JP2001085504A - Electrostatic attractive control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smooth attracting and detaching of an object by determining the parameter for determining operating input voltage waveform, thereby determining the operating input voltage waveform, and outputting it as the voltage, and thereby to control the temperature of the object to be attracted by controlling electrostatic attraction during processing. SOLUTION: A desired electrostatic attraction profile, which is a preset waveform ys(t) of the potential difference across a gap, is determined in advance. A transfer function G(s) between the input voltage supplied to an electrostatic chuck when an object is electrostatically attracted and the output voltage which is the potential difference across the gap is determined. Laplace transformation Ys(s) of the preset waveform ys(t) is determined, and the operating input voltage waveform which is the inverse Laplace transformation of Ys(s)1/G(s) is calculated. The operating input voltage waveform is inputted to the electrostatic chuck. Then, ys(t), which is the inverse Laplace transformation of Ys(s), is outputted as the potential difference across the gap. Consequently, the potential difference across the gap can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck type substrate processing apparatus used for a plasma CVD apparatus, an etching apparatus, and a sputtering apparatus.

[0002]

2. Description of the Related Art Conventionally, when an object to be adsorbed such as a silicon wafer is adsorbed and desorbed by an electrostatic chuck, a constant voltage is conventionally applied for a certain time in accordance with the process time of the object to be adsorbed, and then the applied voltage is reduced to zero.
On-off control, such as returning to the original, was fundamental.
However, even if the applied voltage is set to 0, the electrostatic attraction force may remain, and it may take time to remove the silicon wafer or the like from the electrostatic chuck. Therefore, the following inventions have conventionally been made. A method of applying a reverse voltage for a certain period of time in order to remove the residual electrostatic attraction force (Japanese Patent Publication No. 10-2)
779950, JP-A-11-69855). A method of applying an AC voltage (Japanese Patent Application Laid-Open No.
-44332). An attempt to remove residual charges by discharging (Japanese Patent Laid-Open No. 9-260475). A material in which the material properties and structure of an electrostatic chuck are controlled (Japanese Unexamined Patent Application Publication No. Hei 5-21228,
JP-A-5-63062, JP-A-7-130826, JP-A-7-32187, and JP-B-9-2733091). Method of applying external pressure by ultrasonic waves (Japanese Unexamined Patent Application Publication No. 11-5460)
4).

[0003]

Regardless of the invention described above, the residual electrostatic attraction force is particularly low when an insulating oxide film is formed on the back surface of the silicon wafer as the object to be attracted, that is, on the attracting surface side. This was noticeable and had a large adverse effect on the overall throughput of the silicon wafer processing apparatus. Furthermore, in recent years, attention has been paid to a process at 0 ° C. or lower, but as the temperature becomes lower, the attenuation of the residual electrostatic attraction force becomes slower. Further, even when the surface roughness of the adsorption surface of the object to be adsorbed is very small, the treatment of the object to be adsorbed has been hindered.

As a further problem, the electrostatic attraction force changes during the process of the object to be attracted, the heat transfer coefficient between the object to be attracted and the electrostatic chuck changes, and as a result, the temperature of the object to be attracted changes during the process. It can be raised.

[0005] It is an object of the present invention to smoothly perform adsorption and desorption of an object to be adsorbed and to reduce electrostatic attraction force during a process, even when the object to be adsorbed has different properties and under different temperature conditions. An object of the present invention is to provide a control device for controlling the temperature of an object to be adsorbed through control.

[0006]

SUMMARY OF THE INVENTION An electrostatic attraction force control device according to the present invention controls the temperature of an object to be attracted during a process so that the object can be quickly removed from an electrostatic chuck at the end of the process. For this purpose, an electrostatic attraction force profile which is a response characteristic of the electrostatic attraction force to the voltage application time is set in advance. An operation input voltage waveform supplied to the electrostatic chuck so that the electrostatic chucking force is output according to the profile was obtained from a transfer function of an electric circuit including the electrostatic chuck and the object to be chucked. As the transfer function, a method of determining from a parameter, a method of actually measuring a current flowing through the object to be attracted, or a method of determining from a database of physical property values and structures of the electrostatic chuck and the object to be attracted is used.

In order to solve the above-mentioned problems, the present invention provides, as a first invention, an electrostatic chuck type substrate processing apparatus which applies a voltage to an electrostatic chuck containing an electrode and chucks an object by electrostatic force. In a voltage control device that comprises a computer unit and a voltage application unit and controls the voltage application,
Means for determining a parameter for determining an operation input voltage waveform supplied to the electrostatic chuck, means for determining the operation input voltage waveform according to the parameter, and means for outputting the operation input voltage waveform as a voltage And characterized in that: According to the voltage output according to the present invention, an electrostatic attraction force in accordance with an initially set profile is obtained, and substantially the same attraction performance or / and / or attraction to the objects having different characteristics is obtained.
Further, it is possible to provide an electrostatic attraction force control device having a performance of detaching the object after the treatment.

As a means for determining a parameter for calculating an operation input voltage waveform to be supplied to the electrostatic chuck, a preferred embodiment of the present invention is to measure a current flowing when an object to be attracted is electrostatically adsorbed, This is a means to determine according to the value.

In another preferred embodiment, the volume resistivity, the thickness, the relative dielectric constant of the insulating film formed on the electrostatic chuck and the object to be attracted and the distance between the gap between the electrostatic chuck and the object to be attracted and the contact resistance are determined. This is a means for determining from the database such as the physical values of the electrostatic chuck and the object to be attracted.

In another preferred embodiment, after a transfer function is obtained from an electric circuit composed of an electrostatic chuck and an object to be attracted by computer simulation such as electric circuit simulation, the operation input voltage waveform is further converted to mathematical software or the like. It is a means to calculate by computer simulation.

A preferred embodiment of the present invention is a control output device in a case where a preset waveform of the potential difference of the gap is a rectangular wave.

A preferred embodiment of the present invention as a means for calculating an operation input voltage waveform in accordance with the parameters is a means for determining a transfer function of an electric circuit composed of an electrostatic chuck and an object to be attracted, and a method for determining the transfer function of the determined transfer function. This is a means for performing a Laplace inverse transform on a product of a reciprocal number and a Laplace transform of a set waveform of a potential difference of a gap corresponding to a preset electrostatic attraction force profile.

According to a preferred aspect of the present invention, a current measuring device is provided, which calculates a parameter for calculating an operation input voltage waveform from the measured current, and performs the transfer function, the reciprocal of the transfer function, and the Laplace transform of the set waveform. It is characterized by comprising a computer section for performing Laplace inversion of the product and having means for outputting a calculated value as a voltage value. A preferred embodiment of the present invention as means for outputting the calculated value as a voltage is a means for amplifying the value calculated by a computer by an amplifier or the like after D / A conversion.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show equivalent circuits when an object to be attracted is electrostatically attracted to an electrostatic chuck. FIG. 1 is an equivalent circuit in the case where an object to be adsorbed electrostatically adsorbs an object that can be regarded as a conductor such as bare silicon.
Is a case where the insulating film electrostatically attracts the silicon wafer formed on the attracting surface side of the electrostatic chuck.

Incidentally, the electrode of the electrostatic chuck has a monopolar structure for the sake of simplicity, and the equivalent circuit is as shown in FIG. 3 in the case of a bipolar structure.

Next, a method for controlling the electrostatic attraction force will be described. The electrostatic attraction force is, as shown in Equation 1, the potential difference of the gap 2
It is proportional to the power. (Formula 1) f = σ ² / 2ε ₀ = (Q ₁ / S) ² / 2ε ₀ where f is the electrostatic attraction force, Q ₁ is the charge accumulated in the capacitance of the gap, and σ is The charge density, S, is the area where the electrostatic chuck and the object to be attracted contact and overlap, and ε ₀ is the dielectric constant of vacuum. Therefore, controlling the electrostatic attraction force is the same as controlling the gap potential difference (output y in FIGS. 1 to 3).

Therefore, a method for controlling the potential difference of the gap will be described below. In explaining, the function of time y
The Laplace transform of (t) is represented as Y (s).

1. Set the desired electrostatic adsorption profile. That is, the setting waveform y _s (t) of the potential difference of the gap is set in advance.

2. The transfer function G (s) between the input voltage e (t) supplied to the electrostatic chuck and the output voltage y (t) of the potential difference of the gap when the object is electrostatically attracted is obtained.

3. Laplace transform Y _{s of} set waveform y _s (t)
Based on (s), an operation input voltage waveform e _c (t) obtained by Laplace inverting Y _s (s) · 1 / G (s) is calculated. When the output waveform of the potential difference of the gap, which is the response waveform of the operation input voltage waveform e _c (t), becomes the same as the set waveform y _s (t) of the potential difference of the gap originally set, the potential difference of the gap can be controlled in advance. .

Operation input voltage waveform e_c(T)
Laplace transform of the output of the potential difference of the gap when input to
Is Y (s) = E_c(S) · G (s) = ｛Y_s(S) · 1 / G
(S)｝ · G (s) = Y _s(S). Where E_c(S) is the operation input voltage waveform e
_cThis is the Laplace transform of (t). Therefore, Y_s(S)
Plus inverted y_s(T) is the potential difference of the gap
Will be output. y_s(T) is set in advance
Concludes that the potential difference in the gap can be controlled
You.

From the above theory, the transfer function G between the input voltage supplied to the electrostatic chuck and the output of the potential difference between the gaps is obtained.
As long as (s) is determined theoretically or experimentally, the electrostatic attraction force can be controlled.

Next, a method for theoretically obtaining the transfer function G (s) will be described. When the object to be attracted is obtained by the electrostatic chuck, when the object to be attracted is made of a silicon wafer or other conductive material, it is given by Expression 2. (Equation 2)

If an insulating film is formed on the back surface of the silicon wafer (on the suction surface side of the electrostatic chuck), Equation 3 is derived. (Equation 3) Here, the parameters Ci and Gi (i = 1, 2, 3) appearing in the equations are given by the equations 4 to 9 and described in the description of the reference numerals. (Formula 4) C ₁ = ε ₀ · S / δ R ₃ = 1 / G ₃ = ρ ₃ · d ₃ / S (Formula 5) C ₂ = ε ₀ ε _r2 · S / d ₂ (Formula 6) C ₃ = ε ₀ ε _r3 · S / d ₃ (Formula 7) R ₁ = 1 / G ₁ (Formula 8) R ₂ = 1 / G ₂ = ρ ₂ · d ₂ / S (Formula 9) R ₃ = 1 / G ₃ = ρ ₃ · d ₃ / S By substituting these into Equations 2 and 3, the transfer function G (s) can be obtained. δ is the distance between the gap between the surface of the electrostatic chuck and the object, ρ ₂ is the volume resistivity of the dielectric layer of the electrostatic chuck, ρ ₃ is the volume resistivity of the insulating film formed on the object, and d ₂ is the static resistance. The thickness of the dielectric layer of the electric chuck, d ₃
Is the thickness of the insulating film formed on the object, ε _r2 is the relative permittivity of the electrostatic chuck dielectric layer, and ε _r3 is the relative permittivity of the insulating film formed on the object.

Next, as shown in FIG. 4, a single rectangular wave is assumed as the set waveform y _s (t) of the electrostatic adsorption profile of the object to be adsorbed when the insulating film is present on the back surface, that is, the potential difference of the gap. The calculation method of the operation input voltage waveform e _c (t) supplied to the electrostatic chuck at this time will be described. Making the profile of the electrostatic attraction force a single rectangular wave means that the setting waveform of the potential difference of the gap is a single rectangular wave.
When a single rectangular wave is input, after a fixed electrostatic adsorption time T corresponding to the pulse width of the single rectangular wave elapses from the start of supply of the voltage value V, the potential difference between the gaps becomes zero, that is, the electrostatic attractive force Is set to 0, the object to be sucked can be smoothly removed from the electrostatic chuck suction surface. The Laplace transform Y _s (s) of the single rectangular wave is represented by Expression 10. (Equation 10)

Therefore, the Laplace transform E _c (s) of the operation input voltage waveform e _c (t) to be supplied to the electrostatic chuck is given by the following equation (11). (Equation 11)

Next, an experimental example will be described. As an experiment, a silicon wafer with an oxide film is electrostatically adsorbed on an electrostatic chuck, and the voltage application time response characteristic of the electrostatic adsorption force and the attenuation characteristic of the residual electrostatic adsorption force after the end of the adsorption time are compared with the conventional single rectangular wave. Comparison was made between the case where the voltage was supplied to the electrostatic chuck and the case where the operation input voltage waveform e _c (t) calculated by performing the Laplace inversion of Equation 11 was supplied.

The thickness of the dielectric layer of the electrostatic chuck is 300 μm,
The volume resistivity is 2.3 × 10 ¹¹ Ωcm, the relative dielectric constant is 8.4, the thickness of the oxide film of the adsorption target is 3500 angstroms, the volume resistivity is 1.2 × 10 ¹⁵ Ωcm, and the relative dielectric constant is 4.

In order to determine the coefficient in the equation of the transfer function G (s), the following current analysis was performed. When a voltage is supplied to the electrostatic chuck, the current flowing through the object is calculated by Expression 12. (Equation 12) Thus, by supplying an appropriate voltage waveform, for example, a single rectangular wave, a theoretical equation is derived. The parameters Ci and Gi (i = 1, 2, 3) of the circuit can be determined by actually measuring this and the current flowing through the object to be adsorbed and comparing it with a theoretical formula.

In this experiment, after applying 300 V for 60 seconds,
V was applied for 60 seconds. Then, as shown in FIG. 5, the parameters were determined such that the theoretical formula and the measured value approximately matched. Equation 13 calculates the transfer function using the parameters at this time. At this time, S was calculated as 1 cm ² . (Equation 13)

FIG. 6 shows an operation input voltage waveform e _c (t) obtained by subjecting Y _s (s) · 1 / G (s) to Laplace inversion. At this time, if a waveform appears in the form of an impulse, it may exceed the withstand voltage value of the electrostatic chuck dielectric layer. In that case, it is necessary to convert the impulse-like waveform into a rectangular wave-like shape with the value equal to or lower than the withstand voltage as the upper limit.

FIG. 7 shows a waveform when the upper limit value is calculated as 1000V. The conversion method determines the pulse width of the rectangular wave so that the integral value of the impulse waveform is equivalent to that of the rectangular wave. Alternatively, the operation input voltage waveform e _c (t) may be input to an equivalent circuit, and the pulse width may be determined so that the output waveform of the potential difference of the gap has a substantially rectangular waveform.

In FIG. 8, the measurement point plot of “rectangular wave input (before control)” is as follows. An electrostatic chuck is installed in a vacuum chamber, and a voltage is applied to the object to be suctioned at 300 V for 60 seconds, and then pulled after a lapse of a predetermined time. This is the tensile strength at the start of the test. The measurement point plot of “operation input voltage waveform” is obtained by inputting the operation input voltage waveform shown in FIG. 7 and performing a tensile test similarly after 60 seconds. The adsorption response characteristic and the attenuation characteristic of the electrostatic adsorption force had a remarkable difference, and the effect was confirmed.

In this experiment, a method of analyzing the current flowing through the object to be determined to determine the circuit parameters was performed according to the calculation flow of FIG. 9, but the volume resistivity and thickness of the electrostatic chuck and the object to be chucked were determined in advance. If the physical property values such as relative permittivity, the capacitance of the gap at the time of electrostatic attraction, the distance, the contact resistance, and the like are stored in a database, the operation input voltage waveform can be calculated without performing current measurement.

The calculation flow in that case is as shown in FIG.

The coefficient of the transfer function varies depending on the physical properties of the electrostatic chuck, temperature, structure such as surface roughness and thickness, and physical properties of the object to be attracted. Therefore, if the transfer function is determined according to the environment in which the electrostatic chuck is used, the electrostatic attraction force can be controlled in any environment.

As described above, if the equivalent circuit at the time of electrostatic attraction is known, the transfer function can be obtained as a theoretical equation, and the operation input voltage waveform can be calculated. When the surface of the electrostatic chuck is covered with an insulating film, has a multilayer structure, or has a complicated structure, the equivalent circuit becomes complicated. In this case, it is difficult to derive the theoretical formula of the transfer function. In this case, since it can be obtained by a computer simulation using an electric circuit simulator or mathematical software,
Similar processing can be performed.

[0038]

As described above, according to the present invention, it is possible to control the electrostatic attraction force to a preset profile even if the object to be attracted has different properties and the electrostatic chuck has a different temperature. Therefore, the temperature control becomes easy through the control of the electrostatic attraction force during the process of the object to be adsorbed, including the smooth adsorption and desorption of the object to be adsorbed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of electrostatic attraction when an object to be attracted is conductive and its equivalent circuit.

FIG. 2 is a schematic diagram of electrostatic attraction when an insulating film is formed on an object to be attracted and an equivalent circuit thereof.

FIG. 3 is an equivalent circuit at the time of electrostatic chucking by a bipolar electrostatic chuck.

FIG. 4 shows a single rectangular power supply waveform supplied to an electrostatic chuck.

FIG. 5 shows measured values of the current flowing through the object to be adsorbed and calculated values after determining the parameters.

[Fig. 6] Calculated value of the operation input voltage waveform by Lars inversion of Y _s (s) · 1 / G (s)

FIG. 7: Y _s after correcting by limiting the wave height of the impulse-like waveform
Calculated value of operation input voltage waveform by inverse transformation of (s) / 1 / G (s)

FIG. 8 shows measured values of electrostatic chucking force when a single rectangular wave and a control output are supplied to the electrostatic chuck.

FIG. 9 is a calculation flow when an operation input voltage waveform is obtained by actually measuring a current flowing through an object to be adsorbed;

FIG. 10 is a calculation flow for obtaining an operation input voltage waveform from a database of physical property values and structures of an electrostatic chuck and an object to be attracted.

[Explanation of symbols]

1a: · The Bu Yaffu ° capacitance C ₁ 1b: key Bu Yaffu ° resistance (contact _{resistance) R 1 = 1 / G 1} 2: electrostatic chuck dielectric layer of the electrostatic capacitance 2a: the electrostatic chuck dielectric layer capacitance C ₂ 2b : resistance of the electrostatic chuck dielectric layer _{R 2 = 1 / G 2 3} : insulating film 3a: capacitance C ₃ 3b of the insulating film: the resistance of the insulating film _{R 3 = 1 / G 3 4} : the adsorbent 5: Ground 6: Input power supply 7: Electrode

Claims (7)

[Claims] 1. An electrostatic chuck-type substrate processing apparatus for applying a voltage to an electrostatic chuck containing electrodes and adsorbing an object to be attracted by electrostatic force, comprising: a computer unit and a voltage applying unit. In the voltage control device that controls
Means for determining a parameter for determining an operation input voltage waveform supplied to the electrostatic chuck, means for determining the operation input voltage waveform according to the parameter, and means for outputting the operation input voltage waveform as a voltage And a control device for controlling electrostatic attraction force. 2. The electrostatic attraction force control device according to claim 1, wherein the means for determining the parameter is a means for actually measuring a current value flowing through the object to be determined and determining the parameter. 3. The method according to claim 1, wherein the means for determining the parameters includes a volume resistivity, a thickness, a relative dielectric constant of an insulating film formed on the electrostatic chuck and the object to be attracted, and a distance between a gap between the electrostatic chuck and the object to be attracted. 2. The electrostatic attraction force control device according to claim 1, wherein the control unit is a unit that determines from a database including contact resistance and contact resistance. 4. The means for determining the operation input voltage waveform includes:
The electrostatic attraction control device according to claim 1, wherein an electric circuit simulator is used. 5. The electrostatic attraction force control according to claim 1, wherein the operation input voltage waveform is an input voltage waveform determined by setting a voltage waveform output to the gap to a rectangular wave. apparatus. 6. A method for controlling a voltage applied to an electrode included in an electrostatic chuck, comprising: setting a waveform (setting waveform) of a potential difference between a gap between the electrostatic chuck and an object to be attracted in advance; Obtaining a transfer function between the input voltage supplied to the electrostatic chuck and the potential difference of the gap when the object to be suctioned is electrostatically adsorbed; and Laplace transform of the set waveform and the reciprocal of the transfer function. A method for calculating a Laplace inverse transform of the product and a step of outputting the calculated value as a voltage. 7. An electrostatic chuck-type substrate processing apparatus for applying a voltage to an electrostatic chuck containing electrodes and chucking an object to be attracted by electrostatic force, comprising a current measuring device, a computer unit, and a voltage applying unit. A voltage control device for controlling the voltage application, a means for measuring and calculating a parameter for calculating a voltage waveform (operation input voltage waveform) to be supplied to the electrostatic chuck, according to the parameter; An electrostatic attraction force control device comprising: means for calculating the operation input voltage waveform; and means for outputting the calculated value as a voltage.