JP3458548B2 - Work potential measurement method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitably implemented in an apparatus for irradiating a workpiece such as a wafer with charged particles such as an ion implantation apparatus or a plasma etcher, and adsorbs the workpiece. The present invention relates to a method for measuring a work potential for detecting an undesired change in the work potential due to the irradiation of the charged particles. 2. Description of the Related Art In the above-described ion implantation apparatus, for example, a wafer is irradiated with an ion beam, the wafer is charged, and the potential rises or falls, that is, a so-called charge-up phenomenon occurs. If it fluctuates as desired, problems such as dielectric breakdown of devices formed on the wafer occur. Therefore, it is necessary to measure the potential of the wafer. FIG. 7 is a simplified plan view for explaining a typical prior art potential measuring method. FIG. 7 (a)
In this prior art, the ion beam 3 is applied to the wafer 2 held by the holder 1 over a predetermined irradiation area W. The charge sensor 4 for measuring the electric potential of the wafer 2 is arranged apart from the irradiation area W so as not to hinder the irradiation of the ion beam 3, and therefore, is arranged from FIGS.
As shown in (b), the potential measurement is performed in a state where the holder 1 is displaced in the direction of the arrow 5 and the charge sensor 4 is close to the surface of the wafer 2. The output of the charge sensor 4 is input to a charge measuring device 6, and the potential of the wafer 2 is obtained from the detected charge. FIG. 8 is a simplified front view for explaining another prior art potential measuring method. In this prior art, a plurality of wafers 2 are held on a disk-shaped holder 11 at intervals in the circumferential direction. The holder 11 is rotationally displaced in the direction of arrow 12. Therefore, the charge sensor 4 is disposed downstream of the irradiation area W in the direction of the arrow 12, and after the ion beam 3 is irradiated,
The charge of the wafer 2 conveyed by the rotation of the holder 11 is detected by the charge sensor 4, and the potential of the wafer 2 is obtained. The above-mentioned prior art detects an electric field generated by a change in the potential of the wafer 2, and the charge sensor 4 is brought close to the wafer 2 as described above. You need to take measurements. Therefore, it is necessary to displace the wafer 2 which has been irradiated with the ion beam 3 as described above to the vicinity of the charge sensor 4 or to interrupt the irradiation of the ion beam 3 to displace the charge sensor 4 on the wafer 2. is there. Therefore, there is a time lag between the end of the irradiation of the ion beam 3 and the displacement of the wafer 2 or the charge sensor 4 to actually start the measurement. On the other hand, the electric charge charged on the wafer 2 is discharged according to a time constant determined by the electrical characteristics such as the C component and the R component of the peripheral components such as the wafer 2 and the holders 1 and 11. On the other hand, occurrence of troubles such as electrostatic breakdown of the elements formed on the wafer 2 is most likely to occur during irradiation of the ion beam 3 where the potential of the wafer 2 rises most. Therefore, it is extremely important to measure the potential of the wafer 2 under the irradiation state of the ion beam 3. FIG. 9 is a simplified front view for explaining still another prior art potential measuring method capable of satisfying such a demand. It is to be noted that, similar to the conventional technique shown in FIG. 8 described above, corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this prior art, the charge sensor 4 is spaced apart from each other in the circumferential direction on the downstream side of the irradiation area W in the direction of the arrow 12 and at measurement positions P1, P2, and P3 on the same circumference, respectively. Is provided. Therefore, from the potentials E1, E2, and E3 measured at the measurement positions P1 to P3, as shown in FIG. 10, the irradiation region W is set as a base point P0, and the measurement positions P1, The potential drop curves at P2 and P3 are obtained, and the base point P0, that is, the potential E0 at the irradiation area W is estimated. However, even in such a conventional technique, it is still impossible to measure the fluctuation of the potential of the wafer 2 irradiated with the ion beam 3 in real time. Further, the potential measurement method according to the prior art is based on the assumption that parameters such as the C component and the R component that determine the discharge time constant of the charge from the wafer 2 are constant for all wafers, and are inaccurate. is there. An object of the present invention is to provide a work potential measuring method capable of measuring a work potential accurately and in real time. According to the present invention, there is provided a method of measuring a work potential by supplying a suction voltage from a power supply for suction to an electrode embedded in a mounting table made of a dielectric material. Is a method for measuring a workpiece potential in an electrostatic chuck device for adsorbing the workpiece to the mounting table, wherein a probe for charging and a probe for measuring a potential are respectively attached, and the same sample workpiece as the workpiece to be processed is previously placed on the mounting table. Placed thereon, apply a variable voltage from the charging probe, record the data of the adsorption current corresponding to each potential of the potential measurement probe measured corresponding to the variable voltage, A workpiece to be processed is placed on the workpiece, the adsorption current is measured while irradiating the workpiece with charged particles, and the measurement result is compared with the recorded data to determine a workpiece potential. It is characterized by seeking. According to the above arrangement, in a device for irradiating a workpiece such as a wafer with charged particles, such as an ion implantation device, in measuring an electric potential of the work, the electrostatic chuck is used for measuring the potential of the work. Utilizes the adsorption current of the device. That is, in the electrostatic chuck device, an electrode is embedded in a mounting table made of a dielectric material, and a suction voltage is supplied from a power supply for suction to the electrode, so that the workpiece is sucked to the mounting table. Is configured. Therefore, in the present invention, the same sample work as the work to be processed is previously mounted on the mounting table, and the data of the attraction current is recorded. The data is data of an adsorption current corresponding to each potential of the potential measuring probe measured in accordance with the variable voltage when a variable voltage is applied from the charging probe of the sample work, and therefore, the pseudo charging is performed. It reproduces a state in which the workpiece is irradiated with particles, and expresses the relationship between the potential of the measurement probe and the adsorption current in that state. From the data obtained in this way, a work to be actually processed is placed on a mounting table, and while the work is irradiated with charged particles, the attraction current is measured, and the measurement result is recorded. The actual work potential is determined by contrasting the data that is present. Therefore, while irradiating the charged particles,
Work potential can be obtained in real time, the charge-up phenomenon can be quickly detected, and, for example, when the measured potential is equal to or higher than a predetermined potential, irradiation of the charged particles is stopped, thereby preventing damage to the work. Can be prevented. In addition, since the measurement can be performed in real time in this manner, an accurate potential can be obtained without being affected by a variation in a time constant component in a peripheral component such as a holder. BEST MODE FOR CARRYING OUT THE INVENTION
The following is a description based on FIGS. 1 to 3. FIG. 1 is a view for explaining a potential measuring method according to an embodiment of the present invention, and FIG. 2 is a simplified plan view showing a configuration of an ion implantation apparatus 21 using the measuring method. . In the ion implanter 21, the ions extracted from the ion source 22 are input to the acceleration tube 24 after only the desired ions are extracted by the analysis electromagnet 23. In the acceleration tube 24, the ion beam accelerated or decelerated to a desired speed corresponding to the implantation depth into the target is subjected to a sweep magnet after energy contamination is removed in a FEM (Final Energy Magnet) 25. The laser beam is swept by a beam source 26 to have a desired beam width, and is injected into a wafer 29 in a target chamber 28 via a collimator magnet 27. The wafer 29 is stored in the end station 3
After being loaded into the target chamber 28, the transfer robot 31 loads the electrostatic chuck device 41 provided at a predetermined position in the target chamber 28. The wafer 29 after the ion implantation is taken out to the end station 30 by the transfer robot 31. Referring to FIG. 1, electrostatic chuck device 41
Is made of a dielectric material such as SiC, for example, and is provided with a mounting table 42 on which the wafer 29 can be mounted, and flat electrodes 43 and 44 embedded in the mounting table 42 and parallel to the wafer 29. A holder 45 made of a conductive material such as aluminum and holding the mounting table 42;
6 and 47. In the adsorption power supplies 46 and 47 which are DC power supplies, the negative electrode of the adsorption power supply 46 is grounded, the positive electrode is connected to the electrode 43 via a line 48, and the positive electrode of the adsorption power supply 47 is grounded. The negative electrode is connected to the electrode 44 via the line 49.
The holder 45 is grounded. Therefore, the electrostatic chuck device 41 is a bipolar electrostatic chuck device having the positive electrode 43 and the negative electrode 44. In the present invention, ammeters 51 and 52 are interposed in the lines 48 and 49, respectively.
The adsorption currents Iesc ₊ and Iesc ₋ flowing through 49 are measured and input to the measuring device 53. The measurement result of the voltmeter 54 for measuring the potential Vwafer of the wafer 29 is also input to the measuring device 53. In connection with the measuring device 53, a memory 55 realized by a random access memory or the like is provided.
And the measurement result of the voltmeter 54 is recorded. When measuring the potential of the wafer 29 using the above-described configuration, first, as shown in FIG. 1A, the same material and the same shape as the wafer 29 are formed on the mounting table 42. The sample wafer 29a to be sampled is placed. A charging probe 56 is connected to the center of the sample wafer 29a with a low contact resistance by a conductive adhesive. Similarly, a potential measuring probe 57 is attached to the outer peripheral edge of the sample wafer 29a. They are connected by a conductive adhesive. The charging probe 56, the holder 45,
That is, the variable voltage Vps is applied to the ground potential by the DC power supply 58. Thereby, the DC power supply 5
From 8, the current Ibeam is supplied to the sample wafer 29a, and the irradiation state of the ion beam is reproduced in a pseudo manner on the sample wafer 29a. By the supply of the current Ibeam, charges are charged on the sample wafer 29a, and a potential gradient is generated from the center of the sample wafer 29a where the charging probe 56 is attached to the outer peripheral edge where the potential measuring probe 57 is attached. . In response to the charging of the electric charge by the current Ibeam, the voltmeter 54 can measure the voltage between the potential measuring probe 57 and the holder 45, that is, the potential of the sample wafer 29a with respect to the ground potential. A change in the potential Vwafer due to the charging of the electric charge can be detected by the voltmeter 54. The measuring device 53 reads the attraction currents Iesc ₊ and Iesc ₋ by the ammeters 51 and 52 in accordance with the change in the potential Vwafer, and records them in the memory 55. FIG. 3 is a graph showing the experimental results of the present inventor. In FIG. 3, reference numeral α1 indicates an ammeter 51.
Represents attraction current Iesc ₊ change in the positive electrode 43 is measured by a reference mark α2 adsorption current Iesc negative electrode 44 that is measured by the ammeter 52 _- shows the change in the. However, the attracting voltages Vesc ₊ , applied to the electrodes 43, 44 by the attracting power supplies 46, 47, respectively.
Vesc _- a reference voltage V0, are respectively located + 500V and -500V at -V0. The outer peripheral edge of the sample wafer 29a is grounded via the holder 45. As is apparent from FIG. 3, as the wafer potential Vwafer increases toward the positive potential side, reference numeral α1
The adsorption current Iesc ₊ on the positive electrode side indicated by the symbol decreases linearly, and the adsorption current Iesc ₊ on the negative electrode indicated by the reference symbol α2.
_- it will slide into linearly increase. On the other hand, in FIG. 3, reference numeral α3 denotes an attraction current Ies with respect to a difference voltage ΔV when the attraction voltage Vesc ₊ of the attraction power supply 46 is changed with reference to the aforementioned 500V.
It represents a change in the c _+, reference numeral α4 adsorption voltage Vesc by the suction power supply 47 _- shows the change in the _- attraction current Iesc against differential voltage ΔV when changing from the -500 V. As described above, it is understood that the adsorption currents Iesc ₊ and Iesc ₋ are changed by a substantial potential difference between the electrodes 43 and 44 and the sample wafer 29a. As described above, the attracting currents Iesc ₊ and Iesc with respect to the wafer potential Vwafer recorded in the memory 55
esc _- data using the, as shown in FIG. 1 (b), the to measure the potential of the wafer 29 during actual ion implantation. That is, in a state where the wafer 29 is irradiated with the ion beam 59 from the ion source 22, the measuring device 53 uses the ammeters 51 and 52 to attract the current Iesc.
_+, Iesc _- to measure, and control the measurement result to the data shown in FIG. 3, which is recorded in the memory 55, obtains the wafer potential Vwafer. When the wafer potential Vwafer thus obtained becomes a predetermined value, for example, 20 V or more, the measuring device 53 controls, for example, the ion source 22 to deactivate the ion beam 59 or controls the sweep magnet 26. To prevent the ion beam 59 from being irradiated on the wafer 29. Further, the ion source 22 is controlled to reduce the beam current of the ion beam 59, or the ion beam lens installed in the acceleration tube 24 (not shown) is controlled to control the beam diameter and beam current density distribution of the ion beam 59. The feedback control is performed such that the wafer potential Vwafer falls within the above-mentioned predetermined value by, for example, changing the parameters of the process conditions such as changing the temperature. In this way, the change in the potential of the wafer 29 due to the irradiation of the ion beam 59 can be measured in real time and accurately.
Feedback control such as de-energization of the wafer 29
Damage can be prevented beforehand. Another embodiment of the present invention will be described below with reference to FIG. FIG. 4 is a diagram for explaining a potential measuring method according to another embodiment of the present invention. This embodiment is similar to the above-described embodiment, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted. In this embodiment, as in the embodiment shown in FIG. 1A, the attraction currents Iesc ₊ and Iesc ₋ with respect to the wafer potential Vwafer are obtained using the sample wafer 29a and are recorded in the memory 55. This embodiment shows a specific example of the feedback control performed when the ion beam 59 is irradiated on the wafer 29 to be processed, instead of the method shown in FIG. 1B. In this embodiment, the irradiation of the electron shower 61 is performed to prevent the positive charge from being charged up by the irradiation of the ion beam 59, and the electron source 62 for generating the electron shower 61 is used. The electron source control circuit 63 is feedback-controlled by the measuring device 53. That is, the electron source controller 63 reduces the electron shower 61 as the potential Vwafer is negative and the absolute value of the potential Vwafer is larger, corresponding to the potential Vwafer of the wafer 29 input from the measuring device 53. And the potential Vwafe
As r is positive and its absolute value increases, the electron shower 6
Increase one. When the irradiation of the electron shower 61 is performed, the wafer 29 is negatively charged up even if the irradiation of the electron shower 61 is excessive, and the elements formed on the wafer 29 are damaged. There is a risk that it will. In this respect, in the present invention, as determined from FIG. 3, the attraction currents Iesc ₊ , Iesc ₊ and Iesc ₊
esc _- it is changing both about 5%. Therefore,
Highly sensitive feedback control can be performed in real time, and the fluctuation of the potential Vwafer of the wafer 29 can be sufficiently maintained within a required range of about ± 10 V, more preferably about ± 5 V. Regarding still another embodiment of the present invention,
The following is a description based on FIG. FIG. 5 is a diagram for explaining a potential measuring method according to still another embodiment of the present invention. This embodiment is similar to the above-described embodiment, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted. This embodiment is implemented in place of the method shown in FIG. 1B, similarly to the embodiment shown in FIG. It should be noted in this embodiment that an electrostatic chuck control device 65 is interposed between each of the ammeters 51 and 52 and the measuring device 53a. When the wafer 29 to be processed is mounted on the mounting table 42, the electrostatic chuck controller 65 first
Before the irradiation of the ion beam 59 is started, the adsorption power supplies 46a and 47a are controlled to control the adsorption voltage Vesc ₊ ,
Vesc _- a pre-determined voltage V0, -V0, for example the 500V, with reference to the -500 V, while changing only the difference voltage [Delta] V, attraction current Iesc at that time _+, Iesc _-
Is measured. That is, Vesc ₊ = V0−ΔV Vesc ₋ = −V0−ΔV. Thus, in FIG.
Data as indicated by 3, α4 is obtained. Next, the electrostatic chuck controller 65 controls the attraction power supplies 46a and 47a so that the attraction voltages Vesc ₊ ,
Vesc _- wherein each reference voltage V0, and -V0.
In this state, the wafer 29 is irradiated with the ion beam 59,
The electrostatic chuck controller 65 controls the chucking currents Iesc ₊ , Iesc
_- to measure. Thereafter, the electrostatic chuck control device 65
In FIG. 3 recorded in the memory 55, reference numeral α
1, the data indicated by [alpha] 2, the reference numeral .alpha.3, corrected respectively data indicated by alpha 4, resulting attraction current the measured data Iesc _+, Iesc _- in contrast to, determine an accurate wafer potential Vwafer . The calculation for the correction is performed by using a reference numeral α.
It may be obtained by correcting the data indicated by reference numerals α1 and α2 by a linear expression or a polynomial based on the data indicated by reference numerals α3 and α4, respectively, or the data indicated by reference numerals α1 and α2 may be replaced by reference numerals α3 and α4. It may be performed by fitting each of the indicated data using a predetermined function. For example, the data indicated by the reference symbol α1 is approximated by a linear expression y1 = a1 · x1 + b1, and the difference voltage Δ
The value of the attracting current Iesc _{+ (0)} when V is zero is intercept b
Substitute for 1. Therefore, from Iesc _{+ (0)} = a1 · Vwafer + b1, it is possible to obtain Vwafer = (Iesc _{+ (0)} −b1) / a1. Further, for example, a plurality of data indicated by the reference numeral α3 is obtained by changing the differential voltage ΔV, and is approximated by a linear expression y3 = a3 · x3 + b3, and the wafer potential Vwafe is compared with the attracting current Iesc ₊ .
r can be obtained from Iesc ₊ = a3 × 3 + b3 by Vwafer = (Iesc ₊ −b3) / a3. In this case, the data indicated by the reference numeral α1 becomes unnecessary. As described above, by the electrostatic chuck control device 65, for example, the material and the mounting table 42 of each wafer 29 are previously determined.
The wafer potential Vwafer can be accurately measured by compensating for variations in characteristics and states, such as differences in the degree of adhesion to the electrostatic chuck device, and variations in characteristics of the electrostatic chuck device 41 over time. Thus, for example, when a feedback loop is configured as shown in FIG. 4, stable operation can be performed. In each of the above embodiments, both the positive and negative power supplies 46, 47; 46a,
Although the electrostatic chuck device 41 of the bipolar type provided with the chuck 47a is used, like the electrostatic chuck device 71 shown in FIG. A monopolar electrostatic chuck device provided with the electrode 73 may be used. The present invention provides an ion implantation apparatus 2 as described above.
The present invention is not limited to the above, and the present invention can be suitably applied to other charged particle irradiation devices using the electrostatic chuck devices 41 and 71 such as a plasma processing device. According to the method for measuring the work potential according to the present invention,
As described above, in the electrostatic chuck device of the device that irradiates the charged particles to the work, the state in which the variable particles are applied in advance using the sample work and the charged particles are simulated to the work is reproduced. The value of the attracting current with respect to the work potential in step (1) is determined in advance, and the work potential is determined from the measured attracting current when the charged particles are actually irradiated on the work. Therefore, the work potential can be obtained in real time while irradiating the charged particles, the charge-up phenomenon can be quickly detected, and the irradiation of the charged particles is stopped when the measured potential is higher than a predetermined potential. By doing so, it is possible to prevent damage to the work. Also, by being able to measure in real time,
An accurate potential can be obtained without being affected by the variation of the time constant component in the surrounding components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a potential measuring method according to an embodiment of the present invention. FIG. 2 is a simplified plan view showing a configuration of an ion implantation apparatus using the measurement method shown in FIG. FIG. 3 is a graph showing a change in a chucking current with respect to a change in a wafer potential or a chucking voltage, which is a basis of the potential measuring method of the present invention. FIG. 4 is a diagram for explaining a potential measuring method according to another embodiment of the present invention. FIG. 5 is a diagram illustrating a potential measurement method according to still another embodiment of the present invention. FIG. 6 is a sectional view showing another example of the electrostatic chuck device. FIG. 7 is a simplified plan view illustrating a typical prior art potential measuring method. FIG. 8 is a simplified front view for explaining another prior art potential measuring method. FIG. 9 is a simplified front view for explaining still another prior art potential measuring method. FIG. 10 is a graph for explaining the principle of the conventional potential measurement method shown in FIG. DESCRIPTION OF SYMBOLS 21 Ion implanter 22 Ion source 24 Accelerator tube 28 Target chamber 29 Wafer 29a Sample wafer 30 End station 41 Electrostatic chuck device 42 Mounting table 42a Mounting table 43 Electrode 44 Electrode 45 Holder 46 Power supply 46a for suction Power supply for adsorption 47 Power supply for adsorption 47a Power supply for adsorption 51 Ammeter 52 Ammeter 53 Measuring device 53a Measuring device 54 Voltmeter 55 Memory 56 Charging probe 57 Potential measurement probe 58 DC power supply 59 Ion beam 61 Electron shower 62 Electron source 63 Electron Source control device 65 Electrostatic chuck control device 71 Electrostatic chuck device 72 Power supply for suction 73 Electrode

Claims (1)

(57) [Claims 1] An electrostatic device that attracts a work to the mounting table by supplying a suction voltage from a power supply for suction to an electrode embedded in a mounting table made of a dielectric material. A method for measuring a workpiece potential in a chuck device, wherein a charging probe and a potential measuring probe are respectively attached, and the same sample workpiece as a workpiece to be processed is previously mounted on the mounting table, and the charging probe is provided. A variable voltage is applied from above, and the data of the adsorption current is recorded corresponding to each potential of the potential measuring probe measured according to the variable voltage, and the work to be processed is mounted on the mounting table described above. Measuring the adsorption current while irradiating the workpiece with charged particles, and determining a workpiece potential based on the measurement result against the recorded data. .