JPH11172429A - Production of supersmooth film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a film extremely small in surface roughness by executing the discharge of a cathode by using a mechanism in which the vicinity of the cathode is provided with a coil for rf inductive coupling discharge for supporting magnetron discharge under a low discharge pressure. SOLUTION: As the main operations of an rf inductive coil, the promotion of the ionization of sputtering particles and a sputtering gas and the control of the plasma potential between the coil and a substrate are cited. The sputtering particles having a high ionization rate are made incident on the substrate at relatively high kinetic energy, by which the densification and flattening of the film can be attained. The discharge electric powder for the rf inductive coil is preferably regulated to 20 to 65 W. Moreover, in the case a reactive sputtering method is used, it is preferable that the partial pressure of a reaction gas is regulated to 5×10<-3> to 1×10<-2> Pa, and the ion energy of the sputtering particles ionized by rf inductive coupling discharge is regulated to 1.2 to 40 eV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an ultra-smooth film, and more particularly, to maintaining a flat element surface when forming an element pattern having a structure in which a plurality of films are stacked as in a semiconductor process. The present invention relates to a method for producing an ultra-smooth film that can be used for.

[0002]

2. Description of the Related Art It has been known to form an oxide thin film on a substrate by PVD and CVD.

[0003]

The conventional PVD method and C
In a thin film formed on a substrate by the VD method, the morphology (roughness) of the formed film surface is greatly affected by its manufacturing conditions, for example, in the case of a vapor deposition method, the substrate surface temperature at the time of film formation. In the case of the sputtering method, in addition to the influence of the substrate surface temperature at the time of forming a film, the pressure is largely affected by the inert gas pressure at the time of film formation. Further, the form of the surface of the film to be manufactured is affected by the form (roughness) of the surface of the substrate on which the film is deposited. The effect is particularly large when the size of the morphology of the substrate surface is close to the thickness of the film to be formed or when the film is extremely thin. Among these thin film production methods, it is known that the influence of the substrate surface morphology is smaller when the sputtering method is used. This is because the sputtering method is based on a surface evaporation source, and the sputtered particles jumping out of the target are scattered in space before reaching the substrate and are incident on the substrate in a random direction. This is because, even in the case where the surface is opened, the influence of the shadow due to the unevenness of the substrate surface on the obtained thin film is unlikely to occur.

[0004] Even when the target film has a nanometer-scale surface roughness, it is often the case that the surface roughness of the substrate to be used is larger than that.

In the prior art, if the surface roughness of a film to be formed is made smaller than that of a substrate surface or if a thin film element is formed on a substrate and a surface step is generated by the element, the step on the element is eliminated. The upper film is formed (for planarization: for the purpose of forming a three-dimensional device, etc.)
For this purpose, a bias film forming method in which the substrate holder has an electrode structure so that a potential can be applied to the substrate surface during film formation has been used. In this case, the power applied to the substrate is often rf power, and the substrate holder at this time must have a complicated cathode structure so that rf discharge can be performed stably and must not adjust the cathode impedance. There is a problem that it does not. Further, when a potential is applied, damages such as structural defects, film crystallinity deterioration, film composition change, and film internal stress increase occur in the film deposited on the substrate during film formation. In some cases, it can cause process constraints. Conversely, applying a potential to the substrate may improve various characteristics of the film. That is, by applying an electric potential to the substrate on which the film is deposited, energy for depositing the film material particles on the substrate can be added, and a dense film can be formed or the crystal orientation of the film can be controlled. Although it can be done, the system configuration is complicated, resulting in an expensive system. In addition, since the number of deposition parameters increases, their control becomes very difficult.

In the conventional sputtering apparatus and method,
At a sputtering pressure of about 1 × 10 ⁻¹ Pa or less, the discharge becomes unstable. Therefore, in order to perform stable film formation, the pressure must be increased to a higher pressure. As a result, the sputtered film material is scattered. As a result, the deposition rate becomes extremely slow. In order to avoid such a problem, it is conceivable to bring the substrate and the target close to each other, but in this case, a problem of substrate damage such that the substrate is susceptible to plasma damage occurs.
Devices and methods for stabilizing discharge in an environment with a low degree of vacuum have been proposed (Japanese Patent Application Laid-Open Nos. 8-269705 and 8-302264).

An object of the present invention is to solve such a problem,
An object of the present invention is to provide a method for producing a smooth film having extremely small surface roughness.

[0008]

According to a manufacturing method of the present invention, in a method of forming an ultra-smooth film on a substrate by a sputtering method, a discharge at a cathode is reduced at a discharge pressure lower than a conventional discharge pressure. This is performed by using a mechanism provided with a coil for rf inductively coupled discharge that supports magnetron discharge in the vicinity to form an ultra-smooth film on the substrate.

R for the rf inductively coupled discharge coil
f Inductively coupled discharge power is generally 20 to 65 W (film surface roughness is 0.9 nm or less), preferably 35 to 50 W.
It is desirable to set it to W (the film surface roughness becomes about 0.8 nm). When the sputtering method is a reactive sputtering method, the partial pressure of the reaction gas at this time is set to 5 ×
The operation is performed at 10 ⁻³ to 1 × 10 ⁻² Pa, and the ion energy of the sputtered particles ionized by the rf inductively coupled discharge is generally about 1.2 to 40 eV (the film surface roughness becomes 0.9 nm or less). , Preferably approximately 1.6 to 2
It is desirably 4.2 eV (the film surface roughness is 0.8 nm or less), and more preferably approximately 3.2 to 12.2 eV (the film surface roughness is 0.6 nm or less). If the partial pressure of the reaction gas is less than 5 × 10 ⁻³ , a film having good insulating properties cannot be obtained, and if it is higher than 1 × 10 ⁻² Pa, the discharge becomes unstable.

[0010] r for assisting discharge near the sputter cathode
By applying power to the rf induction coil during the formation of a film by sputtering using a mechanism provided with an f induction coil (so-called inductively coupled rf plasma-assisted magnetron sputtering method), the degree of vacuum at which the discharge was not conventionally stable By using a low environment, particles sputtered from the target are not scattered by atmospheric gas molecules,
In addition, the energy at the time of jumping out is maintained until it reaches the substrate without being attenuated, and the energy is controlled by the power supplied to the rf induction discharge coil, so that the film is deposited on the substrate. In this method, the surface is flattened while acting as a mechanism for reducing the surface roughness.

The main functions of the rf induction coil used in the present invention are (1) that ionization of sputter particles and sputter gas is promoted, and (2) that the plasma potential between the coil and the substrate can be controlled. The reason (1) is that particles and sputter gas sputtered from the target are excited and ionized by collision with electrons in the plasma when passing through the plasma zone formed by the rf induction coil. In the case (2), in the case of the inductively coupled plasma by the rf induction coil, the energy is more efficiently absorbed from the electric field than in the case of the capacitive plasma from the target (conventional planar magnetron discharge). This is because the potential of the plasma and the potential difference between the plasma and the floating substrate can be easily increased. Therefore, in the method of the present invention, the sputtered particles having a high ionization rate enter the substrate with a relatively high kinetic energy, so that the film can be densified and flattened. According to the method of the present invention, it is considered that the same action as that of the bias film forming method of the prior art is performed.

According to the present invention, it is possible to make the surface roughness of the film smaller than the surface roughness of the substrate, and it is possible to easily realize the formation of the element which cannot be achieved by the conventional method, and to improve the smoothness of the element. Since a simple insulating film has good electric characteristics (that is, a high withstand voltage value and a small leakage current value), it can be effectively used even when an electric insulating film needs to be formed on the surface of a substance.

[0013]

Embodiments of the present invention will be described below. These examples are merely illustrative of the invention and do not limit the invention in any way.

FIG. 1 shows an example of a manufacturing apparatus used in an embodiment of the present invention. In this apparatus, the inside of the film forming chamber 1 is connected to a vacuum evacuation system 2 such as a vacuum pump via an exhaust valve 3 so that the inside of the film forming chamber 1 can be set to a predetermined pressure. The chamber 1 is connected to a gas supply source having a mass flow controller 5 via a gas introduction system 4, and a sputtering gas, for example, an argon (Ar) gas is introduced from the gas introduction system 4.
A substrate 6 for forming a thin film is disposed above the film forming chamber 1, and a target 7 is positioned below the substrate 6 via a cathode 9 having a magnet 8 at a position facing the substrate 6. Is arranged. Power is applied to the cathode from an rf power source 10 to sputter the target 7. Substrate 6
A shutter 11 is provided between the target 7. Further, a rf induction coil 12 made of, for example, Cu is provided above the cathode 9 and at a position where the target material sputtered does not reach the substrate 6. In the device thus configured, the cathode 9
To the target 7 by applying power from the rf power supply 10 and applying power from the induction coil rf power supply 13 to the rf induction coil 12 to support the magnetron discharge of the cathode 9 and stably even under a low pressure. It was made to discharge. In the figure, 14 is an earth shield of the cathode 9, 15 is a matching box of the rf power supply 10, 1
6 is a matching box for the induction coil rf power supply 13, 1
Reference numeral 7 denotes a valve of the gas introduction system 4.

Embodiment 1 (in the case where an alumina film is produced from an alumina target by sputtering with rf power) In this embodiment, sintered alumina (99.9
%), The shape of the cathode 9 is 2 mm in diameter, and a 3-turn rf induction coil 11 made of Cu having an outer diameter of 86 mm and an inner diameter of 76 mm is provided on the cathode, and an Ar gas atmosphere of 8 × 10 ^{-4 is used} as a discharge pressure. Torr, input rf2 to cathode 9
00 W, the substrate temperature during film formation was room temperature, and the distance between the substrate 6 and the target 7 was 200 mm. At this time, the rf power to the rf induction coil 12 was changed between 0 and 100W. The thickness of the produced alumina film was 500 °. A Si wafer was used as a substrate. Substrate surface roughness is Rma
x ± 1 nm was used.

First, the target 7 was placed on the cathode 9, and the substrate 6 was held at a predetermined position in the film forming chamber 1.
The shutter 11 was closed. Next, the deposition chamber 1
After the inside pressure was evacuated by the evacuation system 2, Ar gas was introduced from the gas introduction system 4, and the Ar gas atmosphere pressure in the film forming chamber 1 was set as described above. Subsequently, with the shutter 11 opened, the rf of 200 W is applied to the cathode 9.
Power was applied to perform sputtering, and rf power in the above range was applied to the rf induction coil 12 to support the magnetron discharge by the action of the inductively coupled discharge of the rf induction coil 12. In this way, a film thickness of 50
A 0 ° alumina film was formed. With respect to the alumina film thus formed, a change in film surface roughness due to a change in rf inductive coupling discharge power was examined. The result is shown in FIG. According to the conventional sputtering method, for a substrate having a surface roughness of ± 1 nm, the thickness of the substrate surface becomes the same as the film surface roughness as it is at a film thickness of about 500 °, but extremely thin using the sputtering method of the present invention. When producing a film, an ultra-smooth film having a surface roughness smaller than 1 nm was obtained by controlling the rf inductively coupled discharge power while keeping the discharge pressure at the cathode constant. That is, as shown in FIG. 2, the surface roughness of the film becomes smaller than 1 nm as the rf inductive coupling discharge power is applied and the power is increased, and starts to rise after reaching a certain value. Surface roughness is again 1n
m. 0.9nm at almost 20-65W
A film having the following film surface roughness was obtained, and a film having a surface roughness of about 0.8 nm at approximately 35 to 50 W was obtained.

Example 2 (In the case where an alumina film is produced from an Al target by reactive sputtering with DC power.) In this example, a target made of metallic Al
(99.999%) and the sputtering gas is Ar
A gas was used, and oxygen was used as a reaction gas. In addition, a Cu three-turn coil having an outer diameter of 86 mm and an inner diameter of 76 mm was used as the rf induction coil. Under such conditions, the method described in Example 1 was repeated. However, the DC power applied to the target is kept constant, and the ion energy (eV) of the sputtered particles ionized by the rf inductively coupled discharge and the pressure of the oxygen gas as the reactive gas (5 × 10 ^{−3 to} 9 × 10 ⁻³ Pa) While changing the value of (a), an alumina film having a thickness of 500 ° was formed. The change in film surface roughness of the alumina film thus obtained was examined, and the results are shown in FIG.

As is apparent from FIG. 3, in the case of such reactive film formation, the surface roughness of the obtained film is smaller as the oxygen partial pressure is smaller, and is smaller than 1 nm by controlling the ion energy. A film having a surface roughness was obtained.
That is, as the ion energy increases, the surface roughness of the film becomes smaller than 1 nm, starts to rise after reaching a certain value, and when it exceeds approximately 50 eV, the surface roughness of the film again exceeds 1 nm. A film having a surface roughness of 0.9 nm or less is obtained at approximately 1.2 to 40 eV, a film having a surface roughness of 0.8 nm or less is obtained at approximately 1.6 to 24.2 eV, and approximately 3 to 40 eV. A film having a surface roughness of 0.6 nm or less at 0.2 to 12.2 eV is obtained. If the oxygen partial pressure is smaller than the indicated value, an environment in which oxygen is deficient in the process of depositing the film becomes an environment, and an alumina film having good insulating properties cannot be produced. Was too high, the target surface was oxidized and the discharge was likely to be unstable. When no rf inductively coupled discharge power was applied, the magnetron discharge on the cathode was not stable.

[0019]

According to the present invention, the discharge at the cathode is
At a discharge pressure lower than the conventional discharge pressure, the rf induction coupling discharge coil is used in the vicinity of the cathode to support a magnetron discharge. Because it is done within
A film with a very smooth surface can be produced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an apparatus for performing a manufacturing method according to the present invention.

FIG. 2 is a graph showing the relationship between rf inductively coupled discharge power and film surface roughness for a smooth film obtained by the method of the present invention.

FIG. 3 is a graph showing the relationship between ion energy of sputtered particles and film surface roughness when the pressure of oxygen gas is changed for a smooth film obtained by the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Film-forming chamber 2 Vacuum exhaust system 3 Exhaust valve 4 Gas introduction system 5 Mass flow controller 6 Substrate 7 Target 8 Magnet 9 Cathode 10 rf power supply 11 Shutter 12 rf induction coil 13 Induction coil rf power supply

Claims (3)

[Claims] In a method for producing an ultra-smooth film on a substrate by a sputtering method, a discharge at a cathode is performed by an rf inductively coupled discharge supporting a magnetron discharge near the cathode at a discharge pressure lower than a conventional discharge pressure. A super-smooth film produced on a substrate by using a mechanism provided with a coil for use in a super-smooth film. 2. The method according to claim 1, wherein the rf inductive coupling discharge power for the rf inductive coupling discharge coil is 20 to 65 W. 3. The sputtering method is a reactive sputtering method, wherein a partial pressure of a reaction gas is 5 × 10
^-3 performed as ~1 × 10 ^-2 Pa, claim 1, the ion energy of the ionized sputtered particles by the rf inductive coupling discharge is characterized by a 1.2~40eV
The method for producing an ultra-smooth film according to the above.