JPH04357657A - Ion treatment device - Google Patents

Abstract

PURPOSE:To make an amount of secondary electron variable, depending upon the position of an ion beam radiated to a wafer, and enable the wafer to be thereby protected more properly from being electrified. CONSTITUTION:A disc 40 and an optical sensor 44 detect the translational position of a wafer disc 4, and a signal corresponding to the position is sent to an arithmetic circuit 58 via a counter circuit 54 and a D/A converter 56. The counter circuit 54 is set at the position of a wafer 6 on the disc 4 where an ion beam 2 begins to be radiated, according to a signal from a set/reset circuit 52, and is reset at the position of the wafer 6 where the ion radiation ends. The arithmetic circuit 58 uses a signal from the D/A converter 56 as an angle theta, and generates a signal of E=a-bsintheta. Thereafter, the circuit 58 sends the signal to a differential amplifier circuit 32 as a set value for disc current ID.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an ion processing apparatus, such as an ion implantation apparatus, which irradiates a wafer with an ion beam in a vacuum and performs a process such as ion implantation on the wafer. Concerning improvements in means for preventing this.

0002

2. Description of the Related Art FIG. 4 is a diagram partially showing an example of a conventional ion processing apparatus.

[0003] This device is of a so-called mechanical scan type, and basically uses a vacuum container (not shown).
For example, a plurality of wafers 6 mounted on the peripheral edge of a wafer disk 4, which is rotated as shown by arrow A and translated as shown by arrow B, are irradiated with an ion beam 2 and subjected to processing such as ion implantation. It is configured. 8 is a motor for rotating the wafer disk 4, and 10 and 12 are motors for translating the wafer disk 4 and a rotating shaft.

On the path of the ion beam 2, on the upstream and downstream sides of the wafer disk 4, secondary electrons emitted when the ion beam 2 hits the wafer disk 4, etc. constitute a Faraday system. a neutral cup 14 which receives the ion beam 2 and prevents it from escaping to ground; and a catch plate 16 which receives the ion beam 2 in its place when the wafer disk 4 is translated outward.
are provided for each.

Then, the wafer disk 4 and the catch plate 16 are connected in parallel, and the neutral cup 14 is connected in parallel to this through a disk current measuring resistor 28, and a beam current measuring device 38 such as a current integrator is connected. This allows the beam current IB of the ion beam 2 to be measured accurately.

In addition, in order to prevent the surface of the wafer 6 from becoming positively charged during irradiation with the ion beam 2, especially when the surface is an insulator, causing problems such as discharge,
A filament 18 constituting a primary electron emission source is provided on the side of the neutral cup 14, and the primary electrons 21 emitted from the filament are applied to the opposing surface of the neutral cup 14 to emit secondary electrons 22 from there. The neutral cup 14 is used as a secondary electron emission source, and the secondary electrons 22 are supplied to the wafer 6 in the ion beam irradiation area on the wafer disk 4 to neutralize the positive charge caused by the ion beam 2 on the surface thereof. ing. 2
4 is a filament power supply for heating the filament 18;
Reference numeral 6 denotes an extraction power source for extracting the primary electrons 21.

When processing the wafer 6, the disk current measuring resistor 28 is charged with a combination of the beam current IB and the secondary electron current I2 caused by the secondary electrons 22 in the opposite direction, that is, expressed by the following equation. A disk current ID flows. ID=IB-I2

...(1) This causes the disk current measurement resistor 28
A voltage corresponding to the disk current ID is generated across the
This is input to the differential amplifier circuit 32 via the isolation amplifier 30. A set value is also input from the disk current setting circuit 34 to the differential amplifier circuit 32. The differential amplifier circuit 32 determines the difference between both inputs and provides it to the control circuit 36. The control circuit 36 increases or decreases the filament current by controlling the filament power supply 24, and controls the disk current ID to reach a set value. Thereby, the amount of secondary electrons 22 supplied to the wafer 6 on the wafer disk 4 can be set to a desired value, thereby suppressing charging of the wafer 6.

[0008]

However, in the above ion processing apparatus, since the disk current ID is fixed by the set value, the beam current IB flowing through the disk current measuring resistor 28 is independent of the position of the wafer disk 4. Since it is constant (for example, the beam current IB flows through the catch plate 16 even if the wafer disk 4 is translated outward), the amount of secondary electrons 22 (i.e., the secondary electron current I2)
is controlled to be constant. However, since the density of the ion beam 2 varies depending on its location (generally, it is dense in the center and light on the outside), for example, at the position where the wafer disk 4 is translated and the ion beam 2 begins to hit the wafer 6, An excess or deficiency of the secondary electrons 22 supplied to the wafer 6 occurs, such as an oversupply of secondary electrons 22 and a shortage of secondary electrons 22 when the wafer 6 reaches the center of the ion beam 2. The problem is that it cannot be reliably prevented.

Therefore, the present invention provides an ion processing apparatus that can change the amount of secondary electrons depending on the position where the ion beam hits the wafer, thereby more reliably preventing the wafer from being charged. The main purpose is to provide

0010

[Means for Solving the Problems] In order to achieve the above object, the ion processing apparatus of the present invention includes a disk current measuring circuit that measures a disk current flowing through the wafer disk, and a disk current measuring circuit that detects the position of the wafer disk. disk position detection means that generates a pulse signal according to the position;
a set/reset means for detecting the start and end positions of the ion beam hitting the wafer on the wafer disk, generating a set signal at the start position and generating a reset signal at the end position of the hit; and detecting the disk position. A counter circuit for counting pulse signals from the set/reset means, which is set by a set signal and reset by a reset signal from the set/reset means, and a D/A converter for converting the output signal from the counter circuit into an analog signal. The output signal from this D/A converter is used to obtain a large value at the beginning and end positions of the ion beam hitting the wafer on the wafer disk, and a smaller value between the two positions. an arithmetic circuit that generates an output signal; a differential amplifier circuit that calculates the difference between the output signal from the arithmetic circuit and the disk current measured by the disk current measurement circuit; and a control circuit that controls the primary electron emission source and controls the amount of primary electrons emitted therefrom.

[0011]

[Operation] According to the above structure, the counter circuit operates between the start and end positions of the ion beam hitting the wafer on the wafer disk, and during that time, the disk current applied to the differential amplifier circuit is controlled. The set value is changed to have an inverse relationship to the density of the ion beam. As a result, when the wafer is hit by a faint area of the ion beam, the amount of secondary electrons decreases, and when the ion beam hits the wafer at a dark area, the amount of secondary electrons increases, which more reliably prevents the wafer from being charged. can do.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram partially showing an ion processing apparatus according to an embodiment of the present invention. The same reference numerals are given to the same or corresponding parts as in the conventional example shown in FIG. 4, and the differences from the conventional example will be mainly explained below.

In this embodiment, instead of using the conventional disk current setting circuit 34 described above, the setting value of the disk current ID for the differential amplifier circuit 32 is determined according to the translational position of the wafer disk 4 using the following configuration. I'm trying to change it.

That is, at the other end of the rotating shaft 12 of the motor 10 for translating the wafer disk 4, as shown in FIG.
is attached, and this slit 42 is read by an optical sensor 44 and a pulse signal P is then outputted, thereby forming the above-mentioned disk position detection means. In this example, the structure is such that the wafer disk 4 is translated by 1 cm when the rotating shaft 12, that is, the disk 40 rotates once.
The pulse signal P is output from the optical sensor 44 once per 0.5 cm of translation.

Furthermore, a shielding plate 50 is attached to a portion that translates in conjunction with the wafer disk 4, such as a portion connected to the case of the motor 8, and this shielding plate 50 is used to direct the ion beam to the wafer 6 on the wafer disk 4. Two optical sensors 46 and 48 are provided for detecting the position where the optical sensor 2 starts hitting and the position where the optical sensor 4 ends, respectively.
When the shielding plate 50 is detected at step 6, the set signal S is output, and when the optical sensor 48 detects the shielding plate 50, the reset signal R is output, or when the wafer disk 4 is translated in the opposite direction, this is done. A set-reset circuit 52 that outputs a set signal S and a reset signal R in a reverse relationship is provided to constitute the set-reset means described above.

The pulse signal P from the optical sensor 44 is
The signal is input to the counter circuit 54 and counted. That is, here the position of the wafer disk 4 is converted into a certain value (digital value). However, this counter circuit 54 is set by the set signal S from the aforementioned set-reset circuit 52 and reset by the reset signal R. That is, the counting operation is performed only between the position where the ion beam 2 starts hitting the wafer 6 and the position where the ion beam 2 ends hitting the wafer 6.

The output signal from the counter circuit 54 is a D/A
The signal is input to a converter 56, where it is converted into an analog signal, and this is input to an arithmetic circuit 58.

In this example, the arithmetic circuit 58 is a-b sin
It includes a function generator that generates a function θ, and D/
An analog signal representing the position of the wafer disk 4 from the A converter 56 is input as this θ. That is, this θ is
The position at which the ion beam 2 starts hitting the wafer 6 is 0.
°, the end position is 180°, the middle between both positions is 90°
°. a and b are constants. Therefore, this arithmetic circuit 5
The output signal E from 8 has a waveform as shown in FIG. 3, for example. That is, it becomes a at the positions where the ion beam 2 starts and ends hitting the wafer 6 on the wafer disk 4, and then decreases in a sinusoidal curve toward the center of both positions, and the minimum value becomes a-b. The values of a and a-b are
In order to cancel out the positive charge caused by the ion beam 2 and the negative charge caused by the secondary electrons 22, theoretically a=IB, a-b
= 0 may be sufficient, but in reality it may not always work as theoretically possible due to various factors, and it may be better to select a value close to the above value.

The output signal E from this arithmetic circuit 58
is inputted to one input portion of the differential amplifier circuit 32 described above to be used as a set value for the disk current ID. The operations of the differential amplifier circuit 32 and the control circuit 36 are similar to those of the conventional example.

According to the above configuration, the setting value for controlling the disk current IB (that is, the setting value from the arithmetic circuit 58 to the differential amplifier circuit 3
The value of the output signal E given to the ion beam 2) is changed so that it has an inverse relationship with the density of the ion beam 2, as shown in FIG. It will be done. That is, the set value of the disk current ID is large at a position where the wafer 6 is hit by a light part of the ion beam 2, and this set value becomes small at a position where a dark part is hit by the wafer 6.

However, as described above, since the beam current IB flowing through the disk current measuring resistor 28 is constant regardless of the position of the wafer disk 4, as can be seen from the above equation (1), the ion beam does not reach the wafer 6. At the position where the pale part of 2 is in contact, the disk current measuring resistor 2
The secondary electron current I2 flowing through the ion beam 2 is controlled to be small, that is, the number of secondary electrons 22 is decreased, and conversely, the secondary electron current I2 is controlled so that the number of secondary electrons 22 is reduced. It is controlled so that it becomes large, that is, the number of secondary electrons 22 increases. Specifically, as described above, the control circuit 36 controls the current flowing through the filament 18 so that the output from the differential amplifier circuit 32 becomes 0, and the primary electrons 21 emitted from the filament 18 This is done by controlling the amount of As a result, the secondary electrons 22 are supplied to the wafer 6 in just the right amount, so that charging of the wafer 6 can be more reliably prevented.

Note that the function used in the arithmetic circuit 58 is preferably the aforementioned a-bsin θ in the sense that it relatively approximates the density distribution of the ion beam 2; however, it is not limited to this; in short, It is sufficient if the output signal E of the arithmetic circuit 58 is a function that takes a large value at the start and end positions of the ion beam 2 hitting the wafer 6 and takes a smaller value between the two positions.

[0023]

[Effects of the Invention] As described above, according to the present invention, the amount of secondary electrons can be changed depending on the position where the ion beam hits the wafer. Since the amount of secondary electrons can be reduced and the amount of secondary electrons can be increased when a dark area is being hit, charging of the wafer can be more reliably prevented.

[Brief explanation of drawings]

FIG. 1 is a diagram partially showing an ion processing apparatus according to an embodiment of the present invention.

FIG. 2 is a front view of the disk and optical sensor in FIG. 1.

3 is a diagram showing an example of the waveform of an output signal from the arithmetic circuit in FIG. 1. FIG.

FIG. 4 is a diagram partially showing an example of a conventional ion processing apparatus.

[Explanation of symbols]

2 Ion beam 4 Wafer disk 6 Wafer 18 Filament 21 Primary electron 22 Secondary electron 24 Filament power supply 28 Disc current measurement resistor 32 Differential amplifier circuit 36 Control circuit 40 Disk 44, 46, 48 Optical sensor 50 Shielding plate 52 Set reset circuit 54 Counter circuit 56 D/A converter 58 Arithmetic circuit

Claims (1)

[Claims] 1. An apparatus for processing a wafer mounted on a wafer disk that is rotated and translated in a vacuum chamber by irradiating the wafer with an ion beam, the apparatus comprising: a primary electron emission source that emits primary electrons; A secondary electron emission source that receives primary electrons and emits secondary electrons is provided, and the secondary electrons are supplied to the wafer in the ion beam irradiation area, and the disk current flowing through the wafer disk is measured. a disk current measuring circuit; a disk position detection means for detecting the position of the wafer disk and generating a pulse signal according to the position;
a set/reset means for detecting the start and end positions of the ion beam hitting the wafer on the wafer disk, generating a set signal at the start position and generating a reset signal at the end position of the hit; and detecting the disk position. A counter circuit for counting pulse signals from the set/reset means, which is set by a set signal and reset by a reset signal from the set/reset means, and a D/A converter for converting the output signal from the counter circuit into an analog signal. The output signal from this D/A converter is used to obtain a large value at the beginning and end positions of the ion beam hitting the wafer on the wafer disk, and a smaller value between the two positions. an arithmetic circuit that generates an output signal; a differential amplifier circuit that calculates the difference between the output signal from the arithmetic circuit and the disk current measured by the disk current measurement circuit; and a control circuit that controls the primary electron emission source to control the amount of primary electrons emitted from the primary electron emission source.