JPH04338663A - Measuring equipment for plasma - Google Patents

Abstract

PURPOSE:To stably perform the measurement of the intensity of emission of plasma when plasma moves in response to the movement of magnetic field. CONSTITUTION:A high frequency voltage is applied between electrodes 2 and 3 in a vacuum chamber 1, a magnet portion 5 is rotated and then plasma is rotated on a wafer 4. Light with a predetermined intensity of emission at a predetermined point on the wafer 4 is led to a photoelectric converter 8 and converted to an analog electric signal; and this is sampled by using pulses from a rotary encoder 6 as timing signal. With respect to each sampling value, the mean value of movement is determined and the intensity of emission is determined. Since the sampling values at each rotating period corresponds to the position of plasma, the results of treatment contain no change in the intensity of emission accompanied with the plasma movement.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma measuring device.

0002

2. Description of the Related Art Currently, in the manufacturing process of semiconductor devices, many processes using gas plasma are used. For example, gas plasma is used to perform etching, resist ashing, and the like.

Among such processes, to take an example of etching process, a pair of parallel plate electrodes are placed facing each other in a chamber, a processing gas such as a halogenated gas is introduced therein, and a high frequency voltage is applied between the electrodes. This is applied to generate gas plasma, and its active species etch polysilicon, silicon nitride, or an oxide film.

[0004] In such processing using plasma, the concentration of chemical substances in the plasma may correspond to the processing state, so it is necessary to focus on a certain type of chemical substance in the plasma and monitor its emission intensity. There are times when it is meaningful to do so. For example, the emission intensity of the same chemical substance as the reaction product generated by etching decreases after etching a certain film by the amount that was generated by etching, so the end point of etching can be detected by capturing this change. can do.

Conventionally, for example, a window is formed in a vacuum chamber, and a condensing lens placed outside the window condenses light at a certain point on the wafer, which is then converted into an electrical signal by a photoelectric converter. Monitoring of luminescence is being carried out.

[0006]

[Problems to be Solved by the Invention] For example, a method of generating plasma using parallel plate electrodes and performing etching using this method enables highly uniform processing, but it is relatively difficult to generate plasma. Since a high gas pressure is required, the collision energy of the active species is large, and as the integration of devices progresses further in the future, there is a risk that damage to the wafer due to etching will affect the device characteristics.

For this reason, consideration has been given to incorporating into etching a method that traps electrons by forming a magnetic field in an electric field and generates high-density plasma even in low gas pressure. Because it is difficult to create a magnetic field in the entire area at the same time, for example, a permanent magnet is installed outside the chamber, and this magnet is rotated around a vertical axis to rotate the magnetic field, which spreads the processing area. Structures such as earning money are being considered.

However, when the magnetic field moves, the plasma also moves, so the conventional method of simply monitoring the light emission intensity at a single point on the wafer will cause the plasma to change due to changes in the light emission intensity as the plasma moves. It is not possible to accurately capture changes in its own luminescence intensity. In this case, a method of moving the light receiving system to follow the plasma can be considered, but the equipment configuration is complicated and factors such as reflection are added depending on the surrounding conditions of the measurement point, so it is still difficult to perform stable measurements. Can not.

The present invention was made under these circumstances, and its purpose is to provide an apparatus that can stably measure the emission intensity of plasma when the plasma moves due to the movement of a magnetic field. It is about providing.

0010

[Means for Solving the Problems] The present invention generates plasma by forming an electric field and a magnetic field in a vacuum chamber into which gas is introduced, and while repeatedly moving the magnetic field along a predetermined movement path. In an apparatus for moving plasma, a light receiving section receives light emitted from the plasma and converts it into an electrical signal, a sampling means samples the electrical signal from the light receiving section at a timing that matches the movement of the magnetic field, and the sampling means comprises: A signal processing unit that processes the obtained sampling values is provided.

[0011]

[Operation] For example, when rotating a permanent magnet placed outside the vacuum chamber to rotate the plasma along a circular path, if the electrical signal from the light receiving section is sampled using pulses from a rotary encoder as a timing signal, Each sampling value corresponds to a predetermined rotation angle position of the permanent magnet. Therefore, the sampling values during each rotation period of the plasma become data corresponding to the position of the plasma, and by processing this data, the measurement of the emission intensity of the plasma becomes stable.

0012

[Embodiment] An embodiment of the present invention will be described below. As shown in FIG. 1, in a vacuum chamber 1 constituting a reaction vessel, flat electrodes 2 and 3 are arranged vertically facing each other. For example, the upper electrode 2 is In addition to being grounded, the lower electrode 3 is connected to a high frequency power source RF via a capacitor C. These electrodes 2 and 3 constitute parallel plate electrodes, and may also serve as the vacuum chamber 1.

The vacuum chamber 1 has a structure in which a predetermined vacuum can be drawn and a reactant gas and a predetermined additive gas can be introduced between the parallel plate electrodes 2 and 3. A semiconductor wafer 4, which is an object to be processed, is placed on the upper surface of the lower electrode 3, and a clamper or the like is provided to securely fix the wafer 4.

Above the vacuum chamber 1, a rectangular rod-shaped magnet portion 5 magnetized with an N pole and an S pole protruding from one end and the other end, respectively, is mounted on a vertical axis of rotation located above the center of the wafer 4. The rotary encoder 6 is provided to be rotated by a motor M around a shaft 51, and a rotary encoder 6 is attached to the rotary shaft 51, which outputs a pulse at every fixed angle.

Further, a window 11 is formed on the side wall of the vacuum chamber 1 for transmitting the plasma generated between the electrodes 2 and 3 to the outside. A condensing lens 71 and an optical fiber 72 are installed to condense the light transmitted through the spectrometer 7 and transmit it to the spectrometer 7 . The light separated by the spectrometer 7 is converted into an electrical signal by a photoelectric converter 8, and is input to the sampling means 9 via an amplifier 81. In this example, the condenser lens 71
, the optical fiber 72, the spectroscope 7, and the photoelectric converter 8 constitute a light receiving section 70 for receiving plasma and converting it into an electrical signal.

The sampling means 9 is an analog/digital (A/D) system that samples an analog signal from an amplifier 81 and converts it into a digital signal using, for example, a pulse from the rotary encoder 6 as a timing signal.
D) Consisting of a converter. Further, on the output side of the sampling means 9, there is a signal processing section 91 such as a CPU that stores the digital signal sampled by the sampling means 9 in a memory and performs processing such as a moving average to be described later.
is connected.

Next, the operation of the above-mentioned embodiment will be explained based on the etching process specifically performed. A wafer 4, in which a silicon oxide film is formed on a silicon wafer and a resist film mask is formed on its surface, is placed on the lower electrode 3, and CHF3 gas, for example, is introduced into the vacuum chamber 1 at a flow rate of 50 SCCM. , evacuate and set the gas pressure to, for example, 40 mm Torr. Furthermore, high-frequency power with a frequency of 13.56 MHz and a power value of 600 W is applied between the electrodes 2 and 3, and the magnet part 5 is rotated at a speed of 3.5 seconds per rotation to generate plasma, which causes the silicon oxide film of the wafer 4 to be heated. was etched.

[0018] And the emission wavelength of CO is 483,5n
A high-precision spectroscope 7 extracts light with a wavelength of m, and an electric signal (voltage value) corresponding to the intensity of the spectroscopic light is output from an encoder 6 that outputs, for example, 100 pulses per rotation of the magnet section 5. sample the pulse as a timing signal.

Further, the signal processing section 91 outputs the luminous intensity (sampled value) corresponding to each sampled voltage value as time series data, for example, in a graph, and also calculates the sum of data for one rotation of the magnet section 5. The result (total sum) or averaged value is monitored as an index of plasma emission intensity.

Regarding the calculation of the total sum of data, first, 1 from the encoder 6 corresponding to one rotation of the magnet section 5 is
When the next pulse is input to the sampling means 7 and new data is taken in, the oldest data is subtracted from the sum of the previous data and new data is added. The sum of the light emission intensities for the next one rotation is calculated based on the position rotated by one pulse angle from the data acquisition start position of the magnet part 5, and by repeating such calculation, each of the magnet parts 5 The total sum of the light emission intensity for one rotation based on the angular position is sequentially determined.

Therefore, for each summation, the number of samplings,
In other words, by dividing and averaging by the number of pulses of the encoder 6 for one rotation, a moving average of the plasma emission intensity has been calculated. It corresponds to the emission intensity of the plasma and can be used as an indicator.
The processing results of these data can be treated as plasma emission intensity, for example, when monitoring wafer processing status or equipment operating status by capturing changes in emission intensity or deviations from reference intensity. can.

Here, the signal processing section 91 plots each sampling value of the emission intensity in time series in the example of the etching process described above and graphs the results, which is shown by a solid line A in FIG. Note that the vertical axis is an arbitrary value corresponding to the emission intensity.

As can be seen from this result, vacuum chamber 1
The emission intensity at the measurement points within the range fluctuates greatly at regular intervals from around 600 to around 1700 immediately after the start of measurement, for example, due to the movement of plasma accompanying the rotation of the magnetic field. However, in this graph, the distance between adjacent peak values corresponds to one cycle, that is, one rotation of the magnet section 5.

When plotting each sampling time series and making a graph like this, the luminescence intensity changes at a constant period, but the pattern of change depends on the measurement point and the state of light reflection inside the vacuum chamber 1. For example, in FIG. 2, two upper limit peak values appear in each cycle.

Further, in FIG. 2, the solid line B is a graph (moving average line) showing the transition of the moving average value of the luminescence intensity mentioned above, and in this example, the moving average value decreases by about 10% around 160 seconds after the start of measurement. are doing. This is because light with the emission wavelength of CO is detected by spectroscopy, so when etching is completed, the amount of CO that was generated during etching is
This corresponds to a decrease in O concentration.

In order to confirm that the point at which the moving average value decreases as described above is the etching end point, etching was performed under exactly the same conditions as described above, and plasma generation was performed before and after the moving average value decreased. When we checked the surfaces of the wafers when they were stopped using SEM photographs, we found that a very thin silicon oxide film remained on the wafers before the reduction, but on the wafers after the reduction, the surface of the underlying single-crystal silicon substrate remained. It was completely exposed. Therefore, it is confirmed that the above-mentioned decrease in the moving average value is due to the completion of etching.

As a result, it can be seen that the moving average value of the data obtained by the signal processing section 91 described above corresponds to the light emission state of the plasma.

According to the present invention, in order to rotate the magnetic field, instead of rotating the permanent magnet, for example, three-phase alternating current may be applied to the three-phase winding to form the magnetic field of the motor. In this case, the above-mentioned sampling may be performed based on the current flowing through the winding.

Furthermore, the present invention is not limited to etching using plasma, but can also be applied to ashing of a resist film, or to generating ions by applying plasma to a target.

Furthermore, the present invention can be applied to the case of repeatedly moving along a predetermined movement path, and therefore can be applied not only to the case of rotating the magnetic field but also to, for example, the case of linearly reciprocating movement.

[0031]

[Effects of the Invention] According to the present invention, since the luminescence intensity is sampled at a timing that matches the movement of the magnetic field, even if the luminescence measurement point is fixed and the luminescence intensity at that point changes greatly, e.g. For example, the nth data of the first cycle and the nth data of the second cycle correspond to each other in terms of the plasma position, and therefore, for example, the sampling values (emission intensity) in the movement cycle are the data that corresponds to each other with respect to the plasma position. If we perform processing such as calculating the sum or moving average of the components and take the processing result as the plasma emission intensity, the value will correspond to the emission intensity of the plasma itself without incorporating changes due to the movement of the plasma. In the end, the luminescence intensity can be measured stably.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing measurement results in an example of the present invention.

[Explanation of symbols]

1 Vacuum chamber 2, 3 Electrode 5 Magnet part 6 Rotary encoder 70 Light receiving part 91 Signal processing section

Claims (1)

[Claims] 1. An apparatus that generates plasma by forming an electric field and a magnetic field in a vacuum chamber into which gas is introduced, and moves the plasma by repeatedly moving the magnetic field along a predetermined movement path. a light receiving section that receives the light emitted from the light receiving section and converts it into an electrical signal; a sampling means that samples the electrical signal from the light receiving section at a timing that matches the movement of the magnetic field; and a sampling means that processes the sampling value obtained by the sampling means. A plasma measuring device characterized by comprising: a signal processing section.