(12) United States Patent
`Masuda et al.
`
`US006506686B2
`(io) Patent No.: US 6,506,686 B2
`Jan. 14,2003
`(45) Date of Patent:
`
`(54) PLASMA PROCESSING APPARATUS AND
`PLASMA PROCESSING METHOD
`
`(75)
`
`Inventors: Toshio Masuda, Toride (JP); Kazue
`Takahashi, Kudamatsu (JP); Ryoji
`Fukuyama, Kudamatsu (JP); Tomoyuki
`Tamura, Kudamatsu (JP)
`
`(73) Assignee: Hitachi, Ltd., Tokyo (JP)
`
`( * ) Notice: Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 13 days.
`
`(21) Appl. No.: 09/790,702
`(22) Filed:
`Feb. 23, 2001
`(65)
`Prior Publication Data
`US 2001/0018951 Al Sep. 6, 2001
`(30)
`Foreign Application Priority Data
`Mar. 6, 2000 (JP) .............................................. 2000-065769
`(51)
`Int. Cl.7..................................................... H01L 21/00
`(52) U.S. Cl................. 438/715; 156/345.44; 156/345.46;
`156/345.48; 156/345.49; 216/68; 216/70;
`438/729
`(58) Field of Search ........................... 156/345 P, 345 C,
`156/345 ME, 345 MG, 345 PH; 438/710,
`715, 728, 729, 732; 216/67, 70, 71, 68
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,846,885 A * 12/1998 Kamata et al................... 438/729
`6,251,792 Bl * 6/2001 Collins et al.................... 438/729
`FOREIGN PATENT DOCUMENTS
`* 10/1993
`5-275385
`JP
`8-144072
`*
`JP
`6/1996
`* 12/1999
`11-340149
`JP
`* cited by examiner
`Primary Examiner—-William A. Powell
`(74) Attorney, Agent, or Firm—Antonelli, Terry, Stout &
`Kraus, LLP
`(57)
`ABSTRACT
`In a plasma processing apparatus that has a vacuum
`chamber, a process gas supply means of supply gas to a
`processing chamber, an electrode to hold a sample inside
`said vacuum chamber, a plasma generator installed in said
`vacuum chamber opposite to said sample, and a vacuum
`exhaust system to decrease pressure of said vacuum
`chamber, a bias voltage of Vdc=-300 to -50 V is applied and
`the surface temperature of said plate ranges from 100 to 200°
`C. In addition, the surface temperature fluctuation of the
`silicon-made plate in said plasma processing apparatus is
`kept within ±25° C.
`
`10 Claims, 7 Drawing Sheets
`
`Page 1 of 15
`
`APPLIED MATERIALS EXHIBIT 1030
`
`

`

`U.S. Patent
`US. Patent
`
`Jan. 14,2003
`Jan. 14, 2003
`
`Sheet 1 of 7
`Sheet 1 0f 7
`
`US 6,506,686 B2
`US 6,506,686 B2
`
`FIG. 1
`FIG. 1
`
`120
`
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`
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`145 - - 142143
`
`106
`
`144
`
`141
`
`Page 2 of 15
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`Page 2 of 15
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`

`

`U.S. Patent
`US. Patent
`
`Jan. 14,2003
`Jan. 14, 2003
`
`Sheet 2 of 7
`Sheet 2 0f 7
`
`US 6,506,686 B2
`US 6,506,686 B2
`
`FIG. 2
`FIG. 2
`
`12
`
`121
`
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`
`122
`
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`
`125
`
`114
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`
`115?
`
`Page 3 of 15
`
`Page 3 of 15
`
`

`

`U.S. Patent Jan. 14,2003 Sheet 3 of 7
`
`US 6,506,686 B2
`
`Si ETCHING RATE ( um/h)
`
`FIG. 3
`
`• 50-75 °C
`a 100-105 °C
`o 125-130 °C
`
`40
`
`30
`
`20
`
`10
`
`0
`
`0
`
`i i i___ i i___ i i i___ i___ i i
`-400
`-500
`-100
`-200
`-300
`
`-600
`
`Vdc (V)
`
`FIG. 4
`
`Page 4 of 15
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`

`

`U.S. Patent
`
`Sheet 4 of 7
`Jan. 14,2003
`FIG. 5
`
`TEMPERATURE (deg)
`200
`
`US 6,506,686 B2
`
`150
`
`100
`
`50
`
`0
`
`10 12 14 16 18 20 22 24 26 28 30
`
`TIME (min)
`
`FIG. 6
`
`TIME (min)
`
`Page 5 of 15
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`

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`U.S. Patent
`
`Jan. 14,2003
`
`Sheet 5 of 7
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`US 6,506,686 B2
`
`FIG. 7
`
`115A
`
`Page 6 of 15
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`

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`U.S. Patent
`
`Jan. 14,2003
`
`Sheet 6 of 7
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`US 6,506,686 B2
`
`FIG. 8
`
`TIME (min)
`
`FIG. 10
`
`ETCHING DEPTH (nm)
`1600
`
`ETCH RATE (nm/min)
`
`1400
`
`1200
`1000
`
`800
`
`600
`
`400
`200
`
`0
`
`0 12
`TIME (min)
`
`3
`
`4
`
`Page 7 of 15
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`

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`U.S. Patent
`
`Jan. 14,2003
`
`Sheet 7 of 7
`
`US 6,506,686 B2
`
`FIG. 9
`
`OES INTENSITY (a.u.)
`
`TIME (min)
`
`ANT Vdc
`
`0 -
`
`100
`-200
`-300
`-400
`-500
`
`i *-BIAS-Vpp
`
`0
`
`1
`
`2
`TIME (min)
`
`3
`
`4
`
`BIAS Vpp
`2000
`1800
`1600
`1400
`1200
`1000
`
`Page 8 of 15
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`

`

`1
`PLASMA PROCESSING APPARATUS AND
`PLASMA PROCESSING METHOD
`
`US 6,506,686 B2
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a plasma processing
`apparatus and processing method, particularly to a plasma
`processing apparatus and processing method suitable for
`formation of ultrafine pattern in semiconductor production
`process.
`2. Related Background Art
`In semiconductor production process, a plasma process­
`ing apparatus is widely used in fine processing such as
`etching, film formation and ashing. In plasma processing,
`process gas introduced into a vacuum chamber (reactor) is
`converted to plasma by a plasma generation means, and is
`made to react on the semiconductor wafer surface to provide
`fine processing, and volatile reaction products are exhausted,
`thus a predetermined process is performed.
`This plasma processing is strongly affected by tempera­
`ture of the reactor inner wall and wafer and deposition of
`reaction products on the inner wall. Furthermore, if the
`reaction products deposited inside the reactor have peeled
`off, partilcle may be produced, resulting in deterioration of
`device characteristics or reduction of yields. In the plasma
`processing apparatus, therefore, it is important to control
`temperature inside the reactor and deposition of reaction
`products on the surface, in order to ensure process stability
`and to prevent particle contamination.
`For example, Official Gazette of Japanese Patent Laid­
`Open NO. 144072/1996 discloses a dry etching apparatus
`which controls and maintains the temperature of each part
`inside the reactor to a high temperature of 150 to 300° C.
`(preferably 200 to 250° C.), at least 150° C. higher than that
`of etching stage, within the accuracy of ±5° C., wherein the
`purpose is to improve the selectivity in a silicon oxide dry
`etching process. This is intended to reduce deposition of
`plasma polymer on the inner wall of the reactor by control­
`ling each part inside the reactor to high temperature, thereby
`increase the deposition of plasma polymer on the semicon­
`ductor wafer, with the result of improved selectivity.
`Also, Official Gazette of Japanese Patent Laid-Open NO.
`275385/1993 discloses a parallel plate plasma processing
`apparatus wherein a heating means is provided on at least
`one of a clamp ring (object holding means) or focus ring
`(plasma concentration means) to raise and keep the tem­
`perature in order to prevent deposition of plasma process
`reaction products. As a heating means, a resistance heater is
`used. Since deposition of reaction products can be prevented
`by heating, peeling off of reaction products and particles on
`the object surface are reduced.
`However, when the reactor inner wall is set to a high
`temperature of 200 to 250° C. or more as described above,
`a problem arises that etching characteristics becomes very
`sensitive to the temperature of the inner wall surface, and
`repeatability and reliability of the process can be reduced.
`For example, S. C. McNevin, et al., J. Vac. Sci. Technol.
`B15(2) March/April 1997, R21, “Chemical challenge of
`submicron oxide etching” indicates that oxide film etching
`rate increases 5% or more, in the inductively coupled plasma
`when side wall temperature changes from 200 to 170° C.,
`therefore, surface temperature inside the reactor is required
`to be kept to a high accuracy of 250 ±2° C. in order to ensure
`stability of process characteristics.
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`Furthermore, since the surface of the processing chamber
`inner wall is exposed to high density plasma, it is not easy
`to control the wall surface temperature with high accuracy in
`the high temperature range. A highly accurate in-situ tem­
`perature measuring means and a heating means such as
`resistance heater or lamp are to be used for temperature
`control. However, the temperature control mechanism and
`means will be quite complicated and large in scale, resulting
`in complicated equipment with high cost. In a high tem­
`perature range of more than 200° C., another problem exists
`that the materials applicable for the inner wall are limited.
`In this respect, the present applicants discloses in the
`Japanese Patent Application No. 147672/1998 (Official
`Gazette of Japanese Patent Laid-Open NO. 340149/1999) by
`the same applicants that the process can be insensitive to
`temperature changes and stable process repeatability can be
`ensured despite the temperature accuracy of about ±10° C.,
`when the temperature of the processing chamber inner wall
`is set to the temperature range of lower than 100° C.,
`wherein said applicants use a magnetic field UHF band
`electromagnetic wave radiation discharge type plasma etch­
`ing apparatus as one Embodiment.
`The same application discloses that, by applying bias at
`least partly to the components (or inner wall surface) in
`contact with plasma, and by reducing the thermal capacity of
`the components to keep component temperature in the range
`from 150 to 250° C., it is possible to come to the level that
`the temperature fluctuation of components does not affect
`the process substantially.
`The present applicants in the Japanese Patent Application
`No. 232132/1999 by the same applicants also disclose that,
`when higher bias power of no deposition occurrence is
`applied to the silicon-made focus ring set outside the sample,
`and when the surface temperature is higher than 150° C.,
`surface reaction dependency upon temperature on the silicon
`surface is reduced and stable process repeatability can be
`ensured.
`However, as for the plate installed on the top antenna (or
`upper electrode or top plate) opposite to the sample wafer,
`although the plate has a big influence on process stability,
`said application only states that the plate has a role of
`stabilizing the process by preventing reaction product from
`deposition by application of bias, and said applicants did not
`reach sufficient understanding of the mechanism nor succeed
`in quantifying the required conditions.
`SUMMARY OF THE INVENTION
`From said technological standpoint, the present inventors
`made a strenuous effort to solve said problems, and found
`out temperature range and accuracy required to ensure
`process stability and requirements for surface state control
`by bias application, regarding the top plate installed opposite
`to the sample wafer.
`The present invention was developed on the basis of the
`aforementioned findings, and is intended to provide a
`plasma processing apparatus and processing method with
`excellent process stability and repeatability.
`The present invention provides a plasma processing appa­
`ratus comprising; a vacuum chamber, a process gas supply
`means to supply gas to said vacuum chamber, an electrode
`to hold a sample inside said vacuum chamber, a plasma
`generator installed in said vacuum chamber opposite to said
`sample, and a vacuum exhaust system to evacuate said
`vacuum chamber;
`wherein said plasma generator is installed a silicon-made
`plate inside the processing chamber, and bias voltage of
`
`Page 9 of 15
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`

`3
`Vdc=-50 to -300 V (i.e. -300 VgVdcS-50 V) is
`applied to said silicon-made plate, and the surface
`temperature of said plate is kept in the range from 100
`to 200° C.
`Another characteristic of the present invention is that the
`fluctuation of the surface temperature of the silicon-made
`plate on said plasma processing apparatus is kept within
`±25° C.
`Still further characteristic of the present invention is that
`said plasma generator of plasma processing apparatus is
`based on magnetic field or non-magnetic field UHF band
`electromagnetic wave radiation discharge method in the
`frequency range from 300 MHz to 1 GHz, and that the
`resistivity of said silicon-made plate is 1 to 10 Qcm, and that
`the thickness of said silicon-made plate is 5 to 20 mm,
`desirably up to 10 mm.
`According to the present invention, dependency of reac­
`tion on temperature on the silicon surface decreases by
`temperature control and bias application for silicon-made
`plate installed opposite to the sample and plasma state and
`process characteristics are stabilized for surface temperature
`fluctuation of the plate within ±25° C., thus a plasma
`processing apparatus and processing method with excellent
`stability and repeatability can be provided.
`The present invention is still further characterized as
`follows: the skin depth of the UHF band electromagnetic
`wave transmitting inside the silicon-made plate and silicon
`plate thickness are almost equal, and current resulting from
`UHF band electromagnetic wave flows the entire plate. As
`a result, the plate is effectively heated by self-heat genera­
`tion due to the internal resistance of silicon itself, which
`enables to set surface temperature of the silicon-made plate
`in the range from 100 to 200° C. where dependency of
`surface reaction on temperature decreases. As a result
`plasma state and process characteristics are stabilized, thus
`a plasma processing apparatus and processing method with
`excellent stability and repeatability can be provided.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram representing the vertical
`section of the first Embodiment where the present invention
`is applied to a magnetic field UHF band electromagnetic
`wave radiation discharge type plasma processing apparatus;
`FIG. 2 is a schematic diagram representing the vertical
`section of the embodiment of an antenna structure according
`to the first Embodiment;
`FIG. 3 shows the result of evaluating consumption rate of
`the plate in the first Embodiment;
`FIG. 4 represents the temperature fluctuation of the plate
`in the first Embodiment;
`FIG. 5 represents the temperature fluctuation of the plate
`in the steady state in the first Embodiment;
`FIG. 6 represents the temperature fluctuation where the
`plate has different resistivity in the first Embodiment;
`FIG. 7 is a schematic diagram representing the vertical
`section of the second Embodiment where the present inven­
`tion is applied to a magnetic field UHF band electromagnetic
`wave radiation discharge type plasma processing apparatus;
`FIG. 8 represents the temperature fluctuation of the plate
`in the second Embodiment;
`FIG. 9 represents the changes of plasma optical emission,
`discharge voltage and antenna bias voltage with time in the
`second Embodiment; and
`FIG. 10 represents the result of measuring the dependency
`of etching depth and etching rate upon etching time in the
`second Embodiment.
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`US 6,506,686 B2
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`4
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`The following describes the embodiments according to
`the present invention with reference to the drawings.
`FIG. 1 shows an embodiment where the present invention
`is applied to the magnetic field UHF band electromagnetic
`wave radiation discharge type plasma etching apparatus. It is
`a cross sectional view of said plasma etching apparatus in
`schematic form.
`The processing chamber 100 in FIG. 1 is a vacuum vessel
`providing a vacuum of about 10-6 Torr. An antenna 110,
`which radiates electromagnetic wave, is installed on the top
`thereof, and a bottom electrode 130 to mount a sample W
`such as a wafer is installed on the bottom thereof. Antenna
`110 and bottom electrode 130 are installed so as to be
`opposite to and in parallel with each other. A magnetic field
`forming means 101 composed of an electromagnetic coil
`and a yoke, for example, is installed around the processing
`chamber 100. Process gas introduced into the processing
`chamber is converted into plasma by interaction between the
`electromagnetic wave radiated from the antenna 110 and
`magnetic field produced by the magnetic field forming
`means 101, and plasma P is generated to perform processing
`of the sample W on the bottom electrode 130.
`Evacuation of the processing chamber 100 is provided by
`vacuum exhaust apparatus 106 connected to vacuum cham­
`ber 105 and the inner pressure can be controlled by a
`pressure control means 107. The processing pressure is
`adjusted in the range from 0.1 to 10 Pa, more desirably from
`0.5 to 4 Pa. The processing chamber 100 and the vacuum
`chamber 105 are at the ground potential. A side wall inner
`unit 103 having a temperature control function is replace­
`ably installed on a side wall 102 of the processing chamber
`100. The temperature on the inner surface is controlled by a
`heat transfer medium supplied in circulation to the side wall
`inner unit 103 from the heat transfer medium supply means
`104. Alternatively, the temperature can be feedback-
`controlled by a heater mechanism and a temperature detect­
`ing means. The temperature control range is from 0 to 100°
`C., desirably 20 to 80° C., and is controlled within ±10° C.
`It is desirable that the side wall 102 of the processing
`chamber 100 and side wall inner unit 103 are made of
`non-magnetic metallic material without containing heavy
`metal, featuring high thermal conductivity, for example
`aluminum, and that the surface is provided with surface
`process of anti-plasma, for example anodized aluminum
`oxide or the like.
`Antenna 110 installed on the vacuum vessel consists of a
`disk formed conductor 111, a dielectric 112 and a dielectric
`ring 113, and is held by a housing 114 as a part of the
`vacuum vessel. Furthermore, a plate 115 is installed on the
`surface of the disk formed conductor 111 on the side in
`contact with plasma. A outer ring 116 is installed further on
`the outside. The temperature of the disk formed conductor
`111 is kept at a predetermined value by a temperature control
`means (not illustrated), namely by heat transfer medium
`circulating inside, and the surface temperature of the plate
`115 in contact with the disk formed conductor 111 is
`controlled. The process gas used to perform sample etching
`and film formation is supplied at a predetermined flow rate
`and mixing ratio from the gas supply means 117 and is
`introduced into processing chamber through numerous holes
`provided on the disk formed conductor 111 and the plate
`115, controlled to a designed distribution.
`The antenna 110 is connected to an antenna power source
`121 and antenna bias power source 122 as an antenna power
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`Page 10 of 15
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`5
`system 120 through matching circuit-filter systems 122 and
`124, and is also connected to the ground through a filter 125.
`The antenna power source 121 supplies power at a UHF
`band frequency in the range from 300 MHz to 1 GHz. By
`setting diameter of the disk formed conductor 111 to a
`specified characteristic length, inherent excitation mode,
`such as TM01 mode, is formed. In the present Embodiment,
`frequency of the antenna power source 121 is 450 MHz, and
`the diameter of the disk formed conductor 111 is 330 mm.
`Meanwhile, the antenna bias power source 122 controls
`the reaction on the surface of the plate 115 by applying bias
`power at a frequency in the range from several tens of kHz
`to several tens of MHz to the antenna 110. Particularly in
`case of oxide film etching using CF-series gas, use of high
`purity silicon as a material of the plate 115 enables the
`reaction of F radical and CFx radical to be controlled, thus
`radical composition ratio can be adjusted. In this
`Embodiment, antenna bias power source 122 is set at a
`frequency of 13.56 MHz and a power of 50 W to 600 W. In
`this case, bias voltage Vdc is generated to the plate 115 due
`to self-bias. The Vdc value is about Vdc=-300 V to -50 V
`(i.e. -300 V=Vdc = -50 V), although it may vary with
`plasma density and pressure. The present Embodiment is
`characterized in the point that the self-bias applied to the
`plate 115 is controlled independent of the plasma generation,
`unlike so-called parallel plate capacitively coupled plasma
`system. Especially, by setting the bias voltage to a low value
`of Vdc=-100 V or less (for example -10 V) (i.e. -100
`V=Vdc = -10 V), it becomes possible to reduce silicon
`consumption, resulting in running cost reduction, and
`becomes also possible to reduce silicon sputtering, which
`results in less etching residue on the sample W.
`The distance between the bottom of the plate 115 and the
`sample W (hereafter called “gap”) is in the range of 30 to
`150 mm, or desirably 50 to 120 mm. Since the plate 115
`having wide area is placed opposite to the sample W, it has
`the biggest influence to the process. The major point of the
`present invention is to stabilize surface reaction on the plate
`115, and to get process characteristics with excellent repeat­
`ability by bias application to the surface of the plate 115 and
`by temperature control within a specific range. This will be
`described later in details.
`On the bottom of the processing chamber 100, a bottom
`electrode 130 is installed opposite to the antenna 110. To the
`bottom electrode 130, a bias power source 141 is connected
`through matching circuit filter system 142. The bias power
`source 141 supplies bias power in the range from 400 kHz
`to 13.56 MHz, for example, and controls the bias applied to
`the sample W. The bottom electrode 130 is connected to the
`ground through filter 143. In the present Embodiment,
`frequency of the bias power source 141 is set to 800 kHz.
`On the top surface of the bottom electrode 130, namely,
`on the sample mounting surface, a sample W such as a wafer
`is mounted on an electrostatic chucking unit 131. Electro­
`static chucking dielectric layer (hereafter called “electro­
`static chucking film”) is formed on the surface of the
`electrostatic chucking unit 131. By applying hundreds of
`volts to several kilovolts (kV) of DC voltage from an
`electrostatic chucking DC power supply 144 through filter
`145, sample W is chucked and held on the bottom electrode
`130 by electrostatic chucking force. As for the electrostatic
`chucking film, dielectric of aluminum oxide or aluminum
`oxide mixed with titanium oxide is used. Surface tempera­
`ture of the electrostatic chucking unit 131 is controlled by
`temperature control means (not illustrated). Inactive gas, for
`example helium gas, set to a specified flow rate and pressure,
`is supplied to the surface of the electrostatic chucking unit
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`6
`131, and raise heat conductivity with the sample W. This
`allows surface temperature of the sample W to be controlled
`with high precision in the range from about 100 to 110° C.,
`for example. On the top surface of the electrostatic chucking
`unit 131, a focus ring 132, a ring formed member made of
`high purity silicon, is installed outside the sample W. The
`focus ring 132 is isolated from electrostatic chucking unit
`131 by an insulator 133. An electrode outer cover 134 is
`settled outside the electrode. Alumina and quartz are suitable
`for the insulator 133 and the electrode outer cover 134. In
`this Embodiment, alumina is used for the insulator 133 and
`electrode outer cover 134. This configuration enables bias
`power applied to the bottom electrode to be applied to the
`focus ring 132 by partial leakage through the insulator 133.
`Intensity of the bias applied to the focus ring 132 can be
`adjusted according to dielectric constant and thickness of the
`insulator 133. The focus ring 132 is thermally isolated from
`the insulator 133, and is not in thermal contact. This enables
`highly efficient temperature rise through heating by plasma
`and bias. Furthermore, use of silicon as material of the focus
`ring 132 allows scavenging function of the silicon on the
`surface of focus ring 132 to adjust the reaction of F radical
`and CFx radical or radical composition. This makes it
`possible to adjust etching uniformity, especially on the outer
`periphery of the wafer.
`The plasma etching apparatus according to the present
`Embodiment is structured as described above. Regarding the
`temperature control of the side wall in the above
`Embodiments, the results disclosed in the Japanese Patent
`Application No. 14767/1998 by the applicants of the present
`invention can be used. Likewise, regarding the focus ring
`structure, what is disclosed in the Japanese Patent Applica­
`tion No. 232132/1999 by the applicants of the present
`invention can be employed.
`With reference to FIG. 1, the following describes a
`process of etching silicon oxide film as an example, using
`this plasma etching apparatus:
`Firstly, the wafer W as an object of processing is loaded
`into the processing chamber 100 from a sample loading
`mechanism (not illustrated) and is mounted on the bottom
`electrode 130 and chucked thereon. The height of the lower
`electrode is adjusted, and the gap is set to a predetermined
`value. Then gases required for sample W etching process,
`for example, C4F8, Ar and 02 are supplied into the process­
`ing chamber 100 from gas supply means 117 through the
`plate 115 at a predetermined flow rate and mixing ratio. At
`the same time, the pressure inside the processing chamber
`100 is adjusted to a predetermined processing pressure by
`the vacuum exhaust system 106 and the pressure control
`means 107. Then 450 MHz UHF power is supplied from the
`antenna power supply 121, and electromagnetic wave is
`radiated from the antenna 110. Plasma is generated inside
`the processing chamber 100 by interaction with approxi­
`mately horizontal magnetic field of 160 gausses (electron
`cyclotron resonance magnetic field intensity for 450 MHz)
`formed inside the processing chamber 100 by the magnetic
`field forming means 101. Process gas is dissociated to
`generate ion and radical. Composition and energy of ion and
`radical in plasma are controlled by antenna bias power from
`the antenna bias power source 122 and bias power from the
`bias power supply 141 of the bottom electrode, and etching
`process is performed to the wafer W. Then, upon completion
`of etching, supply of power, magnetic field and process gas
`are terminated, and etching process is completed.
`The plasma processing apparatus in the present Embodi­
`ment is structured as described above. The following
`describes a specific method for controlling the temperature
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`7
`of the plate 115 by the system in the present Embodiment.
`After considering temperature setting of the plate 115, result
`of temperature measurement of the plate 115 will be shown.
`Firstly, with reference to FIG. 2, the following describes
`the method for controlling the temperature of plate 115,
`namely, a cooling and heating mechanism. FIG. 2 is a
`detailed cross sectional view of antenna 110 shown in FIG.
`1. It represents an arrangement for temperature control of the
`plate 115. As explained with reference to FIG. 1, the antenna
`110 comprises a disk formed conductor 111, dielectric 112
`and dielectric ring 113. The plate 115 is installed on the side
`of the disk formed conductor 111 in contact with plasma.
`The plate 115 is settled to the disk formed conductor 111 by
`means of setscrews on the periphery.
`The following describes the cooling mechanism of the
`plate 115: Temperature of the disk formed conductor 111
`installed on the back of the plate 115 is controlled at a
`predetermined value with the heat transfer medium, which is
`introduced into disk formed conductor 111 from inlet 118A
`and discharged, after circulating inside, from the outlet
`118B. The material of the disk formed conductor 111 is
`desirably aluminum with high thermal conductivity. The
`temperature of the heat transfer medium is desirably normal
`temperature, for example 30° C. Meanwhile, process gas is
`supplied to the disk formed conductor 111 from the gas
`supply means 117. After dispersed inside the disk formed
`conductor 111, the process gas is supplied into the process­
`ing chamber through numerous gas holes provided on the
`plate 115. Accordingly, during the processing, the process
`gas exists between the plate 115 and the disk-formed con­
`ductor 111. The temperature of the plate 115 is adjusted by
`cooling from the disk formed conductor 111 with heat
`transfer of the process gas. Furthermore, in the Embodiment
`shown in FIG. 2, a space lllAis provided on the surface of
`the disk formed conductor 111 on the side in contact with the
`plate 115, and the process gas accumulated there increases
`heat transfer efficiency between the disk formed conductor
`111 and the plate 115, to ensure that the plate 115 is cooled
`with high efficiency. The diameter of the gas hole is 2 mm
`for the disk formed conductor 111, and 0.5 mm for the plate
`115.
`On the other hand, heating mechanism of the plate 115
`consists of plasma heating from plasma P, ion heating by
`antenna bias and self-heat generation of the plate 115 itself.
`The plasma heating is, needless to say, heating that the
`plate 115 is heated by high temperature electrons and ions in
`plasma P.
`The ion heating is heating by energy of ion pulled into the
`plate 115. Radio frequency antenna bias is applied to the
`antenna 110 by antenna bias power source 122, and bias
`voltage Vdc is generated by self-bias. Antenna bias power is
`approximately in the range from 50 to 600 W, and self-bias
`of about Vdc=-300 to -50 V is applied to the plate 115. Ions
`are pulled in by this energy to heat the plate 115.
`Self-heat generation of the plate 115 is resistance heating
`by internal resistivity of silicon as a material of the plate 115.
`UHF band frequency electromagnetic wave (hereafter called
`“UHF wave”) supplied from antenna power source 121
`transmits in the dielectric 112 as indicated by 121A, and is
`discharged into the processing chamber 100 from the dielec­
`tric ring 113 (as indicated by 121B), meantime UHF wave
`transmits in the plate 115 and is discharged into the pro­
`cessing chamber 100 from the surface of the plate 115
`(indicated by 121C).
`Now, propagation of the UHF wave through the plate 115
`greatly varies according to the resistivity of the plate 115.
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`The resistivity of silicon, as a material of the plate 115, can
`be adjusted by the amount of B (boron) to be added, and can
`be set to, for example, about 5 Qcm at concentration of
`about 1014, and about 0.01 Qcm at B concentration of from
`1018 to 1019.
`In case of silicon resistivity of 5 Qcm, skin depth of 450
`MHz UHF frequency electromagnetic wave is about 7 mm.
`In other words, the UHF wave current transmits through the
`area to a depth of about 7 mm from surface. On the other
`hand, thickness of the plate 115 is desirably in the range
`from 5 to 20 mm according to the flexible rigidity and
`strength of the plate, and is more desirably to be about 10
`mm or less when considering the cost of material and
`production. As a result, thickness of the plate 115 is about
`twice the skin depth at most, thus the UHF wave current
`transmits throughout the entire plate interior. In this case,
`since resistivity of the silicon plate 115 is as high as 5 Qcm,
`Joule heating is generated by the current. This phenomenon
`particularly occurs at the silicon resistivity of 1 to 10 Qcm.
`In other words, in case of silicon resistivity of 1 to 10 Qcm
`for 450 MHz UHF frequency, self-heat generation occurs
`due to the resistance heating by UHF wave current which
`transmits inside the plate, as a result temperature of the plate
`115 increases.
`In case that the silicon resistivity is as low as 0.01 Qcm,
`skin depth for 450 MHz UHF frequency is about 0.1 to 0.5
`mm. In this case, UHF wave current transmits the top
`surface of the plate 115, accordingly self heat generation
`hardly occurs to the plate 115 because of the current con­
`centrated to the top surface and low silicon resistivity. As
`described above, the self-heat generation of the plate 115
`greatly differs according to the resistivity of the silicon as a
`material.
`Herein above, mechanism of temperature rise and fall of
`the silicon plate 115 in the Embodiment shown in FIG. 1 has
`been clarified. The temperature of the plate 115 is controlled
`to a predetermined value by adjusting the balance of these
`mechanisms. In the following, temperature setting of the
`plate 115 will be considered.
`In qualitative terms, it can be easily supposed that, at low
`temperature of the plate 115, reaction products are more
`likely to deposit on the plate surface and the surface state
`tends to change with time. Moreover, the deposited reaction
`products may result in a source of particle contamination
`when peeled off. However, not only that, the present inven­
`tors have found out that dependency of the reaction state on
`the silicon surface upon temperature change increases, par­
`ticularly when the temperature of the plate 11