JP2869558B2 - Ion implantation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an ion implantation method.

(Prior Art) In general, the ion implantation technique is used, for example, for implanting impurities into a semiconductor wafer in a semiconductor manufacturing process.

Conventionally, an ion implantation apparatus provided with a so-called hot cathode ion source, for example, a Freeman ion source, has been widely used for ion implantation into a semiconductor wafer.

That is, in an ion implantation apparatus using such a Freeman-type ion source, a rod-shaped tungsten filament provided in an arc chamber made of, for example, molybdenum is energized and heated, and an arc is supplied between the filament and the arc chamber. A predetermined gas, for example, AsH ₃ , PH ₃ , BF ₃ or the like is introduced into the arc chamber while a voltage is applied to generate ions. Then, the ions are electrically extracted, sorted, accelerated, focused, and scanned to irradiate the semiconductor wafer. The arc voltage is usually set to about 80 to 100 V when BF ₃ gas is used, and is usually set to about 60 to 70 V when AsH ₃ or PH ₃ gas is used.

(Problems to be Solved by the Invention) However, when the ion implantation is performed as described above, the life of the ion source is about 20 hours in the past, and the ion source needs to be frequently replaced. Has become a major obstacle in improving the

The present invention has been made in view of such a conventional situation, and provides an ion implantation method capable of extending the life of an ion source as compared with the conventional one and improving productivity as compared with the conventional one. It is something to offer.

[Structure of the Invention] (Means for Solving the Problems) That is, according to the invention of claim 1, a filament provided in an arc chamber is energized, and an arc voltage is applied between the arc chamber and the filament. In this state, a predetermined gas is introduced into the arc chamber to generate ions, and when extracting and injecting the ions into an object to be processed, if the gas is PH ₃ gas or AsH ₃ gas, the arc It is characterized in that the voltage is 25 to 40V.

(Operation) In the ion implantation method of the present invention, the arc voltage applied between the arc chamber and the filament is set to a voltage value near a limit voltage value at which sputtering does not occur in the filament.

As shown in the graph of FIG. 2 in which the vertical axis represents the consumption rate of the tungsten filament and the horizontal axis represents the arc voltage value, the voltage value is, for example, about 60 V when the BF ₃ gas is used.
₃ If for example 30V about using a gas, for example 25V about when using AsH ₃ gas. Therefore, when BF ₃ gas is used, the arc voltage value is, for example, about 50 V to 70 V, and when PH ₃ gas or AsH ₃ gas is used, the arc voltage value is, for example, 25 to 40.
It is preferable to be about V.

Therefore, the consumption of the filament due to sputtering can be suppressed as compared with the related art, and the life of the ion source can be prolonged, and the productivity can be improved.

(Embodiment) An ion implantation method of the present invention will be described below with reference to the drawings.

For example, a rod-shaped filament 2 is provided in an arc chamber 1 made of molybdenum or the like so as to penetrate the arc chamber 1.
For example, the filament power supply 3 is connected so as to generate a DC current of 150 A to 180 A. An arc power source 4 is connected between the arc chamber 1 and the filament 2 so as to apply an arc voltage (DC voltage) as described below. Further, the arc chamber 1 includes:
The arc chamber 1 is provided with a gas inlet 5 for introducing a predetermined gas, such as AsH ₃ , PH ₃ , BF _3, or the like, which serves as a source of ions, and an ion outlet 6 for extracting generated ions. On the outside, a magnet 7 is provided in the arc chamber 1 so as to form a magnetic field as shown by an arrow H in the drawing.

In this embodiment, ions such as boron ions are implanted in the following manner using the apparatus having the above-described configuration.

That is, the inside of the arc chamber 1 is evacuated, and the above-described DC current, for example, 150 A to 180 A is supplied to the filament 2 by the filament power supply 3. In addition, the arc power supply 4 applies an arc voltage of, for example, about 25 to 40, between the arc chamber 1 and the filament 2, which is a voltage near a limit voltage value at which sputtering does not occur on the filament 2, to generate thermoelectrons. AsH ₃ gas is introduced into the arc chamber 1 from the gas inlet 5. Then, the AsH ₃ gas molecules collide with thermionic electrons to generate ions. Note that the magnetic field H is for generating a spiral motion of the thermoelectrons, increasing the possibility of collision with gas molecules, and generating a large amount of ions. Then, this ion is extracted from the ion extraction port 6, and
Sorting, accelerating, focusing, and scanning by a mass analysis magnet, an acceleration tube, an electrostatic lens, a scanning electrode (all not shown), etc., irradiate a semiconductor wafer held on a platen, for example, and implant arsenic ions. .

That is, in the ion implantation method of this embodiment, the arc voltage applied between the arc chamber 1 of the hot cathode type ion source (Freeman type ion source) and the filament 2 is shown in the graph of FIG. Then, ions are implanted at a voltage value near the limit voltage value at which sputtering does not occur on the filament 2, for example, 25 to 40V. Thus, if the arc voltage, using a BF ₃ gas 80~100V
60 to 7 when PH ₃ gas or AsH ₃ gas is used
Compared to the conventional method of setting the voltage to 0 V, the consumption of the filament 2 can be greatly reduced, the life of the ion source can be extended, and the productivity can be improved.

The limit arc voltage value at which sputtering does not occur in the filament 2 differs depending on the type of gas used as shown in the graph of FIG. That is, approximately 60 V for BF ₃ gas and approximately 30 V for solid phosphorus or PH ₃ gas.
V, approximately 25V for solid arsenic or AsH ₃ gas. Therefore, when PH ₃ gas or AsH ₃ gas is used, it is preferable that the arc voltage value is, for example, about 25 to 40 V, and when other gas is used, a limit arc voltage value at which sputtering does not occur is determined in advance by an experiment. Need to be kept.

[Effect of the Invention] As described above, according to the ion implantation method of the present invention, the life of the ion source can be prolonged as compared with the related art, and the productivity can be improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ion source for explaining an ion implantation method according to one embodiment of the present invention, and FIG. 2 is a graph showing a result of measuring a relationship between a consumption rate of a filament and an arc voltage value. 1 ... arc chamber, 2 ... filament, 3 ... filament power supply, 4 ... arc power supply, 5 ... gas introduction port, 6 ... ion extraction port, 7 ... magnet.

Claims (1)

(57) [Claims] 1. An electric current is applied to a filament provided in an arc chamber, an arc voltage is applied between the arc chamber and the filament, and a predetermined gas is introduced into the arc chamber in this state. The method according to claim 1, wherein, when the gas is PH ₃ gas or AsH ₃ gas, the arc voltage is 25 to 40 V when extracting the ions and injecting the ions into the object.