(cid:55)(cid:82)(cid:78)(cid:92)(cid:82)(cid:3)(cid:40)(cid:79)(cid:72)(cid:70)(cid:87)(cid:85)(cid:82)(cid:81)(cid:3)(cid:47)(cid:76)(cid:80)(cid:76)(cid:87)(cid:72)(cid:71)
`(cid:40)(cid:59)(cid:43)(cid:44)(cid:37)(cid:44)(cid:55)(cid:3)(cid:20)(cid:19)(cid:19)(cid:25)
`(cid:44)(cid:51)(cid:53)(cid:3)(cid:51)(cid:72)(cid:87)(cid:76)(cid:87)(cid:76)(cid:82)(cid:81)(cid:3)(cid:73)(cid:82)(cid:85)
`(cid:56)(cid:17)(cid:54)(cid:17)(cid:3)(cid:51)(cid:68)(cid:87)(cid:72)(cid:81)(cid:87)(cid:3)(cid:49)(cid:82)(cid:17)(cid:3)(cid:53)(cid:40)(cid:23)(cid:19)(cid:15)(cid:21)(cid:25)(cid:23)
`
`Page 1 of 7
`
`

`

`(19) JAPAN PATENT OFFICE (JP)
`
`(11) PUBLICATION NUMBER
`
`(12) PATENT APPLICATION
`LAID-OPEN PUBLICATION (A)
`
`JP 3-196206 A
`
`IDENTIFICATION CODE: JPO REFERENCE NUMBER
`J
`8835-5H
`7124-2H
`8835-5H
`
`F
`
`(43) DATE OF PUBLICATION
`27. 08. 1991
`
`B
`Z
`310 C
`
`(51) Int.Cl5
`G05D 23/19
`G03F 7/26
`G05D 23/00
`H01L 21/027
` 21/205
` 21/31
` 21/324
`H05B 3/00
`
`7739-5F
`6940-5F
`7738-5F
`7719-3K
`H
`361
`H01L 21/30
`2104-5F
`Request for Examination: Not Filed Number of Claims: 1 (6 pages total)
`(54) Title of the Invention HEAT TREATMENT DEVICE
`(21) Japanese Patent Application No. H1-335774
`(22) Filing Date: 25. 12. 1989(H1)
`(72) Inventor: Kimiharu MATSUMURA
`c/o TEL Kyushu KK, 2655 Tsukure, Kikuyoumachi, Kikuchi-gun,
`Kumamoto
`c/o TEL Kyushu KK, 2655 Tsukure, Kikuyoumachi, Kikuchi-gun,
`Kumamoto
`(71) Applicant: Tokyo Electron LTD
`1-26-2 Nishishinjuku, Shinjuku-ku, Tokyo
`(71) Applicant: Tokyo Erekutoron Kyushu KK, 2655 Tsukure, Kikuyoumachi, Kikuchi-gun, Kumamoto
`(74) Representative: Patent Attorney Masami SATO
`
`(72) Inventor: Hidekazu SHIRAKAWA
`
`Description
`
`1. Title of the Invention
`Heat Treatment Device
`
`2. Claim(s)
`A heat treatment device for heating a subject to be
`treated by a heating means and thus performing a
`predetermined treatment thereon, characterized in that
` a heat flux detection means is provided for detecting a
`heat flux imparted from the heating means to the subject,
`and
` the heating means is controlled based on an output of
`the heat flux detection means.
`
`3. Detailed Description of the Invention
`[Industrial Applicability]
` The present invention relates to a heat treatment
`[0001]
`device.
`[Description of the Prior Art]
` In processes of manufacturing a semiconductor
`[0002]
`integrated circuit, various heat treatment processes are
`employed; e.g., baking, depositing and ashing in a
`photolithography process.
`
` Conventionally, the heat treatment, e.g. the baking is
`[0003]
`performed in such a manner that for example, in a case of
`single wafer processing, a substrate to be treated is
`mounted on a heating plate made of, for example, SUS or
`aluminum and having a heating resistor such as a
`nichrome wire built therein, a temperature sensor such as
`a thermocouple or a thermometric resistor is embedded,
`for example, in the heating plate, and then a temperature
`is monitored by the temperature sensor, thereby
`controlling a treatment temperature.
`[Problem to be solved by the Invention]
` As described above, a temperature control technique
`[0004]
`in the conventional heat treatment device is a type, in
`which a temperature is monitored for temperature
`control, and thus causes a delay in control. Accordingly,
`when a temperature of a subject to be treated is increased
`to a predetermined temperature or decreased to a
`predetermined temperature, or when a change in
`temperature is likely to be caused due to an influence of a
`disturbance and the like, a precise control with a good
`responsiveness is difficult.
` Specifically, the heating plate and thus the substrate to
`[0005]
`be treated are heated by a heat flux generated from a
`heating body such as a heater (heat flux is calorie per unit
`area and unit time; the unit is kcal/m2·h), and in general,
`
`Page 2 of 7
`
`

`

` a temperature is an integral value of a heat flux with
`respect to time and coordinate (the following thermal
`diffusion equation (1) and Fourier’s law equation (2)).
`Accordingly, when a heat flux is determined,
`temperatures of the heating plate and the subject to be
`treated are determined as a result thereof. Thus, a
`predetermined correlation exists between the heat flux and
`the temperature (the following thermal diffusion equation
`(3))
`
`(cid:16904)(cid:16084)(cid:16093)(cid:16085)
`
`(cid:16904)(cid:16084)(cid:16094)(cid:16085)
`
`(cid:16904)(cid:16084)(cid:16095)(cid:16085)
`where T: temperature, q: heat flux, t: time, y: coordinate,
`ρ: density, Cp: thermal capacity and k: thermal
`conductivity.
` Accordingly, as a change in phenomenon, a heat flux
`[0006]
`tend to be detected earlier than a temperature, and thus a
`delay in control is occurred when the temperature is
`monitored. Therefore, in the conventional temperature
`control technique using the temperature monitoring, when
`a change in temperature is likely to be caused due to a
`disturbance and the like, it is impossible to predict a
`change in temperature caused by the disturbance based on
`the state of a set temperature and to perform control so as
`to suppress the disturbance.
`
` For example, as shown in Fig. 2, a substrate to be
`[0009]
`treated is set to a predetermined temperature T1 by a
`heating plate and then is heated during a predetermined
`set time D2 in a state where the temperature T1 is kept.
` However, in Fig. 2, the related art performs a temperature
`[0010]
`management in such a manner that during a period of the
`set temperature T1, the temperature is kept constant, but
`does not manage a history (temperature change pattern) at
`all such as temperature change gradients during a
`temperature increasing period D1 and a cooling period D3
`and time lengths thereof.
` As such, because a temperature change pattern during
`[0011]
`increasing or decreasing of the temperature is not
`managed, even if substrates to be treated are
`semiconductor wafers of the same type, the pattern of
`each substrate is different from each other and thus
`physical properties of the resist in each substrate is also
`different from each other, thereby causing a problem in
`that reliability lacks.
` In addition, recently, a resist pattern becomes finer as a
`[0012]
`density and a degree of integration of a semiconductor
`device increase.
`
` Also, when attempting to control a temperature
`[0007]
`history during increasing or decreasing the temperature to
`a predetermined temperature, it is impossible to predict
`and control a temperature in accordance with a
`predetermined temperature history. In addition, even if a
`disturbance is occurred during increasing and decreasing
`of the temperature and thus a heat flux is varied from an
`initial value thereof, a timing at which an action can be
`taken with respect thereto in the temperature monitoring
`type is after a change in temperature is exhibited, and
`thus a delay in control is inevitable. Therefore, in the
`conventional temperature control technique, it is difficult
`to precisely and accurately obtain a desired temperature
`change pattern during increasing or decreasing of the
`temperature.
` Further, a baking process is a heat treatment for
`[0008]
`removing a solvent in a photoresist after application of
`the photoresist, exposure of the photoresist film,
`development thereof and the like and also controlling
`physical properties (photosensitivity, resolution and the
`like) of the resist while imparting a thermal resistance to
`the resist, and is intended to heat a semiconductor wafer
`or the like at a predetermined desired temperature during
`a predetermined period of time, for example, as disclosed
`in Japanese Patent Application Publication No. S61-
`201426.
`
`Therefore, physical properties of the photoresist, such as
`resolution or photosensitivity are gradually non-
`negligibly influenced by a temperature change pattern
`during a temperature increasing period or a temperature
`decreasing period, which has been conventionally
`ignored in the baking process. Accordingly, it is
`necessary to control a history, such as temperature
`change patterns during increasing or decreasing of the
`temperature, so that the history takes a predetermined
`pattern and thus to obtain better resist physical
`properties.
` Thus, it may be considered to perform temperature
`[0013]
`control even during the temperature increasing period
`and the temperature decreasing period; but as described
`above, because the conventional temperature control
`technique is a type in which a temperature is controlled
`by monitoring the temperature, a delay in control is
`occurred, in particular in a case where a sharp
`temperature change occurs. Thus, it is impossible to
`predict a temperature change and to control a temperature
`history so that the history follows a desired pattern.
` In view of the above, an object of the present
`[0014]
`invention is to provide an improved heat treatment device
`addressing the above problems by allowing a prediction
`and contol of the temperature change.
` [Means for Solving Problem]
`
`Page 3 of 7
`
`

`

` According to the present invention, there is provided a
`[0015]
`heat treatment device for heating a subject to be treated by
`a heating means and thus performing a predetermined
`treatment thereon,
` characterized in that wherein a heat flux detection means
`is provided for detecting a heat flux imparted from the
`heating means to the subject, and
` the heat treatment device is configured to control the
`heating means based on an output of the heat flux
`detection means.
`[Function]
` As described above, as a phenomenon, the change in a
`[0016]
`heat flux may respond more quickly than that in
`temperature. In addition, due to a predetermined
`correlation between the heat flux and the temperature, a
`change in temperature can be predicted by monitoring the
`heat flux (the foregoing equation (3)). Accordingly, even
`in a situation where a disturbance exists, the temperature
`can always be stably controlled and a desired temperature
`increasing or decreasing characteristics can be precisely
`managed.
`[Embodiments]
` Now, one embodiment of a heat treatment device
`[0017]
`according to the present invention, which is applied to a
`baking apparatus that performs a photolithograph process,
`will be described by way of example with reference to the
`accompanying drawings.
` In Fig. 1, a hot plate 1 is made of a metal and has a
`[0018]
`
`heating resistor 2 embedded therein. A semiconductor
`wafer 3 is mounted on the hot plate 1 and controllably
`heated by the hot plate 1 as described below.
` The heating resistor 2 of the heating plate 1 is
`[0019]
`supplied with an electric power, for example, from a
`commercial alternating current power source 4 via a
`switching element, in this example via SSR (Solid State
`Relay) 5. In this case, the SSR 5 is controllably switched
`by a PWM (pulse width modulation) signal SM from a
`temperature control circuit 10 having a computer as
`described above, and thus an alternating current is
`allowed to flow through the heating resistor 2 during a
`period of time corresponding to a pulse width of the
`signal SM, so that the heating resistor 2 generates heat
`corresponding to an amount of supplied electric power.
`Therefore, by changing a pulse width of the PWM signal
`SM, an amount of electric power per one cycle T of the
`signal SM to be supplied to the heating resistor 2 can be
`adjusted and thus a temperature of the hot plate 1 can be
`controlled. Namely, in this case, a temperature of the hot
`plate 1 corresponds to the average of a temperature
`achieved by microscopic rise caused by the supply of an
`electric power to the heating resistor 2 during a period of
`time of a pulse width W of the PWM signal SM, and a
`temperature achieved by microscopic decrease caused by
`the interruption of the electric power to the heating
`resistor 2 during a period of time after the period of time
`of the pulse width.
`
`[0020]
`
`Thus, assuming that temperature increasing and
`decreasing characteristics of the hot plate 1 are the same,
`the temperature of the hot plate 1 does not change, for
`example, when the pulse width W of one cycle T of the
`PWM signal SM is 1/2T, namely, when a duty ratio
`thereof is 50%. When the pulse width W of the PWM
`signal SM is wider than 1/2T, the temperature of the hot
`plate 1 rises with a gradient corresponding to the pulse
`width W, whereas when the pulse width W of the PWM
`signal SM is narrower than 1/2T, the temperature of the
`hot plate 1 lowers with a gradient corresponding to the
`pulse width W. In this way, by changing the pulse width
`W of the PWM signal SM, the temperature of the hot
`plate 1 can be freely controlled.
` A temperature sensor 6 including, for example, a
`[0021]
`thermocouple or a thermometric resistor is provided in the
`vicinity of a surface of the hot plate 1, where the wafer 3
`is to be mounted, and an output of the temperature sensor
`6 is supplied to a thermometer 7. Then, an output signal
`of the thermometer 7 corresponding to a detected
`temperature is supplied to the temperature control circuit
`10.
` A heat flux sensor 8 is provided in the vicinity of a
`[0022]
`surface of the wafer 3 and an output of the heat flux
`sensor 8 is supplied to a heat flux meter 9,
`
` whereby a heat flux q is obtained. Then, the heat flux q
`is supplied to the temperature control circuit 10. The
`heat flux sensor 8 is configured with a thin plate material
`(thickness d) having a thermal conductivity λ small
`enough to detect a very small temperature error, and a
`heat flux q flowing through the thin plate can be obtained
`by the following equation.
`
`…(4)
` Because ΔT is a difference in temperature between both
`[0023]
`front and back surfaces of the thin plate and λ and d are
`known, a heat flux q can be obtained through the heat
`flux meter 9 by measuring ΔT, for example, using a
`differential thermocouple provided in the heat flux sensor
`8. The temperature control circuit 10 predicts a change
`in temperature of the wafer 3 from the heat flux q (based
`on the principle of the above equation (3)).
` In addition, the hot plate 1 has a pin, not shown,
`[0024]
`inserted therethrough for lifting a semiconductor wafer 3
`from the hot plate 1 while supporting the wafer 3. The
`semiconductor wafer 3 is transported onto the hot plate 1
`by a transport mechanism, not shown, and is loaded onto
`or unloaded from the hot plate 1 by the lifting or
`lowering of the pin.
`
`Page 4 of 7
`
`

`

` Next, a baking process using the heat treatment device
`[0025]
`configured as in Fig. 1 will be described.
`[0026]
` First, the pin, not shown, as described above is lifted
`from a surface of the hot plate 1. Then, a transported
`semiconductor wafer 3 is mounted onto the lifted pin.
`Subsequently, the pin is lowered so that the semiconductor
`wafer 3 is mounted and then held on the hot plate 1 by
`adsorption. Then, the semiconductor wafer 3 is heated by
`heat conduction from the hot plate 1 in accordance with a
`temperature control as follows.
`[0027]
` In the case described here, as described above, the
`temperature control circuit 10 has a computer, and thus a
`specification (recipe) intended to exhibit a suitable
`temperature history depending on types of subjects such
`as the semiconductor wafer 3 is inputted and stored by a
`baking pattern input means 11 such as a keyboard. A
`temperature control is performed in accordance with the
`recipe.
`[0028]
` Fig. 3 shows, as an example of the recipe, a heat
`history, in which a temperature rises from a room
`temperature of 20(cid:16989) to 120(cid:16989) with a predetermined
`gradient over 60 seconds,
`
` and then the temperature of 120(cid:16989) is kept for 60 seconds
`before decreasing to the room temperature of 20(cid:16989) over
`60 seconds. In order to reproduce this heat history, for
`example, points P0 to P8 as in Fig. 3 are defined and then
`time and temperature information at each of the points P0
`to P8 is inputted, thereby the recipe is input.
` The temperature control circuit 10 calculates a
`[0029]
`temperature gradient between two adjacent points (e.g.,
`P1-P0) during a temperature increasing period of points
`P0 to P3 and a temperature decreasing period of points
`P5 to P8, based on information of the two points, and
`then supplies a PWM signal SM, which has a pulse width
`W corresponding to the temperature gradient, to the SSR
`5. Then, at this time, the heat flux meter 9 detects a heat
`flux from the hot plate 1, based on an output signal
`proportional to a temperature difference detected by the
`heat flux sensor 8, and thus the pulse width W of the
`signal SM is controlled to gradually correct an error
`between a temperature calculated from the recipe and a
`temperature of the wafer 3 estimated from the heat flux
`while referring to a correlation, as previously obtained,
`between the heat flux and a change in the temperature of
`the wafer (the following equation (5)).
`
`(cid:16163)(cid:16148)(cid:16145)(cid:16158)(cid:16145)
`
`(cid:16904)(cid:16084)(cid:16097)(cid:16085)
`
` where T: temperature, t: time, q: heat flux, y; coordinate
` L: a distance between the wafer and the heat flux sensor
` ρ: density of air, Cp: thermal capacity of air
` : body of the heat flux sensor, s: wafer surface
` f(L, t): a function representing a predetermined
`relationship between q and qs.
`[0030]
` In addition, during the temperature increasing period
`P0 to P3 and the temperature decreasing period P5 to P8,
`verification of results of temperature control is performed
`by additionally referring to temperature information from
`the temperature sensor 6.
`
` In a period between points P3 to P5, during which a
`[0031]
`temperature is settled, the temperature control circuit 10
`controls the heating resistor 2 by referring to only
`temperature information measured from the temperature
`sensor 6. This is because the hot plate 1 has a relatively
`large thermal capacity and thus is hardly influenced by a
`disturbance after the temperature has been settled.
`Basically, in a state where the hot plate 1 is being
`influenced by a disturbance, it is preferable to control the
`heat resistor 2 by additionally referring to the heat flux
`from the heat flux meter 9.
`[0032]
` Meanwhile, in this case, for example, a liner control
`technique such as a PID control technique can be
`employed as a temperature control technique. Namely, a
`temperature (reference temperature) at every moment is
`obtained, for example, based on a gradient calculated
`from information of two points during the temperature
`increasing period, and then an error between the
`reference temperature and a temperature of the wafer 3
`estimated from the heat flux detected by the heat flux
`meter 9 is obtained. Then, an amount of electric power
`to be supplied is calculated from the temperature error,
`and correspondingly, a pulse width W of the PWM signal
`SM is adjusted.
`
`Page 5 of 7
`
`

`

` Meanwhile, the heat flux sensor 8 can be attached on
`[0035]
`any position so long as a heat flux imparted to a subject
`can be detected; the heat flux sensor 8 may be provided
`inside the hot plate 1, for example.
`[0036]
` The heating means is not limited to the configuration
`in which the heating resistor is embedded in the hot plate,
`and accordingly, may employ configurations in which
`various heat generation means are used, e.g., a
`configuration in which a thin plate-shaped heat generator
`is attached on the hot plate. In this case, if in order to
`reduce a thermal capacity of the hot plate, a hot plate
`which is as thin as possible is used, it is possible to
`further enhance a performance of temperature control by
`heat flux as described above.
` Further, the subject to be treated is not limited to the
`[0037]
`semiconductor wafer, and accordingly, it will be apparent
`that the present invention may be also applied to, for
`example, LCD substrates, glass substrates, printed boards
`and the like.
`[0038]
` Further, although the foregoing illustrates single wafer
`processing, it is apparent that the present invention may
`also be applied to batch processing.
`
` Fig. 1 is a view showing one embodiment of a case
`where a heat treatment device according to the present
`invention is applied to a baking apparatus, Fig. 2 is a
`view showing an example of a temperature history during
`baking, and Fig. 3 is a view explaining an example of a
`recipe for control a temperature in a baking process.
` 1: Hot plate
` 2: Heating resistor
` 3: Semiconductor wafer
` 8: Heat flux sensor
` 9: Heat flux meter
` 10: Temperature control circuit
`
`Representative: Patent Attorney Masami SATO
`
`[0033]
` In this way, by detecting a heat flux flowing through
`the wafer 3, which is a subject, by the heat flux meter 9
`and then predicting and controlling a temperature based
`on the heat flux, it is possible to precisely control the
`temperature increasing period and the temperature
`decreasing period in the baking treatment with a good
`responsiveness and also to allow uniform resist physical
`properties to be imparted to wafers of the same type.
`Further, a thermal history during the temperature
`increasing period and the temperature decreasing period
`can be also controlled, and thus an effect is also achieved
`in which desired resist physical properties are obtained.
` Although the wafer 3 is directly mounted on the hot
`[0034]
`plate 1 in the foregoing example, at least three ball-shaped
`points may be provided to protrude from the hot plate 1
`by a few μm, so that the semiconductor wafer 3 is
`supported at three points. Accordingly, the semiconductor
`wafer 3 cannot directly come in contact with the hot plate
`1 and thus even if a dust exists on the hot plate 1, the dust
`can be prevented from being attached on a back surface of
`the semiconductor wafer 3. In this case, air can enter
`between the wafer 3 and the hot plate 1, and
`correspondingly temperature control on the wafer 3 can be
`delayed. However, the present invention is not intended
`to monitor a temperature, but to monitor a heat flux,
`thereby providing a good heating control by predicting a
`temperature of the wafer 3 and therefore also providing a
`feature of reducing a delay in control.
`
` Further, although the foregoing embodiment is applied
`[0039]
`to baking after application of a resist, the present
`invention may be applied to baking after application of a
`developing solution, baking before or during processes
`such as ion implantation, CVD, etching and ashing, and
`the like.
` In addition, it will be easily understood that the present
`[0040]
`invention is not limited to the baking apparatus, but may
`be applied to deposition apparatuses, ashing apparatuses
`and any other heat treatment devices.
`[Effect of the Invention]
` As described above, the present invention is
`[0041]
`configured to detect a heat flux from a heating means
`flowing through a subject to be treated using a heat flux
`sensor and then to predict and control a temperature based
`on the heat flux. Accordingly, a delay in control can be
`reduced, increase and decrease of temperature can be
`quickly performed, and histories of increase and decrease
`of temperature can be controlled.
` In addition, in a state where a disturbance exists, the
`[0042]
`disturbance can be detected as change in heat flux before
`an influence of the disturbance is phenomenally revealed
`as a change in temperature, whereby a stabilized
`temperature control can be achieved.
`
`4. Brief Description of the Drawings
`
`Page 6 of 7
`
`

`

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`Page 7 of 7
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