METHOD OF IGNITING PLASMA AND PLASMA GENERATING SYSTEM

Abstract

Provided is a method of igniting a plasma to quickly ignite a plasma without causing undesirable arcing. The method of igniting a plasma according to the present invention includes: a supplying step of supplying a process gas into a chamber 1 provided in a plasma generating system; an igniting step of igniting a plasma by irradiating the process gas supplied into the chamber with laser light L emitted from a semiconductor laser 10 and applying a high frequency power to a coil 2 or an electrode 91 for generating plasma provided in the plasma generating system; and a stopping step of stopping emission of the laser light from the semiconductor laser after the plasma is ignited. Preferably, the coil is a cylindrical coil, and in the igniting step, the laser light is obliquely irradiated from above the cylindrical coil toward below the cylindrical coil.

Claims

1. A method of igniting a plasma, comprising: a supplying step of supplying a process gas into a chamber provided in a plasma generating system; an igniting step of igniting a plasma by irradiating the process gas supplied into the chamber with laser light emitted from a semiconductor laser and applying a high frequency power to a coil or an electrode for generating plasma provided in the plasma generating system; and a stopping step of stopping emission of laser light from the semiconductor laser after the plasma is ignited.

2. The method of igniting a plasma according to claim 1, wherein in the igniting step, a high frequency power is started to be applied to the coil or the electrode after irradiation of the laser light is started.

3. The method of igniting a plasma according to claim 1, wherein in the igniting step, the laser light is irradiated near the coil or the electrode.

4. The method of igniting a plasma according to claim 1, wherein the plasma generating system includes a cylindrical coil as the coil, and in the igniting step, the laser light is irradiated at a location upstream of the cylindrical coil.

5. The method of igniting a plasma according to claim 4, wherein in the igniting step, the laser light is irradiated obliquely from above the cylindrical coil toward below the cylindrical coil.

6. The method of igniting a plasma according to claim 1, wherein the laser light has a wavelength in a visible light range.

7. The method of igniting a plasma according to claim 1, wherein the process gas is of at least one of the following gases: Cl.sub.2 gas, O.sub.2 gas, SF.sub.6 gas, CF.sub.4 gas, or C.sub.4F.sub.8 gas.

8. A plasma generating system, comprising: a chamber; a coil or an electrode for generating plasma; a semiconductor laser; and a controller, wherein the controller is capable of executing: a supplying step of supplying a process gas into the chamber; an igniting step of igniting a plasma by irradiating the process gas supplied into the chamber with laser light emitted from a semiconductor laser and applying a high frequency power to the coil or the electrode for generating plasma; and a stopping step of stopping emission of laser light from the semiconductor laser after the plasma is ignited.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is a schematic view illustrating a schematic configuration of a plasma processing system according to an embodiment of the present invention in a partial cross-section view.

[0035] FIG. 2 is a timing chart schematically illustrating a procedure of a supplying step, an igniting step, and a stopping step of a method of igniting a plasma according to an embodiment of the present invention.

[0036] FIGS. 3A and 3B are schematic views illustrating examples of other irradiation directions of laser light in the igniting step.

[0037] FIGS. 4A and 4B are schematic views illustrating schematic configurations of other plasma generating systems to which the method of igniting a plasma according to the present invention is applicable in partial cross-section views.

[0038] FIG. 5 illustrates principal conditions and results of tests associated with examples and comparative examples of the present invention.

DESCRIPTION OF EMBODIMENTS

[0039] With reference to accompanying drawings, a plasma processing system including a plasma generating system according to an embodiment of the present invention and a method of igniting a plasma using the system will now be described.

[0040] FIG. 1 is a schematic view illustrating a schematic configuration of a plasma processing system according to an embodiment of the present invention in a partial cross-section view.

[0041] As illustrated in FIG. 1, a plasma processing system 100 of the present embodiment includes a chamber 1, a coil 2 for generating plasma, a mounting table 3, a semiconductor laser 10, and a controller 20. The plasma generating system of the present embodiment is composed of the chamber 1 (an upper chamber 1a), the coil 2, the semiconductor laser 10, and the controller 20.

[0042] The chamber 1 is composed of the cylindrical upper chamber 1a and a cylindrical lower chamber 1b. A plasma generation space 11 to which process gas is supplied and plasma is generated is provided in the upper chamber 1a, and a plasma processing space 12 in which plasma processing is performed by generated plasma is provided in the lower chamber 1b. At least a portion of the upper chamber 1a through which laser light L emitted from the semiconductor laser 10 passes is formed of a material transparent to the wavelength of the laser light L. In the present embodiment, the entire upper chamber 1a is formed of a transparent material such as quartz.

[0043] The coil 2 is disposed outside the upper chamber 1a so as to surround the plasma generation space 11. The coil 2 of the present embodiment is a cylindrical coil (more specifically, a helical coil). However, the present invention is not limited thereto, and any other forms of coil can be applied, such as a planar coil, a tornado coil used in “Tornado ICP” available from Samco Inc., and a three-dimensional coil used in “Advanced-ICP” available from Panasonic Corporation. When a planar coil is used, the planar coil is disposed above the upper chamber 1a.

[0044] The mounting table 3 is disposed in the plasma processing space 12, and a substrate S to be subjected to plasma processing is mounted on the mounting table 3. The mounting table 3 may be attached to a lifting means (not illustrated) for vertically moving the mounting table 3, or may be fixed to the chamber 1 in a non-liftable manner. The mounting table 3 is provided with a mounting table body 31 formed of metal such as Al, and an electrostatic chuck 32 formed of a dielectric located on the mounting table body 31 and including an embedded electrode (not illustrated) connected to a DC power supply.

[0045] The plasma processing system 100 includes a lifting device 4 passing through the mounting table 3 and configured to vertically move lift pins, which are to come into contact with the bottom face of the substrate S, a high frequency power supply 5 connected to the coil 2 via a matching unit (not illustrated), a high frequency power supply 6 connected to the mounting table 3 (mounting table body 31) via a matching unit (not illustrated), a gas supply source 7, and an exhaust device 8.

[0046] The gas supply source 7 supplies a process gas for generating plasma to the plasma generation space 11. The high frequency power supply 5 applies a high frequency power to the coil 2. This allows the process gas supplied to the plasma generation space 11 to be turned into plasma, and inductively coupled plasma is generated. The high frequency power supply 6 applies a high frequency power to the mounting table body 31 of the mounting table 3. This allows the generated plasma to move toward the substrate S.

[0047] The exhaust device 8 exhausts gas in the chamber 1 to the outside of the chamber 1.

[0048] The substrate S to be subjected to plasma processing is transported from the outside of the chamber 1 into the chamber 1 by a transport mechanism (not illustrated), and mounted on the lift pins projected above the top face (the top face of the electrostatic chuck 32) of the mounting table 3. Subsequently, the lift pins are lowered by the lifting device 4, and thereby the substrate S is mounted on the mounting table 3 (electrostatic chuck 32). Once the plasma processing is completed, the lift pins are raised by the lifting device 4, and the substrate S is raised accordingly. The raised substrate S is to be transported to the outside of the chamber 1 by the transport mechanism.

[0049] The semiconductor laser 10 is disposed outside the upper chamber 1a such that the process gas supplied into the upper chamber 1a is irradiated with emitted laser light L. The semiconductor laser 10 of the present embodiment emits laser light L that has a wavelength in a visible light range (for example, 405 nm). However, the present invention is not limited thereto, and any other semiconductor lasers that emit laser light that has other wavelength such as a wavelength in the ultraviolet light region can be used. Although the semiconductor laser 10 of the present embodiment is of a continuous wave (CW) type, the present invention is not limited thereto, and a semiconductor laser of a pulsed mode type can be used to increase the energy density per unit time.

[0050] The semiconductor laser 10 of the present embodiment is provided with a lens (planar convex lens) disposed on the emission face side of laser light L such that emitted laser light L is to be parallel luminous flux. The laser light L thereby has substantially the same beam spot size throughout the path, and therefore, the process gas in any position is to be irradiated with the laser light L with substantially the same energy density neglecting the energy attenuation of the laser light L on the path.

[0051] The semiconductor laser 10 of the present embodiment is disposed such that the laser light L is irradiated near the coil 2. Specifically, the semiconductor laser 10 is disposed such that the laser light L is irradiated at a location upstream of the coil 2 (in the example illustrated in FIG. 1, the laser light L is upstream of the coil 2 on the left side of FIG. 1). More specifically, the semiconductor laser 10 is disposed such that the laser light L is obliquely irradiated from above the coil 2 toward below the coil 2 (in the example illustrated in FIG. 1, the laser light L is passing above the coil 2 on the left side of FIG. 1 and the laser light L is passing below the coil 2 on the right side of FIG. 1).

[0052] The controller 20 is electrically connected to the high frequency power supply 5, the gas supply source 7, and the semiconductor laser 10 and has a function of controlling the operation thereof. As the controller 20, PLC (Programmable Logic Controller) or a computer can be used.

[0053] Other components and operation of the plasma processing system 100 are similar to a general plasma processing system and therefore the detailed description will be omitted.

[0054] A method of igniting a plasma according to the present embodiment using thus configured plasma processing system 100 (plasma generating system) will now be described.

[0055] The method of igniting a plasma according to the present embodiment includes a supplying step, an igniting step, and a stopping step. The steps will each be described below in this order.

<Supplying Step>

[0056] In the supplying step, the process gas is supplied from the gas supply source 7 into the plasma generation space 11 in the chamber 1 (upper chamber 1a). Specifically, in response to a control signal transmitted from the controller 20, an MFC (Mass Flow Controller) (not illustrated) is controlled, the MFC being provided in a tubing connecting the gas supply source 7 and the chamber 1 and configured to control the flow rate of the process gas. The process gas at a predetermined flow rate is supplied into the chamber 1.

[0057] In the present embodiment, for example, Cl.sub.2 gas is used as the process gas. However, the present invention is not limited thereto, and various types of process gas can be used. In particular, since a highly electronegative gas such as Cl.sub.2 gas, O.sub.2 gas, SF.sub.6 gas, CF.sub.4 gas, or C.sub.4F.sub.8 gas is difficult to be turned into plasma, the method of igniting a plasma according to the present embodiment is effectively applicable.

<Igniting Step>

[0058] In the igniting step, the process gas supplied into the chamber 1 is irradiated with the laser light L emitted from the semiconductor laser 10. Specifically, in response to a control signal transmitted from the controller 20, the power supply of the semiconductor laser 10 is turned on, causing the laser light L to be emitted.

[0059] Further, in the igniting step, a high frequency power is applied from the high frequency power supply 5 to the coil 2. Specifically, in response to a control signal transmitted from the controller 20, the high frequency power supply 5 is turned on, causing a high frequency power to be applied to the coil 2.

[0060] FIG. 2 is a timing chart schematically illustrating a procedure of the supplying step, the igniting step, and the stopping step of the present embodiment.

[0061] As illustrated in FIG. 2, in the igniting step of the present embodiment, after the supplying step is started (after “Process gas supply” illustrated in FIG. 2 is turned “On”), irradiation of the laser light L from the semiconductor laser 10 is started, and thereafter (after “Semiconductor laser” illustrated in FIG. 2 is turned “On”), application of a high frequency power from the high frequency power supply 5 to the coil 2 is started (“High frequency power supply” illustrated in FIG. 2 is turned “On”). Specifically, after time T1 has elapsed since the irradiation of the laser light L was started, the application of the high frequency power to the coil 2 is started. For example, the time T1 is about 0.5 to 1.0 seconds. The irradiation of the laser light L may be started before the supplying step is started.

<Stopping Step>

[0062] In the stopping step, after the plasma is ignited, emission of the laser light L from the semiconductor laser 10 is stopped. Specifically, in response to a control signal transmitted from the controller 20, the power supply of the semiconductor laser 10 is turned off, causing the emission of the laser light L to be stopped.

[0063] As illustrated in FIG. 2, in the present embodiment, period of time T2 from the start of the application of the high frequency power to the coil 2 until the ignition is properly made is determined in advance and the period of time T2 is set and stored in the controller 20. After the start of the application of the high frequency power to the coil 2, the controller 20 transmits a control signal for turning off the power supply of the semiconductor laser 10 at the timing when the set and stored period of time T2 is reached. For example, the period of time T2 is about 2.0 to 3.0 seconds.

[0064] However, the present invention is not limited thereto, and it is possible to adopt stopping the emission of the laser light L after it is determined that plasma has actually been ignited.

[0065] For example, it is conceivable to provide a sensor for detecting the amplitude of a reflected wave signal in an internal circuit or the like of a matching unit (not illustrated) interposed between the high frequency power supply 5 and the coil 2 once a high frequency power is applied to the coil 2, to input an output signal of the sensor to the controller 20, and to determine that ignition is made when the amplitude of the reflected wave signal detected by the controller 20 through the sensor falls to a predetermined value or less. It is also conceivable to provide a spectroscope or the like for detecting the intensity of light generated in the chamber 1, to input the intensity of light detected by the spectroscope or the like to the controller 20, and to determine that ignition is made when the intensity of light detected by the controller 20 reaches a predetermined value or more.

[0066] According to the method of igniting a plasma according to the present embodiment described above, since in the igniting step, the process gas is irradiated with the laser light L emitted from the semiconductor laser 10, and in the stopping step, after the plasma is ignited, the emission of the laser light L from the semiconductor laser 10 is stopped, it is possible to quickly ignite a plasma in the chamber 1 without causing undesirable arcing.

[0067] Further, in the igniting step, the application of the high frequency power to the coil 2 is started after the start of the irradiation of the laser light L. Therefore, when compared to a case in which the irradiation of the laser light L is started after the start of the application of the high frequency power to the coil 2, the possibility of applying a high frequency power to the coil 2 in a state in which plasma is not ignited can be reduced. In this way, it is possible to prevent failure or the like of the plasma processing system 100.

[0068] Further, since in the igniting step, the laser light L is irradiated near the coil 2 where reaction products in the chamber 1 are less likely to remain as deposited film, the possibility that the laser light L is absorbed or scattered by the deposited film is reduced, so that the process gas can be irradiated with the laser light L of a desired intensity.

[0069] Further, since in the igniting step, the laser light L is obliquely irradiated from above the coil 2 toward below the coil 2, it is possible to most quickly ignite a plasma.

[0070] FIGS. 3A and 3B are schematic views illustrating examples of other irradiation directions of the laser light L in the igniting step. FIGS. 3A and 3B each illustrate only near the upper chamber 1a.

[0071] In the example illustrated in FIG. 1, although the description has been made as to a mode in which in the igniting step, the laser light L is obliquely irradiated from above the coil 2 toward below the coil 2, the present invention is not limited thereto. For example, as illustrated in FIG. 3A, it is possible to irradiate the laser light L on a horizontal path passing above the coil 2. Further, as illustrated in FIG. 3B, it is possible to obliquely irradiate the laser light L from below the coil 2 toward above the coil 2.

[0072] FIGS. 4A and 4B are schematic views illustrating schematic configurations of other plasma generating systems to which the method of igniting a plasma according to the present invention is applicable in partial cross-section views.

[0073] In the plasma generating system illustrated in FIG. 4A, plasma generation spaces 11 in two locations (inner plasma generation space 11a and outer plasma generation space 11b) are formed by the upper chamber 1a, and the process gas is supplied to each of the plasma generation spaces 11. The coil is composed of an inner coil 21 and an outer coil 22 disposed in a concentric manner with respect to the coil 21. The process gas supplied to the plasma generation spaces 11 in two locations of the plasma generating system illustrated in FIG. 4A is irradiated with the laser light L, each beam of which is emitted from two semiconductor lasers 10.

[0074] As with FIG. 1, although in FIG. 4A, the illustration has been made as to a mode in which the laser light L is obliquely irradiated from above the coil 21 or 22 toward below the coil 21 or 22, the present invention is not limited thereto. As with FIG. 3A, it is possible to irradiate the laser light L on a horizontal path passing above the coil 21 or 22. Further, as with FIG. 3B, it is possible to obliquely irradiate the laser light L from below the coil 21 or 22 toward above the coil 21 or 22. Further, in FIG. 4A, a semiconductor laser 10 for irradiating the laser light L to the inner plasma generation space 11a and another semiconductor laser 10 for irradiating the laser light L to the outer plasma generation space 11b are disposed, and it is preferable to dispose two or more semiconductor lasers 10 depending on the number of plasma generation spaces 11 in this way in order to increase margin for plasma ignition. However, the inner plasma generation space 11a and the outer plasma generation space 11b are in communication with each other, and therefore, the plasma is to be dispersed between the plasma generation spaces 11. Accordingly, it is still possible to quickly ignite a plasma with a configuration in which only a semiconductor laser 10 for irradiating the laser light L to the inner plasma generation space 11a is disposed, or a configuration in which only a semiconductor laser 10 for irradiating the laser light L to the outer plasma generation space 11b is disposed. Further, the plasma generating system may not necessarily have the inner plasma generation space 11a illustrated in FIG. 4A and may have only the outer plasma generation space 11b.

[0075] The plasma generating system illustrated in FIG. 4B is a parallel-plate plasma generating system including a shower head-type upper electrode 91 provided with a number of holes for passing the process gas and a lower electrode 92 on which the substrate S is mounted, the electrodes being disposed in parallel with each other. Applying a high frequency power to the upper electrode 91 of the plasma generating system causes capacitively coupled plasma to be generated in the plasma generation space 11. In the case of the plasma generating system illustrated in FIG. 4B, the process gas supplied to the plasma generation space 11 is irradiated with the laser light L emitted from the semiconductor laser 10.

[0076] In the example illustrated in FIG. 4B, although illustration has been made as to a mode in which the laser light L is irradiated on a horizontal path passing between the upper electrode 91 and the lower electrode 92, this is not necessarily a limitation, and the irradiation may be made on a path from above the upper electrode 91 toward below the upper electrode 91 if it is possible in view of equipment.

[0077] Examples and comparative examples of the present invention will now be described.

[0078] Tests for evaluating time taken to ignite a plasma was conducted by using the plasma generating system and the irradiation direction of the laser light L illustrated in FIG. 1 and FIG. 3A for Examples 1 to 8, while conditions such as gas flow rate, pressure in the chamber 1, and power density of a high frequency power applied to the coil 2 were changed. In all test cases, Cl.sub.2 gas was used for the process gas. For the semiconductor laser 10, a CW (continuous) type semiconductor laser that could emit the laser light L having a wavelength of 405 nm at an optical power of 20 mW. A planar convex lens was disposed on the emission face side of the semiconductor laser 10 used in the tests, which allowed the laser light L that was parallel luminous flux and had a beam spot size of about 2 to 3 mm to be emitted. With the beam spot size of 2 to 3 mm, the irradiance of the laser light L reaches 2.2×10.sup.3 to 5.0×10.sup.3 W/m.sup.2.

[0079] For comparative examples 1 to 8, tests for evaluating time taken to ignite a plasma were conducted without irradiation of the laser light L. The comparative examples 1 to 8 were each conducted under the same conditions as that of Examples 1 to 8, the number of which corresponds to the comparative example, excepting the fact that the laser light L was not irradiated.

[0080] FIG. 5 illustrates principal conditions and results of the tests. In the tests, the condition in the chamber 1 was visually checked, and it was determined that ignition was made when illumination was observed. The period of time from the start of the application of a high frequency power to the coil 2 until the ignition was made was defined for evaluation as time taken for ignition. The “power density of high frequency power” in FIG. 5 refers to “the high frequency power applied to the coil 2” divided by “the surface area of an inner surface of the chamber 1 contacted by the plasma”.

[0081] As illustrated in FIG. 5, in any of Examples 1 to 8, the time taken to ignite a plasma was 1 second or less, and therefore, plasma could be quickly ignited. Further, no undesirable arcing occurred during ignition of plasma. In contrast, in comparative examples 1 to 8, the time taken to ignite a plasma exceeded at least 2 seconds, and therefore, plasma could not be quickly ignited.

[0082] Although all of Examples 1 to 8 took no more than 1 second to ignite a plasma, Examples 1 to 6 (the irradiation direction of the laser light L being illustrated in FIG. 1) ignited the plasma several tenths of a second faster than Examples 7 and 8 (the irradiation direction of the laser light L being illustrated in FIG. 3A). The reason why ignition is likely to be made most quickly in the case of the laser light irradiation direction illustrated in FIG. 1 is assumed to be (a) and (b) below.

[0083] (a) In the case of the irradiation direction of the laser light L illustrated in FIG. 1, since the laser light L is obliquely irradiated from above the coil 2 toward below the coil 2, the laser light L may pass through the center of the coil 2, where it is considered that the strength of the electromagnetic field is at the highest and therefore the generation of plasma is facilitated.

[0084] (b) The energy density of the laser light L reaches the highest on the entry side to the plasma generation space 11. In the case of the irradiation direction of the laser light L illustrated in FIG. 1, since the entry side where the energy density of the laser light L reaches the highest is located upstream of the coil 2, it is considered that the probability of generation of plasma increases because the process gas located in the upper part in the coil 2 is irradiated with the laser light L which has high energy density.

REFERENCE SIGNS LIST

[0085] 1 . . . chamber [0086] 2 . . . coil [0087] 10 . . . semiconductor laser [0088] 20 . . . controller [0089] 91 . . . electrode (upper electrode) [0090] 100 . . . plasma processing system [0091] L . . . laser light