JP3444098B2 - Neutralization system for ion implanter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an ion implantation apparatus, in which an electron shower is applied to a sample to neutralize the sample into which positive ions are implanted. Related to the device. The ion implanter excites the gas into plasma,
An ion beam is extracted from this by the action of an electric field, accelerated to an appropriate energy, and implanted into a sample. [0002] An ion implantation apparatus includes, for example, an ion source, a mass separator, a Q lens, an acceleration tube, and a scanning device. The ion source guides the source gas and converts it into high frequency, microwave,
The plasma is excited by the action of a DC electric field or the like, and an ion beam is formed by the action of the extraction electrode. Usually, when the ion beam is narrow, it is called an ion implantation apparatus, and when the ion beam has a large diameter, it is sometimes called an ion doping apparatus. When the beam is narrow, mass separation is performed. In this method, the trajectories of ions having different masses are made different by a fan-shaped magnet, and only ions having a desired mass are extracted. If the ion beam is thin and the sample is a large-area wafer, the ion beam must be scanned two-dimensionally. [0004] The scanning mechanism is divided into those using an electric field and those using a magnetic field. In some cases, the sample is scanned one-dimensionally by an electric field or a magnetic field, and the sample is mechanically scanned in a direction orthogonal to the one. Some scan two-dimensionally by electric and magnetic fields. The problem here is the neutralization device.
Since ions have a positive charge, if they are implanted in large quantities, a positive charge is injected into the sample. In the case of a non-conductive sample, the sample is positively charged because a positive charge does not escape from the sample. This is called charge-up. A strong electric field generates a strong electric field. This may destroy the device formed on the sample surface. In order to suppress charge-up, electrons may be applied to the surface of the sample to neutralize the sample. The neutralizer is for this. [0006] A neutralizing device is a device for heating a filament to generate thermoelectrons and guiding the thermoelectrons to the surface of a sample to neutralize a positive charge. Several innovations have been made for the neutralization device. First, the neutralization device will be described. Since an ion beam is a collection of positive charges, it draws low-energy electrons by Coulomb force. What used to have only positive charges until then becomes an ion beam with a cloud of electrons. This reaches the sample surface and is driven into the sample. At this time, ions penetrate deeply into the sample, and electrons stop near the surface. The positive charge of the sample can be canceled. [0008] Such an electron is sometimes referred to as an electron shower. This is because it is a low-energy electron group generated excessively. A device that generates an electron shower and neutralizes positive charges is also referred to as a shower, a shower device, and a neutralizing device. Or a shower assembly or an E-gun. Both are synonyms. [0009] One conventional shower device is provided in the beam transport system. This is filament and filament power,
It consists of a power supply for applying a bias to the filament. The filament power supply has the effect of heating the filament to a high temperature and emitting thermoelectrons. The bias power supply is also called a gate power supply. This gives the negative voltage of the filament to the transport system and determines the kinetic energy of the thermoelectrons. Since the beam is narrow and the sample is wide, the beam is scanned right and left. The thermoelectrons emitted from the neutralizer have little energy and thus little directionality. However, if the beam energy is high, it is impossible to follow the scanning of the beam, so that the amount of electrons attached to the beam is not always constant. The in-plane uniformity of the beam is determined by the purpose. The fluctuation is defined as a maximum of 1% or 0.5%. There is no rule on the amount of neutralizing electrons. However, if the supply amount of electrons is non-uniform in the plane, the energy of beam irradiation changes. It is desired that the amount of electron irradiation be uniform within the sample surface. Thus, there are a number of problems with the neutralizer. Several proposals have been made accordingly. JP-A-2-278647 discloses an ion beam.
One neutralization device is installed in the transport route of the system. The electrons collide with the wall and produce secondary electrons. This irradiates the wafer provided at the last position of the beam transport system. The wafer is neutralized by electron irradiation. Kinetic energy alone
Is smaller than the ion beam. The electrons also reach the sample stage outside the wafer. In other words, the sample stage outside the wafer is negatively charged, rather than neutralizing. In order to avoid this and control the amount of electrons, a ring-shaped control electrode is provided immediately before the wafer. A negative voltage is applied to the control electrode with respect to the neutralizing filament. The electron distribution is narrowed to the vicinity of the center by the negative voltage. The irradiation area of the electrons and the irradiation area of the ion beam become substantially equal. It is said that the voltage of the control electrode is adjusted according to the size of the wafer so that the size of the electron distribution can always be matched with the spread of the ion beam distribution. Japanese Patent Application Laid-Open No. 3-145047 discloses one neutralizing device provided in an ion beam transport system. Tar
The required amount of neutralized electrons was determined by measuring the current incident on the get.However, the current of electrons incident on portions other than the wafer was also added, and strict neutralization conditions were required. Since it cannot be realized, the current of the neutralizing filament is adjusted so that the wafer current is measured and becomes zero. JP-A-5-217543 is the applicant of the present invention. This is not to control the total amount of neutralizing electrons, but to match the ion beam center with the electron beam center. In other words, it is a device for spatially matching positive ions and negative charges. Two neutralizers are provided on the wall of the path through which the beam passes. Further, an electrostatic lens is provided in the electronic beam path to freely adjust the direction of the electronic beam. The direction of the electron beam can be freely changed by the voltage applied to the electrostatic lens. For that purpose, the distribution of the electron beam must be known. For the measurement of the spatial distribution, the wafer is removed and, instead, a measuring device in which a number of Faraday cups are arranged two-dimensionally is placed at the position of the wafer. In this state, two neutralizers are operated to obtain a spatial two-dimensional distribution when electrons enter the wafer surface. The center position of the ion beam is known from the beginning, otherwise it can be measured by the same means. When the center of the ion beam is deviated from the center of the electron beam, the azimuth of the electron beam is finely adjusted by an electrostatic lens. Thus, the electron beam can be adjusted to the spread of the ion beam. [0015] Thermions are called thermoelectrons. In practice, electrons emitted from the filament are applied to an appropriate voltage (for example, 2
00V), it has considerable kinetic energy. Since the thermoelectrons have the same energy as the temperature of the filament, they have a small energy of about 0.3 eV. However, it cannot be extracted by itself, so a voltage must be applied between the filament and the extraction electrode. The (primary) electrons exiting the filament and accelerated by the electric field collide with the transport system walls to produce secondary electrons. The primary electrons themselves are reflected. The energy of secondary electrons is low. The collection of primary electrons and secondary electrons having different energies is a shower. Even though many low-energy electrons are included, the distribution of showers from one shower device is still uneven. This is because it is provided at one location on the wall. If the wafer (sample) is small, the effect of non-uniform electron distribution does not appear strongly. However, the size of Si wafers and glass substrates is gradually increasing. This is to increase the throughput. Then, the spatial non-uniformity of the neutralized electrons becomes more remarkable. It is a first object of the present invention to provide a neutralizing device capable of making the distribution of neutralizing electrons uniform over the entire surface of a wafer even when the wafer is wide. It is a second object of the present invention to provide a neutralization device that can make the distribution of electrons uniform over the entire surface of a sample wafer even when a narrow beam scans over a wide wafer. Although the above-mentioned Japanese Patent Application Laid-Open No. Hei 5-217543 is provided with two neutralizing devices, it is impossible to know the respective thermoelectron currents emitted from them. In addition, a new configuration is required like an electrostatic lens, and the structure is complicated. It would be desirable to have a simpler and more uniform distribution of neutralizing electrons. In order to solve such a problem, the present invention provides two equivalent neutralizing devices at symmetric positions in the beam transport path. Furthermore, the emission currents of the two neutralizers are made equal. The two devices will be referred to as a first neutralizing device or shower device A and a second neutralizing device or shower device B.
The emission current is an electron current. This is the shower device A (A ₁ ) and the shower device B (A ₂ )
To be equal. That is, the requirements of the present invention are the following two. 1. Two equivalent neutralizers are provided at symmetric locations. 2. Make the emission currents of the two devices equal. A ₁
= And A _2. DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an ion implantation apparatus comprises an ion source, a mass separator, an acceleration tube, a scanning system, a neutralizing device, a wafer support device, and the like. In each case, the inside is vacuum. Two neutralization devices of the present invention are provided in the transport path. This is shown in FIG. The ion source, the mass separator, the accelerating tube, etc. are further forward than this and do not appear in the figure. 2 shows a mechanism after the scanning device X. The beam transport path is partitioned by a beam transport system wall W. Sample table Q (susceptor) supporting sample (wafer) S at the end of transport path
Is provided. Since the ion beam is scanned, it may have a fan-shaped distribution as described above. With another scanning device, the bent beam may be bent in the opposite direction so that it is always perpendicular to the sample. Not all beams depicted here appear at once. There is only one of them at each time. Ions can be implanted into the entire surface only by scanning left and right. Two shower devices A and B are provided on the left and right of the beam path. Shower equipment is equivalent. From these, a shower of thermionic electrons is emitted equally to the beam. Electrons are attracted into the ion beam by the Coulomb force. Electrons are carried along with the ion beam and reach the sample surface. As shown in FIG.
And a filament 2 stretched therein, an extraction electrode 4 on the transportation path side having an outlet 3, an extraction power source 5, a filament power source 6, and the like. The filament 2 is a thin wire of tungsten, and is supplied with current by a filament power supply 6. When current flows through the filament, it generates heat because of the resistance. The temperature rises and thermoelectrons are emitted from the filament. Since the electrons do not go out to the outside by itself, a negative voltage is applied between the electron and the extraction electrode 4. Electrons having the energy of this voltage exit from the outlet 3. The words are defined as follows. The filament voltage Vf is a voltage applied to the filament. The filament current If is a current flowing through the filament. The intensity of thermionic emission increases in proportion to the filament current.
The extraction voltage is a voltage between the extraction electrode and the filament, and is a voltage for extraction. It is divided here into two parts. Two power supplies, an emission power supply and a gate power supply, are connected in series, and an extraction voltage is given as the sum of the two power supplies. In practice, the gate voltage is negative, and the voltage obtained by subtracting this voltage from the emission power supply is the voltage applied between the electrode 4 and the filament. The emission current A is an electron current emitted from each filament. These parameters are defined one by one for the two shower devices, which are distinguished by subscripts of 1 and 2. [0028] In the present invention it is to equalize the emission current A _1, A ₂ in two neutralizer which A ₁
It can be easily represented by = A _2. First, the meaning of this is explained. As described earlier, the primary electrons emitted from the shower device collide with the facing wall surface to generate secondary electrons. Primary electrons are also reflected. The energy distribution has roughly two peaks. Since the energy is low, it looks like a cloud of electrons, but if there is an ion beam, it is attracted to ions by Coulomb force. It is not clear what shape a cloud of electrons would have from one shower device. It is presumed that the distribution does not often have high symmetry with respect to the sample surface. In the present invention, two neutralizers are installed at positions symmetrical with respect to the wall of the beam transport system, so that the electron cloud formed thereby has a symmetric distribution with respect to the center line of the sample. There will be. The distribution of injection of electrons into the sample is
It should be more uniform than with a single shower device. This is the reason for providing two shower devices.
Another feature of the present invention is that a device is devised to equalize the distribution of electron clouds created by the two shower devices. Although the shape and dimensions are the same, the amount of emitted thermoelectrons is not always the same. The present invention measures the electron current of each shower device. Then, the electron current (emission current) is made the same by adjusting the filament current (A ₁ = A ₂ ). FIG. 3 is an electric circuit diagram of the shower device (neutralizing device) of the present invention. The shower device A is the same as that shown in FIG. A filament 2 is provided inside the box 1, a current of the filament is supplied by a filament power supply 6, and thermoelectrons are emitted from an outlet 3 of the electrode 4. The shower device B has substantially the same structure. Both have the same dimensional structure and are provided at symmetrical positions on the transport path. The shower device B has a filament 12 inside a box 11, and an extraction electrode 14 having an outlet 13 perforated at the front. The filament power supply 16 is a variable power supply. This is different from the shower device A. No filament current is measured. The sample S is set at the last point of the beam transport system. The target current detection circuit 23 and the beam current detection circuit 8 are provided in series between the sample S and the ground. A first emission current detection circuit 21 and an emission power supply 7 are connected in series between the filament 2 and the beam current detection circuit 8. Similarly, a second emission current detection circuit 2 is provided between the filament 12 and the beam current detection circuit 8.
2 and the emission power supply 7 are connected in series. A gate power supply 9 is connected between the positive electrode of the emission power supply 7 and the extraction electrodes 4 and 14. The ion beam flowing through the sample S is measured by the beam current detection circuit 8. This is A4. The electrons emitted from the filament 2 and hit the sample return from the sample S through the target current detection circuit 23 to the emission power source 7 and the first emission current detection circuit 21 to the filament 2. The electron current is measured by the first emission current detection circuit 21. This is referred to as A _1. Electrons that have come out of the filament 12 and collide with the sample return to the filament 12 through the target current detection circuit 23, the emission power supply 7, and the second emission current detection circuit 22. The electron current can be obtained by the second emission current detection circuit 22. The electron current is detected by the emission current detection circuit 2
1, 22. These values A ₁ and A ₂ are equal to the amount of thermionic emission. The comparison circuit 10 determines these A ₁ , A
Compare ₂ When these are the same, the voltage of the filament power supply 16 of the shower device B is maintained as it is. If they do not match, device B
The filament power supply 16 is adjusted. That is, A ₁ > A ₂
If, raising the filament voltage Vf ₂ devices B. Conversely, if A ₁ <A ₂ , the filament voltage Vf of device B
Lower ₂ The voltage Vex applied between the filament and the extraction electrode is changed from the voltage Ve of the emission power source to the gate voltage Ve.
g is subtracted. Vex = Ve-Vg. Ve
Is constant. The gate voltage Vg is variable. When the voltage Vg of the gate power supply 9 is changed, which electrode 14, 4
Similarly, the voltage changes. That is, the electron current fluctuates similarly. The gate voltage Vg changes both the shower devices A and B in the same manner. How is the gate voltage controlled? This is adjusted so that an excessive electron current can be appropriately applied to the sample S. A positive charge enters the sample S by an ion beam, and a negative charge enters by the arrival of electrons. The current by the ion beam flows through the sample S → A3 → A4 → ground. Electron current is filament → A ₁ , A ₂ → V
It flows in the order of e → A3 → sample S → filament. Then, the current flowing through A3 is obtained by subtracting the negative electron current (A ₁ + A ₂ ) from the positive ion current (A4). _{A3 = A4-A 1 -A 2} . In other words, A3 measures the total current flowing through the sample including the sign. Therefore, this is called a target current detection circuit 23.
When A3 is 0, I an ion beam current (A4) = electron current (A ₁ + A _2), a state just cancel. However, in practice, it is better to set the electron current (A ₁ + A ₂ ) to be slightly higher. These charges are counted as current not only when they enter the sample but also when they enter the sample stage Q. Electrons are poor in directionality and convergence, and more electrons hit the sample table Q than ions. Thus, a slight excess of electrons will just cancel the charge on the sample surface. Therefore, the gate voltage Vg is adjusted so that A3 becomes an appropriate negative voltage. Since the gate voltage is given as a negative voltage, reducing this reduces the electron current. Increasing this increases the electron current. A3 can be held at an appropriate value by increasing or decreasing Vg. EXAMPLE The filament has a diameter of 0.6φ and a length of 10
0 mm tungsten. This is installed in both shower devices. Determine the voltage of the filament power supply appropriately,
A current of about 20 A flows through the filament. 200V is applied to this as an emission voltage. On the other hand, the beam current (A4) is about 1 mA. Target current (A
3) is set to about -600 μA (the electron current is about 1.6 mA). The gate voltage outputs a voltage Vg enough to obtain an emission current required for neutralization. This is typically between 100V and 150V. Since this is so designed, it naturally operates as such. On the other hand, the current A of the filaments 2 and 12
_1, there is circuitry that monitors the A _2, and controls the current of the filament by changing the Vf ₂ to A ₁ and A ₂ are the same. As a result, the same shower amount is given to the target from the assembly of the shower device A and the shower device B. The electron distribution becomes almost uniform in the plane. In FIG. 1 and FIG. 3, there are two shower assemblies on the left and right, and the filament current of each can be controlled independently. For the emission current, the values (A ₁ , A ₂ ) of the device A and the device B can be measured independently. On the other hand, the left and right gate voltages are controlled by the same voltage. Beam current (A4) and shower current (A ₁ + A ₂ ) for target
Flows. Since it is desirable that the shower currents A ₁ and A ₂ are the same for both the left and right sides, the voltage Vf _{2 of the} filament 12 is changed and controlled (the filament voltage Vf ₁ is fixed at this time). Absolute amount of electron current (A ₁ + A ₂ )
Is controlled by the gate voltage Vg. According to the present invention, two neutralization devices are provided in the beam transport path of the ion implantation device so that the electron current for neutralization is equal in both devices. Even if the ion beam is scanned left and right and the electron distribution is different at the scanning point, the neutralized electrons are supplied from the two electron sources, so that the electron distribution is always uniform in the sample plane. Therefore, charge-up can be prevented over the entire surface of the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view schematically showing a beam transport tube of an ion implantation apparatus of the present invention provided with two shower devices. FIG. 2 is a schematic perspective view of a shower device. FIG. 3 is an electric circuit diagram of two shower devices and a sample current measuring device. [Description of Signs] 1 Box 2 Filament 3 Exit of shower device 4 Extraction electrode 5 Extraction power supply 6 Filament power supply 7 Emission power supply 8 Beam current detection circuit 9 Gate power supply 10 Comparison circuit 11 Box 12 Filament 13 Shower device exit 14 Extraction Electrode 16 Filament power supply 21 First emission current detection circuit 22 Second emission current detection circuit 23 Target current detection circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 37/317 C23C 14/48 H01J 37/20 H01L 21/265 H01J 37/04

Claims (1)

(57) [Claim 1] An ion source that excites a source gas into an ion beam, a beam transport system that transports an ion beam emitted from the ion source, and a scanning device that scans the ion beam. In an ion implanter including a sample stage for holding a sample, two electron shower devices for generating thermoelectrons by a filament at symmetric positions with respect to the sample in the beam transport system are provided, and emission currents of the two electron shower devices A and B are provided. A neutralization system for an ion implantation apparatus, characterized in that A1 and A2 are measured and the filament voltage is controlled so that they are the same.