JP3264987B2 - Ion implanter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus.

[0002]

2. Description of the Related Art An ion implantation technique is a method in which impurity ions generated in an ion source are accelerated by a high electric field, and impurities are mechanically introduced into a semiconductor wafer by using the kinetic energy thereof. This is a very effective method in that the total amount of the impurities thus obtained can be accurately measured as a charge amount.

Conventionally, such ion implantation is performed, for example, by referring to FIG.
Is performed using the apparatus shown in FIG. That is, gas or solid vapor is turned into plasma in the ion source 1, positive ions in the plasma are extracted at a predetermined energy by the extraction electrode 11, and then mass analysis is performed on the ion beam by the mass analyzer 12. The desired ions are separated, and the ions are completely separated by the decomposition slit 13. Then, the ion beam of the separated desired ions is accelerated to the final energy through the accelerating tube 14, and then irradiated to the wafer W, thereby introducing a desired impurity to the surface of the wafer W.

Further, for example, the front side of the wafer W (the ion source 1)
By arranging the Faraday cup 15 on the (side), the ion beam current can be measured. However, since this current value corresponds to the amount of impurities implanted into the wafer W, this current is measured. The amount of impurities to be introduced can be controlled, for example, a current value of 20 mA (Faraday cup 15).
The voltage (energy) for extracting ions from the ion source 1 is set to about 100 kV in order to obtain a detected current value flowing through the ion source 1.

[0005] By the way, DRAMs from 4M to 16M, 32
As the capacities have increased to M and 64M, devices have tended to become more and more highly integrated. For this reason, it is sometimes necessary to implant impurities very shallowly into the wafer.
Conventionally, in this case, the voltage at the accelerating tube 14 is set to a voltage opposite to that at the time of acceleration, and the ion beam passing therethrough is decelerated to lower the energy of the ions so that the ions are implanted shallowly. I was

[0006]

However, the path through which the ion beam passes is not completely vacuum, but contains gas molecules at a pressure of, for example, about 5.times.10@-6 Torr. Are neutralized by colliding with the gas molecules. Since the neutralized particles are not decelerated by the deceleration voltage, they are driven into the wafer with large kinetic energy, and as a result, some of the impurity particles are driven into the wafer deeper than expected, and There has been a problem that the implantation depth varies, and a predetermined characteristic cannot be obtained for the device.

On the other hand, in order to reduce the kinetic energy of ions at the time of collision with the wafer, a method of reducing the extraction voltage of ions from the ion source to about 10 kV is conceivable. For example, the extraction voltage is set to 10 k
When the ions are implanted at a low speed at V, the current detection value in the Faraday cup is a predetermined current value, for example, 10 to 10.
It is about 0.5 mA, which is considerably lower than 20 mA, so that efficient ion implantation cannot be performed.

The present invention has been made under such circumstances, and an object of the present invention is to make it possible to increase the value of a current flowing through an object to be processed while using a low-energy ion beam, thereby improving efficiency. An object of the present invention is to provide an ion implantation apparatus capable of performing ion implantation.

[0009]

According to a first aspect of the present invention, there is provided an apparatus for irradiating an object with an ion beam from an ion source through a mass analyzer and an accelerating tube sequentially to implant ions into the object. In, the discharge gas is discharged to generate plasma
And supplying the electrons in the plasma to the ion beam.
A plasma generator for the ion source and mass spectrometry
Provided between the vessel, pull electrons in the plasma in the ion beam
Weakened repulsion of positive charge in ion beam
Therefore, the divergence of the ion beam is suppressed .

[0010] According to a second aspect of the invention, in order through the apparatus for implanting ions to the object to be processed by irradiating the object to be processed the acceleration tube and a mass analyzer with an ion beam from the ion source, discharge a discharge gas Let me get the plasma, this plasma
Plasma for supplying electrons in the ion beam
A generator is provided between the ion source and an acceleration tube ,
The electrons in the plasma are attracted to the ion beam and
Weakens the repulsion of positive charges in the
The feature is to suppress the divergence of the game .

A plasma generator can be used as the electron supply means. In this case, electrons in the plasma are attracted to the ion beam emitted from the ion source, and positive and negative charges are generated in the ion beam. It will be mixed. As a result, the voltage distribution in the beam cross section of the ion beam is flattened, and the repulsive force of the positive charges is weakened, so that the divergence of the ion beam is suppressed. Therefore, even if the extraction energy of the ion beam from the ion source is reduced, the current flowing through the object to be processed by the irradiation of the ion beam can be increased.

[0011]

FIG. 1 is a configuration diagram showing the overall configuration of an embodiment of the present invention. In FIG. 1, reference numeral 2 denotes a first vacuum chamber. In the vacuum chamber 2, a vaporizer 3 for accommodating a solid material and sublimating an impurity component by a heating means is detachably mounted from the outside. 3 has an ion source 3
1 are connected.

The ion source 31 is, for example, a Freeman-type apparatus for applying a voltage between a rod-shaped filament and an anode electrode to convert the raw material gas from the vaporizer 3 into plasma, or converting an inert gas into a plasma to convert the raw material gas into a plasma. An electron excitation type device that causes electrons to collide with a source gas can be used. An ion extraction electrode 32 is disposed on the outlet side of the ion source 31. By applying an extraction voltage between the extraction electrode 32 and the apparatus body of the ion source 31, positive ions in the plasma are converted into an ion beam. Drawn out.

On the downstream side of the extraction electrode 32 with respect to the ion beam, there is provided a variable slit portion 33 capable of changing the slit width, and a position facing the ion beam passage is provided between the extraction electrode 32 and the variable slit portion 33. Further, an electron supply means for supplying electrons to the ion beam, for example, a plasma generator 4 is provided. As shown in FIG. 2, the plasma generator 4 includes a filament 42 made of tungsten or the like in a plasma generation chamber 41 made of, for example, molybdenum, and connects a DC power source of a voltage Vf to both ends of the filament 42.
And a wall of the plasma generation chamber 41 connected to a DC power supply of voltage Vd. In the plasma generation chamber 41, a discharge gas inlet 43 for introducing a discharge gas such as argon gas, xenon gas, krypton gas, etc., and an outlet 44 for electrons in the plasma formed by the discharge of the discharge gas are formed. ing.

On the downstream side of the ion beam in the first vacuum chamber 3, a mass analyzer 5, a second vacuum chamber 6, an acceleration tube 7, and a processing chamber 8 are installed in this order. In the mass analyzer 5, the orbit of the ion beam is bent by the mass analysis magnet 51 in the bent passage tube 52, and only desired ions are extracted by utilizing the difference in the degree of bending according to the mass of the ions. Work. Further, in the ion beam mass-analyzed by the mass spectrometer 5, there may be a case where ions having similar masses are mixed with each other. Therefore, the separation slit portion 61 for excluding ions other than necessary ions is provided in the second beam. Is provided in the vacuum chamber 6.

The accelerating tube 7 has a function of applying an accelerating voltage to the ion beam to accelerate the ion beam. In the processing chamber 8, there is provided a rotating disk 82 in which a wafer W as an object to be processed is arranged in a circumferential direction, is rotatable vertically by a horizontal rotating shaft 81, and sequentially stops each wafer at an ion beam irradiation position. A Faraday cup 83 is provided at a position facing the rotating disk 82 so as to surround the ion beam. In FIG. 1, the lower portion of the rotating disk 82 is cut away and the rotating shaft 81 is located at the center of the rotating disk 82. The Faraday cup 83 is for confining the secondary electrons generated at the time of ion implantation so as not to flow out, and accurately measuring the beam current. In the figures, Ga and Gb are gate valves,
Reference numeral 84 denotes a beam gate for controlling the irradiation and interruption of the ion beam on the Faraday cup 83 side.

Next, the operation of the above embodiment will be described.
First, the area related to the path of the ion beam including the vacuum chamber 2 is decompressed to a degree of vacuum of, for example, 5.times.10@-6 Torr, and the wafer W (only one wafer is shown in FIG. Is set to the irradiation position of the ion beam, the beam gate 84 is closed, and a drawing voltage of, for example, 5 kV is applied between the drawing electrode 32 and the apparatus main body of the ion source 31 so that the arsenic is discharged from the ion source 31, Extract an ion beam containing ions.

On the other hand, a discharge gas such as an argon gas is supplied into the plasma generation chamber 41 of the plasma generator 4 at a flow rate of, for example, 0.1.
Introduced at 1 SCCM, for example, 3V filament voltage V
f and a discharge voltage Vd of 20 to 30 V are applied between predetermined terminals, whereby the discharge gas is excited by the thermoelectrons generated from the filament 42 to generate plasma. Since the ion beam IB is formed before the outlet 44 of the plasma generation chamber 41, the electrons in the plasma in the plasma generation chamber 41 are attracted to the ion beam IB, and as a result, the ion beam IB is And electrons are mixed.

FIGS. 3A and 3B show the distribution of electric charge and the distribution of voltage in the beam cross section of the ion beam, respectively. However, the horizontal axis in the figure represents the position of the ion beam in the left-right direction, and the dotted and solid lines correspond to the case where electrons are not supplied to the ion beam and the case where electrons are supplied. As can be seen from the results, the charge distribution and voltage distribution of the ion beam rise sharply from both ends as shown by the dotted lines. However, as in this embodiment, electrons are supplied into the ion beam to neutralize the charge. Thereby, the charge distribution and the voltage distribution are flattened. Therefore, the repulsive force of the positive ions in the ion beam is reduced, so that the divergence of the ion beam is suppressed.

The ion beam supplied with electrons from the plasma generator 4 as described above is
After passing through 3, mass analysis is performed by the mass analysis magnet 51 to extract only desired ions, and further, ions having a mass very close to the mass of the desired ions (for example, sputtered from the inner wall of the ion source) at the separation slit portion 61. Particles). Thereafter, the ion beam is driven into the wafer W on the rotating disk 82 after being accelerated by the acceleration tube 7. For example, by moving the rotating disk 82 side in a direction orthogonal to the ion beam, impurities are introduced into the surface of the wafer W in a predetermined pattern. The beam gate 84 is opened after the plasma is ignited in the plasma generator 4, for example.

According to this embodiment, since the divergence of the ion beam is suppressed, the extraction energy of the ion source is reduced while the extraction voltage between the extraction electrode 32 and the apparatus body of the ion source 31 is reduced to about 5 kV. , A current of about 10 to 20 mA (a current flowing through the Faraday cup 83) can flow through the wafer W, and efficient ion implantation can be performed. Since impurities can be introduced into the wafer W with a large current while reducing the energy of the ions, when implanting shallow impurities, the implantation depth is uniform and efficient ion implantation can be performed. Very effective.

In the above embodiment, the electron supply device is disposed near the outlet of the ion source 31. However, the electron supply device is not limited to this position and may be provided between the ion source 31 and the acceleration tube 7 (including the inside of the acceleration tube 7). If so, it can be provided at any position.

The present invention may be applied to an ion implanter in which the acceleration tube 7 is installed in front of the mass analyzer 5 (upstream of the ion beam). In this case, the electron supply device is an ion source. 31 and mass spectrometer 5 (including inside mass spectrometer 5)
And the same effect can be obtained.

The present invention can also be applied to a device without the accelerating tube 7 or a device in which the Faraday cup 83 is disposed on the back side of the rotary disk 82. The present invention can be applied to a device for introducing a wafer into a wafer, and can also be applied to a case where ions are implanted into an object to be processed other than a wafer.

In the above, the present invention can be applied not only to the case where arsenic ions are implanted but also to the case where phosphorus or boron is implanted. In order to obtain impurity ions, a vaporizer is used. Alternatively, the source gas may be directly introduced into the ion source.

The electron supply device is not limited to the plasma generator 4, but may be any device capable of supplying electrons to the ion beam.

[0026]

According to the present invention, since electrons are supplied to the ion beam extracted from the ion source to flatten the voltage distribution on the beam cross section, the divergence of the ion beam can be suppressed, and Efficient ion implantation can be performed on the processing body.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a schematic perspective view for explaining the operation of the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a charge distribution and a voltage distribution of an ion beam according to an example of the present invention and a comparative example.

FIG. 4 is a configuration diagram showing a conventional ion implantation apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 Ion source 32 Extraction electrode 4 Plasma generator 41 Plasma generation chamber 42 Filament 5 Mass analyzer 7 Accelerator tube 83 Faraday cup W Wafer

Claims (2)

(57) [Claims] An apparatus for irradiating an object with an ion beam from an ion source through a mass analyzer and an accelerating tube sequentially to inject ions into the object to obtain a plasma by discharging a discharge gas. In this plasma
Plasma generation for supplying electrons to the ion beam
An apparatus provided between the ion source and the mass analyzer ;
The electrons in the plasma are attracted to the ion beam and
Weakens the repulsion of positive charges in the
An ion implanter characterized by suppressing the divergence of a beam . 2. An apparatus for irradiating an object with an ion beam from an ion source through an accelerating tube and a mass spectrometer sequentially to implant ions into the object to obtain a plasma by discharging a discharge gas. In this plasma
Plasma generation for supplying electrons to the ion beam
An apparatus is provided between the ion source and an acceleration tube, and a plasma is provided .
The electrons inside are attracted to the ion beam and the ion beam
Weakens the repulsive force of the positive charge inside, thereby reducing the ion beam
An ion implanter characterized by suppressing divergence of ions.