Umted States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,753,886
`
`Iwamura et al.
`
`[45] Date of Patent:
`
`May 19, 1998
`
`US005753886A
`
`
`
`..
`
`[54] PLASMA TREATMENT APPARATUS AND
`0
`METH D
`.
`-
`.
`-
`Inventors’ {:L'£y;'1i"s3:"}';m;lYas"ts“g"A°k"
`'
`pa
`.
`.
`.
`
`[73] Assign“:
`
`Jsgigl’ E950“ C°"P°‘“t'°“’T°k-"’°'
`
`[75]
`
`5.340.618
`5.368.685
`5 384167
`.,
`5.391.855
`5.399.830
`5.407.121
`.
`.
`
`5.2493292:
`
`5.597.438
`
`511992 i§§E§‘§2".=...1.
`
`1/1997 Grewal eta].
`
`........................ 427/488
`8/1994 Tanisaki eta].
`11/1994 Kumihashi et al.
`156/643.1
`1/1995 151' hi
`aki
`tal
`4 7/569
`.1swe....
`..2
`2/1995 Tanisaki
`.........
`. 219/121.43
`3/1995 Maruyama
`. 219/121.43
`4/1995 Koopman et 2].
`...... 228/206
`.........
`156/643.1
`
`.......................... 156/345
`
`228/42
`
`[21] Appl, No‘; 593,032
`
`FOREIGN PATENT DOCUMENTS
`
`Feb. 7, 1996
`[22] Filed:
`[30]
`Foreign Application Priority Data
`
`Feb. 7,
`Japan .................................. .. 7-019191
`Dec. 5, 1995
`Japan .................................. .. 7-344404
`[51]
`Int. Cl.‘ ..................................................... B23K 1o/no
`
`[52] U.S. Cl.
`.. 219/121.43: 219/121.44;
`219/121.5]; 156/345; 156/646.1
`[58] Field of Search ......................... 219/121.43. 121.36.
`219/121.4. 121.59. 121.52. 121.51; 156/345.
`643.1; 204/298.34. 298.06. 192.1. 298.37.
`
`59
`.
`
`.
`.
`-
`60-1861
`61-127866
`1_l25829
`2_190_/139
`
`$1333
`1/1985
`6/1986
`5/1989
`7/1990
`
`3419032
`3-236475
`4186619
`5-82473
`62149
`
`9,1991
`10/1991
`7/1992
`4/1993
`1/1994
`
`1‘-ur°1>ea-1 Pat 011--
`apan .
`Japan .
`Japan.
`I
`Japan‘
`:53:
`JaPan_
`_'[apan_
`Japan .
`Japan-
`Japan.
`
`Primary Examiner—Mark H. Paschall
`Attomey, Agent, or Fima-Stroock & Stroock & Lavan LLP
`[57]
`ABSTRACT
`
`A plasma treatment and apparatus which enables improved
`uniform plasma treatment over the entire surface of an
`object to be treated. improved yield. and higher treatment
`speed is provided. In a gas introduction passage. the gas
`capable of plasma discharge is preexcited to raise its level of
`excitation. A first pair of plasma generation electrodes
`downstream along the gas flow passage use the preexcited
`gas to generate a plasma in a first plasma generation posi-
`tion. Further downstream. a second pair of plasma genera-
`tion electrodes positioned in a second plasma generation
`position. where the activated state of the gas activated in the
`first plasma region is maintained. activates the gas to gen-
`erate a plasma containing activated gas species. The object
`to be treated is treated by the activated gas species in the
`.
`second plasma region.
`
`37 Claims, 9 Drawing Sheets
`
`-
`R f
`E emnces Cited
`US. P TENT DOCUMENTS
`A
`10/1973 Hou ........................................ 117/93.1
`3/1977 Phillips
`204/192
`
`2/1984 Yoneda el 21.
`219/121
`..
`ll/1987 Haigh et al.
`156/535
`11/1987 Hyneoek ..........
`159643
`6/1988 Blackwood et a]
`159646
`8/1989 Liu et al.
`5/1990 Dishon et 211.
`.
`3/1991 Pedder el al.
`9/1991 Bobbio .............
`6/19% Schnurmans et 11].
`6/1992 Okazaki et al.
`9/199Q Bobbio .............
`1/1993 Tsukamoto et al.
`4/1993 Reisman et 2].
`..
`7/1993 Kusano et 3].
`8/1993 lshida
`3/1994 Knsano et al.
`3/1994 Tsai et al.
`5/1994 Yoshikawa et
`
`.
`
`156/643
`_ 204,192
`__ 427/37
`_. 427/39
`204/192
`118/722
`-- 155/546
`" 249/121
`'.'... 456/666
`156/272
`156/345
`.................... 422/186
`
`
`
`.
`
`[56]
`
`3.762.941
`4.012.307
`4.430.547
`4.705593
`4,708,766
`4.749.440
`4.857,382
`4.921.157
`5,000,819
`5.045.166
`5.120.568
`5,126,164
`5,147,520
`S,l78.682
`5,201,995
`5.225.659
`5,240,559
`5,290,378
`5,292,370
`5,316,739
`
`
`
`INTEL 1107
`INTEL 1307
`INTEL 1307
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 1 of 9
`
`5,753,886
`
`F/G. /
`
`20
`
`i
`
`:
`
`*
`
`E
`
`I
`
`22
`
`fl
`\
`
`g
`
`r ——--
`
`i
`I
`
`E
`
`r
`
`24
`
`200
`
`"r
`
`30a
`
`32a
`
`B
`
`‘
`
`7 ‘
`
`a@nnnunnnu
`
`LI
`S j-ll
`1‘
`
`30b
`
`I
`
`la
`
`32b
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 2 of 9
`
`5,753,886
`
`F/6.2
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 3 of 9
`
`5,753,886
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 4 of 9
`
`5,753,886
`
`F/G.4
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 5 of 9
`
`5,753,886
`
`F/6.5
`
`6O
`
` ii [2
`5
`W J—n—.
`
`
`
`30b
`
`1
`
`IO
`
`32b
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 6 of 9
`
`5,753,886
`
`
`
`‘
`
`\
`
`\
`
`\
`
`‘
`
`\
`
`.
`
`\
`
`J
`
`.
`
`
`
`
`
`
`i
`I
`i
`72b 70b 3
`
`300
`320
`E
`3
`
`Ee3—II--I__I_u:=
`‘
`r'
`/IIYIIIIA
`
`L
`
`1 D
`
`"H"
`
`
`
`j 9.7“
`
`
`
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 7 of 9
`
`5,753,886
`
`
`’2”
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 3 of 9
`
`5,753,886
`
`F/6‘. 8
`
`
`
`‘.
`
`
`
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 9 of 9
`
`5,753,886
`
`F/6‘. 9
`
`
`
`
`
`

`
`5.753.886
`
`1
`PLASMA TREATMENT APPARATUS AND
`METHOD
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates generally to a plasma treat-
`ment apparatus and method which can treat an object with
`activated gas species formed by a plasma. In particular. the
`present invention relates to a plasma treatment apparatus and
`method which can treat an object by generating a plasma at
`a plurality of positions along the flow path of a gas capable
`of plasma discharge. and by forming activated gas species
`by the plasma generated in the most downstream position
`and applying the activated gas species to the object. The
`invention further relates to a plasma treatment apparatus and
`method which includes preexciting the gas capable of
`plasma discharge upstream from the first plasma generation
`position along the flow path of the gas. and treating the
`object to be treated by means of activated gas species in the
`plasma formed in the most downstream plasma generating
`position.
`2. Description of Prior Art
`There are two forms of plasma treatment apparatus.
`known as vacuum plasma treatment apparatus and atmo-
`spheric pressure plasma treatment apparatus. Examples of
`the atmospheric pressure plasma treatment apparatus are
`disclosed in. for example Japanese Patent Application Laid-
`Open No. l-125829 and Japanese Patent Application Laid-
`Open No. 6-190269. The atmospheric pressure plasma treat-
`ment apparatus applies a high frequency voltage to form a
`discharge in a gas at atmospheric pressure to generate a
`plasma. The plasma forms activated gas species which are
`then applied to the object to be treated to carry out an ashing
`or etching process.
`More specifically. in this method a high-frequency volt-
`age is applied to a gas capable of plasma discharge being
`supplied from a gas supply to generate the plasma by
`activating the gas fonning activated species. Then the acti-
`vated gas species react with either the object to be treated or
`with a film formed on the surface thereof. and the reaction
`products are removed by vaporization.
`Since an atmospheric pressure plasma treatment appara-
`tus allows the treatment to be carried out at atmospheric
`pressure. the construction of the apparatus can be simplified.
`and handling made easy. There are the additional advantages
`that the treatment can be carried out rapidly and at low cost.
`On the other hand. in a conventional atmospheric pressure
`plasma treatment apparatus. since the plasma is generated at
`atmospheric pressure. the uniformity and stability of the
`plasma is not always adequate. As a result. problems occur.
`including non-uniformities in the treatment or the existence
`of untreated portions of the object to be treated. The further
`drawback with this type of atmospheric pressure plasma
`treatment apparatus has been pointed out that. in general. the
`ashing rate or etching rate is low.
`These problems are most severe in the case of an atmo-
`spheric pressure plasma treatment apparatus. but similarly a
`vacuum plasma treatment apparatus typically also requires
`improvement in the treatment rate.
`SUMMARY OF THE INVENTION
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`In view of the above problems the present invention
`provides a plasma treatment apparatus and method which
`generates a stable plasma and is able to improve the treat-
`ment rate and yield from the treatment.
`
`65
`
`2
`Generally speaking. in accordance with the invention. a
`plasma treatment apparatus for treating a surface of an
`object
`to be treated is provided. The plasma treatment
`apparatus includes a treatment chamber in which the object
`to be treated is disposed. A gas supply is in fluid commu-
`nication with the treatment chamber and supplies a gas
`capable of plasma discharged to the chamber. Aplurality of
`plasma generafion units for activating the gas to generate a
`plasma are provided at different locations along the flow
`path of the gas through the gas supply. The plasma genera-
`tion unit downstream along the flow path of the gas supply
`activates the gas to generate activated gas species in a gas
`that has been preactivated by the plasma generation unit
`upstream along the flow path of the gas supply. The plasma
`generation unit downstream can also serve to maintain the
`activated state of the gas generated by the plasma generation
`unit upstream.
`The present invention also provides a method of plasma
`treating a surface of an object to be treated. including the
`steps of supplying a gas capable of plasma discharge through
`a gas supply and towards an object to be treated disposed in
`a treatment chamber. A plasma is then generated in the gas
`at different locations along the flow path of the gas through
`the gas supply. The plasma generated at a downstream
`position can maintain the activated state of the gas generated
`by a plasma generation at the upstream position. The plasma
`generated upstream can be a preactivated state plasm. The
`object to be treated is treated by the activated gas species
`from the downstream plasma generation position along the
`flow path of the gas supply.
`According to the present plasma treatment apparatus and
`method.
`the gas can be activated downstream from the
`upstream plasma preactivation position before the complete
`preactivated state of the gas is lost. In other words. the gas
`reaching the downstream plasma generation position main-
`tains the ionized or near-ionized state. formed by
`preactivation. i.e.. the gas is not yet fully ionized. but its
`excitation level is high. due to the upstream plasma preac-
`tivation. Thus. the generation of a plasma and formulation of
`activated gas species in the downstream region is made
`easier and more uniform and stable.
`
`By treafing the object to be treated with activated gas
`species formed by the plasma. the yield of the treatment is
`improved. Again. since the uniformity of the downstream
`plasma density is improved. the uniform surface treating of
`the object to be treated is also improved. Furthermore. since
`the density and excitation level of the activated gas species
`in the downstream plasma region are increased. the ashing
`rate. etching rate and other treatment rate can also be
`improved.
`Another aspect of the present invention provides a plasma
`treatment apparatus for treating a surface of an object to be
`treated which includes a treatment chamber in which the
`object to be treated is disposed. A gas supply for supplying
`a gas capable of discharge is in fluid communication with the
`treatment chamber. A first plasma generation unit for pre-
`activating the gas to generate a plasma is positioned
`upstream along the flow path of the gas in the gas supply;
`and a second plasma generation unit for activating the gas to
`generate a plasma downstream along the flow path of the gas
`in the gas supply is also provided. Thus. the first plasma
`generation unit preactivates the gas and the second plasma
`generation unit activates the gas and forms activated gas
`species. Then.
`the activated gas species formed by the
`second plasma generafion unit treat the object to be treated.
`Furthermore. in accordance with this invention. the first
`plasma generation unit may include a first pair of electrodes
`
`

`
`5.753.886
`
`3
`and a first alternating current power source connected across
`the first pair of electrodes. while the second plasma genera-
`tion unit may comprise a second pair of electrodes and a
`second alternating current power source connected across
`the second pair of electrodes. In this case it is preferable that
`the frequency of the first alternating current power source be
`lower than that of the second alternating current power
`source.
`
`The higher the frequency of the second alternating current
`power source used to generate the plasma close to the object
`to be treated (i.e.. downstream along the gas supply). the
`lower is the degree of plasma damage sulfered by the object
`to be treated. The reason for this is hypothesized as follows.
`The plasma damage suffered by the object to be treated
`depends on the magnitude of the energy imparted to elec-
`trons and ions of the activated gas species in the plasma. and
`on the number of electrons and ions reaching the object to
`be treated.
`that
`is. on the degree of movement of the
`electrons and ions. In other words. the larger the electron or
`ion energy imparted to the electrons and ions. and the higher
`the degree of movement of the electrons and ions. the larger
`is the plasma damage. Furthermore.
`increasing the fre-
`quency reduces the electrostatic capacitance impedance
`((nC=l/zrrfc) between the electrodes and the gas. allowing an
`adequate current to be supplied through the gas. This there-
`fore increases the energy imparted to the electrons and ions.
`which in itself tends to increase the plasma damage.
`On the other hand. when the frequency is increased. it is
`more diflicult for the electrons and ions to move in step with
`the frequency. andin particular the ability of the heavier ions
`to move in step is much more sharply reduced than that of
`the electrons. For this reason the total number of electrons
`and ions reaching the object to be treated is reduced. This
`latter reason appears to be oveniding. and as a result. the
`charge voltage occurring on the object
`to be treated is
`reduced. and the charge damage to the object to be treated
`is reduced. Therefore. the yield of the treatment on the object
`to be treated is thus improved by using a higher frequency
`in the downstream plasma generation unit.
`On the other hand. lowering the frequency of the first
`alternating current power source used to generate the plasma
`further removed from the object to be treated. (i.e.. the
`plasma generation unit upstream along the gas supply flow
`path) increases the alternating peak-to-peak voltage. allow-
`ing the gas to be adequately activated. As a result. the
`generation of the plasma downstream becomes easier. and
`the density and excitation levels of the activated gas species
`in the downstream plasma can be increased.
`In order to reduce the plasma damage in this way. in
`general the frequency of the second alternating power may
`be set to be higher than the conventional commercial fre-
`quency of 13.56 MHZ. In experiments it was confirmed that
`using a frequency of 40.68 MHZ produced less damage than
`a frequency of B56 MHZ. On the other hand. the frequency
`of the first alternating power is preferably in the range of
`about 400 kHz to about 13.56 MHZ The upper limit for this
`frequency. that is. 13.56 MHZ. has already been established
`as the frequency for generating a plasma. and if the fre-
`quency is below the lower limit of about 400 kHz. an
`abnormal discharge tends to occur.
`It is also preferable that the first alternating current power
`source has a greater voltage than the second alternating
`current power source. This allows the gas to be adequately
`activated in the upstream plasma region. and ensures the
`stability of the plasma even in the lower-powered down-
`stream plasma region. Moreover. since less power is used for
`
`4
`generating the downstream plasma which is used for treating
`the object to be treated. the plasma damage suffered by the
`object to be treated can be reduced.
`In the case where the gas supply has a gas flow path with
`a cross-sectional area smaller than the cross-sectional area of
`
`5
`
`the treatment chamber. it is preferable that the first pair of
`electrodes in the upstream plasma discharge unit be disposed
`opposite each other with the gas flow path therebetween.
`Thus. the gap between the pair of electrodes in the upstream
`plasma discharge unit can be made small. the plasma density
`in the upstream plasma region increased. and the gas
`adequately activated.
`Alternatively.
`the pair of electrodes disposed in the
`upstream plasma generation unit may be disposed within the
`treatment chamber. In this case the first pair of electrodes
`may be parallel to the treatment surface of the object to be
`treated. With this arrangement. each of the first pair of
`electrodes should have holes formed therethrough for allow-
`ing the gas to flow. and may be made of. for example. a
`porous metal sheet.
`the
`Of the first pair of electrodes disposed upstream.
`electrode closer to the object
`to be treated should be
`grounded. In this case. charged particles such as electrons
`and ions in the plasma can be captured by the grounded
`electrode. As a result. since only neutral activated gas
`species are directed toward the object to be treated. it is
`possible to prevent charging and damage to the object to be
`treated caused by exposure to ions.
`the electrodes
`is.
`that
`The second pair of electrodes.
`disposed in the downstream plasma discharge unit. may
`comprise a mounting electrode on which is mounted the
`object to be treated. and an opposite electrode disposed
`opposite the mounting electrode with the object to be treated
`therebetween. With this arrangement. the opposite electrode
`should have holes formed therethrough for allowing the gas
`to flow. and may be made of. for example. a porous metal
`sheet.
`
`As an alternative arrangement. the second pair of elec-
`t:rodes may be disposed upstream from the object
`to be
`treated along the flow path of the gas and parallel to the
`treatment surface of the object to be treated. With this
`arrangement. each of the second pair of electrodes should
`have holes formed therethrough for allowing the gas to flow
`therethrough.
`Of the second pair of electrodes disposed upstream from
`the object to be treated. it
`is preferable for the electrode
`closer to the object to be treated to be grounded. Thus.
`charged particles such as electrons and ions in the plasma
`can be captured by the grounded electrode. and only neutral
`activated gas species are directed toward the object to be
`treated. This prevents charging and damage to the object to
`be treated caused by exposure to ions. As an alternative
`arrangement. the opposing surfaces of the second pair of
`electrodes disposed upstream from the object to be treated
`may be orthogonal to the object to be treated. In this case
`there is no necessity for the second pair of electrodes to be
`provided with holes therethrough for the gas to pass since
`the gas passes directly between the two electrodes of the
`second pair.
`The first and second plasma generation unit may also
`comprise three electrodes all
`together. In this case.
`the
`treatment chamber has provided therein a mounting elec-
`trode on which the object to be treated is mounted. an
`opposite electrode disposed upstream from the object to be
`treated along the flow path of the gas and parallel to the
`treatment surface of the object to be treated. and a middle
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`

`
`5.753.886
`
`5
`electrode disposed between the mounting and opposite elec-
`trodes and parallel
`to the object
`to be treated. In this
`configuration. the opposite and middle electrodes form the
`fi.rst plasma generation unit. and the mounting and middle
`electrodes form the second plasma generation unit.
`In this case. the middle electrode. i.e.. the one in between
`the mounting electrode and the opposite electrode. may be
`grounded. the opposite electrode connected to a first alter-
`nating power supply. and the mounting electrode connected
`to a second alternating power supply. Alternatively.
`the
`middle electrode may be connected to an alternating power
`supply. and the mounting and opposite electrodes grounded.
`however in this case the power and frequency of both plasma
`generation units will necessarily be the same.
`A preexcitation unit for raising the excitation level of the
`gas capable of discharge may also be included further
`upstream from the most upstream plasma generation unit
`along the flow path of the gas in the gas supply. Thus. the
`preexcitation unit makes it easier to generate a plasma in the
`most upstream plasma unit. and the excitation level of the
`gas in the plasma can be further increased. Furthermore.
`even with a low gas flow rate. a plasma can be reliably
`generated in the most upstream plasma unit. The preexcita-
`tion unit may be. for example. one which exposes the gas to
`ultraviolet radiation. or to microwave radiation.
`
`invention provided
`Yet another aspect of the present
`includes a plasma treatment apparatus for treating an object
`to be treated having a treatment chamber in which the object
`to be treated is disposed. A gas supply in fluid communica-
`tion with the treatment chamber supplies a gas capable of a
`plasma discharge to the treatment chamber. A preexcitation
`unit for raising the excitation level of the gas is disposed
`upstream along the flow path of the gas in the gas supply. A
`plasma generation unit for exciting the gas to generate a
`plasma is also provided along the flow path of the gas
`downstream from the preexcitation unit relative to the gas
`flow direction. where the energy of the gas whose excitation
`level has been raised by the preexcitation unit is maintained.
`and where the plasma generation unit activates the gas to
`form activated gas species within the gas. Then. the acti-
`vated gas species activated by the plasma generation unit
`treat the object to be treated.
`Still another aspect of the present invention provides a
`method of plasma treating an object to be treated including
`supplying a gas capable of plasma discharge in a treatment
`chamber. with an object
`to be treated disposed therein.
`through a gas supply. The gas is preexcited upstream along
`the flow path of the gas in the gas supply. and then the gas
`is excited so as to generate a plasma along the flow path of
`the gas downstream from the position where the preexciting
`is carried out and where the energy of the gas whose
`excitation level has been raised by the preexciting is main-
`tained. Then. the object to be treated is treated by exposure
`to activated gas species formed by the plasma.
`According to the plasma treatment apparatus and method
`of the present invention. before the energy of the gas whose
`excitation level has been raised by preexciting is lost. the gas
`can be readily excited to generate a plasma in a down stream
`plasma generation unit. and thus the yield of the treatment
`on the object to be treated can be improved.
`Moreover. since the uniformity of the plasma density in
`the downstream plasma generation unit
`is improved. the
`uniform treatment over the surface of the object to be treated
`is also improved. Since the density and excitation levels of
`the activated gas species in the downstream plasma are
`increased. the treatment rate is also increased.
`
`6
`The above-described plasma treatment apparatus and
`method of the present invention are preferably applied to a
`conventional atmospheric pressure plasma treatment appa-
`ratus and method for which the uniform treating and stability
`of the plasma have not been satisfactorily obtained so far.
`Another object of the present invention is to provide a
`plasma treatment apparatus and method which is able to
`improve the uniform treatment of the object to be treated by
`improving the uniformity of the plasma density.
`A further object of the present invention is to provide a
`plasma treatment apparatus and method which is able to
`improve the ashing rate or etching rate by increasing the
`plasma density and uniformity.
`Another object of the present invention is to provide a
`plasma treatment apparatus and method which is able to
`improve the yield of the treatment by reducing the damage
`suffered by the object to be treated while subjected to the
`plasma.
`Still other objects and advantages of the invention will in
`part be obvious and will
`in part be apparent from the
`specification.
`The invention accordingly comprises the several steps and
`the relation of one or more of such steps with respect to each
`of the others. and the apparatus embodying features of
`construction. combinations of elements and arrangements of
`parts which are adapted to effect such steps. all as exempli-
`tied in the following detailed disclosure. and the scope of the
`invention will be indicated in the claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a fuller understanding of the invention. reference is
`had to the following description taken in connection with the
`accompanying drawings. wherein like numbers represent
`like parts. in which:
`FIG. 1 is a schematic elevational sectional View of a
`plasma apparatus constructed in accordance with a first
`embodiment of a treatment the present invention;
`FIG. 2 is a schematic elevational sectional view of a
`plasma treatment apparatus constructed in accordance with
`a second embodiment of the present invention;
`FIG. 3 is a schematic elevational sectional view of a
`plasma treatment apparatus constructed in accordance with
`a third embodiment of the present invention:
`FIG. 4 is a partial schematic elevational sectional view of
`a modification of the ultraviolet lamp position from that
`shown in FIG. 3;
`FIG. Sis a partial schematic elevational sectional view of
`a modification of the plasma treatment apparatus from those
`shown in FIGS. 1 and 2 by including an ultraviolet lamp;
`FIG. 6 is a schematic elevational sectional view of a
`plasma treatment apparatus constructed in accordance with
`a fourth embodiment of the present invention;
`FIG. 7 is a schematic elevational sectional view of a
`modification of a plasma treatment apparatus using an
`intermediate electrode to replace the two electrodes in the
`embodiment shown in FIG. 6;
`FIG. 8 is a schematic elevational sectional view of yet
`another modification of a plasma treatment apparatus using
`an intermediate electrode to replace the two electrodes in the
`embodiment shown in FIG. 6: and
`FIG. 9 is a schematic elevational sectional view of a
`plasma treatment apparatus constructed in accordance with
`a fifth embodiment of the present invention.
`PREFERRED EMBODDVIENTS OF THE
`INVENTION
`
`A first embodiment of the present invention is described
`with reference to FIG. 1. FIG. 1 is a sectional elevational
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`

`
`5.753.886
`
`7
`View of an atmospheric treatment device has a treatment
`chamber 10 in which is disposed an object to be treated. for
`example a semiconductor wafer 1. and a gas supply 20 in
`fluid communication with treatment chamber 10 and sup-
`plying a gas capable of plasma discharge toward semicon-
`ductor wafer 1. In this embodiment. gas supply 20 is in fluid
`communication with the upper wall of treatment chamber
`10.
`
`In the wall of first gas supply pipe 20a of gas supply 20
`is formed a transparent window 22. An ultraviolet lamp 24
`is disposed therearound window 22 and functions as a
`preexcitation unit. Below transparent window 22 is disposed
`a first pair of plasma generation electrodes 26 disposed
`opposing each other on the peripheral wall of gas supply 20.
`A first electrode 26a of first pair of plasma generation
`electrodes 26 is connected to a first high-frequency power
`source 28. and the second electrode 26b is grounded.
`First gas supply pipe 20a. in which is formed transparent
`window 22. can be formed of metal or the like. Gas supply
`20 also includes a second gas supply pipe 20b downstream
`of first gas supply pipe 20a. which has disposed therein first
`pair of plasma generation electrodes 26. and which is formed
`of an insulating material such as quartz.
`Treatment chamber 10 is in fluid communication with gas
`supply 20 and generally has a larger cross-sectional area
`than gas supply 20. Treatment chamber II) is formed of. for
`example. quartz. and is in fluid communication with an
`exhaust pipe 12 in a side wall thereof.
`In the interior of treatment chamber 10 is disposed a
`second pair of plasma generation electrodes 30. Second pair
`of plasma generation electrodes 30 comprises an upper
`electrode 300 and a lower electrode 3%. Lower electrode
`301: thus functions as a mounting electrode for mounting
`semiconductor wafer 1 with its upper treatment surface la
`facing upstream. relative to the direction of the flow of gas
`along gas supply 20.
`In order to allow the passage of a gas. upper electrode 30a
`is formed of. for example. a porous metal. Upper electrode
`300 has a dielectric member 32a of a porous material such
`as a ceramic. on its lower surface. Similarly. lower electrode
`30b has a dielectric member 32b of a porous material such
`as a ceramic on the upper surface. Dielectric members 32a
`and 32b are provided to prevent an abnormal discharge
`between electrodes 30a and 30b. Upper electrode 300 is
`connected to a second high-frequency power supply 34. and
`lower electrode 301: is grounded.
`The description now turns to the operation of the atmo-
`spheric pressure plasma treatment apparatus. First. an inert
`gas such as helium or argon is introduced through gas supply
`20 to replace the air in treatment chamber 10. At this stage.
`treatment chamber 10 is at or about atmospheric pressure.
`Thereafter. ultraviolet lamp 24. first high-frequency power
`source 28. and second high-frequency power source 34 are
`activated simultaneously or sequentially from top to bottom.
`Ultraviolet lamp 24 provided in an upstream position of
`the gas supply path exposes the helium or other inert gas to
`ultraviolet radiation through transparent window 22. In this
`way.
`the energy of the ultraviolet radiation causes
`photoionization. and excites the gas. At this stage. however.
`no plasma is observed in the inert gas.
`The inert gas. with a raised excitation level. is activated in
`a plasma region A between first pair of plasma generation
`electrodes 26. and a plasma is thus generated In the case of
`helium gas. this plasma is observed as a faint blue discharge.
`which is determined to be a glow discharge.
`Next. in treatment chamber 10. the activated helium gas
`is supplied through porous upper electrode 30a and dielec-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`8
`tric member 324 to treatment surface la of semiconductor
`wafer 1 supported by lower electrode 301) and dielectric
`member 32b.
`
`In a plasma region B between second pair of plasma
`generation electrodes 30. the activated helium gas is further
`activated. generating a plasma at or about atmospheric
`pressure. Again in the case of helium gas. this plasma is
`observed as a faint blue discharge. which is determined to be
`a glow discharge.
`In this way. the plasma state is maintained in plasma
`regions A and B. and then a treatment gas is added to the
`helium gas supplied through gas supply 20. After the treat-
`ment gas is added. treatment chamber 10 is maintained at or
`about atmospheric pressure. If it is desired that organic
`substances adhering to treatment surface 1a of semiconduc-
`tor wafer 1 are to be removed by ashing. the treatment gas
`may be molecular oxygen (02). Adding oxygen changes the
`discharge in plasma regions A and B to a white color.
`Thus. activated gas species such as oxygen ions and
`oxygen radicals present
`in plasma region B react with
`organic substances adhering to treatment surface la. In this
`reaction the organic substances are broken up into carbon
`monoxide. carbon dioxide and water vapor. and expelled
`through exhaust pipe 12.
`Various other substances may be used as the treatment
`gas. and if. for example. the desire is to remove a silicon
`oxide film formed on treatment surface la by etching.
`carbon tetrafluoride (CF4) may be used. Thus a variety of
`treatment gases may be used for various treatments such as
`etching and ashing.
`In the first embodiment. since the gas is first exposed to
`ultraviolet radiation in an upstream portion of the gas supply
`path. the excitation level of the gas is raised. As a result it
`is easier to generate a plasma in the downstream plasma
`region A. and a more stable plasma can be created in plasma
`region A. Since the activated gas in plasma region A is
`activated again in downstream plasma region B. the gen-
`eration of a plasma in plasma region B is also stable. and the
`yield of the treatment of semiconductor wafer 1 can be
`improved. Furthermore. in plasma region B. the density and
`excitation levels of activated gas species such as helium
`radicals and oxygen radicals can be increased. Therefore. the
`uniformity of treatment over surface la of semiconductor
`wafer 1 can be improved. and the treatment rate can be
`increased.
`
`It is thus necessary to position downstream plasma region
`B so as to maintain the activated state of the gas activated in
`plasma region A. The lifetime of the activated gas species
`created in plasma region A depends on the voltage and
`frequency applied to create the plasma in plasma region A.
`Therefore. the distance between plasma regions A and B
`should be set appropriately to meet t