JP6083219B2 - Plasma flood gun and ion implanter - Google Patents

Description

  The present invention relates to a plasma flood gun and an ion implantation apparatus.

  For manufacturing a semiconductor device, an ion implantation apparatus for ion-implanting impurities into a semiconductor wafer (hereinafter simply referred to as “wafer”) is used.

  As the impurity ions are implanted, positive charges are accumulated on the wafer. For example, when impurities are ion-implanted into a wafer on which a MOS transistor is formed, a large amount of positive charge may be accumulated in the electrically floating gate electrode, and the gate insulating film may be destroyed. In order to avoid such a problem, a general ion implantation apparatus is provided with a device for neutralizing positive charges.

  One apparatus for neutralizing positive charges is a plasma flood gun (PFG). The plasma flood gun generates plasma, and draws out low-energy electrons from the plasma and supplies the electrons to the wafer, thereby neutralizing charges accumulated in the wafer.

Japanese Patent Laid-Open No. 11-260309

  It is an object of the present invention to provide a plasma flood gun and an ion implantation apparatus that can further reduce the adhesion of fine particles emitted from a filament to a wafer as compared with the prior art.

According to one aspect of the disclosed technology, a guide tube, an arc chamber attached to the guide tube, a filament disposed in the arc chamber and having a curved shape, and between the filament and the guide tube disposed, possess a aperture and a hole provided in the top portion of the projection and projecting portion projecting toward the filaments, the holes in a plan view, a plasma which is disposed inside the filament A flood gun is provided.

According to another aspect of the disclosed technology, an ion generator that generates ions, an ion implantation chamber in which a wafer is disposed, and specific ions are selected from the ions generated in the ion generator and the ion implantation is performed. An ion transmission unit that transmits to the chamber; and a plasma flood gun that is disposed in the ion implantation chamber and emits electrons. The plasma flood gun includes a guide tube and an arc chamber attached to the guide tube. , A filament disposed in the arc chamber and having a curved shape, a protrusion disposed between the filament and the guide tube, projecting toward the filament, and a hole provided at the top of the protrusion possess the aperture with bets, the hole in a plan view, disposed inside the filament Ion implantation apparatus is provided that is.

  According to the plasma flood gun and the ion implantation apparatus according to the above aspect, the aperture is provided with a protruding portion that protrudes toward the filament, and a hole is provided at the top of the protruding portion. For this reason, compared with the case where an aperture is a flat plate, the number of fine particles which pass through a hole is reduced. As a result, the number of fine particles adhering to the wafer is reduced.

FIG. 1 is a schematic view showing an ion implantation apparatus according to the first embodiment. FIG. 2 is a cross-sectional view showing the structure of the plasma flood gun. FIG. 3 is an enlarged view of the plasma flood gun in a portion surrounded by a broken-line circle in FIG. 4A is a plan view showing the positional relationship between the filament and the aperture, and FIG. 4B is a cross-sectional view at the position indicated by the line I-I in FIG. 4A. FIG. 5A is a plan view showing an example of a filament and aperture of a conventional plasma flood gun, and FIG. 5B is a cross-sectional view taken along the line II-II in FIG. 5A. FIG. 6 is a cross-sectional view showing an arc chamber of a plasma flood gun according to the second embodiment. FIG. 7 is a plan view showing the positional relationship between the filament and the aperture of the plasma flood gun according to the second embodiment. FIG. 8 is a diagram (part 1) illustrating dimensions of each part of the arc chamber. FIG. 9 is a diagram (part 2) illustrating dimensions of each part of the arc chamber.

  The conventional plasma flood gun has a problem that fine particles emitted from the filament adhere to the wafer and contaminate the wafer.

  In the following embodiments, a plasma flood gun and an ion implantation apparatus that can further reduce the adhesion of fine particles emitted from a filament to a wafer as compared with the prior art will be described.

(First embodiment)
FIG. 1 is a schematic view showing an ion implantation apparatus according to the first embodiment.

  As shown in FIG. 1, the ion implantation apparatus according to this embodiment includes an ion generation unit 11, an analyzer magnet unit 12, a variable aperture unit 13, a focus unit 14, and an ion implantation chamber 15. A plasma flood gun 16 and a beam stop portion 17 are disposed in the ion implantation chamber 15. The wafer 20 to be ion-implanted is disposed in the ion implantation chamber 15.

  Gas is supplied to the ion generator 11 from the gas cylinder 21 via the valve 22. This gas contains an element that is ion-implanted into the wafer 20, such as As (arsenic) or P (phosphorus). In the ion generation part 11, the molecule | numerator in the gas supplied from the gas cylinder 21 is ionized, and ion is generated.

  An extraction electrode 11 a is provided at the end of the ion generator 11. Ions having a positive charge generated in the ion generation unit 11 are extracted to the analyzer magnet unit 12 by a negative voltage applied to the extraction electrode 11a.

  The analyzer magnet unit 12 is a kind of mass analyzer using an electromagnet. In the analyzer magnet unit 12, only specific ion species are selected from the ions extracted from the ion generation unit 11 and transmitted to the variable aperture unit 13. The analyzer magnet unit 12 is an example of an ion transmission unit.

  The variable aperture portion 13 is provided with a carbon plate 13a provided with a gap through which the ion beam passes. By changing the gap between the carbon plates 13a, the ionic species are further selected.

  The focus unit 14 is provided with a lens (electromagnetic lens) 14a. In the focus unit 14, the ion beam that has passed through the variable aperture unit 13 is shaped by the lens 14a.

  The ion beam that has passed through the focus unit 14 is injected into the wafer 20 through the plasma flood gun 16 in the ion implantation chamber 15.

  A gas such as Xe (xenon) is supplied to the plasma flood gun 16 from a gas cylinder 23 through a valve 24. Low energy electrons are extracted from the plasma flood gun 16 and move toward the wafer 20 together with the ion beam. The detailed structure of the plasma flood gun 16 will be described later.

  The beam stop unit 17 measures a current generated by ions implanted into the wafer 20. Based on the current value measured by the beam stop unit 17, the ion implantation amount (dose amount) is adjusted.

  FIG. 2 is a sectional view showing the structure of the plasma flood gun 16. In addition, the white arrow in FIG. 2 has shown the ion beam which passes through the inside of an arc chamber.

  FIG. 3 is an enlarged view of the plasma flood gun in a portion surrounded by a broken-line circle in FIG. 4A is a plan view showing the positional relationship between the filament and the aperture, and FIG. 4B is a cross-sectional view at the position indicated by the line I-I in FIG. 4A.

  As shown in FIG. 2, the plasma flood gun 16 is provided with a cylindrical guide tube 25, and the ion beam passes through the guide tube 25.

  An arc chamber 26 is attached to the peripheral surface of the guide tube 25. As shown in FIG. 3, a filament 31, an aperture 32, an extraction electrode 33, and a filament shield 34 are disposed in the arc chamber 26. Further, gas is supplied into the arc chamber 26 from the gas cylinder 23 described above.

  The filament 31 is made of tungsten, and has a shape curved in an oval shape as shown in FIG. The filament 31 generates heat when a predetermined voltage is applied during ion implantation.

  Further, a predetermined voltage is applied between the filament 31 and the wall surface of the arc chamber 26, and a discharge is generated in the arc chamber 26. By this discharge, the gas introduced into the arc chamber 26 is turned into plasma.

  The aperture 32 is a plate-like member and is disposed in the vicinity of the filament 31. A part of the aperture 32 protrudes toward the filament 31 to form a protrusion 32b. A hole 32a is provided at the top of the protrusion 32b. As shown in FIGS. 4 (a) and 4 (b), the hole 32a is disposed inside the filament 31 curved in an oval shape.

  In addition, although the material of the aperture 32 is not specifically limited, In this embodiment, the aperture 32 shall be formed with high purity carbon. In the present embodiment, the filament 31 has an oval shape. However, the filament 31 may have a circular shape.

  As shown in FIG. 3, the extraction electrode 33 is disposed outside the aperture 32 (on the guide tube 25 side). The extraction electrode 33 is provided with a hole 33a having a diameter larger than that of the hole 32a at a position aligned with the hole 32a of the aperture 32.

  The filament shield 34 is disposed outside the extraction electrode 33. The filament shield 34 is provided with a hole 34a having a diameter larger than the hole 32a and smaller than the hole 33a at a position aligned with the hole 32a of the aperture 32.

  The space in the arc chamber 26 communicates with the space in the guide tube 25 through the hole 32a of the aperture 32, the hole 33a of the extraction electrode 33, and the hole 34a of the filament shield 34.

  Hereinafter, the operation of the above-described plasma flood gun 16 will be described.

  As described above, a predetermined voltage is supplied to the filament 31 during ion implantation, and the filament 31 generates heat. Further, a discharge is generated in the arc chamber 26, and plasma is generated in the arc chamber 26 by this discharge.

  On the other hand, a predetermined voltage is applied to the extraction electrode 33. Low-energy electrons contained in the plasma in the arc chamber 26 are extracted into the guide tube 25 by the voltage applied to the extraction electrode 33 and move toward the wafer 20 together with the ion beam passing through the guide tube 25.

  By the way, along with the discharge, tungsten fine particles (hereinafter referred to as “tungsten particles”) are emitted from the filament 31. The tungsten particles emitted from the filament 31 move linearly.

  FIG. 5A is a plan view showing an example of a filament and aperture of a conventional plasma flood gun, and FIG. 5B is a cross-sectional view taken along the line II-II in FIG. 5A.

  In the conventional plasma flood gun, as shown in FIGS. 5A and 5B, the aperture 42 is a flat plate. For this reason, most of the tungsten particles jumping out from the filament 31 easily pass through the hole 42a of the aperture 42 as indicated by an arrow in FIG.

  Even in a conventional plasma flood gun, a filament shield is disposed outside the aperture 42 to prevent tungsten particles from entering the guide tube. However, it is difficult to sufficiently block the tungsten particles only with the filament shield, and the tungsten particles that have passed through the hole 42a of the aperture 42 are repeatedly reflected and enter the guide tube.

On the other hand, in the plasma flood gun 16 according to the present embodiment, as shown in FIGS. 4A and 4B, the portion provided with the hole 32a of the aperture 32 protrudes toward the filament 31 and becomes the protruding portion 3 2 b. ing. Therefore, as indicated by arrows in FIG. 4B, most of the tungsten particles that have jumped out of the filament 31 collide with the outer wall of the protrusion 3 2 b and are prevented from moving to the guide tube 25 side.

In other words, in the plasma flood gun 16 according to the present embodiment, even if the diameter of the hole 32a is the same as the hole 42a of the aperture 42 shown in FIGS. The number is remarkably reduced, and contamination of the wafer 30 with tungsten particles can be further suppressed.

(Second Embodiment)
FIG. 6 is a sectional view showing an arc chamber of the plasma flood gun according to the second embodiment, and FIG. 7 is a plan view showing the positional relationship between the filament and the aperture of the plasma flood gun.

  This embodiment is different from the first embodiment in that the diameter and number of holes provided in the aperture are different, and the other configurations are basically the same as those in the first embodiment, and thus overlap. The description of the part is omitted.

  In the present embodiment, a part of the aperture 51 arranged in the vicinity of the filament 31 protrudes toward the filament 31 to form a protruding portion 51b. The shape of the protrusion 51b is an oval shape following the shape of the filament 31 in plan view as shown in FIG. 7, and five holes 51a are arranged in a line along the longitudinal direction of the protrusion 51b at the top. It is formed with. The total opening area of these holes 51a is set to be the same as the opening area of the hole 33a of the aperture 33 of the first embodiment.

  In the present embodiment, since the diameter of the hole 51a of the aperture 51 is set smaller than that in the first embodiment, the number of tungsten particles passing through the hole 51a can be further reduced as compared with the first embodiment. Further, since the total opening area of the holes 51a is the same as the opening area of the holes 33a of the aperture 33 of the first embodiment, the amount of electrons withdrawn from the arc chamber 26 to the guide tube side is the same as that of the first embodiment. It is almost the same as the form. Thereby, the electric charge accumulated on the wafer can be sufficiently neutralized.

  Hereinafter, the result of actually manufacturing the plasma flood gun according to the second embodiment, attaching it to the ion implantation apparatus, performing ion implantation, and examining the tungsten contamination amount of the wafer will be described.

  First, as an example, a plasma flood gun including the arc chamber 26 shown in FIGS. 6 and 7 was manufactured.

  The dimensions of the arc chamber 26 are as follows. The width a shown in FIGS. 8 and 9 is 29 mm, the length b is 41.5 mm, and the height c is 14.1 mm. Moreover, the height d of the protrusion 51b of the aperture 51 is 2.5 mm, and the diameter φ of the hole 51a is 2 mm. Further, the number of holes 51a is five. Furthermore, the distance e between the filament 31 and the protrusion 51b of the aperture 51 is 0.8 mm.

As was used as an element for ion implantation into the wafer, As was used, the implantation energy was 5 keV, the implantation amount (dose amount) was 3.43 × 10 ¹⁴ ions / cm ² , and the ion beam current was ^2.5 mA.

As a result, when the plasma flood gun of the example was used, the amount of tungsten contamination of the wafer was 0.0041 atoms / cm ² . On the other hand, when the conventional plasma flood gun having the aperture 42 shown in FIGS. 5A and 5B is used, if ion implantation is performed under the same conditions as in the embodiment, the tungsten contamination amount of the wafer is 0.55 atoms / cm. ² .

  That is, in the ion implantation apparatus having the plasma flood gun according to this embodiment, the tungsten contamination amount of the wafer can be reduced to about 1/100 or less as compared with the conventional ion implantation apparatus.

  DESCRIPTION OF SYMBOLS 11 ... Ion generating part, 12 ... Analyzer magnet part, 13 ... Variable aperture part, 14 ... Focus part, 15 ... Ion implantation chamber, 16 ... Plasma flood gun, 17 ... Beam stop part, 20 ... Wafer, 21, 23 ... Gas cylinder 22, 24 ... Valve, 25 ... Guide tube, 26 ... Arc chamber, 31 ... Filament, 32, 42, 51 ... Aperture, 32a, 42a, 51a ... Hole, 32b, 51b ... Projection, 33 ... Extraction electrode, 34 ... filament shield.

Claims (5)

A guide tube,
An arc chamber attached to the guide tube;
A filament disposed in the arc chamber and having a curved shape ;
Wherein arranged between the filament and the guide tube, it has a and aperture and a hole provided in the top portion of the projection and projecting portion projecting toward the filament,
The plasma flood gun, wherein the hole is disposed inside the filament in a plan view .   The plasma flood gun according to claim 1, wherein a plurality of the holes are provided in a top portion of the projecting portion of the aperture. Plasma flood gun according to claim 1 or 2 shape is characterized by a circular or oval shape the curvature.   The plasma flood gun according to any one of claims 1 to 3, wherein the filament is made of tungsten. An ion generator that generates ions;
An ion implantation chamber in which the wafer is placed;
An ion transmission unit that selects specific ions from the ions generated in the ion generation unit and transmits the selected ions to the ion implantation chamber;
A plasma flood gun disposed in the ion implantation chamber for emitting electrons;
The plasma flood gun is
A guide tube,
An arc chamber attached to the guide tube;
A filament disposed in the arc chamber and having a curved shape ;
Wherein arranged between the filament and the guide tube, it has a and aperture and a hole provided in the top portion of the projection and projecting portion projecting toward the filament,
The ion implantation apparatus characterized in that the hole is arranged inside the filament in a plan view .

Images