow discharge between a holder-cum-electrode holding a substrate and a discharge electrode facing the electrode. A pulsed DC voltage is applied between the discharge electrode and the holder-cum-electrode, and two or more gases having the same or almost the same binding energy between atoms are used as the raw material gas for film formation. A thin film forming method characterized by the above.