JPH0325846A - Charge neutralization device in ion beam irradiation device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a device that neutralizes charge-up with electrons in order to reduce charge-up that occurs on the surface of an insulating film of a target during ion beam irradiation in an ion beam irradiation device. The aim is to realize a charge neutralization device that eliminates the increase in energy levels and at the same time enables highly accurate dose control. a means for introducing a gas for ionization, and a means for ionizing the ionization gas in the ionizing region to 10 to 20e.
In order to generate low-energy electrons of V or less, a high-energy electron generating means for injecting electrons having an energy higher than the ionization energy of the ionization gas into the ionization region, and accelerating and decelerating the low-energy electrons; An electron transport means for transporting electrons to a vicinity of an ion beam irradiation region on a target, and a connecting means surrounding the electron transport means to create a gas pressure difference between the ionization region and the ion beam irradiation region. Construct it in a certain way. [Industrial Field of Application] The present invention is an ion beam irradiation device for implanting impurities into semiconductor substrates etc. by ion implantation, in order to reduce charge-up that occurs on the surface of an insulating film of a target during ion beam irradiation. The present invention relates to a device that neutralizes the charge-up using electrons.

[Conventional technology]

(1) Overview of the ion beam irradiation device ■ Overview of the device Figure 5 is a diagram explaining the outline of the ion beam irradiation device, (a) is a schematic diagram of the entire device, and (b) is a schematic diagram of the target. .

The ion beam 11 is obtained by extracting ions produced by the ion source 1 and separating and accelerating only the necessary ions.

For example, 1) Introducing a gas containing impurities to be implanted into the ion source,
The ion source 1 is driven by the ion source power source 2 to generate a plasma state, and ions are created therein. By the way, the gas pressure inside the ion source 1 is 10"" to 10't.
It is about orr.

2) The ions of 1) are extracted by the extraction electrode 4, extracted by the vacuum container 5, and separated by mass by the magnet section 6 and slit 7 to separate only the necessary target ions.In the vacuum container 5, 10 by vacuum pump not shown in the figure
The degree of vacuum is maintained at about −' to 10” torr.

3) The ions that have passed through the slit 7 are accelerated by the potential difference between the casings 8 and 9, and are irradiated onto the target 13 in the end station 12. By the way, the vacuum level at the end station is maintained at about 10-'torr. The ion beam 11 is obtained in the above manner.

Note that the extraction of ions in 2) above is based on the ions fl
Due to the potential difference of the power supply 141 between l and the extraction electrode 4, the above 3
) is accelerated by the power supply E between the casings 8 and 9.
The ion source 1 and the vacuum container 5 are insulated with an insulating material 3, and the casings 8 and 9 are insulated with an insulating material IO. By the way, El is about 30 to 80KV, and E2 is about O to 170KV. On the other hand, the target 13 has a semiconductor wafer 15 placed on a disk 14, and the disk 14 is rotated at high speed and simultaneously moved up and down in the upward direction in the figure, and the entire surface of the wafer 15 is irradiated with the ion beam II. FIG. 6 is a diagram illustrating the potential of each part of the ion beam irradiation device.

Although the potential of the end station 12 is O (ground potential), the vacuum container (ion extraction section) 5 has a potential E2, and the ion source 1 has a potential E2 + El.

Further, the magnet section 6 is located in the middle of the vacuum container (ion extraction section) 5.

(2) Advantages of the ion implantation method The advantage of the ion implantation method is that the amount and energy of impurity ions implanted into the wafer 15 can be accurately controlled.

That is, by measuring the current flowing between the target 13 and the ground using the ammeter 17, the amount of ions (dose amount) implanted into the wafer 15 can be accurately determined.

Further, the amount of energy during ion implantation can be accurately determined by the ion acceleration voltage.

(2) Charge-up of insulating film In recent years, the use of ion implantation technology in the high dose region has increased, and high current ion implantation equipment reaching 20 to 30 mA is being put into practical use.

However, in these high-current ion implanters, the amount of charge supplied to the target surface per unit time increases, so there is a problem that the insulating film of the target may break down due to charge-up.

On the other hand, on the device side into which ions are implanted, the thickness of the insulating oxide film is decreasing due to finer processing of elements. Also,
Due to the contact 1 with the semiconductor substrate, the small window area, etc., the resistance to the charge amplifier is reduced, which aggravates the above-mentioned problem.

For example, in recent LSIs and the like, even a charge-up of about 20 V can cause dielectric breakdown.

Therefore, charge-up is neutralized by electrons. This is the charge neutralization device 16 shown in FIG.

(2) Conventional charge neutralization device FIG. 7 is a diagram illustrating a conventional charge neutralization device.

This charge neutralization device performs neutralization using secondary electrons, and is installed just before the target 13.

That is, the filament 2 heated by the power source E5
0, a bias voltage of -100 to -300 V is applied by a power source E6, and a voltage regulator 21 with a lower potential of several tens of volts is provided around the filament 20 by a power source E4.

Therefore, the primary electrons 23 emitted from the filament 20 are accelerated by the mesh electrode 22 at ground potential, cross the ion beam 11, and are irradiated onto the opposing Faraday electrode 19 (secondary electron generating section).

As a result, low-energy secondary electrons 24 are emitted from the wall of the Faraday electrode 19, and the secondary electrons 24 are attracted by the ion beam 11 and the positive charge on the wafer 15, reach the wafer 15, and are charged up. This cancels out the positive charge on the insulating film.

In addition, the subreduction electrode l8 has two roles.
The first is to prevent the secondary electrons 24 emitted from the Faraday electrode 19 from moving in the direction opposite to the target 13 and leaking, and the second is to prevent the wafer 15 from being irradiated with the ion beam l1. This is to prevent secondary electrons emitted from the wafer 15 from leaking out of the Faraday electrode 19 when this happens.

For this purpose, the subreduction electrode 18 has a voltage of -1000V.
A bias voltage of approximately 100 mL is applied by power source E3.

If the secondary electrons emitted from the wafer 15 are not captured by the Faraday electrode 19 and leak, the current due to the secondary electron emission is added to the ammeter 17, causing an error in measuring the dose amount. .

(3) Conventional charge neutralization device■ FIG. 8 is a diagram illustrating a conventional charge neutralization device (2).

This charge neutralization device (2) introduces a gas such as Ar into the ion beam irradiation area 26 immediately in front of the target 13, ionizes the Ar gas, and performs neutralization with low-energy electrons generated at that time.

Ionization occurs when introduced gas molecules are excited by the ion beam 1l, and high-energy electrons are injected into the gas in order to create more actively ionized low-energy electrons.

That is, a bias voltage of -100 to -300V is applied to the filament 20 heated by the electric current IE5, and a repeller 21a is provided to surround the filament 20 and the ion beam irradiation area 26, A potential several tens of volts lower is applied to the electrode 21a by the voltage aU4.

Therefore, the electrons 23 emitted from the filament 20
The rays a are accelerated by the mesh electrode 27 and enter the Ar gas to excite and ionize the Ar gas molecules.

In addition, the electron 23a is decelerated and reflected by the lever electrode 21a, and the electron 23a repeats the reciprocating motion as shown in FIG.
The r gas molecules are excited and eventually captured by the mesh electrode 27.

In the figure, Ar' indicates an ionized positive ion, and e- indicates an ionized low-energy electron.

The ionized low-energy electrons are attracted by the ion beam l1 and the positive charges on the wafer 15, reach the wafer 15, and cancel out the charged-up positive charges on the insulating film. On the other hand, the Ar'' ions are attracted and captured by the blade electrode 21a. The role of the subtraction electrode 18 is the same as that of the charge neutralization device (2) described above.

[Problems to be Solved by the Invention] (1) Problem with the conventional charge neutralization device (■) However, in the charge neutralization device described above, there is a problem that high-energy recoil electrons 25 are incident on the wafer 15. .

That is, when the recoil charges 25 are incident on the insulating film on the wafer 15, the insulating film is negatively charged up, causing breakdown of the insulating film in the same way as when positive charges are charged up.

(2) Problem with conventional charge neutralization device (2) Also, in the charge neutralization device (2) described above, there is a problem that the degree of vacuum near the target decreases due to the introduction of ionizing gas. Ru.

In other words, in order to promote ionization and generate many low-energy electrons, it is necessary to increase the gas pressure, but increasing the gas pressure reduces the degree of vacuum. When the degree of vacuum decreases, the introduced gas flows through the subreduction electrode l.
The low energy electrons excited and ionized by the ion beam 11 are combined with the ion beam l1 at the outflow portion to generate a neutral beam.

However, since the neutral beam is not measured by the ammeter 17, an error will occur in dose control.

Therefore, at present, in order to suppress the adverse effect on dose control accuracy, the standard degree of vacuum is limited to about 1 to 2×10 −'torr, and electron supply efficiency by gas ionization cannot be fully utilized.

Note that a neutral beam is also generated within the repeller electrode 21a, but within the repeller electrode 21a, Ar" ions (positive ions) having the same charge as the low-energy electrons consumed for neutralizing the ion beam are detected by the ammeter 17. The present invention solves the above-mentioned problems with charge neutralization devices in conventional ion beam irradiation equipment, and eliminates the problem of charge neutralization devices in conventional ion beam irradiation equipment. The object of the present invention is to realize a charge neutralization device that eliminates target charge-up and at the same time enables highly accurate dose control by providing an ionization region.

[Means to solve the problem]

FIG. 1 is a diagram explaining the basic principle of the present invention.

The present invention provides an ionization region that serves as a source of low-energy electrons at a location separate from the ion beam irradiation region, and provides a means for transporting low-energy electrons between the two regions, and at the same time provides a means for transporting low-energy electrons between the two regions. The feature is that the conductance to gas is small. That is, this is a charge neutralization device in an ion beam irradiation device having the following configuration.

An ionization region 30 surrounded by electrodes 29 with a voltage of ±20 V or less with respect to the ground potential, a stage 31 for introducing an ionization gas 31a into the ionization region 30, and a step 10 for ionizing the ionization gas in the ionization region 30. Low energy electrons below ~20eV34
In order to generate electrons 3 having higher energy than the ionization energy of the ionization gas in the ionization region 30,
3 constitutes a source of low energy electrons. Then, the low energy electrons 34 are transferred to the target 13a.
In order to transport the ion beam to the vicinity of the upper ion beam irradiation area 37,
By means of an electron transport means 35 that accelerates and decelerates the low energy electrons 34, and a connecting means 36 that surrounds the electron transport means 35 and creates a gas pressure difference between the ionization region 30 and the ion beam irradiation region 37. , the low-energy electron transport part, which has low conductance for gases, should be avoided.

(Function) The device of the present invention excites and ionizes the ionizing gas molecules by injecting high-energy electrons 33 from the high-energy electron generating means 32 into the ionizing gas introduced into the ionizing region 30. Energy electrons 34 are generated.

In this case, the ionization region 30 is provided in a separate location from the ion beam irradiation region 37, and both regions 37 and 30 are connected by a low conductance connecting means 36, so that the gas in the ionization eM region 30 is Even if the pressure is increased, the gas pressure in the ion beam irradiation region can be kept low, and a low pressure that does not affect dose control can be ensured in the ion beam irradiation region.

Of course, the gas in the ionization region 30 also diffuses into the ion beam irradiation region 37, but it is possible to ensure a pressure difference corresponding to the conductance of the 1,000-stage connection 36.

On the other hand, since the gas pressure in the ionization region 30 can be increased, it is possible to promote ionization in the ionization region 30 and increase the amount of ionized low-energy electrons generated. By transporting the ion beam to the ion beam irradiation region 37 using the electron transport means 35, charge-up of the target 13a can be sufficiently canceled.

In this case, the potential of target l3a is the ground potential,
The potential of the electric tri region 30 is set to ±20V by the electrode 29.
Since the target 13a is maintained within the range of 13a, negative charge-up by electrons that would lead to destruction of the target 13a does not occur.

In addition, in order to transport the low-energy electrons 34, the low-energy electrons 34 are accelerated and transported so as not to be diffused, and at the same time, they are decelerated at a position just before the ion beam irradiation region 37, and the energy of the electrons is reduced to the value in the ionization region 30. is returning to.

〔Example〕

FIG. 2 is a diagram explaining the embodiment.

(1) Structure and action■Low-energy electron generation part (ionization part) In this embodiment, the electrode region 30a is covered with a mesh-like electrode 29a, and the mesh-like electrode 29a is brought to a potential within ±20V by the power source EOa. I keep it.

Furthermore, Ar gas is introduced from the gas introduction section 3lb because of its low ionization voltage and which does not cause contamination of semiconductor wafers and the like.

On the other hand, the filament 2 (K
, a bias voltage of 100 to -300V is applied to the power supply H6, and a power supply [!] is applied around the filament 20. 4, a leveler 2lb with a potential lower by several tens of volts is provided, and electrons emitted from the filament 20 are accelerated by a mesh electrode 29a and made to enter the ionization region 30a. In the case of this example, a magnetic field of about 60 Gauss was applied to the entire ionization region 30a to give swirling motion and drift motion to the incident electrons, thereby further increasing the ionization efficiency of the Ar gas.

(2) A cylindrical portion 36a is provided to connect the ionization region 30a above the connecting means and the transport means and the ion beam irradiation region 37. Incidentally, the size of the cylindrical portion was 3 cmφ×4 cm.

A mesh-like acceleration/deceleration electrode 35a was provided inside the cylindrical portion 36a, and a maximum potential of approximately 200 V was applied to the acceleration/deceleration electrode 35a by a power source E7. Also,
A mesh electrode 22a is provided at a position where the cylindrical portion 36a is connected to the Faraday electrode 19a.
A mesh electrode 29a covering the ionized region 30a
By making the potential the same as that of the ion beam irradiation area 3,
The electric field of the acceleration/deceleration electrode 35a to 7 is shielded.

■Target and ion beam current measurement Target 13
The wafer 15 is placed on the disk 14, and the S
The ion beam current is measured by connecting the boar disk 14 and the Faraday electrode 19a and connecting it to the ground via the ammeter 17. In addition, subreduction electrode l
8 is given a potential of about -1000V by the power source E3.

■Effects of acceleration/deceleration electrodes FIG. 3 is a diagram illustrating the action of the acceleration/deceleration electrode.

The acceleration/deceleration electrode 35a has an arcuate shape on the ionization region 30a side and the ion beam irradiation region 37 side, and equipotential surfaces 39a .
39b also has an arc shape as shown in the figure.

Therefore, the force that the electron shown by e- in the figure receives at each point shown by A-D in the figure is as follows.

1) The electrons at points A and B receive a force perpendicular to the equipotential surface 39a and toward the high potential side.

Therefore, at point A, the force is applied in the FI3 direction, and at point B, the force is applied in the F24 direction.

Therefore, at point A, a force F that accelerates the electrons and a force F3 that focuses the electrons act. Further, at point B, a force F2 that accelerates the electrons and a force F4 that focuses the electrons act.

2) The electrons at points C and D receive a force perpendicular to the equipotential surface 39b and toward the high potential side.

Therefore, at point C, in the F'st direction, and at point D, F61
Receives force in one direction.

Therefore, at point C, a force F5 that decelerates the electrons and a force F that focuses the electrons act. Further, at point D, a force F that decelerates the electrons and a force F8 that focuses the electrons act.

As a result of the above, electrons can be transported along the travel path shown in the figure without spreading or failing. In addition, the equipotential surface 39a
Since the amount of energy accelerated by and the amount of energy decelerated by the equipotential surface 39b are equal, no change in the amount of energy is given when electrons are transported by the acceleration/deceleration electrode 35a.

■Electron arrival efficiency and potential of the ionized part Figure 4 is a diagram explaining the relationship between the electron arrival efficiency and the potential of the N region. (a) is a diagram when transported electrons go straight to the Faraday electrode; (b) is a diagram in which the progress of transported electrons is blocked by a potential barrier generated at the Faraday electrode, and (c) is a diagram showing the potential energy of electrons at each part.

Figure (a) shows that electrons transported by the acceleration/deceleration electrode 35a travel straight and are captured by the Faraday electrode 19a.

Therefore, the transported electrons cannot contribute to canceling the charge-up of the insulating film of the wafer 15.

This situation occurs because the potential of the ionized region is low, and can be prevented by making the potential a little higher (positive), allowing the transported electrons to move along the ion beam 11 onto the wafer 15. Can be attracted to positive charges.

The figure (b) shows that when the ion beam 11 was irradiated onto the wafer 15, a sputtering phenomenon occurred on the insulator such as the resist material on the wafer 15, and the resist material adhered to the Faraday electrode 19a as dirt 40. This shows that the dirt 40 is charged by the transported electrons and the secondary electrons ejected from the wafer 15, creating a potential barrier.

Therefore, the transported electrons become difficult to overcome the potential barrier and cannot contribute to canceling out the insulating film charge amplifier of the wafer 15.

In such a case, by making the potential of the ionization region slightly lower (negative), it becomes possible to pass through the potential barrier, and the transported electrons are attracted to the positive charges on the wafer l5 along the ion beam l1. Can be done.

Figure (c) shows the case of (a) and the case of (b),
This is explained using the potential energy of a thunderbolt, with the vertical axis representing the potential energy of the electron and the horizontal axis representing the position (distance M) of each region.

That is, the potential energies of electrons in the ionized region 30a and the mesh electrode 22a have the same value within the range of ±20 eV, and the acceleration/deceleration electrode 35a located between them has a potential energy of 200 eV.

Therefore, if the potential energy of the electrons is decreased by increasing the potential of the ionized region 30a (positive), the acceleration and
The potential energy of the electrons transported by the deceleration electrode 35a also decreases, and they no longer go straight to the Faraday electrode 19a.

On the other hand, if a barrier 41 due to dirt is formed between the target 13 and the target 13, the potential energy of the electrons can be increased by lowering the potential of the ionized region 30a (to make it negative), thereby accelerating the electrons.
The potential energy of the electrons transported by the deceleration electrode 35a also increases, allowing them to proceed beyond the barrier 41 caused by the dirt.

Further, the reason why the potential of the ionized region is set to ±20V is to reduce the potential difference with the target l3 which is at the ground potential. That is, by reducing the potential difference, negative charge-up due to electrons on the wafer l5 is prevented.

(2) Example of use of the embodiment device In the device (1) above, when Ar gas is introduced into the ionization section 38 at a flow rate of 0.3 cc/sin and the pressure in the ionization region 30a is set to approximately I x 10-' torr. , the pressure in the ion beam irradiation region 37 of target l3 could be maintained at about 2×10-'torr.

As a result, the error in dose measurement became negligible.

In this case, the pressure in the ionization region 30a is approximately five times higher than the conventional pressure (gas molecule density), and the ionization efficiency of the Ar gas is also good, making it possible to almost completely prevent charge-up of the target port 3. did it.

〔Effect of the invention〕

As described above, according to the present invention, an ionization region serving as a source of low-energy electrons is provided at a location different from the ion beam irradiation region, and a means for transporting low-energy electrons is provided between the two regions. By reducing the conductance of the transport means to the gas, it is possible to increase the gas pressure introduced into the ionization region and increase the ionization efficiency, and at the same time, it is possible to increase the ionization efficiency by increasing the gas pressure in the ion beam irradiation region. The pressure can be reduced to no pressure.

Therefore, charging up of the target can be completely prevented without affecting dose control.

As a result, by using the charge neutralization device of the present invention, it is possible to realize an ion beam irradiation device that enables highly accurate dose control.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the basic principle of the present invention, and FIG. 2 is a diagram explaining the basic principle of the present invention.
Figure 3 is a diagram explaining the action of the acceleration/deceleration electrode. Figure 4 is a diagram explaining the relationship between the electron arrival efficiency and the potential of the ionized region. (a) is a diagram explaining the transport (b) is a diagram where the transported electrons are blocked from advancing by a potential barrier generated at the Faraday electrode.
(c) is a diagram showing the potential energy of electrons in each part, FIG. 5 is a diagram explaining the outline of the ion beam irradiation equipment, (a) is a diagram of the entire equipment, (b) is a diagram of the target, FIG. 6 is a diagram explaining the potential of each part of the ion beam irradiation device. FIG. 7 is a diagram explaining a conventional charge neutralization device. FIG. 8 is a diagram explaining a conventional charge neutralization device. , is. In the figure, 1 is an ion source, 2 is a power source for the ion source, and 3.
10 is an insulating material, 4 is an extraction electrode, 5 is a vacuum container (ion extraction part), 6 is a magnet part, 7 is a slit, 8.9
is a housing, l1 is an ion beam, 12 is an end station, 13, 13a is a target, 14 is a disk, 15
is a wafer, l6 is a charge neutralization device, 17 is an ammeter, 18
is a subreduction electrode, 19. 19a is a Faraday electrode, 20 is a filament, 21.21a. 2lb beam electrode, 22.22a is mesh electrode, 23. 23
a is a primary electron, 24 is a secondary electron, 25 is a recoil electron, 26
27 is the ion beam irradiation area, 27 is the mesh electrode, and 28 is the ion beam irradiation area.
．． 38 is an ionization part, 29 is an electrode, 29a is a mesh electrode, 30. 30a is an ionization region, 3l is an ionization gas introduction means, 3.1a is an ionization gas, 3lb is a gas introduction part, 32
33 is a high energy electron, 34 is a low energy electron, 35 is an electron transport means, 35
36 is an acceleration/deceleration electrode, 36 is a connecting means, 36a is a cylindrical portion, 37 is an ion beam irradiation area, 39a and 39b are equipotential surfaces, 40 is dirt, and 4l is a dirt barrier.

Claims (1)

[Scope of Claims] An ionization region (30) surrounded by electrodes (29) with a voltage of ±20V or less with respect to the ground potential, and means (31) for introducing an ionization gas (31a) into the ionization region (30). , ionizing the ionizing gas in the ionizing region (30)
In order to generate low-energy electrons (34) of ~20 eV or less, electrons (33) having energy higher than the ionization energy of the ionization gas are placed in the ionization region (30).
a high-energy electron generation means (32) that injects the low-energy electrons (34); and an electron transport means (35) that accelerates and decelerates the low-energy electrons (34) and transports them to the vicinity of the ion beam irradiation area (37) on the target (13a). , comprising a connecting means (36) surrounding the electron transport means (35) and creating a gas pressure difference between the ionization region (30) and the ion beam irradiation region (37). Charge neutralization device for ion beam irradiation equipment.