JP2004235090A - Method for correcting sensitivity of ion energy analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for correcting sensitivity of an ion energy analyzer for accurately measuring an energy distribution. <P>SOLUTION: When the measurement value of an ion current is set to I<SB>ion</SB>(ε)<SP>meas</SP>and the dependence of sensitivity (S) of the ion energy analyzer on an energy (ε) is set to S(ε), the dependence S(ε) of the ion energy analyzer on the energy (ε) is obtained so that a value of an area of an ion energy distribution (IED) obtained by a formula ∫<SB>0</SB><SP>∞</SP>I<SB>ion</SB>(ε)<SP>meas</SP>/S(ε)dε to express the area of the ion energy distribution (IED) may become constant to bias electric power, thereby the sensitivity (S) of the analyzer is corrected. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sensitivity correction of an ion energy analyzer for process plasma used in an etching apparatus for etching semiconductors, electronic components, and other substances on a substrate, a plasma CVD or a sputtering apparatus for depositing a film on the substrate, and the like. It is about the law.
[0002]
[Prior art]
As an energy filter of an energy analyzer for ions incident on a high-frequency bias electrode of a plasma processing apparatus, there are a coaxial type (for example, see Patent Document 1) and a sector type (for example, see Patent Document 2).
[0003]
The coaxial type has the advantages that the analyzer configuration is simple and the number of electrodes is small, so it is easy to manufacture, the cost is low, and the operation at the time of measurement is simple.On the other hand, since the sensitivity depends on energy, low energy There is a disadvantage that the signal intensity in the high frequency region cannot be compared with the signal intensity in the high energy region, and thus an accurate energy distribution cannot be obtained.
[0004]
On the other hand, in the sector type, since the sensitivity does not depend on the energy, it is possible to compare the signal intensity in the low energy region with the signal intensity in the high energy region, and thus obtain an accurate energy distribution. On the other hand, there are drawbacks in that the analyzer is complicated and the number of electrodes is large, so that it is difficult to manufacture, the cost is high, and the operation at the time of measurement is complicated.
[0005]
FIG. 1 of the accompanying drawings shows a coaxial configuration.
A substrate electrode 1 is provided to face a plasma generation electrode (not shown) arranged in a plasma generation chamber (not shown), and the substrate electrode 1 attracts ions to a position in contact with plasma generated in the plasma generation chamber. Opening or orifice 1a, and is connected to a high frequency power supply 2 for bias.
[0006]
An energy analyzer 3 is arranged outside the substrate electrode 1, and the energy analyzer 3 includes a pull-in electrode 5, a lens electrode 6, an outer cylinder electrode 7, and an inner cylinder electrode 8 arranged in a vacuum container or envelope 4. These electrodes are connected to respective power sources as shown. A quadrupole-type mass spectrometer 10 and an ion detector 11 are disposed downstream of the energy analyzer 3 via a hole electrode 9. A base flange 13 is connected to a front end of the envelope 4 via an insulator 12.
[0007]
The potential of the pull-in electrode 5 is set to be several tens of volts to 100 volts lower than the potential of the substrate electrode 1, thereby preventing the low energy ion flux of several tens eV or less from spreading due to the space charge effect. When the ion current value determined by the plasma density and the diameter of the orifice 1a of the substrate electrode 1 is large (about 10 ⁻⁷ A or more) and the space charge effect cannot be ignored, the ion flux is too wide unless the drawing in by the drawing electrode 5 is performed. Therefore, the sensitivity is lowered in a low energy region. The lens electrode 6 acts to correct the ion trajectory and reduce the decrease in sensitivity. The ion trajectory is bent by the electric field between the outer cylinder electrode 7 and the inner cylinder electrode 8, passes through the hole electrode 9, and only ions of specific energy pass through the energy analyzer 3 and are carried to the mass spectrometer 10. . Energy analysis is performed by keeping Vout constant and sweeping Vscan. Energy analysis requires four power supplies.
[0008]
FIG. 2 shows the configuration of a sector type energy analyzer. In FIG. 2, reference numeral 21 denotes a substrate electrode provided to face a plasma generation electrode (not shown) disposed in a plasma generation chamber (not shown). The substrate electrode 21 is generated in the plasma generation chamber. An opening for ion drawing, that is, an orifice 21a is provided at a position in contact with the plasma, and is connected to a high frequency power supply 22 for bias. Outside of the substrate electrode 21, a pull-in electrode 23, a lens electrode 24 for generating a lens effect, a transport tube 25, four deflection electrodes 26 arranged in the transport tube 25, and a sector portion without expanding the trajectory of low-energy ions. An electrode 27 for generating a lens effect, a sector inner electrode 28 and a sector outer electrode 29 forming a sector portion are provided in this order at the lower end of the transport tube 25 that carries the light to the transport tube 25. Reference numeral 30 denotes a hole electrode, which is connected to a quadrupole mass spectrometer (not shown) and an ion detector via the hole electrode 30. Each of these electrodes is connected to a power source as shown.
[0009]
In the configuration shown in FIG. 2, in addition to the pull-in electrode 23 and the lens electrode 24, a transport tube 25 for transporting the low-energy ions to the sector portion without expanding the trajectory of the low-energy ions is provided. Set lower. Since the ion orbit is bent in the sector portion, the mass spectrometer is mounted so as to be bent. Therefore, the mass spectrometer must be separated from the substrate electrode 22 due to the space for mounting the mass spectrometer. Therefore, the transport pipe 25 is required. When the transport unit becomes longer, the axis of the ion beam needs to be adjusted. For this purpose, four deflection electrodes 26 are provided for the positive and negative directions in the X and Y directions, respectively. Since the transport tube 25 and the sector portion have different potentials, a lens effect is generated between the transport tube 25 and the sector portion. Therefore, it is necessary to sweep Vscan and Vtube in consideration of the lens effect. The ion trajectory is bent by an electric field in the sector portion, and only ions having a specific energy are passed, and energy analysis is performed by sweeping Vscan. Therefore, ten electrodes and a power source are required, which is more complicated and more expensive than the coaxial type.
In both the coaxial type and the sector type, it is possible to reduce the space charge effect by lowering the ionic current by superimposing a mesh with low transmittance on the lead-in electrode.
[0010]
3 and 4 show examples of the incident angle distribution when there is no collision with the sheath. The normal incidence is set to 0 degree. FIG. 4 shows the angular distribution after integration with φ. The incident angle distribution of collisionless ions is determined by the lateral velocity distribution at the ion sheath end, that is, the ion lateral temperature (for example, see Non-Patent Document 1). The ion lateral temperature at the ion sheath end is about 0.1 eV, and one graduation on the horizontal axis in FIGS. 3 and 4 is on the order of 1 degree. The angle of incidence of ions generated by charge exchange collision is smaller (about 0.03 eV in lateral temperature), and the angle of incidence of ions that have caused elastic collision is larger than that (for example, see Non-Patent Documents 1 and 2).
[0011]
In general, in an energy filter type analyzer installed in front of a mass spectrometer, the range of incident angles that can be analyzed is within several degrees. Therefore, here, non-collision ions and ions generated by charge exchange collision are considered.
[0012]
In the sector type, as shown in FIG. 5, even within several degrees, it is possible to take in all energies with uniform sensitivity (for example, see Patent Document 2). That is, since all incident ions of all energies are taken in, there is no problem of energy dependence of sensitivity. However, as described above, the configuration and operation of the apparatus are complicated and difficult, and the production cost is high.
[0013]
On the other hand, the coaxial type takes in only a part of the angular distribution due to the shape of the analyzer. When there is no space charge effect and the electric field after the orifice is parallel to the substrate electrode, the capture range changes with energy in a relationship similar to the angular distribution as shown in FIG. In this case, valid measurement data can be obtained if the capture range depending on energy is clearly shown. However, in reality, there are components of the electric field due to the structure of the back surface of the orifice electrode and components due to the lens, and the configuration is not as shown in FIG. Even if they are eliminated, it is difficult to completely eliminate the space charge effect, and as shown in FIG. 7, the capturing range depends on the energy, and there is no similar relation to the collision-free angular distribution. Accordingly, the situation falls into that "only a part of the angular distribution is captured, and the capturing range is not clear", which means "I do not know what was measured". This is considered to be the same when the axis of the analyzer is misaligned.
[0014]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-265937 [Patent Document 2]
JP-A-11-250854 [Non-Patent Document 1]
N. Mizutani et al. , J. et al. Vac. Sci. Technol. A 19, 1298 (2001)
[Non-patent document 2]
N. Mizutani et al. , Jpn. J. Appl. Phys. 38 , (1999) 4206. ,
[Non-Patent Document 3]
N. Mizutani et al. , Thin Solid Films 374 (2000) 167
[0015]
[Problems to be solved by the invention]
The present invention provides a simple coaxial type even with the same performance as the sector type, that is, a case in which all incident ions within a range of several degrees from normal incidence, that is, all ions generated by collisionless ions and charge exchange collisions in the sheath are captured. It is an object of the present invention to provide a method for correcting the sensitivity of an ion energy analyzer, which enables an accurate energy distribution to be measured.
[0016]
[Means for Solving the Problems]
To achieve the above object, according to the present invention, an energy-dependent sensitivity in an ion energy analyzer having a coaxial energy filter for measuring energy of ions incident from plasma of a plasma processing apparatus is corrected. In the method
When the measured value of the ion current is Ι _ion (ε) ^meas and the dependency of the sensitivity (S) of the ion energy analyzer on the energy (ε) is S (ε), the area of the ion energy distribution (IED) is It represents formula _{^{∫ 0 ∞ Ι ion (ε)}} meas / S (ε) dε
The dependence S (ε) of the sensitivity (S) of the ion energy analyzer on the energy (ε) is determined so that the value of the area of the ion energy distribution (IED) determined in the above becomes constant with respect to the bias power. Is used to correct the sensitivity (S) of the ion energy analyzer.
[0017]
In the method according to the present invention, the concept of capturing only a part of the coaxial type is considered to be a concept of reduced sensitivity. The correction is performed so as to obtain a result of capturing all ions within a range of several degrees.
[0018]
In the coaxial ion energy analyzer, the dependence S (ε) of the sensitivity S on the energy ε is obtained, and the measurement result is corrected using the obtained value. S (ε) is obtained as follows.
When plasma is mainly generated on the plasma source side of the process plasma apparatus and ions are drawn in on the bias side, the area of the ion energy distribution (IED) is constant regardless of the electrode of the bias side power supply. On the other hand, the position of the ion energy distribution (IED) with respect to the energy changes according to the power on the bias side. Area of the ion energy distribution (IED), when the ion current value iota _ion (epsilon), the formula _{^{∫ 0 ∞ Ι ion (ε)}} dε (1)
Is represented by
[0019]
Therefore, the area of the ion energy distribution (IED) after the sensitivity correction is represented by the following equation, where the measured value of the ion current is Ι _ion (ε) ^meas .
∫ ₀ ^∞ Ι _ion (ε) ^meas / S (ε) dε (2)
[0020]
S (ε) is determined such that the value given by equation (2) becomes constant with respect to the bias power. In this case, the function form of S (ε) is assumed for the derivation of S (ε), the area of the IED after sensitivity correction is obtained for each bias power value by equation (2), and the values are compared. This is performed by obtaining S (ε) while changing the function form of S (ε).
If S (ε) is obtained in this way, ｉ _ion (ε) ^meas / S (ε) is the ion current value with sensitivity corrected, and therefore, if plotted against energy, the ion energy distribution (IED) with sensitivity corrected It becomes.
[0021]
In addition, for the derivation of S (ε), the energy dependence of the current value of ions generated by charge exchange collision in the sheath can be used. When the collision frequency is not so large, it is known that the baseline of the current value hardly depends on the energy (for example, see Non-Patent Documents 2 and 3). Available to
[0022]
By the above method, S (ε) is derived in the coaxial ion energy analyzer, and the measurement result is corrected to ｍｅ _ion (ε) ^meas / S (ε). In this ion energy analyzer, a correct ion energy distribution can be obtained.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0024]
FIG. 8 shows an example of the ion energy distribution (IED) when the “frequency of collision with the sheath” determined by the relationship between the “sheath length” and the “mean free path of collision with background gas atoms and molecules” is small. The bias frequency is 2 MHz, and the bias power value has been changed to three values. As the bias power increases, it changes to a solid line, a broken line, and a dotted line in the figure. One scale on the horizontal axis is on the order of 50 to 500 eV, and varies depending on conditions such as the plasma apparatus, gas used, and input power. When plasma is mainly generated on the source side and does not contribute to generation on the bias side, the area of the ion energy distribution (IED) should not change as shown in FIG. Therefore, if the measurement result is as shown in FIG. 9, it can be determined that the sensitivity is lowered in the high energy region.
[0025]
In the method of the present invention, as described above, the expression (2)
∫ ₀ ^{∞ ｏｎ} _ion (ε) ^meas / S (ε) dε
S (ε) may be obtained so that is equal in the three ion energy distributions (IED) (FIG. 10), and Ｓ _ion (ε) ^meas / S (ε) is obtained using the S (ε) thus obtained. If so, it becomes a correct ion energy distribution (IED) with sensitivity corrected.
[0026]
Note that the ion energy distribution (IED) is not limited to three, and S (ε) can be obtained with higher accuracy as the number increases. In addition, although the example of the sensitivity decrease in the high energy region has been described, the sensitivity decrease in an arbitrary energy region can be similarly handled.
[0027]
FIG. 11 shows an example in which charge exchange collision occurs in the sheath. This is a case where all ions within a range of several degrees from normal incidence are taken in. Non-collision ions and ions generated by charge exchange collisions fall within that range. This is an expansion in a low energy region, that is, a region having lower energy than the saddle-shaped distribution shape caused by collisionless ions. When the bias frequency is 2 MHz, there is no peak as shown, and when the collision frequency is not so large, the distribution becomes almost flat. Peaks appear at higher frequencies, but their baselines are also nearly flat.
[0028]
Therefore, if the measurement result of the ion current value due to the charge exchange collision in this region is not flat, it can be determined that the sensitivity S (ε) is not constant but changes with energy. Since the measurement result of the ion current value is proportional to S (ε), the behavior of the ion current measurement value with respect to ε in this region directly reflects that of S (ε). If the charge exchange collision is used to derive the sensitivity S (ε), S (ε) can be derived more accurately.
[0029]
In the present invention, a correction is made so as to obtain a result of capturing all ions within a range of a few degrees from normal incidence in a coaxial type in which only a part of the incident angle range is captured. Since the bias power is different and the space distribution effect is different when the energy distribution is different, there is a possibility that the capture angle range at a certain energy also changes. Therefore, it is impossible to make a complete and consistent correction, which is an unavoidable problem due to the measurement principle. However, the result of actually measuring with the coaxial type and correcting it according to the present invention is not particularly different from the result of measurement with the sector type, and it is recognized that this correction method can be used sufficiently in practice. The result of measurement by the coaxial type and corrected by the present invention matches well with the calculation result, and the result of measuring both energy and angle, that is, also agrees well with the correct measurement result of capturing all ions in a wide incident angle range, The effectiveness of the correction method of the present invention can be recognized.
[0030]
Even if it is a sector type, if the space charge effect cannot be eliminated, that is, if the plasma density is high and the orifice diameter cannot be reduced due to the plasma produced by deposition, the ion beam spreads in a low energy region, so The sensitivity may be reduced in a low energy region, but even in such a case, the sensitivity can be corrected by the method of the present invention.
[0031]
【The invention's effect】
As described above, in the ion energy sensitivity correction method in the ion energy analyzer according to the present invention,
When the measured value of the ion current is Ι _ion (ε) ^meas and the dependency of the sensitivity (S) of the ion energy analyzer on the energy (ε) is S (ε), the area of the ion energy distribution (IED) is It represents formula _{^{∫ 0 ∞ Ι ion (ε)}} meas / S (ε) dε
The dependence S (ε) of the sensitivity (S) of the ion energy analyzer on the energy (ε) is determined so that the value of the area of the ion energy distribution (IED) determined in the above becomes constant with respect to the bias power. Compensates for the sensitivity (S) of the ion energy analyzer, so that accurate ion energy distribution can be measured even with a simple coaxial ion energy analyzer, that is, the same as when all ions within a few degrees from normal incidence are captured. Is obtained. This eliminates the need for a sector-type ion energy analyzer with a complicated device configuration, enables downsizing, reduces the number of electrodes, reduces manufacturing costs, and simplifies measurement operations. Play.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a coaxial ion energy analyzer.
FIG. 2 is a configuration diagram of a sector type ion energy analyzer.
FIG. 3 is a graph showing the definition of the incident angle and an outline of the angular distribution at 20 eV and 200 eV (before integration at φ).
FIG. 4 is a graph schematically illustrating the incident angle distribution (after integration at φ) at 20 eV and 200 eV.
FIG. 5 is a graph showing an outline of an incident angle range that can be captured at 20 eV and 200 eV by a sector-type ion energy analyzer.
FIG. 6 is a graph schematically showing a range of incident angles that can be captured at 20 eV and 200 eV in an ideal case where there is no space charge effect and no lens effect in a coaxial ion energy analyzer.
FIG. 7 is a graph schematically showing a range of incident angles that can be captured at 20 eV and 200 eV in a coaxial ion energy analyzer in a case where a space charge effect and a lens effect exist.
FIG. 8 shows three different ion energy distributions in which the collision frequency at the sheath is low, the bias frequency is 2 MHz, and all the collisionless ions within a few degrees from normal incidence and the ions generated by the charge exchange collision are captured. Schematic diagram at bias power.
FIG. 9 is a schematic diagram showing a case where sensitivity is reduced in a high energy region when measured by a coaxial type under the same plasma and bias conditions as in FIG. 8;
10 is a schematic diagram of a sensitivity S (ε) obtained from the measurement result of FIG. 9 to obtain a plurality of ideal and consistent energy distributions of FIG. 8;
FIG. 11 is an enlarged view of a low energy region of an ion energy distribution.

Claims (3)

In a method of measuring the energy of ions incident from plasma of a plasma processing apparatus, a method of correcting energy-dependent sensitivity in an ion energy analyzer having a coaxial energy filter,
When the measured value of the ion current is Ι _ion (ε) ^meas and the dependency of the sensitivity (S) of the ion energy analyzer on the energy (ε) is S (ε), the area of the ion energy distribution (IED) is It represents formula ^{_{∫ 0 ∞ Ι ion (ε)}} meas / S (ε) dε
The dependence S (ε) of the sensitivity (S) of the ion energy analyzer on the energy (ε) is determined so that the value of the area of the ion energy distribution (IED) determined in the above becomes constant with respect to the bias power. A sensitivity correction method for an ion energy analyzer, wherein the sensitivity (S) of the ion energy analyzer is corrected by: The dependence of the sensitivity (S) of the ion energy analyzer on the energy (ε), S (ε), is determined by comparing the area of the ion energy distribution (IED) for each of a plurality of different bias power values by the above equation, 2. The sensitivity correction method for an ion energy analyzer according to claim 1, wherein the sensitivity is determined by changing the function form of S ([epsilon]) so that they match. Dependency of sensitivity (S) of ion energy analyzer on energy (ε) S (ε) can be determined by utilizing the energy dependence of the current value of ions generated by charge exchange collision in the sheath. The sensitivity correction method for an ion energy analyzer according to claim 1, wherein:

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