JPH04300137A - Wafer holding device - Google Patents

Abstract

PURPOSE:To provide an electrostatic chuck which can follow up temperature change in a wide range, holds a necessary attraction force and shorten a necessary responsive time for attraction and its cancellation of a wafer. CONSTITUTION:A film electrode 5 is formed on a main face 2a of a ceramic base body 2. A ceramics dielectric layer 4 is formed in such a way to cover the film electrode 5. Temperature of a wafer attraction surface 6 is detected by a temperature detector 9. An electric signal from the temperature detector 9 is sent to an electrostatic chuck control part. Thereby, the most suitable voltage value in accordance with the temperature of the wafer attraction surface is computed and an electric power source part for the chuck is controlled in accordance with an electric signal from the electrostatic chuck control part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer holding device for, for example, semiconductor manufacturing equipment.

0002

[Prior Art] Conventional semiconductor wafer fixing techniques include mechanical fixing, vacuum chuck, and electrostatic chuck.
It is used for exposure, film formation, microfabrication, cleaning, dicing, etc.

[0003] In semiconductor wafer heating and temperature control in film forming processes such as CVD, sputtering, epitaxial, etc., if the temperature of the semiconductor wafer cannot be made uniform, it will cause a decrease in yield during semiconductor production. In this case, mechanical fixing requires a presser foot because the pins or rings come into contact with the outer periphery of the semiconductor wafer surface, which reduces the area that can be deposited and reduces the number of semiconductor chips that can be produced from one semiconductor wafer. Decrease. In addition, particles are generated when the pins and rings move to hold and release the wafer, which causes impurity contamination and defective film formation. Further, since the entire surface of the semiconductor wafer is not evenly suppressed, the semiconductor wafer is warped and distorted. Furthermore, so-called vacuum chucks cannot be used under medium-high vacuum conditions such as in sputtering, CVD equipment, and the like. For these reasons, electrostatic chucks that can be used even under medium-high vacuum conditions and that can heat-treat semiconductor wafers while adsorbing them are viewed as promising.

0004

However, conventionally, semiconductor wafers have been held by supplying a constant voltage to the electrostatic chuck, regardless of the temperature of the wafer suction surface. Also, when you want to release the hold on the semiconductor wafer,
The applied voltage was removed, or a voltage with the opposite sign to that during adsorption was momentarily applied. However, the properties of the dielectric, such as its relative dielectric constant, vary greatly depending on its temperature, and the wafer adsorption force also varies accordingly. In particular, for example thermal CVD
In equipment, etc., the temperature is between room temperature and 200℃ or higher, sometimes
A cycle of heat rise and heat fall is repeated between the temperatures of 600°C and 600°C. Conventional electrostatic chucks were unable to cope with such wide-ranging temperature changes.

[0005] Furthermore, even if a voltage is applied to the electrostatic chuck,
A considerable response time is required before the necessary adsorption force is actually developed, which increases the time required for semiconductor production and processing. Further, when releasing a semiconductor wafer from an electrostatic chuck, a similar delay in response occurs.

An object of the present invention is to provide a wafer holding device that can follow a wide range of temperature changes, maintain the necessary adsorption force, and shorten the response time required to adsorb and release the wafer. The goal is to provide the following.

[0007]

[Means for Solving the Problems] The present invention provides: a ceramic substrate; a membrane electrode formed on one principal surface of the ceramic substrate; a membrane electrode formed on the one principal surface so as to cover the membrane electrode; a ceramic dielectric layer; a power supply section that supplies charges of opposite polarity to the film electrode and the wafer; a temperature detector that detects the temperature of the wafer attraction surface of the ceramic dielectric layer; and the power supply section and the temperature The wafer holding device has a control unit electrically connected to a detector, the electrical signal from the temperature detector being sent to the control unit, and the control unit determining the optimum temperature according to the temperature of the wafer suction surface. The present invention relates to a wafer holding device configured to calculate a voltage value of and control the power supply section using an electric signal from the control section.

[0008]

[Example] First, an electrostatic chuck with a heater developed by the present inventor will be explained. FIG. 1 is a schematic cross-sectional view showing such a monopolar electrostatic chuck.

For example, a resistance heating element 3 is buried inside the disc-shaped ceramic base 2, and the resistance heating element 3 is wound in a spiral shape, for example. Electrode terminals 8 are connected and fixed to both ends of the resistance heating element 3, respectively, and the end surface of each electrode terminal 8 is joined to a power supply cable 10. The pair of power supply cables 10 are each connected to a heater control section, and can cause the resistance heating element 3 to generate heat by operating a switch (not shown). The disc-shaped ceramic substrate 2 has principal surfaces 2a and 2b that face each other. The main surface here refers to a surface that is relatively wider than other surfaces.

One main surface 2 of the disc-shaped ceramic substrate 2
For example, a circular membrane electrode 5 is formed along the line a. Then, one main surface 2a is formed so as to cover this film-like electrode 5.
A ceramic dielectric layer 4 is formed thereon and integrated. Thereby, the membrane electrode 5 is connected to the ceramic base 2.
and the ceramic dielectric layer 4. An electrode terminal 7 is buried inside the ceramic base 2, and a membrane electrode 5 is connected to one end of the electrode terminal 7.
A power supply cable 12 is connected to the other end. This power supply cable 12 is connected to, for example, a positive terminal of a chuck power supply section, and its negative terminal is connected to a ground wire 14.

When heat-treating the wafer W, the wafer W is placed on the wafer attraction surface 6 of the ceramic dielectric layer 4, and the ground wire 14 is brought into contact with the wafer W. Then, positive charges are accumulated in the membrane electrode 5 to polarize the ceramic dielectric layer 4. At the same time, negative charges are accumulated on the wafer W, and the wafer W is attracted to the wafer attraction surface 6 by the Coulomb attraction between the ceramic dielectric layer 4 and the wafer W. At the same time, the resistance heating element 3 generates heat to heat the wafer suction surface 6 to a predetermined temperature.

A temperature sensor 9 is embedded in the ceramic base 2 and the ceramic dielectric layer 4. An example of the temperature detector 9 is a thermocouple. This temperature detector 9 detects the temperature of the wafer suction surface 6, and sends this as an electric signal to the heater control section and the electrostatic chuck control section through the conductor wire 11. In response to this electrical signal, an optimal voltage value is calculated in the electrostatic chuck control section. This calculation method will be described later. The result of this calculation is then sent to the chuck power supply unit through the conductor 13, where the applied voltage is changed in accordance with the result of the calculation.

[0013] According to such a wafer holding device, the wafer W can be attracted to the wafer suction surface 6 on the entire surface by Coulomb force, and at the same time, the wafer suction surface 6 can be heated to heat the wafer. Therefore, the wafer W can follow the entire surface of the wafer W well, especially in a medium-high vacuum, and can be heated uniformly, and the thermal uniformity of the wafer W is not deteriorated due to the gap between the wafer W and the wafer suction surface. Therefore,
The heat treatment of the wafer W can be performed uniformly over the entire surface of the wafer, and for example, in semiconductor manufacturing equipment, a decrease in semiconductor yield can be prevented.

Furthermore, since the dielectric film 4 is also made of ceramics, the dielectric film 4 has high heat resistance and can be used satisfactorily in, for example, a thermal CVD apparatus. In addition, the dielectric film 4 has good durability against wear and deformation caused by chucking the wafer 10,000 times or more.

Furthermore, since the resistance heating element 3 is embedded inside the ceramic base 2 and the membrane electrode 5 is built in between the ceramic dielectric layer 4 and the ceramic base 2, it is different from the conventional metal heater. This can prevent contamination such as Further, since the wafer W is directly heated while being adsorbed to the wafer adsorption surface 6, the problem of deterioration of thermal efficiency as in the indirect heating method does not occur.

Moreover, the temperature detection section 9 detects the temperature of the wafer suction surface 6, and based on this detected value, the electrostatic chuck control section calculates the optimum applied voltage, thereby controlling the chuck power supply section. , it is possible to follow a wide range of temperature changes, maintain the necessary adsorption force, and shorten the response time required to adsorb and release the wafer.

As the resistance heating element 3, it is appropriate to use tungsten, molybdenum, platinum, or the like. The film electrode 5 is preferably made of tungsten, molybdenum, platinum, or the like. In the example of FIG. 1, the wafer suction surface 6 is directed upward, but the wafer suction surface 6 may be directed downward.

The overall shape of the heating device 1 is preferably disk-shaped in order to uniformly heat the circular wafer W, but other shapes such as a square disk, hexagonal disk, etc. are also possible. Such a heating device can also be applied to a heating device in an epitaxial device, a plasma etching device, a photoetching device, etc. Furthermore, as the wafer W, not only semiconductor wafers but also conductor wafers such as Al wafers and Fe wafers can be adsorbed and heat-treated.

Next, a specific control method in the electrostatic chuck control section will be further explained. First, the electrostatic chuck attraction force is given by equation (1). (1) F=1/2 ・ε′・εO ・S(V/
d) 2ε': relative dielectric constant,
εO: Dielectric constant of vacuum, S: Area of wafer adsorption site V: Applied voltage (V) d: Thickness of dielectric layer (m)

Furthermore, the following equations (2) and (3) hold true. (2) Q=CV=ε'・εO. (S/d)
・V(3) F=1/2 ・CV2 /dF: Adsorption force (N), C: Capacitance of dielectric layer (F) Q: Amount of electric charge (C) As a result, the electric charge present in the dielectric layer It can be seen that the adsorption force F is proportional to the amount.

[0021] The dielectric layer is made of a ferroelectric material, for example BaTiO.
3, PbTiO3, etc., it is controlled as follows. If the membrane electrode and the wafer to be attracted are regarded as a pair of opposing electrodes, the electric circuit of the electrostatic chuck can be replaced as shown in FIG.

Now, when a DC voltage V is instantaneously applied at t=t1, the dielectric layer is first instantaneously charged up to Q1, as shown in FIG. 3, and then gradually increases until the final value is reached. It reaches Q2 and becomes constant. Next, at t2, when the applied voltage is momentarily returned to O, the charge is first Q
1 momentarily discharges, and then gradually discharges to 0. Q1 is called instantaneous charge, charge that increases with time during charging is called absorbed charge, and charge that decreases with time during discharge is called residual charge.

Now, if the absorbed charge is QC (t), then
The total charge Q2 during charging is given by equation (4). (4) Q2 = Q1 +QC (t) Instantaneous charge Q1
C1 is the capacitance corresponding to , and the total charge after polarization is Q2
If the capacitance corresponding to is C2, the following equation (5) holds true. (5) Q1 = C1V = C1(T) V, Q2
=C2V = C2(T)VT: Temperature (°C). Also C1
(T), C2(T) indicates that C1, C2 are functions of temperature T.

Conventionally, in equation (3), the target adsorption force FO is substituted for F, C2 is substituted for C, and the applied voltage V
had decided. Therefore, the operation was as shown in FIG. 3. Furthermore, since it takes a considerable amount of time for the absorbed charge to become saturated, the response of the electrostatic chuck during adsorption was poor.

QC (t), which determines the response, is determined by the physical properties of the material and is also a function of temperature. On the other hand, the instantaneous charge Q1 is also generally determined by the physical properties of the material and is also a function of temperature. Therefore, (6) Q1 = C1V = C1(T)・V(7)
QC (t) = QC (T, t) The same applies to the residual charge Qd (t). (8) Qd (t) = Qd (T, t) (5
) to (8) The functions of the equations are obtained by actual measurement from the change in current over time at each temperature of the dielectric layer.

[0026] The faster the adsorption/desorption response of an electrostatic chuck, the better, so if possible, it is desirable to develop the adsorption force using only an instantaneous charge. To do this, it is sufficient to obtain an instantaneous charge amount Q2 by initially applying a high voltage, and then reduce the voltage to V2 as shown in FIG. The response can be improved by applying a high voltage during discharging with the polarity of the applied voltage being opposite to that during charging. That is, it is sufficient to apply a voltage V1 that satisfies (9) Q2 = C1 V1.

This control will be explained again with reference to the flowchart of FIG. 6. First, the temperature of the wafer suction surface is detected,
(3) Calculate V2 from the formula. Also, in equation (5), V
Substitute 2 to calculate Q2. Then, V1 is calculated by substituting Q2 and C1 into equation (9). If V1 is smaller than the guaranteed voltage Vabs (T), this V1
The value of is transferred to the chuck power supply unit, and a voltage is applied in a pattern as shown in FIG.

However, the value of V1 is the guaranteed voltage Vabs (
T) In the above case, if the operation shown in FIG. 4 is performed, there is a risk that the electrostatic chuck will be damaged. here,
The guaranteed voltage Vabs (T) is the dielectric strength voltage of the electrostatic chuck divided by a safety factor (usually about 2 to 3), and is usually the maximum value that can be applied. This is also a function of the temperature T, and is actually measured in advance and stored in the electrostatic chuck control section. In this case, a voltage of V1=Vabs(T) is applied. As a result, charges are first accumulated by an instantaneous charge Q1 that satisfies Q1 = C1·Vabs(T). like this,
A voltage of Vabs (T) is applied for a time period of Δt. The value of this response time Δt is obtained from equations (10) and (7). (10) Q2 = Q1 +QC (T, t) (10
) is similar to equation (4).

Vabs (T) thus obtained = V1, Δt
The value of is transferred to the chuck power supply section, and voltage is applied in the pattern shown in FIG. Then, the accumulated charge changes from Q1 to Q2
, and from Q2 −Q1 to 0, Δ
A response time of t is required. By performing the control shown in FIGS. 4 to 6, the fastest response operation can be achieved in principle.

Note that once the control shown in the flowchart of FIG. 6 is completed, the temperature is detected again and the same control is repeated. Here, the interval of temperature detection or sampling should be determined from the rate of temperature change in the electrostatic chuck. In a normal semiconductor device, it is considered sufficient to detect the temperature once every few seconds.

Next, control of an electrostatic chuck using the so-called Johnson-Rahbek effect will be described. Such dielectric materials include CaTi, which is a paraelectric material;
O3, SrTiO3, Al2O which is an electrical insulating material
3, MgO, Si3N4, AlN, mullite, spinel, zirconia, etc. An equivalent circuit of this type of electrostatic chuck is shown in FIG.

In an electrostatic chuck using the Johnson-Rahbek effect, an extremely small space is formed between the wafer to be attracted and the dielectric layer, and the attraction force is developed by accumulating charges in this space. Therefore, the amount of accumulated charge (adsorption force) is determined by the surface condition of the dielectric layer rather than the dielectric constant of the dielectric layer itself. The dielectric layer mainly acts as a resistance R. Even if we use the Johnson-Rahbek force, the adsorption force is (3)
Follow the formula. However, as mentioned above, the charge storage layer involved in adsorption is not present in the ceramic layer, so even if the adsorption force is calculated from the dielectric constant of the material, it does not match the actual adsorption force. However, it is known that there is actually a correlation with the amount of accumulated charge in the ceramic layer, so from equation (3),
(11) F=αQ = αCV, α=f(V,
T). α is determined by actually measuring the relationship between the saturated adsorption force FO and the voltage V. In this equation, C is the capacitance of the ceramic dielectric layer.

On the other hand, the response during adsorption and desorption (release) is empirically correlated with the charge accumulation rate or charge release rate of the ceramic dielectric layer. The accumulated charge Q(t) of the ceramic dielectric layer is expressed by the formula 1

[Math 1] i indicates current.

As mentioned above, in the electrostatic chuck using the Johnson-Rahbek effect, since the charge storage layer is not the ceramic dielectric layer itself, t of equation (12) expressing the charge storage rate of the ceramic dielectric layer does not represent the adsorption response itself. Therefore, in order to replace the time t in equation (12) with the adsorption response Δt, a coefficient β is introduced. (13) Q(t) =CV(1-exp(-β・Δt
/CR))

As data, the temperature characteristics of C and R of the ceramic dielectric layer (C(T), R(T))
Measure. The guaranteed voltage Vabs (T) is determined from the actual measurement value of the dielectric strength voltage. α(V,T) is determined from the relationship between the saturated adsorption force and the applied voltage. Furthermore, β is also determined from adsorption and sponse measurements. Then, the target suction force FO and the target response time Δt are determined and input in advance.

[0036] Here, conventional adsorption and desorption responses will be explained with reference to FIG. Conventionally, it was necessary to first apply the voltage V2 and wait until the attraction force F reached FO. The same thing happened when the wafer was attached and detached.

In contrast, in this embodiment, FIGS. 9 and 10
Control the applied voltage as shown in . Specifically, first, the temperature of the wafer adsorption surface is measured, and FO is added to F in equation (11).
Substitute and find V2 and Q. Then, the target response time Δt is substituted into equation (13), and Q(
t) Substitute Q for , and find V1. V1 <Vab
If it is s(T), this value of V1 is transferred to the chuck power supply section, and a voltage is applied in the pattern shown in FIG. The response time during wafer adsorption and desorption is Δt.

If V1 is greater than or equal to Vabs(T), set V1 = Vabs(T) and transfer this value to the chuck power supply section. In FIG. 10, V1
=Vabs(T). In this case, the response time becomes longer than Δt, but it is impossible in principle to make the response time shorter than this without destroying the ceramic dielectric layer.

Finally, a simple method in which the control itself is relatively simple will be described. This method is applicable to any type of electrostatic chuck.

First, as shown in FIG. 11, the target adsorption force F
O and the target response time Δt are set in advance. and,
The applied voltage V1 is measured so that the adsorption force F reaches FO in a time of Δt. Also, the applied voltage V2 at which the saturated adsorption force becomes FO is measured. V1 is the guaranteed voltage Vabs
(T), set V1 = Vabs(T). These measurements are performed at various temperatures, and as shown in FIG. 12, the values of V1 and V2 are plotted against temperature T to create a calibration curve. When the electrostatic chuck is actually used, the values of V1 and V2 are determined according to the detected temperature with reference to FIG. 12 and the calibration curve. Then, these values of V1, V2, and Δt are transferred to the chuck power supply section, and voltages are applied, for example, as shown in FIG. 10. However, when V1 exceeds Vabs(T), we set V1 = Vabs(T), so the response time is Δ
It will be longer than t.

In FIG. 1, a resistance heating element 3 is embedded in a disc-shaped ceramic base 2. However, the present invention
It can also be applied to ordinary electrostatic chucks that do not have a built-in heater type.

[0042]

According to the present invention, the temperature of the wafer suction surface is detected in the temperature detection section, and the optimum applied voltage is calculated in the electrostatic chuck control section based on this detected value. Since the wafer is controlled, it is possible to follow a wide range of temperature changes, maintain the necessary adsorption force, and shorten the response time required to adsorb and release the wafer.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an electrostatic chuck with a heater according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of an electrostatic chuck using a ferroelectric material.

FIG. 3 is a graph showing a conventional charge accumulation pattern.

FIG. 4 is a graph showing patterns of voltage application and charge accumulation according to the present invention.

FIG. 5 is a graph showing voltage application and charge accumulation patterns when V1 exceeds the guaranteed voltage.

FIG. 6 is a flow diagram showing a control procedure for an electrostatic chuck using a ferroelectric material.

FIG. 7 is an equivalent circuit diagram of an electrostatic chuck using the Johnson-Rahbek effect.

FIG. 8 is a graph showing conventional voltage application and response patterns.

FIG. 9 is a flow diagram showing a control procedure for an electrostatic chuck using the Johnson-Rahbek effect.

FIG. 10 is a graph showing voltage application and response patterns according to the present invention.

[Figure 11] Applied voltage, target adsorption force FO, and response time Δ
It is a graph showing the relationship between t.

FIG. 12 is a graph schematically showing a pattern of temperature changes in V1 and V2.

[Explanation of symbols]

2 Disc-shaped ceramic substrate 2a One main surface 3 Resistance heating element 4 Ceramic dielectric layer 5 Membrane electrode 6 Wafer suction surface 9 Temperature detector

Claims (2)

[Claims] 1. A ceramic substrate; a film-like electrode formed on one main surface of the ceramic substrate; a ceramic dielectric layer formed on the one main surface so as to cover the film-like electrode; the film a power supply unit that supplies charges of opposite polarity to the shaped electrode and the wafer; a temperature detector that detects the temperature of the wafer attraction surface of the ceramic dielectric layer; and an electrical connection to the power supply unit and the temperature detector. The wafer holding device has a control section configured to send an electrical signal from the temperature detector to the control section, and the control section calculates an optimal voltage value according to the temperature of the wafer suction surface. A wafer holding device configured to control the power supply section by an electric signal from a control section. 2. The wafer according to claim 1, wherein a resistance heating element is embedded in the ceramic base, and the wafer attracted to the wafer attraction surface can be heated by supplying electric power to the resistance heating element. Wafer holding device as described.