JP4003308B2 - Beam quantity measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used, for example, in an ion beam irradiation apparatus (including an ion implantation apparatus) that performs ion implantation, surface modification, thin film formation, etc. by irradiating a workpiece such as a semiconductor substrate with an ion beam. In particular, the present invention relates to a beam amount measuring apparatus that measures the beam amount of an ion beam applied to an object to be processed, and more specifically, to a means for accurately measuring the beam amount.
[0002]
[Prior art]
In the ion beam irradiation apparatus as described above, in order to measure the beam amount of the ion beam irradiated to the object to be processed, the position where the ion beam is incident in the vicinity of the object to be processed, on the upstream side or the downstream side. In addition, a beam amount measuring device is provided.
[0003]
A conventional example of this type of beam amount measuring apparatus is shown in FIG. This beam quantity measuring apparatus includes a bottomed cylindrical Faraday cup 10 that receives the ion beam 2, and a beam ammeter 12 that measures an ion beam current I ₁ that flows when the ion beam 2 enters the Faraday cup 10. And a suppressor electrode 6 provided near the entrance of the Faraday cup 10 and to which a negative voltage (for example, about several hundreds V to -600 V) is applied from the suppressor power supply 8. A mask 4 is usually provided near the upstream side of the suppressor electrode 6 as in this example. The negative potential suppressor electrode 6 pushes back the secondary electrons 14 emitted from the Faraday cup 10 in accordance with the incidence of the ion beam 2 and suppresses the secondary electrons 14 from escaping from the Faraday cup 10. There is an effect of preventing an error from occurring in the measurement of I ₁ .
[0004]
[Problems to be solved by the invention]
From the Faraday cup 10, not only the secondary electrons 14 described above but also positive secondary ions 16 are generated with the incidence of the ion beam 2. That is, sputtered particles are generated from the Faraday cup 10 as the ion beam 2 is incident. Most of the sputtered particles are neutral particles, but a part (for example, about several percent) is ionized. This is the secondary ion 16.
[0005]
In particular, in an ion implantation apparatus, by performing ion implantation on a semiconductor substrate (wafer) to which a resist has been applied, a gas (outgas) is released from the resist, and this outgas diffuses into the Faraday cup 10 and becomes Faraday. The inside of the cup 10 tends to get dirty. Moreover, not only the outgas from the resist, but also sputtered particles caused by the ion beam 2 hitting a structure near the path also jump into the Faraday cup 10. As a result, the bottom surface 11 of the Faraday cup 10 becomes semiconductive (semi-insulating). In such a state, the portion is positively charged (charged up) with the ion beam irradiation, and is positive. Secondary ions 16 are likely to be generated from the bottom surface 11.
[0006]
The negative potential suppressor electrode 6 not only prevents the positive secondary ions 16 from escaping from the Faraday cup 10, but also acts to actively extract the secondary ions 16 on the contrary. 16 escapes from the Faraday cup 10 and flows into the suppressor electrode 6 and the mask 4. Therefore, the measured value of the ion beam current I ₁ by the beam ammeter 12 is reduced from the true value due to the escape of the secondary ions 16 from the Faraday cup 10, and a measurement error occurs.
[0007]
Further, the secondary ions 16 are accelerated by the voltage applied to the suppressor electrode 6 from the suppressor power source 8 (for example, accelerated to about 600 eV) and collide with the suppressor electrode 6. The secondary electrons 18 are emitted and flow into the Faraday cup 10. Also by the inflow of the tertiary electrons 18, the measurement value of the ion beam current I ₁ by the beam ammeter 12 is reduced from the true value, and a measurement error occurs.
[0008]
In addition, the contamination in the Faraday cup 10 changes with time, and the generation amount of the secondary ions 16 also changes with time. Therefore, even if the beam amount of the ion beam 2 is constant, the beam ammeter 12 apparently appears. It is also possible that the beam amount measurement value changes with time.
[0009]
Therefore, the present invention suppresses the escape of the secondary ions and secondary electrons from the Faraday cup even if they are generated in the Faraday cup, and makes it possible to accurately measure the beam amount of the ion beam. The main purpose is to provide a quantity measuring device.
[0010]
[Means for Solving the Problems]
The beam amount measuring apparatus according to the present invention has a structure in which the Faraday cup is electrically divided into a cylindrical side wall portion and a bottom portion that receives the ion beam, the beam ammeter is connected to the bottom portion, and the side wall portion A DC power supply for applying a positive voltage to the former is provided between the bottom and the bottom, and the bottom of the Faraday cup is sharpened toward the side on which the ion beam enters. (Claim 1).
[0011]
According to the above configuration, even if secondary ions are emitted from the bottom of the Faraday cup as the ion beam enters, a positive voltage is applied to the bottom of the Faraday cup from the DC power source. The positive ions push the secondary ions back to the bottom. Therefore, it is possible to suppress the escape of secondary ions from the Faraday cup.
[0012]
On the other hand, secondary electrons emitted from the bottom of the Faraday cup with the incidence of the ion beam are drawn by the positive voltage applied to the side wall and flow into the side wall. Even if the secondary electrons are going to go upstream from the entrance of the side wall, a negative potential suppressor electrode is provided in the same way as in the conventional example. Is pushed back to flow into the side wall.
[0013]
In this way, since secondary ions and secondary electrons can be prevented from escaping from the Faraday cup, the beam amount of the ion beam can be accurately measured.
[0014]
Moreover the bottom of the Faraday cup, the ion beam is to pointed shape toward the side coming incident, the secondary ions and secondary electrons generated from the bottom is not easily jump out toward the entrance of the Faraday cup Therefore, it is possible to more reliably suppress the secondary ions and secondary electrons from escaping from the Faraday cup.
[0015]
By the way, when the ion beam collides with gas molecules in the atmosphere, a part of the ion beam becomes neutral and becomes a neutral beam. However, in ion implantation for an object to be processed, the neutral beam is ion-implanted in the same manner as the ion beam. Therefore, it is necessary to measure the neutral beam amount. However, since the device that measures the ion beam current I ₁ flowing through the Faraday cup 10 as in the conventional example cannot measure the amount including the neutral beam amount, a measurement error is generated accordingly.
[0016]
On the other hand, as in the second and third aspects of the invention, a secondary electron ammeter that measures the current flowing between the side wall portion and the bottom portion of the Faraday cup, and the secondary electron ammeter measures the current. By further providing a calculator for multiplying the current value by a predetermined coefficient and calculating the sum of the amount of ion beams incident on the Faraday cup and the amount of neutral beams, the amount of ion beams and the amount of neutral beams can be calculated. The sum can be measured.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view showing an example of a beam amount measuring apparatus according to the present invention. Parts identical or corresponding to those of the conventional example of FIG. 5 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.
[0018]
In this embodiment, the Faraday cup 20 corresponding to the conventional Faraday cup 10 is electrically divided into a cylindrical side wall portion 21 and a bottom portion 22 for receiving the ion beam 2. In this example, the side wall portion 21 and the bottom portion 22 are electrically insulated by an insulator 23.
[0019]
The beam ammeter 12 described above is connected to the bottom portion 22 (more specifically, between the bottom portion 22 and the ground).
[0020]
Further, a DC power source 24 that applies a positive voltage of, for example, about several tens of volts to several hundreds of volts to the former (side wall portion 21) is provided between the side wall portion 21 and the bottom portion 22.
[0021]
In this way, even if the secondary ions 16 are emitted from the bottom portion 22 as the ion beam 2 is incident, the positive voltage is applied to the side wall portion 21 with respect to the bottom portion 22. As a result, the secondary ions 16 are pushed back to the bottom 22. Therefore, the escape of the secondary ions 16 from the Faraday cup 20 can be suppressed. As a result, it is also possible to prevent the above-described tertiary electrons 18 from being generated from the suppressor electrode 6 or the like due to the collision of the secondary ions 16 and flowing into the Faraday cup 20.
[0022]
On the other hand, the secondary electrons 14 emitted from the bottom part 22 with the incidence of the ion beam 2 are drawn by the positive voltage applied to the side wall part 21 and flow into the side wall part 21. Even if the secondary electrons 14 are about to exit from the entrance of the side wall portion 21 to the upstream side, the suppressor electrode 6 having a negative potential is provided in the same manner as in the conventional example. 14 is pushed back into the side wall 21 and flows into the side wall 21.
[0023]
Since the secondary ions 16 and the secondary electrons 14 can be prevented from escaping from the Faraday cup 20 in this way, the beam amount of the ion beam 2 can be accurately measured by the Faraday cup 20 and the beam ammeter 12. Can do. In addition, since the secondary ions 16 do not escape from the Faraday cup 20, the contamination in the Faraday cup 20 changes with time, and even if the generation amount of the secondary ions 16 changes, the measured beam amount varies. Stable and accurate measurement values can be obtained without generating them.
[0024]
The bottom portion 22 is directed toward the side on which the ion beam 2 is incident, that is, toward the entrance of the Faraday cup 20 (specifically, the side wall portion 21) as in the example shown in FIGS. A pointed shape is preferable. By doing so, the area of the tip portion of the bottom portion 22 becomes very small and the area of the portion orthogonal to the incident direction of the ion beam 2 becomes very small, so that the secondary ions 16 and secondary generated from the bottom portion 22 are reduced. It becomes difficult for the electrons 14 to jump out toward the entrance of the Faraday cup 20. In other words, since the secondary ions 16 and the secondary electrons 14 are likely to jump out toward the wall surface of the side wall portion 21 of the Faraday cup 20, the secondary ions 16 and the secondary electrons 14 can more reliably escape from the Faraday cup 20. Can be suppressed. Therefore, the beam amount measurement of the ion beam 2 can be performed more accurately.
[0025]
Specifically, the shape of the bottom portion 22 is, for example, a cone shape (for example, a cone shape or a pyramid shape), a wedge shape, or the like. Which one should be adopted may be determined according to the shape of the side wall portion 21 and the like. For example, when the side wall portion 21 is a rectangular tube having a rectangular cross section, the bottom portion 22 may be wedge-shaped as shown in FIG. 2, or a plurality of the bottom portions 22 may be arranged. A plurality may be arranged. Moreover, what is necessary is just to make the bottom part 22 cone shape etc. when the side wall part 21 is cylindrical.
[0026]
An example of the cross-sectional shape of the bottom 22 is shown in FIG. In FIG. 3A, the slope 22b is convex upward, in FIG. 3B, the slope 22b is flat, and in FIG. 3C, the slope 22b is downward. The latter is preferable because the tip 22a is sharper. 1 and 2 has a cross-sectional shape as shown in FIG. 3C.
[0027]
The material of the bottom 22 is preferably, for example, carbon (C), silicon (Si), aluminum (Al), silicon carbide (SiC), or the like. The reason is as follows.
[0028]
Since carbon has high heat resistance and a low sputtering rate, the amount of secondary ions 16 emitted is small. Further, although the secondary electron emission coefficient k described later is small, the sensitivity to the temperature change is small (that is, the change of the secondary electron emission coefficient k with respect to the temperature change is small). high.
[0029]
Silicon has substantially the same heat resistance, sputtering rate, and secondary electron emission coefficient k as carbon. Moreover, since the object to be processed at the time of ion implantation is usually a silicon substrate, even if sputtered particles reach the silicon substrate, they are the same silicon, so there is little adverse effect.
[0030]
Aluminum has little adverse effect even if sputtered particles reach the silicon substrate because it is a light metal. In addition, since the secondary electron emission coefficient k is large, the calculation accuracy of the total beam amount B according to Equation 1 described later is increased.
[0031]
Silicon carbide has high heat resistance and a low sputtering rate. Moreover, even if sputtered particles reach the silicon substrate, the adverse effect is the second smallest after silicon. Further, since the secondary electron emission coefficient k is small, but the sensitivity to the temperature change is small, the stability of the secondary electron emission coefficient k is high.
[0032]
By the way, when the ion beam 2 collides with gas molecules in the atmosphere, a part of the ion beam 2 becomes neutral and becomes a neutral beam. As described above, particularly when ion implantation is performed on a semiconductor substrate provided with a resist, the degree of vacuum is easily deteriorated by the outgas from the resist, so that the ratio of neutral beam becomes high.
[0033]
As described above, even if a part of the ion beam is converted into a neutral beam and is incident on the object to be processed, it contributes to ion implantation and the like as in the case of the ion beam incident. That is, the neutral beam also contributes as a dopant (implanted impurity) to the object to be processed, like the ion beam, and the amount of dopant incident on the object is the sum of the amount of ion beam and the amount of neutral beam. .
[0034]
However, since the conventional beam amount measuring apparatus shown in FIG. 5 measures the ion beam current I ₁ flowing through the Faraday cup 10 with the beam ammeter 12, it cannot measure a neutral beam without flowing current. Therefore, there is an error corresponding to the neutral beam between the beam amount measured by the beam amount measuring apparatus and the beam amount actually irradiated to the object to be processed. Specifically, since the measured value by this beam amount measuring device is smaller, if the amount of injection to the object to be processed is controlled using this beam amount measuring device, excessive injection occurs.
[0035]
One way to solve this problem is to increase the evacuation speed of the evacuation apparatus. For example, a semiconductor device requires an implantation amount control with an error of 1% or less. It is necessary to suppress the conversion rate to at least 1% or less. However, in order to realize this, the exhaust speed of the vacuum exhaust device must be extremely increased, which is not realistic in terms of the size and cost of the vacuum exhaust device.
[0036]
The above problems can be solved by the following means. That is, for example, as shown in FIG. 1, a secondary electron ammeter 26 for measuring the current I ₂ flowing between the side wall portion 21 and the bottom portion 22 of the Faraday cup 20 described above is provided. This current I ₂ is called a secondary electron current because it flows when the secondary electrons 14 emitted from the bottom 22 enter the side wall 21.
[0037]
Further, the value of the secondary electron current I ₂ measured by the secondary electron ammeter 26 is multiplied by a predetermined coefficient 1 / k, so that the total amount of the ion beam 2 and the neutral beam incident on the Faraday cup 20 is obtained. A computing unit 28 for computing B, that is, computing the following equation is provided. k is a secondary electron emission coefficient of the bottom 22.
[0038]
[Expression 1]
B = I ₂ / k
[0039]
To prove the calculation basis of this equation, the neutral beam generated by neutralizing a part of the ion beam 2 also has almost the same energy as the ion beam 2, so that the bottom 22 of the neutral beam is generated. The secondary electron emission coefficient is substantially the same as that of the ion beam 2, and this secondary electron emission coefficient is k here. Accordingly, the emission amount of the secondary electrons 14 from the bottom portion 22, that is, the magnitude of the secondary electron current I ₂ is proportional to the total amount B of the ion beam 2 incident on the Faraday cup 20 and the neutral beam. Is expressed by the following equation.
[0040]
[Expression 2]
I ₂ = kB
[0041]
The formula 1 is obtained by modifying the formula 2. That is, the sum B can be obtained by multiplying the value of the secondary electron current I _{2 by} a coefficient 1 / k.
[0042]
By controlling the injection amount for the object to be processed using this sum B, even if the degree of vacuum of the atmosphere deteriorates due to outgas or the like, the above-described abnormality in the injection amount (specifically, excessive injection) can be prevented. Can do. Thereby, for example, even when the degree of vacuum of the atmosphere is poor, it is possible to achieve the above-described injection amount control with an error of 1% or less.
[0043]
Alternatively, at the start of implantation of the object to be processed, the degree of vacuum is high and the ion beam 2 is hardly neutralized, and the measured value by the beam ammeter 12 is accurate. When the ion beam hits and outgas starts to be emitted, the total amount B may be used to control the implantation amount.
[0044]
Since the secondary electron emission coefficient k varies depending on the material of the bottom portion 22 and the conditions of the ion beam 2 (for example, ion species, energy, etc.), before performing processing by irradiating the workpiece with the ion beam 2, It is preferable to obtain in advance under the same conditions as the time and apply it in actual processing.
[0045]
An example of how to determine the secondary electron emission coefficient k will be described. When the degree of vacuum of the atmosphere is good (for example, at a pressure of 1 × 10 ⁻⁶ Torr or less), the ion beam 2 is incident on the Faraday cup 20, The ion beam current I ₁ is measured by the beam ammeter 12 and the secondary electron current I ₂ is measured by the secondary electron ammeter 26. Both measured values are I ₁₀ and I ₂₀ , respectively. At this time, since the neutralization of the ion beam 2 is negligibly small, it can be considered that only the ion beam 2 enters the Faraday cup 20. Therefore, the secondary electron emission coefficient k of the bottom 22 can be obtained by the following equation.
[0046]
[Equation 3]
k = I ₂₀ / I ₁₀
[0047]
The secondary electron emission coefficient k is preferably obtained at a time as close as possible to the actual ion beam irradiation processing for the object to be processed. This is because the secondary electron emission coefficient k can be obtained most accurately under the conditions closest to the processing of the workpiece, and the secondary electron emission coefficient k can be obtained most accurately.
[0048]
In addition, referring to FIG. 1, an ammeter (not shown) that measures a current I ₃ flowing through a portion 32 between a connection point 30 between the beam ammeter 12 and the secondary electron ammeter 26 and the bottom 22. ) May be provided to monitor that the following equation holds when the beam amount is measured. As a result, it is possible to confirm the presence or absence of charged particles escaping outside the Faraday cup 20 or flowing in from outside the ion beam 2, so that the reliability of the beam amount measurement by this beam amount measuring device is confirmed. be able to.
[0049]
[Expression 4]
I ₃ = I ₁ + I ₂
[0050]
As in the example shown in FIG. 4, the DC power source 24 may be provided between the connection point 30 and the bottom portion 22 with the latter on the negative electrode side. The operation of the DC power supply 24 is the same as that in the example of FIG.
[0051]
【The invention's effect】
Since this invention is comprised as mentioned above, there exist the following effects.
[0052]
According to the first aspect of the present invention, even if secondary ions and secondary electrons are generated in the Faraday cup, they can be prevented from escaping from the Faraday cup. Can be done. Moreover, since the secondary ions do not escape from the Faraday cup, even if the contamination of the Faraday cup changes with time, and the amount of secondary ions generated thereby changes, the beam quantity measurement value does not change, Stable and accurate measurement values can be obtained.
[0053]
In addition, since the bottom of the Faraday cup is pointed toward the side on which the ion beam enters, secondary ions and secondary electrons generated from the bottom of the Faraday cup are unlikely to jump out toward the entrance of the Faraday cup. Do Ri can secondary ions and secondary electrons can be more reliably prevented from escaping from the Faraday cup. Therefore, the beam amount can be measured more accurately.
[0054]
According to the second and third aspects of the invention, since the total amount of the ion beam and the neutral beam can be measured, when a part of the ion beam becomes a neutral beam due to the deterioration of the vacuum degree of the atmosphere However, the total beam amount irradiated to the object to be processed can be correctly measured. Therefore, for example, by performing injection amount control on the object to be processed using this measurement result, it is possible to prevent an abnormality in the injection amount.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a beam amount measuring apparatus according to the present invention.
2 is a perspective view of the bottom of the Faraday cup in FIG. 1. FIG.
FIG. 3 is a cross-sectional view showing an example of the bottom of a Faraday cup.
FIG. 4 is a sectional view showing another example of a beam amount measuring apparatus according to the present invention.
FIG. 5 is a cross-sectional view showing an example of a conventional beam amount measuring apparatus.
[Explanation of symbols]
2 Ion beam 6 Suppressor electrode 12 Beam ammeter 14 Secondary electron 16 Secondary ion 20 Faraday cup 21 Side wall 22 Bottom 23 Insulator 24 DC power supply 26 Secondary electron ammeter 28 Calculator

Claims (3)

A bottomed cylindrical Faraday cup that receives the ion beam, a beam ammeter that measures the ion beam current that flows when the ion beam enters the Faraday cup, and a negative voltage that is provided near the entrance of the Faraday cup. In a beam quantity measuring device including a suppressor electrode to be applied, the Faraday cup has a structure in which the Faraday cup is electrically divided into a cylindrical side wall portion and a bottom portion for receiving an ion beam, and the beam ammeter is connected to the bottom portion. And a DC power supply for applying a positive voltage to the former is provided between the side wall and the bottom , and the bottom of the Faraday cup is sharpened toward the side on which the ion beam is incident. and beam quantity measuring device, characterized in that it is. A bottomed cylindrical Faraday cup that receives the ion beam, a beam ammeter that measures the ion beam current that flows when the ion beam enters the Faraday cup, and a negative voltage that is provided near the entrance of the Faraday cup. In a beam quantity measuring device including a suppressor electrode to be applied, the Faraday cup has a structure in which the Faraday cup is electrically divided into a cylindrical side wall portion and a bottom portion for receiving an ion beam, and the beam ammeter is connected to the bottom portion. And a DC power source for applying a positive voltage to the former between the side wall portion and the bottom portion, and a secondary electron current for measuring a current flowing between the side wall portion and the bottom portion of the Faraday cup. And the amount of ion beam incident on the Faraday cup by multiplying the current value measured by the secondary electron ammeter by a predetermined coefficient. Beam quantity measuring device, characterized in that it e Bei a calculator for calculating the sum of the amounts of the neutral beam. A bottomed cylindrical Faraday cup that receives the ion beam, a beam ammeter that measures the ion beam current that flows when the ion beam enters the Faraday cup, and a negative voltage that is provided near the entrance of the Faraday cup. In a beam quantity measuring device including a suppressor electrode to be applied, the Faraday cup has a structure in which the Faraday cup is electrically divided into a cylindrical side wall portion and a bottom portion for receiving an ion beam, and the beam ammeter is connected to the bottom portion. And a DC power supply for applying a positive voltage to the former is provided between the side wall and the bottom, and the bottom of the Faraday cup is sharpened toward the side on which the ion beam is incident. and which, furthermore, the secondary electron current meter for measuring the current flowing between the side wall and bottom of the Faraday cup, the secondary Multiplied by the predetermined coefficient to a current value measured by the child ammeter, characterized in that it e Bei a calculator for calculating the sum of the amount and quantity of the neutral beam of an ion beam incident on the Faraday cup Beam quantity measuring device.

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