JP2902474B2 - Plasma etching end point detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching end point detecting device used for plasma etching of an integrated circuit or the like.

[Prior Art] In recent years, plasma etching for performing high-frequency electric discharge machining using an integrated circuit as one electrode in a plasma container for processing an integrated circuit has become widespread, and a plasma etching end point detection device has been used for this. However, this plasma etching end point detection device converts the change in the emission intensity of the plasma into a change in the current to judge the progress of the etching and detects the end point, but the electric signal obtained by converting the emission intensity of the plasma into electricity is used. Since the plasma etching apparatus generates a very small current and the plasma etching apparatus generates a strong high frequency wave, the electric signal of the very small current is converted into an optical signal by a sensor head in order to prevent the influence of the noise due to the high frequency wave on the end point detection. Place where the effect of noise can be prevented by fiber (for example, shielded room)
And the end point is detected by this main body. In this case, since the distance between the sensor head and the main body is several tens of meters or less, an optical fiber system using a plastic optical fiber, which is the cheapest and easy to use at this distance, has conventionally been used for the plasma etching end point detecting device. The reason for using plastic optical fiber is that the optical attenuation is large compared to glass optical fiber, but it can be used if it is several tens of meters or less, and the connection is easy because it has excellent flexibility and the core diameter can be increased. This is because simple and inexpensive connecting parts allow easy connection, and the attenuation characteristics of the plastic optical fiber with respect to each light wavelength match the wavelength of the cheapest light emitting / receiving element. Since the core diameter is large, the applicable frequency is in a low frequency range, which is not suitable for high-speed digital communication, but is most suitable for short-range analog communication.

Hereinafter, a conventional plasma etching end point detecting device using a plastic optical fiber will be described with reference to the drawings.

FIG. 3 is a circuit block diagram of a conventional plasma etching end point detecting device. This conventional example is a sensor head including a light receiving circuit 21 for receiving light emitted from a plasma and converting the light into an electric signal, and an electro-optical conversion circuit 22 for converting the electric signal into light and sending the light to an optical fiber 28. A light-to-electrical conversion circuit 24 for converting light transmitted through the optical fiber 28 into an electric signal, a CPU 26 for detecting an end point,
A plasma etching end point detection device comprising an A / D conversion circuit 25 for taking in data into the PU 26 and a main body control unit 27 comprising an A / D conversion circuit 25, which converts the light intensity of light emitted from the plasma received by the light receiving circuit 21 into an analog voltage signal. , Electrical-optical conversion circuit 22
Then, the analog voltage signal is converted into an analog optical signal, which is transmitted to the main body control unit 27 through the optical fiber 28. The transmitted optical signal is converted into an optical-electrical conversion circuit of the main controller 27.
At 24, the signal is converted into an analog voltage signal proportional to the amount of light, which is converted into a digital signal at the A / D conversion circuit 25, sent to the CPU 26, and compared with the etching standard pattern at the CPU 26 to detect the end point. . In this case, in plasma etching of the integrated circuit, the material to be etched changes with the progress of the etching depth, and the light intensity of the light emission changes according to the change in the material. Therefore, the end point can be detected more easily than the standard pattern.

However, in the above-described conventional example, when the sensor head is moved for the sake of work, the plastic optical fiber also moves and its bending radius changes. If the bending radius changes, the plastic optical fiber has a large core diameter, so that the amount of light attenuation changes, which causes a problem that the amount of light transmitted to the main body changes and the standard pattern cannot be used. To prevent this, a glass optical fiber with a sufficiently small core diameter may be used.However, in the case of a glass optical fiber with a small core diameter, connection is difficult and complicated and expensive connecting parts need to be used and troublesome. Not to be used, it is necessary to use the wavelength of the expensive light emitting / receiving element due to the attenuation characteristics for each wavelength of the glass optical fiber.
Very expensive and cumbersome. Therefore, as before, using a plastic optical fiber with a large core diameter,
It is one of the objects of the present invention to make a plasma etching end point detection device capable of moving a sensor head.

Another object of the present invention is to enable multiplex transmission, in which the conventional technique can transmit only one optical signal related to one plasma etching with one plastic optical fiber.

Means for Solving the Problems In order to solve the above problems, a plasma etching end point detecting device of the present invention receives a predetermined number of light emissions from plasma of plasma etching and converts the light intensity thereof into an analog voltage signal. A light receiving circuit, a predetermined number of V / F converters for modulating the analog voltage signal into an electric frequency signal, a predetermined number of high frequency generation circuits, a switch for performing time division, and an electric circuit for converting the electric signal to an optical signal A sensor head section comprising an optical conversion circuit, an optical-electrical conversion circuit for converting an optical signal into an electric signal, an F / V converter for demodulating an electric frequency signal into an analog voltage signal, a voltage detecting circuit, / D conversion circuit,
The sensor head comprises a main body comprising a CPU for detecting an end point, and a plastic optical fiber for connecting the sensor head and the main body. And then modulate them into a predetermined number of electrical frequency signals, time-division these, cut off a certain value or more, and convert them into a series of ON-OFF two-valued optical rectangular wave frequency signals. And the analog voltage signals are sequentially demodulated from the main body unit through the optical fiber,
U is used to detect the end point.

According to the plasma etching end point detecting device of the present invention, the light emission from each of the plasmas is received by the predetermined number of light receiving circuits by the above-mentioned configuration, and the light is received by each of the light receiving circuits in proportion to the light intensity.
Each analog voltage signal is converted to a predetermined number of analog voltage signals, and the predetermined number of analog voltage signals are modulated into a predetermined number of electric frequency signals by a predetermined number of V / F converters. And oscillates high-frequency signals having frequencies higher than the predetermined number of electric frequency signals one by one, and each of the predetermined number of high-frequency signals is paired with each of the predetermined number of electric frequency signals by a switch. The signal is converted into a series of repetitive electric frequency signals time-divided by combining in step 1
This series of repetitive electric frequency signals is half-wave rectified by an optical conversion circuit and cut off above a certain voltage to form a series of repetitive electric square wave signals. -Converted to a binary optical frequency wave signal of OFF value, transmitted to the main body via a plastic optical fiber, and turned on by the optical-electrical conversion circuit of the main body.
-OFF2 value is converted into an electric frequency signal corresponding to the frequency of the rectangular wave of the optical rectangular wave frequency signal, the analog voltage signal is demodulated from the electric frequency signal by the F / V converter, and this is A / D converted. And a predetermined number of high frequency signals in the demodulated analog voltage signal are detected by the voltage detection circuit, and the predetermined number of electric frequency signals in the analog voltage signal are converted into digital signals. It is sent to the CPU as a discrimination signal after being converted to a voltage signal,
In parallel with this, the demodulated analog voltage signal is converted into a digital voltage signal by the A / D conversion circuit and sent to the CPU, and the CPU determines the predetermined number of digital voltage signals from the digital voltage signal by the determination signal. Each signal of the light receiving circuit is determined, and each end point is detected. In this case, since the frequency domain is lower than that of ordinary digital transmission,
In the plasma etching end point detection device, multiplex transmission not affected by a change in the bending radius of the optical fiber can be performed using a plastic optical fiber having a large core diameter which is not suitable for ordinary digital transmission since it can be applied only to a low frequency region.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit block diagram of one embodiment in which the predetermined number is two in the present invention. Reference numerals 1 and 1 'denote two light receiving circuits, each of which receives light emitted from one plasma and converts the light into two analog voltage signals, one for each of which is proportional to the light intensity. Reference numerals 2 and 2 'denote two V / F converters for modulating the two analog voltage signals into electric frequency signals. Reference numerals 3 and 3 'denote two high frequency generating circuits which generate high frequency signals having different frequencies and higher frequencies than the two electric frequency signals. Reference numeral 4 denotes a time-division switch, which combines each of the high-frequency signal and the electric frequency signal and time-divides it into a series of repeated electric frequency signals. Reference numeral 5 denotes an electro-optical conversion circuit, which performs a half-wave rectification of the series of repeated electric frequency signals and cuts a predetermined voltage or more to form a series of repeated electric square wave signals. Is an optical square wave frequency signal of ON-OFF2 value. Second
(A) shows an optical square-wave frequency signal of the ON-OFF2 values, F ₁ and F ₂ is the radio frequency signal corresponding portion, A and B are the electrical frequency signal counterparts. Reference numeral 6 denotes a sensor head. Reference numeral 7 denotes a plastic optical fiber which transmits light from the sensor head 6 to the main body 13. Reference numeral 8 denotes an optical-to-electrical conversion circuit that converts an optical rectangular wave frequency signal having the ON-OFF binary value into an electric frequency signal corresponding to the frequency of the rectangular wave. 9 is F /
The analog voltage signal is demodulated from the electric frequency signal by a V converter, and the demodulated signal is converted to an A / D conversion circuit 10 and a voltage detection circuit 11.
Transmitted simultaneously. The voltage detection circuit 11 detects the two high-frequency signals in the demodulated analog voltage signal, and uses them as discrimination signals after converting the two electric frequency signals in the analog voltage signal into digital voltage signals. Send to CPU12. In parallel with this, the A / D conversion circuit 10
Converts the demodulated analog voltage signal into a digital voltage signal and sends it to the CPU 12. The CPU 12 discriminates each signal of the two light receiving circuits from the digital voltage signal based on the discrimination signal, and compares these signals with a standard pattern to detect each end point.

The present invention is not limited to this embodiment, and can be configured in various modes. For example, the predetermined number can be freely selected. Further, a method of modulating the light intensity of the light emitted from the plasma into an ON-OFF binary optical rectangular wave frequency signal can be arbitrarily designed in the sensor head by a method other than this embodiment. Also,
A method of determining the end point by demodulating the optical rectangular wave frequency signal of ON-OFF binary value can be arbitrarily designed in the main body by a method other than this embodiment. Further, a scanning method including a high-frequency generation circuit, a switch, and a voltage detection circuit can be arbitrarily designed.

As described above, according to the present invention, since the optical signal transmitted by the plastic optical fiber is an optical rectangular wave frequency signal having ON-OFF2 values, the optical fiber changes its attenuation characteristic by changing its bending radius. However, even if the amount of transmitted light changes, it can be converted into an electric frequency signal without error from now on, so there is no error in the analog voltage signal demodulated from now on, and the CPU can detect the end point more accurately than the standard pattern. It is. Therefore, the plasma etching end point detection device according to the present invention can be used if it is possible to detect a predetermined number of plasma etching end points by multiplexing transmission with one plastic optical fiber using a cheap and easy-to-use plastic optical fiber having a large core diameter. In particular, the measurement position of the sensor head for a predetermined number of plasma etching is moved as appropriate, and even if the bending radius of the plastic optical fiber changes, the special effect that the etching end point can be detected accurately compared with the same standard pattern can be obtained. Play.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of one embodiment of the present invention, FIG. 2 (a) is an explanatory diagram of an optical square wave frequency signal having two ON-OFF values of the present invention, and FIG. 2 (b) is a demodulated analog voltage. FIG. 3 is a circuit block diagram of a conventional example. 1, 1 ': light receiving circuit 2, 2': V / F converter 3, 3 ': high frequency generating circuit 4: switcher 5: electric-optical conversion circuit 6: sensor head unit 7: Plastic optical fiber 8 Optical-electrical conversion circuit 9 F / V converter 10 A / D conversion circuit 11 Voltage detection circuit 12 CPU 13 Main unit processing section

Claims (1)

(57) [Claims] 1. A predetermined number of light receiving circuits for receiving light emitted from a predetermined number of plasmas of plasma etching and converting the light intensity into an analog voltage signal, and a predetermined number of Vs for modulating the analog voltage signal into an electric frequency signal. / F converter, a predetermined number of high-frequency generation circuits, a switch that performs time division, a sensor head unit that includes an electro-optical conversion circuit that converts an electric signal to an optical signal, and converts an optical signal to an electric signal -To-electrical conversion circuit for demodulating an electric frequency signal into an analog voltage signal
An F / V converter, a voltage detection circuit, an A / D conversion circuit, a main unit including a CPU for detecting an end point, and a plastic optical fiber connecting the sensor head unit and the main unit, The sensor head first converts the light intensity of the received light from the received plasma into a predetermined number of analog voltage signals, and then modulates them into a predetermined number of electric frequency signals. Cut, convert to a series of ON-OFF binary optical square wave frequency signals, sequentially transmit them to the main unit via one plastic optical fiber, and the main unit sequentially demodulates the analog voltage signals from there. An end point detecting apparatus for plasma etching, wherein the end point is detected by: