JPH05266839A - Faraday cup - Google Patents

Abstract

PURPOSE:To prevent measuring of an implant current from being affected by gas if generated inside a Faraday cup during ion implantation. CONSTITUTION:An ion beam 1 is implanted through a coil-shaped Faraday cage 7 into a subject 4 to be implanted with ions, and the ion current is measured by an ammeter 6. Gas generated during implanting is expeled from gaps in the coil 7. Secondary electrons are trapped by a magnetic field that the coil 7 generates, and are thereby not emitted outside. Therefore, even if the subject to be implanted with ions is one that readily emits gas, such as a resist- equipped semiconductor wafer, the gas is promptly expeled from the gaps in the coil, so the rate of lowering of the degree of vacuum can be reduced and the ion beam current can be accurately measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for measuring an ion current in an implanting processing chamber of an ion implanting device, and particularly to minimize an error in current measurement even if the vacuum degree at the time of implanting changes. The present invention relates to an ion implantation device that has been devised.

[0002]

2. Description of the Related Art A conventional apparatus has a structure in which a sealed cylindrical electrode is provided in front of an object to be driven, as represented by U.S. Pat. No. 4,001,449.

[0003]

In the above-mentioned prior art, since the current value of the ion beam is accurately measured, secondary electrons or secondary ions generated when the object to be implanted is irradiated with the ion beam are captured. In that respect, it functions well. However, when the ion beam current is in the 10 mA class and gas is generated from the implanting object during ion beam irradiation, there is a resin film or the like on the surface of the implanting object, such as a resist film on a semiconductor wafer. In this case, depending on the outgas when driving,
The degree of vacuum decreases. The gas only escapes from the ion beam inlet of the Faraday cage (cylindrical electrode), so it fills the Faraday cage and further diffuses to the upstream of the beam line through the opening of the ion beam inlet, and the ion beam enters the Faraday cup. It collides with the ion beam before and neutralizes a part of the ion beam. Further, the gas is ionized by colliding with the ion beam in the Faraday cage, and the gas is exhausted in the ion state, so that the same phenomenon as the current leak occurs. In either case, the ion beam current cannot be accurately measured, and there is a problem that the ion beam current fluctuates as the degree of vacuum changes.

Further, when the current measuring system has a high-voltage electrode such as a suppressor electrode for secondary electrons, there is a problem that discharge is likely to occur due to a decrease in vacuum degree. Furthermore, the generated gas substance is mixed into the surface of the object to be implanted due to the mixing action at the time of ion beam implantation, and the gas substance collects and grows to a size as a foreign matter. There is a concern that it will have an adverse effect when it is driven into.

An object of the present invention is to solve the problems caused by the generation and filling of gas in these Faraday cages.

[0006]

The above objective is accomplished by coiling the Faraday cage. Even if gas is generated by driving, the gas is discharged from the clearance of the coil. It does not fill the Faraday cage.

However, if secondary electrons or secondary ions leak together with the generated gas, accurate current measurement cannot be performed. Therefore 1. A strong magnetic field is generated by passing an electric current through the coil, which is a Faraday cage.

2. Determine the thickness and spacing of the coil wire so that the outside of the Faraday cage cannot be seen through the gap of the coil as seen from the target.

In both cases, only a neutral gas having no electric charge is discharged from the clearance of the coil, and charged particles such as electrons and ions are trapped.

[0010]

When a magnetic field is provided in the Faraday cage, only charged particles such as electrons and ions can be bent in the traveling direction by the magnetic field. If the magnetic field is strong enough, not only can the direction of travel be bent, but charged particles can be trapped in the magnetic field.

The magnetic field strength required for secondary electrons will be calculated. If the energy Ee of the secondary electron is several tens of eV and the length L of the particle passage example of the magnetic field is several cm, and the radius R of the electron applied by the magnetic field is smaller than L, the secondary electron passes through this magnetic field. I can't.

[0012]

[Equation 1]

And the relational expression between the charged particles and the magnetic field

[0014]

[Equation 2]

However, Me is the mass of the electron (converted into atomic weight)
B depends on the magnetic flux density (Gauss)

[0016]

[Equation 3]

Therefore, if a magnetic field of about 50 Gauss is present near the coil portion of the Faraday cage, secondary electrons can be trapped by the magnetic field. Although the energy of the secondary ions is almost the same as that of the secondary electrons, the mass of the secondary ions is large, so there is a risk that they will pass through without being trapped in a magnetic field at this level. Therefore, it is desirable that the outside of the coil cannot be seen through the gap of the coil when viewed from the target.

[0018]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 2 shows the structure of a conventional implanting device, in which an ion beam 1 is generated by an ion source 10 and accelerated, and then an analysis tube 11 is provided.
Is mass-separated, passes through the earth electrode 2 and the suppressor electrode 3, is captured by the Faraday cup composed of the driven object 4 and the Faraday cage 5, and is measured by the ammeter 6.

On the other hand, in FIG. 1, the Faraday cage 5
The rear part of the coil was made up of a coil 7 made of pure aluminum, and a coil power source 8 was connected to the coil 7 so that a current could be passed to generate a magnetic field.

Pure aluminum is effective in terms of heat conduction and prevention of heavy metal contamination of the driven object. Since the coil 8 is made of pure aluminum, a supporting part 9 made of alumina or resin is attached in 3 or 4 directions so as to prevent the center from slackening, thereby supporting the coil. Further, the support component 9 is provided with grooves for retaining the coil, so that the coil is supported at equal intervals. In FIG. 1, the ion beam 1 passes through the earth electrode 2, the suppressor electrode 3, the coil-shaped Faraday 7, and the Faraday cylinder 5, and is driven into the target object 4.
Then, the ion current is measured.

The gas generated during the driving is exhausted from the clearance of the coil 7. However, the secondary electrons generated during the implantation are trapped by the magnetic field generated by the coil 7 and do not go out through the clearance of the coil. The secondary ions are
Since the angle deflected by the magnetic field is smaller than that of electrons, it is hard to be trapped in the magnetic field, but the secondary ions generated on the implanting object 4 are coiled so that they do not go straight out of the coil gap to the outside. I have decided the clearance. The same applies to the sputtered material generated on the driven material. If the coil is made of pure aluminum with a diameter of about 6 mm, the clearance should be 3 mm or less. Further, if the coil is made flat as shown in FIG. 3, the particle capture rate increases. In FIG. 3, about 5a≈b is desirable.

According to the present embodiment, even if the object to be implanted is a semiconductor wafer having a resist, which easily emits gas, the gas is immediately exhausted from the clearance of the coil 7, so that the degree of vacuum is not lowered. Therefore, there is an effect that the ion beam current can be accurately measured.

[0024]

According to the present invention, even if a vacuum is lowered due to outgas by implanting an ion beam on a semiconductor wafer having a resist, the current value of the ion beam can be accurately measured without changing. it can. Further, there is no fear of electric discharge at the suppressor electrode or the like which occurs when the degree of vacuum is extremely lowered. Moreover, by performing the driving in a state where the generated gas is in the vicinity of the driving chamber, contamination of the driving target due to the mixing action that the gas substance is driven into the driving target,
There is no fear that the gas substance will be collected and become a foreign substance, which will hinder the normal driving of the object.

Further, the problem of fouling due to the adherence of gaseous substances to the surrounding components, and hence the problem of maintenance, can be alleviated.

[Brief description of drawings]

FIG. 1 is a diagram showing an example in which a part of a Faraday cylinder is formed of a coil in an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a main configuration of a conventional ion implantation device.

FIG. 3 is a diagram showing an example in which a coil is made of a flat material.

[Explanation of symbols]

1 ... Ion beam, 2 ... Ground electrode, 3 ... Suppressor electrode, 4 ... Implanted object, 5 ... Faraday cage, 6 ... Ion ammeter, 7 ... Coil-shaped Faraday, 8 ... Coil power supply, 9 ... Coil support part, 10 … Ion source, 11… Analysis tube, 15… Flat coil.

Claims (6)

[Claims] 1. A Faraday cup, wherein in a vacuum processing chamber, an ion current is measured by an object to be implanted and a cylindrical electrode positioned in front of the object, wherein the cylindrical electrode has a coil shape. 2. In a vacuum processing chamber, wherein an ion current is measured by an implanting object and a tubular electrode positioned in front of the implanting object, the tubular electrode is left in the vicinity of the implanting object, and the tubular electrode A Faraday cup characterized in that the ion beam entrance side is coiled. 3. The Faraday cup according to claim 1, wherein a current is applied to the coil-shaped electrode to generate a magnetic field. 4. A Faraday cup characterized in that the direction of the magnetic force lines of the magnetic field formed in claim 3 is coaxial with the ion beam. 5. The Faraday cup according to claim 1, wherein the coil electrode is made of pure aluminum. 6. An ion implanter using the Faraday cup according to any one of claims 1 to 5.