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`BARCODELABEL
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`|II|I|||I|||||||||||I||l|I||Il|II||||lII|I
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`U-s. PATENT APPLICATION
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`SERIAL NUMBER
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`08/433,623
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`FILING DATE
`
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`GROUP ART UNIT
`
`1109
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`DANIEL L. PLAHM, WALNUT CREEK, CA)
`.
`
`JOHN P. VERBONOOEUR, HAYWARD, CA.
`
`*tcoNTINUING DATAI:tetttwtwattattaatwwn
`VERIFIED _
`I
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`23
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`16655-000100
`
`L
`RICHARD T OGAWA
`TOWNSEND AND TOWNSEND KHOURIE AND CR2
`STEUART STREET TOWER
`ONE MARKET PLAZA 20TH FLOOR
`SAN FRANCISCO CA 94105
`
`ADDRESS
`
`PROCESS OPTIMIZATION IN GAS PHASE DRY ETCHING
`
`that annexed hereto is _a tree co y from‘ the records of the United States
`This is to certi
`Patent and Tra emark Office of the application w ich Is Identified above.
`By authority of the
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`Date
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`Certifying Officerl
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`In
`
`Page 7 0f210
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`
`
`COMMISSIONER OF PATENT AND TRADEMARKS
`Washington, D. C. 20231
`
`Sir:
`
`Transmitted herewith for filing is the
`[x] patent application of
`[ ] design patent application of
`[Icontinuation-in-part patent
`
`Jfivgtor:IDANIEL l7/FLAMM
`
`1'
`
`tion of
`
`VERBONCOEUR
`
` mm “ v
`'Express Mail” Label No.
`T131732}"mags
`
`Date of Deposit
`
`MAY
`
`1
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`I hereby certify that this is being deposited with the
`Uniwd States Postal Service "Express Mail Post Office
`to Addressee" service under 37 CFR 1.10 on the date
`indicated above and is addressed to the Commissioner
`
`
`
`For: PROCESS OPTIMIZATION 1N GAS PHASE DRY ETCHING
`
`Enclosed are:
`
`[x] informal drawing(s).
`
`[Kl _13_
`sheet(s) of [ ] fomiai
`[ ] An assz of the invention to
`[x] A [] signed [x] umigned Declaration & Power of Attomey.
`A [] signed [ ] unsigned Declaration.
`A Power of Attorney.
`A verified statemem to establ'sh small entity status under 37 CFR 1.9 and 37 CFR 1.27.
`A certified copy of a
`application.
`information Disclosure Statement under 37 CFR 1.97.
`
`l—Il—IHI—IHH
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`I—lt—ll—ll—ll—lhfl
`
`In view of the Unsigned Declaration as filed with this application and pursuant to 37 CFR §l.53(d),
`Applicant requests-deferral of the filing fee until submision of the Missing Parts of Application.
`
`DOMCHARGETTIEFEINGFEEATTHISTEJE.
`
`Telephone:
`(415) 543-9600
`APPNOFETRN mm
`
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`
`Reg. No.: 37.692
`Attorneys for Applicant
`
`Page 8 0f210
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`

`Attorney Docket No. 016655—0001
`
`
` PATENT APPLICATION
`
`Inventors:
`
`Daniel L. Flamm, a U.S. citizen,
`residing at
`476 Green View Drive
`Walnut Creek, California
`
`94596; and
`
`John Verboncoeur, a U.S.
`citizen, residing at
`3350 Cakes Drive
`Hayward, California
`
`94542.
`
`Assignee:
`
`Jonathan International
`476 Green View Drive
`Walnut Creek, CA
`94596
`
`Entity:
`
`Small
`
`TOWNSEND and TOWNSEND KHOURIE and CREW
`steuart Street Tower, 20th Floor
`One Market Plaza
`San Francisco, California 94105
`(415) 326-2400
`
`Page 9 0f210
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`
`
`1
`
`‘ *"w‘-1.
`
`EAIEHI
`Attorney Docket No. 016655-0001
`
`PROCESS OPTIMIZATION IN GAS PHASE DRY ETCHING
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to integrated circuits
`
`and their manufacture.
`
`The present invention is illustrated
`
`in an example with regard to plasma etching, and more
`
`particularly to plasma etching in resist strippers in
`semiconductor processing. But it will be recagnized that the
`
`invention has a wider range of applicability in other
`technologies such as flat panel displays,
`large area substrate
`
`processing, and the like. Merely by way of example,
`
`the
`
`invention may be applied in plasma etching of materials such
`as silicon, silicon dioxide, silicon nitride, polysilicon,
`
`photoresist, polyimide,
`
`tungsten, among others.
`
`Industry utilizes or has proposed several techniques
`
`for plasma etching. One such method is conventional chemical
`
`gas phase dry etching. Conventional chemical gas phase dry
`
`etching.relies upon a reaction between a neutral gas phase
`
`species and a surface material layer, typically for removal.
`
`.The reaction generally forms volatile products with the
`
`surface material layer for its removal.
`
`In such method,
`
`the
`
`neutral gas phase species may be formed by way of a plasma
`
`10
`
`15
`
`20
`
`25
`
`discharge.
`
`A limitation with the conventional plasma etching
`
`technique is obtaining and maintaining etching uniformity
`within selected predetermined limits.
`In fact,
`the
`
`30
`
`conventional technique for obtaining and maintaining uniform
`
`etching relies upon a "trial and error" process.
`
`The trial
`
`and error process often cannot anticipate the effects of
`
`parameter changes for actual wafer production. Accordingly,
`
`the conventional technique for obtaining and maintaining
`
`35
`
`etching uniformity is often costly,
`to achieve.
`
`laborious, and difficult
`
`Another limitation with the conventional plasma
`
`etching technique is reaction rates between the etching
`
`species and the etched material are often not available.
`
`Accordingly, it is often impossible to anticipate actual etch
`
`k
`
`Page 10 of210
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`Page 10 of 210
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`

`

` 2
`
`rates from reaction rate constants since no accurate reaction
`
`rate constants are available.
`
`In fact, conventional
`
`techniques require the actual construction and operation of an
`
`etching apparatus to obtain accurate etch rates. Full scale
`
`prototype equipment and the use of actual semiconductor wafers
`
`are often required,
`
`thereby being an expensive and time
`
`consuming process.
`From the above it is seen that a method and
`
`apparatus of etching semiconductor wafers that is easy,
`reliable, faster, predictable, and cost effective is often
`desired.
`
`SUMMARY OF THE INVENTION
`
`According to the present invention, a plasma etching
`
`method that includes determining a reaction rate coefficient
`
`based upon etch profile data is provided.
`
`The present plasma
`
`etching method provides for an easy and cost effective way to
`
`select appropriate etching parameters such as reactor
`
`dimensions,
`
`temperature, pressure, radio frequency (rf) power,
`
`flow rate and the like by way of the etch profile data.
`
`In a specific embodiment, the present invention
`provides an integrated circuit fabrication method.
`The
`
`present method includes steps of providing a plasma etching
`
`apparatus having a substrate therein. The substrate includes
`
`a top surface and a film overlying the top surface.
`
`The film
`
`includes a top film surface.
`
`The present method also includes
`
`chemically etching the top film surface to define an etching
`
`profile on the film, and defining etch rate data which
`
`includes an etch rate and a spatial coordinate from the
`
`etching profile.
`
`A step of extracting a reaction rate
`
`constant from the etch rate data, and using the reaction rate
`
`constant in adjusting a plasma etching apparatus is also
`included.
`
`the present
`In an alternative specific embodiment,
`invention also provides a method of designing a reactor.
`The
`
`present method includes providing a first plasma etching
`apparatus having a substrate therein. The substrate has a top
`
`surface and a film overlying the top surface.
`
`The film has a
`
`10
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`15
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`20
`
`25
`
`30
`
`35
`
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`

`

`3
`
`top film surface.
`
`The present method also includes chemically
`
`etching the top film surface to define an etching profile on
`the film, and defining etch rate data which has an etch rate
`
`and a spatial coordinate from the etching profile.
`
`A step of
`
`extracting a reaction rate constant from the etch rate data,
`
`and using the reaction rate constant in designing a second
`
`plasma etching apparatus is also included.
`A further alternative embodiment provides another
`
`method of fabricating an integrated circuit device. The
`
`present method includes steps of providing a uniformity value
`for an etching reaction. The etching reaction includes a
`
`substrate and etchant species.
`
`The present method also
`
`includes defining etching parameters ranges providing the
`uniformity value.
`A step of adjusting at least one of the
`
`etching parameters to produce a selected etching rate is also
`included.
`The etching rate provides an etching condition for
`
`fabrication of an integrated circuit device.
`
`The present invention achieves these benefits in the
`context of known process technology. However, a further
`
`understanding of the nature and advantages of the present
`
`invention may be realized by reference to the latter portions
`
`of the specification and attached drawings.
`
`BRI F DESCRIPTION OF THE DRAWINGS
`
`Fig. 1/?
`s a simplified diagram of a plasma etching
`apparatus accordingrto the present invention;
`Fig. 1A is a simplified cross-sectional view of a
`wafer profile according;3% the plasma etching apparatus of
`Fig. 1;
`
`Fig. 2,é; a simplified diagram of an alternative
`embodiment of a plasma etching apparatus according to the
`
`present invention:
`Figs. 3Jgagre simplified flow diagrams of plasma
`etching methods ac
`rding to the present invention;
`Fig. SA/i: a plot of uniformity,
`temperature,
`pressure, and gap for an etching process according to the
`
`present invention;
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Page 12 0f210
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`

`4
`
`Fig. 6_is'a simplified plot of 1/ash rate vs. LCD
`
`plate number accor ing to the present invention;
`
`Figs. 74g/illustrate an example with regard to
`circular substrates zgcording to the present invention; and
`Figs. 1dél
`illustrate an example with regard to
`rectangular substrates according to the present invention.
`
`DESCRIPTION OF THE SPECIFIC EMBODIMENT
`
`u ‘
`
`Fig. 1 is a simplified diagram of a plasma etching
`~'
`apparatus 10 according to the present invention.
`The plasma
`
`etching apparatus also known as a co—axial reactor includes at
`least three processing zones.
`The three processing zones are
`defined as a plasma generating zone (PG) 13, a transport zone
`
`(T2) 15, a plate stack zone (PS) 17, and others. Also shown
`are a chemical feed F and exhaust E.
`The plasma generating
`
`zone provides for reactant species in plasma form and others.
`Excitation is often derived from a 13.56 MHz rf discharge 8
`
`and may use either capacitor plates or a wrapped coil, but can
`r?) er
`also be derived from otherniou ces. The co-axial reactor 10
`a;
`salso includes a chemical
`crow—source l4 and a temperature and
`pressure control 12, amogg other features.
`Chemical,effects are often enhanced over ion induced
`
`effects and other effects by way of perforated metal shields
`
`18 to confine the discharge to a region between an outer wall
`16 and shields 1a.
`The co-axial reactor relies substantially
`
`upon diffusion to obtain the desired etching uniformity.
`
`The
`
`co-axial reactgr%3}so relies upon a chemical etch rate which
`is diffusion,L '
`.
`In particular,
`the chemical etch rate
`is generally defined as a chemical reaction rate of etchant
`
`species plus at least a diffusion rate of etchant species.
`
`When the diffusion rate of etchant species is much greater
`
`than the chemical reaction rate,
`
`the chemical etch rate is
`
`‘
`
`10
`
`15
`
`20
`
`25
`
`35
`
`A more detailed
`often determined by the diffusion rate.
`analysis of such chemical etch rate will be described by way
`
`of the subsequent embodiments.
`
`Etchant species from the plasma generating zone
`
`diffuse through the transport zone 15 of the reaction chamber,
`
`Page 13 of210
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`Page 13 of 210
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`

`

`5
`
`and enter the plate stack zone space over surfaces of
`
`substrates 21.
`
`A concentration of etchant in the transport
`
`zone, which is often annular, between the plasma generating
`
`zone and the plate stack zone is defined as non. As etchant
`diffuses radially from the transport zone into the plate stack
`
`5
`
`zone and over surfaces of the substrates, it is consumed by an
`
`etching reaction.
`
`A reactant concentration above the
`
`substrate can be defined as no(r,z), where r is the distance
`from the center of the substrate and z is the distance above
`
`10
`
`the substrate.
`
`A diffusive velocity Vb of etchant species in
`
`“the plate stack zone is characterized by Fick's law.
`Vb
`v=-D °
`°
`
`n O
`
`"$31X
`
`In a specific embbdiment, a gap qu above the
`substrate is much less than the lateral extent dbap<<r and gas
`phase mass transfer resistance across the small axial distance
`is negligible so that the axial
`(z—direction)
`term of the
`concentration gradient can be ignored.
`The embodiment can be
`
`15
`
`applied without this restriction; however, numerical mesh
`
`.computer solutions are then required to evaluate the reaction
`
`rate constant and uniformity.
`
`In the embodiment,
`
`the surface
`
`20
`
`etching reaction bears a first order form:
`
`0+5 - SO
`
`where
`
`S is a substrate atom (e.g., resist unit "mer"); and
`
`O is the gas-phase etchant (for example oxygen
`
`atoms) with certain etching kinetics.
`25
`reaction can be defined as follows:
`a W”‘\
`
`The first order etching
`
`3'31
`’1.) .
`“MN" ~
`
`where
`
`-
`£g,=n,AJTe qmgnr
`
`Ros defines a reaction rate;
`
`no defines a concentration;
`A defines a reaction rate constant;
`
`30
`
`T defines a temperature:
`
`Page 14 0f210
`
`Page 14 of 210
`
`

`

`6
`
`Ehcr defines an activation energy: and
`R defines a gas constant.
`
`An example of the first reaction is described in D.L. Flamm
`and D.M. Manes "Plasma Etching," (1989), which is hereby
`
`incorporated by reference for all purposes.
`
`of course, other
`
`order reactions, reaction relations, and models may be applied
`depending upon the particular application.
`'
`An example of an etched substrate 21 from the plate
`
`stack zone is illustrated by Fig. 1A. The substrate 21 is
`
`defined in spatial coordinates such as 2 and r.
`
`The substrate
`
`includes a bottom surface 23, sides 25, and a top surface film
`27. As can be seen, the top surface film includes a convex
`region, or etching profile.
`The etching profile occurs by way
`
`of different etch rates along the redirection of the substrate
`
`corresponding to different etchant species concentrations.
`
`A
`
`concentration profile n°(rhz) is also shown where the greatest
`concentration of reactant species exists at the Outer
`
`In the present invention,
`periphery of the top surface film.
`an etch rate constant may be obtained by correlation to the
`etching profile.
`By way of the etch rate constant, other
`
`etching parameters such as certain reactor dimensions
`
`including a distance between substrates, pressure,
`
`‘ temperature, and the like are easily calculated.
`
`Fig. 2 illustrates an alternative example of an
`
`etching apparatus 50 according to the present invention.
`
`The
`
`etching apparatus 50 is a single wafer etching apparatus with
`elements such as a chamber 53, a top electrode 55, a bottom
`
`electrode 57, a power source 59, a platen 64, and others.
`
`The
`
`bottom electrode 57 is at a ground potential, and the top
`electrode is operably coupled to the power source 59 at a high
`
`voltage potential.
`
`A plasma exists in a region 54 between the
`
`top electrode 55 and the bottom electrode 57, which is often a
`
`grid configuration or the like. Reactant species are directed
`
`via power source from a plasma source to a wafer substrate 61
`
`by diffusion.
`
`A temperature and pressure controller 67 and a
`
`The etching apparatus also
`flow controller 69 are also shown.
`includes a chemical source feed F and a exhaust E.
`of course,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Page 15 of210
`
`Page 15 of 210
`
`

`

`
`
`7
`
`other elements may also be available based upon the particular
`application.
`
`By way of a plate 63 interposed between the wafer
`
`substrate 61 and the bottom electrode 57,
`
`the reactant species
`
`The plate is _
`do not directly bombard the wafer substrate.
`preferably made of an inert material appropriate for the
`
`particular etching such as pyrex or glass for resist ashing,
`
`alumina for fluorine atom etching of silicon, silicon nitride,
`
`or silicon dioxide, and the like.
`
`In an ashing reaction,
`
`the
`
`plate is placed at a distance ranging from about 5 mm to 50 mm
`and less from the wafer substrate 61.
`of course, other
`dimensions may be used depending upon the particular
`appliCation.
`The reactant species are transported via
`diffusion from the plasma source to the wafer substrate around
`
`the periphery of the plate 63. Accordingly,
`
`the reaction rate
`
`at the wafer substrate is controlled by a balance between
`
`chemical reaction and diffusion effects, rather than
`directional bombardment.
`
`By way of the diffusion effects, an etching rate
`
`constant may be obtained for the etching apparatus 50 of Fig.
`
`the etching rate constant derives from a
`In particular,
`_2.
`etching profile 65, which can be measured by conventional
`
`The present invention uses the etching rate
`techniques.
`constant to select other etching rate parameters such as
`
`10
`
`15
`
`20
`
`6}
`
`25
`
`reactor dimensions,sachets-spacing between the substrate and
`its adjacent surface,
`temperatures, pressures, and the like.
`
`But the present invention can be used with other reactor types
`where etching may not be controlled by diffusion.
`For
`
`example,
`
`the present invention provides a reaction rate which
`
`can be used in the design of reactors where diffusion does not
`control such as a directional etcher and the like.
`The
`
`30
`
`reaction rate constant may also be used in the directional
`
`etcher to predict an extent of, for example, undercutting of
`
`35
`
`unprotected sidewalls while ion bombardment drives reaction in
`a vertical direction.
`of course,
`the invention may be applied
`
`to other reactors such as large batch, high pressure,
`
`chemical, single wafer, and others. The invention can also be
`
`applied to different substrate materials, and the like.
`
`Page 16 of210
`
`Page 16 of 210
`
`

`

`W '
`
`Figs. 3-5 illustrate simplified flow diagrams of
`
`plasma etching methods according to the present invention.
`
`Theapresent methods provide for improved etching conditions.by
`wayta reaction rate constant derived from, for example, an
`etching profile.
`It should be noted that the present methods
`
`as illustrated should not be construed as limiting the
`
`invention as defined in the claims. One of ordinary
`
`ill in
`
`the art would easily recognize other applications ego he
`inventions described here.
`’
`In a specific embodiment, a method of extracting a
`
`rate constant 100 for a plasma etching step according to the
`
`present invention is illustrated by the flow diagram of Fig.
`
`3.
`
`A substrate with an overlying film is placed into a plasma
`
`The overlying film is defined
`etching apparatus or the like.
`as an etching film.
`In the present embodiment,
`the overlying
`
`film is a photoresist film, but can also be other films such
`
`as a silicon film, a polysilicon film, silicon nitride,
`
`silicon oxide, polyimide, and the like.
`
`A step of plasma etching the film is performed by
`The plasma etching step occurs at constant pressure
`lstep 101.
`and preferably constant plasma source characteristicsgm' More
`preferably,
`the plasma etching step occurs isothermally at
`
`10
`
`15
`
`20
`
`25
`
`temperature 13, but can also be performed with changing
`temperatures where temperature and time histories can be
`
`monitored.
`
`Plasma etching of the film stops before the
`
`endpoint (or etch stop). Alternatively, plasma etching stops
`
`The plasma
`at a first sign of the endpoint (or etch stop).
`etching step preferably stops before etching into an etch stop
`
`layer underlying the film to define a ”clean" etching profile.
`
`30
`
`The substrate including etched film is removed from
`
`the chamber of the plasma etching apparatus.
`
`The etched film
`
`includes an etching profile (step 103) made by way of plasma
`
`35
`
`The etching profile converts into a
`etching (step 101).
`relative etch rate, relative concentration ratio, a relative
`
`etch depth, and the like at selected spatial coordinates.
`relative etch rate is defined as an etch rate at a selected
`
`The
`
`spatial coordinate over an etch rate at the substrate edge.
`
`Page 17 of210
`
`Page 17 of 210
`
`

`

`9
`
`The relative concentration ratio is defined as a concentration
`
`of etchant species at a selected spatial coordinate over a
`
`concentration of etchant at the substrate edge.
`
`In x-y—z coordinates,
`the relative etch rate in the
`z-direction, and the spatial coordinates are defined in the x-
`y coordinates.
`The etching profile is thereby characterized
`as a relative etch rate u, a x—location, and a y-locationigu.
`@g y).
`In cylindrical coordinates,
`the relative etch rate13
`also in the z—direction, and the spatial coordinates are
`
`The etching profile is
`defined in the r and e coordinates.
`characterized as a relative etch rate u, a r-location, and a
`e-location (u, r, 9). An array of data points in either the
`
`x-y coordinates or r-e coordinates define the etching
`
`profile.
`
`The array of data points can be defined as an n x 3
`
`array, where n represents the number of points sampled and 3
`
`represents the etch rate and two spatial dimensions.
`
`of
`
`course,
`
`the choice of coordinates depends upon the particular
`
`application.
`Optionally,
`
`_
`in a non-isothermal condition, an
`
`average etch rate is measured.
`
`By approximate integration of
`
`a time dependent etch rate, suitable starting point
`
`'approximations for an etching rate constant pre-exponential
`
`and activation energy can be selected. The etch rate is
`
`integrated over time (and temperature) using measured
`
`temperature-time data (or history). An etched depth profile
`
`and the etching rate from the integration can then be compared
`
`with actual data.
`
`A rate constant is appropriately readjusted
`
`and the aforementioned method is repeated as necessary.
`
`An etch constant (or a reaction rate constant) over
`
`diffusivity (kvo/D) and an etch rate at an edge is calculated
`at step 105. The etch constant over diffusivity correlates
`
`with data points representing the etch rate profile.
`
`In x-y
`
`the rilationship between kvo/D and the relative
`coordinates,
`etch rate u(x,y) {sisgfined as follows:
`where
`
`a and b define substrate lengths in, respectively,
`
`an x-direction and a y-direction.
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`Page 18 of210
`
`Page 18 of 210
`
`

`

`1o_
`
`
`
`V“
`
`In cylindrical coordinates, the relationship between
`the etch constant over diffusivity kvo/D and the relative etch
`rate u(r) is defined as follows:
`
`‘1‘ ¢
`\‘z /
`
`‘
`
`.
`
`u(r)-
`
`k
`13 —i§r
`k
`‘N D3]
`__."°
`
`1’
`
`1
`
`
`
`'"-‘—’
`5
`
`.
`
`'
`”
`JL’
`3|
`
`where
`rx
`a is an outer radius (or edge) of the substrate“}'
`In step 106, a diffusivity is calculated for the
`
`The binary diffusivity DAB may be
`particular etchants.
`calculated based upon the well known Chapman-Enskog kinetic
`
`'“‘-‘~1~\theory equation:
`
`’Yflisi
`
`.__.;Ul..
`
`where
`
`D” - 2.2646 x 10-5
`
`Ti+.1_
`M
`M
`A
`3
`“Maxine
`
`T is a temperature;
`c is a total molar concentration;
`
`MA and Mb are molecular weights;
`
`15
`
`&
`
`,
`
`DAB is a binary diffusivity;
`0A8 is a ceijisagn diameter; and
`9D,AB is abco-i-l-usi-on integral.
`
`The Chapman-Enskog kinetic theory equation is described in
`detail in part III of R.B. Bird, W.B. Stewart, and E.N.
`
`Lightfoot, "Transport Phenomena," Wiley (1960) which is hereby
`
`20
`
`incorporated by reference for all purposes.
`
`of course, other
`
`techniques for calculating a diffusivity may also be used.
`
`Page 19 of210
`
`Page 19 of 210
`
`

`

`p-—A\derived from the diffusivity as follows.
`
`The equivalent volumetric reaction rate constant kvo is
`
`11
`
`.— '. 13/»
`Hz '
`
`~
`
`4
`
`kw
`km" (7%!
`
`the surface
`_*~__—__‘*once the reaction rate constant kvo is extracted,
`reaction rate constant ks may be isolated from the previous
`equation as follows.
`
`5
`
`k,= (kw) aw
`
`"
`
`Repeat steps 101-106 at different temperatures T2,
`
`T3. . .Tn to calculate additional reaction rate constants k(T2),
`k(T3) .
`. .k(Tn).
`The steps are repeated at least two times and
`more, and preferably at least three times and more. Each
`
`10
`
`temperature is at least 5 °C greater than the previous
`
`temperature. Of course, the selection of temperatures and
`
`trial numbers depend upon the particular application.
`
`.-.
`
`15
`Q:
`"Y” "
`
`1
`
`Extract an activation energy Eacc for a first order
`0
`reaction from the data k(T2), k(T3):¢'lik(T ) at T2, T3. . .TI]
`collected via step 109 by way of theorfgfliou equation:
`-B_«
`k,(T) =Av/T' e “T
`
`1‘
`
`-"
`
`—“_—’”_'—"The activation energy is preferably calculated by a least
`
`square fit of data collected at step 109 or any other suitable
`
`statistical technique.
`
`By way of the same equation,
`
`the
`
`present method calculates surface reaction rate constant ks at
`any temperature.
`
`20
`
`6/
`
`3/ 25
`
`In step 111, a concentration :10 at the substrate
`
`edge is calculated.
`The concentration no deduces from the
`following relationship:
`Kn
`no ' Re/kfis
`
`where
`
`Res is an etch rate.
`From the concentration and the surface reaction rate,
`particular etching step can be improved by way of adjusting
`
`the
`
`selected etching parameters.
`
`Page 20 of210
`
`Page 20 of 210
`
`

`

`
`
`12
`
`In an alternative specific embodiment, a method to
`
`"tune? a plasma source using a loading effect relationship (or
`equation)
`is illustrated by the simplified flow diagram 200 of
`
`Fig. 4.
`
`The method includes a step 201 of measuring an etch
`
`The effective
`rate against an effective etchable area Aw.
`etchable area changes by varying the number m of waters in the
`
`reactor, varying the size of the wafer, or the like.
`
`The
`
`effective area can be changed 209 by altering a gap between a
`
`wafer and its above surface 211, changing wafer quantity in
`
`the reactor 213, and varying substrate support member
`dimensions 215.
`The method preferably occurs at constant
`temperature and pressure. However,
`the effective etchable
`
`area may also be varied by way of changing a temperature
`
`and/or a pressure.
`
`The method calculates a uniformity value (step 217)
`from the measured values of etch rate vs. effective area in
`
`10
`
`15
`
`steps 211, 213, and 215.
`~~w~_____ example:
`
`The uniformity is calculated by, for
`
`_wf3%
`
`L7
`
`20
`
`25
`
`30
`
`D"
`uniformi ty=100Ala—“5%"
`2; —1
`.1 m
`
`where
`
`RMAg is a maximum etch rate;
`
`RMIN is a minimum etch rate;
`m is a sample number;
`
`R1 is a general etch rate for an ith sample;
`uniformity is a planarity measurement in
`
`,
`percentage.
`In a specific embodiment, a uniformity of about 90% and
`
`greater or preferably 95% and greater indicates that the
`effective area of the substrate is substantially equal to the
`
`actual substrate area (step 221) via branch 216.
`
`of course,
`
`other methods of calculating a uniformity from etch rates and
`
`effective areas may also be used depending upon the particular
`
`application. Alternatively, an etching profile is measured
`
`and the effective area Aerf is calculated (step 219) by way
`of, e.g.,
`the-loading effect relationship.
`
`Page 210f210
`
`Page 21 of 210
`
`

`

`13
`
`At least two and more different effective etchable
`
`areas (step 223) are measured, or preferably at least three
`
`and more different etchable areas are measured.
`
`Alternatively,
`
`the flow diagram returns via branch 224 to step
`
`5
`
`209, and takes another etch rate measurement at a different
`effective area.
`The flow diagram then turns to step 203.
`
`'
`
`In step 203, a supply of etchant ST in the reactor
`is calculated. Based upon the different etchable areas a
`
`
`10
`
`slope mAeff deduces from the loading effect relationship as
`-.
`‘follpws.
`
`fig
`
`
`
`2..
`
`
`
`
`
`ngm)
`
`k,n,,
`
`k,sT
`
`ST
`
`is the etching rate at the boundary between the
`wherefihuan)
`plate stack zone and transport zone when m substrates are
`
`present in the reactor.
`
`The first term includes a
`
`recombination term proportional to the total effective area Ar
`which acts to catalyze loss of etchant on reactor surfaces in
`
`15
`
`The second term is the
`the reactor plus a convection term F.
`loading effect relation, where the reciprocal etch rate is
`
`proportional to the amount of effective etchable substrate
`
`' area Aeff times the number of substrates m. When the etching
`across a substrate is uniform, Aeff is the geometrical
`substrate area Aw.l When etching is nonuniform, on the other
`
`hand, Aeff is a function of kvo/D and geometrical reactor
`dimensions.
`The supply of etchant ST may be calculated for a
`different plasma source or plasma source parameters such as
`
`temperature, pressure, or the like by repetition 207 of steps
`201 and 203.
`By way of the supply of etchant to the reactor,
`
`other plasma source parameters may be varied to obtain desired
`
`etching rates and uniformity for the particular reactor.
`
`Step 205 provides for the modification of chamber
`materials and the like to reduce slope numerator
`(kt, Ar + F)
`in selecting the desired etching conditions.
`The chamber
`
`the
`materials can be modified to reduce, for example,
`recombination rate in the reactor. The recombination rate is
`
`20
`
`25
`
`30
`
`directly related to the effective reactor recombination area
`
`35
`
`Ar.
`
`In step 205,
`
`the recombination rate can be adjusted by
`
`/:
`
`Page 22 0f210
`
`Page 22 of 210
`
`

`

`14
`
`changing Ar via changing chamber material, coating chamber
`surfaces with, for example, a product sold under the trademark
`
`TEFLON" or KALREZ" and the like, among others. Alternatively,
`
`the slope numerator flow term F is reduced when F contributes
`
`as a substantial loss term. Of course, the particular
`materials used depend upon the application.
`In step 207,
`the method changes plasma source
`
`'
`
`parameters such as rf power,
`
`flow rate, and the like to select
`
`desired etching conditions. Once one of the aforementioned
`
`the method returns to step 201 via
`parameters is adjusted,
`branch 208. At step 201, an etch rate vs. effective etchable
`
`area is measured and the method continues through the steps
`until desired etching condition are achieved.
`of course,
`
`other sequences of the aforementioned steps for tuning the
`
`plasma source may also exist depending upon the particular
`
`application.
`
`Fig. 5 is a simplified flow diagram for a method of
`
`selecting a desired uniformity and desired etching parameters
`
`within selected ranges to provide a desired etch rate for a
`
`particular etching process. The etching parameters include
`process variables such as reactor dimensions, a pressure, a
`
`'temperature, and the like for a particular substrate and
`
`reactants. other etching parameters may also be used
`depending upon the particular application.
`In step 301, select a uniformity for the selected
`substrate and the reactants.
`The selected uniformity becomes
`
`an upper operating limit for the reaction according to the
`
`present method.
`
`The upper operating limit ensures a "worst
`
`case" uniformity value for an etched substrate according this
`method. Uniformity can be defiEed by, for example:
`1-
`R
`‘R
`uniformity=10%—m_“:”j
`212%
`
`where
`
`RMAX is a maximum etch rate;
`
`RMIN is a minimum etCh rate;
`m is a sample number;
`
`10
`
`15
`
`20
`
`25
`
`
`
`Page 23 of210
`
`Page 23 of 210
`
`

`

`15
`
`R1 is a general etch rate for an ith sample;
`uniformity is a planarity measurement in
`
`percentage.
`
`In certain embodiments,
`
`the selected uniformity ranges from
`
`about 90 % and greater or more preferably 95 % and greater.‘
`
`of course, other uniformity values may be selected based upon
`
`the particular application.
`Based upon the selected uniformity, use the selected
`
`uniformity as a stating point to extract a plurality of
`reaction rate constants k .
`The reaction rate constants may
`be also be obtained by an input activation energy for the
`
`etching process, among other techniques (step 303).