JP2007154224A - Sputtering method and sputtering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering method and a sputtering apparatus capable of preventing the film deposition rate from being changed even when an insulation film is deposited on a wall surface of a vacuum container, and realizing a consistent discharge by one power supply. <P>SOLUTION: In the reactive sputtering method: a plurality of conductive targets consisting of a part of or the whole of components of a thin film to be deposited are arranged in a vacuum container; a gas containing at least a reactive gas is introduced in the vacuum container; plasma is generated in the vacuum container by applying the voltage to at least one target out of the plurality of conductive targets; and an insulation film is deposited thereby. At least one target is set to be the ground potential, and the positive-negative alternately inverting voltage is applied to at least one remaining target. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for forming a thin film by sputtering.

  In the manufacturing process of a semiconductor integrated circuit (hereinafter referred to as “IC”), various dielectric films are formed. The purpose is, for example, an interlayer insulating film, a mask for etching, selective ion implantation and selective electrode formation, passivation, a dielectric film of a capacitor, etc. The material and plasma processing method ( Plasma CVD, dry etching, sputtering, etc.) are selected.

  In recent years, in order to reduce the size of an IC, it has been studied to perform plasma treatment of a high dielectric material such as barium strontium titanate (BST) or strontium titanate (STO) on a dielectric film of a capacitor. Further, plasma processing of ferroelectric materials such as lead zirconate titanate (PZT) and strontium bismastantalate (SBT) has been studied for sensors, actuators, and nonvolatile memory devices.

  A conventional sputtering apparatus will be described with reference to the drawings.

  FIG. 5 is a longitudinal sectional view conceptually showing this.

  In the conventional sputtering apparatus, a sputtering chamber is formed by a vacuum-evacuable container 91, and a conductive target 92 is fixedly held by a lower electrode 93 below the sputtering chamber. Further, on the back surface of the target 92, an inner magnet 94 and an outer magnet 95 having a magnetization component opposite to the inner magnet 94 are arranged so as to surround the inner magnet 94, and both magnets (94 and 95) are magnetically coupled by a yoke 96. ing. The magnets (94 and 95) form arc-shaped magnetic field lines 97 on the surface of the conductive target 92. The lower electrode 93 is electrically insulated from the container 91. The lower electrode 93 incorporates a water cooling mechanism to prevent the temperature of the target 92 from rising, but is not shown.

  A wafer holder 98 is disposed in parallel above the sputtering chamber so as to face the lower electrode 93. The wafer holder 98 is electrically insulated from the container 91 and has a floating potential. Then, a substrate such as a semiconductor wafer 99 is placed on the wafer holder 98. The wafer holder 98 incorporates a heating mechanism for maintaining the wafer 99 at a predetermined temperature, which is not shown. And predetermined DC electric power is given by the power supply 910 between the lower electrode 93 and the container 91 (grounding).

In order to perform a film forming process with this sputtering apparatus, a substrate (for example, a wafer 99) is placed on the wafer holder 98, and is evacuated by a vacuum pump (not shown) connected to an exhaust port (not shown). A variable conductance valve (not shown) interposed between an exhaust port (not shown) and a vacuum pump (not shown) while introducing a predetermined gas (for example, Ar gas and O ₂ gas) containing a reactive gas from the port. (Not shown) is adjusted to a predetermined pressure.

Then, a negative DC voltage is applied to the target to cause glow discharge and generate plasma. The generated electrons in the plasma are trapped by arc-shaped magnetic field lines 97 arranged on the back surface of the target 92 and generated by magnets (94 and 95), further promoting ionization and improving the plasma density. The + ions (eg, Ar ⁺ , O ₂ ^+, etc.) in the generated plasma are attracted to the target by a negative DC voltage, and the constituent atoms of the target are sputtered. The sputtered particles that have jumped out react with the reactive gas in the space to become a compound, reach the substrate, and become a thin film. At that time, the compound not only adheres to the wall surface of the vacuum vessel and the members in the vacuum vessel, but also reattaches to a portion of the target surface that is not sputtered so much.

  In the case where the compound is an insulator, the surface of the insulator reattached to the target 92 is charged up and causes dielectric breakdown. At that time, arc discharge occurs, but the glow discharge shifts to arc discharge starting from the arc discharge, and the arc discharge once shifted does not return to glow discharge. If it becomes so, it will become difficult to perform sputtering film-formation any longer. In order to prevent this, the power source 910 detects the arc discharge and turns off the DC voltage for several microseconds and then applies the DC voltage again. Film formation becomes difficult. Therefore, it is common to release the charged up charge by periodically applying a positive voltage of several tens of volts to the target.

The invention described in Patent Document 1 describes that two targets are sputtered alternately by applying a positive voltage and a negative voltage to two targets and periodically switching them. As a result, one of the targets always becomes the anode, and the charged up charge is removed. Further, since both targets are sputtered, the metal surface is always exposed, so that the discharge is stabilized.
JP 2001-200377 A

  Usually, the negative DC voltage applied to the target is generally controlled so that the product of the flowing current (voltage × current), that is, the power becomes constant. The power, current, and voltage are uniquely determined as long as the discharge impedance (voltage / current ratio) is constant and do not fluctuate. This indicates that the plasma state is constant and the reproducibility such as the deposition rate can be secured. However, in reactive sputtering for forming an insulator, the insulator adheres to the vacuum vessel wall (ground potential) or the like, and the area of the ground potential varies. This indicates that the impedance changes, and even if the electric power is controlled to be constant, the current and voltage change, and the film formation rate also changes.

  Strictly speaking, the capacitor structure is a metal member-attached insulating member-plasma, and has a very large capacity due to its area and film thickness. As the film deposition of the insulator progresses, the film thickness changes, and the capacitance formed inevitably varies. This also causes impedance fluctuations and changes the deposition rate.

FIG. 6 shows the transition of the discharge current of DC reactive sputtering using a Si target having an outer diameter of 200 mm in a conventional sputtering apparatus and introducing Ar gas and O ₂ gas. It can be seen that the discharge current for 120 minutes after discharge continues to rise.

  From the above, the conventional sputtering method and apparatus have a problem that when the insulating film adheres, the discharge state changes and the deposition rate changes, and high reproducibility cannot be ensured.

  In addition, in order to apply positive and negative voltages to the two targets, two power supplies are required, and there is a problem that the apparatus becomes expensive.

  In view of the above-described conventional problems, the present invention provides a sputtering method and apparatus capable of performing stable discharge with a single power source without changing the deposition rate even when an insulating film adheres to the wall of the vacuum vessel. is there.

  The sputtering apparatus according to the first aspect of the present invention includes a vacuum vessel, a target holder that is placed in the vacuum vessel and on which a plurality of conductive targets are placed, and a gas that introduces a gas containing a reactive gas into the vacuum vessel. A sputtering apparatus comprising: an introduction unit; a gas exhaust unit that exhausts gas in the vacuum vessel; and a power source that applies a voltage capable of alternately reversing positive and negative to at least one of the plurality of target holders, At least one of the plurality of target holders is set to a ground potential, and the inner wall surface of the vacuum vessel is covered with an inner vessel having a floating potential.

  At this time, it is preferable that the waveform of the voltage that is alternately inverted between positive and negative is a rectangular wave.

  More preferably, the frequency of the voltage that alternates between positive and negative is preferably 1 MHz or less.

  More preferably, it is desirable that all the conductive members surrounding the plurality of conductive targets in the vacuum vessel have a floating potential.

  More preferably, it is desirable to insert a fixed capacitor of 1 pF to 1 μF between the floating potential member and the ground potential.

  Further, the sputtering method of the second invention of the present application is such that gas is introduced into the vacuum vessel and exhausted, and positive and negative are alternately placed on at least one of the target holders arranged in the vacuum vessel and mounting a plurality of conductive targets, respectively. A sputtering method for generating a plasma in a vacuum vessel by applying a reversible voltage to the substrate to process a substrate, wherein at least one of the plurality of target holders is set to a ground potential, and the inside of the vacuum vessel The wall surface has a structure covered with an inner container having a floating potential.

  At this time, it is preferable that the waveform of the voltage that is alternately inverted between positive and negative is a rectangular wave.

  More preferably, the frequency of the voltage that alternates between positive and negative is preferably 1 MHz or less.

  More preferably, it is desirable that all the conductive members surrounding the plurality of conductive targets in the vacuum vessel have a floating potential.

  More preferably, it is desirable to insert a fixed capacitor of 1 pF to 1 μF between the floating potential member and the ground potential.

  Even if an insulating film adheres to the vacuum vessel wall surface, the deposition rate does not change, and a sputtering apparatus and method capable of stable discharge with a single power source can be provided.

(Embodiment 1)
FIG. 1 shows a first embodiment of the present invention.

This is an example of a DC reactive magnetron sputtering apparatus in which a substrate 99 (this time using a Si substrate) is placed in a vacuum vessel 91 and a SiO ₂ thin film as a dielectric is formed by sputtering. A target 11b and a lower electrode 12b having an outer diameter of 100 mm were disposed at the lower part of the vacuum vessel 91, and a donut-shaped target 11a and a donut-shaped lower electrode 12a having an outer periphery of 200 mm and an inner periphery of 110 mm were disposed on the outer periphery thereof.

  As the target 11b and the doughnut-shaped target 11a, a material made of an element constituting a desired insulating film or a material capable of forming a desired insulator by reacting with a reactive gas is preferable. Using. Si is a single crystal, doped with B in order to obtain conductivity and having a resistivity of 0.01 Ω · cm. A pair of magnets 16a and 16b (16a and 16b have opposite magnetization characteristics) are disposed on the back surfaces of the target 11b and the lower electrode 12b and are magnetically coupled via the yoke 14b. Arc-shaped magnetic field lines 97 are formed on the surface of 11b.

  Also, ring-shaped magnets 15a, 15b, and 15c are arranged on the back surfaces of the donut-shaped target 11a and the donut-shaped lower electrode 12a, and 15a and 15c have the same magnetization direction, and 15b is opposite to 15a and 15c. Have the magnetization. These magnets 15a, 15b and 15c are magnetically coupled via a donut-shaped yoke 14a. As a result, arc-shaped magnetic field lines 97 are formed on the donut-shaped target 11a. The space inside the vacuum vessel 91 is covered with the inner vessel 13 which is a floating potential and has a double structure.

  The inner container 13 was made of stainless steel, and the surface was blasted so that no insulating film adhered. A substrate holding mechanism 98 capable of arranging the substrate 99 is provided on the upper part of the vacuum vessel 91, and the distance between the target 92 and the substrate 99 is set to 60 mm. The substrate holding mechanism 98 is also made of stainless steel and is insulated from the vacuum vessel 91 and has a floating potential.

The targets 11a and 11b were already sputtered for about 2 hours, the erosion part was exposed with the Si surface, and the non-erosion part was used with SiO ₂ reattached. The inside of the vacuum vessel 91 was evacuated to a pressure of 8 × 10 ⁻⁴ Pa by a turbo molecular pump (not shown) and a rotary pump (not shown). Next, Ar gas and O ₂ gas (Ar / O ₂ flow rate = 100 sccm / 100 sccm) are introduced into the vacuum vessel 91, and the internal pressure of the vacuum vessel 91 is set to 0.3 Pa (glow discharge) using a conductance valve (not shown). Is sufficient if the pressure can be maintained). The doughnut-shaped lower electrode 12a was set to the ground potential, and a rectangular wave voltage of ± 300 V, frequency 40 kHz, duty ratio 1: 1 was applied to the lower electrode 12b by the power source 910. The time change of the discharge current at that time is shown in FIG. Although the initial stage of discharge changed, there was almost no change in the discharge current for 10 minutes after 10 minutes from the start of discharge, and stable discharge was realized. Furthermore, arc discharge during this period was also suppressed.

  From the above results, even when an insulating film adheres to the vacuum vessel wall surface, the deposition rate does not change, and stable discharge can be performed with one power source.

(Embodiment 2)
FIG. 3 shows a second embodiment of the present invention.

As in the first embodiment, this is an example of a DC reactive magnetron sputtering apparatus in which a substrate 99 (this time using a Si substrate) is put into a vacuum vessel 91 and a SiO ₂ thin film as a dielectric is formed by sputtering. is there. The difference from the first embodiment is that a fixed capacitor 31 of 30 pF is inserted between the inner container 13 which is a floating potential and the vacuum container 91 which is a ground potential. The capacitance of the capacitor 31 may be between 1 pF and 1 μF. Although the fixed capacitor 31 is inserted this time, the same effect can be obtained even if it is realized by filling the space between the vacuum vessel 91 and the inner vessel 13 with an insulating member such as Teflon (registered trademark).

The inner container 13 is made of stainless steel as in the first embodiment, the surface is blasted, and no insulating film is attached. The targets 11a and 11b were also sputtered for about 2 hours, the erosion part was exposed with the Si surface, and the non-erosion part was re-attached with SiO ₂ . The inside of the vacuum vessel 91 was evacuated to a pressure of 8 × 10 ⁻⁴ Pa by a turbo molecular pump (not shown) and a rotary pump (not shown). Next, Ar gas and O ₂ gas (Ar / O ₂ flow rate = 100 sccm / 100 sccm) are introduced into the vacuum vessel 91, and the internal pressure of the vacuum vessel 91 is set to 0.3 Pa (glow discharge) using a conductance valve (not shown). Is sufficient if the pressure can be maintained).

  The doughnut-shaped lower electrode 12a was set to the ground potential, and a rectangular wave voltage of ± 300 V, frequency 40 kHz, duty ratio 1: 1 was applied to the lower electrode 12b by the power source 910. The time change of the discharge current at that time is shown in FIG. Although the initial stage of the discharge changed, there was almost no change in the discharge current for 10 minutes after 10 minutes from the start of discharge, and a more stable discharge than that in the first embodiment was realized. Furthermore, arc discharge during this period was also suppressed.

  From the above results, even when an insulating film adheres to the vacuum vessel wall surface, the deposition rate does not change, and stable discharge can be performed with one power source.

  The sputtering method and apparatus according to the present invention are useful as a method for forming an insulating film in a semiconductor device such as an LSI or a dielectric film in an optical device.

Sectional drawing which showed the structure of the magnetron sputtering apparatus used in the 1st Embodiment of this invention The figure which shows transition of the discharge current in the 1st Embodiment of this invention Sectional drawing which showed the structure of the magnetron sputtering apparatus used in the 2nd Embodiment of this invention The figure which shows transition of the discharge current in the 1st Embodiment of this invention Sectional drawing showing the configuration of the magnetron sputtering device used in the conventional example Diagram showing transition of discharge current in conventional example

Explanation of symbols

91 Vacuum vessel 11b, 92 Target 11a Donut-shaped target 12b, 93 Lower electrode 12a Donut-shaped lower electrode 15a, 15b, 15c, 16a, 16b, 94, 95 Magnet 14a, 14b, 96 Yoke 31 Fixed capacitor 97 Arc-shaped magnetic field line 98 Substrate holding Mechanism 99 Substrate 910 Power supply

Claims (10)

A vacuum vessel, a target holder disposed in the vacuum vessel and mounting a plurality of conductive targets, gas introduction means for introducing a gas containing a reactive gas into the vacuum vessel, and gas in the vacuum vessel A sputtering apparatus comprising: a gas exhaust means for exhausting gas; and a power source for applying a voltage capable of reversing positive and negative alternately to at least one of the plurality of target holders, wherein at least one of the plurality of target holders is A sputtering apparatus characterized by having a structure in which a ground potential is provided and an inner wall surface of the vacuum vessel is covered with an inner vessel having a floating potential. The sputtering apparatus according to claim 1, wherein the waveform of the voltage that reverses positive and negative alternately is a rectangular wave. 3. The sputtering apparatus according to claim 1, wherein the frequency of the voltage that alternately reverses positive and negative is 1 MHz or less. The sputtering apparatus according to claim 1, wherein all conductive members surrounding the plurality of conductive targets have a floating potential. The sputtering apparatus according to claim 1, wherein a fixed capacitor of 1 pF to 1 μF is inserted between the floating potential member and the ground potential. The vacuum vessel is evacuated while introducing a gas, and a vacuum is applied by applying a voltage capable of alternately reversing positive and negative to at least one of the target holders placed in the vacuum vessel and mounting a plurality of conductive targets, respectively. A sputtering method for generating a plasma in a container and processing a substrate, wherein at least one of the plurality of target holders is set to a ground potential, and an inner wall surface of the vacuum container is covered with an inner container having a floating potential. A sputtering method characterized by having a structure. The sputtering method according to claim 6, wherein the waveform of the voltage that reverses positive and negative alternately is a rectangular wave. The sputtering method according to claim 6 or 7, wherein the frequency of the voltage that reverses positive and negative alternately is 1 MHz or less. The sputtering method according to claim 6, wherein all the conductive members surrounding the plurality of conductive targets have a floating potential. The sputtering method according to claim 6, wherein a fixed capacitor of 1 pF to 1 μF is inserted between the floating potential member and the ground potential.

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