JP3460242B2 - Negative 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 a negative ion implanting device for implanting negative ions into an object to be ion-irradiated.
The present invention relates to a negative ion implanter capable of reducing charge-up of an ion irradiation target due to negative ion implantation.

[0002]

2. Description of the Related Art An ion implanter ionizes impurities to be diffused, extracts ions by an electric field to form an ion beam, then forms a beam of desired ions by mass spectrometry using a magnetic field, By accelerating and irradiating the ion irradiation target with an ion beam, impurities are injected into the ion irradiation target, and the impurities that determine the device characteristics can be controlled at an arbitrary amount and depth with good controllability. The ability to inject makes it an important device in current integrated circuit manufacturing.

As the above-mentioned ion implanter, a positive ion implanter for extracting positive ions from a positive ion source to form a positive ion beam and implanting positive impurity ions into an ion irradiation target has been put into practical use.

For example, in the injection of positive ions in the manufacture of a TFT liquid crystal display panel, as shown in FIG. 7, a glass substrate 61 is held by a substrate holding member 62 made of a conductor such as metal in an injection station. In this state, the positive ion beam 50 is irradiated. Then, in order to measure the dose amount, the Faraday cup 6 is placed at a place different from the actual injection position (setting position of the glass substrate 61).
3 is provided, and the current of the positive ion beam 50 incident on the Faraday cup 63 is measured by the current measuring device 64 provided between the Faraday cup 63 and the ground portion.

By the way, in the above case, the conductor portion 61b formed on the surface of the glass substrate 61 is in a floating state. Therefore, by the implantation of positive ions, both the insulator portion 61a and the conductor portion 61b on the surface of the glass substrate 61 are positively charged.
In addition, secondary electrons fly out from the irradiation surface of the positive ion beam 50. Some of the ejected secondary electrons (having relatively low emission energy) return to the surface of the glass substrate 61 again, and the other secondary electrons (having relatively high emission energy) are emitted from the glass substrate 61. Will end up. The surface of the glass substrate 61 is further positively charged by the emitted secondary electrons. Therefore, assuming that the leakage resistance of the insulator portion 61a can be ignored, the change in the surface potential of the glass substrate 61 with respect to the positive ion implantation amount is
As shown in FIG. 8, the insulator portion 61 a and the conductor portion 61
In both b, the potential rises almost in proportion to the increase in the injection amount (positive charge-up phenomenon). Due to the increase in the surface potential of the glass substrate 61, an electric field is generated between the surface of the glass substrate 61 and the substrate holding member 62, and when the electric field becomes large,
Eventually, there arises a problem that the device is destroyed due to dielectric breakdown.

Further, for example, when implanting positive ions in the manufacture of an LSI, as shown in FIG. 4, an ion irradiation target having an insulator portion 51a such as a polysilicon film on the surface portion at an implantation station is used as an ion irradiation target. A silicon wafer 51 is a wafer holding member 52 made of a conductor such as metal.
While being held in the Faraday cup 53, the Faraday cup 53 for measuring the implantation dose is irradiated with the positive ion beam 50.

The wafer holding member 52 and the Faraday cup 53 are grounded for current measurement, and the beam current is measured by the current measuring device 54 provided between the wafer holding member 52 and the Faraday cup 53 and the grounding portion. It Then, the dose amount is obtained from the measured value of the beam current, and the dose amount is controlled by an implantation controller (not shown).

By the way, in the above case, the insulator portion 51a of the silicon wafer 51 is positively charged with the positive ion implantation. Also, the silicon wafer 5
Since secondary electrons are emitted from the irradiation surface of the positive ion beam 50 in No. 1, the insulator part 51a is further charged to the positive polarity. Therefore, assuming that the leakage resistance of the insulator part 51a is negligible, the change of the surface potential with respect to the implantation amount is such that the conductor part 51b is always at the ground potential as shown in FIG. The potential rises almost in proportion to the increase in the amount (positive charge-up phenomenon). An electric field is generated between the insulator part 51a and the conductor part 51b due to the increase in the potential of the insulator part 51a, and when the electric field becomes large, a problem occurs that dielectric breakdown eventually occurs and the device is destroyed. Become.

Therefore, in order to suppress the above positive charge-up phenomenon, it is necessary to take measures such as electron shower, plasma bridge, or gas introduction for charge compensation. The electron shower generates thermoelectrons and causes the thermoelectrons to collide with the Faraday cup 53,
The secondary ions ejected from the collision surface electrically neutralize the positive ion beam 50 to suppress the charge-up phenomenon. Further, in the plasma bridge, a plasma source is installed in the passage of the positive ion beam 50, and an inert gas such as argon is turned into plasma by the plasma source, so that the positive potential of the positive ion beam 50 in the plasma is changed. The electron is attracted and the positive ion beam 50 is electrically neutralized. Further, in the gas introduction, by introducing an inert gas such as argon into the vicinity of the silicon wafer 51, the introduced gas is ionized into plasma by collision of positive ions, and plasma is generated in the positively charged silicon wafer 51. The electrons of are attracted to prevent charge-up.

As described above, the positive ion implanter requires a means for charge compensation, resulting in high cost. In addition, since it is very difficult to control the charge compensation using the above-mentioned means for charge compensation, it is difficult to sufficiently suppress the charge-up.

On the other hand, when the negative ion beam 50 'is irradiated to the silicon wafer 51 to perform the negative ion implantation process, the negative ion beam 50' is irradiated on the insulator portion 51a of the silicon wafer 51. At the same time that the negative charges are accumulated by the negative ions, secondary electrons are emitted from the ion irradiation surface, and as a result, it is difficult for the charges to be accumulated in the insulator portion 51a. Therefore, the negative ion implantation process using the negative ion implanter is less likely to cause a charge-up phenomenon than the ion implantation process using the positive ion implanter that implants positive ions, and is effective in creating a device. I can say.

[0012]

However, even in the case of the above-mentioned negative ion implantation process, if the silicon wafer 51 is grounded to measure the beam current, the conductor portion 51b on the surface of the silicon wafer 51 becomes the ground potential. Therefore, the conductor portion 51b serves as a secondary electron emission source, and the insulator portion 51a is charged to a negative potential by the secondary electrons emitted from the conductor portion 51b.

That is, in the insulator part 51a, when the charged particles are not supplied from the outside except for the irradiation of the negative ion beam 50 ', a current amount equal to the injection beam current amount is obtained after a predetermined time from the start of the injection. The secondary electrons (and secondary ions) are released, and the insulator part 51a should be saturated at a certain potential. The secondary electrons emitted here are apparent ones, and are low-energy secondary electrons that return to the insulator part 51a after being emitted from the beam irradiation surface.
Second electron is not included. However, in reality, the secondary electrons emitted from the conductor portion 51b are not included in the insulator portion 5b.
Assuming that the leakage resistance of the insulator portion 51a is negligible, the change in surface potential with respect to the implantation amount is such that the conductor portion 51b is always at the ground potential, as shown in FIG. However, the insulator part 51a is negatively charged up substantially in proportion to the increase of the injection amount (negative charge-up phenomenon).

When the secondary electrons emitted from the conductor portion 51b are excessively supplied to the insulator portion 51a, the electric field between the insulator portion 51a and the conductor portion 51b is strengthened and the negative ion implantation process is performed. Also in the above, there is a possibility that the dielectric breakdown of the insulator part 51a may occur and the device may be destroyed.

The present invention has been made in view of the above, and an object thereof is to prevent device breakdown due to charge-up in a negative ion implanter which is less likely to cause a charge-up phenomenon than a positive ion implanter and is effective in producing a device. It is to provide a negative ion implanter capable of preventing the negative ion implanter.

[0016]

A negative ion implanting apparatus according to the invention of claim 1 has an insulator portion and a conductor portion on an ion irradiation surface.
A holding member for holding the ion irradiation object such as a silicon wafer having bets, the Io held by the holding member
The above-mentioned ion irradiation target by irradiating the irradiation target with negative ions
In a negative ion implanter that implants negative ions into an object ,
In order to solve the above problems, the following means are taken.

That is, in the negative ion implanter, the holding member is made of an insulator.

[0018] The negative ion implantation apparatus according to the invention of claim 2 is the configuration of the invention described in claim 1, said ion
It is characterized in that it is provided with a current measuring means for collecting secondary electrons emitted from the irradiation surface of the negative ions in the irradiation object and measuring the current.

[0019]

According to the structure of the first aspect of the invention, the object to be ion-irradiated is held by the insulating holding member and is irradiated with the negative ions. That is, during the implantation of negative ions,
The ion irradiation target becomes a floating state. Therefore, after a predetermined time has passed since the negative ion implantation was started,
The number of ions injected into the ion irradiation target becomes equal to the number of secondary electrons emitted from the ion irradiation target, and the surface potential of the ion irradiation target is saturated at a certain potential (several V), Device destruction due to charge-up does not occur.

Further, as described above, when the surface potential of the ion irradiation target is saturated, the number of secondary electrons emitted is equal to the number of negative ions injected, so that the structure of the invention of claim 2 is adopted. In addition, by collecting the secondary electrons emitted from the ion irradiation target by the current measuring means and measuring the current, the negative ion implantation amount can be accurately measured, and the accurate ion implantation amount can be controlled. It will be possible.

[0021]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

The negative ion implanter according to the present embodiment basically produces negative ions in the plasma chamber and extracts negative ions from the chamber into vacuum by an electric field to form a negative ion beam. A source part, a mass spectrometric part for selecting and extracting only predetermined implanted ions, a beam line part for accelerating the ions as needed while transporting the beam, and shaping and deflecting the beam, and an injection station for performing an injection process. The negative ion beam passage path in each of these sections is a high vacuum.

In this embodiment, an example in which the above negative ion implanter is used for manufacturing a silicon LSI will be described.

At the implantation station of the negative ion implantation apparatus, as shown in FIG. 1, there is provided a rotating disk 3 on which a plurality of silicon wafers 1 as ion irradiation objects can be mounted on the circumference. . This rotating disk 3
Is driven by a disk drive mechanism (not shown) to make a reciprocating translational movement while rotating at a constant speed, so that the surface of all the silicon wafers 1 set on the rotating disk 3 is substantially uniform. Is irradiated with a negative ion beam.

The rotating disk 3 basically comprises a metal disk body 3a and a holding member 3b which is provided near the peripheral end of the disk body 3a and holds the silicon wafer 1. . The holding member 3b is made of an insulator, so that the silicon wafer 1 is held in the holding member 3b of the rotating disk 3 so that the silicon wafer 1 is in a floating state.

A cylindrical metal Faraday cup 4 is disposed on the upstream side of the rotating disk 3 in the beam traveling direction so as to surround the passage of the negative ion beam 2. The Faraday cup 4 is for collecting secondary electrons emitted from the irradiation surface of the silicon wafer 1 with the negative ion beam 2. A suppressor electrode 6 to which a negative voltage is applied from the suppressor power supply 5 is provided near the beam entrance opening of the Faraday cup 4 to suppress the outflow of secondary electrons from the Faraday cup 4.

A mask member 7 having a beam passage hole 7a for allowing the negative ion beam 2 to enter the Faraday cup 4 is provided on the upstream side of the suppressor electrode 6 in the beam traveling direction.

A catch plate 8 for catching the negative ion beam 2 when the rotary disk 3 withdraws from the passage of the negative ion beam 2 is provided behind the rotary disk 3 (downstream of the beam). There is. Further, in order to prevent the secondary electrons emitted from the beam irradiation surface from escaping from the gap between the Faraday cup 4 and the catch plate 8, a gap formed between the Faraday cup 4 and the catch plate 8 is negatively charged by the absorber power source 9. Electrode 10 to which the voltage of 10 is applied
・ 10 is provided.

The disc body 3a of the rotary disc 3, the Faraday cup 4 and the catch plate 8 are also provided.
Is grounded for current measurement.
The current flowing in these 3a, 4 and 8 is measured by the current measuring device 11 provided between 8 and the ground portion.

Further, the negative ion implanter is provided with an implant controller (not shown) for controlling the amount of ion implant based on the current value measured by the current measuring device 11.

The operation of the negative ion implanter having the above structure will be described below.

First, after the silicon wafers 1 ... Are set on the holding member 3b of the rotary disk 3, the rotary disk 3 is set.
Is driven by a disk drive mechanism, and reciprocally translates while rotating at a constant speed.

On the other hand, a beam composed of a plurality of types of negative ions extracted from the negative ion source is subjected to mass analysis by a mass analyzer, whereby a specific negative ion (for example, C
^- ) Will be formed. And
The negative ion beam 2 is subjected to processing such as acceleration, shaping, deflection, etc., if necessary, and then the beam passage hole 7 of the mask member 7 is formed.
After passing through a, the light enters the Faraday cup 4 and is irradiated onto the silicon wafers 1 ... Held by the holding member 3b of the rotating disk 3.

With the implantation of the negative ions, secondary electrons fly out from the beam irradiation surface of the silicon wafer 1. The secondary electron emission energy distribution is expressed as shown in FIG. Assuming that the surface potential of the silicon wafer 1 before the implantation is approximately 0 V, immediately after the start of the implantation, the silicon wafer 1 jumps out from the beam irradiation surface of the beam 2.
Most of the secondary electrons are emitted without returning to the surface of the silicon wafer 1 regardless of the emission energy. Therefore, the emission ratio of secondary electrons due to negative ion implantation (emission secondary per incident ion) The number of electrons) γ is 1 or more. In the case of this embodiment, since the silicon wafer 1 is held by the holding member 3b made of an insulating material so that the whole wafer is in a floating state, such as a polysilicon film forming the surface of the silicon wafer 1 is not formed. Immediately after the start of the injection, the insulator portion 1a and the conductor portion 1b are positively charged with an increase in the injection amount.

As described above, as the positive charging potential of the insulator portion 1a and the conductor portion 1b of the silicon wafer 1 increases, the emission energy of secondary electrons emitted from the beam irradiation surface is low. The thing is pulled back to the insulator part 1a and the conductor part 1b, and the emission ratio γ of the secondary electrons gradually decreases.

Then, after a predetermined time from the start of the negative ion implantation, the secondary electron emission ratio γ becomes 1 (that is, the number of incident ions becomes equal to the number of emitted secondary electrons), and the insulation The surface potentials of the body portion 1a and the conductor portion 1b are saturated. That is, in the energy distribution curve of FIG. 3, from the lower end E ₁ (eV) of the integration limit when the integrated value when integrated from the high energy side to the low energy side (the integrated value in the shaded area in the figure) becomes 1 Even if the secondary electrons of low energy go out from the beam irradiation surface, they return to the emission surface again,
Apparently, only secondary electrons having an energy of E ₁ (eV) or more are in an equilibrium state in which they are emitted from the beam irradiation surface.

Therefore, assuming that the leakage resistance of the insulator portion 1a is negligible, the changes in the surface potentials of the insulator portion 1a and the conductor portion 1b with respect to the implantation amount of negative ions are as shown in FIG.

As described above, the surface of the silicon wafer 1 is saturated at a certain potential (several V) in both the insulator portion 1a and the conductor portion 1b, so that device breakdown due to charge-up does not occur. Then, in a state where the surface potential is saturated, the number of secondary electrons emitted from the surface of the silicon wafer 1 becomes equal to the number of injected negative ions. Therefore, 2 emitted from the surface of this silicon wafer 1
The amount of negative ions can be measured by collecting and collecting secondary electrons and measuring the amount of current.

In the case of the present embodiment, the secondary electrons emitted from the surface of the silicon wafer 1 are collected in the Faraday cup 4 and the current measuring device 11 provided between the Faraday cup 4 and the ground portion. The amount of current is measured. The Faraday cup 4 and the current measuring device 11
The current measuring means according to claim 2 is constituted by the above.

During the overscan, the disk body 3a of the rotating disk 3 is also irradiated with the negative ion beam 2. However, the current measuring device 11 uses the disk body 3a.
The beam current amount is also measured during overscan. Then, the measurement value obtained by the current measuring device 11 is fetched by an implantation controller (not shown), and the implantation controller controls the ion implantation amount.

As described above, in the negative ion implantation apparatus of this embodiment, the holding member 3b for holding the silicon wafer 1 as the ion irradiation target is made of an insulator. As a result, the entire silicon wafer 1 is brought into a floating state, and a predetermined time after the negative ion implantation is started, the insulator portion 1a forming the surface portion of the silicon wafer 1 is formed.
Both the conductor portion 1b and the conductor portion 1b are saturated at a certain potential (several V), and the device breakdown due to charge-up does not occur.

In the negative ion implanter of this embodiment, the holding member 3b is made of an insulator as described above, and the Faraday which collects secondary electrons emitted from the surface of the silicon wafer 1 irradiated with negative ions. The configuration is provided with a current measuring unit including a cup 4 and a current measuring device 11 that measures the current of secondary electrons collected by the Faraday cup 4. As described above, when the surface potential of the silicon wafer 1 is saturated, the number of secondary electrons emitted from the surface of the silicon wafer 1 becomes equal to the number of injected negative ions. It is possible to accurately measure the amount of negative ion implantation from the current value measured by
Therefore, it is possible to accurately control the amount of ion implantation.

In the present embodiment, an example of implanting negative ions into the silicon wafer 1 has been described, but the present invention is not limited to this, and any ion irradiation target may be implanted with negative ions. As described above, the charge-up can be prevented and the dose amount can be measured.

The above-mentioned embodiments are intended to clarify the technical contents of the present invention, and should not be construed in a narrow sense by limiting to such specific examples. Various modifications can be made within the scope of the claims.

[0045]

As described above, the negative ion implanter according to the invention of claim 1 has an insulator portion and a conductor portion on the ion irradiation surface.
The holding member for holding the ion irradiation target having a is made of an insulator.

Therefore, the number of ions injected into the ion irradiation target becomes equal to the number of secondary electrons emitted from the ion irradiation target after a predetermined time from the start of the negative ion injection. The surface potential of the irradiation target is saturated at a certain potential (several V), and the device destruction due to charge-up can be prevented.

Further, as described above, the negative ion implanting apparatus according to the invention of claim 2 is the structure of the invention of claim 1, wherein the secondary electrons emitted from the surface of the ion irradiation target of the negative ions are irradiated. Is configured to collect the current and measure the current.

Therefore, in addition to the effect of the invention of claim 1, an accurate beam current can be obtained by measuring the current of the secondary electrons emitted from the irradiation surface of negative ions, and therefore,
Since the injection amount of negative ions can be measured accurately,
This has the effect of enabling accurate control of the ion implantation amount.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a schematic cross-sectional view showing a main part of an implantation station in a negative ion implantation apparatus.

FIG. 2 is an explanatory diagram showing changes in surface potentials of an insulator portion and a conductor portion on a surface of a silicon wafer with respect to an implantation amount of negative ions when negative ion implantation is performed by the negative ion implantation apparatus.

FIG. 3 is an explanatory diagram showing a secondary electron emission energy distribution.

FIG. 4 is a schematic cross-sectional view for explaining the ion implantation into the silicon wafer at the time of manufacturing the LSI and showing a main part of the implantation station in the conventional ion implantation apparatus.

FIG. 5 is an explanatory diagram showing changes in surface potentials of an insulator portion and a conductor portion on a surface of a silicon wafer with respect to a positive ion implantation amount when positive ion implantation is performed by the ion implantation apparatus.

FIG. 6 is an explanatory diagram showing changes in surface potentials of an insulator portion and a conductor portion on the surface of a silicon wafer with respect to the amount of negative ions implanted when negative ions are implanted by the ion implanter.

FIG. 7 is a schematic transverse cross-sectional view for explaining positive ion implantation into a glass substrate when manufacturing a TFT liquid crystal display panel and showing a main part of an implantation station in a conventional ion implantation apparatus.

FIG. 8 is an explanatory diagram showing changes in surface potentials of an insulator portion and a conductor portion on a surface of a glass substrate with respect to a positive ion implantation amount when positive ion implantation is performed by the ion implantation apparatus.

[Explanation of symbols]

1 Silicon wafer (Ion irradiation target) 1a Insulator part 1b Conductor part 2 Negative ion beam 3 rotating discs 3a disk body 3b holding member 4 Faraday cup (current measuring means) 11 Current measuring device (current measuring means)

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Japanese Patent Laid-Open No. 1-155619 (JP, A) Japanese Patent Laid-Open No. 1-315935 (JP, A) Japanese Patent Laid-Open No. 2-37656 (JP, A) Actual Flat 1- 166955 (JP, U) Japanese Patent Publication Sho 56-7292 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37/317 H01J 37/20

Claims (2)

(57) [Claims] 1. An insulator part and a conductor part are provided on the ion irradiation surface.
A holding member for holding the ion irradiation object to be, in the negative ion implantation apparatus for injecting negative ions in the ion irradiation object is irradiated with negative ions in the ion irradiation object held by the holding member, A negative ion implanting device, wherein the holding member is made of an insulator. 2. An insulator part and a conductor part are provided on the ion irradiation surface.
A holding member for holding the ion irradiation object to be, in the negative ion implantation apparatus for injecting negative ions in the ion irradiation object is irradiated with negative ions in the ion irradiation object held by the holding member, The holding member is made of an insulator, and is provided with a current measuring unit that collects secondary electrons emitted from the irradiation surface of the negative ions in the ion irradiation target and measures a current. Ion implanter.