JPH07153599A - Automatic tuning method and device for plasma generating microwave circuit - Google Patents

Abstract

PURPOSE:To perform automatic variable value control on a desired operational condition value by a stub adjuster to drive slidably a directional coupler, an E surface stub and an H surface stub on respective two driving shafts by a motor in a wave guide. CONSTITUTION:The tip surfaces of an E surface stub and an H surface stub are adjusted to the same plane with the inner wall surfaces 6e and 6h (reference surface) of a wave guide 6. A silicon wafer as a dummy or a standard material is inserted as a load in a bell jar 8a of a plasma generating chamber 8. Constant power is made incident on the load from a microwave generator 3. At this time, though incident electric power in the wave guide 6 and load impendance are not adjusted to each other, the incident electric power and reflected electric power are measured by a directional coupler 5, and are sent to a controller through a power meter 9. The controller calculates reflectance, and stores it in respective coordinates on a RAM10b. Only by determining desirable incident electric power and reflectance and setting them in a controller when they are used, the controller tunes them automatically to a vicinity value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic impedance tuning device and an automatic impedance matching method for a microwave circuit for plasma generation.

[Prior art]

Conventionally, when a plasma device using microwaves is used, a high voltage is first applied to a magnetron to generate microwaves (hereinafter, also referred to as incident power), and a reflected wave measuring device attached to the device. Thus, three (three stub type) or four probes Se inserted in the microwave waveguide P so that the reflected power is about 3% of the incident power are detected and the protrusion amount of the same number of stubs St in the waveguide is detected. The impedance of the microwave generation source M and the load W are adjusted automatically or manually through the control device C (Japanese Patent Laid-Open No. 3-174803) to generate a desired microwave power in the plasma generation chamber (hereinafter referred to as load). (Also called) (FIG. 4). However, the reflectance often fluctuates abnormally due to contamination of the load, changes in the gas flow rate, changes over time in the magnetron, etc. during or during each plasma treatment. It was difficult to return to the setting conditions of, the reproducibility was poor, the plasma discharge became unstable, and the accuracy and workability were poor.

[0003]

Microwaves are used in various fields, and particularly in the manufacture of ICs, highly reproducible and precisely controlled plasma is required. It is well known that a so-called hysteresis occurs in which microwaves increase / decrease in output power of the generation source and the impedance of the plasma load changes linearly within a certain range and becomes discontinuous at a certain point. It is very difficult to match the impedance with four or three stubs due to such microwave characteristics, and a more stable control method is being demanded.

Further, a wafer which is an IC substrate is a conventional 4
The diameter has been expanded from one with 6 inches to that with 6 inches to 8 inches, and the power up of the microwave is required accordingly, but the conventional rod-shaped stub and the standing wave detection antenna are microwave. In the case of a matching device protruding into the passage (waveguide), microwaves may be discharged to its antenna or stub, and it is difficult to increase the power beyond the power currently used, and future challenges It is being done.

[Means for Solving the Problems]

In order to solve the above problems, the present invention provides
Between the microwave generator and the load, i.e., the directional coupler in the waveguide, the rectangular cross-section is provided with branch pipes on two adjacent surfaces in the middle, and the cross-section of the waveguide is provided in this branch pipe. A stable stub and a high stub matching device, which has an E-shaped stub and an H-shaped stub each of which has almost the same shape and the same size and a flat tip, are slidably mounted by a motor with two drive shafts, respectively. Measures have been taken to cope with the increase in power and to automatically control desired operating condition values as additional values.

In this method, the operator can set an arbitrary reflectance to E /
When input to the H tuner controller (hereinafter referred to as the controller) and instructing a predetermined operation procedure, the controller measures the incident power and the reflected power over the entire movable range of the E-plane stub and the H-plane stub for the load. Then, the reflectance is calculated and stored in the storage element (hereinafter referred to as a table map). Then, an area in which the set reflectance is relatively large is searched from the table map, and the E-plane stub and the H-plane stub existing at the center position are driven and set. In addition, the operator can display a table map stored in advance as a three-dimensional diagram on the display via a computer, and confirm the optimum position for obtaining the desired reflectance from the diagram and check the E-plane stub and H-plane stub. It is also possible to drive and set with the manual key of the controller.

With the above settings, microwaves are incident from the microwave generator through the waveguide toward the load. The directional coupler always detects the incident power and the reflected power at the current position of the stub, receives the signal, calculates the reflectance by the controller, and calculates the difference between the value and the reflectance of the initial condition (hereinafter, deviation and When the deviation exceeds a predetermined value, the E-plane stub and H-plane stub are moved from the current position by a predetermined amount according to the deviation, and the surrounding reflected power is measured. In addition, the automatic tracking value type control method in which the reflectance is calculated, the movement direction and the movement amount are determined based on the result, and the stepping motor is rotated by the signal from the controller to move the E surface stub and the H surface stub are adopted. Is.

[Action]

According to the present invention, when the optimum reflectance for the treatment of the load as the object to be processed is determined as the initial condition and input to the controller as described above, the reflectance or its value is determined by the table map showing the reflectance. The area where a lot of close reflectances exist is automatically selected, and the E surface stub and H surface stub are moved and set to the position corresponding to the reflectance at the center of the area. Become.

As described above, the initial condition is set by selecting the center position of the region where many reflectances or values close to the initial condition exist on the table map.
If the small condition variation that occurs during operation of the device is within a range close to the initial value, there is almost no need to move the E-plane stub and H-plane stub from the current position, and even if it is necessary to move it by tuning, Since the moving range is comparatively small, it can be relatively easily returned to the initial condition.

As described above, since the control of the present invention is set on the basis of the reflectance as the characteristic value of the device, it is a device for matching the impedance with the load, the E-plane stub,
The H-face stub must move accurately. For this reason, by moving each stub by two simultaneously rotating drive shafts, the inclination of the stub is eliminated and a setting error hardly occurs. Therefore, reproducibility of the characteristic value (reflectance) is ensured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an essential part of an IC plasma dry etching apparatus using microwaves, and FIGS. 2 and 3 show the structure of a stub matching device in this microwave plasma processing apparatus. A description will be given below with reference to these figures. This microwave plasma processing apparatus 1 includes a microwave power source 2, a microwave generator 3, an isolator 4, a directional coupler 5, a waveguide 6, and branch pipes 7e and 7h in a part of the waveguide. Stub matching device (E / H tuner) equipped with E-side stub 20 and H-side stub 21
7, a plasma generation chamber (also referred to as a load) 8, a power meter 9, an E / H tuner controller 10 (hereinafter referred to as a controller), and a personal computer 11 (hereinafter referred to as a computer) as standard equipment. 10 to 60 mm in the waveguide 6 depending on the object to be processed.
The extension waveguide 12 having a length is connected.

As shown in FIGS. 2 and 3, the stub matching device 7 is located in the middle of the waveguide 6 having a rectangular cross section, and has two surfaces adjacent to each other, which have substantially the same shape and size as the cross section of the waveguide 6. The E-plane stub 20 in the branch pipe 7e that is branched at a right angle to the direction of the magnetic field in the waveguide (hence, in a plane parallel to the electric field).
An H-plane stub 21 is slidably inserted into a branch pipe 7h that branches in a direction parallel to, and the tip of the stub is flat. Since the drive mechanism of the stub is the same for both the E-side stub 20 and the H-side stub 21, the H-side stub 2
1 will be described. The H-face stub 21 is screwed and fixed 30 to a sliding board 29 in the branch pipe 7h, and a stepping motor 23 is attached to two female screws 28, 28 formed on the upper surface of the sliding board 29 via a coupling 27. A main drive shaft 24 having a male screw connected thereto and a sub drive shaft 25 having a male screw that is interlocked with the main drive shaft 24 via a timing belt 26 and a pulley 26a are screwed together. These shafts 24 and 25 are rotatably attached to the frames 32a and 32b, which are screwed 7c to the branch pipe, via bearings 33 and 33.

The comb-teeth-shaped slide plate 31 wound around the entire sides of the slide plates 29, 29 is made of a thin plate of non-ferrous metal such as copper, brass, beryllium-copper alloy or the like, and has a comb-teeth-shaped base portion. It has a slight radius and is folded back at about 180 °, and the radius is springy. Since the tip of the comb-shaped portion is elastically in contact with the wall surface in the branch pipe 7e, a smooth movement of the sliding board can be obtained.

In FIG. 3, 34, 34 are limit switches for determining the limit of vertical movement, 35 is a sensor for measuring the reference position of the H-plane stub 21 (the zero point is on the same plane as the waveguide inner surface 6h). 36 is a limit switch pressing rod attached to the sliding board 29, and 7b is a cover. As described above, these structures are the same for the matching device of the E-plane stub 20.

Although not shown, the microwave generator 3 is equipped with a magnetron, which generates microwaves when a high voltage is applied from a microwave power source, and reaches the plasma generation chamber 8 using the waveguide as a line. The plasma generation chamber 8 is provided with a bell jar 8a, the inside of which is kept in a vacuum or an appropriate gas atmosphere, and a load, for example, a silicon wafer as an object to be processed is loaded at a predetermined position. The above is an outline of hardware.

A method of using the above device will be described. First, the E-side stub 20 and the H-side stub 2 have the above-described standard device configuration.
The tip surface of 1 is aligned with the inner wall surfaces 6e and 6h (reference surface) of the waveguide 6 (confirmed by the sensor 35). A dummy or a silicon wafer as a standard material is loaded into the bell jar 8a of the plasma generation chamber 8 as a load, and a microwave having a constant power, for example, 500 W, is incident from the microwave generator 3 toward the load. At this stage, the impedance of the incident power in the waveguide 6 and the impedance of the load are naturally not matched, but the incident power and the reflected power in the waveguide are detected by the directional coupler 5 and are output as a signal by the power meter 9
Is sent to the controller 10 via. Controller 1
0 calculates the ratio (reflectance%) of the reflected power to the incident power after A / D conversion of this signal and stores it in the EH coordinate (0, 0) on the RAM 10b. Then, the H-face stub 21
(Or E-plane stub 20, which is omitted because it is the same below) is retracted from the inner wall surface 6h of the waveguide 6 by an arbitrary amount, for example, 2 mm. In this state, the incident power and the reflected power in the waveguide 6 are detected again in the same manner as described above, the power meter 9 sends them to the controller 10, the reflectance is calculated, and the EH on the RAM 10b is calculated.
Store at coordinates (0, 2). Further, the H-plane stubs 21 are sequentially retracted at equal intervals to 30 mm, and the same operation is repeated to write the respective reflectances up to (0, 30) of the EH coordinate of the RAM 10b.

When the measurement of the retreat amount of the H-plane stub 21 up to 30 mm and the storage of the reflectance are completed, the E-plane stub 20 is retracted by 2 mm, and the H-plane stub 21 is moved backward (or the tip end surface of the waveguide 6 is (Proceeding from the same surface as the wall surface 6h), the same power measurement, reflectance calculation, and writing to the ROM 10a as described above are performed. This operation is sequentially repeated up to the movable limit of the E-plane stub 21, and the reflectance at each coordinate value is calculated for each RO.
Write and store in M10a. In this way, the two-dimensional data as shown in Table 1 for the reflectance in the waveguide 5 under the condition of constant microwave power, for example, 500 W, is stored in the controller 20 by the standard device. In this measurement procedure, when the reflectance reaches 50% or more on a certain measurement line, the measurement on that line is stopped at that position, the E-face stub is sent to the next stage, and the H-face stub is moved backward. It is more reasonable to do so. The data created in this way is a table map. Although the measurement interval is set to 2 mm in the above description, the measurement points are linearly complemented on the controller.

Further, the reflectivity in the waveguide 5 is measured in accordance with the above procedure by sequentially changing the incident power from 1000 W to 1500 W and the power is changed to 10, 20, 3 in the waveguide 6.
An extension waveguide 12 having a length of 0, 40 mm or the like is additionally provided, and the reflectance inside the waveguide 5 is measured and stored by the above-described operation procedure. The reflectance data stored in this manner represents the device characteristics, and the controller 11 is accessed from the computer 11 as necessary to display the data on the display 11a in the form of a table or as a three-dimensional graph with high reflectance. Or referred to as printed by a printer (not shown). Table 1 is a table map showing the reflectance when the 20 mm extension waveguide 12 is connected and the incident power is used as 500 W.

[0019]

[Table 1]

To describe one embodiment of the present invention, at the beginning of an etching operation on a semiconductor, an operator first determines any incident power value and reflectance that seem most desirable for etching the semiconductor to be processed. If the values are, for example, 500 W and 5%, respectively, 500
Using a W microwave generator, E / H the reflectance value of 5%.
It is set on the tuner controller 10. The controller 10 refers to the stored table map, finds the area where the designated reflectance of 5% is most present, and tunes to the center position. If there are multiple areas where the numerical value exists, the standard deviations are calculated for eight surrounding points, and the area with the smaller value is tuned preferentially, and the position corresponding to the coordinate value (predetermined from the waveguide inner surfaces 6e, 6h is determined. The main drive shaft 24 and the sub drive shaft 25 are rotated via the stepping motor 23 to set the E surface stub 20 and the H surface stub 21.

As described above, the stable condition for setting the condition by selecting the reflectance value required by the operator from the area in which a relatively large amount exists by referring to the table map and selecting the one in the center of the table. The setting can be performed quickly, and since the values close to the ideal conditions are gathered in the vicinity of the set position, there is an effect that the number of times of tuning required during the operation is reduced.

Immediately after the condition is set and the apparatus is started up, the E surface stub and the H surface stub are driven to be programmed so as to always maintain the set reflectance, and the automatic tuning is performed accordingly. The outline is shown in the flowchart (FIG. 5), but prior to the explanation, the terms related to the automatic tuning function will be explained. Reference position (e, h) Initial position or position immediately after movement by calculation Interval (intv) Distance between four points around the reference position Reflectance (VSWR) (%) Reflected power / incident power × 100 (Equation 1) Setting Value (setv) (%) This is the value of reflectance to be set. Measured value (MSV) (%) Reflectance obtained from actually measured incident power and reflected power Reflected power / incident power × 100 (Equation 2) Deviation (DIF) (%) Difference between measured value and set value, for example DIF (e, h) = setv-MSV (e, h) (Equation 3) Transfer rate (MVR) Ratio of change in stub position to change in reflectivity MVR = Change in transfer amount (mm) / Change in reflectivity (MVR) %) (Equation 4) For example, change in movement amount = (e, h-intv) change in reflectance = MSV (e, h-intv) -MSV (e, h) movement amount movement amount = MVR × deviation 5) Movement rate table This is a data table prepared to control the movement direction and movement amount of the stub, which is composed of a reference position and five surrounding points. When point A is the reference position on the EH coordinate of FIG. 6, B, C, D, and E are the four surrounding points. The following data is recorded in each table. (1) EH coordinate (2) Measured value (3) Movement rate (only four points around are recorded) (4) Confirmation of data existence (only four points around are recorded) Set between the reference position and the current point It is determined whether or not there is a value, and if the set value is 5% and the VSWR at the reference position is 3% and the VSWR at the point B is 8%, it is determined that there is a target position in the negative direction of the E surface.

Next, the method of automatic additional value control of the present invention will be described with reference to the flowchart. At the time when the device starts up, the transfer rate table in the RAM 10b has been initialized (a). The optimum positions of the E-plane stub and the H-plane stub obtained from the above table map are set by the manual button of the controller 10, or the reflectance is input and the controller 10 positions the load and the position of the E-plane stub and the H-plane stub. The reflectance is obtained from the incident power and the reflected power according to the relationship, and the values are stored as a table map, and the E-plane stub and the H-plane stub are driven through the stepping motor to the optimum position for the set value by the map. After that, the auto tuning state (a) is entered, the incident power and the reflected power are sampled (b) by the directional coupler 5, and the controller 1
Calculate the measured value at 0. Next, it is determined whether or not the transfer rate table of (c) is updated. As described above, since the migration rate table has been initialized at the start point, it is necessary to create the migration rate table.

Here, the movement rate table is created or updated as follows. First, a deviation DIF obtained by subtracting the measured value from the set value is obtained. A predetermined movement amount is obtained from the deviation, for example, from Table 2 or from the movement rate table already created, and the E surface stub and the H surface stub are moved by the movement amount from the reference position (A in FIG. 5). The reflected power at four surrounding points (B, C, D, E) is sequentially measured, and the reflectance is calculated from the measured value (measured value). And B, C, D,
From the deviation between the measured value at E point and the set value, the moving rate is calculated by the equation 4, and it is confirmed whether or not the data exists, that is, the set value exists within the range. 3).

Next, in (e), the deviation between the measured value at the reference position and the set value is obtained. Next, in (f), if the deviation is within a predetermined value, for example, 1%, the process returns to sampling (b) of the reference position again. If the deviation is equal to or larger than the predetermined value, the process proceeds to (g) to refer to the moving rate table, and if there is a set value, the moving amount is calculated by the equation 5 and the process proceeds to (j).

If there is no set value, the process proceeds to (h), and if the move rate is obtained, the move rate in the direction judged to approach the set value is adopted, and the move amount is moved by the equation 5 to move. Then, it is determined to be a new reference position, and it is determined in (i) whether the position after movement of all four points exceeds the stub movable range. If not, the process proceeds to (j). If it exceeds the movable range, proceed to (m), and set the measured value at the moved position as the measured value at the reference position (A), and set the measured value at the original position as the measured value at the position exactly opposite to the moving direction. . The measured values at other points are invalidated, and the movement rate is calculated between the reference position after movement and the original position. In this way, the moving rate table is updated with (n) and the procedure returns to the sampling (b) of the reference position.

As described above, when the process proceeds to (j), if there is only one location for the set value, the amount of movement is calculated by equation 5, and the location is moved to that location. In addition, if there are a plurality of locations for the set value, the amount of movement of each is calculated, and the amount of movement of the measurement point in the positive direction (directions E and D in FIG. 6) when viewed from the reference position is positive or when viewed from the reference position. When the amount of movement of the measurement point in the negative direction (also B and C directions) is negative, this amount of movement is used, and the largest amount of movement (the most gradual change in reflectance) Object) is determined as the movement amount, and the direction of the adopted movement amount is determined as the optimum movement direction. Here, the movement amount is further limited as shown in Table 4 according to the magnitude of the deviation.

Next, in (k), the new destination is set as a reference position, and in (l), the movement rate table is updated at the reference position. Here, the measured value at the position after movement is taken as the measured value at the reference position (point A), and the measured value at the original position is taken as the measured value at the position exactly opposite to the moving direction. The measured values for other points are invalid. Then, the movement rate is calculated between the reference position after the movement and the original position. The migration rate is invalid for other points. Then, proceed to (b).

[0029]

[Table 2] Deviation of reflectance (%) Movement amount (mm) 10 to 35 to 102 3 to 5 1 2 to 3 0.5 1 to 2 0.2 0.5 to 1 0.1

[0030]

[Table 3] Example of movement rate table (set value 5 and movement amount 0.5)

[0031]

[Table 4] Deviation of reflectance and maximum movement amount Deviation of reflectance (%) Maximum movement amount (mm) 5 to 3 3 to 5 2 2 to 3 1 1 to 2 0.5 0.5 to 1 0.2

In order to always maintain the set reflectance, the above is E
It is a flow of automatic additional value control for driving the surface stub and the H surface stub. The program according to this flow is written in the ROM 10a of the controller 10, so that the optimum setting conditions are always maintained.

[0033]

With respect to the reflectance inside the waveguide 6 according to the present invention, the microwave reflectance inside the waveguide 6 over the entire movable range of the E-plane stub and the H-plane stub is stored in the RAM 10b of the controller 10 as a table map. Therefore, the reference can be made when setting the operating condition, and the optimum condition can be quickly obtained without repeating trial and error.

When setting the operating conditions, the E-face stub and the H-face stub should be set by adopting the value of the arbitrarily determined reflectance value at the center position of the area in which a relatively large number is gathered on the table map. For example, the conditions will not change significantly even if there are some factor changes during operation.

In the tuning device using the E-plane stub and the H-plane stub, the reflectance is obtained from the measurement of the incident power and the reflected power, and the automatic additional value control is performed by the controller. Therefore, the strictness required for the etching operation of the IC circuit etc. Stable maintenance of various conditions.

Since the two drive screw shafts are used to drive the E-side stub and the H-side stub, the movement during sliding becomes smooth and the stub surface does not tilt. Therefore, the correlation accuracy between the stub position and the microwave reflectance is high, and therefore the reliability of the table map storing the reflectance data measured in advance is high.

Since the E-plane stub and the H-plane stub do not project into the waveguide, there is no possibility of discharge with the conventional stub. Therefore, the incident power can be increased, and it is possible to cope with the future increase in the size of silicon wafers.

[Brief description of drawings]

FIG. 1 is a configuration diagram of essential parts of a plasma processing apparatus that is an embodiment of the present invention.

FIG. 2 is a perspective view showing an appearance of a stub matching device.

FIG. 3 is a partial cross-sectional front view showing the internal structure of the stub matching device.

FIG. 4 is a configuration diagram of a three-stub type matching box.

FIG. 5 is an EH coordinate diagram showing a movement trajectory and reflectance of a stub.

FIG. 6 is a flowchart of automatic additional value control.

[Explanation of symbols]

 1 Microwave Plasma Processing Device 2 Microwave Power Supply 3 Microwave Generator 4 Isolator 5 Directional Coupler 6 Waveguide 7 Stub Matching Device (E / H Tuner) 8 Plasma Generation Room (Load) 9 Power Meter 10 E / H Tuner controller 11 Personal computer 7e, 7h Branch pipe 20 E-side stub 21 H-side stub 23 Stepping motor 27 Coupling 26 Timing belt 24 Main drive male screw 25 Sub drive male screw 28 Female screw 29 Sliding plate 30 Tightening 31 Comb-shaped sliding Plates 32a, 32b Frame 33 Ball bearing 34 Limit switch 35 Sensor 36 Limit switch pressing rod

Claims (3)

[Claims] 1. An automatic tuning apparatus for a microwave circuit for plasma generation by a stub tuner used in a microwave circuit, wherein a directional coupler, a waveguide, and this waveguide are provided between a microwave power source and a load. E-plane stubs and H-plane stubs each having two drive shafts provided in a direction orthogonal to the two wall surfaces, a pulse motor for driving the E-plane stubs and H-plane stubs, and E
It has a sensor for measuring the zero point position of the surface stub and the H surface stub, a power meter, an E / H tuner controller and a personal computer, and obtains the reflectance from the incident power and the reflected power detected by the directional coupler. An automatic tuning apparatus for a microwave circuit for plasma generation, characterized in that an E-plane stub and an H-plane stub are slid by a controller through a stepping motor to maintain a set reflectance to perform impedance matching with a load. 2. An automatic tuning device for obtaining impedance from an incident power and a reflected power detected between a microwave power source and a load of a microwave circuit and driving an E-plane stub and an H-plane stub for impedance matching. , The relationship between the reflected power and the distance from the waveguide wall surface of the E-plane and H-plane stub is measured by the waveguide length, the incident power, and the load of the dummy or the workpiece to be determined in advance. The reflectance is calculated and a table map showing the relationship between the E-plane stub and H-plane stub positions and the reflectance is created and stored in the E / H tuner controller, and at least the desired reflectance is input to the controller as an initial operating condition. As a result, the E / H tuner controller refers to this table map and automatically sets the E-plane stub and the H-plane stub at the optimum position for obtaining the desired reflectance. It is set by driving dynamically, and the current reflectance is calculated from the incident power and the reflected power that are constantly measured after the device is activated.If there is a deviation more than a predetermined value from the set reflectance, it is stored or calculated by itself. According to the created movement rate table, the E-plane stub and the H-plane stub are sequentially moved from the current point, and the reflectance is obtained by sampling four points around the current point, whereby the direction in which the set reflectance is obtained and the required moving distance of the stub. Is obtained by a predetermined calculation formula, and the E-plane stub and the H-plane stub are repeatedly moved to that position, so that the set reflectance is constantly tracked. 3. An E-face stub and an H-face stub inserted in a pipe branched into two wall surfaces of a waveguide are fixed to a sliding board having internal threads, and the internal threads of the sliding board are pulsed by a signal from a computer. A main drive shaft with a male screw that is driven by a motor and a sub drive shaft with a male screw that is interlocked with the main drive shaft by a timing belt are screwed together.
2. The automatic tuning apparatus for a microwave circuit for plasma generation according to claim 1, further comprising a stub matching device having a structure in which a comb-teeth spring sliding plate made of a non-ferrous alloy is attached to a side surface of the sliding board.