Patent Application
20060138353
The present invention relates to an ion-implanting apparatus, an ion-implanting method, and devices manufactured by the apparatus and method. The present invention relates to control of a beam current value of an ion-implanting apparatus for radiating an ion beam onto a subject to be processed, such as a semiconductor wafer, and implanting ions.
In introduction of impurities using an ion-implanting apparatus, the concentration and depth of implantation are easily controlled. For this reason, ion-implanting apparatuses are generally used in the step of introduction of impurities in production of semiconductor devices.
On the side of the ion extracting direction in arc chamber 9, ion outlet 13 is provided. In a position facing with ion outlet 13, extracting electrode 14 is provided. Extracting electrode 14 has an ion through-hole 22. The ion through-hole is aligned with the center of the body of ion-implanting apparatus 16, in ion source chamber 15. Extracting electrode 14 is supported by ring-shaped base electrode 23 via electrically conductive struts. Base electrode 23 is supported by ground electrode 24 via insulating members, such as insulators. One end of ground electrode 24 is supported by a supporting post in intimate contact with supporting hole provided in the sidewall of ion source chamber 15. The other end of ground electrode 24 is supported by supporting rod 26 that can project through the sidewall radially of ion source chamber 15. Extracting electrode 14 and base electrode 23 have the same electric potential, and are structured to be supported by ground electrode 24 via the insulating members.
During ion-implantation, a predetermined gas is introduced in arc chamber 9, and a predetermined high current is applied to filament 10 from a power source for generating thermal electrons. This current is a DC current of 150 A, for example. Further, a predetermined negative DC voltage of −100V, for example, is applied from a power source for generating arc discharge. Thus, discharge occurs between filament 10 and arc chamber 9, and a predetermined processing gas dissociates to generate plasma. At this time, a power source for extracting ions applies a predetermined high DC voltage of 80 kV, for example, across arc chamber 9 and extracting electrode 14. This extracts only positive ions in the plasma generated in arc chamber 9 in the direction of extracting electrode 14 to form ion beam 2. The part where ion beam 2 passes is kept at a vacuum of approximately 10−5 Torr, using a turbo-molecular pump or a cryopump.
Ion-implanting apparatuses supply ion beams 2 with high energy resolution. For this purpose, some ideas are considered to prevent fluctuations of the voltage of extracting electrode 14 and the accelerating voltage of accelerating electrode 5 and keep these voltages constant. For example, in an ion-extracting power source for outputting a predetermined DC voltage to ion source 1 and extracting electrode 14, general commercial AC power is converted into desired DC power for use. The AC components left after conversion, i.e. ripple components, cause variations in the energy of ion beams 2. To address this problem, as shown in a technique of reducing the ripple components in low energy injection disclosed in Japanese Patent Unexamined Publication H10-112277, keeping high energy resolution is important.
As to ion source 1, the shape of ion outlet 13, the position of extracting electrode 14, the gas flow and pressure supplied into arc chamber 9, current and voltage applied to filament 10, arc voltage, arc current, the magnetic field strength for trapping electrons inside of arc chamber 9 are optimized, according to the desired type of ions and extracting electrode. Additionally, according the implantation conditions, the shape of ion outlet 13 is changed or extracting voltage is adjusted before ion beam 2 is set. Further, a device for changing the position of extracting electrode 14 to change the distance to ion outlet 13 is generally provided.
An ion-implanting apparatus controls variations in a beam current value by giving feedback on the beam current value measured by a beam current measuring means to at least one parameter selected from a group consisting of the shape of the ion outlet provided in the arc chamber of the ion source, the position of the extracting electrode, dopant gas flow, dopant gas pressure, current and voltage applied to the filament, arc voltage, arc current, the magnetic field strength for trapping electrons inside of the arc chamber, and the position of the arc chamber.
Active devices and passive devices are manufactured by using the above ion-implanting apparatus.
An ion-implanting method controls variations in a beam current value by giving feedback on the beam current value measured by a beam current measuring means to at least one parameter selected from a group consisting of the shape of the ion outlet provided in the arc chamber of the ion source, the position of the extracting electrode, dopant gas flow, dopant gas pressure, current and voltage applied to the filament, arc voltage, arc current, the magnetic field strength for trapping electrons inside of the arc chamber, and the position of the arc chamber.
During ion implantation, it is desirable that fluctuations of the value of beam current radiated onto a subject to be processed are small. However, with a conventional method, a beam current value actually fluctuates by approximately 5% and is not kept constant.
One of the factors of the above problem is that the condition of ion source 1 in the conventional ion-implanting apparatus changes with time. In other words, filament 10 and the surface condition of the inner wall of arc chamber 9 change, thermal expansion changes the dimension of arc chamber 9, temperature change in the gas piping from gas source 12 to gas supply nozzle 11 changes the volume of dopant gas, and the ion density in the plasma changes with time. These changes change the condition of ion source 1 previously set according to the desired type of ions and extracting electrode, thus causing fluctuations of a beam current value. On the other hand, it is difficult to control the change in condition so that the condition is kept constant.
Incidentally, as described in the Background Art, for example, a device for changing the position of the extracting electrode in a vertical, horizontal, or rotational direction is generally used. However, this device is mainly used at setting of ion beam 2 before ion implantation. In other words, this device statically changes the position of the extracting electrode, and cannot control a dynamic change in beam current value with time.
Thus, there is a need of a technique of keeping a beam current value constant irrelevant to the change in the condition of ion source 1 with time. However, energy to be injected must be kept within a certain range including a desired value. In other words, a measure of changing extracting voltage to inhibit the fluctuations of a beam current value, which causes a change in energy, cannot be taken.
As described above, it is required to provide an ion-implanting apparatus that can dynamically control a beam current value of an ion beam with time and does not change the energy.
The present invention provides an ion-implanting apparatus and an ion-implanting method capable of addressing the above problems, and devices manufactured by the apparatus and the method. The present invention is described with reference to
In an ion-implanting apparatus of the present invention, a beam current measuring means measures the beam current value of ion beam 2, and feedback on the measurement allows control of a dynamic change in the beam current value with time. The feedback on the measurement is given to at least one parameter selected from a group consisting of the shape of the ion outlet provided in the arc chamber of the ion source, the position of the extracting electrode, dopant gas flow, dopant gas pressure, current and voltage applied to the filament, arc voltage, arc current, the magnetic field strength for trapping electrons inside of the arc chamber, and the position of the arc chamber. In other words, the present invention changes at least one of the above parameters to control a beam current value, according to the change in the condition of ion source 1, which has been difficult to control as described as problems of the conventional method.
How to vary the shape of ion outlet 13 is described. The shape of ion outlet 13 is made into a variable structure using a mechanism of a slit, shutter, valve, door, or nozzle. As a driving method, the use of deformation of a piezoelectric element, gas pressure, liquid pressure, thermal deformation, or motor force allows control of minute dimensional change. As to a motor, the use of a servo motor, linear motor, stepping motor, or ultrasonic motor allows precise driving. It is desirable that the mechanism for varying the shape of ion outlet 13 is attached to lid 20 together with arc chamber 9. It is also desirable that lid 20, arc chamber 9, and the mechanism for varying the shape of ion outlet 13 are made as a structure detachable by removing lid 20 from ion source chamber 15. This is because such a structure can keep the labor hour taken for maintenance, such as cleaning of ion source 1, at the same level as a conventional standard.
Means for measuring beam current include Faraday cup 8, a beam current measuring device, and DC converter. The beam current measuring device at least includes: (a) a detecting section for detecting or collecting a magnetic field corresponding to beam current; (b) measuring section including: (i) a superconducting quantum interference device (SQUID) sensitive to magnetic flux; and (ii) a feedback coil for carrying feedback current to cancel out a change in the magnetic flux penetrating through the SQUID. It is desirable that the beam current measuring device also includes a magnetic flux transfer section for transferring the magnetic flux detected or collected by the detecting section to the measuring section, because its sensitivity can be adjusted. It is desirable that the beam current measuring device further includes a magnetic shielding section made of a superconductor for magnetically shielding the detecting section, the magnetic flux transfer section, and the measuring section from an external space including a space carrying ion beam 2, because external magnetic noises can be reduced. When Faraday cup 8 is used as a means for measuring the beam current, Faraday cup 8 is generally placed behind or a side of a disk carrying a subject to be processed for measurement. In this case, radiation of the beam onto the subject to be processed and measurement of the beam current value cannot be performed at the same time. Additionally, there is a problem of several percent of error included in the measurement caused by outgas 28 emitted from semiconductor wafer 7. In contrast, when a beam current measuring device or a DC converter is used, the following advantage is provided. When such a device is placed on the side of ion source 1, i.e. on the upstream side, of a subject to be processed, on a beam line, measurement of the beam current value and radiation of ion beam 2 onto the subject to be processed can be performed at the same time. Further, because the beam current value can be measured before contact of outgas 28 and ion beam 2, the measurement does not have error caused by outgas 28. It is desirable to use a DC converter, when a beam current of a milliampere or higher is measured with an error of several microamperes. On the other hand, it is desirable to use a beam current measuring device when a beam current ranging from several dozens nanoamperes to several microamperes is measured with an error of several nanoamperes, or beam current ranging from several microamperes to several dozens of milliamperes is measured with an error of 0.1% or smaller.
The present invention can provide an ion-implanting method and ion-implanting apparatus that can dynamically control a beam current value of an ion beam with time and does not change energy.
The present invention is further detailed.
[Mechanism for Varying Shape of Ion Outlet]
A further description is provided with reference to
With such a structure, partition plates 39 can translate in a direction perpendicular to the traveling direction of ion beam 2, by using rotation of ball screws A 33 caused by small servo motors 30 as force. In other words, the shape of ion outlet 13 can be changed by using the mechanism of a slit. Positioning accuracy and positioning time of partition plates 39 are determined by the performance of small servo motors 30, drivers 40, and an actuator including the ball screws. The positioning accuracy can be set to approximately 10 to 100 μm. The positioning time can be set to approximately 50 to 100 ms.
The part of extracting electrode 14 has a structure that is employed in a conventional Freeman ion source.
[Mechanism for Varying Position of Arc Chamber]
In the portion where lid 20 is in contact with shaft 55, as shown in
The use of the above mechanism can move ion outlet 13 in arc chamber 9 in parallel with the traveling direction of ion beam 2, using the rotation of ball screw E 50 caused by small servo motor 58 as force. The part of extracting electrode 14 has a structure that is generally employed in a conventional Freeman ion source.
[Procedure for Controlling Beam Current Value]
A description is provided of a procedure for controlling a beam current value, using a mechanism for varying the shape of ion outlet 13. Ion outlet 13 is shaped to have a small lateral width and a large longitudinal dimension, for example. For such a shape, it is known that changing the longitudinal dimension can change a beam current value, without decreasing the energy resolution of ion beam 2. In other words, the larger the longitudinal dimension, the larger the beam current value. The smaller the longitudinal dimension, the smaller the beam current value. By utilizing the above property, the beam current value can be controlled within a desired range. Specifically, a threshold value is provided in the measurements of beam current taken with a beam current measuring device. Then, when a measurement exceeds the threshold value, the longitudinal dimension of ion outlet 13 is changed so that the beam current value is smaller than the threshold value. For example, when a measurement of beam current is smaller than the threshold value, controller 59, which will be described later, instructs drivers 40 to activate small servo motors 30. Then, partition plates 39 move so that the longitudinal dimension of ion outlet 13 is increased. Thereafter, when the measurement of beam current reaches a desired value, small servo motors 30 are stopped. Thus, a beam current value is controlled within a predetermined range.
Next, a description is provided of a procedure for controlling a beam current value, using a mechanism for varying the position of arc chamber 9. This mechanism can move the position of arc chamber 9 toward and away from extracting electrode 14. When arc chamber 9 is nearer to extracting electrode 14, the extracting electric field increases. On the other hand, arc chamber 9 is farther from extracting electrode 14, the extracting electric field decreases. This mechanism utilizes this phenomenon. However, because the ion density in plasma at a given point is not known, it is also unknown in which direction arc chamber should be moved to increase or decrease a beam current value. Thus, the following method is employed. When a measurement of beam current exceeds a threshold value, controller 59 slightly moves arc chamber 9 in either direction. Then, depending on whether the measurement of beam current at that time has increased or decreased, controller 59 determines if the moving direction is right or not. If the measurement of beam current has changed to a value smaller than the threshold value, arc chamber 9 is moved in that direction. On the other hand, if the measurement of beam current has changed to a value larger than the threshold value, arc chamber 9 is moved in the opposite direction. Thereafter, when the measurement of beam current reaches a desired value, small servo motor 48 is stopped. In this manner, an appropriate extracting electric field can be set during ion implantation, according to the ion density in plasma that changes with time. Additionally, the above method can control a beam current value within a desired range. The procedure is the same for the use of a mechanism for varying the position of the extracting electrode.
[Structure of Ion-Implanting Apparatus]
Further, a description is provided with reference to
This exemplary embodiment describes a method of controlling a beam current value dynamically varying with time so that the beam current value is kept constant. However, it is obvious that the beam current value can be controlled so that it varies arbitrarily instead of being constant. Additionally, in the same manner, the beam current density of an ion beam can be controlled.
The present invention can provide an ion-implanting method and ion-implanting apparatus that can dynamically control a beam current value of an ion beam with time and does not change energy. In the same manner, the beam current density of an ion beam can be controlled. Thus, by this ion-implanting apparatus or this ion-implanting method, a various kinds of devices are manufactured.
