JPH01122557A - Target surface potential control device - Google Patents

Abstract

PURPOSE:To maintain the target surface potential at the potential before the ion implantation by controlling the electron beam fed overlappingly with ions implanted on the surface of a target based on the experiment results on the secondary electron beam emission ratio determined by the combination of the type of molecules or atoms constituting ions, the type of a target material, and the kinetic energy of implanted ions. CONSTITUTION:Multiple targets 3 to be implanted with ions are fitted at a distance in the peripheral direction on the face of a disk-shaped stage 4 arranged in an ion implantation chamber 2 and rotated by a rotary shaft 8 together with the stage 4. Slits 9 are provided on this stage 4, a pulse-shaped electron beam 11 overlapped with an ion beam 7 is radiated to the targets 3 from an electron feed chamber 10 in the device 20. This ion beam 7 passes the slits 9 and flows into an ammeter 13 via a Faraday cup 12 arranged in the ion implantation chamber 2, the current value is added to an arithmetic unit 19, a power unit 17 is controlled according to the results calculated based on the various information, thereby the output of the electron beam 11 is controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is particularly applicable to a large current ion implantation device, in which positively charged particles are injected and positive charges are accumulated. The present invention relates to a target surface potential control device that controls the potential of the target surface by supplying electrons to the surface of the target in a manner that overlaps with the charged particles.

[Conventional technology]

An example of this type of device is disclosed in Japanese Unexamined Patent Publication No. 59-204231. FIG. 4 is a diagram showing the arrangement of the device. An ion beam 7 formed by positively charged particles extracted from an ion source of an ion implanter 1 whose upstream side is not shown is implanted into a wafer 3, which may be a target on a stage 4 disposed in an ion implantation chamber 2. At the same time, the electron beam 6 generated by the electron gun 5 overlaps and irradiates the ion beam irradiation location on the wafer 3, thereby canceling out the positive charges accumulated on the wafer surface and suppressing the increase in the surface potential of the wafer 3. .

[Problem that the invention seeks to solve]

However, such conventional devices do not have a system that accurately cancels the positive charges accumulated on the target surface by injection of positively charged particles, and therefore it is difficult to supply the optimum amount of electrons to the target surface. As a result, the surface potential of the wafer increases during operation of the ion implantation apparatus, resulting in dielectric breakdown between the wafer surface and the wafer substrate.

An object of the present invention is to provide a target surface potential control device that can maintain the surface potential of a target at the potential before positively charged particles are injected by accurately canceling the positive charges accumulated on the target surface. The goal is to provide the following.

[Problem that the invention seeks to solve]

In order to achieve the above object, according to the present invention, positively charged particles are injected into the surface of the target where positive charges are accumulated, by supplying electrons to the surface of the target by superimposing them on the charged particles. A target surface potential control device for controlling the potential of the target surface includes an electron source formed such that the amount of electrons supplied to the target surface can be controlled by an external control signal, and molecules or atoms constituting the charged particles to be injected. , the type of target material, and the kinetic energy of the charged particles immediately before injection. The control means is provided for calculating and outputting the control signal based on the emission rate of secondary electrons emitted from the target surface during charged particle injection and the ion current due to the injected charged particles.

[Effect]

First, the principle of the present invention will be explained. Note that in the following description, positively charged particles will be simply referred to as ions.

When ions collide with a wafer, they emit secondary electrons, and the total charge of secondary electrons emitted from the wafer in a unit time per ampere of ion current injected into the wafer, i.e. the secondary electron current [ampere]. ] varies depending on the combination of the type of molecules or atoms constituting the ion, the type of wafer material, and the kinetic energy that the ion has just before implantation. Since the emission of electrons from the wafer is equivalent to the accumulation of ions, when an ion beam of ■ [amperes] is implanted into the wafer, secondary electrons of Ip (amperes) are emitted. , the accumulation of positive charges on the wafer surface is I(1+p)
/e (number).Here, e is the charge amount of one electron.Therefore, the same number of electrons (I+I when converted to current).
By supplying p (ampere) to the wafer surface, the wafer surface potential is maintained at the same level as before ion implantation (usually ground potential).

If the electron current is less than I+Ip (ampere), the wafer surface will have a positive potential, and if it is more, it will have a negative potential, and in the worst case, dielectric breakdown of the wafer will occur.

The secondary electron emission rate p is the type of target material.

Detailed experimental results have been obtained for each combination of the type of molecule or atom that constitutes the ion, that is, the type of ion species, and the kinetic energy immediately before implantation, so these can be memorized.
Based on the separately measured ion beam current ■ [Ampere], calculate the required amount of electrons (1-1-p)C Ampere]
This amount or the amount corresponding to this amount in a one-to-one relationship is output to the electron source as a control signal, and electrons are emitted so that the current 1 (1+p) (ampere) is obtained from the electron source. For example, when the electron source is configured using a hot cathode, the number of emitted electrons is controlled by the voltage applied to the accelerating electrode arranged in front of the hot cathode by the input control signal. This is done by changing the .

As described above, according to the present invention, the number of electrons supplied in addition to the ions implanted into the target surface can be controlled depending on the type of molecules or atoms that make up the ions.

This is done using experimental results for the secondary electron emission rate, which is determined by the combination of the type of target material and the kinetic energy of the implanted ions, so that the positive charges accumulated on the target surface are canceled out with high accuracy, and the target surface is The potential is maintained substantially at the potential before ion implantation.

〔Example〕

FIG. 1 shows the structure of a target surface potential control device according to an embodiment of the present invention, and FIG. 2 and FIG. The relative positional relationship in the ion implantation apparatus between the electron source and the ion implantation chamber where ion implantation is performed is shown in detail below, and FIG. 3 is a vertical cross-sectional view of the position of the ion implantation chamber in FIG. 2. . As shown in FIG. 3, a plurality of wafers 3, which are targets for ion implantation, are attached to the surface of a disc-shaped stage 4 at intervals in the circumferential direction, and the stage 4 rotates around a rotation axis 8. At the same time, the ion beam 7 is irradiated with the ion beam 7 while reciprocating in the radial direction on the surface of the stage 4 by a mechanism not shown.
Ions are implanted in a pulsed manner by crossing the

The ion beam current during implantation is measured by using an ammeter 13 to measure the amount of ions flowing through the slit 9 (Figure 2) provided in the stage 4 and into the Faraday cup 12 (Figure 3) placed on the back side of the stage. This allows constant monitoring. This slit 9 is provided, for example, at an intermediate position between 20 wafers arranged at equal intervals in the circumferential direction of the disc-shaped stage 4 (see FIG. 2), and the Faraday cup 12 is Since it is fixed at a position on the extension line of the ion beam traveling direction behind the stage 4 in the vacuum chamber 20 of the apparatus, the ion beam flows into the Faraday cup only when the slit crosses the ion beam and the beam current is increased. It has a mechanism to measure it.

Note that it is practically sufficient to have one or more slits on the stage.

The wafer that has passed through the ion beam is irradiated with an electron beam 11 from an electron source disposed in the electron supply chamber 10 (FIG. 1) as it crosses the electron supply chamber 10 (FIG. 2). In this embodiment, this electron source includes a filament 15 that emits thermoelectrons by applying electricity to generate heat, and a filament 15 that is connected to the same potential as the filament 15 to block the thermoelectrons from flowing from the filament 15 toward the vacuum container 2o. A blocking electrode 16;
and an accelerating electrode 14 that accelerates thermoelectrons emitted from the filament 15 toward the stage, and a 9 that changes the voltage applied to the accelerating electrode 14 in response to a control signal from the outside.
The power supply device 17 includes a charging power source. The filament 15 may be a tungsten filament or a metal oxide hot cathode.

The amount of electrons supplied from the electron source configured in this manner is controlled as follows.

The ion beam current flowing out from the Faraday cup 12 is measured by the ammeter 13, and this current value Ii is input to the calculator 19, while the quantity A representing the type of molecules or atoms constituting the ions, that is, the type of ion species , the kinetic energy immediately before implantation of the ion beam, that is, the total accelerating voltage B for the ions to the target position, and the quantity C representing the type of target material are input to the function generator 18 to calculate the secondary electron emission rate p, and the calculator 19 calculates the secondary electron emission rate p. Enter. Arithmetic unit 1
9 is the input secondary electron emission rate p and the current value 1i
Calculate (1+pHi) using (1+pHi), input this value as a control signal to the power supply 17, and control the acceleration voltage output from the power supply 17 so that an electron beam current equal to (1+pHi) is obtained. For example, when ions are implanted into a wafer on which a Si0g film is formed at a total acceleration voltage of 160 kV, the secondary electron emission rate p is 10, and on the other hand,
If the ion beam current at this time is 20IIIA,
Since 200 mA of secondary electrons are emitted from the wafer 3, the amount of electrons emitted from the electron source is 20 + 200
= 22On+A (7) The amount must be sufficient to form 11 electron beams. The amount of electrons is determined by the potential difference ΔV between the filament 15 and the accelerating electrode 14. For example, if a tungsten filament is used as the filament, the wire diameter is 1 m, the effective length is 45 fi, and the temperature is 25 mm.
It has been confirmed that if the distance between the electron beam and the accelerating electrode 14 is 5n at 00K, an electron beam of 2oowlA can be obtained at ΔV-600V. Therefore, the electron beam current Ie and the potential difference Δ■
By memorizing the relationship between the wafer and the wafer surface, it is possible to provide a potential difference that can accurately cancel out the positive charges accumulated on the wafer surface.

FIG. 5 shows a combination of the shape of the ion beam implantation region and the shape of the electron beam implantation region on the wafer 3. In the same figure (al, the shapes of both are exactly the same, and in (b), the electron beam area 11A is wider than the ion beam area 7A. Therefore, in the case of a mountain), the electron beam current is accumulated on the wafer. Even if the ion beam is configured with an amount of electrons that can accurately cancel out positive polarity charges, the irradiation area is large, so there is a shortage of electrons within the ion beam implantation region. Therefore, it is necessary to make the width of the electron beam implantation region in the stage radial direction as equal as possible to the ion beam implantation region by adjusting the shape of the accelerating electrode 14 (see FIG. 1).

〔Effect of the invention〕

As described above, according to the present invention, positively charged particles are injected and electrons are supplied to the surface of the target where positive charges are accumulated, thereby increasing the potential of the target surface. A target surface potential control device for controlling the target surface potential includes an electron source formed such that the amount of electrons supplied to the target surface can be controlled by an external control signal, and the type of molecules or atoms that constitute the charged particles to be injected. , is determined by a combination of the type of target material and the kinetic energy of the charged particles immediately before injection.

The control means calculates and outputs the control signal based on the emission rate of secondary electrons emitted from the target surface during charged particle injection and the ion current due to the injected charged particles. The amount of electrons supplied to the target surface was accumulated on the target surface. It is precisely controlled to be equal to the positive charge amount including the accumulated charge due to secondary electron emission, and the surface potential of the target is substantially brought to the potential before ion implantation without excessively increasing the size of the electron source. A sustainable effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the configuration of a target surface potential control device according to an embodiment of the present invention, FIG. 2 is a plan view showing the relative positional relationship between the electron source and the ion implantation chamber, and FIG. 4 is an explanatory diagram showing the configuration of a conventional target surface potential control device, and FIG. 5 is a diagram showing the shape of the ion implantation region on the wafer (target) and the electron beam implantation region. FIG. 6 is a diagram showing a combination with shapes, where ta+ shows a case where the image shapes are the same, and (b) shows a case where the image shapes are different. 2: Ion implantation chamber, 3: Wafer (target), 6.
11: Electron beam, 7: Ion beam, 9 Nisrits,
10: Electron supply chamber, 12: Faraday cup, 13: Ammeter, 17: Power supply, 18: Function generator, 19: Arithmetic unit (control means), A: Input representing ion species, B: Total acceleration of ions Voltage, C: Input representing the type of target material. (C1) (b) IIs diagram

Claims (1)

[Claims] 1) A target surface potential control device that controls the potential of the target surface by supplying electrons to the surface of the target in which positively charged particles are injected and positive charges are accumulated, overlapping with the charged particles. , an electron source formed such that the amount of electrons supplied to the target surface can be controlled by an external control signal, the type of molecules or atoms constituting the charged particles to be injected, the type of target material, and the charged particles. control means for calculating and outputting the control signal based on the emission rate of secondary electrons emitted from the target surface during charged particle injection and the ion current due to the injected charged particles, which is determined by a combination of kinetic energy immediately before the injection; A target surface potential control device comprising: