Abstract:
A plasma based ion implantation system capable of generating a capacitively coupled plasma having beneficial characteristics for an ion implantation, including the generation of necessary ions and radicals only for an ion implantation process instead of generating an inductively coupled plasma, which generates unnecessary ions and excessively dissociates radicals. The plasma based ion implantation system easily controls plasma ions implanted by cleaning a vacuum chamber, minimizes problems of unnecessary deposition and occurrence of contaminants and increases the number of components used only for the plasma ion implantion by reducing the deposition of polymer layer on a workpiece. The plasma based ion implantation system easily control uniformity of the plasma by using a flat type electrode, thereby easily ensuring uniformity of plasma ions implanted into the workpiece.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2007-0050132 filed on May 23, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a plasma based ion implantation system. More particularly, the present invention relates to a plasma based ion implantation system capable of controlling an implantation of ions in an easy way as compared with an ion beam based ion implantation and reducing a problem of unnecessary deposition, and contamination on a surface of a wafer. 
         [0004]    2. Description of the Related Art 
         [0005]    A plasma based ion implantation (PBII) technology is a core technology, which is essentially necessary to develop a semiconductor device having a line width of 80 nm or below. The PBII technology is an ion doping technology for a Si device for realizing a CMOS (complimentary metal oxide semiconductor). As a line width of a semiconductor device gradually becomes narrow, a shallower junction depth is required and much more ions must be implanted so as to improve an operational speed of the semiconductor device. However, when using a conventional ion implantation technology based on ion beam line (BL), the productivity of the semiconductor devices is significantly reduced to satisfy the above process condition. The advantage of the plasma based ion implantation process, which represents an improved productivity as compared with that of a conventional BL scheme, is more prominent as the energy of ion implantation is lowered. Further, the plasma based ion implantation process can be performed by using equipment having a simple structure, a small size and a low price. In addition, the PBII scheme represents the substantially same result as compared with the BL scheme in terms of reproducibility and uniformity of the process and a generation of contaminants. 
         [0006]    Recently, several types of plasma based ion implantation systems, such as U.S. Pat. Nos. 6,528,805 and 6,716,727, have been suggested. Most of the systems directly apply a square high-voltage pulse to a wafer to precisely adjust the energy of implanted ions. However, they represent difference in plasma generation schemes. The simplest scheme is to simultaneously generate plasma and implant the ions using the high voltage plasma applied to the wafer. According to other scheme, the high voltage pulse for generating plasma is used independently from the high voltage pulse for the ion implantation process. Recently, an inductively coupled plasma (ICP) generator is extensively used to generate plasma by using radio frequency (RF), instead of pulse. 
         [0007]    The inductively coupled plasma (ICP) using RF has advantages of a wider process region and a lower occurrence of arching as compared with the plasma generated by using the high voltage pulse. The most advantageous point of the ion implantation process using the inductively coupled plasma is that the amount of ions and the energy can be adjusted independently from each other. That is, a density of plasma is adjustable by varying RF power application, thereby adjusting the amount of implanted ions. In addition, the high voltage pulse applied to the wafer enables the energy of ions to be adjusted. 
         [0008]    In the case of the inductively coupled plasma generator, a metallic coil is installed on an upper portion of a chamber having a cylindrical shape for flowing current and is separated from the chamber while interposing a plate including insulating material therebetween. Such an inductively coupled plasma generator can generate high density plasma at various discharge conditions (for example, the type of gas, pressure, power, etc.). 
         [0009]    Such an inductively coupled plasma generator easily generates high density plasma, so the inductively coupled plasma generator is generally used in various semiconductor manufacturing processes. However, if the inductively plasma generator is used for the PBII process, the following problems occur. 
         [0010]    According to the PBII process, the plasma ions generated by the plasma generator are strongly accelerated by using the high voltage pulse such that the plasma ions can be deeply implanted into a surface of the wafer. In order to effectively perform the ion implantation process, plasma capable of facilitating the ion implantation by restraining dissociation of process gas and minimizing the formation of unnecessary layers on the surface of the wafer must be generated. However, the inductively coupled plasma has an electron temperature higher than that of capacitively coupled plasma, so that ions and radicals are excessively generated. As a result, the ions are unnecessarily implanted and process gas is excessively dissociated, thereby exerting a bad influence on the process efficiency such as deposition of the layer and generation of contaminants on the wafer surface. In addition, the ICP scheme forms a strong field around a coil, so that plasma is concentrated, causing a difficulty in controlling uniformity of plasma. Further, the use of dielectric causes a complicated structure of the plasma generator. 
       SUMMARY 
       [0011]    Accordingly, it is an aspect of the present invention to provide a plasma based ion implantation system capable of performing an effective discharge in a wide process region while solving the problem that an inductively coupled plasma generator represents, and improving the process efficiency and ensuring uniformity of plasma by reducing unnecessary ionization and dissociation. 
         [0012]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
         [0013]    The foregoing and and/or other aspects of the present invention are achieved by providing a plasma based ion implantation system used for implanting ions on a surface of a workpiece, the plasma based ion implantation system comprising a vacuum chamber, in which the workpiece is disposed, having a reactive space for generating plasma; a first gas supply unit for supplying reactive gas into the vacuum chamber; a second gas supply unit for supplying cleaning gas into the vacuum chamber; an upper electrode and a lower electrode that are disposed in the vacuum chamber while facing each other; a radio frequency supply unit that supplies the upper electrode with radio frequency power to generate plasma; and a high voltage supply unit that supplies the workpiece and the lower electrode with a high voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0015]      FIG. 1A  is a schematic view representing an plasma based ion implantation system according to a first embodiment of the present invention; 
           [0016]      FIG. 1B  is a schematic view representing an plasma based ion implantation system according to a second embodiment of the present invention; 
           [0017]      FIG. 1C  is an enlarged view representing a structure of an upper electrode shown in  FIG. 1A ; 
           [0018]      FIG. 2  is a schematic view representing a plasma based ion implantation system according to a third embodiment of the present invention; 
           [0019]      FIG. 3  is a view representing an arrangement of nozzles of a gas supply apparatus installed at both sidewalls of a vacuum chamber shown in  FIG. 1A ; 
           [0020]      FIG. 4  is a schematic view representing a plasma based ion implantation system according to a fourth embodiment of the present invention; 
           [0021]      FIGS. 5A to 5C  are views schematically illustrating a shape of high voltage bias pulse applied to a workpiece; 
           [0022]      FIG. 6  is a view representing a network configuration of the ion implantation system and an external system according to the present invention; 
           [0023]      FIG. 7A  is an enlarged view representing a voltage interconnection between the workpiece and a high voltage modulator and a voltage interconnection between a lower electrode and a DC power supply; 
           [0024]      FIG. 7B  is a view representing various geometric arrangements of multiple contact points between the workpiece and the high voltage modulator shown in  FIG. 7A , in which the multiple contact points form a symmetrical configuration in axial and azimuth directions; and 
           [0025]      FIG. 7C  is a view representing an application of a negative constant voltage to the lower electrode by the DC power supply shown in  FIG. 7A . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0027]    Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
         [0028]    A plasma based ion implantation system according to an embodiment of the present invention is illustrated in  FIGS. 1A to 4 . As shown in  FIG. 1A , a workpiece  501  is positioned on a lower electrode  553  in a vacuum chamber  500 . The vacuum chamber  500  includes a sidewall  504  and a ceiling  503  having an RF capacitively coupled upper electrode  502 . The sidewall  504  of the vacuum chamber  500  has an area larger than that of workpiece  501 . The upper electrode  502  is disposed at a front portion of the workpiece  501  while being spaced apart from the workpiece  501  by a predetermined distance. Radio frequency supply units  508  and  509  are electrically connected to the upper electrode  502 . The radio frequency supply units  508  and  509  include an RF generator  508  and a RF matcher  509 . Reactive gas is transferred to a process zone through gas supply units  534 ,  535  and  538 . As an example of the present invention, BF 3  and O 2  are transferred from an upper gas supply unit  534  through a plurality of shower head type gas injection ports  502 - 1  which are formed on the upper electrode  502 . Such a gas is transferred to a side of the vacuum chamber  500  through a specific duct  511  formed in the middle of the upper electrode  502  and is distributed by the gas injection port  502 - 1 . Other gases required for a process, chamber cleaning and phase control are transferred through a nozzle formed on the sidewall  504 . The gas supply unit  535  provided at the sidewall  504  is used for transferring cleaning gases such as NF 3  and Ar and includes a gas distributing ring  536  and a gas nozzle  537 . Other gas supply unit  538  includes a gas distribution ring  539  and a gas nozzle  537 - 1 . The vacuum chamber  500  is maintained in an optimum pressure suitable for a discharge operation by means of a vacuum unit including a vacuum pump  513  and a vacuum valve  514 . 
         [0029]    Another example of the present invention is illustrated in  FIG. 1B . As shown in  FIG. 1B , a remote cleaning plasma generator  507  is used in order to clean the vacuum chamber  500 . The remote cleaning plasma generator  507  is spaced apart from the vacuum chamber  500  and is connected to the inside of the vacuum chamber  500  through a specific duct  511 . An insulator  510  is provided to prevent RF power from incoming into the remote cleaning plasma generator  507 , Similarly to  FIG. 1A , the cleaning gas such as NF 3  is transferred from an upper gas supply unit  507 - 1  and the reactive gas such as BF 3  is transferred from a gas supply unit  530  formed on the sidewall  504  and provided with a gas distribution ring  531  having an annular shape and a gas nozzle  532 . 
         [0030]    A workpiece  501  is electrically connected to high voltage supply units  505  and  506 . The high voltage supply units  505  and  506  include a high voltage modulator  505 , which applies a specific square high voltage to the workpiece  501 , and a DC power supply  506 , which applies a constant voltage to a lower electrode  553 . The high voltage modulator  505  and the workpiece  501  are electrically connected with each other through a specific interconnection and a transferring member which are represented as reference numerals of  501 - 01  and  551 - 1 , respectively. The workpiece  501  is attached to a support  550  by a static electricity formed between the workpiece  501  and the lower electrode  553  by means of an insulator layer  552 . The DC power supply  506  is connected to the lower electrode  553 . 
         [0031]      FIG. 1C  is a detailed view representing the upper electrode  502  which has a surface including Al and is covered with a specific material exerting an influence on a implantation characteristic of ions. According to an embodiment of the present invention, the upper electrode  502  is covered with Si  502 - 3  and includes the gas injection port  502 - 1  disposed at a position corresponding to the upper electrode  502 . Alternately, an Al 2 O 3  oxide coating layer having a thickness of 10 μm to 50 μm is used in order to prevent the workpiece  501  from being contaminated by Al. 
         [0032]    Referring to  FIG. 2 , an upper electrode  502 - 10  does not have a shower head shape and the reactive gas such as BF 3 , O 2  and Ar are transferred from the gas supply unit  530  of a first sidewall to the vacuum chamber  500  through a gas nozzle  532 . The cleaning gas such as NF 3  and Ar is transferred from the gas supply unit  535  of a second sidewall to the vacuum chamber  500 . 
         [0033]    The plasma is formed in the vacuum chamber  500  by the upper electrode  502 - 10  which is connected to the RF generator  508  through the proper RF matcher  509 . 
         [0034]    Meanwhile, in  FIGS. 1A to 2 , a distance between the upper electrode and the lower electrode is set to a predetermined value limited by the lower electrode and is determined by electrical parameters of an electric pulse. 
         [0035]      FIG. 3  represents an example of the gas nozzle formed at the sidewall of the vacuum chamber  500 . As shown in  FIG. 3 , openings of the nozzle are uniformly disposed along the sidewall  504  of the vacuum chamber  500  in such a way that the gas nozzles  537  for the reactive gas including SiH 4 , He, H 2  and Ar are disposed on a first plane, and the gas nozzles  537 - 1  for the cleaning gas including NH 3  and Ar are disposed on a second plane different from the first plane. In order to minimize a shading region in which the cleaning gas is not transferred, each gas nozzle  537 - 1  for the cleaning gas is disposed corresponding to each gas nozzle  537  for the reactive gas. A length of the nozzle is optimized according to the condition of the vacuum chamber  500 . For example, the nozzle has a length of 10 to 80 mm. 
         [0036]      FIG. 4  represents a distance  520  between the upper electrode and the lower electrode serving as important elements when designing the vacuum chamber  500 . The distance is determined such that the distance exceeds plasma sheath thickness during the application of the high voltage pulse. The plasma sheath thickness is determined according to the child-langumuir law such as a following equation 1 or 2. 
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         [0037]    Here, j is a current density, e is an electric charge of an electron, M is a mass of an electron, V 0  is potential difference between the electrodes, and s is a distance between the electrodes. 
         [0038]    A maximum moving distance of ions from a boundary of the plasma can be obtained. An ion current of the parameters for the ion implantation is in a range of 1 to a few A (ampere). 
         [0039]    A gap between the plasma and the electrode is determined as 20 to 30 mm based on the parameters. In detail, the measurement represents that the plasma may move from the electrode by 24 mm in the case of B and move by 17 mm in the case of BF 2  when −5000V of voltage is applied to the electrode and the current density is 1 mA/cm 2 . 
         [0040]    When the voltage of −10000V is applied, the gap size may increase up to 68 mm and 48 mm, respectively, in a state in which the current density remains at the same level. Considering that the general capacitively coupled plasma reaction apparatus has a gap of 0 to 30 mm, when the gap is large in the plasma based ion implantation system, the discharge may begins between the upper electrode and the walls, other than between the upper electrode and the lower electrode. 
         [0041]    According to an operational process of the present invention, the reactive gas is injected into the process chamber  500  through a series of the nozzles  532 ,  537 ,  502 - 1  shown in  FIGS. 5A and 5B , and RF power is applied to the upper electrode  502  through the RF matcher  509  corresponding to the RF generator  508 . When the power is applied, an oscillating electromagnetic field is filled in a space of the vacuum chamber  500  to which gas is transferred, and a capacitive coupling operation begins between the upper electrode  502  and the conductive chamber wall  504 , and among the upper electrode  502 , workpiece  501  and other structures (for example, a ring  551  surrounding the workpiece  501 ) into which implanted ions are directed. Accordingly, a capacitive sheath is formed between the gas having an initial zero potential and the upper electrode  502 . RF current passes through the sheath to cause a stochastic collisionless heating, in which electrons do not collide with each other in a random way, and ohmic heating in the bulk gas plasma. 
         [0042]    If the workpiece  501  includes crystalline silicon into which p-type conductive impurities are partially implanted, the gas supply unit  530  or  534  supplies BF 3  including boron as an impurity. In general, dopant containing gas represents a chemical material that includes boron serving as a p-type conductive impurity in silicon and impurities such as a volatile component. In the plasma including fluoride of dopant gas such as BF 3 , various ion components, such as BF2+, BF+, B+, F+ and F−, etc., are distributed. All kinds of components are accelerated by passing through the sheath and implanted into a surface of the workpiece  501 . 
         [0043]    A dopant atom is generally dissociated from the volatile component when colliding with the workpiece  501  at a higher energy. 
         [0044]    A dopant component is formed in the plasma  540  generated in a reaction space in the vacuum chamber  500 . In order to direct the doping component toward the workpiece  501 , a continuous high voltage pulse having a negative property of 1 to 10 kV is applied from the high voltage modulator  505  to the lower electrode  550 , particularly to the workpiece  501  and the conductive ring  551  surrounding the workpiece  551 . The conductive ring  551  allows the electrostatic field to be uniformly formed in a region adjacent to the workpiece  501 . If the electrostatic field is not uniform, the ion component directing toward the workpiece  501  may deviate from the surface of the workpiece  501  or slantingly collides with the surface of the workpiece  551 , thereby lowering the implantation effect on a corner area of the workpiece  501  or lowering the implantation effect. 
         [0045]    As shown in  FIG. 6 , in several cases, the upper electrode  502  is covered with specific layers including different conductive materials. This is for reducing the contaminant on the inner surface of the vacuum chamber  500  or the surface of the workpiece  501 . As an example, a shallow positive dielectric layer  502 - 4  including Al 2 O 3  is used to protect the vacuum chamber  500  from Al particles falling to the workpiece  501 . As a result of biasing on the dielectric layer, the voltage is not high at the front of the plate. Since the plate has a shallow depth of 10 to 50 μm, the plate has high capacitance so that it can be charged within a predetermined time during which high voltage is applied from the high voltage modulator  505  to the plasma. The dielectric layer can be discharged during a pulse-off time. As another example, the Si layer  502 - 3  is used on the Al electrode. The Si is considered as a conductor that has a low bias voltage at a front portion thereof and prevents a sputtering from actively occurring. 
         [0046]    As shown in  FIGS. 1A and 3 , the gas nozzles  537  and  537 - 1  transfer various types of gas into the vacuum chamber  500 . A set of gas nozzles is used to transfer the cleaning gas such as NF 3  for cleaning the apparatus. In this case, the remote cleaning plasma generator  507  is not necessary. In addition, the gas nozzle  537 - 1  is used for purge gas (Ar) of the vacuum chamber  500  and a gas line, and dilute gas (He) for transferring SiH 4 . In addition, the gas nozzle  537 - 1  is used for cleaning and controlling the chamber  500  by use of H 2 . The H 2  removes F through a reaction of H 2 +F→HF+H. Further, the SiH 4  is transferred into the vacuum chamber  500  without being discharged in order to remove the excessive F from the walls of the chamber  500 . In several cases, the reactive gas is transferred from the sidewall to clean the chamber  500  through the shower head. 
         [0047]    As shown in  FIG. 4 , when the high voltage pulse is applied, the sheath  560 - 01 , in which the ion components are accelerated, is formed between the workpiece  501  and the bulk plasma  540 . When 10 kV of voltage is applied according to a specific technology condition, the sheath  560 - 1  has a width of 20 to 70 mm. 
         [0048]      FIGS. 5A to 5C  schematically represent the shapes of high voltage bias pulse applied to the workpiece  501 . The pulse has a negative polarity. A U-pulse  571  has a magnitude of 1 to 10 kV, and a T-pulse  572  has a duration time of 1 to 10 μs. A T-offset  573  has a pulse interval of 10 to 100 μs. A rising time and a falling time of the applied pulse are about 50 to 100 ns. 
         [0049]    During a cycle of the T-offset  573 , the voltage is applied to the workpiece  501 . At the same time, a non-zero offset voltage is applied as shown in  FIGS. 5B and 5C . As shown in  FIG. 5B , a U-offset non-zero positive voltage  574  is applied, and as shown in  FIG. 5C , a U-offset non-zero negative voltage  575  is applied. The application of offset voltage solves the problem related to deposition of a polymer layer. One of advantages in the implantation system using the pulse is that the polymer layer is deposited during a temporary stop time between the pulses. Accordingly, an etching can be properly performed on the surface of the substrate while preventing the surface from being contaminated by applying a negative bias of 0 to 200V. 
         [0050]    Since energy of the accelerated doping ions is reduced while passing through the sheath area due to a collision, the energy does not correspond to the voltage applied to the workpiece  501 . In a pressure condition of 20 mTorr, even if the voltage applied to the workpiece  501  is 5 to 7 kV, the effective energy of the ion components colliding with the workpiece  501  is 1 to 2 kV. Accordingly, an independent system may be required for monitoring the ion energy. Since the total implantation effect is determined depending on the amount of ions deposited on the surface of the workpiece  501 , the measurement of the ion current is important. As shown in  FIG. 4 , the measurement of the ion energy and the ion current are accomplished by a specific technology such as a diagnostic system  560  and  570  including a faraday cup  560  and an ion energy analyzer  570 . The diagnostic systems  560  and  570  are connected with a data acquisition system  580  that traces and monitors a relevant data in real time. 
         [0051]    A conductivity of the implantation area of the semiconductor is determined according to a junction depth, and a volume concentration of the implanted dopant components which is activated after a sequential annealing process. The junction depth is determined by the bias voltage, which is applied to the workpiece  501  and controlled by the voltage level of the high voltage modulator  505 . The dopant concentration of the implantation area is determined by an implantation moment of dopants and a dopant ion flux on the surface of the workpiece  501  during the duration time of ion flux. The total ion flux is called an ion dose. The dopant ion flux is determined by a magnitude of the RF power emitted from the RF generator  508 . Such an arrangement allows the conductivity of the implantation area and the junction depth to be independently controlled. In general, the control parameter such as a power output level of the high pressure modulator  505  and the RF generator  508  is selected to satisfy a target value of the conductivity and the junction depth and to reduce the implantation time. In order to directly control the ion energy and the dose, the bias electrode has the specific diagnostic system such as the faraday cup  560  for measuring the ion dose and the ion energy analyzer  570  for measuring the ion energy. 
         [0052]    The present invention provides a method capable of preventing a contamination of the chamber  500  by periodically cleaning the inner surface of the vacuum chamber  500 . In the process cycle, etching components are dissociated by the remote cleaning plasma generator  507  based on the discharge of etching gas such as NF 3 . In addition, the activating fluoride is reacted with a contaminated portion of the walls  504  of the vacuum chamber  500  or the lower electrode  553  to remove a polymer film contaminant and is pumped out through the pumping apparatuses  513  and  514 . In this case, the inner surface of the vacuum chamber  500  maintains a constant conductivity, so that a self biasing is prevented from occurring on the dielectric film formed on the walls  504  of the vacuum chamber  500 , thereby reducing the risk of losing power and/or the occurrence of the arc. 
         [0053]    In addition, as shown in  FIG. 6 , the present invention includes the data acquisition system  580 , which receives data from the diagnostic systems  560  and  570 , and is connected to a cluster tool controller  600  which controls and monitors the parameter of the process chamber through a computer network. The reference numerals  601  to  603  represent the data lines. 
         [0054]    As shown in  FIG. 7A , the high voltage modulator  505  is connected to the workpiece  501  at multiple contact points  555 - 1 ,  555 - 2  and  555 - 3 , and. as shown in  FIG. 7B , the multiple contact points form a symmetrical configuration when making contact with the workpiece  501 . 
         [0055]    As shown in  FIG. 7A , the voltage applied to the lower electrode  553  from the DC power supply  506  through the interconnection  553 - 1  has a positive polarity that reduces the voltage applied to a ground unit of the system from the dielectric layer  552 . Meanwhile, in the case of  FIG. 7C , the voltage generated from a DC power supply  506 - 1  has a negative polarity relative to a ground potential such that the entire voltage applied to the workpiece  501 , the dielectric layer  552 , and the lower electrode  553  can be reduced. For example, if the voltage pulse from the high voltage modulator  505  has a magnitude of −10 kV and the voltage from the DC power supply  506  has a magnitude of −1 kV, the total voltage difference is just 9 kV. The voltage difference between the two electrodes is high enough to provide a force for an electrostatic clamping. Between the high voltage pulses, the workpiece  501  has a potential of zero and the lower electrode  553  has a potential of −1 kV, so that the electrostatic system passing through the dielectric layer  552  aligned in opposition to the workpiece  501  still exists such that the workpiece  501  can be clamped at its original position. 
         [0056]    According to the present invention, the capacitively coupled plasma has advantageous characteristics for an ion implantation process as compared with inductively coupled plasma which excessively generates unnecessary ions and causes dissociation of radicals due to the high electron temperature. The capactively coupled plasma generates the ions and radicals required only for the ion implantation process and easily controls the implanted ions in plasma, and reduces the deposition of polymer layer on a surface of the workpiece, thereby reducing the problem derived from unnecessary deposition and contaminants. In addition, the capacitively coupled plasma increases the density of components which are used for the plasma based ion implantation and ensures uniformity of the plasma ions implanted into the workpiece by easily controlling uniformity of plasma through a flat type electrode. 
         [0057]    In addition, according to the present invention, parameters of plasma and ion energy are independently controlled. The plasma is ignited by capacitively coupled plasma generator and is stably maintained. 
         [0058]    In addition, the cleaning process for the vacuum chamber is essentially necessary regardless of the types of the plasma generators, and low energy polymer components always exist. Accordingly, a method for maintaining electrical characteristics of the vacuum chamber must be considered when designing the chamber. According to the present invention, in order to efficiently clean the chamber, a remote cleaning plasma generator and other relevant system are suggested. For the cleaning process and the balance of power distribution, a duct of the remote cleaning plasma generator is integrally formed with an RF transporting structure for the capacitively coupled plasma, so that the cleaning process and the power distribution from the RF generator can be preferably achieved. 
         [0059]    In addition, according to the present invention, a specific voltage pulse is provided to control a state of the surface of the workpiece. A square high voltage pulse is applied to precisely distribute ion energy. Simultaneously, a positive voltage offset or a negative voltage offset is applied between main pulses to control the deposition of ions and radicals on the workpiece, thereby preventing a polymer layer from being deposited on the workpiece and preventing accelerated ions from exerting a bad effect on the subsequent ion implantation. 
         [0060]    In addition, according to the present invention, the higher frequency input from the RF generator controls a plasma concentration and an ion flux on the surface of the workpiece without exerting a bad influence on a sheath voltage or the ion energy. The higher frequency of 30 MHz or 50 Hz or above can lead to a better result and significantly widen the coverage of use in several cases having a source power frequency of 160 MHz or 200 MHz. 
         [0061]    In addition, according to the present invention, an area of a dielectric ceiling is reduced as compared with a dielectric dome of the inductively coupled plasma (ICP) discharge. In the case of the inductively coupled plasma, a surface of the dome is easily sputtered by a high energy ion which applies an impact to the surface of the dome. 
         [0062]    Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.