Abstract:
An implanter is equipped with an ion beam current detector, a temperature sensor, a temperature controller and a cooling system to increase the ratio of a specific ion cluster in the ion source chamber of the implanter. Therefore, the implanting efficiency for a shallow ion implantation is increased consequently.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a method and device of ion source generation and, in particular, the method and device can enhance the implanting efficiency of a shallow ion implantation. 
     2. Background of the Related Art 
     As shown in  FIG. 1 , an ion implanter uses a filament  100  to ionize the atoms and/or atom clusters to form ions and/or ion clusters in source chamber  200 . An electric field accelerates the ions/ion clusters to form an ion beam  610  and, after passing a mass spectrometer  400 , the ions/ion clusters of the ion beam  610  are filtered to have a specific charge-mass ratio. And, then the ion beam  610  injects into the implantation chamber  500  after passing the channel  300 . 
     A target base  510  and a Faraday cup  600  are configured in the implantation chamber  500 , and a wafer  520  is settled on the target base  510 . The ion beam  610  collides with the wafer  520  with a specific collision depth, which proportionally depends on the kinetic energy of the ions/ion cluster of the ion beam  610 . The implanting efficiency proportionally depends on the current of the ion beam  610 , and an ion beam current detector  700 , which electrically couples with the Faraday cup  600 , can detect the current. The current detector  700  can be implemented by an ampere meter. 
     An ion cluster will distribute averagely the energy to each ion of the ion cluster, so the ion implanting energy should be reduced to be suitable for a shallow ion implantation. 
       FIG. 2  shows the curves of the temperature T and the ion beam current I, which vary with time t, where T is the shell temperature of the source chamber  200  and I is the current of ion beam  610  detected by the ion beam current detector  700 . As shown in  FIG. 2 , from t=0, the time of lighting up the filament  100 , to t=t 1 , ion beam current I increases and approaches to the maximum. In the meanwhile, temperature T increases and approaches a minimum threshold temperature T m . T increases continuously with time, till time t=t 2 , and the ion beam current I surpasses the maximum ion beam current value and begins to decrease to a minimum threshold ion beam current I m  and keep decreasing to be less than I m . 
     It is very important to keep a high ratio ion cluster for obtaining a high ion beam current, and a skill is proposed in this invention. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a method and a device of ion source generation. The method uses a temperature controller to read an ion beam current detected by an ion beam current detector and a temperature of the source chamber sensed by a thermometer to adjust a cooling system for controlling the source chamber temperature, so a specific ratio of ion cluster in the source chamber can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an ion implanter according to a prior art. 
         FIG. 2  shows the relationship of the ion beam current and the temperature with time according to a prior art. 
         FIG. 3  shows an ion implanter according to an embodiment of this invention. 
         FIG. 4  show the flow chart of controlling ion beam current according to an embodiment of this invention. 
         FIG. 5  shows the relationship of the ion beam current and the temperature with time according to an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows an ion implanter, which is the combination of an ion implanter shown in  FIG. 1  and an ion source generation device, according to an embodiment of this invention. The device of an ion source generation further includes a cooling system  800 , a temperature sensor  810  and a temperature controller  900 , where the cooling system  800  may operate on circulating coolant fluid or water. 
     The cooling system  800  and the temperature sensor  810  are disposed on the shell of the source chamber  200  to sense the temperature of the source chamber  200 , and to control the temperature of the source chamber  200  efficiently, respectively. 
     The temperature controller  900  electrically connects to the temperature sensor  810  and an ion beam current detector  700 , such as an ampere meter, to obtain the temperature of the source chamber  200  and the current of the ion beam  610 . According to the relationship of the temperature and the ion beam current, the temperature controller  900  adjusts the fluid flow rate of the cooling system  800  to control the temperature of the source chamber  200  to be within a range. Therefore the ion beam current I can be controlled to stay above a minimum threshold ion beam current I m , where the minimum threshold ion beam current I m  may be predetermined or a current value within a range from 90% to 95% of the maximum ion beam current. 
     According to an embodiment of this invention, a method of controlling the ion source generation is illustrated and the flow chart is shown in  FIG. 4 . Accompanying  FIG. 5 , which shows the relationship of the temperature T of the source chamber  200  and current I of the Faraday cup with time t. The method is illustrated as follows. 
     During the period of heating the source chamber  200  (increasing the temperature T), the ion beam current detector  700  detects the current of the Faraday cup and the temperature controller  900  reads the detected ion beam current and compares it with the minimum threshold ion beam current I m (step S 10 ). According to the comparison results, when the temperature controller  900  determines that the current I has come to or fallen below I m  and, in the meanwhile, the temperature T has gone to or risen up above a maximum threshold temperature T M  (as shown in  FIG. 5 ), the temperature controller  900  starts up the cooling system  800  or increases the fluid flow rate of the cooling system  800  to reduce the temperature T (step S 20 ). The step S 20  can avoid break of the ion cluster caused by the increasing temperature. The minimum threshold ion beam current I m  can be predetermined or set to a current value within 90% to 95% of the maximum ion beam current. 
     During the period of cooling the source chamber  200  (reducing the temperature T), the temperature controller  900  continuously reads temperature T sensed by the temperature sensor  810 , denoted as step S 30 , and compares the temperature T with a minimum threshold temperature T m  (as shown in  FIG. 5 ). According to the comparison results, when the temperature controller  900  determines that the temperature T has come to or fallen below the minimum threshold temperature T m , the temperature controller  900  shuts down the cooling system  800  or reduces the fluid flow rate of the cooling system  800  to ensure the formation of the specific ion cluster (step S 40 ). The minimum threshold temperature T m  may be predetermined or set to a temperature value, which holds the ion beam current between 90% to 95% of the maximum ion beam current. 
     According to the above, the temperature T of the source chamber  200  can be controlled in a range from the minimum threshold temperature T m  to the maximum threshold temperature T M , denoted T m ≦T≦T M . Within this temperature range, the current can be hold above the minimum threshold ion beam current I m  and approaches the maximum, so the method can improve the ion implanting efficiency of a shallow ion implantation. 
     Although this invention has been explained in relation to its preferred embodiment, it is to be understood that modifications and variation can be made without departing the spirit and scope of the invention as claimed.