JP2001068459A - End point detector for plasma etching system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To finely and stably detect the end point by adding an electric end point detecting function to a plasma etching system having a function of optically detecting the end point. SOLUTION: A high frequency sensor 14 reads the high frequency power of a plasma etching system, an AD converter 19 in a computer converts into digital signals, a max. value, a min. value and a mean value are obtained by software, and the end point is detected by comparison with a preset slope. An end point detect signal is sent to a controller 31 of the plasma etching system to proceed with the process, acquired data are stored in a memory and can be reproduced whenever required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for monitoring the progress of an etching process and detecting an end point of a plasma etching apparatus typified by the manufacture of a semiconductor silicon wafer or a compound semiconductor wafer.

[0002]

2. Description of the Related Art As a method of detecting the end point of a conventional plasma etching apparatus, the state of plasma emission in an etching chamber, that is, a change in a specific wavelength spectrum from by-product ions or etching seed ions generated in an etching process is determined by one method. One or a plurality of elements such as a photodiode with an optical filter are used to convert the intensity of an electric signal into an electric signal and monitor the progress of etching. As an example of the etching process, a change in the plasma emission spectrum occurs when the process proceeds from the uppermost resist and the film to be etched to the base, and the change is captured to detect the end point. The etching process is controlled by detecting the end point.
That is, it is determined whether to proceed to the next step or to end the process. However, if the change amount is small and the end point detection is unstable, a process of adding an etching time by a timer can be considered. Further, when it is difficult to detect the optical end point, the end point is not detected, and the etching process is performed only by the timer. In this case, a redundant time is set.

[0003]

In the conventional end point detecting device for optical detection, the sensitivity often decreases due to dirt on the window of the light receiving portion, the filter effect due to dirt, the temperature characteristic of the photodiode, and the like. There are non-productivity factors, such as the need for calibration. Also, since optical detection is usually performed from one location in the chamber, it is not possible to capture all changes on the wafer. Depending on the type of the film to be etched and the combination of the resist and the base, the optical change amount may be small. Further, even when the ratio of the area of the film to be etched to the total area of the wafer exposed in the plasma represented by the etching of the oxide film contact hole, that is, the aperture ratio is several percent or less, the optical change amount is small and the end point detection becomes difficult. Due to the above unstable factors, it may be necessary to set the etching time by a timer in addition to the optical end point detection. Alternatively, the process may be performed only by the timer. In these cases, redundant time is set, which is unproductive. Further, the etching depth for each wafer is not uniform. According to the electrical end point detection of the present invention, a minute change can be captured with good reproducibility, and the process progress monitor with high reproducibility contributes to improvement in productivity.

An object of the present invention is to make it possible to add an electric end point detecting function to an existing plasma etching apparatus equipped with an end point detecting apparatus by optical detection. Further, it can be newly incorporated in a plasma etching apparatus. That is, the present invention can be used in combination with the optical end point detecting device or the present invention can be used alone, and it is possible to obtain more stable end point detection. The etching at a stable depth can be performed, and the redundant etching time by a timer can be reduced to increase the productivity.

[0005]

FIG. 1 is a schematic view of a plasma etching apparatus, in which an etching chamber 2 is closed by a lower electrode 3 during etching, and a vacuum pump 21 is used to maintain a constant degree of vacuum determined by process conditions. . After the gas 4 necessary for the etching is supplied, the lower electrode 3 is supplied with the high frequency power from the high frequency power supply 5 via the coaxial cable 7, the high frequency sensor 14, the matching network 6, and further via the coaxial cable 7 via the sensor 14. Supplied.
Therefore, plasma 8 is generated in the chamber. A wafer 9 is mounted on the lower electrode 3, and the film layer 10 to be etched is etched. As the etching progresses, the current emission spectrum of the film to be etched changes in the process of shaving off the uppermost film layer 10 to be etched and forming the next layer. Further, the spectrum of plasma emission changes depending on the material of the film to be etched of the next layer. Therefore, in the conventional endpoint detection method, an optical sensor 11 such as a phototransistor or cds equipped with a filter and an optical final inspection device 12 composed of an amplifier convert the signal into an electrical signal to detect the endpoint, and the plasma etching device. The control signal 13 is supplied to the control device 31 of.

The present invention focuses on the fact that a change in the plasma state due to such etching changes the impedance of the chamber.
That is, the end point can be detected by capturing changes in current and voltage and comparing them with expected changes.

[0007]

According to the present invention, the high-frequency sensor 14 is connected to the high-frequency power line between the matching network 6 and the lower electrode 3 shown in FIG.
Insert The high frequency sensor outputs a small signal proportional to the high frequency power by induction and partial pressure. The output is guided to a converter 46, and analog data obtained by rectifying high-frequency power, that is, a current signal Vp15, a voltage signal Ip16, and a bias voltage value Vdc signal 17 are detected, and a computer having software 20 included in the system of the present invention is provided. The signal is input to the system 18 'and converted into a digital value by the AD converter 19. The digital value is read into a computer, and an average value, a maximum value, and a minimum value are calculated, stored, and displayed every predetermined time (for example, 0.5 seconds for one data point). It is conceivable that the sensor 14 'is inserted between the high-frequency power supply 5 and the matching network 6 and leads to the converter. Further, a sensor built in a matching network or a high-frequency power supply may be used.

The ability to read data into a computer and perform A / D conversion depends on the performance of the computer and the A / D converter. However, in order to obtain an average value, the data is read as fast as possible, that is, a large amount of data is collected and converted. And calculate it. The method of starting reading of the high-frequency power data can be selected, the first method starts when the keyboard is pressed, and the second method starts when the Vp
Or, the case where the value of Ip exceeds the set threshold value, and the third is performed by receiving a start signal from the plasma etching apparatus. 1 of data reading end method
The second is when the keyboard is pressed again, the second is V
The case where the value of p or Ip falls below the threshold value, and the third case where the start signal from the plasma etching apparatus is turned off. Further, it is possible to select to read and collect data up to the maximum value of the set etching time axis ignoring the stop signal. Data can be automatically and repeatedly collected by setting the loop.

FIG. 6 shows a schematic diagram of the operation. The following is an example of the operation. By inputting R in the main menu, the data can be reproduced as a graph. Then enter the file name you want to reproduce. Enter * to reproduce the last collected data. ? When "5" is input, data of five files is reproduced by overwriting. When "-2" is input, the data collected two times before is reproduced on the display device 27.

The behavior of the collected data can be easily observed by processing the average value, and the stability of the end point detection can be provided. Further, since the data has fluctuation, a change equal to or less than the resolution of the AD converter can be captured by obtaining an average value. Since the data contains components such as noise and arcing and power components including fluctuations, the maximum and minimum values in the determined time interval are stored, and this change causes abnormal changes in the impedance of the chamber. Can also be caught.

The obtained data can be stored in the storage device 28 in waveform units or process units. Further, it can be displayed on the display device 27. FIG. 2 is an example of the display,
The vertical axis 23 (for example, the maximum value of Vp 1000) of the graph along the data collection number order shown on the horizontal axis of the graph, that is, along the etching time axis 22 (for example, the maximum value 1000 points × set time).
The waveform of the graph changes in the direction of the maximum value of V, Ip 25A) depending on the amount of the current value Ip or the voltage value Vp. In the high frequency ON / OFF, the waveforms of the current and the voltage 34 sharply rise and fall like 24 and 25. However, when the film to be etched is scraped off and the next layer appears, the current and voltage gradually change like a waveform 26. The increase or decrease in the amount of change is determined by the first step 1 depending on the material and the order of the layer to be etched.
The waveform is displayed as a waveform 35, a second step 2 waveform 36, and a third step 3 waveform 37. In the case of FIG. 2, a negative slope (-) is expected, and the magnitude of the slope can be displayed on the screen as a slope 32, a slope 33, and a slope 33 '. This change in impedance appears as a change in Vp and Ip.

FIG. 3 shows the variation 34. The setting of the amount of change 48, the setting of the amount of change 49, and the setting of the amount of change 49 ', which are expected to check the range of the inclination, are expressed in different manners as shown in FIGS.
Are displayed as the slope 32, the slope 33 and the slope 33 ', so that it is easy to confirm the setting. The software can be compared at any time by software, and if it is within the range of the slope for the set time, the possibility of detecting the end point is recognized. Further, whether the average value during the set time is positive or negative, or the expected value is a value exceeding the value 33 'derived from a fixed ratio (X%, 10%) of the change amount setting 49'. It is determined based on whether or not this is the case, and the final determination of end point detection is made. As a specific example of the setting, when the end point is detected with a negative slope of Vp, the change amount setting 48 is -0.5 V, the change amount setting 49 is 1 V, and the change amount setting 49 'is 10% of 1 V, that is, In the setting where determination is made with five points of data with 0.1V, the slope is 32 in FIG.
33 ', 33. That is, the slope 32 is (0.5
x5) / 5, and the slope 33 becomes-(1x5) / 5. The slope 33 'is (1x5x0.1) / 5.

An end point is detected within an end point detection range 40 that satisfies the Vp value or Ip value range 38 and the time axis range 39 shown in FIG. 2, and the result is graphically displayed as an end point detection signal 45. I do. Also, a display for confirming an output signal is performed as an EPD 41 and an EPD OUT 42 in which a timer can be set.

FIG. 4 shows an example of a waveform having a small amount of change. When there are slopes 46 and 45 similar to the end point detection range 43, X% of the maximum value is detected after the maximum value 44 of the waveform is detected.
The end point detection 47 is made by the slope 45 at the lower value.
Is an example.

The end point detection signal is displayed on the display device 27 of FIG.
Control device 31 of plasma etching apparatus 1 via 9
And sends an end point detection signal 30 to control the process. FIG. 7 shows a partial flow of the program.

[0016]

FIG. 5 shows an example in which the end point detecting device 18 of the present invention is connected to the plasma etching device 1. In this example, in which a new sensor and cable are laid, a general desktop computer is used, but a laptop computer or a dedicated computer that can be built in the device may be used. That is, such modifications are included in the scope of the present invention.

[0017]

As described above in detail, according to the present invention, it is possible to increase the possibility that the end point of the plasma etching apparatus can be finely and stably detected. In addition, a new end point detection function can be added by slightly changing the plasma etching apparatus. In addition, since the process can be monitored in real time and data such as Vp, Ip, Vdc, end point detection time, and data collection time can be obtained, it is possible to contribute to improvement of quality control and operation control of the apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a plasma etching apparatus and an end point detection apparatus for the plasma etching apparatus.

FIG. 2 is a graph display example 1 of collected data.

FIG. 3 shows the amount of change in the data displayed in FIG.

FIG. 4 is a graph display example 2 of collected data.

FIG. 5 is a schematic diagram of connection between a plasma etching apparatus and an end point detection apparatus for the plasma etching apparatus.

FIG. 6 is an operation schematic diagram.

FIG. 7 is a partial flow of a program.

[Explanation of symbols]

Schematic diagram 1 of a plasma etching apparatus, etching chamber 2, lower electrode 3, etching gas 4, high frequency power supply 5, matching network 6, coaxial cable 7, plasma 8, wafer 9, wafer layer 10, optical sensor 11, optical sensor End point detection device 12, control signal 13, high frequency sensor 14, Vp signal 15, Ip signal 16, Vd
c signal 17, end point detector 1 for plasma etching apparatus
8. Computer system 18 ', AD converter 1
9, software 20, vacuum pump 21, etching time axis 22, vertical axis 23 of graph, rising waveform 24, falling waveform 25, slope waveform 26 due to etching,
Display device 27, hard disk 28, interface 29, control signal 30, control device 31 of etching apparatus,
Detection setting slope 32, detection setting slope 33, detection setting slope 33 ', change amount 34, step 1 waveform 35,
Step 2 waveform 36, Step 3 waveform 37, Vertical axis range 3
8, horizontal axis range 39, end point detection range 40, EPD41, E
PD OUT 42, end point detection range 43, maximum value of waveform 4
4. Slope 45 by etching, converter 46, end point detection 47, setting of change amount 48, setting of change amount 49, setting of change amount 49 ', slope 50 by etching

Claims (1)

[Claims] 1. A high-frequency power amount supplied to an etching chamber of a plasma etching apparatus is read into a computer as a voltage value and a current value by a sensor, and a value derived from the current value and the voltage value and a change amount thereof are used for an etching process. An end point detector for a plasma etching apparatus that monitors a state and detects an end point, sends an end point detection signal to the outside, and controls the plasma etching apparatus.