Abstract:
The nominal position value for the impact point of an electron beam on a medium located in a crucible is input to a device having a screen on which the contours of the crucible are represented. Light pen means establish a plurality of nominal positions of impact of the electron beam within the represented contours of the crucible.

Description:
BACKGROUND 
     The invention concerns a device to initial aim or direct an electron beam in a crucible. During heating, melting or evaporation of metallic or other materials, high energy electron beams are often used, which impact onto the material to be heated, melted, or evaporated. Therefore, it is usually required that the electron beam be brought into predetermined positions in order that the attempted purpose be fulfilled. 
     The effect of electrical or magnetic fields, the change of which causes a change of the position of the electron beam, is utilized for the positioning of a electron beam. It is common to position the beam by means of adjustable currents which in turn build up a deflecting magnetic field. This technique is particularly advantageous. The adjustment is usually manually performed, hereby an operator observes the electron beam through a window and adjusts the currents required for the x position and the y position of the beams by adjusting two potentiometers. 
     If, within a crucible, several points of the medium are to be sequentially impacted by the electron beam, this type of manual adjustment is very time consuming. This is particularly true if the electron beam is to have different tarrying times at the various positions. 
     Such different tarrying times are required for specific applications, e.g., if several vapor sources are to be formed on the surface of the contents in one single evaporation crucible such that an electron beam is fired onto the surface of the contents of the crucible in specific surface patterns (DE-OS No. 28 12 285). In order to be able to simply preprogram the power input of the electron beam into a device of such nature, it is already known to represent this power input on a screen in the form of a bar diagram (DE-OS No. 33 30 092), whereby the bars in the bar diagram may be changed by means of a light stylus. However, in this case, the screen is not used for representation of specific coordinates in the plane or in the space. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Consequently, the purpose of the invention is to predetermine, in a simple manner, various nominal positions of an electron beam on the surface of a medium and to approach this nominal position with the electron beam automatically and sequentially. 
     The invention concerns a device for inputting a nominal position value for the impact point of an electron beam onto a medium which is located in a crucible. This device has a screen on which the contours of the crucible are represented. By means of a light stylus, various nominal positions can be established for the electron beam within the represented contours of the crucible. 
     With the present invention, various points on the surface of a material in a crucible can be automatically and precisely approached with only one electron beam including consideration of different tarrying times of the beam at the individual points. Hereby, the circulation time of the electron beam, i.e., the time required for it to return to the starting point, is extremely short. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a crucible with an electron gun arranged above the crucible; 
     FIG. 2 is an enlarged top view of the crucible; 
     FIG. 3 is a representation of the principle of the arrangement according to the invention; and 
     FIG. 4 is a schematic diagram of a control switching arrangement according to the invention, shown for control of the x position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 represents an electron beam gun 1 with a deflector system 2 above a crucible 3. In this crucible 3, there is a medium 4, which is heated by means of a electron beam 5. Thereby, the electron beam 5 is to be sequentially guided to the points P 1  . . . P 8  and repeatedly run through the cycle of P 1 . 
     FIG. 2 again shows the crucible, in a top view, namely on a larger scale. Here, one can again recognize the points P 1  . . . P 8  which are to be sequentially approached by the electron beam. Next to these points, the related x, y coordinates are indicated, e.g., x 1 , y 1 , in order to express that these are approached by means of the x, y deflector system 2. In addition, each one of the points P 1  . . . P 8  displays information on the applicable tarrying time of the electron beam 5. If the electron beam is moved from P 1  to P 2 , it is guided to P 2  only on the basis of a position command x 2 , y 2 , i.e., currents I x , I y  affect the x, y deflector system 2, which leads the electron beam 5 to P 2  at an almost shocking speed; the time t s1 , which the electron beam 5 requires for the distance between P 1  and P 2 , is practically limited by nothing but the inductivity of the deflector system 2. By preprogramming the currents I x , I y , the electron beam is not, however, guided very precisely to point P 2 , but it may arrive at P 2  &#39;. This causes an error ΔS. This error ΔS is equalized by means of a nominal/actual control, i.e., the beam 5 is moved to exactly the point P 2  . 
     Consequently, there is no continuous control of the beam guidance from P 1  to P 2 , but the beam 5 is guided directly to P 2  and corrected for the small deviation ΔS only thereafter. This shortens the correction time. 
     The same procedure is then also repeated when the beam moves from P 2  to P 3 , from P 3  to P 4 , etc. 
     During the first circulation of the electron beam 5 from P 1  to P 8 , the tarrying times at t v  1, t v  2 . . . at P 2 , P 3 , etc. do not yet correspond to the final tarrying times but initial tarrying times amount to e.g., 10,000 times these final times. 
     During the second circulation of the electron beam 5, the tarrying times t v  1, t v  2 . . . t v  8 amount to only 1,000 times the correct nominal value, etc., until finally the nominal position of the electron beam will be the actual tarrying time. 
     Hereby, it is achieved that for each run of the electron beam 5 through the nominal positions P 1 , P 2 , P 3  . . . P 8 , only minor corrections of the related current value are required. 
     FIG. 3 shows a representation of the principle of the invention, in which one again recognizes the electron beam gun with the deflector system 2. The crucible 3 is arranged below the electron beam gun 1, and the contents 4 thereof are impacted by the electron beam 5. Next to the crucible 3 there is a sensor for actual position, or a detector 6, which identifies the impact point of the electron beam. This detector 6 may be an X-ray detector, as described in German Patent Application No. P 34 42 207.7. 
     From this detector 6, a connection leads to a memory 7 and to a microcomputer 8 which, in turn, is connected to a monitor 9 and an x deflection 10, as well as with a y deflection 11. These x/y deflections 10, 11 are connected to the deflection system 2. 
     The monitor 9 has a screen 12 which shows the edge 13 (border, rim or outer ridge) of the crucible as a contour 13&#39;. By means of a light stylus 14, which is powered via the cable 15, it is possible to input nominal beam impact positions within the contour 13&#39;. 
     At its front end, this light stylus has a sensor, by means of which the impact of an electron beam can be picked up by the monitor 9. If the electron beam is brought into a specific nominal position within the edge 13 of the crucible, it is then possible to indicate this nominal position within the representation 13&#39; of the edge of the crucible 13 by means of the tip of the light stylus 14. 
     This tip is placed on the specific nominal position and with short intervals, it receives an impulse through the line by line sensing of the screen 12 by means of an electron beam from the monitor 9. This impulse is transmitted from the light stylus 14 to the microcomputer 8. In the microcomputer, the position of the tip of the light stylus 14 within the edges 13&#39; can be detected with precision. The impulses transmitted from the light stylus 14 define the times at which the electron beam of the monitor 9 impacts on the tip of the light stylus. Since this time information can be utilized in order to scan the conditions of the related line and column deflection of the electron beam of the monitor, it is possible to recognize the x/y coordinates of the electron beam from the monitor. Those x/y coordinates for the contact point of the electron beam from the monitor, which have been detected by the microcomputer and which correspond to the nominal value of the position of the electron beam 5, are automatically stored in the memory 7 or in the microcomputer 8. 
     By means of the light stylus 14, it is possible to sequentially input and store several positions, according to approximately the pattern shown in FIG. 2. In addition to the nominal positions P 1  . . . P 8 , which are indicated to represent far more numerous nominal positions, e.g., 64, it is also possible to input the tarrying times t v  1 . . . t v  8 assigned to the respective nominal positions, namely by means of a device which is not shown in FIG. 3. 
     These tarrying times can be input, e.g., by entering the applicable tarrying time on a keyboard of the microcomputer 8 and then depressing the &#34;Enter&#34; key when the tip of the light stylus 14 touches the screen 12. 
     When the nominal positions P 1  . . . P 8  and the related tarrying times t v  1 . . . t v  8 have been stored, the electron beam 5 can be guided into the predetermined positions via a microcomputer 8, via the x/y deflection 10, 11, and via the deflection system 2. In order to achieve a precise approach to the nominal positions, the actual position of the electron beam 5 is identified by the detector 6 and input into a memory 7 or directly into the microcomputer 8. By means of a control switching, the electron beam is brought from its actual position into the nominal position. Such a control switching is shown in FIG. 4, namely for the control of the x position only. The y position is set in the same manner. The monitor 9 and the memory 7 are not included in FIG. 4 since they are not necessary for the understanding of the control switching. 
     From this representation, one can recognize that the detector 6 feeds the actual position value P act  of the impact point of the electron beam 5 onto the target material 4 to a subtraction point 16, where this actual value P act  is subtracted from the nominal position value P nom , which is input to the subtraction point 16 by the microcomputer 8. The deviation ΔP between actual and nominal position is fed to an adding point 17, the output signal of which arrives to a power regulator 18 (current controller), which in turn influences the x deflection vial a coil 19 and a resistor 20. 
     The actual value I act  of the current flowing through the coil 19 is input to a subtraction point 21, where it is subtracted from the nominal current value I nom  which is provided by the microcomputer 8. The deviation ΔI is then fed into the adding point 17, and the output signal from this adding point is transmitted to the current regulator 18. 
     Thus, the microcomputer 8 stores, e.g., two different types of nominal values: one, a specific number of points as current values, and the other, the same number of points as position values for the x/y coordinates. 
     At first, only the nominal value I nom  is significant for the positioning of the electron beam 5, since actual or nominal values for position do not yet exist. Not until these are given, will Δ I and ΔP be utilized for correction purposes.