JP2960940B2 - Scanning controller for ion beam in ion implanter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ion beam scanning control device in an ion implantation apparatus.

[Prior Art] As shown in FIG. 7 of the accompanying drawings, a conventional ion implantation apparatus is an ion source A, a mass separator B, an accelerating tube C, a focusing lens D, and a dipole static electrode forming a Y scan plate. Electrodeflector E
And a bipolar electrostatic deflector F forming an X scan plate. The ion beam generated from the ion source A is converted into a single atom or molecular ion of the same charge by the mass separator B, After being accelerated by C, the light is focused by a focusing lens D, and scanned by a Y scan plate E and an X scan plate F to irradiate a target G.

The X scan plate F performs scanning by applying a triangular wave voltage of, for example, 833 Hz while adding an offset for shifting the deflection direction by about 7 °. In the Y scan plate E, for example, a 167 Hz triangular wave voltage is applied, and scanning is performed so that the Lissajous figure scans the target uniformly by XY scanning. The scanning pattern is schematically shown in FIG.

[Problems to be Solved by the Invention] By the way, in the ion implantation technique, the diameter of the target is increased from 6 inches to 8 inches, and 4M bits, 16M
As the integration of bits and DRAMs has increased, trench structures have become essential.

However, in the conventional ion implantation apparatus, even if the distance between the deflector and the target is set to 160 cm, the incident direction differs depending on the place where the ion beam is incident on the target.
In the case of an inch target, the incident direction of the ion beam incident on the edge is 2.7 ° different from that of the ion beam incident on the center, and for an 8 inch target, it is 3.6 °.
The ends of the target will differ by up to 5.4 ° for a 6 inch target and 7.2 ° for an 8 inch target. Due to different angles of incidence of the ion beam on the target, the area where the target cuts the beam ret of the same solid angle will vary depending on the location of the target,
As a result, the distribution of the ion implantation amount becomes non-uniform. This has a remarkable effect particularly when attempting to implant ions into the side walls of trenches of a 4 Mbit or more CMOS-DRAM. In the case where ions are implanted into the bottom of the trench, shadowing occurs because the angle of incidence of the ion beam varies depending on the location.

In order to solve such a problem, an ion implantation apparatus capable of scanning with a parallel scan beam which is incident on the entire area of the target at the same incident angle is proposed. A first multiplex that is disposed on the same optical axis behind the multipole electrostatic deflector and the first multipole electrostatic deflector, and makes the direction of the ion beam deflected by the first multipole electrostatic deflector constant; A second multipole electrostatic deflector having the same number of poles as the polar electrostatic deflector is provided, and each electrode of the second multipole electrostatic deflector is illuminated with respect to each corresponding electrode of the first multipole electrostatic deflector. There is a deflection system arranged in the same plane including the axis and arranged on the opposite sides with respect to the optical axis. FIG. 1 of the accompanying drawings illustrates a case where each multipole electrostatic deflector consists of an octopole, and each electrode in the first octopole electrostatic deflector H has a second symmetrical position with respect to the central axis. It was proposed that a voltage as shown be applied to each electrode of each deflector in order to be connected to the electrodes of the octopole electrostatic deflector I and satisfy the conditions of parallel scanning.

Therefore, an object of the present invention is to provide an ion beam scanning control device capable of generating a voltage to be applied to each electrode so as to satisfy a condition of parallel scanning in such an ion implantation device proposed above.

Means for Solving the Problems In order to achieve the above object, an ion beam scanning control apparatus according to the present invention in an ion implantation apparatus provided with two multipole electrostatic deflectors in an ion beam deflection system includes: A first storage device for recording information related to the first reference voltage U; a first storage device connected to the first storage device for generating a reference clock pulse in accordance with an operation control signal preset in the first storage device. An up / down counter that counts to a predetermined number and outputs a predetermined digital value; and a first output from the digital output of the up / down counter.
A first D / A converter for generating a reference voltage U, and outputting another predetermined digital value in synchronization with another reference clock signal when the count value of the up / down counter reaches a predetermined value. A second storage device for recording information related to the second reference voltage V, a second D / A converter for generating a second reference voltage V from a digital output from the second storage device, The first and second D / A converters respectively generated by the first and second D / A converters;
And an arithmetic circuit for arithmetically processing the second reference voltages U and V to form voltages to be applied to the respective electrodes of the two multipole electrostatic deflectors.

In a preferred embodiment of the present invention, each of the first and second D / A converters can be provided with a potentiometer for adjusting the absolute value of each reference voltage.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 6 of the accompanying drawings.

FIG. 2 is a block diagram showing one embodiment of an ion beam scanning control apparatus according to the present invention applied to an ion implantation apparatus having two octopole electrostatic deflectors in an ion beam deflection system. In the first storage device, the first storage device 1
Information on the reference voltage U and a preset operation control signal, that is, when the up / down counter 2 connected to the first storage device 1 is stopped and the up / down operation is switched between the up / down operation. Is stored. An up / down counter 2 that performs an up-count operation or a down-count operation in response to an operation control signal from the first storage device 1
The first clock pulse signal generator 3 supplies a fast clock pulse signal for increasing and decreasing the voltage U to the up / down counter 2. The fast clock pulse signal from the clock pulse signal generator 3 is counted up or down according to the operation control signal from the first storage device 1. The output of the up / down counter 2 is the first
And to the other input of the comparison circuit 5. The other input of the comparison circuit 5 is connected to the first storage device 1, so that the comparison circuit 5 stores the fast clock pulse signal counted by the up / down counter 2 at an address of the first storage device 1. Is compared with the set value. The output of the comparison circuit 5 is connected to one input of a shift register 6, and the other input of the shift register 6 has a second clock pulse signal generator 7
Is connected. The second clock pulse signal generator 7 generates a slow clock pulse signal for setting the time for turning back the scan of the voltage U. Shift register 6
Is connected to the up / down counter 2 on the one hand and to the counter 8 on the other hand. When the count value from the up / down counter 2 in the comparison circuit 5 reaches a value preset in the first storage device 1, the shift register 6 outputs an output signal from the comparison circuit 5 to a second clock. The signal is passed to the counter 8 in synchronization with the clock pulse signal from the pulse signal generator 7, thereby acting to increase the count value of the counter 8 by one. The output of the counter 8 is connected to a second storage device 9 and a first storage device 1 for storing information related to another reference voltage V, and the second storage device 9 responds to the count value from the counter 8. And outputs a V output numerical value corresponding to the value. The first storage device 1 changes the operation control signal at its output according to the count value from the counter 8.

The output of the second storage device 9 is connected to a second D / A converter 10 having substantially the same configuration as that of the first D / A converter 4, and the output of the second D / A converter 10 Is connected to the analog operation circuit 11 together with the output of the first D / A converter 4.

FIG. 3 shows an example of the circuit configuration of the analog arithmetic circuit 11, in which two inverting circuits 12, 13 connected to the outputs of the first D / A converter 4 and the second D / A converter 10, respectively. And each inverted,
It has four summing circuits 14 to 17 each composed of an operational amplifier having a function of adding and varying a gain, these circuits are connected as shown, and two octuple electrostatic deflections (not shown) are provided at eight outputs. It is configured to generate a different voltage to be applied to each electrode of the vessel.

The operation of the illustrated apparatus configured as described above will be described below.

The up / down counter 2 counts a fast clock pulse signal from the first clock pulse signal generator 3 according to a preset operation control signal from the first storage device 1, and the counted value is It is converted to an analog voltage + U by one D / A converter 4. Further, the output count value of the up / down counter 2 is compared with a preset value in the first storage device 1 by the comparison circuit 5, and when the output count value coincides with the preset value, the comparison circuit 5 shifts the output signal. Supply to register 6. The shift register 6 is shifted by several periods of the period of the slow clock pulse signal from the second clock pulse signal generator 7, during which the up / down counter 2 stops counting. On the other hand, the shift register 6 increases the count value of the counter 8 by one in synchronization with the slow clock pulse signal from the second clock pulse signal generator 7, and in accordance with the increase of the output count value of the counter 8, The V output numerical value stored at a predetermined address of the storage device 9 is sent to the second D / A converter 10 and converted into an analog voltage + V. The output count value of the counter 8 is supplied to the first storage device 1, and the value output from the first storage device 1 is updated to another value stored at another address.

After the operation stop set time by the shift register 6, the up / down counter 2 restarts the counting operation and continues counting until it becomes equal to the newly set (updated) output value from the first storage device 1, and The operation of is repeated.

The analog voltages + V, + U thus generated have waveforms as shown in FIGS. 4 and 5, and
The signals + U and + V are output as they are in the analog arithmetic circuit 11 shown in the figure, and −U and −V are obtained by inverting them by the inverting circuits 12 and 13, respectively. The four output voltages are subjected to arithmetic processing by the adders 14 to 17, respectively, to obtain the remaining four output voltages as shown.

In this case, by incorporating a potentiometer in each D / A converter, the absolute values of the voltages U and V can be changed, thereby changing the original values of the analog voltages + U and + V, thereby octopole electrostatic deflection. The voltage to be applied to each electrode of the vessel can be changed simultaneously. This is very advantageous from the viewpoint of the actual voltage adjustment operation because it is necessary to adjust the voltage to be applied to each electrode of the octupole electrostatic deflector when changing the ion acceleration voltage.

FIG. 6 shows a beam scanned on a target (not shown) as a result of scanning each electrode of the octopole electrostatic deflector by these voltages.

The clock pulse signal from the first clock pulse signal generator 3 is scanned in the lateral direction of the target by the voltage U proportional to the value counted by the up / down counter 2, and the ion beam is scanned to the end of the target. At this point, the output value of the up / down counter 2 matches the value set in the first storage device 1, and when the comparator 5 outputs a match signal, the second clock pulse signal generator After a certain repetition time set by the clock pulse signal from 7, the ion beam is scanned in the opposite direction. The next horizontal scan is commanded by the data in the first storage device 1 addressed by the output from the counter 8, thus repeating the scan sequentially as shown, and the entire target area without overscanning of the ion beam. Can be scanned in parallel.

By the way, as a method of filling the beam on the target surface in the vertical scanning, a vertical interval of one scanning is set to δ in each of the storage devices 1 and 9, and 1 / each time one scanning is completed. A method of storing all these points in the vertical direction by 2 δ and 1/4 δ, and storing data from one scan to several scans from top to bottom or from bottom to top in each of the storage devices 1 and 9. It is conceivable that a method of inputting and inputting a gap is input as an offset voltage, and the latter method requires a circuit for the offset voltage, but a finer filling is possible as compared with the former method. .

In the above embodiment, the case where the present invention is applied to the octupole electrostatic deflector has been described. The same can be applied by redesigning the circuit.

Further, as a method of painting the beam on the target (wafer) surface, the number of divisions of δ may be determined by a method of determining an offset voltage instead of the above two methods.

Further, changing the data in the first storage device to change the scanning density in the vertical direction, and adjusting the first clock pulse signal generator to change the speed in the horizontal direction to drive the beam into the target; The positional dose amount can be corrected using the sheet resistance measurement map.

[Effects of the Invention] As described above, according to the present invention, two reference voltages U and V are generated and applied to each electrode of the multipole electrostatic deflector based on a function of these voltages. Since the configuration is such that the voltage can be controlled, it is possible to scan a beam with a parallel beam incident angle on a target in an ion implanter using a parallel ion beam. Can be adjusted at a fixed ratio.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an electrical connection relationship between deflection electrodes and a voltage applied to each electrode in an ion implantation apparatus having two octupole electrostatic deflectors to which the present invention is applied, and FIG. FIG. 3 is a schematic block diagram showing an embodiment of the present invention, FIG. 3 is a block diagram showing an example of an analog arithmetic circuit in FIG. 2, and FIGS. 4 and 5 are voltages U and V, respectively.
FIG. 6 is a schematic diagram showing a manner of scanning on a target surface, FIG. 7 is a schematic diagram showing an example of a conventional ion implantation apparatus, and FIG. FIG. 4 is a schematic diagram showing a scanning form by the conventional ion implantation apparatus shown in FIG. In the figure, 1: first storage device 2: up / down counter 3: first clock pulse signal generator 4: first D / A converter 5: comparator 6: shift register 7: second clock pulse Signal generator 8: Counter 9: Second storage device 10: Second D / A converter 11: Analog operation circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 1-157047 (JP, A) JP-A 62-287557 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 37/317 H01J 37/147 H01L 21/265

Claims (2)

(57) [Claims] 1. An ion beam scanning control apparatus in an ion implantation apparatus having two multipole electrostatic deflectors in an ion beam deflection system, wherein a first information for recording information related to a first reference voltage U is recorded. A storage device, connected to the first storage device, for counting reference clock pulses to a predetermined number in accordance with an operation control signal preset in the first storage device and outputting a predetermined digital value; A down counter and a first output from the digital output of the up / down counter
A first D / A converter for generating a reference voltage U, and outputting another predetermined digital value in synchronization with another reference clock signal when the count value of the up / down counter reaches a predetermined value. A second storage device for recording information related to the second reference voltage V, a second D / A converter for generating a second reference voltage V from a digital output from the second storage device, The first and second D / A converters respectively generated by the first and second D / A converters;
And an arithmetic circuit for calculating the second reference voltages U and V to form voltages to be applied to the respective electrodes of the two multipole electrostatic deflectors. Scan control device. 2. The ion according to claim 1, wherein each of the first and second D / A converters includes a potentiometer for adjusting the absolute value of each of the reference voltages U and V. Beam scanning controller.