JP2003506890A - System and method for providing a uniform implantation dose between surfaces of a substrate - Google Patents

Abstract

(57) SUMMARY The method and system of the present invention provides an implant dose across a surface of a substrate, such as a semiconductor wafer (w), implanted in a processing chamber (12) of a plasma immersion ion implanter (10). Is provided for uniformity. Plasma generated in the processing chamber contains desired dopant ions. Prior to processing the wafer, the ion current extracted from the plasma is determined at a plurality of locations on the platen by a dose detector (42). The plurality of locations correspond to locations on the surface of the wafer to be implanted. The plurality of electromagnets (34, 36, 38, 40) generate a magnetic field in the processing chamber (12). The size, position, and current rate of the electromagnet are selected to create a vertical and uniform magnetic field on the surface of the wafer in the processing chamber. The dose detector detects ion current extracted from the plasma at a plurality of positions in the processing chamber, and outputs a feedback signal indicating the detected ion current to the controller (50). In response to the feedback signal, the controller outputs a controller signal to the power supply and controls the amount of current in the plurality of electromagnets. This current varies as needed to achieve a uniform dose rate across the wafer. In a preferred embodiment, the plurality of electromagnets comprises a plurality of annular electromagnets and is disposed around the outside of the processing chamber.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to plasma immersion ion implantation systems (Plasma im
mersion ion implantation system). In particular, the present invention relates to improved apparatus and methods for providing a uniform implant dose across the surface of a substrate implanted by such a system.

[0002]

[Prior art]

Ion implantation has evolved as a desirable technique in industry for the incorporation of impurities in semiconductors in large scale manufacturing of integrated circuits. Ion dose is one of two important variables in defining a particular ion implantation process. (The other is the ion energy that determines the ion implantation depth.) The ion dose is related to the concentration of implanted ions for a given region or volume of semiconductor material. Generally, high current ion implanters (generally having an ion beam current up to about 1 mA)
Is used for low doses.

A conventional ion implanter is generally composed of three parts or subsystems. That is, (i) an ion source for outputting an ion beam, (ii) a beamline containing a mass analysis magnet for analyzing the ion beam, (iii) a semiconductor wafer or other substrate to be implanted by the ion beam. Including target room. The ion source in an ion implanter generally produces an ion beam by ionizing the ion source gas and components that are the desired dopant elements in the ion source chamber and further extracting the ion source gas in the form of an ion beam. To do. The ion beam is directed along a beam path in a vacuum provided by the beam line.
Ions excited in the beam strike the substrate in the target chamber where they are implanted. In such an ion implantation system, it is important to prevent the implanted ions from being charged on the surface of the wafer to the extent that the circuit elements on the wafer are damaged.

Plasma immersion ion implantation (PI cube, or PI ³ ) is a technique for injecting a substrate such as a wafer on a platen into plasma in a processing chamber. Then, this processing chamber has the function of the plasma source as well as the function of the processing chamber. Generally, a voltage difference is periodically created between the walls of the process chamber and the platen to attract the ions in the plasma to the substrate. A sufficient voltage difference causes ion implantation to occur on the surface of the substrate. In conventional ion implantation systems, it is important to have a uniform implant dose across the surface of the substrate.

[0005]

[Problems to be Solved by the Invention]

Accordingly, it is an object of the present invention to provide a system and method for providing a uniform implant dose across the surface of a substrate that has been ion implanted by a plasma immersion ion implantation system.

[0006]

[Means for Solving the Problems]

The ion implantation system and method of the present invention are provided to equalize the implant dose across the surface of a substrate, such as a semiconductor wafer, implanted in the process chamber of a plasma immersion ion implanter. The plasma generated in the processing chamber contains desired dopant ions. Ion implantation is accomplished by applying a negative pulsed flow to the platen holding the wafer. Prior to processing the wafer, the ion current extracted from the plasma is determined by a dose detector at multiple locations on the platen. The plurality of locations correspond to locations on the surface of the wafer to be implanted.

The plurality of electromagnets generate a magnetic field in the processing chamber. The size, position and current rate of the electromagnets are selected to create a vertical and uniform magnetic field on the surface of the wafer in the process chamber. The dose detector detects the ion current extracted from the plasma at a plurality of positions in the processing chamber, and outputs a feedback signal representing the ion current to the controller. In response to this feedback signal, the controller outputs a controller signal to the power source to control the amount of current in the plurality of electromagnets. This current varies as needed to achieve a uniform dose rate across the wafer. In a preferred embodiment, the plurality of electromagnets comprises a plurality of annular electromagnets and is arranged around the outside of the processing chamber.

[0008]

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 discloses a plasma immersion type ion implanter, indicated generally by the reference numeral 10. The system includes a vacuum processing chamber 12, which is electrically grounded with a platen 14 supporting an electrically active wafer mounted on an insulator 18 and a conductive wall 17. Processing chamber housing 1
6 and a quartz window 19. The plasma generated in the processing chamber contains the desired dopant ionic species (eg, arsenic), which has a negative voltage at the platen 1.
4 is added to the substrate, such as a semiconductor wafer W or the like, which is placed in the processing chamber. As shown in FIG. 1, the wafer W is lifted from the platen by the pins 23 operated by the pin device 25. In this way
Wafers can be quickly inserted into and removed from the plasma chamber via a load lock assembly (not shown).

Plasma is generated in the processing chamber 12 as follows. The ionizable gas is introduced into the processing chamber 12 via an inlet 21 provided in the upper peripheral portion of the processing chamber and a perforated annular path 21A. A radio frequency (RF) generator 22 generates an RF signal (on the order of 13.5 megahertz (MHZ)), which is sent to a matching network 24. The matching network comprises a capacitor 26 that capacitively couples RF signals to a generally planar antenna 28, which has a lead 30.
, 32 via inner and outer annular coils. In order to match the impedance of the RF generator 22 and the load impedance, the maximum output of the antenna 28 is maintained by minimizing the reflection effect of the RF signal returning to the generator. As one embodiment of such a matching network, the capacitor 2
"Inverted L-shaped" networks are known in which the capacity of 6 is changed by a servomotor.

The RF current generated in the antenna 28 generates a magnetic field that passes through the quartz window 19 and enters the processing chamber 12. This magnetic field line advances in the direction indicated by arrow B based on the direction of the current in the antenna coil. This magnetic field passing through the quartz window 19 and penetrating the processing chamber induces an electric field in the processing chamber. This electric field accelerates the electrons, and the electrons ionize the dopant gas introduced into the processing chamber through the annular path 21A to generate plasma. The plasma contains positively charged ions with the desired dopants, which are implanted into the wafer W when a suitable suppression voltage is applied to the platen 14 by the modulator 27. Since this ion implantation process occurs in vacuum, the processing chamber 12 is exhausted by the pump (not shown) via the pump manifold 29.

The electric field induced in the processing chamber is generated by an annular magnetic field line that is parallel to the plane of the antenna 28 (that is, the X position and the Y position in the cross section of FIG. 1) and is concentrated in the lower ring (annular body). It is formed. Therefore, the plasma in the processing chamber 12 concentrates along this annular magnetic field line. This plasma diffuses toward the wafer. According to the diffusivity and the height of the processing chamber, the plasma density on the wafer becomes maximum (including a uniform state) from the annular portion to the central portion. However, the diffusivity depends on the state of the plasma (ion species, pressure RF power) and is selected to optimize wafer processing. Thus, only the height of the process chamber remains as the control variable for achieving uniformity. This is an inconvenient variable for uniform control.

The present invention solves the problem of uniformly controlling the plasma density by disposing the annular magnetic coils 34, 36, 38, 40 outside the processing chamber 12. In the preferred embodiment, Helmholtz coils (electromagnets) are used. The purpose of this coil is to change the magnetic field within the process chamber 12 to effectively change the plasma diffusivity, which changes the radial distribution of plasma density across the wafer surface.

In a preferred embodiment, the electromagnetic coils are arranged on the upper side and the lower side, respectively.
It includes two large main coils 34, 40 and two small adjustment coils 36, 38 closely adjoining the process chamber 12. The large main coils 34, 40 are supplied by a first current source 44, and the smaller regulation coils 36, 38 are supplied by a second current source 46 (see FIG. 2).
Supplied). Generally, a first current value is applied to the larger main coil and a second, smaller current value is applied to the smaller conditioning coil. Alternatively, a single current source could be used to supply current to all four coils.

Wafer platen 14 includes a plurality of Faraday current collectors or dose detectors, such as Faraday cups 42, which are used to measure plasma current densities and thereby allow implantation doses to be measured. Gives an index of.
The Faraday cup can be configured as shown in commonly assigned US patent application Ser. No. 09 / 218,770. In the preferred embodiment, seven Faraday cups are placed to match the radius of the wafer platen.

Faraday cup 42 includes a surface that is electrically biased and that is parallel to the implant surface and that collects charged ions. During processing, when the wafer is on the platen,
The radially outermost Faraday cup can be used to measure the plasma current density and provides a real-time feedback indication of the dose injected into the wafer. Prior to processing, when the wafer is not on the platen, all Faraday cups can be used to provide an indication of the radial distribution in plasma current across the surface of the wafer, which directly corresponds to the ion dose.

As will be further described below, the magnetic field in the process chamber 12 is varied to adjust the radial distribution of the plasma current density to establish a uniform implant dose, and the process chamber 12 is then modified.
Effectively change the distribution of plasma density inside. This magnetic field is changed by changing the current flowing through the magnetic coil.

FIG. 2 shows a block diagram of a control device for controlling the current flowing through the magnetic coil. The seven Faraday cups 42a-42g provide output signals to the controller 50. Based on the reading of the Faraday cup, the controller outputs control signals 51a, 51b to the current sources 44, 46 to operate the large main coil and the small adjustment coil, respectively. Thus, a closed loop control system is provided to control the plasma distribution on the wafer.

FIG. 3 is a cross-sectional view of the magnetic field created in the processing chamber of the system of FIG. 1 using magnets 34, 36, 38, 40. The processing chamber 12 is schematically indicated by an imaginary line on the wall 17 of the processing chamber. Only half of the process chamber, as seen along the process chamber centerline C _L , is shown in FIG. The magnetic field created by the coils 34, 36, 38, 40 is almost identical to the other half of the process chamber not shown.

The magnetic field lines B in FIG. 3 form a magnetic field created in the processing chamber by the Helmholtz coil. As is apparent from these lines of magnetic force, a uniform magnetic field up to 30 gauss is generated across the surface of the wafer W in the processing chamber 12 depending on the position of the coil related to the processing chamber 12 and the magnitude of the current flowing therethrough. Let This uniform magnetic field
It is orthogonal to the wafer surface and passes uniformly over the wafer surface. In order to avoid any charge storage problems due to non-uniform electron trajectories during the ion implantation process, this magnetic field is
It is important that the wafer is evenly and vertically across the entire surface. The diameter of the wafer in this case is 300 mm (30 cm).

As shown in FIG. 3, these coils provide a uniform magnetic field on both sides of approximately 20 cm radially outward from the center line C _L of the processing chamber. As a result, the magnetic field becomes uniform in the region where the entire wafer W is arranged. The uniform magnetic field in the region near the top of the wafer W controls the plasma across the surface of the wafer to be uniform. The plasma homogenization ensures a uniform implant across the surface of the wafer.

FIG. 4 illustrates the normalized plasma density across the wafer in the process chamber of FIG. 3 for different values of current flowing through the magnet. The graph in FIG.
For an Argon plasma excited by an RF source operating at 00 watts. The magnetic field lobe of the antenna 28 (positions X and Y in FIG. 3) is 20 cm
Apart (i.e., each 10cm in both sides of the center line C _L) are arranged. The current values from 6 to 16.9 amps shown in the symbol list represent the current flowing through the large main coils 34, 40. The current flowing through the small conditioning coils 36, 38 was 0.33 (33%) of the main coil current, and this coil current in the experiments was found to be in the proper ratio.

The normalized plasma electron density shown in FIG. 4 can be determined by known means, eg
Measured 2 cm above the surface of the wafer by a mobile Langmuir probe. The Langmuir probe is repeatedly moved along the plane of the wafer,
The plasma density is measured against the current through various magnets. Alternatively, the Faraday cup 42 can be used to measure the plasma density at the wafer surface.

Plasma density across the surface of the wafer is determined using either a mobile Langmuir probe or a Faraday cup array. The controller 50 can change the magnetic field by adjusting the current in the magnets 34, 36, 38, 40 until the desired uniform magnetic plasma density is obtained. If a Faraday cup is used, the output signal of the Faraday cup can be used as feedback in a closed loop control system (see FIG. 2) to alter the current through the magnet, resulting in lateral uniformity of plasma density. To achieve.

As shown in FIG. 4, two stable plasma modes are obtained. In the first mode, lower main magnet current (6-8 amperes), the plasma density is concentrated along the center line C _L of the processing chamber. In the second mode, at high main magnet current (12-17 amps), two positions (+10 cm from C _L ) where the plasma density matches the magnetic lobes of antenna 28
And -10 cm). At intermediate currents (9-11 amps), a more uniform plasma density is achieved across the surface of the wafer. However, this is an unstable region, and the plasma density has the property of moving to one of the two more stable modes.

The reason why there are two distinct plasma modes can be explained by the different diffusivities of the plasma away from the electric field represented by the annulus below the antenna 28. When using a low magnetic field created by the magnets 34, 36, 38, the plasma lateral diffusion rate is increased, the center of the annular body begins to be filled with plasma, and finally, the peak at the center line C _L . With the high magnetic fields created by the magnets 34, 36, 38, 40, the lateral plasma diffusivity is reduced and the toroidal shape of the plasma is maintained.

Thus, the present invention contemplates two methods of achieving a uniform plasma density across the surface of the wafer W. Using either a Faraday cup array or a moving Langmuir probe, the exact current through the main coils 34, 40 will be determined, resulting in a uniform plasma density across the surface of the wafer W. The wafer can also be implanted using a single ion implantation step.

Alternatively, a two-step ion implantation can be performed if the method involves an unstable region of the plasma. A first implant is performed using a first plasma mode and a second implant is performed using a second plasma mode, using either a Faraday cup array or a mobile Langmuir probe. This two-step method provides a more stable plasma in each mode, as compared to the single-step method, although the two separate ion implantation process steps take a lot of time.

Accordingly, the preferred method and system of the present invention for providing a uniform ion implantation dose across the surface of a substrate has been described above. With the present invention, 300
A uniform dose amount that achieves a variation of 2% or less across the surface of the mm wafer is achieved. However, the above description is provided as an example of the present invention, and the present invention is not limited to the particular embodiments described individually, and various reconfigurations, modifications, and changes are claimed. Are possible in connection with the above description without departing from the scope of the invention, which is defined by the scope of the invention and its equivalent constructions.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a plasma immersion ion implantation system that includes one form of a dose uniformity mechanism constructed in accordance with the principles of the present invention.

2 is a block diagram illustrating a closed loop controller for controlling the current flowing through a magnet in the system of FIG.

3 is a cross-sectional view of the magnetic field created in the processing chamber of the system of FIG. 1 using the magnet shown in this figure.

FIG. 4 shows that for different values of the magnetic current flowing through the magnet in the system of FIG.
4 is a graph showing the normalized plasma density across the surface of the wafer in the processing chamber of FIG.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H01L 21/265 T (72) Inventor Stesick, George United States Wisconsin 53132 Franklin Catherine Court 6810 F Term (Reference) 5C030 DD01 DE07 DE09 5C034 CC01 CD02 CD06 [Summary of Continuation] In one embodiment, the plurality of electromagnets comprises a plurality of annular electromagnets arranged around the outside of the process chamber.

Claims (21)

[Claims] 1. A process chamber (12) is provided, and ions in plasma generated in the process chamber are used to
In a plasma immersion type ion implantation system (10) for implanting ions into a substrate (W) in a processing chamber, an implantation dose control mechanism (i) includes a plurality of magnetic fields for generating a magnetic field in the processing chamber (12). Electromagnet (34,36,38,40
), And (ii) at least one power supply (44, 46) for supplying current to the plurality of electromagnets.
And (iii) a feedback mechanism (42) for detecting either the extracted ion current or the plasma density in the plasma at a plurality of positions in the processing chamber and outputting an output feedback signal (43) representing the detected ion current or the plasma density. ), And (iv) inputting the feedback signal and controlling the amount of current in the plurality of electromagnets to achieve a uniform plasma density or a uniform implantation dose distribution at a plurality of positions in the processing chamber, An ion implantation system comprising: a controller (50) for outputting the at least one control signal (51) to the at least one power supply. 2. The feedback mechanism (42) is disposed on a surface of a platen (14) in the processing chamber (12), a substrate is disposed on the platen during processing, and the controller (50). Controls the amount of current in the plurality of electromagnets to control the platen (14).
The ion implantation system according to claim 1, wherein a uniform plasma density or a uniform implantation dose amount is achieved on the surface of the ion implantation system. 3. The ion implantation system according to claim 2, wherein the plurality of electromagnets (34, 36, 38, 40) are arranged outside the processing chamber. 4. The ion implantation system according to claim 3, wherein the plurality of electromagnets (34, 36, 38, 40) are a plurality of annular electromagnets arranged around the outside of the processing chamber. 5. The plurality of electromagnets (34, 36, 38, 40) are at least one large main electromagnet (34,
40) and at least one small adjusting electromagnet (36, 38), the adjusting electromagnet operating at a lower current than the main electromagnet. 6. The ion implantation system of claim 2, wherein the feedback mechanism (42) is a plurality of Faraday current collectors. 7. The ion implantation system according to claim 2, wherein the feedback mechanism (42) is a mobile Langmuir probe. 8. A substrate (w) in a processing chamber (12) of a plasma immersion ion implanter (10).
(I) plasma is generated in the processing chamber (12), and (ii) a magnetic field is generated in the processing chamber by using a plurality of electromagnets (34, 36, 38, 40). And (iii) the ion current in the plasma is detected by using a feedback mechanism arranged at a plurality of positions in the processing chamber, and (iv) a feedback signal (43) representing the detected ion current is output. (V) The feedback signal is input to the controller (50) to control the amount of current in the plurality of electromagnets to achieve a uniform plasma density or a uniform implantation dose distribution at a plurality of positions in the processing chamber. In order to perform, at least one control signal (51) is output from the controller to at least one power supply. 9. The feedback mechanism (42) is disposed on a surface of a platen (14) in the processing chamber (12), a substrate is disposed on the platen during processing, and the controller (50). 9. The method of claim 8, wherein controlling the amount of current in the plurality of electromagnets to achieve a uniform plasma density or a uniform implant dose on the surface of the platen (14). 10. The method of claim 9, wherein the plurality of electromagnets (34, 36, 38, 40) are located outside the process chamber. 11. The method of claim 10, wherein the plurality of electromagnets (34, 36, 38, 40) comprises a plurality of annular electromagnets arranged around the outside of the processing chamber. 12. The plurality of electromagnets (34, 36, 38, 40) are at least one large main electromagnet (34,
40) and at least one small adjusting electromagnet (36, 38), the adjusting electromagnet operating at a lower current than the main electromagnet. 13. The method of claim 9, wherein the feedback mechanism (42) is a plurality of Faraday current collectors. 14. The method of claim 9, wherein the feedback mechanism (42) is a mobile Langmuir probe. 15. A substrate (w) in a processing chamber (12) of a plasma immersion ion implanter (10).
(I) plasma is generated in the processing chamber (12), and (ii) a magnetic field is generated in the processing chamber using a plurality of electromagnets (34, 36, 38, 40). And (iii) detecting an ion current in the plasma using a feedback mechanism arranged at a plurality of positions in the processing chamber, and (iv) generating a first feedback signal (43) representing the detected ion current. And (v) inputting the first feedback signal to the controller (50) to control the amount of current in the plurality of electromagnets to obtain the first plasma density or the implantation dose distribution between the plurality of positions in the processing chamber. First to power from the controller to achieve
Outputting a control signal, (vi) arranging the substrate (W) in the processing chamber and performing the first implantation, and (vii) using a feedback mechanism at a plurality of positions in the processing chamber to perform plasma treatment in the plasma. (Viii) outputting a second feedback signal (43) representing the detected ion current, and (ix) inputting the second feedback signal to the controller (50), Outputting a second control signal from the controller to a power source to control the amount of current in the electromagnet to achieve a second plasma density or an implantation dose distribution between a plurality of positions in the processing chamber; (x) the substrate A method comprising the steps of performing a second implant above. 16. The feedback mechanism (42) is disposed on a surface of a platen (14) in the processing chamber (12), and a substrate is disposed on the platen during processing, the substrate (w)
Is removed from the process chamber after the first injection and the steps (viii) and (ix)
16. The method of claim 15, wherein the method is repositioned in the process chamber prior to the second injection to allow 17. The method according to claim 16, wherein the plurality of electromagnets (34, 36, 38, 40) are arranged outside the processing chamber. 18. The method of claim 17, wherein the plurality of electromagnets (34, 36, 38, 40) comprises a plurality of annular electromagnets arranged around the outside of the processing chamber. 19. The plurality of electromagnets (34, 36, 38, 40) are at least one large main electromagnet (34,
Method according to claim 18, characterized in that it comprises 40) and at least one small adjusting electromagnet (36, 38), which operating at a lower current than the main electromagnet. 20. The method of claim 16, wherein the feedback mechanism (42) is a plurality of Faraday current collectors. 21. The method of claim 16, wherein the feedback mechanism (42) is a mobile Langmuir probe.