JP2895981B2 - Silicon oxide film forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma CVD apparatus used for forming a thin film in a semiconductor manufacturing process, wherein a microwave plasma generating section utilizing electron cyclotron resonance and a plasma space of the microwave plasma generating section are formed. A microwave plasma CVD apparatus comprising a plasma chamber to be processed and a reaction chamber containing a stage on which a wafer to be processed is placed and communicating through an opening of the plasma chamber is used to supply oxygen gas to the plasma chamber and to perform a reaction. The present invention relates to a method for forming a silicon oxide film when a silane gas is supplied to a chamber to form a silicon oxide film on the surface of a wafer to be processed.

[0002]

2. Description of the Related Art Conventionally, for forming an interlayer insulating film or the like in a semiconductor manufacturing process, as shown in FIG. 5, a wafer stage 3 on which a wafer 31 is mounted is used as a ground electrode, and is formed facing the ground electrode. A shower electrode 4 having a large number of pores for supplying a mixed gas of, for example, O ₂ and SiH ₄ as a raw material gas for a film is arranged, and a high-frequency voltage is applied to the shower electrode 4.
RF plasma C that forms a plasma by generating plasma between
The VD method is used.

In such an apparatus, the source gas pressure for forming a stable plasma is increased, so that the reaction in the gas phase proceeds and it is impossible to form a dense film. The necessary film quality is obtained by reducing the substantial partial pressure of the reaction gas as a diluent gas for the source gas. However, this has led to a decrease in the productivity of the apparatus. Further, there is a disadvantage that a large amount of gas that does not substantially contribute to production is consumed.

In view of the above, attempts have recently been made to utilize microwave plasma that can be made into plasma even at low pressure.

[0005] As an apparatus for utilizing a microwave to convert a gas into a plasma, a microwave plasma generator using electron cyclotron resonance, a plasma chamber forming a plasma space of the microwave plasma generator, and an opening of the plasma chamber are provided. Microwave plasma C comprising a reaction chamber containing a stage on which a wafer to be processed is mounted, which is communicated through the section.
The development of the VD device is being actively pursued. This device consists of a microwave plasma generator, a cylindrical microwave resonator with a vacuum sealing window on one end face and a plasma lead-out opening on the other end face, and an electron cyclotron. A coil for generating resonance, which generally encloses a microwave resonator concentrically, and arranges the coil so that the geometric center of the coil is located on the atmosphere side with respect to the vacuum sealing window and oxygen gas A supply port is arranged on the end face of the microwave resonator on the vacuum sealing window side, and several mtorr
Enables the formation of high-density plasma at low pressure, effectively generates accelerated electrons, oxygen ions and neutral oxygen atoms, and communicates through the opening of the microwave resonator (hereinafter also referred to as a plasma chamber). In the reaction chamber, the wafer is arranged so as to be perpendicular to the straight line extending from the center of the vacuum sealing window toward the center of the opening, and the gas density reaching the wafer surface downstream of the plasma generation unit is substantially uniform. The silane gas is supplied in the direction as follows, and the silane gas is dissociated and activated by accelerated electrons in the plasma moving into the reaction chamber from the plasma outlet of the microwave resonator, and the above-mentioned oxygen which uniformly irradiates the wafer surface It is intended to cause a surface reaction effectively between atoms and ions and the wafer surface to form a high quality oxide film.

[0006]

However, even when the film is formed at such a low pressure, silane gas (SiH ₄ ) is present in the formed silicon oxide film (hereinafter referred to as SiO ₂ film). ) Contains a large amount of H, and there is a problem that a sufficiently dense film cannot be obtained.

It is an object of the present invention to provide a fuel cell having a low H content,
To provide a SiO ₂ film forming method SiO ₂ film having high denseness is obtained.

[0008]

According to the present invention, there is provided a microwave plasma generating unit utilizing electron cyclotron resonance, and a plasma chamber forming a plasma space of the microwave plasma generating unit. An oxygen gas is supplied to the plasma chamber and a silane gas is supplied to the reaction chamber using a microwave plasma CVD apparatus comprising a reaction chamber including a stage on which a wafer to be processed is placed, the reaction chamber communicating with the plasma chamber through an opening. The method of forming a silicon oxide film on the surface of a wafer to be processed by supplying a microwave power to a flow rate of an oxygen gas when a microwave is injected into a plasma chamber to convert the oxygen gas into plasma. Is set to 15 to 40 W / SCCM, and the flow rate of silane gas supplied to the reaction chamber is set to 0.8 of the flow rate of oxygen gas supplied to the plasma chamber. The SiO ₂ film is formed as 1.1, Si and supplying a high-frequency bias power to the processed wafer
When forming the O ₂ film, the ratio of the product of the microwave power and the high frequency bias power to the oxygen gas flow rate is set to 4 × 10
^It is assumed that the SiO ₂ film is formed at ⁴ W ² / SCCM or less.

[0009]

The present invention has been made based on the following phenomenon analysis during film formation.

In a microwave plasma CVD apparatus utilizing electron cyclotron resonance, a plasma generator, a wafer position,
At the gas supply position, the electrons are accelerated while rotating around the lines of magnetic force by the microwave electric field and the coil magnetic field component orthogonal thereto, have high energy, and effectively ionize and dissociate the oxygen gas. The electrons are rotating in a manner constrained by the magnetic field lines formed by the coil, and are accelerated in a diverging direction (a direction from the vacuum sealing window toward the opening) by interaction with the magnetic field formed by the coil. Because of its intrinsic properties, the plasma maintains its electrical neutrality, so that ions are also accelerated in the direction of electron movement and the plasma is transported in the direction of divergence of the magnetic field (ambipolar diffusion).

When the plasma formation pressure is kept low at several mtorr, electrons are restrained by the lines of magnetic force formed by the coil.
As a result, the range to reach the wafer or the vessel wall is long and has a sufficient probability of collision with molecules and atoms, but ions are only bipolar diffusion that can not follow the microwave electric field,
Further, since neutral atoms and molecules are only thermal motions, the probability of collision between reactive radicals until they reach the wafer or the vessel wall is extremely small, and the reaction in space can be ignored.
Therefore, only the action with electrons needs to be considered for the space reaction system, and only the reaction between products in space needs to be considered for the surface reaction system.

Focusing on the reaction in the plasma chamber, the amount of generated radicals and the energy level are determined by the ratio of microwave power to oxygen gas. That is, when the microwave power for the supplied oxygen gas increases, the density of the plasma increases, and the amount of oxygen radicals increases. At the same time, the acceleration energy of electrons from collision to collision increases, and the activation level of oxygen increases. Also, the degree of dissociation of silane increases with the density of plasma, but when the energy of electrons increases, silane radicals of hydrogen poor relatively form. As a result, the number of reactive species reaching the wafer surface increases with an increase in microwave power, and the deposition rate increases. However, if the dissociation rate of oxygen is too high compared to the dissociation rate of silane, the reactive species reaching the wafer surface will be in an excess state of oxygen radicals, and the oxygen-hydrogen bond (-OH ) Will be promoted. The —OH group is released as H ₂ O out of the film over a long period of time or when the temperature rises, and this is not preferable because it causes unstable characteristics of the film. Therefore, in order to obtain good film quality, there is a certain ratio relationship between the magnitude of the microwave power to the oxygen gas amount and the flow rate of the silane gas.

In the case where an oxide film is used as an insulating layer of an aluminum wiring or the like, radicals fly from the entire plasma space on the wiring and on the edge, but the width of the space and the width of the wiring are in the space. Since only radicals fly from the space within the solid angle of the opening determined by the height, the film forming speed in the space becomes slower than the film forming speed on the wiring and the edge. In severe cases, a cavity is formed. In order to prevent this, a favorable coverage shape can be obtained by applying a bias to the wafer and forming a film while shaving the film on the wiring and the edge portion, particularly the edge portion, by sputtering by ion bombardment with high energy. .

The ions at this time are mainly oxygen ions, and an excessive bias causes an excessive supply of active oxygen, resulting in -O
This leads to deterioration of film quality due to promotion of generation of H groups. In other words, the sputtering action by ions (the number of molecules jumping out per collision ion) is related to the energy of ions, which is proportional to the square of the energy in the low energy region, proportional to the first energy in the medium energy region, Is proportional to the half power of the energy. Further, the bias voltage is proportional to the high frequency bias power (hereinafter referred to as RF power) applied to the stage and inversely proportional to the plasma density. Therefore, in order to obtain good film quality, there is a certain ratio relationship between the microwave power and the RF power with respect to the gas flow rate.

Therefore, the present inventors focused on the above-mentioned ratio relationship, and conducted experiments to inject microwave into the plasma chamber to convert oxygen gas into plasma regardless of whether high-frequency bias power was supplied to the wafer to be processed. In this case, the value of the microwave power with respect to the flow rate of the oxygen gas is set to 15 to 40 W / SCCM, and the flow rate of the silane gas supplied to the reaction chamber is set to 0.8 to 1.1 times the flow rate of the oxygen gas supplied to the plasma chamber.
_When the SiO ₂ film is formed by forming _two films and supplying a high frequency bias power to the wafer to be processed, the ratio of the product of the microwave power and the high frequency bias power to the oxygen gas flow rate is 4 × 10 ⁴ W ² It has been confirmed that if a SiO ₂ film is formed at a ratio of / SCCM or less, a high-quality film with a small number of —OH groups and a small residual stress after annealing can be obtained.

[0016]

FIG. 1 shows an example of the configuration of a microwave plasma CVD apparatus to which a method for forming an SiO ₂ film according to the present invention is applied. In the figure, reference numeral 1 denotes a reaction chamber, which includes a wafer stage 3 on which a wafer 31 is set. The wafer 31 is loaded and unloaded by a transfer mechanism (not shown) from a wafer transfer port 32 that can be opened and closed by the gate valve 15. The gas supply port 41 is connected to a gas supply system (not shown), and silane gas is supplied.

A plasma chamber 2 is hermetically connected to a side of the reaction chamber 1 facing the wafer stage 3. The plasma chamber 2 is connected with a waveguide 7 for supplying microwave power through a microwave window 21 also used for vacuum sealing.
The coil 8 is arranged so that its geometric center is located closer to the atmosphere than the vacuum-side end face of the microwave window 21. Reference numeral 42 denotes a gas supply port to which oxygen gas is supplied from a gas supply system (not shown). The exhaust port 16 is connected to an exhaust system (not shown) to maintain the pressures in the plasma chamber 2 and the reaction chamber 1 at predetermined values. Also, the wafer stage 3
Is supplied from the power supply 9 via the capacitor 91.

Table 1 shows an example of data relating to the correlation between the residual stress of the SiO ₂ film, the microwave power, and the gas flow rate when the current flowing through the coil 8 is constant.

[0019]

[Table 1] ○ Compressive stress immediately after film formation / after annealing, × Compressive stress immediately after film formation, tensile stress after annealing.

As a result of a characteristic check by a detailed experiment based on this table, characteristics as shown in FIGS. 2 and 3 were obtained.
The characteristics shown in FIG. 2 were obtained while keeping the flow rate ratio between the silane gas and the O ₂ gas constant. As a result, (1) The value of the microwave power with respect to the oxygen gas flow rate is 15 to
40W / SCCM (2) The value of silane gas flow rate with respect to oxygen gas flow rate should be 0.8 ~
1.1 times was found to be good.

[0021] Figure 4 shows the change in residual stress of the microwave power and RF power and by oxide film when fixing the gas flow rate and the ratio, SiO ₂ film was formed by supplying an RF power to the wafer stage I have. As a result of a similar experiment in which the gas flow rate and its ratio were changed, (3) (microwave power) × (RF
It was found that the value of (power) is preferably 4 × 10 ⁴ W ² / SCCM or less.

[0022]

According to the present invention, high-density oxygen plasma is obtained in a low pressure region of several mtorr using microwave plasma, and silane gas is dissociated by accelerated electrons in the plasma.
The spatial reaction is mainly radical generation only, the inter-radical reaction is performed on the wafer surface, and the relationship between the gas flow rate and the microwave power and the RF power, which are the plasma control factors, for controlling the radical density ratio. Reveals. As a result, (1) the gas phase reaction in space becomes only radical generation,
A dense film can be formed. (2) Since the gas phase reaction in space is only radical generation,
A high deposition rate can be obtained.

In the method of the present invention, as a method of forming a SiO ₂ film by converting a raw material gas into plasma, an apparatus capable of forming a stable plasma under a low pressure in which a plasma generation space and a reaction space are separated. And a gas having a different element constituting the SiO ₂ film is introduced into each space, and S
Because the iO ₂ film is formed, the two spaces are not separated
Compared with (for example, FIG. 5), (1) the radical shape and the ion acceleration can be controlled independently of each other, so that the coverage shape control becomes easy. (2) The film can be formed using oxygen gas and silane 100% gas, and does not require a carrier gas, and is economical. Etc.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration example of a microwave plasma CVD apparatus to which an SiO ₂ film forming method according to the present invention is applied.

FIG. 2 is an O ₂ gas flow rate-microwave power characteristic diagram obtained by an experiment using the microwave plasma CVD apparatus having the configuration shown in FIG.

FIG. 3 is a diagram showing a relationship between a gas flow ratio and a microwave power for reducing residual stress in an SiO ₂ film to zero, obtained by an experiment using a microwave plasma CVD apparatus having a configuration shown in FIG. 1;

FIG. 4 shows the relationship between microwave power and RF power when an RF power is supplied to a wafer stage and a SiO ₂ film is formed by using a microwave plasma CVD apparatus having the configuration shown in FIG. Diagram showing changes in residual stress due to electric power

FIG. 5 is a longitudinal sectional view showing an example of a configuration of a conventional SiO ₂ film forming apparatus using plasma.

[Description of Signs] 1 Reaction chamber 2 Plasma chamber 3 Wafer stage 9 RF power supply (high frequency bias power supply) 10 Microwave power supply 31 Wafer stage

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-185979 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 16/00-16/56

Claims (2)

(57) [Claims] 1. A microwave plasma generator using electron cyclotron resonance, a wafer to be processed, which is communicated with a plasma chamber forming a plasma space of the microwave plasma generator through an opening of the plasma chamber. Microwave plasma CV comprising a reaction chamber containing a stage to be moved
A method for forming a silicon oxide film on a surface of a wafer to be processed by supplying oxygen gas to a plasma chamber and supplying silane gas to a reaction chamber using a D apparatus, wherein a microwave is supplied to the plasma chamber. When the oxygen gas is turned into plasma by injecting oxygen, the value of the microwave power with respect to the flow rate of the oxygen gas is set to 15 to 40 W / SCCM, and the flow rate of the silane gas supplied to the reaction chamber is set to 0. A method for forming a silicon oxide film, wherein the thickness is 8 to 1.1 times. 2. A wafer to be processed, which is connected to a microwave plasma generator using electron cyclotron resonance, a plasma chamber forming a plasma space of the microwave plasma generator, and an opening of the plasma chamber. Microwave plasma CV comprising a reaction chamber containing a stage to be moved
A method for forming a silicon oxide film on a surface of a wafer to be processed by supplying an oxygen gas to a plasma chamber and a silane gas to a reaction chamber by using a D apparatus. When forming a silicon oxide film by supplying bias power, the ratio of the product of the microwave power and the high frequency bias power to the oxygen gas flow rate is set to 4 × 10 ⁴ W ² / SCCM or less. Film formation method.