JPH06177231A - Electrostatic chuck - Google Patents

Abstract

(57) [Summary] [Structure] The electrostatic electrode 2 is attached to the ceramic body 1 having a volume resistivity of 10 ⁸ to 10 ¹³ Ωcm in the temperature range of 250 ° C. or higher.
To constitute an electrostatic chuck. [Effect] Even when used in a CVD apparatus, a PVD apparatus, a high-temperature etching apparatus, or the like at a temperature of 250 ° C. or higher, the wafer can be adsorbed well, and fixing, transfer, and straightening can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck used to fix and convey a wafer such as silicon in a semiconductor manufacturing apparatus or the like, and more particularly to a CVD.
The present invention relates to an electrostatic chuck for use under high temperature in a PVD device or the like.

[0002]

2. Description of the Related Art Conventionally, a clamp ring, a vacuum chuck, and an electrostatic chuck have been used for fixing and transporting a silicon wafer in a semiconductor manufacturing apparatus, but the vacuum chuck cannot be used in a vacuum, and the clamp ring is warped. There was a problem that it was difficult to obtain uniform heat as the wafer size was large and the wafer size was large. Therefore, an electrostatic chuck is effective for fixing and transporting a silicon wafer in an electron beam drawing device, a dry etching device, a CVD device, a PVD device and the like.

Such an electrostatic chuck has a structure in which an electrostatic electrode is embedded in an insulator, and its attracting force F is F = S / 2 × ε ₀ × ε _r × (V / d) ² F: Adsorption force S: Area of electrostatic electrode ε ₀ : Dielectric constant of vacuum ε _r : Relative permittivity of insulator V: Applied voltage d: Thickness of insulating layer

Therefore, in order to increase the adsorption force, a method of forming an insulating layer with a high dielectric and thinning the insulating layer to which a high voltage is applied can be considered from this formula. The applicant of the present invention has already proposed an electrostatic chuck in which ceramics containing calcium titanate, which is a high dielectric material, as a main component is used as the insulator (see Japanese Patent Laid-Open No. 4-206948). The method (1) is not practical because it leads to dielectric breakdown of the insulating layer and is dangerous.

In addition to the above items, there is also an electrostatic chuck which uses a ceramic material in which a transition metal such as titanium is added to an alumina raw material and then fired in a reducing atmosphere to reduce the volume resistivity (Japanese Patent Laid-Open No. 22166/1990). See the bulletin). This is because when a ceramic having a low volume resistivity is used as an insulating layer, a minute leakage current is generated when a voltage is applied, and the leakage current enhances the adsorption force.

[0006]

However, the electrostatic chuck utilizing the leakage current as disclosed in Japanese Patent Laid-Open No. 22166/1990 has various problems as described below.

First, this electrostatic chuck is used in an electron beam drawing apparatus, a dry etching apparatus, etc., from -100 to 150.
It was intended to be used near ℃, and was not suitable for use at higher temperatures. That is, in this electrostatic chuck, the volume resistivity of the insulator decreases as the temperature rises, so that the leakage current in the temperature range of 250 ° C. or higher used in a vapor deposition apparatus such as CVD or PVD or a high temperature dry etching apparatus. However, there is a disadvantage that the circuit becomes too large and the circuit formed on the wafer is destroyed.

Next, since the volume resistivity of the ceramics constituting this electrostatic chuck is controlled by the firing conditions, it is necessary to make the entire furnace have the same atmosphere. Since the specific resistance is different, it is difficult to control the volume specific resistance by this method, and it is not possible to obtain a uniform product.

Furthermore, since the above ceramics are a mixture of alumina and titanium, the adsorption force has a time dependency,
There is a fatal defect that the adsorption force cannot be obtained immediately even when a voltage is applied. This is because titanium is not uniformly dispersed in alumina, and titanium is oxidized to form titania, which makes the material having a very different relative dielectric constant (alumina = 1).
0, titania = 46) are considered to be dispersed. Further, there is a problem in that the suction force has a time dependency, which leads to a reduction in the wafer processing capability in the semiconductor manufacturing apparatus.

On the other hand, an electrostatic chuck using high-dielectric ceramics as disclosed in Japanese Patent Laid-Open No. 4-206948 has low mechanical strength of the high-dielectric ceramic itself and is also weak against thermal shock. It was not practical to use at 250 ° C or higher.

Generally, an electrostatic chuck is used as a CVD device, a PV
When used at a temperature of 250 ° C. or higher in a D device or a high temperature etching device, the following several characteristics are required.

Demonstration of high adsorption force Responsiveness of adsorption / desorption Low leakage current Mechanical strength that can withstand assembly and high rigidity Strong against heat shock It has high thermal conductivity. It is a material that does not adversely affect the wafer. With respect to the above, in order to improve the contact between the electrostatic chuck and the wafer due to the high adsorption force, it is possible to bring the temperature of the wafer close to the temperature of the electrostatic chuck. This is because the temperature distribution of the wafer becomes small, uniform film formation on the wafer can be achieved by CVD or PVD, and pattern accuracy can be improved by high temperature etching. Further, is an essential element for improving the throughput capacity of the wafer.

With regard to the above, as one of the properties of the insulator, there is a decrease in the volume specific resistance due to the temperature rise, and the leakage current also increases accordingly, and if the leakage current is too large, the pattern formed on the wafer may be destroyed. This is because there is a risk of being connected. With regard to, since it is difficult to use the adhesive when assembling the electrostatic chuck into the device at high temperature, it is necessary to mechanically fix the screw etc., so there is a difference in thermal expansion when screwing or using the device. It must have a mechanical strength that it can withstand. Further, in order to form a highly accurate pattern on the wafer, the surface shape of the electrostatic chuck must be finished with high accuracy, so that high rigidity is also required.

With respect to the above, as for the case of cooling from the lower surface of the electrostatic chuck for controlling the wafer temperature and it is necessary to withstand the thermal strain due to the temperature distribution in the electrostatic chuck at the time of high temperature use, the thermal shock resistance is improved. Must be excellent. As for the material, if a temperature distribution is formed on the surface of the wafer during wafer processing, it will be difficult to achieve uniform film formation and high precision of the pattern. The better the better. Further, as for the electrostatic chuck, since the electrostatic chuck is in direct contact with the wafer, it must be composed of an element that does not adversely affect the silicon wafer so that the constituent elements do not deteriorate the characteristics of the silicon wafer.

However, as described above, the conventional electrostatic chuck using the ceramics in which titanium is added to alumina has large leakage current and poor responsiveness.
On the other hand, since the electrostatic chuck using the high dielectric ceramics has poor mechanical properties, none of them satisfies the above properties (1) to (3).

Therefore, the present invention satisfies the above characteristics and
The object is to obtain an electrostatic chuck that is preferably used in a high temperature region of 50 ° C. or higher.

[0017]

The electrostatic chuck of the present invention has a volume resistivity of 10 ⁸ to 250 ° C. in the temperature range.
It is characterized in that it is formed by providing an electrostatic electrode on a ceramic of 10 ¹³ Ωcm. Here, the reason why the volume specific resistance is set to 10 ⁸ to 10 ¹³ Ωcm is that if the volume specific resistance is larger than 10 ¹³ Ωcm, the leakage current when a voltage is applied is too small to obtain a sufficient adsorption force. Resistance is 10
^This is because if it is less than ⁸ Ωcm, the leakage current is too large and the circuit of the adsorbed wafer is destroyed, which may have an adverse effect.

The ceramics are composed of oxides or nitrides of silicon (Si), aluminum (Al), and have a bending strength of 20 kg / mm ² or more and a thermal conductivity of 10 W / m · K or more, Thermal shock resistance ΔT is 150 ° C
A material having the above characteristics is used.

[0019]

EXAMPLES Examples of the present invention will be described below.

As shown in FIG. 1, the electrostatic chuck of the present invention is one in which an electrostatic electrode 2 is embedded in a ceramic body 1, and a voltage 4 is applied to this electrostatic electrode 2 and an object 3 to be attracted. The adsorption force is generated by the
Can be fixed. The ceramic body 1, as large as the volume resistivity of 10 ¹⁴ [Omega] cm or more at normal temperature, but the leakage current is not so small because the suction force is most occur in the temperature range of not lower than 250 ° C. volume resistivity of 10 ⁸ ~
Since it is lowered to 10 ¹³ Ωcm, the leakage current becomes large and the adsorption force is generated.

These ceramics are made of alumina (Al
₂ O ₃ ), sapphire which is a single crystal of alumina, silica (SiO ₂ ), aluminum nitride (AlN), and silicon nitride (Si ₃ N ₄ ) are the main components, and exhibit the above volume resistivity. For this purpose, a material containing 85% by weight or more of these main components is used. Further, as will be described later, in order to eliminate contamination on the wafer, a total of 0.2 weight parts (impurities) of elements other than aluminum (Al), silicon (Si), oxygen (O) and nitrogen (N) are contained. % Or less is preferable.

For example, in the case of alumina ceramics, the main component Al ₂ O ₃ is contained in an amount of 85% by weight or more, and the balance is S.
With iO ₂ , the total amount of other components such as Ca and Na is 0.2
Al ₂ O ₃ which is the main component or less
Is preferably 99.8% by weight or more. Further, in the case of aluminum nitride ceramics, Y ₂ which is a sintering aid is used.
It is preferable that AlN, which is the main component, be made 99.8% by weight or more by evaporating O ₃ or the like during firing. Further, in the case of silicon nitride ceramics, S which is the main component
i ₃ N ₄ is contained by 85% by weight or more, and the balance is Al ₂ O ₃ ,
It is preferable that the amount of impurities is 0.2% by weight or less.

The ceramic body 1 can be obtained by press-forming the raw materials having these compositions or laminating green sheets to form a plate and firing the plate under predetermined conditions. In the case of forming with sapphire, after pulling up into a plate shape by a manufacturing method such as the EFG method,
The ceramic body 1 can be obtained by processing into a predetermined shape.

Further, the above-mentioned ceramics have a high mechanical strength of 20 kg / mm ² or more in bending strength, a thermal shock resistance ΔT of 150 ° C. or more, and a heat shock resistance, and a thermal conductivity of 10 W / m · K or more. Use one with good conductivity. Further, as described above, these ceramics are aluminum (Al), silicon (Si), oxygen (O), nitrogen (N).
Since it is composed of the above element, it does not adversely affect the wafer. Furthermore, since the above ceramics are materials composed of a single main component, they have a good response when adsorbed, and a homogeneous material can be easily manufactured.

In the above embodiment, the monopolar type electrostatic chuck is shown, but by forming a plurality of electrostatic electrodes 2 and applying a voltage between these electrostatic electrodes 2, a bipolar type electrostatic chuck is formed. Can also be

Further, as shown in FIG. 2 in another embodiment of the present invention, the electrostatic chuck can be constructed by embedding the heater 5 together with the electrostatic electrode 2 in the ceramic body 1.
In this case, the ceramic body 1 is heated to 250 ° C. or higher by applying the voltage 6 to the heater 5, and the voltage 4 is applied between the electrostatic electrode 2 and the attracted object 3 at this time, thereby A minute leakage current can be generated in the body 1 to generate an attractive force. In this way, the heater 5
The electrostatic chuck having embedded therein can easily control the temperature of the ceramic body 1 so as to obtain a predetermined attracting force, and can be used more preferably.

Experimental Example 1 The electrostatic chuck of the present invention obtains an attractive force by a minute leak current, and the volume resistivity becomes important in order to obtain an appropriate attractive force. Therefore, alumina with a volume resistivity of 10 ¹⁴ Ωcm or more at room temperature is used as the ceramic body 1.
A single-pole type electrostatic chuck having a built-in heater 5 shown in FIG. 2 was manufactured, and 300 V was applied between the electrostatic electrode 2 of the electrostatic chuck and the attracted object 3 in a vacuum of 10 ⁻¹ Torr.
The adsorption force was measured by applying the voltage 4 and peeling the adsorbent 3 vertically while increasing the temperature.

As a result, as shown in FIG. 3 which shows the relationship between the adsorption force and the temperature, the adsorption force rapidly increases near 250 ° C.,
It can be seen that it becomes almost constant at 400 ° C. and a sufficient adsorption force of 100 g / cm ² or more is generated. Comparing this result with the graph (FIG. 4) showing the relationship between the volume resistivity of the alumina ceramics and the temperature (FIG. 4), sufficient adsorption force can be generated when the temperature is 250 ° C. or higher and the volume resistivity is 10 ¹³ Ωcm or less. It could be confirmed. However, considering that the circuit on the wafer is destroyed if the leakage current becomes too large, the volume resistivity is preferably 10 ⁸ to 10 ¹³ Ωcm, and the electrostatic chuck made of alumina ceramics is 250 to 50
It can be seen that it can be preferably used in the temperature range of 0 ° C.

Further, as shown in FIG. 4 which shows the relationship between the volume resistivity and the temperature of ceramics made of silicon nitride and aluminum nitride, these ceramics are also 250 to 50.
In the temperature range of 0 ° C, the volume resistivity is 10 ⁸ to 10 ¹³
It becomes Ωcm. When an electrostatic chuck was constructed from these ceramics, it was confirmed that a sufficient adsorption force of 100 g / cm ² or more was generated at a temperature of 250 ° C. or more, similar to the above alumina ceramics.

Since sapphire, which is a single crystal of alumina, has a large volume resistivity, it can be sufficiently used even in a temperature range of 500 ° C. or higher.

Experimental Example 2 Next, in order to examine the time dependence of the attraction force of the electrostatic chuck, the volume resistivity at room temperature was 10 ¹⁴ Ωcm or more, and 4
Alumina electrostatic chuck whose temperature drops to 10 ¹¹ Ωcm at 00 ° C. (Example of the present invention) A transition metal such as titanium was added to an alumina raw material, followed by firing in a reducing atmosphere to obtain a volume resistivity of 10 at room temperature.
Two electrostatic chucks of ¹¹ Ωcm electrostatic chuck (comparative example) were prepared.

In order to match the values of the volume resistivity, the time dependence of the adsorption force was measured at room temperature and at 400 ° C. (in both cases, the vacuum degree was 10 ^-1 Torr).
r, applied voltage is 300V). The results are shown in FIG.
In (Comparative Example), 2 until the predetermined suction force is obtained.
It takes about 00 seconds, but in the (Example of the present invention), the result is that a predetermined adsorption force can be obtained in only about 1 second, and the electrostatic chuck of the present invention has no time dependence, and adsorption,
It was found that the responsiveness of withdrawal was good.

This is because, as described above, the comparative example is made of a composite material, whereas the inventive examples are made of a single material.

Experimental Example 3 Next, an experiment was conducted to confirm the possibility of using the electrostatic chuck at high temperature in terms of thermal stress. Using ceramics with various characteristics shown in Table 1, prepare a φ6 inch electrostatic chuck with a built-in heater, and rapidly raise the temperature to 500 ° C at 50 ° C / min. An experiment was conducted in which the temperature was slowly raised to 500 ° C. In Table 1, the strength means the bending strength at room temperature, and the thermal shock resistance means the temperature difference ΔT at which cracks are generated when dropped in water.

As shown in the results in Table 1, thermal shock resistance ΔT
Those having a temperature of less than 150 ° C. (Samples C and D) were cracked in the experiment, and those having a strength of less than 20 kg / mm ² (Samples B and D) were cracked in the experiment. Therefore, in order to use it in the high temperature range, the strength is 20k.
It is necessary to use ceramics having a g / mm ² or more and a thermal shock resistance of 150 ° C. or more.

[0036]

[Table 1]

Experimental Example 4 An experiment was carried out to improve the soaking property by using an electrostatic chuck and confirm the thermal conductivity required for soaking. As shown in Table 2, ceramics having various thermal conductivities
Prepare a φ6 inch electrostatic chuck with a built-in heater as shown in, heat the center of the electrostatic chuck to 300 ° C, place the wafer on the electrostatic chuck, and check the temperature distribution on the surface with a thermoviewer (surface thermometer). After heating the center to 300 ° C., the wafer was placed on the electrostatic chuck, the wafer was adsorbed by the electrostatic chuck, and the temperature distribution of the surface was confirmed by a thermoviewer (surface thermometer). The results are shown in Table 2.

It is considered that a temperature difference of 20 ° C. or less is possible for forming a uniform film on the wafer. From Table 2, the range is that the electrostatic conductivity is 10 W / m · K or more. Only when the chuck (Samples C and D) is used for adsorption. Therefore, ceramics having a thermal conductivity of 10 W / m · K or more may be used.

Furthermore, it is more preferable to use aluminum nitride ceramics, since the thermal conductivity is extremely high at 170 W / m · K or more.

[0040]

[Table 2]

Experimental Example 5 The amount of impurities in the ceramic constituting the electrostatic chuck,
An experiment was conducted to examine the relationship between the degree of contamination on the wafer. As shown in Table 3, an electrostatic chuck was made of ceramics containing alumina as a main component and different amounts of impurities Na and Ca, and a silicon wafer with an amount of Na and Ca of 1 ppm or less was used as an object to be adsorbed. After adsorption with an electric chuck, the wafer was checked and the contamination degree (content of Na and Ca) was measured.

The results are shown in Table 3. From these results, as shown in Samples C and D, the total amount of impurities in the alumina ceramic forming the electrostatic chuck was 2000 ppm (0.2 ppm).
It can be seen that the degree of contamination with respect to the adsorbed wafer is small when the content is less than (wt%). Further, although only the alumina ceramics are shown in this experimental example, adverse effects on the wafer can be prevented by similarly reducing the amount of impurities in other ceramics, and sapphire is particularly preferable. It should be noted that the impurities are silicon (S
i), aluminum (Al), oxygen (O), nitrogen (N)
It is a component containing elements other than.

[0043]

[Table 3]

[0044]

As described above, according to the present invention, the volume resistivity in the temperature range of 250 ° C. or higher is 10 ⁸ to 10 ¹³ Ωc.
Since the electrostatic chuck is configured by providing the electrostatic electrode on the ceramic of m, the wafer can be favorably adsorbed even when used at a temperature of 250 ° C. or higher in a CVD device, a PVD device, a high temperature etching device, or the like. It can be fixed, transported and straightened.

Silicon (S
i), made of aluminum (Al) oxide or nitride, having a bending strength of 20 kg / mm ² or more and a thermal conductivity of 1
By using a material having 0 W / m · K or more and thermal shock resistance ΔT of 150 ° C. or more, it can withstand thermal stress even when used at a temperature of 250 ° C. or more, and has a high thermal conductivity, so the entire surface of the wafer It is possible to achieve uniform heating, uniform film formation on the wafer, high precision processing pattern, etc. Also, the processing capacity of the wafer can be improved, and the problem of contamination of the wafer is eliminated. A high-performance electrostatic chuck can be provided.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an electrostatic chuck of the present invention.

FIG. 2 is a vertical sectional view showing another embodiment of the electrostatic chuck of the present invention.

FIG. 3 is a graph showing the relationship between the attraction force and the temperature of the electrostatic chuck of the present invention.

FIG. 4 is a graph showing the relationship between temperature and volume resistivity of ceramics that form the electrostatic chuck of the present invention.

FIG. 5 is a graph showing a relationship between attraction force and time of electrostatic chucks of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ceramic body 2 ... Electrostatic electrode 3 ... Object to be adsorbed 4 ... Voltage 5 ... Heater 6 ... Voltage

Claims (1)

[Claims] 1. An electrostatic chuck comprising a ceramic having a volume resistivity of 10 ⁸ to 10 ¹³ Ωcm in a temperature range of 250 ° C. or higher and an electrostatic electrode.