JP2537492B2 - Ion implanter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention is an ion implantation apparatus for irradiating a target (hereinafter referred to as “wafer”) with an ion beam to perform ion implantation on the wafer. Regarding

More specifically, the present invention relates to an ion implantation apparatus that scans an ion beam within a contour of a wafer and controls a scanning speed of the ion beam so that a sheet resistance value of the wafer becomes uniform.

(Prior Art) Conventionally, when irradiating an ion beam on a wafer by an ion implantation apparatus, the ion beam is scanned on the wafer at a constant speed.

(Problems to be Solved by the Invention) By the way, in the above-mentioned ion implantation, there is a drawback that the variation of the implantation concentration or the so-called uniformity deteriorates due to the fluctuation of the beam current or the characteristics of the implantation apparatus.

The present invention was created in view of the above circumstances,
It is an object of the present invention to provide an ion implantation device capable of achieving uniform ion implantation concentration.

(Means for Solving the Problem) That is, the ion implantation apparatus of the present invention is a device that scans a target (wafer) 8 with an ion beam and implants ions into the wafer. Storage means 21 for storing digitized correction data (binarized data) for correcting and equalizing the subsequent sheet resistance value for each value obtained by dividing the wafer into a large number in the vertical and horizontal directions, and this storage. The scanning speed of the ion beam at each position of the wafer is determined based on the digitized correction data (binarized data) for correcting the sheet resistance value at each position of the wafer stored in the means. And a scanning control means 10 for controlling the sheet resistance value to be constant.

(Operation) In the ion implantation apparatus of the present invention, the scanning control means 10
However, the sheet resistance value becomes constant at the scanning speed of the ion beam at each position of the wafer based on the binarized data for correcting the sheet resistance value at each value of the wafer stored in the storage means 21. By thus controlling the scanning speed of the ion beam, it is possible to make the ion implantation concentration uniform.

(Example) Hereinafter, the detail of the Example of this invention is described based on drawing.

FIG. 2 is a diagram showing an ion implantation apparatus according to an embodiment of the present invention, in which 2 is an ion source, 3 is an analyzer magnet, 4 is an accelerating tube, 5 is a lens, 6 is a Y scan plate, Reference numeral 7 is an X scan plate, and 8 is a wafer. The ion beam generated from the ion source 2 is converted into a single atom ion beam with uniform electric charge by an analyzer magnet 3, accelerated by an accelerating tube 4, and then converged by a lens 5 by a Y scan plate 6 and an X scan plate 7. The wafer 8 is irradiated while being scanned.

FIG. 1 is a block diagram showing an X-direction scanning control circuit that controls the scanning range and scanning speed by the X scan plate 7 described above.

The X-direction scanning control circuit shown in the figure is mainly composed of a scanning position control circuit 9 and a scanning speed control circuit 10.

The scanning position control circuit 9 has two ROMs 12 for outputting memory contents according to a clock input to the counter 11.
13 are provided. As shown in FIG. 3, these ROMs 12 and 13 have start points Xstr and Xstr of each X coordinate of the contour of the substantially circular wafer 8 placed on an area divided by n × n irradiated with an ion beam. Endpoint Xe
nd data is listed.

The optimum number n for dividing the area is appropriately determined based on the required correction accuracy and processing speed, but may be, for example, 50 × 50 to 1000 × 1000.

More specifically, as shown in FIG.
Data of each X coordinate start point Xstr and end point Xend are alternately stored for each scanning line in the Y direction.

An up / down counter 14 is arranged on the output side of the ROM 12, while a comparator 15 is arranged on the output side of the ROM 13.

The up / down counter 14 includes an 8-bit up / down counter 14a and an m-bit up / down counter 14b (8
+ M = n), and has a resolution of n bits. Further, 1 is output by the output of the flip-flop 16.
The 8-bit up / down counter 14a for each line scan
Further, the m-bit up / down counter 14b is adapted to be switched up or down.

Furthermore, on the output side of the up / down counter 14,
8-bit up / down counter with adder 17
The digital outputs from the 14a and the m-bit up / down counter 14b are added, and the added digital output is input to the X scan plate 7.

The digital output from the m-bit up counter 14b is input to the adder 17 via the selector 18. This selector 18 is not shown
By the control signal from the latch circuit 19 which holds the control signal of the CPU, whether the output from the m-bit up / down counter 14b is input to the adder 17, that is, the resolution is switched. .

The scanning position control circuit 10 includes an X scan plate 7,
The Y scan plate 6, its drive circuit (not shown), and the like constitute a means for scanning the ion beam within the contour position of the wafer.

On the other hand, the scanning speed control circuit 10 is provided with a memory (RAM) 21 for outputting the memory contents according to the address clock input to the counter 20 which is output according to each X-direction scanning position. In this RAM 21, binarized data (digitized correction data for correcting the difference in sheet resistance value after constant-speed ion beam scanning at each value obtained by dividing the beam scannable range up to n × n ) Is stored.

That is, in the memory 21, after scanning the wafer with an ion beam at a constant speed, based on the sheet resistance value data obtained as a result of measuring the sheet resistance value of this wafer, the sheet resistance value becomes equal over the entire surface of the wafer. Thus, data for controlling the scanning speed of the ion beam is stored for each wafer position.

This focuses on the fact that the physical properties of multiple targets (wafers) obtained from one lot are uniform. By acquiring data for one wafer, this data can be used for other wafers. It utilizes the knowledge that it is possible, and the data on the variation in the sheet resistance value obtained as a result of scanning one wafer with an ion beam at a constant speed is also used for other wafers.

The memory (RAM) 21 is addressed by the address clock from the counter 20, and is binarized data (digitized correction data for correcting the difference in sheet resistance value after constant-speed ion beam scanning at each value. ) Is read.

A programmable divider 23 is arranged on the output side of the RAM 21 via a multiplexer 22. The programmable divider 23 uses a basic clock output from a clock generation circuit (not shown) as a maximum value and divides the basic clock based on the binarized data for correcting the difference in the sheet resistance value. Output. The frequency-divided signal is input to the clock input terminal of the up / down counter 14.

The clock signal input side of the RAM 21 is provided with a selector 24 and a latch circuit 25 for holding a control signal from a CPU (not shown). The control signal causes the selector 24 to write a data write signal from the CPU (not shown) or the counter. RAM21 from any of the 20 address clocks
Switch to input to.

In the ion beam scan control circuit according to the present invention, the X-direction scan control circuit is configured as described above. On the other hand, Y
The directional scanning control circuit includes substantially the same part as the scanning position control circuit 9 in the X-direction scanning control circuit, and the data stored in the ROM has the X coordinate start point Xstr and the end point Xend. Since the Y-coordinate start point Ystr and the end point Yend may be used, the description thereof will be omitted, and the operation of this apparatus will be described in detail below.

First, using the ion implantation apparatus according to the present invention, the wafer 8 is scanned with an ion beam at a constant speed to implant ions. Then, the sheet resistance value at each position of this wafer is measured. A correction value of the scanning speed is calculated based on the obtained variation of the sheet resistance value. The correction value obtained by the calculation is stored in the memory 21 corresponding to each position on the wafer.

After this preparation is completed, a wafer having the same characteristics as the reference wafer is prepared as a target and the ion implantation process is executed.

First, in the X-direction scanning control circuit, the data of the address stored in the ROM 12 is input to the up / down counter 14 by the clock from the counter 11. A digital signal based on the data of the address is input to the X scan plate 7 from the up / down counter 14. On the other hand, a similar digital signal is input to the Y scan plate 6 as well. In this case, as shown in FIG. 3 (a), the ion beam is scanned from a position which is substantially on the left side of the wafer 8 based on the address data and the like.

Next, the binarized data of the sheet resistance value corresponding to the data position of the address read from the RAM 21 is input to the multiplexer 22. The multiplexer 22 outputs to the value programmable divider 23 proportional to the binarized data. The programmable divider 23 outputs a divided clock obtained by dividing the basic clock to the up / down counter 14 according to this output value. This up-down counter 14
Is counted up by the frequency division signal, and the counted up digital signal is input to the X scan plate 7. As shown in FIG. 3B, the ion beam is scanned up to a position advanced by 1 / n at a speed according to the frequency division signal.

Hereinafter, the reading of the RAM 21 and the control of the scanning speed based on the read data are performed at the X-axis end point Xend.
(Fig. 3 (c)) When reaching the position where the scanning of the ion beam becomes the outline portion on the right side of the wafer 8 until reaching, the comparator 15 is operated by the data of the address stored in the ROM 13. During this period, the Y scan plate 6 is input with the digital signal which is the initial value.

The output of the comparator 15 is an X-direction scanning end signal as shown in FIG. The X direction scanning end signal is input to the counters 11 and 20 and the mono-multi circuits 24 and 25. The signal input to the counters 11 and 20 is the counter 1
Step 1,20.

The mono-multi circuit 25 outputs the signal shown in FIG. 5 (c) to the mono-multi circuit 26 in response to the X-direction scanning end signal input from the comparator 15, and the mono-multi circuit 26 receiving this signal outputs the signal to the fifth multi-circuit 26. The signal shown in FIG. 3D is output to the load terminal of the up / down counter 14. The 8-bit up / down counter 14a enables the output from the ROM 12 to be read while this signal is present, and the m-bit up / down counter 14b
Is cleared by this signal.

The X-direction scanning end signal input to the mono-multi circuit 24 causes the mono-multi circuit 24 to output the signal shown in FIG. 5 (b) and is input to the RD terminals of the ROMs 12 and 13 for a predetermined time. The scan end point data of the new address corresponding to the second line in the direction is read from the ROM 12 and the scan start point data is read from the ROM 13. Therefore, the scan end data of the address is set in the up / down counter 14a, and the scan start data of the address is input to the B input terminal of the comparator 15.

Then, the counters 11 and 20 cause the data output from the ROMs 12 and 13 to be addresses, and the data output from the RAM 21 to be at a position corresponding to the address, thus completing the scanning of one line.

Next, the address data stored in the ROM 12 is input to the up-down counter 14, and the digital signal based on the address data is input from the up-down counter 14 to the X scan plate 7. On the other hand, a similar digital signal is input to the Y scan plate 6 as well. In this case, as shown in FIG. 3 (d), the ion beam is scanned from a position on the right side of the wafer 8 which is substantially a contour portion according to the address data and the like.

Then, the frequency dividing signal based on the binarized data for correcting the sheet resistance value at the position corresponding to the data of the address stored in the RAM 21 is a programmable divider 23.
Is input to the up / down counter 14. The up / down counter 14 is set so as to "down-count" by a signal from the flip-flop 16 at the end of the above-mentioned one-line scanning.

Therefore, the up / down counter 14 counts down based on the divided signal, and the counted down digital signal is input to the X scan plate 7. On the other hand, the Y scan plate 7 receives the digital signal, which is the initial value of the second row. In this case, the ion beam is scanned up to the position shown in FIG. 3 (e) at a speed according to the frequency division signal. Hereinafter, such scanning is sequentially performed for each X-coordinate, and the above-described one-line scanning in the right direction in the drawing or one-line scanning in the left direction in the drawing is repeatedly performed in sequence, as shown in FIG. ) Position, that is, Y
When the scanning end point of the nth line in the direction is reached, the scanning ends.

That is, according to this embodiment, the ion beam is
Based on the X-coordinate start point Xstr and the end point Xend of the outline of the wafer 8 stored in the wafers 2 and 13, the wafer 8 is controlled to be scanned inside the outline. For this reason, the ion beam is less likely to be scanned at a position other than the wafer 8, the number of wasted ion beams is reduced, and the throughput can be improved.

Further, the ion beam has a constant sheet resistance value based on the binarized data which is stored in the RAM 21 and uniformly corrects the sheet resistance value after the ion beam constant speed scanning at each value of the wafer 8. Is controlled to be.
That is, the scanning speed becomes slower at a position where the sheet resistance value of the wafer 8 is large and becomes faster at a small position, so that the ion implantation concentration can be made uniform.

Furthermore, since the up / down counter 14 is composed of two stages of the 8-bit up / down counter 14a and the m-bit up / down counter 14b, it is possible to have a high resolution of 8 + m bits.

(Effects of the Invention) As described above, according to the ion implantation apparatus of the present invention, once the data regarding the sheet resistance value of a wafer is acquired, the ion implantation rate of another wafer in the same manufacturing lot can be determined based on this data. Since the sheet resistance value can be controlled to be constant, the ion implantation concentration can be made uniform by a simple means.

[Brief description of drawings]

FIG. 1 shows the X of the ion implanter according to one embodiment of the present invention.
FIG. 2 is a block diagram showing a directional scanning control circuit, FIG. 2 is a sectional view showing an ion implantation apparatus of this embodiment, FIG. 3 is a view showing an ion beam scanning direction of this embodiment, and FIG. 4 is a ROM of this embodiment. FIG. 5 is a timing chart showing the control signals of this embodiment. 2 ... Ion source, 3 ... Analyzer magnet, 4 ...
Accelerator, 5 ... Lens, 6 ... Y scan electrode, 7 ...
X scan electrode, 8 ... Wafer, 9 ... Scan position control circuit, 10 ... Scan speed control circuit, 11 ... Counter, 12,1
3 …… ROM, 14 …… Up / down counter, 15 …… Comparator, 16 …… Flip-flop, 17 …… Adder, 18
...... Selector, 19 …… Latch circuit, 20 …… Counter, 21
…… RAM, 22 …… Multiplexer, 23 …… Programmable divider, 24 …… Selector, 25 …… Latch circuit.

Claims (2)

(57) [Claims] 1. A target is scanned with an ion beam,
In an ion implantation apparatus that implants ions into a target so that the sheet resistance value of the target becomes uniform, a digitized correction for correcting and equalizing the sheet resistance value after constant-speed scanning of the ion beam Data (binarized data) for storing the target in each of a plurality of vertical and horizontal sections, and a digital for correcting the sheet resistance value at each position of the target stored in the storage means. Scanning control means for controlling the scanning speed of the ion beam at each position of the target based on the converted correction data (binarized data) so that the sheet resistance value of the target becomes constant. An ion implanter characterized by being provided. 2. The ion implantation apparatus according to claim 1, wherein means for scanning the ion beam is provided within the contour position of the target stored in the storage means.