JP2863991B2 - Ion beam range measuring device, ion beam range measuring method using the device, and method for controlling implantation depth in ion irradiation using the device - 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 beam range measuring apparatus for measuring a range of an ion beam accelerated by an ion accelerator in an irradiation material with high accuracy, and an ion beam range using the apparatus. The present invention relates to a measurement method and a method for controlling an implantation depth in ion irradiation using the apparatus.

[0002]

2. Description of the Related Art A conventional ion beam range measuring device is typically a solid state track detector, and a spread resistance measuring device used in special cases. The range measurement method of the ion beam using the solid state track detector, for example,
It is disclosed in Japanese Patent Application No. 5-85898. Here, a method of measuring the range of an ion beam using a solid state track detector will be specifically described. First, the standard test material, test foil, and track etch film are stacked and irradiated with an ion beam.
From the track etch film visualized by the chemical treatment, the thickness of the test foil through which ions can pass is examined. The sum of the thickness of the standard test material and the thickness of the test foil through which ions can pass corresponds to the ion implantation depth.

Conventional methods for controlling the implantation depth in ion irradiation include a method of controlling ion energy using an ion accelerator of variable energy and a method of controlling the thickness of the absorbing material using an energy absorbing material. There is.
In any case, the ion energy and the thickness of the energy absorbing material can be determined by calculation using a computer or the like. In this case, in order to improve the accuracy of the implantation depth, the actual ion range used by the irradiation, the irradiation material, and the energy absorbing material are used to reduce the actual ion range by several hundredths of the range. Irradiation must be performed based on these measured data after measuring with high accuracy.

[0004]

However, of the above-described conventional ion beam range measuring devices, the method of measuring the range of an ion beam using a solid state track detector requires a chemical treatment, which makes the operation complicated. There were problems such as being difficult to use online. On the other hand, in the method of measuring the range of an ion beam using a spread resistance measuring instrument, the usable materials are limited to semiconductors such as silicon, and the problem is that the range of ions is not necessarily measured. Was.

In the above-described conventional method of controlling the implantation depth in ion irradiation, the range of calculation is affected by uncertainties in the calculation parameters such as the density of the irradiation material, the density of the energy absorbing material, and the ion energy. It is difficult to control the implantation depth with hundreds of precision.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ion beam range measuring apparatus capable of quickly and easily measuring an ion beam range with high accuracy, an ion beam range measuring method using the apparatus, and an ion beam range measuring method. An object of the present invention is to provide a method for controlling the implantation depth in ion irradiation using the above-described apparatus.

[0007]

According to the present invention, there is provided a collimator for limiting an incident angle of an ion beam, a thin plate of the same quality as the irradiation material, a pedestal disposed behind the thin plate, and First to measure the current flowing through the pedestal
A second ammeter, a cylindrical case supporting the collimator, the thin plate, and the pedestal; and a permanent magnet for applying a magnetic field of a predetermined magnitude in the vicinity of the cylindrical case in a direction perpendicular to the direction of irradiation of the ion beam. An ion beam range measurement device characterized by being provided with a plurality of tracing styluses having magnets is obtained.

According to the present invention, there is provided a collimator for limiting an incident angle of an ion beam, a thin plate having the same quality as an irradiation material, a pedestal disposed behind the thin plate, and a current flowing through the thin plate and the pedestal, respectively. The collimator, the thin plate, a cylindrical case supporting the pedestal, and a pair of electrodes respectively connected to a high-voltage power supply and arranged so as to sandwich the thin plate. An ion beam range measurement device characterized by being provided with a plurality of tracing elements configured as described above is obtained.

Further, according to the present invention, there is provided an ion beam range measuring apparatus, wherein the plurality of thin plates have different thicknesses.

According to the present invention, the thickness of the plurality of thin plates is measured, and the current flowing from the thin plate and the pedestal of each of the plurality of tracing styluses by causing the ion beam to enter from the front of the range measuring device. Measure the value, calculate the ratio of the current value flowing from the pedestal to the total current value flowing from the thin plate and the pedestal as the ratio of the transmitted beam, using the least square method the thickness of the plurality of thin plates and the ratio of the transmitted beam A method for measuring the range of the ion beam, characterized by obtaining the average range and the standard deviation of the ion beam in the irradiation material by fitting.

According to the present invention, there is provided a method for controlling a depth of implantation in an irradiation material in ion irradiation by controlling a thickness T of an energy absorbing material. mean range as each m _e in the energy-absorbing material and radiation material measured ion beam by, and m _t, if you want to set a driving depth in said irradiated material _{D, T = m e -m e} · D / M
_A method of controlling the implantation depth in the irradiation material in ion irradiation, wherein the thickness T of the energy absorbing material is obtained by substituting and calculating m _e , m _t , and D into an expression _t . can get.

[0012]

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows the depth X (μm) and the stopping probability Z.
It is a standard normal distribution figure showing the relation of (X). The stop probability Z (X) on the vertical axis is a probability when the standard deviation (σ) is apart from the average value (m). The equation of this standard normal distribution is shown in the following Equation 1.

[0013]

(Equation 1) The stop position (depth X) of the ion beam in a certain substance has a Gaussian distribution, m (μm) is the average range of the ion beam, and σ (μm) is the standard deviation. The ion beam range measuring device of the present invention is a device that can determine a solution by a measuring method described later, using m (μm) and σ (μm) as variables (unknown numbers).

The present invention basically employs a technique for measuring the ion beam current with high accuracy in order to measure the range of the ion beam quickly and with high accuracy. FIG. 2 is an external perspective view showing the structure of the ion beam range measuring device. In FIG. 2, an ion beam range measuring device 10 is composed of nine independent tracing styluses 1 for obtaining the two unknowns (m, σ). In this case, at least two or more measuring elements are required. The structure of each probe 1 is shown in FIGS. Here, FIG.
The structure of the tracing stylus 1 will be described with reference to FIG. Reference numeral 7 denotes a cylindrical case, which is a cylindrical body in the embodiment. The cylindrical case 7 includes a cylindrical body 7a on the ion beam incident side made of a conductive material, for example, aluminum, and a cylindrical body 7b connected to one end of the cylindrical body 7a and made of an insulating material, for example, Teflon. ing. Reference numeral 3 denotes a collimator, which is provided at both ends of the cylindrical body 7a, and has a hole formed at the center to restrict the incidence of an ion beam having an inclined angle. Numeral 4 is a thin plate made of a material having the same quality as the material to which the ion beam is incident.
Is provided in the middle part of. Reference numeral 5 denotes a pedestal, which is made of the same material as the cylinder 7a, and is provided at the end of the cylinder 7b on the side opposite to the collimator. The thin plate 4 and the pedestal 5 are each grounded via an arm wire, and an ammeter 2a on the thin plate side and an ammeter 2b on the pedestal side are provided in the middle of the ground wire. The cylindrical body 7a is also grounded via a ground wire. Reference numeral 6 denotes a permanent magnet disposed so as to face each other near the cylindrical body 7b.

The ion beam whose incidence angle is restricted in the vertical direction by the collimator 3 is incident on a thin plate 4 of the same quality as the substance to be evaluated, that is, the material irradiated by the ion beam. Here, each ion is divided into those that stop in the thin plate 4 and those that pass through according to the probability distribution of the above equation (1). The ions transmitted through the thin plate 4 finally stop in the pedestal 5. On the other hand, the ions are neutralized at the stopped position, so that a current flows between the ions and the ground. The value of the current I _b flowing in the current I _a and the pedestal 5 flowing through the thin plate 4, precision ammeter 2a respectively are measured at 2b.

Since the thin plate 4 and the pedestal 5 are completely electrically insulated from the ground except for the detection line, a highly accurate current measurement can be realized. Further, in order to draw secondary electrons generated by the impact of the ion beam back to the location where they were generated, a permanent magnet 6 forms a magnetic field of an appropriate magnitude in a direction perpendicular to the direction of irradiation of the ion beam. The thickness of the thin plate 4 of each tracing stylus 1 is different, and the thickness of the thin plate 4 of each tracing stylus 1 is changed at a pitch (a hundredth of an average range pitch) obtained in advance by calculation. . The thickness of the thin plate 4 of each of these tracing styluses 1 is accurately measured using a micrometer or an electronic balance.

When an ion beam is irradiated from the front of the range measuring device 10, currents _Ia and _Ib are obtained from the respective measuring elements 1 having different thicknesses of the thin plate 4. Note that, for the sake of accuracy, a value obtained by integrating the respective currents over time may be used. Here, the thickness of the thin plate 4 is u (μm), the ratio of the transmitted beam is P (u), and the ratio P (u) of the transmitted beam is P
Using the equation of (u) = I _b / (I _a + I _b ), u is plotted on the horizontal axis.
_{When i} and P _i (u _i ) are plotted on the vertical axis, a data distribution as shown in FIG. 5 is obtained. In addition, i represents the number of the tracing stylus 1 by 1 to N (N is a natural number).

By the way, the ratio P (u) of the transmitted beam is theoretically expressed by the following equation (2) when considering the measurement method.

[0019]

(Equation 2) Here, when the values shown in Table 1 below are plotted as shown in FIG. 6 and fitted to the curve shown in the above equation 2, the average range m (μm) of the ion beam and the standard deviation σ
(Μm) is obtained. The curve shown in FIG. 6 indicates that the average range of the ion beam obtained as a result of the fitting is 31.
It is a curve in the case of 6.2 (μm).

[0020]

[Table 1] Next, a method for measuring the range of an ion beam using the range measuring apparatus of the present invention will be specifically described. Here, an ion beam having a nominal energy of 24 (MeV) of ³ He ²⁺ is used, the material of the thin plate 4 is made of high-purity aluminum, and the number of the probes 1 is eight.

First, a nominal energy 2 of ³ He ²⁺
When the range of the ion beam of 4 (MeV) in aluminum was calculated using a computer, the average range was 320.
(Μm) and the standard deviation was 3.1 (μm). here,
The thickness of the thin plate 4 of each tracing stylus 1 was set at a pitch of 2 (μm) based on 320 (μm). It was then accurately measured in each of the thin plate 4 the thickness u _i using a micrometer and an electronic balance. The ion beam is incident from the front of the range measuring device 10 and the currents I _a ,
_Ib is measured, and the ratio P of the transmitted beam is calculated from these values.
_i (u _i ). Table 1 shows the measurement results of u _i and P _i (u _i ). Next, the measured data was plotted as shown in FIG. 6, and fitted to the curve shown in the above equation 2 using the least squares method. At this time, the correlation coefficient by the least squares method was 0.9996. The average range in the irradiated material obtained by the fitting is 316.2.
(Μm) and the standard deviation was 3.3 (μm).
Average range 3 from the calculated standard deviation (3.1 (μm)) and the standard deviation (3.3 (μm)) obtained from the measured data
The standard deviation for 16.2 (μm) is 1.1 (μm)
Is evaluated. Therefore, the measurement accuracy is 1.1 / 3.
16.2, which is about 1/300 or less. As described above, according to the method for measuring the range of an ion beam using the range measuring apparatus of the present invention, highly accurate range measurement can be performed.

Next, a method of controlling the implantation depth in ion irradiation will be described in detail. First, the average range of the energy absorbing material in which is measured using an ion beam of the same energy despite uncertain a m _e (μm), the mean range of irradiation material in m _t (μm). When it is desired to set the implantation depth to the depth D (μm) in the irradiation material using the ion beam, the above-mentioned m is calculated by the following equation (3).
_e, the m _t, and it is obtained by substituting the D T (mu
m) may be used.

[0023]

(Equation 3) Further, as shown in FIG. 7, a part of the ion beam 18 irradiating the irradiation material 17 is devised so as to be incident on the range measuring device 10, and the energy fluctuation of the ion beam 18 during the irradiation is averaged. Observe as a range variation and adjust the energy of ion accelerator 20 or energy absorber 11
If an appropriate method is used to adjust the thickness of the film, the ion irradiation can be accurately performed while finely adjusting the implantation depth online. At this time, a conductive material having good thermal stability, such as silicon or tungsten, is used for the thin plate 4.

Next, a method of controlling the implantation depth in the ion irradiation using the range measuring apparatus of the present invention will be specifically described. Here, an ion beam having a nominal energy of 24 (MeV) of ³ He ²⁺ is used, a silicon semiconductor wafer is used as an irradiation material, high-purity aluminum is used as an energy absorbing material, and a lattice defect layer depth is used. Setting 80
(Μm).

First, using the range measuring apparatus of the present invention, the average range in the energy absorbing material and the irradiation material was measured by the method in the above-described embodiment. The average value of the ion beam in the energy absorbing material _me is 31.
6.2 a ([mu] m), mean range as m _t of the ion beam during irradiation the material was 354.7 (μm). At this time, the required thickness T (μm) of the energy absorbing material is obtained by using the equation shown in the above equation (3), where T = 244.9 (μm)
m) was obtained. Next, the ion beam and 244.9 were used.
The semiconductor wafer was subjected to ion irradiation using an energy absorbing material having a thickness of (μm). After that, when the spreading resistance reflecting the depth distribution of the lattice defect was measured, the peak value of the resistance was obtained at the position of the depth of 79.5 (μm). Therefore, the set value of the lattice defect layer depth is almost 80.
(Μm).

Incidentally, it is known that when ions are implanted into a semiconductor such as silicon, a lattice defect layer is obtained substantially in the vicinity of the ion range, and is used for improving the performance of semiconductor devices. However, at present, the only method for controlling the depth of the lattice defect layer is to rely on calculations in preparation for an error, or to measure the spreading resistance, which can be used only off-line. Therefore, according to the method of controlling the implantation depth in the ion irradiation using the range measuring device according to the present invention, it is possible to control the depth of the lattice defect layer by the ion irradiation almost accurately.

Further, the permanent magnets 6 are formed so that secondary electrons generated by the impact of the ion beam are returned to the generation location again.
Are arranged on both sides of the cylindrical case 7, but a pair of electrodes 8 may be arranged so as to sandwich the thin plate 4 instead of the permanent magnet 6 as shown in FIG. In this case, a high-voltage power supply is connected to each electrode so that the secondary electrons are pushed back to the point of occurrence.

[0028]

According to the present invention, highly accurate ion range measurement, which has been considered difficult, can be performed quickly and easily, and precise on-line control of the implantation depth in ion irradiation becomes possible.

[Brief description of the drawings]

FIG. 1 is a standard normal distribution diagram showing a relationship between a depth X (μm) and a stopping probability Z (X).

FIG. 2 is an external perspective view showing a structure of an ion beam range measuring device.

FIG. 3 is a schematic configuration diagram showing a structure of a tracing stylus included in the range measuring device of FIG. 2;

FIG. 4 is a configuration diagram showing the structure of a tracing stylus in FIG. 3 in more detail;

FIG. 5 is a data distribution diagram obtained by plotting the thickness of a thin plate and the ratio of a transmitted beam on a horizontal axis and a vertical axis, respectively.

FIG. 6 is a graph for explaining a state in which a predetermined curve is fitted using a least squares method from a data distribution of the thickness of a thin plate and the ratio of a transmitted beam.

FIG. 7 is a schematic configuration diagram showing an ion beam irradiation device incorporating the range measuring device according to the present invention.

FIG. 8 is a schematic configuration diagram showing the structure of another tracing stylus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measuring element 2a, 2b Ammeter 3 Collimator 4 Thin plate 5 Pedestal 6 Permanent magnet 7 Cylindrical case 8 Electrode 9 High voltage power supply 10 Range measuring device 11 Energy absorbing material 18 Ion beam 20 Ion accelerator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01T 1/00-1/40 G21K 5/00-5/10 H01J 37/04 H01J 37/30-37 / 317

Claims (5)

(57) [Claims] 1. A collimator for limiting the angle of incidence of an ion beam, a thin plate of the same quality as the irradiation material, a pedestal disposed behind the thin plate, and first and second current sensors for measuring the current flowing through the thin plate and the pedestal, respectively. A second ammeter, a cylindrical case supporting the collimator, the thin plate, and the pedestal; and a permanent magnet for applying a magnetic field of a predetermined magnitude in the vicinity of the cylindrical case in a direction perpendicular to the irradiation direction of the ion beam. An ion beam range measuring device, comprising: a plurality of tracing styluses each comprising: 2. A collimator for limiting the angle of incidence of the ion beam, a thin plate of the same quality as the irradiation material, a pedestal disposed behind the thin plate, and first and second current sensors for measuring the current flowing through the thin plate and the pedestal, respectively. A measurement comprising a second ammeter, the collimator, the thin plate, a cylindrical case supporting the pedestal, and a pair of electrodes respectively connected to a high-voltage power supply and arranged so as to sandwich the thin plate. An ion beam range measurement device characterized by comprising a plurality of elements. 3. The ion beam range measuring apparatus according to claim 1, wherein the plurality of thin plates have different thicknesses. 4. An ion beam range measuring method using the ion beam range measuring device according to claim 1, wherein the thickness of the plurality of thin plates is measured, and the thickness of the plurality of thin plates is measured from the front of the range measuring device. Measure the current value flowing from the thin plate and the pedestal of each of the plurality of tracing stylus by injecting the ion beam, calculate the ratio of the current value flowing from the pedestal to the total current value flowing from the thin plate and the pedestal as a ratio of the transmitted beam, The thickness of the plurality of thin plates and the ratio of the transmitted beam are fitted using a least-squares method to obtain an average range and a standard deviation of the ion beam in the irradiation material. Measurement method. 5. A method for controlling the implantation depth in an irradiation material in ion irradiation by controlling the thickness T of an energy absorbing material, wherein the ion beam measured by the ion beam range measurement method according to claim 4. The average range of the energy absorbing material and the irradiation material is m _e ,
and m _t, when the driving depth in said irradiated material to be set to _{D, T = m e -m e} · D / m t become expressions m _e, m
_A method of controlling the implantation depth in an irradiation material in ion irradiation, wherein a thickness T of the energy absorbing material is obtained by substituting and calculating _t and D.