US20140238637A1

US20140238637A1 - Ion beam irradiation apparatus and method for substrate cooling

Info

Publication number: US20140238637A1
Application number: US14/077,065
Authority: US
Inventors: Kohei Tanaka
Original assignee: Nissin Ion Equipment Co Ltd
Current assignee: Nissin Ion Equipment Co Ltd
Priority date: 2013-02-22
Filing date: 2013-11-11
Publication date: 2014-08-28
Also published as: TW201434075A; TWI506680B; KR101525020B1; KR20140105361A

Abstract

A first cooling mechanism is equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place, and flexible plastic tubing for channeling the cooling medium to the heat exchange unit; a second cooling mechanism for cooling the substrate by heat transfer; and a cooling mechanism control unit which, at least when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing, cools the substrate using the second cooling mechanism while channeling the cooling medium at a temperature higher than the critical cold resistance temperature through the plastic tubing. In addition, comprises temperature sensors are provided that measure the temperature of the substrate and a cooling mechanism control unit which, with controlling the temperature of the cooling medium in the first cooling mechanism, is configured to control the second cooling mechanism.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority under 35 USC 119 to Japanese Patent Application No. 2013-033797 and No. 2013-033798, the content of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field
Aspects of the example implementations relate to an ion beam irradiation apparatus that irradiates a cooled substrate with an ion beam.
2. Related Art
When an abrupt ultra-shallow junction is created in a silicon substrate by ion implantation, it is desirable to amorphize the surface of the substrate. In addition, to amorphize a silicon substrate, the substrate needs to be maintained at a low temperature during ion implantation.
Patent Citation 1 shows an example of an ion implanter 100A equipped with a substrate cooling mechanism. Specifically, this implanter is an apparatus, in which ion implantation is carried out by scanning an ion beam across a substrate W secured in a predetermined position and, as shown in FIG. 6, the implanter has a cooling element 9A, which is provided by securing the element to a side wall of a vacuum chamber VR such that the element protrudes into the vacuum chamber VR, and which has a cooling medium supplied from outside for circulation therein; a heat radiating plate 9B secured to the cooling element 9A; and a Peltier device 9C, whose heat radiating surface is secured to the heat radiating plate 9B and whose heat absorbing surface is secured to the backside of an electrostatic chuck 9D used for chucking the substrate W. In addition, the apparatus is configured to cool the substrate W down to a few tens of degrees Centigrade below zero by using the Peltier device 9C to create a temperature difference between the heat radiating surface and the heat absorbing surface and move the heat of the substrate W sequentially through the electrostatic chuck 9D, the Peltier device 9C, and the heat radiating plate 9B to the cooling element 9A.
Further, there are implanters which, conversely, are configured such that the irradiation location of the ion beam is fixed and the ion beam is scanned across a substrate surface by moving the substrate using a substrate transport mechanism. Such implanters are adapted to cool a substrate by providing flexible plastic tubing between walls forming a vacuum chamber and an electrostatic chuck that chucks the substrate in a substrate transport mechanism within the vacuum chamber and supplying a refrigerant cooling medium to the electrostatic chuck through the plastic tubing. The purpose of using such flexible plastic tubing is to permit tubing deformation or movement depending on the position of the substrate as it is moved by the substrate transport mechanism, and thereby prevent the cooling medium tubing from being damaged as the substrate moves.
Incidentally, when amorphizing the surface of a substrate during ion implantation as described in Patent Citation 2, it is required that the substrate be cooled to a cryogenic temperature such as, for example, a temperature of −40° C. to −100° C.
However, cooling a substrate to such a cryogenic temperature using the above-described prior-art substrate cooling mechanism is difficult. For example, if a high current is directed through the Peltier device of the ion implanter described in Patent Citation 1 in an attempt to create a temperature difference from room temperature to a cryogenic temperature between the heat radiating surface and heat absorbing surface thereof, the amount of Joule heat generated as a result will also be increased and the substrate cooling efficiency will be considerably decreased. In addition, if the electric current directed through the Peltier device becomes excessively high, the temperature of the substrate reaches a point at which it cannot be decreased any more, which is why using Peltier devices alone permits cooling only to about −20° C. or −30° C., as described in Patent Citation 1.
On the other hand, it has also been contemplated to cool substrates to cryogenic temperatures not by using Peltier devices, but by supplying a cooling medium cooled to a cryogenic temperature to an electrostatic chuck, to which substrates are chucked.
However, when such a cooling medium cooled to a cryogenic temperature is directed through the plastic tubing, its temperature drops below the critical cold resistance temperature of the plastics and the plastic tubing becomes brittle and loses flexibility. Consequently, if the substrate is moved by the substrate transport mechanism while the cryogenic-temperature cooling medium is channeled therethrough, the plastic tubing becomes damaged. On the other hand, when using metal tubing, whose characteristics remain practically unchanged even with a cryogenic-temperature cooling medium, the position of the substrate must be fixed to avoid damaging the tubing because the tubing has almost no flexibility or degrees of freedom. Additionally, if the position of the substrate is fixed, the degree of freedom during ion implantation is impaired, inter alia, as a result of limitations imposed on the region of the substrate surface where ion beam irradiation is possible.
Further, in the ion implanter described in Patent Citation 2, a substrate is pre-chilled to a predetermined temperature in a substrate load lock chamber provided in proximity to an ion implantation chamber. In addition, the apparatus is adapted to load the pre-chilled substrate into the ion implantation chamber and carry out ion implantation without cooling the substrate while it is being irradiated by an ion beam.
However, in methods for substrate cooling such as the one set forth in Patent Citation 2, no consideration is given to the temperature change occurring in a substrate while it is irradiated by an ion beam as described above, and there is a chance that the temperature of the substrate during ion beam irradiation may deviate from temperatures suitable for amorphization. Consequently, there is a risk that substrate characteristics after ion implantation may differ from the desired characteristics.
In other words, heretofore, no substrate temperature control has been practiced in the related art in order to monitor temperature increase due to heat transferred to a substrate as a result irradiation by the ion beam, minimize such temperature increase during ion implantation as much as possible, and continue maintaining a constant substrate temperature. Furthermore, due to the fact that such technical problems have never been rigorously investigated in the past, there are no known specific configurations and methods for substrate cooling suitable for quickly cooling a substrate to a target temperature and constantly maintaining it at this temperature in the event of substrate temperature changes.

RELATED ART LITERATURE

Patent Citations

[Patent Citation 1]

Japanese Patent Application Publication No. 2001-68427.

[Patent Citation 2]

US Publication 7935942

SUMMARY

Problems to be Addressed

It is an object of the example implementation to provide an ion beam irradiation apparatus and a method for substrate cooling that allow for a substrate to be cooled to a cryogenic temperature of, for example, −60° C. to −100° C. even when substrate cooling is performed using a cooling medium, permit free movement of the substrate during ion beam irradiation without impairing the flexibility of the plastic tubing through which the cooling medium is channeled, as well as make it possible to minimize temperature increase of the substrate while the substrate is irradiated by an ion beam and allow for substrate temperature to be maintained constant at a temperature (e.g., predetermined) at all times, even during ion beam irradiation.

Means for Addressing the Problems

Namely, the ion beam irradiation apparatus of the example implementation is an ion beam irradiation apparatus configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, wherein the apparatus comprises a first cooling mechanism equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place, and flexible plastic tubing for channeling the cooling medium to the heat exchange unit; a second cooling mechanism that cools the substrate by heat transfer; and a cooling mechanism control unit which, at least when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing, cools the substrate using the second cooling mechanism while channeling the cooling medium at a temperature higher than the critical cold resistance temperature through the plastic tubing.
Further, the method for substrate cooling of the present example implementation is a method for substrate cooling employed in an ion beam irradiation apparatus that is provided with a first cooling mechanism equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place, and flexible plastic tubing for channeling the cooling medium to the heat exchange unit, and a second cooling mechanism that cools the substrate by heat transfer, and that is configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, wherein, at least when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing, the substrate is cooled by the second cooling mechanism while channeling the cooling medium at a temperature higher than the critical cold resistance temperature through the plastic tubing.
In such a case, when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing, primary substrate cooling is accomplished by directing the cooling medium at a temperature higher than the critical cold resistance temperature to the heat exchange unit of the first cooling mechanism, and the remaining portion of cooling down to the target substrate cooling temperature that could not be accomplished by the first cooling mechanism is accomplished using heat transfer-based secondary cooling provided by the second cooling mechanism, as a result of which the temperature of the substrate can be reduced to the target substrate cooling temperature.
Due to the fact that only a cooling medium at a temperature higher than the critical cold resistance temperature is channeled through the plastic tubing at such time, the flexibility of the plastic tubing is never impaired and the plastic tubing is never damaged even if the position of the substrate is changed by the substrate transport mechanism while cooling the substrate to a cryogenic temperature. Therefore, the substrate can be freely moved by the substrate transport mechanism while the substrate is cooled, and the surface of the substrate can be irradiated by the ion beam in a variety of ways.
Moreover, since the temperature of the substrate has already been reduced to a certain extent by the primary substrate cooling provided by the first cooling mechanism, the substrate can be cooled to the target substrate cooling temperature even though the second cooling mechanism does not remove a very large amount of heat from the substrate by heat transfer. In other words, due to the fact that the second cooling mechanism does not have to perform a large amount of heat transfer work and an excessively strong cooling capability is not required, the substrate can be cooled to the target substrate cooling temperature using, for instance, currently available Peltier devices and the like.
For example, during ion implantation and the like, a target substrate temperature of −60° C. or lower is sufficient to enable high-quality ion implantation by amorphizing a substrate surface and creating ultra-shallow junctions.
As a specific configuration for enabling adequate substrate cooling by efficiently discharging heat transferred from the substrate by the second cooling mechanism to the environment, a configuration is proposed, in which the second cooling mechanism is a Peltier device whose heat absorbing surface is in contact with the substrate holding unit and whose heat radiating surface is in contact with the heat exchange unit.
To enhance the substrate cooling capability of the first cooling mechanism by further increasing the area of direct or indirect contact between the heat exchange unit and the substrate supported by the substrate holding unit in order for the heat exchange between the cooling medium and the substrate to be carried out in an efficient manner, it is sufficient for the heat exchange unit to be composed of a gas reservoir, which is a space between the substrate holding unit and the supported substrate where gas is stored during substrate cooling, a gas pathway for supplying gas to the gas reservoir or discharging gas from the gas reservoir, and a cooling medium channeling unit that is in contact with at least a portion of the gas pathway and has a cooling medium channeled therethrough. In such a case, the cooling medium can effect heat exchange with the substrate not only through the substrate holding unit, but also through the gas in the gas reservoir and the gas pathway, as a result of which the substrate can be cooled more efficiently, even when using the first cooling mechanism alone.
To be able to efficiently discharge the heat removed from the substrate to the environment using heat transfer provided by the Peltier device and maintain the cooling efficiency of the Peltier device at a high level, it is sufficient to bring the heat radiating surface of the Peltier device into contact with the cooling medium channeling unit.
For example, in order to ensure that feedback-control is exercised immediately so as to bring the temperature of a substrate to a target substrate cooling temperature if the temperature rises above the target substrate cooling temperature when the substrate is irradiated by an ion beam and heat is driven into the substrate, and to maintain the substrate constantly at this temperature, the apparatus is further provided with contact-type temperature sensors that are in contact with the substrate supported by the substrate holding unit and measure the temperature of the substrate, and the cooling mechanism control unit, along with controlling the temperature of the cooling medium in the first cooling mechanism so as to keep it constant at a target cooling medium temperature, is configured to control the second cooling mechanism so as to reduce the deviation of a measured substrate temperature sensed by the contact-type temperature sensors from the target substrate cooling temperature.
Further, the ion beam irradiation apparatus of the example implementation is an ion beam irradiation apparatus configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, wherein the apparatus comprises a first cooling mechanism equipped with a heat exchange unit in which heat exchange between a substrate and a cooling medium takes place, a second cooling mechanism that cools the substrate by heat transfer, temperature sensors that measure the temperature of the substrate, and a cooling mechanism control unit which, along with controlling the temperature of the cooling medium in the first cooling mechanism so as to keep it constant at a target cooling medium temperature, is configured to control the second cooling mechanism so as to reduce the deviation of a measured substrate temperature sensed by the contact-type temperature sensors from a target substrate cooling temperature of the substrate.
Further, the method for substrate cooling of the example implementation is a method for substrate cooling employed in an ion beam irradiation apparatus that is provided with a first cooling mechanism equipped with a heat exchange unit in which heat exchange between a substrate and a cooling medium takes place, a second cooling mechanism that cools the substrate by heat transfer, and temperature sensors that measure the temperature of the substrate, and that is configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, wherein along with controlling the temperature of the cooling medium in the first cooling mechanism so as to keep it constant at a target cooling medium temperature, the second cooling mechanism is controlled so as to reduce the deviation of a measured substrate temperature sensed by the temperature sensors from a target substrate cooling temperature of the substrate.
In such a case, by providing primary substrate cooling, the first cooling mechanism cools the substrate to a target cooling medium temperature and keeps it constant at a temperature in the vicinity of the target substrate cooling temperature. For this reason, the second cooling mechanism uses secondary cooling only for the purpose of controlling variation from the substrate temperature maintained by the first cooling mechanism.
Therefore, it is easy to set a high level of responsiveness because it is sufficient for the second cooling mechanism to control only small changes in temperature and there is no need for a large temperature control range. For this reason, for example, even if an increase in the temperature of the substrate due to substrate irradiation by the ion beam does occur, the second cooling mechanism can operate to immediately minimize the temperature increase and can keep the temperature of the substrate constant at all times.
Furthermore, the fact that the temperature of the substrate can be kept constant at all times makes maintaining the surface of the substrate during ion beam irradiation in the desired condition easier than in the past and allows for substrates with more favorable properties to be obtained.
To ensure instant response to substrate temperature changes, it is sufficient for the second cooling mechanism to be a Peltier device whose heat absorbing surface is in contact with the substrate holding unit and whose heat radiating surface is in contact with the heat exchange unit.
To enable a further increase in the magnitude of the reduction in the temperature of the substrate provided by the first cooling mechanism by increasing the area of direct or indirect contact between the heat exchange unit and the substrate supported by the substrate holding unit in order for the heat exchange between the cooling medium and the substrate to be carried out in an efficient manner, it is sufficient for the heat exchange unit to be composed of a gas reservoir, which is a space between the substrate holding unit and the supported substrate where gas is stored during substrate cooling, a gas pathway for supplying gas to the gas reservoir or discharging gas from the gas reservoir, and a cooling medium channeling unit that is in contact with at least a portion of the gas pathway and has a cooling medium channeled therethrough.
As a specific configuration for enabling adequate substrate cooling by efficiently discharging heat transferred from the substrate by the second cooling mechanism to the environment, a configuration is suggested, in which the heat radiating surface of the Peltier device is in contact with the cooling medium channeling unit.
For example, to ensure that feedback-control is exercised immediately so as to bring the temperature of a substrate to a target substrate cooling temperature if its temperature rises above the target substrate cooling temperature when the substrate is irradiated by an ion beam and heat is driven into the substrate, and to maintain the substrate constantly at this temperature, the temperature sensors are optionally contact-type temperature sensors that are in contact with the substrate supported by the substrate holding unit and measure the temperature of the substrate.

Effects

Thus, the ion beam irradiation apparatus and method for substrate cooling of the present example implementation are configured such that when a substrate is cooled to a cryogenic temperature, primary substrate cooling is provided by the first cooling mechanism by directing a cooling medium having a temperature higher than the critical cold resistance temperature through the plastic tubing and the remainder of substrate cooling is accomplished using the heat transfer provided by the second cooling mechanism, as a result of which it becomes possible to cool the substrate to the target substrate cooling temperature while preventing the embrittlement of the plastic tubing through which the cooling medium is channeled. Furthermore, because the apparatus is configured according to feedback-control variations in the measured substrate temperature using the second cooling mechanism while keeping it at a constant temperature in the vicinity of the target substrate cooling temperature using the first cooling mechanism, the range of control of the second cooling mechanism can be narrowed down and temperature control responsiveness can be readily increased. Consequently, even if the temperature of a substrate rises when the substrate is irradiated by an ion beam, the substrate can be instantly cooled to the target substrate cooling temperature and constantly maintained at this temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic oblique view illustrating the configuration of an ion implantation chamber used in an ion implanter according to an example embodiment.

FIG. 2 A schematic enlarged cross-sectional view illustrating structure adjacent to an electrostatic chuck of a substrate transport mechanism used in the same example embodiment.

FIG. 3 A schematic enlarged cross-sectional view illustrating the attachment structure of a contact-type sensor used in the same example embodiment.

FIG. 4 A functional block diagram illustrating the configuration of substrate cooling mechanism control units and other units used in the same example embodiment.

FIG. 5 A schematic graph illustrating the concept of substrate temperature control in the same example embodiment.

FIG. 6 A schematic diagram illustrating a related-art ion implanter equipped with a substrate cooling mechanism.

DETAILED DESCRIPTION OF EXAMPLE IMPLEMENTATIONS

An example embodiment will be described with reference to FIGS. 1 through 5.
The ion beam irradiation apparatus of this example embodiment is an ion implanter 100 that irradiates a semiconductor substrate with an ion beam comprising, for example, arsenic, phosphorus, boron, and other ion species in order to implant these ion species therein. In addition, this ion implanter 100 is configured to be capable of low-temperature ion implantation in a state, wherein a substrate W is cooled to a predetermined cryogenic temperature in order to amorphize the surface of the substrate during ion implantation and create ultra-shallow junctions therein. Furthermore, it is configured to be capable of handling normal-temperature ion implantation as well, which involves cooling to a temperature at which heat-induced deformation of the photoresist on the surface of the substrate does not occur during ion implantation.
As shown in FIG. 1, in the ion implanter 100, the vacuum chamber VR, the inside of which is maintained under a vacuum, is partitioned by a partition 4. In addition, the upper structure 3U and bottom structure 3B of the substrate transport mechanism 3 are coupled through a connecting slit 41 formed in the partition 4, arranged so as to be in communication with the respective compartments of the upper structure 3U and bottom structure 3B.
More specifically, the ion implanter 100 is provided with: a substrate transport mechanism 3 that supports a substrate W using a substrate holding unit 31 and suitably changes the position and attitude of the substrate W relative to the ion beam; an ion implantation chamber 1, which is the upper compartment of the vacuum chamber VR that houses the upper structure 3U of the substrate transport mechanism 3 where the substrate W is irradiated by the ion beam; a linear motion mechanism housing chamber 2, which is the lower compartment of the vacuum chamber VR that houses the bottom structure 3B of the substrate transport mechanism 3 as well as various power supply cords and part of the plastic tubing 5B used for supplying the cooling medium; and a cooling system FS used for cooling the substrate W supported by the substrate holding unit 31.
A description of each unit will now be provided.
In the substrate transport mechanism 3, the upper structure 3U is a unit that mainly provides attitude control for the supported substrate W, whereas the bottom structure 3B is a unit that moves the supported substrate W in the horizontal direction so that it moves through the ion beam. Namely, the upper structure 3U is composed of a vertical-axis tilting mechanism 3R used for rotation about a vertical axis, and the substrate holding unit 31 that supports the substrate W in a detachable manner. The substrate holding unit 31 is an electrostatic chuck adapted for rotation about a vertical axis perpendicular to the surface of the supported substrate W. Part of the cooling system FS is provided in proximity to the substrate holding unit 31 for cooling the supported substrate W.
The bottom structure 3B, which is a linear motion mechanism made up of a motor 32, a ball screw 33, a nut 34, and a guide (not shown), moves the upper structure 3U perpendicular to the short-side direction of the ion beam.
The upper structure 3U and the bottom structure 3B are coupled by a coupling member through the connecting slit 41 formed in the partition 4, and the entire upper structure 3U is moved as a single unit as a result of the linear motion of the bottom structure 3B in the horizontal direction, thereby moving the substrate W supported by the substrate holding unit 31. In addition, the coupling member effects coupling such that the upper structure 3U can perform rotary motion independently from the bottom structure 3B.
The ion implantation chamber 1, which is a compartment shaped generally as a hollow rectangular parallelepiped, has an ion beam inlet 11 used for ion beam introduction formed in the center of a side face thereof, and a ribbon-shaped ion beam extending in a vertical direction is introduced therethrough. An adjacent substrate load lock chamber (not shown) is provided in this ion implantation chamber 1. The substrate transport mechanism 3 receives a substrate W from the substrate load lock chamber and transports the substrate W to an ion beam irradiation location, where ion implantation into the surface of the substrate takes place. Upon completion of ion implantation, the substrate W is transported to a substrate unloading chamber (not shown) provided in proximity to the ion implantation chamber 1.
The linear motion mechanism housing chamber 2 houses part of the bottom structure 3B of the substrate transport mechanism 3. More specifically, the motor 32 is provided on the outside, in other words on the atmospheric side, of the linear motion mechanism housing chamber 2, while the ball screw 33, nut 34, and the guide are housed inside the linear motion mechanism housing chamber 2. Furthermore, the linear motion mechanism housing chamber 2 is configured to have a higher degree of vacuum than in the ion implantation chamber 1.
The cooling system FS is made up of a first cooling mechanism 5, which cools the substrate W using heat exchange between the cooling medium and the supported substrate W; Peltier devices 6 serving as a second cooling mechanism that cools the substrate W by heat transfer from the substrate W; and a cooling mechanism control unit 7, which controls the operation of the first cooling mechanism 5 and the second cooling mechanism. In the discussion below, explanations will be given with reference to the oblique view of FIG. 1 and the enlarged cross-sectional view of FIG. 2 illustrating the vicinity of the substrate holding unit 31.
The first cooling mechanism 5, which executes a so-called refrigeration cycle, has a refrigerant circuit formed therein in such a manner that a cooling medium circulates between a chiller 54 (not shown in FIG. 1), which is disposed outside the vacuum chamber VR, and a heat exchange unit 5A, which is provided in the substrate holding unit 31 within the vacuum chamber VR, in which heat exchange between the substrate W and the cooling medium takes place. Furthermore, as shown in FIG. 1, in the tubing that connects the chiller 54 with the heat exchange unit 5A, the first cooling mechanism 5 uses plastic tubing 5B at least for the tubing that extends up to the heat exchange unit 5A within the vacuum chamber VR. Even if the position of the heat exchange unit 5A shifts as a result of motion of the substrate transport mechanism 3, this plastic tubing 5B, which is flexible, is configured to follow its motion to some extent without impeding the motion of the substrate transport mechanism 3. More specifically, the plastic tubing 5B that passes through the linear motion mechanism housing chamber 2, which is housed in a bellow-like cable guide 35 along with control signal lines (not shown) and electric power cables (not shown) used to supply electric power from outside to the substrate transport mechanism 3, is adapted to be movable throughout a predetermined range in concert with the movement of the substrate transport mechanism 3. In addition, due to the properties of the plastics, this plastic tubing 5B becomes brittle and loses flexibility when the temperature drops below the critical cold resistance temperature, and there is a risk that it may be damaged when following the motion of the substrate transport mechanism 3. For this reason, in the present embodiment, only a cooling medium having a temperature higher than the critical cold resistance temperature is adapted to be channeled therethrough. It should be noted that, as used herein, the term “critical cold resistance temperature” includes, for example, a manufacturer-recommended service temperature, or a temperature at which there is a risk of reduced flexibility and damage to the plastic tubing 5B due to the movement of the substrate transport mechanism 3, and in the present example embodiment, the critical cold resistance temperature is set to −60° C.
As shown in FIG. 2, the heat exchange unit 5A, if described functionally, is composed of a gas reservoir 51, which is a space between the substrate holding unit 31 and the supported substrate W where gas is stored when the substrate W is cooled, a gas pathway 52 used for supplying gas to the gas reservoir 51 or discharging gas from the gas reservoir 51, and a cooling medium channeling unit 53, which is in contact with at least a portion of the gas pathway 52 and has a cooling medium channeled therethrough. As far as the arrangement of the various members is concerned, the following order is used: substrate W, gas reservoir 51, substrate holding unit 31, second cooling mechanism, and cooling medium channeling unit 53.
More specifically, the distal surface of the substrate holding unit 31 has a thin generally-annular ridge 311, with the flat surface of the ridge 311 configured to electrostatically chuck the backside of the substrate W. Therefore, when holding the substrate W, the radially innermost side of the ridge 311 forms a space used as a gas reservoir 51, where gas is stored when the substrate W is cooled.
In this example embodiment, the gas pathway 52 is made up of a gas supply tube, which supplies gas to the gas reservoir 51, and a gas discharge tube, which is used for discharging the gas from the gas reservoir 51. The gas supply tube and the gas discharge tube are adapted to pass through the cooling medium channeling unit 53 and allow for heat exchange between the gas and the cooling medium to take place.
The cooling medium channeling unit 53, which is formed in the general shape of a hollow flat cylinder, is configured so that the cooling medium, which is cooled by the chiller 54, enters through the plastic tubing 5B, is temporarily accumulated inside the unit, and, once the heat exchange with the gas has taken place, again returns to the chiller 54 through the plastic tubing 5B.
The cooling action of such a first cooling mechanism 5 will be described next. When gas is stored in the gas reservoir 51 during the cooling of the substrate W, the efficiency of heat transfer from the substrate W can be improved by placing a heat conductor against the substrate W maintained under a vacuum atmosphere, such that the conductor is in gapless contact with the minute irregularities formed on the backside thereof. Therefore, the cooling medium in the cooling medium channeling unit 53 can exchange heat directly with the substrate W through the gas pathway 52, as a result of which heat conduction takes place and the substrate W can be cooled even if there was no second cooling mechanism. In other words, it is configured such that heat exchange with the substrate W can occur even when using the first cooling mechanism 5 alone. It should be noted that, since in this example embodiment the cooling medium channeling unit 53 is also in contact with the substrate holding unit 3 through the medium of the Peltier devices 6, which are excellent heat conductors, the substrate W can also be cooled by heat exchange via that thermal pathway.
The second cooling mechanism is described below.
Unlike the first cooling mechanism, the second cooling mechanism does not provide cooling for the substrate W by heat exchange. Instead, it is configured to cool the substrate W by heat transfer from the substrate W to the environment outside of the substrate W. As used herein, the term “heat transfer-based cooling” includes cooling methods in which no cooling medium is used and heat is transferred from an object on the low-temperature side to an object on a high-temperature side, thereby enabling a further reduction in the temperature of the object on the low-temperature side. It should be noted that during heat exchange-based cooling, such as in the first cooling mechanism 5, the substrate W is cooled only if the temperature of the cooling medium is lower than that of the substrate W and, therefore, the temperature of the substrate W never becomes lower than the temperature of the cooling medium.
More specifically, the second cooling mechanism, which is the Peltier devices 6 provided such that their heat absorbing surfaces 61 are in contact with the substrate holding unit 31 and their heat radiating surfaces 62 are in contact with cooling medium channeling unit 53, is configured to remove heat from the substrate W through the substrate holding unit 31 by an electron flux and release the removed heat into the cooling medium channeling unit 53.
The functionality of the cooling mechanism control unit 7 is realized by running a software program stored in the memory of what is commonly called a “computer”, which is equipped with a CPU, a memory, an AC/DC converter, input/output structures, and the like. For example, the software program may include, but is not limited to, machine-readable instructions executed by a non-transitory computer readable medium. In addition, at least when the target substrate cooling temperature of the substrate W is not higher than the critical cold resistance temperature of the plastic tubing 5B, this cooling mechanism control unit 7 is configured to cool the substrate W using the second cooling mechanism while channeling the cooling medium at a temperature higher than the critical cold resistance temperature through the plastic tubing 5B.
In addition, as shown in FIG. 3, there are provided contact-type temperature sensors TS that are placed in direct contact with the backside of the substrate W supported by the substrate holding unit 31 and measure the temperature of the substrate W. As shown in FIG. 2, there are several contact-type temperature sensors TS provided for measuring temperature in several locations on the substrate W, the sensors being located on the substrate holding unit 31 in contact with the backside of the substrate W across the gas reservoir 51. The cooling mechanism control unit 7 controls the first cooling mechanism 5 and second cooling mechanism using the measured substrate temperature obtained from these contact-type temperature sensors TS.
More specifically, in this example embodiment, as shown in the functional block diagram of FIG. 4, the cooling mechanism control unit 7 comprises a first cooling mechanism control unit 71, which controls the first cooling mechanism 5, and a second cooling mechanism control unit 72, which controls the cooling capability of the second cooling mechanism. In addition, in the process of cooling medium temperature control by the first cooling mechanism control unit 71, the measured substrate temperature sensed by the contact-type temperature sensors TS is used to determine the target ° C. value, to which the target cooling medium temperature should be set at a temperature higher than the critical cold resistance temperature of the plastic tubing 5B. On the other hand, in the second cooling mechanism control unit 72, the measured substrate temperature obtained from the contact-type temperature sensors TS is subject to continuous feedback, with the unit configured to perform feedback-control of the voltage applied to the Peltier devices 6 so as to reduce the deviation of a measured substrate temperature from a target substrate cooling temperature.
Each control unit will be now described in detail. The first cooling mechanism control unit 71 is provided with a cooling medium temperature control unit 73, which controls the temperature of the cooling medium supplied to the cooling medium channeling unit 53 so as to match a target cooling medium temperature, and a gas control unit 74, which controls the supply and discharge of the gas to/from the gas reservoir 51.
The cooling medium temperature control unit 73, whose operation is configured to be switched depending on the target substrate cooling temperature, is configured to set the target cooling medium temperature to a temperature higher than the critical cold resistance temperature by a predetermined amount when the target substrate cooling temperature is not higher than the critical cold resistance temperature of the plastic tubing 5B, and set the target cooling medium temperature to the same temperature as the target substrate cooling temperature when the target substrate cooling temperature is higher than the critical cold resistance temperature of the plastic tubing 5B. In addition, the cooling medium temperature control unit 73 controls each piece of equipment in the refrigeration cycle such that, for example, the cooling medium temperature measured by the temperature sensors provided in the refrigeration cycle comprising the chiller 54 and other units is maintained at a target cooling medium temperature (e.g., preset).
The gas control unit 74 supplies a fixed amount (e.g., predetermined) of gas to the gas reservoir 51 through the gas pathway 52 when the substrate W is supported by the substrate holding unit 31 and exercises control aimed at preventing the substrate W from falling into the vacuum chamber VR due to a pressure difference when the electrostatic chuck is disengaged by discharging the gas from the gas reservoir 51 and producing practically the same pressure as the pressure within the vacuum chamber VR prior to removing the substrate W from the substrate holding unit 31, in other words, prior to deactivating the voltage applied to the electrostatic chuck.
The second cooling mechanism control unit 72 controls the voltage applied to the Peltier devices 6 based on the deviation of the measured substrate temperature sensed by the contact-type temperature sensors TS from a target substrate cooling temperature. Here, the cooling medium temperature control unit 73 exercises control such that the temperature of the cooling medium is maintained constant at the target cooling medium temperature. As a result, the second cooling mechanism control unit 72 controls the voltage applied to the Peltier devices 6 such that heat corresponding to the difference between the target substrate cooling temperature and the target cooling medium temperature as well as heat generated by the irradiation of the substrate W by the ion beam are transferred from the substrate W to the cooling medium channeling unit 53.
Referring now to the temperature variation graphs of FIG. 5, the operation of the thus configured ion implanter 100 during substrate cooling will be described with reference to a case in which the target substrate cooling temperature is lower than the critical cold resistance temperature of the plastic tubing 5B, and a case in which the target substrate cooling temperature is higher than the critical cold resistance temperature of the plastic tubing 5B.
If the target substrate cooling temperature is set to −100° C., which is lower than −60° C., i.e. the critical cold resistance temperature of the plastic tubing 5B, the cooling medium temperature control unit 73 controls the chiller 54 and other units such that the target cooling medium temperature is set to a temperature higher than the critical cold resistance temperature, for example, to −55° C., and the temperature of the cooling medium is constantly maintained at this temperature. In addition, the second cooling mechanism control unit 72 applies a voltage to the Peltier devices 6 such that the heat corresponding to the temperature differential between −100° C., i.e. the target substrate cooling temperature, and −55° C., i.e. the target cooling medium temperature, is transferred from the substrate W by the Peltier devices 6. For example, the voltage applied by the second cooling mechanism control unit 72 to the Peltier devices 6 is proportionate to, or correlated with, the temperature difference to be set between the heat absorbing surface 61 and the heat radiating surface 62.
As shown in FIG. 5( a), during the ion beam non-irradiation period, when the substrate W is not irradiated by the ion beam, the operation of the first cooling mechanism 5 and second cooling mechanism maintains the temperature of the substrate W at about −100° C., but when the substrate W is irradiated by the ion beam, a corresponding amount of heat is imparted to the substrate W and, as a result, as illustrated in the ion beam irradiation period of FIG. 5( a), the measured substrate temperature sensed by the contact-type temperature sensors TS rises above −100° C. In that case, the magnitude of the deviation of the measured substrate temperature from the target substrate cooling temperature fluctuates and, as a result, the second cooling mechanism control unit 72 uses feedback such that the voltage applied to the Peltier devices 6 is adjusted in accordance with the fluctuation of the deviation so as to maintain the temperature at −100° C.
Namely, while during the ion beam non-irradiation period of FIG. 5( a) the Peltier devices 6 continue cooling aimed at the preset temperature differential between the target cooling medium temperature and the target substrate cooling temperature, during the ion beam irradiation period the Peltier devices 6 operate to maintain the substrate W at the target substrate cooling temperature by performing cooling aimed not only at the temperature differential (e.g., preset) mentioned above, but also at variation due to the temperature increase. In addition, during the ion beam irradiation period the first cooling mechanism 5 acts to constantly maintain the same temperature as during the ion beam non-irradiation period without adjusting the target cooling medium temperature, with only the Peltier devices 6, which are provided in proximity to the substrate W and are capable of instantly adjusting the amount of cooling if the applied voltage changes, being subject to feedback based on the measured substrate temperature. As a result, even if temperature changes occur, the temperature of the substrate W can be maintained essentially constant at −100° C. practically without any time delay.
Operation in situations in which the target substrate cooling temperature is a temperature higher than the critical cold resistance temperature of the plastic tubing 5B, will be described next with reference to FIG. 5( b). Here, a case in which the target substrate cooling temperature is −40° C. and the critical cold resistance temperature is −60° C., will be considered as a specific example.
In this case, the cooling medium temperature control unit 73 sets the target cooling medium temperature to −40° C., i.e. the same temperature as the target substrate cooling temperature. Here, during the ion beam non-irradiation period of FIG. 5( b), there is almost no heat flowing from the outside to the substrate W, which is maintained in a vacuum. As a result, the temperature of the substrate W is maintained at −40° C. substantially by the operation of the first cooling mechanism 5 alone. On the other hand, during the ion beam irradiation period, the substrate temperature rises when the ion beam irradiates the substrate W, as a result of which a deviation develops between the measured substrate temperature sensed by the contact-type temperature sensors TS and the target substrate cooling temperature. Therefore, during the ion beam irradiation period of FIG. 5( b), the operation of cooling is carried out by applying a voltage corresponding to the deviation to the Peltier devices 6. Namely, whereas the first cooling mechanism 5 continues cooling the substrate W using the cooling medium at −40° C. regardless of the measured substrate temperature, the Peltier devices 6 perform practically no cooling during the ion beam non-irradiation period and operate only when the measured substrate temperature deviates from −40° C. during the ion beam irradiation period.
In this manner, the Peltier devices 6, which are provided in the vicinity of the substrate W, perform cooling aimed only at temperature differentials produced by deviations from the target substrate cooling temperature, as a result of which, even when there are fluctuations, the temperature of the substrate W can be maintained constant at the cryogenic temperature with very high responsiveness. More specifically, an attempt to use the first cooling mechanism 5 to apply feedback-control to cooling aimed at a temperature increase due to irradiation of the substrate W by the ion beam changes the operation of the chiller 54, which is located outside the vacuum chamber VR, far from the substrate W, and thus produces a considerable time delay before any results become apparent. For this reason, it is difficult to instantly cancel temperature increases by controlling the temperature of the substrate W using the first cooling mechanism 5 alone. By contrast, as a result of providing temperature control of temperature increases with the help of the Peltier devices 6 located within the vacuum chamber VR in the vicinity of the substrate W, the substrate can immediately, practically without any time delay, be cooled to the target substrate cooling temperature and constantly maintained at this temperature.
In accordance with the ion implanter 100 of the present example embodiment described in detail above, when the target substrate cooling temperature of the substrate W is not higher than the critical cold resistance temperature of the plastic tubing 5B, along with subjecting the substrate W to primary substrate cooling by setting the target cooling medium temperature to a temperature higher than the critical cold resistance temperature and directing a cooling medium at a temperature higher than the critical cold resistance temperature into the heat exchange unit 5A of the first cooling mechanism 5, the amount of heat in the substrate W that is not removed by the first cooling mechanism 5 by cooling down to the target substrate cooling temperature is removed by the heat transfer-based secondary cooling provided by the Peltier devices 6, as a result of which the temperature of the substrate W can be reduced to the target substrate cooling temperature.
Because only a cooling medium at a temperature higher than the critical cold resistance temperature is channeled through the plastic tubing 5B at such time, the flexibility of the plastic tubing 5B is never impaired and the plastic tubing 5B is not damaged even if the position of the substrate W is changed by the substrate transport mechanism 3 while cooling the substrate W to a cryogenic temperature. Therefore, the substrate W can be freely moved by the substrate transport mechanism 3 while the substrate W is cooled to a temperature lower than the critical cold resistance temperature, and the surface of the substrate can be irradiated by the ion beam in a variety of ways.
Furthermore, since the temperature of the substrate W has already been reduced to a certain extent by the primary substrate cooling provided by the first cooling mechanism 5, the substrate W can be cooled to the target substrate cooling temperature even though the Peltier devices 6 do not remove a very large amount of heat from the substrate W by heat transfer, and the Peltier devices 6 are not required to have an excessively large capacity.
In addition, since the apparatus is configured to monitor the temperature of the substrate W in real time using the contact-type temperature sensors TS even during ion beam irradiation and feedback-control of the Peltier devices 6 in accordance with the deviation of the measured substrate temperature from the target substrate cooling temperature, the temperature can be maintained essentially constant at the target substrate cooling temperature even during ion beam irradiation.
Therefore, since temperature control accuracy during low-temperature ion implantation may be improved in comparison with the prior art, the properties of substrates W obtained by low-temperature ion implantation may also be superior to the related art.
A description of other example embodiments will now be given.
The ion beam irradiation apparatus of this example implementation is a concept that includes not only the ion implanter 100, but also e.g. ion doping machines, ion beam deposition machines, ion beam etching machine, and the like. In addition, it can be used in applications involving ion beam irradiation in combination with temperature management not only on substrates W such as silicon wafers, but also on glass substrates, semiconductor substrates, and the like. In addition, when the glass substrates and the like are irradiated with an ion beam, the substrates may be chucked using chucking methods other than electrostatic chucking such that the substrates are supported on the substrate holding unit of the substrate transport mechanism.
Although in the above-described embodiment the second cooling mechanism used Peltier devices 6, devices capable of cooling the substrate W using other kinds of heat transfer may also be used. For example, these may be devices made not of semiconductors, like the Peltier devices 6, but devices adapted to produce the Peltier effect using dissimilar metals.
When the target substrate cooling temperature was higher than the critical cold resistance temperature, the cooling mechanism control unit 7 brought the target cooling medium temperature in agreement with the target substrate cooling temperature. However, it is also possible to set the target cooling medium temperature to a temperature higher than the target substrate cooling temperature. Namely, even in cases in which temperature control of the substrate W is possible only by the operation of the first cooling mechanism 7, the apparatus may also be configured to act on the fluctuations, along with providing cooling for the substrate W using the second cooling mechanism when no fluctuations from the target substrate cooling temperature have occurred, as shown in FIG. 5( a).
The Peltier devices 6 may be used not only for cooling the substrate W, but also for heating if for some reason the substrate W is overcooled by the first cooling mechanism 5. Namely, the second cooling mechanism control unit 72 may also be configured to permit controlling not only the magnitude of the voltage applied to the Peltier devices 6, but also its direction. In this case, the temperature of the substrate W can also be controlled using the control rule shown in the above-described example embodiment if there is a deviation of the measured substrate temperature from the target substrate cooling temperature.
If the target substrate cooling temperature is set to a temperature higher than the critical cold resistance temperature of the plastic tubing 5B and responsiveness requirements are not particularly stringent, it is possible to use feedback-control based on the deviation of the measured substrate temperature from the target substrate cooling temperature in the first cooling mechanism 5 without operating the second cooling mechanism.
Although in the above-described example embodiment the temperature of the substrate W was constantly monitored using contact-type temperature sensors TS, it is also possible to exercise temperature control by measuring the temperature of the substrate W using non-contact temperature sensors.
In addition, various modifications and combinations of embodiments are also possible where consistent with the gist of the present inventive concept.

Claims

I/we claim:

1. An ion beam irradiation apparatus configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, the apparatus comprising:

a first cooling mechanism equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place, and flexible plastic tubing configured to channel the cooling medium to the heat exchange unit;

a second cooling mechanism that cools the substrate by heat transfer; and

a cooling mechanism control unit which, at least when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing, cools the substrate using the second cooling mechanism while channeling the cooling medium at a temperature higher than the critical cold resistance temperature through the plastic tubing.

2. The ion beam irradiation apparatus according to claim 1, wherein the target substrate cooling temperature is −60° C. or lower.

3. The ion beam irradiation apparatus according to claim 1, wherein the second cooling mechanism comprises a Peltier device having a heat absorbing surface in contact with the substrate holding unit and having a heat radiating surface in contact with the heat exchange unit.

4. The ion beam irradiation apparatus according to claim 1, wherein the heat exchange unit comprises:

a gas reservoir comprising a space between the substrate holding unit and the supported substrate, where gas is stored during substrate cooling;

a gas pathway that supplies gas to the gas reservoir or discharges gas from the gas reservoir; and

a cooling medium channeling unit that is in contact with at least a portion of the gas pathway and has a cooling medium channeled therethrough.

5. The ion beam irradiation apparatus according to claim 3, wherein the heat exchange unit comprises:

a gas reservoir comprising a space between the substrate holding unit and the supported substrate where gas is stored during substrate cooling;

6. The ion beam irradiation apparatus according to claim 5, wherein the heat radiating surface of the Peltier device is in contact with the cooling medium channeling unit.

7. The ion beam irradiation apparatus according to claim 1, wherein:

the apparatus further comprises contact-type temperature sensors that are in contact with the substrate supported by the substrate holding unit and measure the temperature of the substrate, and

the cooling mechanism control unit, which is configured to control the temperature of the cooling medium in the first cooling mechanism that keeps the temperature constant at a target cooling medium temperature, is further configured to control the second cooling mechanism to reduce the deviation of a measured substrate temperature sensed by the contact-type temperature sensors from a target substrate cooling temperature.

8. A method for substrate cooling employed in an ion beam irradiation apparatus that comprises:

first cooling, via a first cooling mechanism equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place, and flexible plastic tubing for channeling the cooling medium to the heat exchange unit, and

second cooling, via a second cooling mechanism that cools the substrate by heat transfer, and that is configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, wherein:

at least when the target substrate cooling temperature of the substrate is not higher than the critical cold resistance temperature of the plastic tubing,

the substrate is cooled by the second cooling, while the cooling medium at a temperature higher than the critical cold resistance temperature is channeled through the plastic tubing.

9. An ion beam irradiation apparatus configured to cool a substrate supported by a substrate holding unit of a substrate transport mechanism, the apparatus comprising:

a first cooling mechanism equipped with a heat exchange unit in which heat exchange between a substrate and a cooling medium takes place;

a second cooling mechanism that cools the substrate by heat transfer;

temperature sensors that measure the temperature of the substrate; and

a cooling mechanism control unit which, along with controlling the temperature of the cooling medium in the first cooling mechanism to keep the temperature constant at a target cooling medium temperature, is configured to control the second cooling mechanism to reduce the deviation of a measured substrate temperature sensed by the temperature sensors from a target substrate cooling temperature of the substrate.

10. The ion beam irradiation apparatus according to claim 9, wherein the second cooling mechanism comprises a Peltier device having a heat absorbing surface in contact with the substrate holding unit and a heat radiating surface in contact with the heat exchange unit.

11. The ion beam irradiation apparatus according to claim 9, wherein the heat exchange unit comprises:

a gas pathway configured to supply gas to the gas reservoir or discharge gas from the gas reservoir; and

12. The ion beam irradiation apparatus according to claim 10, wherein the heat exchange unit comprises:

13. The ion beam irradiation apparatus according to claim 12, wherein the heat radiating surface of the Peltier device is in contact with the cooling medium channeling unit.

14. The ion beam irradiation apparatus according to claim 9, wherein the temperature sensors are contact-type temperature sensors that are in contact with the substrate supported by the substrate holding unit and measure the temperature of the substrate.

15. A method for substrate cooling employed in an ion beam irradiation apparatus that comprises:

first cooling, via a first cooling mechanism equipped with a heat exchange unit, in which heat exchange between a substrate and a cooling medium takes place,

second cooling, via a second cooling mechanism, that cools the substrate by heat transfer, and

measuring, via temperature sensors, the temperature of the substrate, wherein cooling a substrate is supported by a substrate holding unit of a substrate transport mechanism, and further wherein:

along with controlling the temperature of the cooling medium in the first cooling so as to keep it constant at a target cooling medium temperature, the second cooling is controlled so as to reduce the deviation of a measured substrate temperature sensed in the measuring by the temperature sensors from a target substrate cooling temperature of the substrate.