JP3927464B2 - Plasma processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method and apparatus, and more particularly to a plasma processing method and apparatus suitable for etching a substrate such as a semiconductor wafer using plasma.
[0002]
[Prior art]
As a technique for maintaining the etching performance, as described in JP-A-9-129594, plasma is generated in a gas containing a reactive gas by applying electric power to the first electrode, and plasma emission analysis is performed. The plasma state during etching is detected by at least one of these methods, such as mass spectrometry of substances in plasma, measurement of plasma self-bias voltage, measurement of plasma impedance, etc., and according to the detected change in plasma state A technique is known in which the bias voltage is controlled, etching uniformity is high, and excellent controllability of pattern dimensions and pattern cross-sectional shapes is obtained.
[0003]
On the other hand, with the miniaturization of semiconductor elements, as a technique that enables element processing with a processing dimension of 1 μm or less, a sample conventionally provided in a vacuum vessel, for example, as described in JP-A-11-297679 is disclosed. A sample is placed on a table, a processing gas is supplied into the vacuum chamber to generate plasma, and a high frequency bias with a frequency of 100 kHz or more is applied to the sample table independently of plasma generation, and the high frequency bias is modulated at a frequency of 100 Hz to 10 kHz. In addition, there is a method of performing surface processing of a sample by controlling on / off of a high-frequency bias voltage that gives a Vpp value larger than the Vpp value with respect to a Vpp value of a continuous high-frequency bias voltage that can obtain the same etching rate. Are known.
[0004]
[Problems to be solved by the invention]
In recent years, with the increase in the speed of semiconductor elements, the processing size of LSI (Large Scale Integrated Circuit) is currently at a level of 0.1 μm. The processing accuracy of the element electrodes and wiring parts must be ± 0.01 μm or less.
[0005]
On the other hand, in an etching apparatus using plasma, there is a problem that the processing dimension slightly varies from wafer to wafer. For example, in an etching apparatus, plasma is affected by the state of the inner wall of the vacuum vessel. That is, when the Si wafer is etched, the reaction product of Si gradually adheres to the inner wall, whereby the surface state of the inner wall changes, or the deposit re-releases from the wall, thereby changing the plasma composition. As a result, if the wafers are continuously processed one by one, even if the wafer processing conditions such as gas flow rate and pressure are always kept constant, a slight shift occurs in the processing line width for each wafer. With the recent miniaturization of elements, it is difficult to meet the required processing accuracy due to this dimensional variation, which was not a problem with a processing size of 0.5 μm level, at a processing size of 0.1 μm level. The problem has become apparent.
[0006]
As one method for solving such a problem, there is a method of cleaning a processing chamber for each wafer by performing single wafer cleaning. However, this method causes a reduction in throughput and is not effective for all plasma treatments. As another method, it is conceivable to perform plasma processing while correcting the processing conditions for each wafer or several wafers. As such a method, there is a feedback control method as shown in the aforementioned prior art.
[0007]
As described above, in the prior art in which the bias voltage is controlled by various information from the plasma, the selectivity at the time of etching changes due to the change of the bias voltage, which is not suitable for a sample with a thin mask or base film. There is.
[0008]
In addition, in the conventional technology for controlling the on / off of the high frequency bias voltage, no consideration is given to controlling the on / off of the high frequency bias voltage according to the change in the process during processing. When the bias voltage, that is, the on / off voltage value (Vpp) is controlled according to various information of the above, the influence on the selection ratio is less than that of the continuous bias, but the element is miniaturized to a level of 0.1 μm or less. The selectivity with respect to the thin base film used is not yet sufficient.
[0009]
It is an object of the present invention to provide a plasma processing method and apparatus capable of processing with high reproducibility while suppressing variations in processing dimensions for each wafer without reducing throughput in device processing with processing dimensions of 1 μm or less. is there.
[0010]
[Means for Solving the Problems]
The above purpose is high frequency bias In the plasma processing method of processing a sample by applying a voltage, one cycle of the high-frequency bias voltage (T) is time-divided into first (T1), second (T2) and third (T3) subregions, the first subregion is CD gain feedback control, and the second subregion is Selection ratio feedback control, the third sub-region is a period for performing CD gain and selection-ratio feedback control, the high-frequency bias applied power is set large in the first sub-region, and the duty ratio is set according to the CD gain. A unit for processing each sample so that the average applied power in one cycle is constant while performing processing under processing conditions set for a plurality of the samples and changing the T1 / T. Feedback according to the processing status of each sample This is achieved by controlling.
[0011]
The above purpose is When the CD gain is larger than a predetermined standard, the duty ratio is decreased. When the CD gain is smaller than the standard, the duty ratio is increased. Is achieved.
[0012]
Also, the duty ratio is changed by measuring the line width after wafer processing, and if it deviates from the specified value, the duty ratio is changed in a direction to correct it. Alternatively, the state of the apparatus having a correlation with the processing dimension such as plasma emission is monitored, and the duty ratio is changed so that it enters the normal range when the monitored amount deviates from the normal value.
[0013]
In addition, in order to stabilize one of the etching characteristics (for example, processing dimensions), in the method of monitoring fluctuations in the apparatus state and feeding back to the etching conditions, other etching characteristics (for example, It is necessary to prevent the etching rate uniformity within the wafer surface from changing. In the present invention, the output (amplitude) of the high-frequency voltage applied to the sample is time-modulated, and the duty ratio is changed to change only the amount of incident ions and the amount of radical adhesion, and other etching characteristics such as plasma composition and plasma distribution. It is possible to suppress variations in the processing dimensions without affecting the process.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments to which the present invention is applied will be described below with reference to the drawings.
[0015]
[Example 1]
First, a first embodiment of the present invention will be described with reference to FIGS. In the first embodiment, the wafer processing dimension by the etching process is measured for each wafer or a plurality of wafers, and the etching conditions are changed according to this value. As the etching conditions, in this case, the high-frequency voltage applied to the wafer, which is the substrate, is modulated on and off, and the duty ratio for turning on and off (the ratio of the on time in one cycle) is changed. Thereby, the fluctuation | variation of a processing dimension is suppressed.
[0016]
FIG. 1 is a diagram showing the overall configuration of a plasma processing apparatus for carrying out the plasma processing method of the present invention in Example 1. As shown in FIG. In this case, the vacuum processing apparatus 1 includes four plasma processing chambers 2a to 2d, a vacuum transfer chamber 3, and lock chambers 4a and 4b. Around the vacuum transfer chamber 3, plasma processing chambers 2a and 2b and lock chambers 4a and 4b are arranged. The plasma processing chambers 2a to 2d are, for example, etching chambers, and the plasma processing chambers 2c, 2d are, for example, ashing chambers. On the lock chambers 4 a and 4 b side of the vacuum processing apparatus 1, a transport apparatus 5 having a transport robot 6 is disposed, and a cassette table 7 on which a plurality of cassettes 8 can be disposed with the transport apparatus 5 interposed therebetween is disposed. An aligner 11 and an inspection device 9 are disposed around the transport device 5 together with the vacuum processing device 1. The measurement result obtained by the inspection apparatus 9 is taken into the control apparatus 10, and the wafer processing conditions in the plasma processing chambers 2a and 2b are adjusted in the etching condition adjusting unit 100 of the control apparatus 10 based on the measurement results. The control device 10 is constituted by, for example, a computer including a CPU, a memory, a program, an external storage device, an input / output unit, and the like, and controls the vacuum processing apparatus 1. Among them, the etching condition adjusting unit 100 stores a program for executing run-to-run control for changing the duty ratio of the high frequency bias for each sample or lot unit based on the measurement result, various data necessary for the control, and the like. Etc.
[0017]
Here, the cassette 8 is stored in a sealed container and is transported by the transport robot 6 of the transport device 5. The movement space of the transfer robot 6 is preferably maintained in a clean gas atmosphere, and is between the cassette 8 and the aligner 11, between the aligner 11 and the lock chambers 4a and 4b, or between the cassette 8 and the lock chambers 4a and 4b. The lock chambers 4a and 4b and the inspection device 9 are preferably isolated from the atmosphere in the clean room. In addition, when the cleanliness of the atmosphere in the clean room is high, the above-described isolation is not necessary.
[0018]
In the plasma processing apparatus described above, the wafer etched by the vacuum processing apparatus 1 is processed by the transfer robot 6 from the lock chamber 4a or 4b to a length measuring scanning electron microscope (hereinafter referred to as “length measuring SEM”). It is sent to the inspection device 9 for measuring the line width. In the inspection device 9, the length (hereinafter referred to as “CD gain”) from the design value of the machining line width is measured by the length measurement SEM. This measurement is performed for each wafer or every predetermined number as necessary, and the data is stored in a storage device in the control device 10. Further, the CD gain has a predetermined allowable value, and the initial etching condition, that is, the etching process condition at the start of lot processing is set so that the CD gain falls within this allowable value. Here, a number of wafers are continuously processed, and if the CD gain exceeds an allowable value, this data signal is sent to the etching condition adjustment unit 100 in the control apparatus 10, and the CD gain is adjusted by the etching condition adjustment unit 100. Conditions are automatically adjusted so as to be within the allowable value, and the control apparatus 10 changes / adjusts the etching process conditions in the plasma processing chamber 2a or 2b of the vacuum processing apparatus.
[0019]
FIG. 2A is a view showing a longitudinal section of the plasma processing chambers 2 a and 2 b of the vacuum processing apparatus 1. The vacuum processing apparatus 1 in this embodiment is an ECR plasma etching apparatus that emits electromagnetic waves from an antenna and generates plasma by interaction with a magnetic field. An Al antenna 22 is disposed above the vacuum processing chamber 20, which is a plasma processing chamber, via a dielectric window 21. A high frequency power source 25 that generates UHF electromagnetic waves (for example, frequency 450 MHz) is connected to the antenna 22 via a coaxial waveguide 23 and a matching unit 24. The dielectric window 21 can transmit electromagnetic waves from the high frequency power supply 25. A magnetic field coil 26 (in this case, a two-stage coil) for forming a magnetic field in the vacuum processing chamber 20 is wound around the outer periphery of the vacuum processing chamber 20.
[0020]
In the vacuum processing chamber 20, a lower electrode 27, which is a sample stage for placing a wafer 32, which is a sample, is provided facing the antenna 22. A space is formed between the dielectric window 21 and the lower electrode 27, and plasma is generated in this space. Connected to the lower electrode 27 are a high-frequency bias power source 28 for giving incident energy to the wafer 32 to ions in the plasma, and an ESC power source 29 for electrostatically attracting the wafer 32 to the lower electrode 27. Although there is no particular limitation on the frequency of the high-frequency bias power source 28, a range of 200 kHz to 20 MHz is usually used. In this case, the frequency of the high frequency bias power supply 28 is 400 kHz.
[0021]
The voltage waveform 33 of the high-frequency voltage applied to the lower electrode by the high-frequency bias power supply 28 is, for example, as shown in FIG. The cycle is controlled repeatedly at an arbitrary cycle, for example, 1 kHz. This on / off control may be performed as run-to-run control for each sample or lot unit or other appropriate unit.
[0022]
In addition, instead of on / off control of the high frequency output by run-to-run control, the value is switched between a value with a high frequency voltage amplitude (a value in a range where etching proceeds) and a value (a value within a range where etching does not proceed). You may make it control. The high frequency bias application method in this case is, for example, periodically applied with different high frequency bias voltages in one period divided into time t1 and time t2.
[0023]
An exhaust port 30 is provided in the lower part of the vacuum processing chamber 20, and an exhaust device (not shown) is connected thereto. A gas supply device 31 supplies a processing gas into the vacuum processing chamber 20 and is connected to a number of gas supply holes (not shown) provided in the dielectric window 21.
[0024]
In the plasma processing apparatus configured as described above, the UHF electromagnetic wave output from the high frequency power supply 25 passes through the dielectric window 21 from the antenna 22 part via the matching unit 24 and the coaxial waveguide 23 and passes through the vacuum processing chamber 20. Supplied in. On the other hand, a magnetic field generated by the magnetic field coil 26 is formed in the vacuum processing chamber 20. The etching gas introduced into the vacuum processing chamber 20 is efficiently converted into plasma by the interaction between the electromagnetic field and the magnetic field of the magnetic field coil. A predetermined etching process is performed on the wafer 32 on the lower electrode 27 by the plasma. In the etching process, the incident energy of ions in the plasma incident on the wafer 32 is controlled by the high frequency bias power source 28 to obtain a desired etching process.
[0025]
FIG. 3 shows the relationship between the CD gain of the polysilicon wiring etched using this plasma processing apparatus, the selectivity ratio, the uniformity of the etching rate of the underlying oxide film, and the duty ratio of the high frequency bias. It is a figure which shows the result calculated | required by. The CD gain means an increase amount of CD, and the selection ratio is a ratio between the etching rate of the polycrystalline silicon and the base oxide film.
[0026]
Usually, in gate processing of a transistor, it is necessary to selectively etch polycrystalline silicon on a thin oxide film of about several nm which is a base film. For this reason, in addition to the CD gain, the selectivity to the base oxide film and the uniformity of the base oxide film etching rate are important. Note that the etching conditions that are the basis of the data in FIG. ₂ (18cc), HBr (82cc), O ₂ A processing pressure of 0.4 Pa was used using (3 cc) mixing. The output of the high-frequency bias power supply 28 is 35 W, and is controlled at a constant power. When the on / off control of the high frequency is performed, the peak value of the power is changed so that the average of one period is 35 W. For example, when the duty ratio is 50%, the average value becomes 35 W by controlling so that the peak value of power is a peak value output when the continuous output is 70 W.
[0027]
As can be seen from FIG. 3, when the duty ratio is controlled with the output of the high-frequency bias constant, that is, with the average power on / off being constant, the CD gain changes depending on the duty ratio. That is, it can be seen that the CD gain is large at a duty ratio of 100% (that is, continuous bias), but the CD gain is small when the value of the duty ratio is small. This is because, when the power is constant, the amplitude of the high-frequency voltage is increased when the duty ratio is reduced as compared with the case where the duty is 100%, so that the incident energy to the wafer given to the ions in the plasma is increased. It was also found that the selection ratio and uniformity hardly depend on the duty ratio. That is, if the output (electric power) of the high-frequency bias is constant and the high-frequency applied to the sample is on / off modulated and the duty ratio is changed, the selection ratio that greatly affects the processing of wiring and the etching rate of the underlying oxide film are uniform. It is possible to change only the CD gain without changing the performance, in other words, without degrading the selectivity and uniformity performance.
[0028]
According to the present invention, variation in the processing dimension of the sample can be suppressed by performing the run-to-run control of the etching using the characteristic of the duty ratio as shown in FIG.
[0029]
This point will be specifically described below. FIG. 4 shows a cross-sectional shape when a sample having a mask 311 on a Poly-Si film 312 which is a gate material is etched. FIG. 4A shows an example of a target shape (CD value is L1), and FIG. 4B is an example of a case where the processing shape is thickened due to a change in etching characteristics (CD value is L2). The variation amount (L2-L1) of the processing dimension of the sample is maintained below a predetermined value by duty ratio feedback control.
[0030]
FIG. 5 shows that the Nth wafer is measured by the inspection apparatus 9 from the processed wafers, and the Nth wafer is measured by the etching condition adjusting unit 100 of the control apparatus 10 based on the measured CD gain of the processed line width. 10 is a flowchart of run-to-run control for controlling the duty ratio of an N + m (m = 1, 2,...) Wafer processed after the wafer, in this case, duty ratio feedback control. The CD of the Nth wafer etched by the etching apparatus is measured by the length measuring SEM of the inspection apparatus 9 (502). The difference between the CD value and the target value (variation amount L2-L1 in FIG. 4) is obtained (504), and it is determined whether or not the variation amount is within the standard value (506). The next new N + m-th wafer is processed with the set value (508). If the fluctuation amount deviates from the standard value, the duty ratio is changed (510), and the next new N + m wafer is processed (508). The N + mth etching process is terminated using an etching end point determination device (512).
[0031]
FIG. 6 shows an example of the initial value of the CD gain in the plasma processing and the CD gain characteristics after the N-sheet processing obtained as a result of monitoring. As shown in FIG. 6, the CD gain has a predetermined allowable value (standard value), and the initial etching conditions, that is, the etching processing conditions at the start of lot processing are set so that the CD gain falls within this allowable value. ing. On the other hand, after a number of wafers, for example, Si wafers, are continuously processed, Si reaction products gradually adhere to the inner wall of the plasma processing chamber, thereby changing the surface state of the inner wall. As a result, the plasma is affected, and the CD gain changes even when the etching conditions are the same. Therefore, when the CD gain exceeds the allowable value, this data signal is sent to the etching condition adjusting unit 100 in the control apparatus 10, and the conditions are automatically set by the etching condition adjusting unit 100 so that the CD gain falls within the allowable value. Then, the control apparatus 10 changes or adjusts the etching process conditions in the plasma processing chamber 2a or 2b of the vacuum processing apparatus.
[0032]
This change / adjustment amount is obtained as shown in FIG. For example, in the initial value, the CD target value is 0.23 μm, and the duty ratio at that time is set to 50%. When the CD fluctuation amount is ± 5 nm and the CD fluctuation amount after etching is increased by 7 nm, the CD gain can be reduced by 7 nm if the duty ratio is reduced by about 10% from the characteristics shown in FIG. Recognize. Therefore, the next wafer is processed by setting the duty ratio to 40% by duty ratio feedback control. By this duty ratio feedback control, the CD value of the next wafer can be returned to the target value of 0.23 μm.
[0033]
The relationship between the CD gain and the duty ratio as shown in FIG. 6 changes when the structure of the wafer to be processed and the etching conditions change. Therefore, in practice, it is necessary to create a database in which data corresponding to each process is stored in advance, or to store the data for each wafer processing to construct a database and make it usable in the control device 10. Become.
[0034]
Even in a method in which a high frequency is continuously applied to increase the power, the ion energy increases, so that the shape gain, that is, the CD gain can be reduced. However, in this case, since there is no bias off period in which the ion energy is increased and ions are not accelerated, the etching rate of the oxide film is increased at the same time, and the selectivity is decreased, resulting in a problem of removing the underlying oxide film.
[0035]
As described above, according to the present embodiment, the duty ratio of the high-frequency bias power supply is set to the CD gain value against a slight deviation in the processing line width for each wafer due to the plasma composition change or fluctuation in the vacuum processing chamber caused by repeated wafer processing. By performing feedback control according to the above, the processing line width of the wafer can be set to an optimum value, and the required processing accuracy can be satisfied. Thereby, there is an effect that processing can be performed with good reproducibility while suppressing variations in processing dimensions for each wafer.
[0036]
Further, since the change of the duty ratio can easily adjust the CD gain of several nanometers, it is suitable for processing a fine semiconductor element of a 0.1 μm to 0.05 μm level in which a variation in processing dimension for each wafer becomes a problem. .
[0037]
Also, as run-to-run control, if a change in the CD gain value starts to appear before the CD gain value after wafer processing exceeds the allowable range, the high-frequency bias is always based on the data stored in the etching condition adjusting unit 100 described above. The feedforward control may be performed so as to maintain the duty ratio.
[0038]
In addition, a length measuring SEM is generally used as an apparatus for measuring a processing dimension. However, the length measuring SEM is thin in order to observe the shape from above, that is, the width of the polycrystalline silicon is smaller than the size of the resist. The width of the polycrystalline silicon cannot be measured. As a method for obtaining the deviation or change in the processing line width in place of the length measurement SEM, a method for obtaining the deviation from the design value of the processing dimension by measuring the electrical resistance of the wiring, or the shape of the wiring by reflection or diffraction of light There are methods for estimation. If these are used in the inspection apparatus 9 and the duty ratio is adjusted by applying feedback control or feedforward control to the etching conditions, it is possible to correct when the processing shape becomes thin.
[0039]
In addition, the step of run-to-run control, that is, the step of adjusting the etching conditions by measuring the processing dimension can be set for each wafer or once for a plurality of wafers, but it may be set according to the processing state of the wafer. .
[0040]
Further, the etching condition that the etching condition adjusting unit 100 adjusts according to the variation of the CD gain is at least the duty ratio, and other conditions such as gas pressure and gas composition may be finely adjusted in addition to the duty ratio.
[Example 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. In FIG. 7, the same reference numerals as those in FIG. The present embodiment is different from the embodiment of FIG. 2 in that means for monitoring plasma light is provided in place of the inspection apparatus 9 so that the duty ratio and the like are controlled in accordance with changes in the plasma generation state. . That is, a light emission window for collecting plasma light corresponding to the plasma generation section serving as a processing space of the vacuum processing chamber 20 is provided, and a light emission monitor 34 for measuring the emission spectrum of the collected plasma light connected to the light extraction window via an optical fiber. The emission spectrum measured by the emission monitor 34 is converted into an electrical signal and input to the control device 10a.
[0041]
The cause of the etching shape changing for each wafer is that a reaction product such as Si chloride adheres to the inner wall of the vacuum processing chamber 20 to change the plasma state. For example, when the reaction product adhering to the inner wall is re-released and adheres to the wafer 32, the CD gain increases. At the same time, when the plasma emission intensity is measured with respect to the wavelength of light, that is, the emission spectrum is measured, a change corresponding to an increase in the reaction product is measured. Although the aspect of the change varies depending on the gas composition and the material to be etched, the relationship between the CD gain and the plasma emission spectrum is measured in advance, and this data is input to the etching condition adjustment unit 100. In the etching condition adjustment unit 100, the change in the output of the light emission monitor 34 is converted into the adjustment amount of the duty ratio, and the duty ratio of the high-frequency bias power supply 28 is changed by the control device 10a.
[0042]
As described above, the etching condition adjustment unit 100 of the control device 10a inputs and stores data on the relationship between the emission spectrum and the CD gain value in advance, or accumulates data for each wafer processing.
[0043]
In the apparatus configured as described above, a plasma emission spectrum is measured by the light emission monitor 34 for each wafer processing, and a small duty ratio or a large duty ratio is selected by the etching condition adjustment unit 100 so that the CD gain is within an allowable range. Alternatively, a signal for adjusting and adjusting the duty ratio of the high-frequency bias power supply 28 and the output peak value (amplitude) of the power is sent from the control device 10a to the high-frequency bias power supply 28, and the duty ratio and peak voltage of the high-frequency bias power supply 28 are adjusted. Thereby, the duty ratio of the high frequency bias from the high frequency bias power supply can be adjusted in real time by the control device 10a in accordance with the fluctuation of the emission spectrum for each wafer process.
[0044]
The above processing flow is shown in FIG. When etching is started (802), the value from the light emission monitor 34 is measured (804), and how much the measured value has changed with respect to the previous monitor value is determined (806). It is determined whether the obtained change amount is within the allowable range with respect to the previous monitor value (808). If it is within the range, the process is performed without changing the conditions. If it is determined in step 808 that it is out of range, duty control for repeatedly turning on and off the high frequency bias, that is, control for changing the duty ratio is performed (810). If the wafer etching process has not been completed after these controls (812), the monitor value measurement (804) is continued and the above-described flow is repeated. Thereafter, if it is determined in step 812 that the etching has been completed, the wafer is unloaded and recovered, and if a predetermined number of wafers have been processed, the process is terminated (814).
[0045]
As described above, according to the second embodiment, the duty ratio of the high-frequency bias power source can be adjusted according to the emission spectrum, in other words, according to the CD gain value. The processing line width can be set to an optimum value, and the required processing accuracy can be satisfied. As a result, as in the first embodiment described above, there is an effect that processing can be performed with good reproducibility while suppressing variations in processing dimensions for each wafer. Further, it is suitable for processing a fine semiconductor element of 0.05 μm to 0.1 μm level in which a variation in processing dimension for each wafer becomes a problem.
[0046]
Note that the signal of the plasma emission spectrum may be treated as the signal intensity of a specific wavelength, or the principal value analysis method generally known as a multivariable analysis method is used to correlate most with the CD gain. May be handled by converting to a parameter obtained by synthesis of a certain principal component or a combination of several principal components.
[0047]
In this embodiment, the plasma emission spectrum is used. However, the monitor quantity indicating the state of the plasma etching apparatus includes the plasma and power supply circuit impedance and the voltage waveform height of the high frequency bias power supply 28 in addition to the plasma emission spectrum. Etc. can also be considered.
[0048]
Example 3
Next, a third embodiment of the present invention will be described. When the plasma emission spectrum and other monitor values mentioned above change suddenly within the plasma processing range, the hardware changes of the device, for example, the wear of components on the electric circuit via the plasma, In this case, the bias voltage is optimized so that the wafer being processed is not defective, and the power value of constant power control during on / off control is changed for this purpose. Control to optimize. The apparatus configuration of this embodiment is the same as that of the second embodiment except for the etching condition adjusting unit 100.
[0049]
FIG. 9 shows a control flow of the etching condition adjusting unit 100 in the third embodiment. When etching is started (902), a value from the light emission monitor 34 is measured (904), and how much the measured value changes with respect to the previous monitor value is determined (906). It is determined whether the obtained change amount is within the range of the set value (allowable value) with respect to the previous monitor value (908). If it is within the range, normal high-frequency bias ON / OFF duty control is performed (910). After these controls, if the etching is not yet completed (912), the monitor value measurement (904) is continued and the above-described flow is repeated. Thereafter, if it is determined that the etching is finished, the etching is finished, and the wafer is unloaded and collected (914). On the other hand, if it is determined in step 908 that it is out of the range, that is, if the obtained change amount exceeds the set value (allowable value) range for the previous monitor value, the hardware change of the apparatus, for example, via the plasma Abnormalities due to wear or deterioration of parts on the electric circuit are considered. In this case, the output value at the on / off control, that is, the power value is optimized to optimize the bias voltage so that the wafer being processed is not defective as long as the plasma processing is possible. Control is performed as follows (916). Even if such control is performed, if it continuously exceeds the set value (allowable value) range for the monitor value (918), it is possible that there is some abnormality in the apparatus and processing conditions. An alarm is issued (920) and a specific action is taken by the line operator.
[0050]
Also in this case, the relationship between the amount of change in the monitor value and the output value of the high frequency bias and the conditions for issuing an alarm are input in advance as data, or the data for each process is accumulated and converted into data. .
Example 4
Next, a fourth embodiment of the present invention will be described. In the first embodiment, the high frequency voltage is controlled to be turned on / off as shown in FIG. 2B. However, in this embodiment, one period is divided into three or more regions, and time T1, T2,. In addition to setting, the applied power (or amplitude) of each high frequency is set to P1, P2,... Pm and controlled.
[0051]
This embodiment will be described with reference to FIGS. FIG. 10 shows a case where one period is divided into three sub-regions. FIG. 11 shows a flow when processing is performed using the high-frequency power shown in FIG. First, the division number (m) per cycle is set to m = 3, T1, T2, T3 and corresponding P1, P2, P3 are determined (1102), and the etching process is started. For example, P1 is set to 100W, P2 is set to 10W, and P3 is set to 30W. The wafer after the etching process is measured for the CD value, the selection ratio, and the etching rate using the above-described measurement / inspection apparatus (1104, 1106, 1108). Without setting the control value, the next wafer is processed (1114). If the fluctuation amount deviates from the standard value, one of T1, T2, T3 and P1, P2, P3 of the sub-region is set. Change (1116) to process the next wafer.
[0052]
For example, as shown in FIG. 10, when one cycle is divided into three sections, characteristics as shown in FIG. 12 are obtained. The section T1 having the largest amplitude is a section for controlling the maximum ion energy, and the ratio of this section becomes a dominant factor of CD. Therefore, the CD is adjusted by controlling the ratio of the section T1 as shown in FIG. Further, the selection ratio can be finely adjusted as shown in FIG. 12B by changing the amplitude of the section T2 having the smallest amplitude, in other words, by changing the applied power. Of course, even if the amplitude of the other section is changed, the selection ratio is changed. In this case, however, the variation of the selection ratio is large and the control becomes difficult, and the CD and the like are also changed at the same time. Accordingly, in order to finely adjust the selection ratio while minimizing the influence on other factors such as CD, it is suitable to slightly change the amplitude of the section T2. The section T3 having an intermediate amplitude can be used for adjusting the etching rate of Poly-Si. For this reason, the amplitude of the section T3 is set slightly higher than the threshold at which wafer deposition occurs, and this affects the etching rate of Poly-Si, but the amplitude is set so as not to affect the oxide film rate as much as possible. It needs to be adjusted. Under this adjustment, the Poly-Si etching rate can be controlled by changing the ratio of the section T3 as shown in FIG.
[0053]
Specifically, if the CD has changed by ΔCD as shown in FIG. 12A after processing N sheets, the ratio of T1 is changed by ΔT1 so that the CD is returned to the target value, and the next wafer is processed. . If the selection ratio is shifted by ΔS as shown in FIG. 12B, the selection ratio can be maintained at the target value by changing the amplitude of the period T2 by ΔP2 and processing the next wafer. Similarly, if the Poly-Si etching rate is shifted by ΔR, the ratio of the section T3 is changed by ΔT3 as shown in FIG. 12C, and the Poly-Si etching rate can be maintained at the target value.
[0054]
Also in this embodiment, the control range in which only the factor to be controlled can be changed while keeping other factors substantially constant is not so large. However, when the same product is processed in large quantities under the same conditions, the shape or the like does not change. Here, the purpose of the present invention is to adjust the temporal change that occurs only slightly, so that the present invention is effective.
Example 5
Next, a fifth embodiment of the present invention will be described. In this embodiment, the number (m) of sub-regions is changed during the process, and one or both of the times T1, T2,... Tm in one cycle and the high frequency applied powers P1, P2,. is there.
[0055]
The processing flow of this embodiment will be described with reference to FIG. First, time T1, T2, T3 and applied power P1, P2, P3 are set as initial settings (1302), and etching is started (1304). After the etching is started, a monitor value of the plasma emission intensity during the etching is measured (1306). A change amount with respect to the monitor value is obtained (1308), and it is determined whether or not the change amount is within an allowable range (1310). If the change amount is within the allowable range, an etching process by duty ratio feedback control is performed as it is (1312). When the etching is completed (1314), the wafer is unloaded and collected (1316). In step 1310, if the number of sub-regions (m) is deviated from the allowable range (1318), the time T1, T2... Tm and the applied powers P1, P2. Change and process. If such a setting change cannot be processed successfully even if it is repeated a plurality of times (1322), an alarm is issued (1324). Since the amount of change changes when the structure of the wafer to be processed and the etching conditions change, a database that stores data corresponding to each process is created in advance, or a database is built by storing data for each wafer process It is necessary to do.
[0056]
In this embodiment, the method of monitoring and controlling the plasma emission intensity during etching has been described. However, as in the embodiment shown in FIG. 5, the wafer after etching is inspected by an inspection apparatus, and the measurement data is obtained. The determination in step 1310 may be performed based on the determination. Further, as a determination condition in step 1310, the CD value, the selection ratio, and the etching rate may be determined as in the embodiment shown in FIG. Example 6
Next, a sixth embodiment of the present invention will be described. In this embodiment, instead of the ECR plasma apparatus of the first embodiment, a plasma processing apparatus using an inductively coupled plasma source is used, and the high frequency voltage for plasma generation is controlled to be turned on / off as on / off control of the high frequency voltage. . This embodiment will be described with reference to FIG. A high frequency of 13.56 MHz is applied to the induction coil 71 provided outside the vacuum processing chamber 20a by on / off control by a high frequency power source 72, and plasma is generated in the vacuum processing chamber 20a. A high-frequency bias power source 28a for accelerating ions is connected to the lower electrode 27a on which the sample is placed.
[0057]
During the on period of the high frequency power source 72, ions are generated in the plasma, and the ions are accelerated by the high frequency bias power source 28a for bias and incident perpendicularly on the wafer, so that the vertical etching of the wafer proceeds. In the off period of the high-frequency power source 72, ions in the plasma disappear and the etching in the vertical direction stops, and at the same time, reaction products contained in the gas diffuse and deposit on the wafer. That is, the same effect as the on / off control of the high-frequency voltage applied to the lower electrode 27a occurs. By this effect, uniformity and selectivity can be maintained, and the etching shape (CD) can be controlled.
[0058]
The on / off control of the high-frequency power source 72 can be controlled in the same manner as described in the first to fifth embodiments. It goes without saying that the high-frequency voltage applied to the lower electrode 27a may be on / off controlled in the apparatus of this embodiment.
[0059]
Example 7
Next, a seventh embodiment of the present invention will be described. In this embodiment, a capacitively coupled plasma processing apparatus is used as the plasma processing apparatus. This embodiment will be described with reference to FIG. Two parallel plate electrodes are provided in the vacuum processing chamber 20b, a high frequency power source 81 for plasma generation is connected to the upper electrode 82, and a high frequency bias power source 28b for ion acceleration is connected to the lower electrode 27b on which the wafer is disposed. Is connected. In this embodiment, as in the sixth embodiment, either of the high-frequency power supplies is controlled to be turned on / off and controlled as shown in the first to fifth embodiments.
[0060]
As described above, according to these embodiments of the present invention, there is an effect that a wafer can be processed with high reproducibility while suppressing variations in processing dimensions for each wafer without reducing throughput.
[0061]
Note that the data of the etching process in these embodiments may be stored in the control apparatus of the plasma processing apparatus, or may be stored in a host control apparatus that controls the semiconductor manufacturing line. Alternatively, a semiconductor manufacturer and a manufacturing apparatus manufacturer may be connected via a network using the Internet, and data stored in the manufacturing apparatus manufacturer may be used.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an example of a plasma processing apparatus to which the present invention is applied.
FIG. 2 is a longitudinal sectional view showing a detailed configuration of an etching apparatus section in the apparatus of FIG.
FIG. 3 is a diagram showing a relationship between an on / off duty ratio of a high-frequency voltage applied to a sample when using the apparatus shown in FIG. 2 and CD gain, selection ratio, and uniformity etching characteristics;
FIG. 4 is a diagram showing an example of a measured (monitor) value of a cross-sectional shape of an etched sample.
FIG. 5 is a flowchart showing a process control method using the apparatus of FIG. 2;
FIG. 6 is a diagram illustrating an example of an initial value of CD gain in a plasma processing chamber and CD gain characteristics after N sheets processing obtained as a result of monitoring.
FIG. 7 is a longitudinal sectional view showing a configuration of an etching apparatus section according to a second embodiment of the present invention.
8 is a flowchart showing a process control method using the apparatus of FIG.
FIG. 9 is a flowchart showing a control method according to a third embodiment of the present invention.
FIG. 10 is a diagram showing a method of applying a high frequency voltage according to a fourth embodiment of the present invention.
FIG. 11 is a flowchart showing a control method of the embodiment of FIG. 10;
12 is a diagram showing the relationship between the duty ratio and CD gain of the high frequency voltage, the amplitude and selection ratio of the high frequency voltage, and the duty ratio of the high frequency voltage and the etching rate in the high frequency power of FIG.
FIG. 13 is a flowchart showing a control method of the fifth embodiment.
FIG. 14 is an overall configuration diagram showing another example of a plasma processing apparatus to which the present invention is applied.
FIG. 15 is an overall configuration diagram showing another example of a plasma processing apparatus to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Vacuum processing apparatus, 2a-2d ... Plasma processing chamber, 3 ... Vacuum transfer chamber, 4a, 4b ... Lock chamber, 5 ... Transfer apparatus, 6 ... Transfer robot, 7 ... Cassette stand, 8 ... Cassette, 9 ... Inspection apparatus DESCRIPTION OF SYMBOLS 10, 10a ... Control apparatus, 11 ... Orientation flat alignment, 20, 20a, 20b ... Vacuum processing chamber, 21 ... Dielectric window, 22 ... Antenna, 23 ... Coaxial waveguide, 24 ... Matching device, 25, 72, 81 ... high frequency power supply, 26 ... magnetic field coil, 27, 27a, 27b ... lower electrode, 28, 28a, 28b ... high frequency bias power supply, 29 ... ESC power supply, 30 ... exhaust port, 31 ... gas supply device, 32 ... wafer, 33 ... High-frequency voltage waveform 34... Emission monitor, 71... Induction coil, 82.

Claims (2)

In a plasma processing method for processing a sample by applying a high frequency bias,
One period (T) of the high-frequency bias voltage is time-divided into first (T1), second (T2) and third (T3) sub-regions,
The first sub-region is a period for performing feedback control of CD gain, the second sub-region is feedback control for selection ratio, the third sub-region is a period for performing feedback control of CD gain and selection ratio, In the sub region, the applied power of the high frequency bias is set to be large, and the duty ratio T1 / T is changed according to the CD gain.
While processing with the processing conditions set for a plurality of the samples,
A plasma processing method , wherein feedback control is performed in accordance with a processing state of each sample for each unit for processing each sample so that an average applied power within one period is constant . The plasma processing method according to claim 1,
A plasma processing method, wherein the duty ratio is decreased when the CD gain is larger than a predetermined standard, and the duty ratio is increased when the CD gain is smaller than the standard .

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