JP2818539B2 - Ion implantation method and apparatus therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation method and apparatus, and more particularly, to an ion implantation method for ion implantation into a semiconductor substrate while controlling a pressure in an ion beam path from an ion mass analyzer to an implantation chamber. The present invention relates to an injection method and an injection device.

[0002]

2. Description of the Related Art In recent years, it has been required to form a junction surface with a high impurity implantation depth in accordance with a higher degree of integration of a semiconductor integrated circuit or formation of a shallow junction surface. Such a precise bonding surface is formed by an ion implantation method, which is considered difficult by a normal thermal diffusion method. However, semiconductor devices manufactured by these ion implantation methods are:
In order to obtain uniform quality, it was necessary to stably obtain the impurity implantation concentration. However, irradiation of the ion beam causes degassing from the workpiece and gas release from the ion beam path and the implantation chamber, causing pressure fluctuations in the ion beam path, causing an ion dose error and degrading the performance of the semiconductor device. There was a problem that it could not be obtained.

FIG. 3 is a diagram showing an ion beam path portion after a mass analyzer for explaining an example of a conventional ion implantation apparatus. FIGS. 4A to 4C show ion implantation times and ion beam paths in the ion beam path. It is a graph which shows the behavior of pressure. An example of an ion implantation apparatus that solves such a problem is disclosed in JP-A-61-271739.

As shown in FIG. 3, the ion implanter includes an ion source 8 for generating ions, an ion source 8 including a mass analyzer for extracting ions from the ion source and forming an ion beam 10, a semiconductor, and the like. Vacuum pump 3 for evacuating injection chamber 16 containing semiconductor wafer 20 as a substrate
0, and an ion beam opening 4 for measuring and measuring the ion dose, which is disposed on the side of the implantation chamber 16 in the ion beam path.
A Faraday current collecting system 36 for detecting the beam current from 0, a dose measuring system 42 for measuring the detected beam current and integrating it with time to obtain a dose, and a vacuum chamber 12 surrounding the ion beam path in a vacuum. A vacuum pump 14 for evacuating, a vacuum pump 30 for evacuating the injection chamber 16, and a vacuum chamber 12 with an ion gauge 66.
The vacuum degree is fed back to the valve controller 70 to control the rotation of the valve motor 64 to change the angle of the blades 62 of the vacuum valve 60, thereby changing the exhaust capacity of the vacuum pump 14.

[0005] The pressure value of the ion gauge 66 is fed back to the valve controller 70 while the interior of the vacuum chamber 12 as an envelope surrounding the ion beam path is evacuated to a high vacuum, and the blade 62 of the variable exhaust capacity mechanism is changed. As a result, as shown in FIG. 4A, the final pressure P _B at the end of the ion implantation and the pressure P _I of the pressure in the implantation chamber 16 at the end of the ion implantation.
And controlling the pressure to be constant pressure P _C of the intermediate with.

[0006] By controlling the pressure in the ion beam path to be constant in this way, the amount of degassing in the vacuum chamber due to the difference in the use condition, the ultimate pressure difference due to the difference in the vacuum pumping speed, or the time of ion implantation By suppressing the pressure rise due to the pressure difference in the vacuum chamber due to degassing from the surface of the workpiece and keeping the neutralization of the ion beam partially constant by the gas molecules in a state where these pressure rises are suppressed, It is characterized by obtaining high ion dose accuracy.

[0007]

In the above-described method for improving the accuracy of the ion dose amount in the conventional ion implantation apparatus,
By adjusting the angle of the blade of the variable exhaust capacity mechanism,
An intermediate pressure (hereinafter abbreviated as P _C ) between a final ultimate pressure (hereinafter abbreviated as P _B ) in the vacuum chamber, which is an ion beam path, and a pressure (hereinafter abbreviated as P _I ) in the implantation chamber 16 containing the semiconductor wafer 20. ), But as shown in FIG. 4 (b), as shown in FIG. 4 (b), even if the angle of the blade is reduced and the exhaust capability is reduced, as long as there is no gas release or leakage, the injection time does not increase. Since P _C necessarily has a lower pressure than P _I, there is a problem that the pressure cannot be constantly controlled when the amount of gas release or leak from the semiconductor wafer or the injection chamber 16 is small or absent.

Further, a large pressure rise due to various factors such as a decrease in vacuum pumping speed capability for gas release in a vacuum or deterioration of a vacuum pump due to the surface material of the semiconductor wafer 20 and peripheral objects or a minute leak of the vacuum chamber 12 is caused. If the pressure rises from the pressure P _I immediately after the start of ion implantation until the pressure P _C is reached, the above-described conventional variable exhaust capacity mechanism cannot cope. In this case, these pressure rises occur instantaneously, and the slow mechanical operation of the large blades of the conventional variable exhaust capacity mechanism cannot cope with pressure fluctuations. For example, FIG.
As shown in (1), it is not possible to follow the pressure fluctuation during the period from the pressure PI to the pressure PC, and the pressure cannot be kept constant.

For example, when the surface of the workpiece is typically made of a material such as a photoresist, which has an extremely large degassing amount during ion implantation, as a masking material during implantation, FIG. as shown in), injection early in becomes sufficiently higher pressure than the P _I by a large amount of degassing, up to a vacuum chamber in pressure due degassing from the mask material falls to approximately P _C pressure control at all Can not.

In addition to the case where such a mask material having a large outgassing is interposed, for example, in order to secure the in-plane uniformity of the ion dose amount of the semiconductor wafer, the semiconductor wafer is exposed to the ion beam. A plurality of disks are radially loaded on the disk and the disk is rotated at 1000 r. p. m. When performing a mechanical scan such as rotating back and forth and performing ion implantation while reciprocating the entire surface of the disk, the ion implantation determines whether any part of the part other than the semiconductor wafer is irradiated with the ion beam by overscanning the ion beam. The amount of released gas varies greatly, and FIG.
A periodic and large amplitude pressure change as shown in (c) is often observed.

As a result, the neutralization of the ion beam by the gas molecules is caused not only in the implantation chamber for accommodating the semiconductor wafer and the vacuum chamber in the Faraday current collecting system, but also in the ion beam after the former ion mass analyzer or accelerator. It also happens in the path. In particular, the neutralization of ions after this mass spectrometer affects the counting of the electrical ion dose by the Faraday current collecting system, and as described above, the pressure fluctuation in this ion beam path causes the counting error of the dose. And the accuracy of the ion dose is remarkably deteriorated.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an ion implantation method and apparatus for suppressing pressure fluctuations in an ion beam path after ion mass spectrometry and improving the accuracy of ion dose.

[0013]

A feature of the present invention is that ions generated from an ion source are extracted by a mass analyzer to extract desired ions, an ion beam is formed, and the semiconductor substrate is irradiated with the ion beam. A gas pressure fluctuation in an ion beam path after the mass spectrometer is introduced into the ion beam path section by introducing an inert gas amount according to the pressure fluctuation. This is an ion implantation method for controlling the evacuation of the section to keep the gas pressure in the ion beam path constant. Also,
Preferably, the gas pressure in the ion beam path maintained constant is higher than the gas pressure in the closed space surrounding the semiconductor substrate.

Another feature is that an ion source that generates ions, a mass analyzer that extracts ions of a desired mass from the generated ions and forms an ion beam, and that the ions are implanted by the irradiation of the ion beam. An implantation chamber for accommodating a semiconductor substrate, a Faraday current collecting system disposed on the implantation chamber side in the path of the ion beam and detecting a beam current of the ion beam, and an ion beam path section and the implantation chamber. In an ion implantation apparatus including a vacuum pump for evacuating each independently, a vacuum gauge for measuring pressure independently on the mass analyzer side and the Faraday current collection system side in the path of the ion beam, and A flow controller for introducing the inert gas into the path of the ion beam; and a gas controller for the flow controller according to a pressure difference from the vacuum gauge. An ion implantation apparatus and a flow regulator controller for controlling the flow rate. Preferably, the flow controller is also provided in the injection chamber.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a view showing an ion apparatus for explaining an embodiment of the ion implantation method and apparatus according to the present invention. As shown in FIG. 1, the ion implantation apparatus includes an ion source 8a and an ion beam 1 extracted from a mass analyzer 7.
Vacuum gauges 2a and 2b attached to the mass analyzer 7 side and the Faraday current collecting system 36 side of the envelope surrounding the path of zero and measuring the degree of vacuum in the ion beam path, the implantation chamber 16a and the ion beam path section Flow controller 1 for adjusting the flow rate of the inert gas of the gas supply device 24a introduced into the
a, 1b and a flow controller controller 3 for controlling the gas flow of the flow controllers 1a, 1b in accordance with the pressure difference in the ion beam path by the vacuum gauges 2a, 2b. The other main parts are essentially the same as the conventional example described above, except that the disk 11 is provided in the injection chamber 16a.

This ion implantation apparatus is designed to suppress the pressure rise in the ion beam path due to the gas emission of each part due to the irradiation of the ion beam and to make the response faster and to keep the pressure constant. the gas pressure P _C higher than the gas pressure PI of the injection chamber discharge is set to a pressure of a degree that does not cause, the flow controllers 1a and optionally with flow regulator 1b depending on the pressure in the ion beam path during a vacuum pump 4, 5 is introduced a small amount of gas is a device aimed to maintain a constant pressure P _C while evacuating.

Here, the details of each main part will be described. First, it is desirable to use an ionization vacuum gauge which is an ion gauge capable of measuring a high vacuum degree as the vacuum gauges 2a and 2b. Particularly, a Baird-Alpert vacuum gauge capable of measuring a wide range of pressure from 1E-2 Torr to 1E-8 Torr is most suitable.

Each of the flow controllers 1a and 1b comprises a flow meter for measuring the flow rate of the inert gas sent from the gas supply devices 24a and 24b, and a flow control valve capable of varying the flow rate. This flow meter uses not a normal flow volume meter for measuring a flow volume but a commercially available mass flow meter for measuring a flow rate by heat loss due to a gas flow flowing through a bypass pipe. The mass flow meter desirably has a time constant as fast as about 1 second so that it can respond quickly to pressure fluctuations.

On the other hand, it is desirable that the flow control valve has a small-diameter valve and a structure capable of variably controlling the flow rate of a small amount of gas quickly and quickly. Typical examples are a thermal valve system in which a current is passed through a heater wound around a needle valve shaft to vary the valve opening by thermal expansion of the valve shaft, and an electromagnetic valve that changes the valve opening by a current flowing through a solenoid coil. Either a valve-type flow control valve or a piezo-valve type flow control valve that adjusts the valve opening degree by a voltage applied to the piezo stack may be used. In particular, a thermal valve system with a fast response speed is desirable. In addition, a flow controller in which such a flow control valve for precisely controlling a flow rate and a mass flow meter are combined is commercially available as a mass flow controller.

The flow controller controller 3 comprises vacuum gauges 2a, 2b
And a valve control circuit for variably operating the valve opening of the flow controllers 1a and 1b, which are mass flow controllers, and a flow rate measuring device for measuring the temperature difference with a thermal resistance. It comprises a bridge circuit for measuring and a valve opening setting circuit for transferring a signal for setting the valve opening to a valve control circuit by an ion current from the vacuum gauges 2a and 2b. In the case where the same workpiece is always processed and the pressure fluctuation due to gas release is known in advance, a gas supply program setting circuit may be provided.

As the inert gas introduced into each part, for example, a gas such as Ar gas, Xe gas, and N ₂ gas is used. It is desirable to select a gas to be used that is not easily affected by the characteristics of the workpiece even when ions are secondarily implanted into the workpiece surface by accelerated ions.

The Faraday current collecting system 36 has a Faraday cage which is a detection part for measuring a cup-shaped ion current as in the conventional example. This Faraday cage is different from the envelope of the ion beam path section. The conductive line 23 is connected to the insulated dose measuring system 42 and the disk 11 which is the earth potential.

Regarding the counting of the ion dose, the Faraday current collecting system 36 located in front of the semiconductor wafer 20 is injected between the disk 11 and the dose measuring system 42 as an integrated system by establishing conduction through the conduction line 23. This is achieved by measuring the flow of electrons that neutralize the charge according to the number of ions. At this time, in order to increase the uniformity of the ion dose in the surface of the semiconductor wafer 20, the dose measuring system 42
At any time, and the scan controller 9 controls the scan speed at any time according to the ion beam amount.

Here, the semiconductor wafer 2 to be processed is
Secondary electrons generated from their surfaces colliding with zero or accelerated ions on the disk 11 leak out of the Faraday current collecting system, causing an error in the ion dose amount count. Therefore, for example, it is desirable to use means such as placing the electrode in an appropriate position to apply a negative bias or applying a magnetic field to prevent the divergence of secondary electrons.
Also, depending on the material of the surface of the workpiece, in order to neutralize the charge on the surface of the workpiece due to the irradiation of the ion beam, the movement speed of the electrons is not enough to prevent the phenomenon that the surface of the workpiece is charged up. The purpose is to supply electrons by using a gun or the like to reduce the charge as needed.

The path of the ion beam is, for example, all in a high vacuum state of about 1E-5 Torr or less.
The ion beam path from the mass spectrometer 7 is a vacuum valve 1
The vacuum pump 4 evacuates the vacuum by opening 8. Further, in the injection chamber 16a, a vacuum valve 19 is provided.
Is opened, vacuum evacuation is performed by the vacuum pump 5. On the other hand, the vacuum valve 21 of the transport unit 13 is closed during the injection. Then, in the atmosphere, the transport unit 13
Lock chamber 1 via a vacuum valve 22 for conveying the atmosphere.
The vacuum valve 21 is opened when the semiconductor wafer 20 transferred to the transfer section 13 in the disk 5 is loaded and unloaded on the disk 11.

FIGS. 2A and 2C are graphs showing the ion implantation time and the pressure behavior in the ion beam path. Next, the operation of the ion implantation apparatus will be described. First, the ion beam 10 generated by the ion source 8a
Is accelerated to a desired energy, passes through a mass analyzer 7 to remove unnecessary mass ions, and passes through a Faraday current collection system 36 for electrically counting the ion dose. Then, the surface of the semiconductor wafer 20 which is the workpiece or the surface of the disk 11 loaded with the semiconductor wafer 20 is irradiated.

At the same time as the start of the ion implantation, the pressure of the vacuum gauges 2a and 2b rises due to the release of gas from the ion beam path or the implantation chamber 16a and the semiconductor wafer and the disk 11 by the irradiation of the ion beam. Pressure value of the gauge 2a at this time an intermediate value of P _c and P _1. Next, the flow controller controller 3 inputs this pressure value and sends an opening signal corresponding to the pressure difference to the flow controller 1a or 1b. The flow controller 1a or 1b is a gas supply device 2
An inert gas is introduced from 4a, 24b into the ion beam path or the implantation chamber 16a. Then, in this way the pressure value of the ion beam _over beam path unit was evacuated by a vacuum pump 4, 5 while introducing the detected gas pressure value constant of P _c. Then, the dose is counted while implanting, and when the count value reaches a predetermined value, the irradiation of the ion beam is stopped to complete the ion implantation. By stopping the ion implantation, the introduction of gas from the flow controllers 1a and 1b is stopped.
As a result, the pressure of the ion beam path portion gradually have not a close to falling to a final ultimate pressure P _B.

When irradiating the photoresist surface deposited on the semiconductor wafer 20 with an ion beam, the method shown in FIG.
As shown in (b), the cycle of degassing and the cycle of gas introduction deviate from each other, so that the fluctuation width is reduced. Moreover, the pressure becomes a constant _{Pc in} balance with the evacuation capacity. The control pressure value P _C in the ion implantation, even taking into account the form of a variety of gas discharge can be set in the range of about 5E-6~5E-4Torr. Further, the control pressure value P _C during ion implantation at a pressure lower than _{P 1} , which could not be _achieved conventionally, is reduced by the vacuum pumps 4 and 5.
This can be clearly realized by introducing a flow rate of the scum that can balance with the exhaust speed of the gas. It should be noted that this pressure control is mainly performed during the ion implantation, and in the pre-implantation stage, the pressure control is not performed unless otherwise required, and the flow controllers 1a and 1b are controlled so that the flow controllers 1a and 1b are fully closed. It is controlled by the container controller 3.

Here, in this ion implantation apparatus, a correction factor can be added to the measured dose value, although the rate of neutralization of ions before being implanted into the workpiece increases according to the pressure. Therefore, it does not affect the counting accuracy of the dose. Rather, the increase in the rate of ion neutralization reduces the charge on the workpiece, and has a new effect of avoiding the breakdown of the insulating film at the gate of the MOS transistor formed on the semiconductor wafer. .

[0031]

As described above, according to the present invention, a vacuum gauge for detecting pressure and a flow controller for introducing a small amount of inert gas and controlling the introduced flow rate are connected to the ion beam path and the implantation chamber. By providing a system that maintains the pressure in the ion beam path higher than the pressure in the implantation chamber and maintains the pressure in the ion beam path even when the pressure in each section fluctuates, the vacuum pumping capacity can be reduced. Over time,
Eliminates pressure fluctuations over time due to minute leaks in the ion beam path or implantation chamber, adsorption of moisture, etc. after opening to the atmosphere, and degassing from the workpiece transported from the atmosphere, resulting in errors in counting the dose. And there is an effect that the accuracy of the ion dose can be improved.

Further, in the present invention, by controlling the ion beam path and the implantation chamber separately, the pressure in the ion beam path can be kept constant even in the case of a small amount of gas emission which cannot be achieved by the prior art. .

[Brief description of the drawings]

FIG. 1 is a view showing an ion apparatus for explaining an embodiment of an ion implantation method and apparatus according to the present invention.

FIG. 2 is a graph showing ion implantation time and pressure behavior in an ion beam path.

FIG. 3 is a diagram illustrating an ion beam path portion after a mass analyzer for explaining an example of a conventional ion implantation apparatus.

FIG. 4 is a graph showing ion implantation time and pressure behavior in an ion beam path.

[Explanation of symbols]

 1a, 1b Flow controllers 2a, 2b Vacuum gauge 3 Flow controller controller 4, 5, 14, 30 Vacuum pump 6 Motor 7 Mass analyzer 8 Ion source etc. 8a Ion source 9 Scan controller 10 Ion beam 11 Disk 12 Vacuum chamber DESCRIPTION OF SYMBOLS 13 Transport part 15 Lock chamber 16, 16a Injection chamber 18, 19, 21, 22, 60 Vacuum valve 20 Semiconductor wafer 23 Conduction line 24a, 24b Gas supply device 36 Faraday current collection system 40 Opening 42 Dose measurement system 62 Blade 64 Valve motor 70 Valve controller

Claims (5)

(57) [Claims] 1. An ion implantation method for extracting desired ions from ions generated by an ion source by a mass analyzer to form an ion beam, irradiating the semiconductor substrate with the ion beam, and implanting the ions into the semiconductor substrate. Controlling the gas pressure fluctuation in the ion beam path after the mass analyzer by controlling the introduction of an inert gas amount and the evacuation of the ion beam path according to the pressure fluctuation in the ion beam path. An ion implantation method characterized in that a gas pressure in an ion beam path is kept constant. 2. The ion implantation method according to claim 1, wherein a gas pressure in said ion beam path maintained constant is higher than a gas pressure in a closed space surrounding said semiconductor substrate. 3. An ion source for generating ions, a mass analyzer for extracting ions of a desired mass from the generated ions to form an ion beam, and a semiconductor substrate into which ions are implanted by irradiation of the ion beam. And a Faraday current collecting system disposed on the side of the implantation chamber in the path of the ion beam for detecting a beam current of the ion beam, and the ion beam path section and the implantation chamber are independently provided. A vacuum pump for measuring pressure independently on the mass analyzer side and the Faraday current collection system side in the path of the ion beam, and the ion beam path. A flow controller that introduces the inert gas into the section, and a gas flow controller that controls a gas flow rate of the flow controller according to a pressure difference of the vacuum gauge. And a flow controller for controlling the flow of ions. 4. The ion implantation apparatus according to claim 3, wherein said flow controller is provided also in said implantation chamber. 5. The ion implantation apparatus according to claim 3, wherein the flow controller is a mass flow controller.