Stage, substrate processing apparatus, plasma processing apparatus, control method for stage, control method for plasma processing apparatus, and storage media

A stage onto which is electrostatically attracted a substrate to be processed in a substrate processing apparatus, which enables the semiconductor device yield to be improved. A temperature measuring apparatus 200 measures a temperature of the substrate to be processed. A temperature control unit 400 carries out temperature adjustment on the substrate to be processed such as to become equal to a target temperature based on a preset parameter. A temperature control unit 400 controls the temperature of the substrate to be processed by controlling the temperature adjustment by the temperature control unit 400 based on a measured temperature measured by the temperature measuring apparatus 200.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stage, a substrate processing apparatus, a plasma processing apparatus, a control method for the stage, a control method for the plasma processing apparatus, and storage media, and in particular relates to a stage on which a substrate to be processed such as a semiconductor wafer is mounted, and a plasma processing apparatus having the stage therein.

2. Description of the Related Art

A plasma processing apparatus constituting a substrate processing apparatus carries out plasma processing such as etching using plasma on semiconductor wafers as substrates processed for manufacturing semiconductor devices.

Such a plasma processing apparatus has a processing chamber for carrying out the plasma processing, an upper electrode and a lower electrode being provided in the chamber for supplying predetermined RF (radio frequency) power for producing the plasma. The lower electrode also acts as a stage (susceptor) on which each semiconductor wafer is mounted. The stage has an ESC (electrostatic chuck) function of electrostatically attracting (chucking) thereto the semiconductor wafer mounted thereon through application of a predetermined voltage.

Moreover, in such a plasma processing apparatus, before carrying out the plasma processing on a semiconductor wafer, reaction by-products or the like attached to an inner wall of the chamber may be removed by carrying out waferless dry cleaning (WLDC) (see U.S. Pat. No. 6,325,948, for example).

However, for such a plasma processing apparatus, each time the plasma processing or the WLDC is carried out, and furthermore each time a semiconductor wafer is attracted onto the stage, the surface state of the stage changes.

Specifically, reaction by-products comprised of fine particles produced through the plasma processing become attached as deposit to low-temperature portions of the surface of the stage in particular. Moreover, the surface of the stage is roughened (worn away) through the WLDC. Furthermore, when a semiconductor wafer is attracted onto the stage, slight movement occurs while a rear surface of the semiconductor wafer is in contact with the surface of the stage, and hence minute undulations on the surface of the stage are smoothed down.

As a result of the above, the actual area over which the surface of the stage and the rear surface of the semiconductor wafer contact one another changes, and hence the thermal transmission characteristics between the stage and the semiconductor wafer change (i.e. ESC drift occurs). This ESC drift is also affected by the time period (or number of times) of usage of the plasma processing apparatus, for example by the time period for which the RF power has been supplied.

In recent years, as semiconductor devices have become smaller in size, very high processing precision has come to be demanded of plasma processing such as etching. To achieve such high processing precision, it is necessary to make each of the semiconductor wafers subjected to the plasma processing be at the same temperature. However, ESC drift causes the thermal transmission characteristics between the stage and a semiconductor wafer to change as described above, and hence directly affects the temperature of each semiconductor wafer. In a plasma processing apparatus, there is thus a problem that even if the plasma processing such as etching is carried out under the same conditions, for example at the same RF power, for each of the semiconductor wafers, the temperature differs between the semiconductor wafers, and hence the processing precision changes, whereby the semiconductor device yield decreases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a stage, a substrate processing apparatus, a plasma processing apparatus, a control method for the stage, a control method for the plasma processing apparatus, and storage media, that enable the semiconductor device yield to be improved.

To attain the above object, in a first aspect of the present invention, there is provided a stage onto which is electrostatically attracted a substrate to be processed in a substrate processing apparatus, the stage comprising: a temperature measuring unit that measures a temperature of the substrate to be processed; a temperature adjusting unit that carries out temperature adjustment on the substrate to be processed such as to become equal to a target temperature based on a preset parameter; and a substrate temperature controlling unit that controls the temperature of the substrate to be processed by controlling the temperature adjustment by the temperature adjusting unit based on a measured temperature measured by the temperature measuring unit.

According to the above stage, the temperature adjustment of the substrate to be processed is controlled based on the measured temperature. As a result, the semiconductor device yield can be improved.

Preferably, the target temperature comprises a temperature profile showing temperature changes over a predetermined time period.

According to the above stage, the target temperature comprises a temperature profile showing temperature changes over a predetermined time period. The temperature of the substrate to be processed tends to change with time. Rather than setting the target temperature to a value that does not change with the passage of time, and adjusting the temperature of the substrate to be processed to match this value, it is thus easier to set the target temperature to a value that changes with the passage of time, and adjust the temperature of the substrate to be processed so as to match this changing value. As a result, the temperature of the substrate to be processed can easily be matched to the target temperature.

Preferably, the substrate temperature controlling unit adjusts the parameter when the measured temperature is different to the target temperature.

According to the above stage, the parameter is adjusted if the measured temperature is different to the target temperature. As a result, the temperature of the substrate to be processed can be stabilized to the target temperature.

Preferably, there is further provided with an alarm output unit that outputs a predetermined alarm when the measured temperature is different to the target temperature.

According to the above stage, a predetermined alarm is outputted if the measured temperature is different to the target temperature. As a result, a user can be notified that the measured temperature is different to the target temperature.

Preferably, the parameter comprises at least one selected from control parameters comprising a temperature and a flow rate of a coolant supplied into the stage, a voltage, a current, and an electrical power supplied to the stage, and a temperature, a flow rate, a pressure, and a type of a heat-transmitting gas supplied onto a rear surface of the substrate to be processed.

According to the above stage, the parameter comprises at least one selected from control parameters comprising a temperature and a flow rate of a coolant supplied into the stage, a voltage, a current, and an electrical power supplied to the stage, and a temperature, a flow rate, a pressure, and a type of a heat-transmitting gas supplied onto a rear surface of the substrate to be processed. As a result, the temperature of the substrate to be processed can be adjusted indirectly by controlling the temperature of the stage, or else the temperature of the substrate to be processed can be controlled directly.

Preferably, the substrate temperature controlling unit separately controls a temperature of each of a central portion and a peripheral portion of the substrate to be processed.

According to the above stage, the substrate temperature controlling means separately controls a temperature of each of a central portion and a peripheral portion of the substrate to be processed. As a result, the temperature of each of the central portion and the peripheral portion of the substrate to be processed can be set to a temperature optimum for semiconductor device manufacture, and hence the semiconductor device yield can be further improved.

To attain the above object, in a second aspect of the present invention, there is provided a substrate processing apparatus having a stage as described above.

To attain the above object, in a third aspect of the present invention, there is provided a plasma processing apparatus having a stage onto which is electrostatically attracted a substrate to be processed that is to be subjected to first plasma processing, the plasma processing apparatus comprising: a varying temperature processing unit that carries out varying temperature processing involving changing a temperature of the substrate to be processed; a temperature measuring unit that measures the temperature of the substrate to be processed; storage unit that stores in advance a first profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a first predetermined number of times or for a first predetermined time period; a comparing unit that comparing the first profile with a second profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a second predetermined number of times or for a second predetermined time period; and a stage recovery unit that carries out second plasma processing on the stage in accordance with results of the comparison.

According to the above plasma processing apparatus, a second profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a second predetermined number of times or for a second predetermined time period is compared with a first profile that was stored in advance after the first plasma processing had been carried out a first predetermined number of times or for a first predetermined time period, and second plasma processing is carried out on the stage in accordance with results of the comparison. As a result, the surface state of the stage can be stabilized, and hence the semiconductor device yield can be improved.

Preferably, the stage recovery unit carries out the second plasma processing on the stage when a difference between the first profile and the second profile not is within a permissible range.

According to the above plasma processing apparatus, the second plasma processing is carried out on the stage if a difference between the first profile and the second profile is not within a permissible range. As a result, the surface state of the stage can be stabilized appropriately.

Preferably, the stage recovery unit carries out processing of roughening a surface of the stage onto which the substrate to be processed is attracted as the second plasma processing when the second profile is lower than the first profile.

According to the above plasma processing apparatus, if the second profile is lower than the first profile, then processing of roughening a surface of the stage onto which the substrate to be processed is attracted is carried out as the second plasma processing. As a result, thermal transmission between the substrate to be processed and the stage can be reduced, whereby the temperature can be made to be the same for each of the substrates to be processed subjected to the first plasma processing.

Preferably, the stage recovery unit carries out processing of smoothing a surface of the stage onto which the substrate to be processed is attracted as the second plasma processing when the second profile is higher than the first profile.

According to the above plasma processing apparatus, if the second profile is higher than the first profile, then processing of smoothing a surface of the stage onto which the substrate to be processed is attracted is carried out as the second plasma processing. As a result, thermal transmission between the substrate to be processed and the stage can be increased, whereby the temperature can be made to be the same for each of the substrates to be processed subjected to the first plasma processing.

Preferably, there is further provided with an alarm output unit that outputs a predetermined alarm in response to a difference between the first profile and the second profile not being within a permissible range.

According to the above plasma processing apparatus, if a difference between the first profile and the second profile is not within a permissible range, then a predetermined alarm is outputted. As a result, a user can be notified that the difference between the first profile and the second profile is not within the permissible range.

To attain the above object, in a fourth aspect of the present invention, there is provided a control method for a stage onto which is electrostatically attracted a substrate to be processed in a substrate processing apparatus, the control method comprising: a temperature measuring step of measuring a temperature of the substrate to be processed; a temperature adjusting step of carrying out temperature adjustment on the substrate to be processed such as to become equal to a target temperature based on a preset parameter; and a substrate temperature controlling step of controlling the temperature of the substrate to be processed by controlling the temperature adjustment in the temperature adjusting step based on a measured temperature measured in the temperature measuring step.

To attain the above object, in a fifth aspect of the present invention, there is provided a control method for a plasma processing apparatus having a stage onto which is electrostatically attracted a substrate to be processed that is to be subjected to first plasma processing, the control method comprising: a varying temperature processing step of carrying out varying temperature processing involving changing a temperature of the substrate to be processed; a temperature measuring step of measuring the temperature of the substrate to be processed; a storage step of storing in advance a first profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a first predetermined number of times or for a first predetermined time period; a comparing step of comparing the first profile with a second profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a second predetermined number of times or for a second predetermined time period; and a stage recovery step of carrying out second plasma processing on the stage in accordance with results of the comparison.

To attain the above object, in a sixth aspect of the present invention, there is provided a computer-readable storage medium storing a control program for causing a computer to implement a control method for a stage onto which is electrostatically attracted a substrate to be processed in a substrate processing apparatus, the control program comprising: a temperature measuring module for measuring a temperature of the substrate to be processed; a temperature adjusting module for carrying out temperature adjustment on the substrate to be processed such as to become equal to a target temperature based on a preset parameter; and a substrate temperature controlling module for controlling the temperature of the substrate to be processed by controlling the temperature adjustment by the temperature adjusting module based on a measured temperature measured by the temperature measuring module.

To attain the above object, in a seventh aspect of the present invention, there is provided a computer-readable storage medium storing a control program for causing a computer to implement a control method for a plasma processing apparatus having a stage onto which is electrostatically attracted a substrate to be processed that is to be subjected to first plasma processing, the control program comprising: a varying temperature processing module for carrying out varying temperature processing involving changing a temperature of the substrate to be processed; a temperature measuring module for measuring the temperature of the substrate to be processed; a storage module for storing in advance a first profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a first predetermined number of times or for a first predetermined time period; a comparing module for comparing the first profile with a second profile relating to the temperature of the substrate to be processed measured when carrying out the varying temperature processing on the substrate to be processed after the first plasma processing has been carried out a second predetermined number of times or for a second predetermined time period; and a stage recovery module for carrying out second plasma processing on the stage in accordance with results of the comparison.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to the drawings showing preferred embodiments thereof.

FIG. 1is a sectional view schematically showing the construction of a substrate processing apparatus having therein a stage according to an embodiment of the present invention. The plasma processing apparatus constituting the substrate processing apparatus is constructed such as to carry out plasma processing such as RIE (reactive ion etching) or ashing on semiconductor wafers W (hereinafter referred to merely as “wafers W”) as substrates to be processed.

As shown inFIG. 1, the plasma processing apparatus10has a cylindrical chamber34made of aluminum having an inner wall thereof coated with alumite. A cylindrical stage35is disposed in the chamber34as a stage on which is mounted a wafer W having a diameter of 300 mm, for example.

In the plasma processing apparatus10, an exhaust path36that acts as a flow path through which gas molecules above the stage35are discharged to the outside of the chamber34is formed between an inner side wall of the chamber34and a side face of the stage35. An annular baffle plate37that prevents leakage of plasma is disposed part way along the exhaust path36. A space in the exhaust path36downstream of the baffle plate37bends round below the stage35, and is communicated with an automatic pressure control valve (hereinafter referred to as the “APC valve”)64, which is a variable butterfly valve. The APC valve64is connected to a turbo-molecular pump (hereinafter referred to as the “TMP”)66, which is an exhausting pump for evacuation, via and an isolator65, and the TMP66is connected to a dry pump (hereinafter referred to as the “DP”)38, which is also an exhausting pump, via a valve V36. The exhaust flow path (main exhaust line) comprised of the APC valve64, the isolator65, the TMP66, the valve V36and the DP38is used for controlling the pressure in the chamber34using the APC valve64, and also for reducing the pressure in the chamber34down to a substantially vacuum state using the TMP66and the DP38.

Moreover, piping67is connected from between the APC valve64and the isolator65to the DP38via a valve V37. The exhaust flow path (bypass line) comprised of the piping67and the valve V37bypasses the TMP66, and is used for roughing the chamber34using the DP38.

A lower electrode radio frequency power source41is connected to the stage35via a feeder rod42and a matcher43. The lower electrode radio frequency power source41supplies predetermined radio frequency electrical power (HV RF power) to the stage35. The stage35thus acts as a lower electrode. The matcher43reduces reflection of the radio frequency electrical power from the stage35so as to maximize the efficiency of the supply of the radio frequency electrical power into the stage35.

A disk-shaped ESC electrode plate44comprised of an electrically conductive film is provided in an upper portion of the stage35. A DC power source45is electrically connected to the ESC electrode plate44. A wafer W is attracted to and held on an upper surface of the stage35through a Johnsen-Rahbek force or a Coulomb force generated by a DC ESC voltage (DC voltage) applied to the ESC electrode plate44from the DC power source45. Moreover, an annular focus ring46is provided on the stage35so as to surround the wafer W attracted to and held on the upper surface of the stage35. The focus ring46is exposed to a space S, described below, and focuses the plasma in the space S toward a front surface of the wafer W, thus improving the efficiency of the plasma processing. Further the focus ring46enlarges a plasma distributing region upto the focus ring46itself, thus preventing the peripheral portion of the wafer F from being subjected to the abnormal processing (for example, the plasma processing is more in ununiformity at the edge portion of the wafer W than at the center portion of the wafer W.

An annular coolant chamber76that extends, for example, in a circumferential direction of the stage35is provided inside the stage35. A coolant, for example cooling water or a Galden (registered trademark) fluid, at a predetermined temperature is circulated through the coolant chamber76via coolant piping70from a chiller unit (not shown). A temperature of the stage35, and hence a processing temperature of the wafer W attracted to and held on the upper surface of the stage35, is controlled through the temperature of the coolant.

A plurality of peripheral heat-transmitting gas supply holes47facing a peripheral portion of the wafer W and a plurality of central heat-transmitting gas supply holes48facing a central portion of the wafer W are provided in a portion of the upper surface of the stage35on which the wafer W is attracted and held (hereinafter referred to as the “attracting surface”).

The peripheral heat-transmitting gas supply holes47and the central heat-transmitting gas supply holes48are connected to a heat-transmitting gas supply unit51respectively by two heat-transmitting gas supply lines49and50provided inside the stage35. The heat-transmitting gas supply unit51supplies helium gas as a heat-transmitting gas (backside gas) via the peripheral heat-transmitting gas supply holes47and the central heat-transmitting gas supply holes48into a gap between the attracting surface of the stage35and a rear surface of the wafer W. The peripheral heat-transmitting gas supply holes47and the central heat-transmitting gas supply holes48, the two heat-transmitting gas supply lines49and50, and the heat-transmitting gas supply unit51together constitute a heat-transmitting gas supply apparatus. Note that the type of the backside gas is not limited to being helium (He), but rather may also be an inert gas such as nitrogen (N2), argon (Ar), krypton (Kr) or xenon (Xe), or oxygen (O2) or the like instead. The heat-transmitting gas supply apparatus separately controls the temperature of each of the peripheral portion and the central portion of the wafer W by controlling the temperature, flow rate, pressure, type and so on of the backside gas supplied from each of the peripheral heat-transmitting gas supply holes47and the central heat-transmitting gas supply holes48. As a result, the temperature of each of the central portion and the peripheral portion of the wafer W can be set to a temperature optimum for semiconductor device manufacture.

A plurality of, for example three, pusher pins52are provided in the attracting surface of the stage35as lifting pins that can be made to project out from the upper surface of the stage35. The pusher pins52are connected to a motor (not shown) by a ball screw (not shown), and can be made to project out from the attracting surface of the stage35through rotational motion of the motor, which is converted into linear motion by the ball screw. The pusher pins52are housed inside the stage35when a wafer W is being attracted to and held on the attracting surface of the stage35so that the wafer W can be subjected to the plasma processing, and are made to project out from the upper surface of the stage35so as to lift the wafer W up away from the stage35when the wafer W is to be transferred out from the chamber34after having been subjected to the plasma processing.

A gas introducing shower head53is disposed in a ceiling portion of the chamber34facing the stage35. An upper electrode radio frequency power source55is connected to the gas introducing shower head53via a matcher54. The upper electrode radio frequency power source55supplies predetermined radio frequency electrical power to the gas introducing shower head53. The gas introducing shower head53thus acts as an upper electrode. The matcher54has a similar function to the matcher43, described earlier.

The gas introducing shower head53has a ceiling electrode plate57having a large number of gas holes56therein, and an electrode support58on which the ceiling electrode plate57is detachably supported. A buffer chamber59is provided inside the electrode support58. A processing gas introducing pipe60is connected from a processing gas supply unit (not shown) to the buffer chamber59. A piping insulator61is disposed part way along the processing gas introducing pipe60. The piping insulator61is made of an electrically insulating material, and prevents the radio frequency electrical power supplied to the gas introducing shower head53from leaking into the processing gas supply unit via the processing gas introducing pipe60. A processing gas supplied from the processing gas introducing pipe60into the buffer chamber59is supplied by the gas introducing shower head53into the chamber34via the gas holes56.

A transfer port62for the wafers W is provided in a side wall of the chamber34in a position at the height of a wafer W that has been lifted up from the stage35by the pusher pins52. A gate valve63for opening and closing the transfer port62is provided in the transfer port62.

Upon supplying radio frequency electrical power to the stage35and the gas introducing shower head53in the chamber34of the plasma processing apparatus10as described above, and thus applying radio frequency electrical power into the space S between the stage35and the gas introducing shower head53, high-density plasma is produced from the processing gas supplied from the gas introducing shower head53into the space S. The wafer W is subjected to the plasma processing by the plasma.

Specifically, when subjecting a wafer W to the plasma processing in the plasma processing apparatus10, first, the gate valve63is opened, and the wafer W to be processed is transferred into the chamber34, and attracted to and held on the attracting surface of the stage35by applying an ESC voltage to the ESC electrode plate44. Moreover, the processing gas (e.g. a mixed gas comprised of CF4gas, O2gas, and Ar gas with a predetermined flow ratio therebetween) is supplied from the gas introducing shower head53into the chamber34, and the pressure inside the chamber34is controlled to a predetermined value using the APC valve64. Furthermore, radio frequency electrical power is applied into the space S in the chamber34from the stage35and the gas introducing shower head53. The processing gas introduced in from the gas introducing shower head53is thus turned into plasma in the space S. The plasma is focused onto the front surface of the wafer W by the focus ring46, whereby the front surface of the wafer W is physically/chemically etched.

Operation of the component elements of the plasma processing apparatus10described above is controlled in accordance with a program for the plasma processing by a system controller shown inFIG. 8, described below. Alternatively, the control may be carried out by a CPU410of a control unit400(seeFIG. 2) connected to the plasma processing apparatus10instead of the system controller.

A central opening35aand a peripheral opening35bare formed in the stage35in the chamber34as shown inFIG. 2, described below, for measuring the temperature of respectively the central portion and the peripheral portion of the wafer W.

FIG. 2is a block diagram schematically showing the construction of a temperature control system including the plasma processing apparatus10shown inFIG. 1.

As shown inFIG. 2, the temperature control system is comprised of the plasma processing apparatus10shown inFIG. 1, a temperature measuring apparatus200that is connected to the plasma processing apparatus10and measures temperatures of a wafer W, and a temperature control unit400that adjusts the temperatures of the wafer W directly or indirectly such as to become substantially equal to target temperatures based on preset parameters.

The temperature measuring apparatus200is comprised of an SLD (superluminescent diode)210as a low-coherence light source having a short coherence length (where the term “coherence length” indicates the maximum optical path difference at which two divided beams can undergo interference), a 2×2 optical fiber coupler220that is connected to the SLD210and acts as a first splitter, a 1×2 optical fiber coupler230that is connected to the optical fiber coupler220and acts as a second splitter, collimating fibers240and250that are connected to the optical fiber coupler230, a collimating fiber260that is connected to the optical fiber coupler220, a photodetector (PD)280as a light receiving element that is connected to the optical fiber coupler220, and optical fibers290a,290b,290c,290d,290e, and290fthat connect the above elements together.

The SLD210is, for example, an SLD that emits light of center wavelength 1.55 μm or 1.31 μm and half width approximately 50 μm at a maximum power output of 1.5 mW. Each of the collimating fibers240,250, and260is comprised of a collimator for which its optical axis adjusting mechanism is connected to a holder so that the optical axis of the collimator is perpendicular to the surface of the object onto which the collimator emits light, and emits parallel light from the optical fiber290c,290d, or290erespectively. The PD280is comprised of a Ge photodiode.

The temperature measuring apparatus200further has a reference mirror270disposed in front of the collimating fiber260, a motor-driven stage272that is comprised of a stage on which the reference mirror270is mounted and a stepping motor that moves the stage horizontally, a motor driver274that drives the stepping motor of the motor-driven stage272, and an amplifier295that is connected to the PD280and amplifies output signals from the PD280. The reference mirror270is comprised of a corner cube prism or a plane mirror.

The collimating fibers240and250are disposed such as to respectively face a lower end of the central opening35aand a lower end of the peripheral opening35bof the stage35, and each emits light from the SLD210as measuring light via the opening35aor35btoward the rear surface of the wafer W which is the object to be subjected to temperature measurement, and also receives reflected light from the wafer W and transmits this reflected light to the PD280. The light-emitting surfaces of the collimating fibers240and250are preferably disposed such that the distance from the optical fiber coupler230to the rear surface of the wafer W, i.e. the optical path lengths, are different from each other, whereby the temperature measurements can be carried out simultaneously for the central portion and the peripheral portion of the wafer W.

The collimating fiber260emits light from the SLD210as reference light toward the reference mirror270, and also receives reflected light from the reference mirror270and transmits this reflected light to the PD280.

The motor-driven stage272moves the stage thereof horizontally in the direction of an arrow A shown inFIG. 2such that a reflecting surface of the reference mirror270remains parallel with a light-emitting surface of the collimating fiber260.

The control unit400is, for example, realized by a computer. The control unit400is comprised of a CPU (central processing unit)410that carries out overall control of the control unit400, a motor controller430that controls, via the motor driver274, the stepping motor of the motor-driven stage272that drives the stage on which the reference mirror270is mounted, an A/D converter460that subjects the output signals from the PD280, which are inputted into the A/D converter460via the amplifier295of the temperature measuring apparatus200, to analogue/digital conversion synchronized with control signals (e.g. driving pulses) outputted to the motor driver274from the motor controller430, and a plasma processing apparatus controller470that controls portions of the plasma processing apparatus10.

The plasma processing apparatus controller470includes a stage controller472that controls portions of the plasma processing apparatus10relating to the stage35. The stage controller472controls the radio frequency electrical power (RF power) supplied from the radio frequency power source41, the temperature, flow rate, and pressure of the backside gas supplied from the heat-transmitting gas supply unit51, the temperature and flow rate of the coolant circulated through the coolant chamber76, the ESC voltage applied to the ESC electrode plate44in the stage35, and so on.

FIG. 3is a drawing useful in explaining a temperature measuring operation of the temperature measuring apparatus200appearing inFIG. 2.

The temperature measuring apparatus200uses a low coherence interferometer having a Michelson interferometer structure as its basic structure. As shown inFIG. 3, light from the SLD210is split into the measuring light and the reference light by the optical fiber coupler220which acts as a splitter, the measuring light being irradiated toward the wafer W which is the object to be subjected to the temperature measurement, and the reference light being irradiated toward the movable reference mirror270. Reflected light obtained from the measuring light being reflected at the rear surface of the wafer W, reflected light obtained from the measuring light being reflected at the front surface of the wafer W, and reflected light obtained from the reference light being reflected at the reference mirror270reenter the optical fiber coupler220. At this time, these types of reflected light undergo interference in accordance with the optical path length of the reference light, and the resulting interference light is detected by the PD280.

The temperature measuring apparatus200of the plasma processing apparatus10is not limited to being one that uses a low coherence interferometer as described above, but rather may instead be comprised of, for example, a sensor that carries out the temperature measurement for a rear surface of the wafer, a sensor that carries out the temperature measurement by observing the surface of the wafer W from above.

FIGS. 4A and 4Bare graphs showing examples of interference waveforms between the reflected light from the wafer W and the reflected reference light detected by the PD280appearing inFIG. 3,FIG. 4Ashowing an interference waveform obtained before changing a temperature of the wafer W, andFIG. 4Bshowing an interference waveform obtained after changing the temperature of the wafer W.

As shown inFIG. 4A, upon the reflected reference light from the reference mirror270and the reflected light from the rear surface of the wafer W undergoing interference with one another, for example an interference waveform400ais obtained over a width of approximately 80 μm, centered on an interference position A μm (interference intensity peak position: approximately 425 μm), as the movement distance of the reference mirror270. Moreover, upon the reflected reference light from the reference mirror270and the reflected light from the front surface of the wafer W undergoing interference with one another, for example an interference waveform400bis obtained over a width of approximately 80 μm centered on an interference position B μm (interference intensity peak position: approximately 3285 μm).

Here, upon the temperature of the wafer W changing, the thickness of the wafer W changes through thermal expansion (or contraction), and accompanying this refractive index also changes. The optical path length through the wafer W being subjected to the measurement, i.e. the distance between the rear surface and the front surface of the wafer W, thus changes.

As shown inFIG. 4B, regarding an interference waveform400a′ at an interference position A′ and an interference waveform400b′ at an interference position B′ obtained for the rear surface and the front surface respectively of the wafer W at a different temperature to inFIG. 4A, the interference positions A′ and B′ indicating the interference intensity peak positions are shifted in a direction corresponding to an increase in the movement distance of the reference mirror270from the interference positions A and B, and moreover the width of the interference waveforms400a′ and400b′ is also changed compared with that of the interference waveforms400aand400b.

The change in the interference intensity peak positions for the front surface and the rear surface of the wafer W can thus be related to the temperature change.

In the present embodiment, temperature conversion data showing the relationship between the interference intensity peak positions and each of a plurality of temperatures is thus stored in the control unit400as a database before the temperature of the wafer W is measured. Then, when the temperature of the wafer W is measured, first, the temperature measuring apparatus200inputs into the control unit400, an output signal from the PD280, i.e. a signal indicating the interference intensity peak positions as shown inFIG. 4Aor4B for each of the central portion and the peripheral portion of the wafer W. Next, the control unit400converts the inputted signal into a temperature for each of the central portion and the peripheral portion of the wafer W using the above temperature conversion data. As a result, the temperature of each of the central portion and the peripheral portion of the wafer W can be measured with no contact and with high precision.

According to the temperature control system shown inFIG. 2, high precision is secured for the wafer W temperature measurement as described above. A first substrate temperature control process as shown inFIG. 6, described below, or a second substrate temperature control process as shown inFIG. 7, described below, is then carried out by the control unit400.

Moreover, reference data as shown inFIGS. 5A and 5Bis also stored in the control unit400.

The reference data of each ofFIGS. 5A and 5Bis comprised of a temperature profile showing data on temperature changes obtained when carrying out predetermined varying temperature processing on a wafer W over a predetermined time period after the plasma processing has been carried out in the plasma processing apparatus10a predetermined number of times or for a predetermined time period (e.g. 1 hour) as an initial value, i.e. showing temperature changes of the wafer W over a predetermined time period. The time 0 in each ofFIGS. 5A and 5Bindicates the time when supply of the RF power was commenced.

The reference data ofFIG. 5Ais, specifically, comprised of a temperature profile showing temperature changes of the peripheral portion of the wafer W obtained when, regarding the pressure of helium as a backside gas (cooling gas), the pressure on the peripheral portion of the wafer W was changed to 40, 30, 20, 10, 5, 3, and 40 torr in seven stages at approximately 1.5 minute intervals, with the pressure on the central portion of the wafer W held constant at 15 torr (2.00 kPa).

The reference data ofFIG. 5Bis, specifically, comprised of a temperature profile showing temperature changes of the peripheral portion of the wafer W obtained when, regarding the pressure of helium as a backside gas (cooling gas), the pressure on the central portion of the wafer was changed W to 15, 1, 5, 10, 20, 30, and 15 torr in seven stages at approximately 1.5 minute intervals, with the pressure on the peripheral portion of the wafer W held constant at 40 torr (5.33 kPa).

These temperature profiles are stored as wafer W target temperatures.

The data inFIG. 5Bshows that even if the pressure of the cooling gas on the peripheral portion of the wafer W is fixed, the temperature of the peripheral portion is affected by the pressure of the cooling gas on the central portion. It can thus be seen that the pressure of the helium cooling gas while the RF power is being supplied to the stage35has a large effect on the temperature of the wafer W. That is, the reference data ofFIG. 5Bshows, for example, that to hold the temperature of the peripheral portion of the wafer W at approximately 45° C., if the pressure on the peripheral portion of the wafer W is 40 torr, then the pressure on the central portion of the wafer W should be set to 15 torr. Moreover, from the reference data ofFIGS. 5A and 5B, a backside gas pressure range over which the temperature of the wafer W does not change (i.e. an upper limit and a lower limit of a permissible range) can be determined.

By storing reference data such as that shown inFIGS. 5A and 5Beach time the plasma processing apparatus10is used, and reading out the reference data in time series order, the size of effects such as ESC drift arising in the stage35can be determined.

Note that the reference data described above is not limited to being stepped data as shown inFIGS. 5A and 5B, but rather may be any data obtained by carrying out varying temperature processing involving changing the temperature of a wafer W.

Moreover, for the temperature control system shown inFIG. 2described above, the wafer W temperatures are measured directly with no contact by irradiating light onto the rear surface of the wafer W, but any method enabling the wafer W temperatures to be measured may be used.

Furthermore, the control unit400may measure the movement position or movement distance of the reference mirror270based on control signals outputted to the motor controller430. In this case, the stage of the motor-driven stage272is preferably provided with a linear encoder.

FIG. 6is a flowchart of a first substrate temperature control process carried out by the control unit400appearing inFIG. 2. Each time reference data as shown inFIGS. 5A and 5Bdescribed above has been stored as target temperatures, and furthermore the plasma processing described above has been repeated in the plasma processing apparatus10another predetermined number of times or for another predetermined time period (e.g. 20 hours), the present process is carried out with a wafer W attracted to and held on the stage35before commencement of or after processing on a lot of the wafers W or during an idle period. Moreover, at this time, the coolant temperature is set to 0° C., for example. The wafer W is preferably a non-product processing substrate (a dummy substrate).

As shown inFIG. 6, first, in step S601, the wafer W is subjected to the varying temperature processing described above. At this time, the control unit400converts signals inputted from the amplifier295into temperatures, so as to measure the temperatures of the central portion and the peripheral portion of the wafer W in contact with the stage35. As a result, a measured temperature profile for each of the central portion and the peripheral portion for when carrying out the varying temperature processing on the wafer W is obtained. The varying temperature processing is realized by varying control parameters related to the wafer W temperature such as the temperature and flow rate of the coolant supplied into the stage35from the chiller unit, the voltage, current, and electrical power applied to the stage35, and the temperature, flow rate, pressure, and type of the backside gas supplied onto the rear surface of the wafer W.

Next, in step S602, it is determined whether or not the measured temperature profile for the wafer W is substantially equal to the stored wafer W target temperatures (the reference data), i.e. whether or not the stage35is adequately thermally transmitting the temperature of the coolant to the wafer W. If the result of the determination is that the measured temperature profile for the wafer W obtained in step S601and the reference data are substantially equal (YES at step S602), then the present process is terminated without carrying out processing for controlling the wafer W temperature.

On the other hand, if the measured temperature profile for the wafer W obtained in step S601and the reference data are different to one another (NO at step S602), then it is judged that the stage35is not adequately thermally transmitting the temperature of the coolant to the wafer W, and hence that ESC drift has arisen in the stage35; a predetermined alarm (warning screen or warning sound) is outputted to notify a user of this (step S603), and moreover automatic correction processing for carrying out temperature adjustment to stabilize the wafer W temperature at the target temperature is carried out in accordance with a predetermined control program (step S604). In this automatic correction processing, the wafer W temperature is adjusted indirectly by controlling the temperature of the stage35, or else the wafer W temperature is controlled directly.

In the indirect wafer W temperature adjustment, to control the temperature of the stage35, at least one control parameter selected from the temperature and flow rate of the coolant supplied into the stage35from the chiller unit, and the voltage, current, and electrical power applied to the stage35is used. As a result, the effect of the ESC drift that has arisen in the stage35can be compensated for. That is, an individual difference for the stage35, in particular a difference in thermal transmission characteristics between the stage35and the wafer W can be eliminated.

On the other hand, in the direct wafer W temperature control, at least one control parameter selected from the temperature, flow rate, pressure, and type of the backside gas supplied onto the rear surface of the wafer W is used. Regarding controlling the type of the backside gas, for example the backside gas can be changed from helium to nitrogen. Because the backside gas is supplied independently toward each of the central portion and the peripheral portion of the wafer W, by supplying a backside gas of a suitable temperature, flow rate, pressure, and type for each of the central portion and the peripheral portion of the wafer W, the temperatures of the central portion and the peripheral portion of the wafer W can be controlled independently of one another.

After the automatic correction processing has been carried out in step S604, step S601is returned to; the processing of steps S601to S604is repeated until the measured temperature profile for the wafer W obtained in step S601becomes substantially equal to the reference data.

According to the process ofFIG. 6, if the measured temperature profile for the wafer W obtained in step S601and the reference data are different to one another (NO at step S602), then the automatic correction processing is carried out so as to stabilize the wafer W temperature at the target temperature (step S604). As a result, the processing precision for the plasma processing can be prevented from decreasing, and hence the semiconductor device yield can be improved.

Moreover, in the first substrate temperature control process shown inFIG. 6described above, the measured temperature profile for the wafer W is compared with the reference data, which is a temperature profile showing temperature changes for the wafer W, i.e. temperature profiles are compared with one another. The temperature of the wafer W tends to change with time. Rather than setting the target temperature to a value that does not change with the passage of time, and adjusting the temperature of the wafer W to match this value, it is thus easier to set the target temperature to a value that changes with the passage of time (i.e. a series of values forming a profile), and make the temperature changes of the wafer W match this profile. As a result, the temperature of the wafer W can easily be matched to each target temperature.

In the above embodiment, the first substrate temperature control process shown inFIG. 6described above is carried out before commencement of or after processing of a lot of the wafers W in the plasma processing apparatus10or during an idle period, but the first substrate temperature control process may also be carried out during the plasma processing.

Moreover, in the first substrate temperature control process shown inFIG. 6described above, the measured temperature profile for the wafer W is compared with the reference data, which is a temperature profile showing temperature changes for the wafer W. However, instead of comparing temperature profiles with one another, an alternative is to carry out temperature control such that the temperature of the wafer W is constant over a certain time period, and compare wafer W temperatures measured at this time with one another.

Moreover, in the above embodiment, the temperature of the coolant is set to 0° C. However, this temperature is determined considering the change over time in the performance of the chiller unit (i.e. the temperature controlling performance) and so on, and is not limited to the above.

FIG. 7is a flowchart of a second substrate temperature control process carried out by the control unit400appearing inFIG. 2. Again, each time reference data (a first profile) as shown inFIGS. 5A and 5Bdescribed above has been stored, and furthermore the plasma processing described above (first plasma processing) has been repeated in the plasma processing apparatus10another predetermined number of times or for another predetermined time period (e.g. 20 hours), the present process is carried out with a wafer W attracted to and held on the stage35before commencement of or after processing on a lot of the wafers W or during an idle period. The wafer W is preferably a non-product processing substrate (a dummy substrate).

As shown inFIG. 7, first, in step S701, the wafer W is subjected to the varying temperature processing described above. At this time, the control unit400converts signals inputted from the amplifier295into temperatures, so as to measure the temperatures of the central portion and the peripheral portion of the wafer W in contact with the stage35. As a result, a measured temperature profile (a second profile) for each of the central portion and the peripheral portion for when carrying out the varying temperature processing on the wafer W is obtained.

Next, in step S702, it is determined whether or not the difference between the measured temperature profile for the wafer W and the reference data as shown inFIGS. 5A and 5Bis within a permissible range stipulated by a predetermined upper limit and a predetermined lower limit, i.e. whether or not the temperature of the wafer W has been controlled sufficiently precisely to trace the reference data (target temperatures). If the result of the determination is that the above difference is within the permissible range (YES at step S702), then the present process is terminated without carrying out the recovery plasma processing (second plasma processing) of step S704described below.

On the other hand, if the above difference is outside the permissible range (NO at step S702), then it is judged that the temperature of the wafer W has not been controlled sufficiently precisely to trace the reference data, and hence that there has been change in ESC drift in the stage35; a predetermined alarm (warning screen or warning sound) is outputted to notify a user of this (step S703), and after the wafer W has been removed from the chamber34, recovery plasma processing (second plasma processing) for stabilizing the surface state of the stage35is carried out in accordance with a predetermined control program (recovery sequence) (step S704).

The recovery sequence carried out in step S704will now be described. The details of the recovery sequence vary in accordance with the relationship between the measured temperature profile for the wafer W and the reference data.

Firstly, in the case that the result of the determination in step S702is that the measured temperature profile for the wafer W exceeds the upper limit of the permissible range, i.e. the measured temperature of the wafer W is higher than the target temperature, as the above recovery plasma processing, low ion energy plasma processing is carried out using a gas having a low specific gravity (a depositing gas) under a high process pressure at a high density. An etching gas such as F(fluorine)-, e.g., CF4—, NF3— and SF6-based gas, as well as Cl(chlorine)-based gas, and o(oxygen)-based gas may also be added as required. The surface of the stage35can thus be smoothed down through low ion energy sputtering and chemical reaction with F-type or Cl-type radicals, and furthermore deposit (e.g. CF-type polymer) attached to the surface of the stage35that would hinder thermal transmission from the wafer W to the stage35can be removed. As a result, the thermal transmission between the stage35and the wafer W is improved, and hence the temperature of the wafer W can be reduced. The temperature can thus be made to be the same for each of the wafers W subjected to the plasma processing. The processing precision of the plasma processing can thus be stably reproduced for each of a plurality of the wafers W, and hence the semiconductor device yield can be improved. Note that when removing the deposit, it is preferable to exhaust the space S in the chamber34while carrying out the low ion energy plasma processing described above on the stage35.

Secondly, in the case that the result of the determination in step S702is that the measured temperature profile for the wafer W is below the lower limit of the permissible range, i.e. the temperature of the wafer W is lower than the target temperature, as the above recovery plasma processing, high ion energy sputter etching is carried out using a heavy gas having a high specific gravity under a high vacuum at a low density. Deposit and so on attached to the surface of the stage35is thus removed, and the surface of the stage35is roughened to a suitable extent. As a result, the thermal transmission between the stage35and the wafer W is worsened, and hence the temperature of the wafer W can be increased. The temperature can thus be made to be the same for each of the wafers W subjected to the plasma processing. The processing precision of the plasma processing, which has decreased, can thus be improved, and hence the semiconductor device yield can be improved.

After the recovery plasma processing has been carried out in accordance with the recovery sequence, step S701is returned to; the processing of steps S701to S704is repeated until the difference between the measured temperature profile for the wafer W and the reference data is within the permissible range.

According to the process ofFIG. 7, if the difference between the measured temperature profile for the wafer W and the reference data is outside the permissible range (NO at step S702), then recovery plasma processing is carried out so as to stabilize the surface state of the stage35(step S704). The processing precision of the plasma processing can thus be prevented from decreasing due to ESC drift. As a result, the semiconductor device yield can be improved.

In step S704, the recovery plasma processing carried out in accordance with the recovery sequence is not limited to being carried out once, but rather may be carried out a plurality of times. Moreover, the size of the effect expected each time the recovery plasma processing is carried out, i.e. the processing conditions in the recovery plasma processing, may be changed in accordance with the relationship between the measured temperature profile for the wafer W and the reference data.

Furthermore, in the above embodiment, the first substrate temperature control process shown inFIG. 6and the second substrate temperature control process shown inFIG. 7may be carried out in combination. In this case, duplicated processing is preferably omitted.

Moreover, in the processes shown inFIGS. 6 and 7described above, the timing at which the alarm processing is carried out may be changed, or the carrying out of the alarm processing may be omitted.

FIG. 8is a diagram schematically showing the construction of the system controller for the plasma processing apparatus10shown inFIG. 1.

As shown inFIG. 8, the system controller has an EC (equipment controller)100, a plurality of, for example three, MC's (module controllers)101,102, and103, and a switching hub104that connects the EC100to each of the MC's101,102, and103. The EC100of the system controller is connected via a LAN (local area network)105to a PC106, which is an MES (manufacturing execution system) that carries out overall control of the manufacturing processes in the manufacturing plant in which the plasma processing apparatus10is installed. In collaboration with the system controller, the MES feeds back real-time data on the processes in the manufacturing plant to a basic work system (not shown), and makes decisions relating to the processes in view of the overall load on the manufacturing plant and so on.

The EC100is a master controller that controls the MC's101,102, and103and carries out overall control of the operation of the plasma processing apparatus10. The EC100has a CPU, a RAM, an HDD and so on. The CPU sends control signals to the MC's101,102, and103in accordance with programs corresponding to wafer W processing method menus, i.e. recipes, specified by a user or the like, thus controlling the operations of the plasma processing apparatus10, and modules such as a TM (transfer module) and an LM (loader module) that may be connected to the plasma processing apparatus10.

The switching hub104selects at least one connection among the connections between the EC100and the MC's in accordance with the control signals from the EC100.

The MC's101,102, and103are controllers that control the operations of the plasma processing apparatus10and the modules. Each of the MC's101,102, and103has a CPU, a RAM, an HDD and so on, and sends control signals to end devices, described below. Note that for controlling the plasma processing apparatus10and the modules, the actual number of MC's possessed by the system controller of the plasma processing apparatus10corresponds to the number of modules plus the plasma processing apparatus10, but inFIG. 8three MC's are shown for convenience.

Each of the MC's101,102, and103is connected respectively to an I/O (input/output) module109,110or111through a DIST (distribution) board107via a GHOST network108. Each GHOST network108is a network that is realized through an LSI known as a GHOST (general high-speed optimum scalable transceiver) on an MC board of the corresponding MC. A maximum of 31 I/O modules can be connected to each GHOST network108; with respect to the GHOST network108, the MC is the master, and the I/O modules are slaves.

The I/O module109is comprised of a plurality of I/O units112that are connected to component elements (hereinafter referred to as the “end devices”) of the plasma processing apparatus10, and transmits control signals to the end devices and output signals from the end devices. Examples of the end devices connected to the I/O units112of the I/O module109are component elements of the plasma processing apparatus10such as the DC power source45, the APC valve64, the TMP66, and the DP38.

Each of the I/O modules110and111has a similar construction to the I/O module109, and hence description thereof is omitted.

Each GHOST network108is also connected to an I/O board (not shown) that controls input/output of digital signals, analog signals and serial signals to/from the I/O units112.

In the plasma processing apparatus10, when carrying out plasma processing such as RIE or ashing, WLDC, or the first or second substrate temperature control process described above, the CPU of the EC100sends control signals to the end devices of the plasma processing apparatus10via the switching hub104, the MC101, the GHOST network108, and the I/O units112of the I/O module109, in accordance with a program corresponding to the process in question.

According to the system controller shown in FIG.8, the plurality of end devices are not directly connected to the EC100, but rather the I/O units112which are connected to the plurality of end devices are modularized to form the I/O modules109,110, and111, and each I/O module109,110, or111is connected to the EC100via the MC101,102, or103and the switching hub104. As a result, the communication system can be simplified.

Moreover, each of the control signals sent by the CPU of the EC100contains the address of the I/O unit112connected to the desired end device, and the address of the I/O module containing that I/O unit112. The switching hub104thus refers to the address of the I/O module in the control signal, and then the GHOST of the appropriate MC101,102, or103refers to the address of the I/O unit112in the control signal, whereby the need for the switching hub104or the MC101,102, or103to ask the CPU for the destination of the control signal can be eliminated, and hence smoother transmission of the control signals can be realized.

Moreover, the MC101monitors the plasma processing apparatus10via the GHOST network108and the I/O units112of the I/O module109during each of the processes, and in the case of detecting a predetermined error condition, sends an interlock (I/L) signal to the EC100via the switching hub104to notify the EC100to prohibit subsequent transfer of wafers W into the plasma processing apparatus10. Upon receiving the interlock signal, the EC100sends a wafer transfer prohibiting signal prohibiting transferring in of wafers W via the switching hub104to the MC that controls operation of the TM (the MC103inFIG. 8). Upon receiving the wafer transfer prohibiting signal, the MC103controls operation of end devices relating to wafer W transfer so as to stop transfer of wafers W into the plasma processing apparatus10.

In the above embodiment, the system controller shown inFIG. 8is in the plasma processing apparatus10shown inFIG. 1. However, the system controller may instead be in the control unit400appearing inFIG. 2.

Furthermore, in the above embodiment, an SLD210that emits light of center wavelength 1.55 μm or 1.31 μm and coherence length approximately 50 μm is used as the low-coherence light source. However, the emitted light preferably has a center wavelength anywhere in a range of 0.3 to 20 μm, preferably 0.5 to 5 μm, and a coherence length anywhere in a range of 0.1 to 100 μm, preferably not more than 3 μm. Moreover, instead of the SLD210, an LED, a high intensity lamp such as a tungsten lamp or a xenon lamp, or an ultra-wide wavelength band light source may be used.

Moreover, in the above embodiment, the PD280is comprised of a Ge photodiode, but instead of this, a Si photodiode, an InGaAs photodiode, an avalanche photodiode, or a photoelectric multiplier tube may be used. Furthermore, in the above embodiment, the motor-driven stage272uses a stepping motor, but instead of this, a voice coil motor may be used.

Moreover, note that the temperature measuring apparatus is not limited to those mentioned above, but any apparatus enabling the temperature of the object to be measured may be used.

Furthermore, in the above embodiment, the substrate processing apparatus is an etching apparatus. However, the substrate processing apparatus is not limited thereto, but rather may instead be a CVD (chemical vapor deposition) apparatus, a PVD (physical vapor deposition) apparatus, or the like. Moreover, in the above embodiment, the substrates processed are semiconductor wafers W. However, the substrates processed are not limited thereto, but rather may instead be, for example, LCD (liquid crystal display) or FPD (flat panel display) glass substrates.

Moreover, it is to be understood that the object of the present invention may also be accomplished by supplying a computer such as the EC100or the control unit400with a storage medium in which is stored a program code of software that realizes the functions of the above embodiment, and then causing a CPU of the computer to read out and execute the program code stored in the storage medium.

In this case, the program code itself read out from the storage medium realizes the functions of the above embodiment, and hence the program code and the storage medium in which the program code is stored constitute the present invention.

Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magnetic-optical disk, an optical disk such as a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, a DVD-RW or a DVD+RW, a magnetic tape, a nonvolatile memory card, and a ROM. Alternatively, the program code may be downloaded via a network.

Moreover, it is to be understood that the functions of the above embodiment may be accomplished not only by executing a program code read out by the CPU of a computer, but also by causing an OS (operating system) or the like which operates on the CPU of the computer to perform a part or all of the actual operations based on instructions of the program code.

Furthermore, it is to be understood that the functions of the above embodiment may also be accomplished by writing a program code read out from a storage medium into a memory provided on an expansion board inserted into a computer or in an expansion unit connected to the computer and then causing a CPU or the like provided on the expansion board or in the expansion unit to perform a part or all of the actual operations based on instructions of the program code.