JPH0395953A - Electrostatic holding type wafer susceptor - Google Patents

Abstract

PURPOSE:To enable fine machining on a wafer without generating variation of wafer temperature as time passes by housing an electrode coated with an insulation film into a metal holder where a part in contact with the wafer is coated with the insulation film. CONSTITUTION:The entire surface of one electrode 2 out of a pair of electrodes 2 and 3 is coated with an insulation film 4, is housed within a metal holder 5, and is in contact with a chamber at the grounding potential. A part of the metal holder 5 which is in contact with the wafer is coated with an insulation film 19 and is isolated from the mounted wafer. On the other hand, the electrode 3 is a solid round bar with a collar and can be moved slightly up and down, is allowed to surely contact the wafer by a coil spring 17, and can be removed easily when pressed from the rear side. A metal holder 6 is at the grounding potential and is insulated from the electrode 3 and the surface which is in contact with the wafer is coated with an insulation film. The electrodes 2 and 3 are connected to a DC high-voltage power supply 12 for electrostatic holding, apply DC bias to the wafer, and can apply a high frequency voltage using a matching circuit 14 and a high-frequency power supply 15.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electrostatic adsorption type wafer susceptor.

[Prior Art] Conventionally, mechanical type wafer susceptors have been generally used for transporting and holding wafers in semiconductor manufacturing equipment.

However, mechanical systems have a complex structure, a large number of parts, and many sliding and moving parts, which can generate particles and cause wafer contamination. This poses problems, such as the fact that the wafer can cause damage to the wafer, and that it is difficult to hold the wafer vertically. Particularly, the generation of particles is an extremely serious problem at present, where it is increasingly necessary to proceed with film formation and etching processes in an extremely clean atmosphere as processing becomes finer.

Therefore, as a wafer susceptor capable of solving this problem, an electrostatic adsorption type wafer susceptor has recently been used.

By the way, conventionally, as an electrostatic adsorption type susceptor,
A structure as shown in FIG. 6 is known. Here, 1 is a square electrode, 2 is a high voltage side electrode, 3 is a low voltage side electrode,
4 is an insulating film, 12 is a power source for applying voltage between the electrodes 2 and 3 (DC high-voltage power source for adsorption), and 13 is a power source for applying a constant potential to the wafer (DC bias power source). .

The force F for adsorbing a wafer in such an electrostatic adsorption type clamper is expressed by the following equation (1).

F=aSVg'/2d2 (1) Here, ■1
is the applied voltage, d is the thickness of the insulating film 4, ε is the dielectric constant of the insulating film 4, and S is the contact area between the wafer 1 and the electrode 2. In this way, the attraction force F is proportional to the square of the applied voltage , and inversely proportional to the square of the thickness d of the insulating film 4. To explain specifically using numerical values, the insulating film 4 is made of polyimide (with a relative dielectric constant of 2).
．． 5), the thickness d of the insulating film is 10 μm.
, when the contact area S between the wafer 1 and the electrode 2 is 10 cm', the applied voltage V required to adsorb a 100 g wafer (the mass of an 8-inch Si cube is approximately 54 g),
is approximately 94V. Since the surface of the insulating film 4 is not completely flat, the actual adsorption force is lower than the calculated value. therefore,
You will need to apply 200 to 300v, keeping in mind the margin.

As the insulating film 4, other than polyimide, Alyona (AIL20,), aluminum nitride (AIN), silicon oxide film (SiO2), etc. can be used. As described above, the electrostatic adsorption type wafer susceptor has a simple construction, and its adsorption force can be controlled by the area of the electrode, the material and thickness of the insulating film, and the applied voltage.

[Problems to be Solved by the Invention] However, it has been found that the conventional electrostatic adsorption type wafer susceptor described above has the following problems. The details are described below.

During film formation and etching processes, DC bias and high frequency are applied to the wafer to increase the energy and momentum of the ions.
It is necessary to precisely control rI and control heating and cooling temperatures to accurately maintain the wafer at a predetermined temperature.

However, if a conventional electrostatic adsorption type wafer susceptor is used as is in a film formation or etching process that uses plasma, the variation in wafer temperature increases over time (i.e., it is difficult to accurately control the wafer susceptor to a predetermined temperature). It was found that microfabrication on wafers became difficult. It should be noted that this is the first finding by the present inventor that such variations in the temperature of Kuehachi occur over time, and such a problem had not been recognized in the past.

The present invention has been made in order to solve the problems of the prior art, and the present invention solves the problem that variations in the temperature of the metal layer occur over time even when used in a film or etching process that uses plasma. It is an object of the present invention to provide an electrostatic adsorption type wafer susceptor that is free from wafers and is capable of fine processing on wafers.

[Means for Solving the Problems] The above problems provide a pair of electrodes in which the surface of at least one electrode is covered with an insulating film, a means for applying a voltage between the pair of electrodes, and at least a wafer. An electrostatic adsorption device comprising a metal holder whose contact portion is covered with an insulating film, and at least an electrode covered with the insulating film is housed in the metal holder. type wafer susceptor.

[Function] The function of the present invention will be explained below along with the findings obtained in making the present invention. The present inventor first investigated why variations in wafer temperature occur over time in the prior art.

There are many factors that can be considered to be the cause of wafer temperature variations, but we first speculated that the cause may lie in the cooling and heating systems, and investigated the cooling and heating systems. However, no clear cause could be found regarding the heating system.

Therefore, when we tried to review the phenomena that occur in plasma space, we discovered the following facts.

In a typical plasma process, high-energy ions collide not only with the wafer but also with the insulating film exposed in the plasma space, sputtering the insulating film. Therefore, the surface of the insulating film is scraped and the insulating performance deteriorates.

In addition, in a reactive plasma process that uses various reactive gases, not only the effects of sputtering but also ions, active species, or reactive gases adsorb and react with the insulating film, changing the characteristics of the film surface. In this way, the deterioration of the insulating film of the electrostatic adsorption type wafer susceptor in plasma progresses extremely rapidly. Figure 7 schematically shows the reaction between the insulating film exposed in the plasma space and the plasma.
It was found that the adsorption force decreased over time due to the progress of deterioration. It was found that when the adsorption force decreases, the adsorption between the wafer and the wafer susceptor becomes insufficient, resulting in insufficient heat transfer between the cooling system or heating system and the wafer, resulting in variations in wafer temperature. It is.

Therefore, in order to compensate for the decrease in the adsorption force and obtain a stable adsorption force, we tried increasing the applied voltage, but as expected, variations in temperature occurred over time, and when the variation occurred, the applied voltage was increased further. Eventually, the insulating film could no longer withstand the high voltage and discharged, resulting in failure.

Therefore, as another means, we tried increasing the thickness of the insulating film to a certain degree.

However, as shown in equation (1), the suction force is inversely proportional to the square of the thickness of the insulating film, so if the film is thick, sufficient suction force cannot be obtained. Furthermore, from the standpoint of wafer temperature control, it is desirable to reduce the thickness of the insulating film. For example, in the case of etching, the wafer is typically cooled to absorb the reaction heat;
It improves the etching characteristics and accelerates the reaction. In order to increase the cooling effect, it is generally necessary to make the insulating film, which has low thermal conductivity, as thin as possible.

Also, in the case of thin film type, plasma CVD? Left, ECR
Even in the low-temperature Si epi-growth method using electron cyclotron resonance (electron cyclotron resonance), heating at several hundred degrees Celsius is required. If the insulating film is thick, a large temperature difference will occur, making it difficult to accurately control the temperature of the wafer. Therefore, the insulating film needs to be made as thin as possible. To put it concretely in numerical terms, when controlling the temperature of the wafer, a suction force of 4.5 kg/crn'' or more is required. Calculate using equation (1).The insulating film is polyimide (relative permittivity: 2.5), alumina and aluminum nitride (relative permittivity: 10), and silicon oxide film (relative permittivity: 3).
．． 9), the thickness of the insulating film is IOOO of the applied voltage.
When V, 5μm, 10μm, 6.2 respectively
Must be less than μm. In the end, increasing the thickness of the insulating film goes against the intended purpose of accurately controlling the temperature of the wafer, and cannot be a fundamental solution to the problems of the prior art.

Therefore, in the present invention, if the electrode insulated with an insulating film is housed in a metal holder and the holder completely blocks off the plasma except for the insulating film that contacts the wafer, the thickness of the insulating film The durability of the insulating film can be maintained even in a plasma atmosphere without increasing the thickness of the insulating film, providing sufficient suction power. Also, since the holder is made of metal, it has good heat transfer properties. The present invention was developed based on the knowledge that the wafer temperature can be maintained accurately and that the wafer temperature can be precisely controlled and microfabrication of the wafer can be performed.

[Example] Embodiments of the present invention will be described below based on the drawings.

(Example 1) Example 1 is shown in FIG.

The wooden example is an example in which only one of the electric scrapers 2 of the pair of electric wires i2.3 is covered with the insulating film 4.

That is, in this example, the entire surface of the electrode 2 (high voltage side electrode) is covered with the insulating film 4.

Here, as the insulating film, for example, polyimide, aluminum, aluminum nitride, silicon dioxide, etc. may be used.

The electric Ti 2 is housed in a holder 5 made of gold Yt. This metal holder 5 is also made of a metal support base 9.
It is electrically connected to the chamber at ground potential through the holder 5, and the holder 5 itself is at ground potential. Therefore, the part of the metal holder 5 that comes into contact with the square is an insulating film 19.
When the metal holder 5 is placed, the metal holder 5 is insulated from the metal holder 5 so as not to cause fluctuations in the wafer potential in the plasma space.

On the other hand, the low voltage side electric g! The configuration of No. 3 is shown in FIG. Electric Vi3 is, for example, a solid round bar with a stainless steel collar, and has a structure that allows it to move slightly up and down. When the electric current 8i3 comes into contact with the wafer, the coil spring 17 enables reliable contact with the wafer. Also, when the power is turned off and the Kuehachi is to be removed, this spring pushes the Kuehachi from the back and allows the Kuehachi to be easily removed. Further, although the electric conductor 8i3 is set in the metal holder 6, the metal surface is exposed at the portion that contacts the wafer, and comes into direct contact with the back surface of the wafer. This also makes it possible to apply a desired constant potential to the wafer. In addition,
The metal holder 6, like the metal holder 5, is at ground potential. Therefore, the electric potential 8i3 and the holder 6 are electrically insulated, and the surface of the holder 6 in contact with the wafer 1 is coated with an insulating film, so that it does not affect the potential of the wafer.

The electrode 2.3 is connected to a DC high voltage power supply 12 for adsorption through wirings 7, 8, a field through 10, and a low-pass filter 11. Reference numeral 9 denotes a support base into which a heating and cooling mechanism is incorporated. A DC bias can be applied to the wafer through electrode 3. 13 is a DC bias power supply. A high frequency can also be applied using the matching circuit 14 and the high frequency power supply 15.

(Example 2) Example 2 is shown in FIG.

In this example, both of the pair of electrodes 2 and 3 are covered with an insulating film 4.

In the wooden example, the electric i2.3 has a metal holder 5a,
It is stored in 5b.

In addition, in the case of the wood type in which both electrodes 2 and 3 are covered with an insulating film, it is preferable to apply the voltage as shown in FIG. In the case of the electrostatic adsorption type Kuehasasabuta according to the first embodiment shown in FIG. When the two electrodes are both of the type with insulated surfaces as in the example type, a part of the applied voltage for adsorption is applied to the wafer. FIG. 2(b) is an equivalent circuit of FIG. 2(a). In this way, it is equivalent to a series connection circuit of two capacitors. The capacitances of the capacitors are C1 and C2, and the applied voltage is V. , CI and C2 as V1, ■2
Then, V1=C2・V,/(C1+C2) V2=C1−V,/(C1+C2) When CI=C2, V1=V2=V,/2. That is, a voltage of v8/2 is applied to the wafer. If V8 is set to 1000V to obtain a strong adsorption force, a voltage of 500V will be applied to the wafer. This has major problems as described below.

(1) The inventor has already separately obtained knowledge that the potential of the wafer must be within ±50V in order to prevent particles from adhering to the surface of the wafer.
When a high voltage such as 00V is applied to the wafer, the wafer attracts particles floating in the chamber and causes them to adhere to the wafer surface C.

(2) Electric discharge is extremely likely to occur in low vacuum areas. The wafer, which was held vertically, falls due to the discharge.

(3) If the wafer comes into contact with the chamber, an overcurrent will flow, placing a burden on the high-voltage power supply for suction.

To prevent this high voltage from being applied to the wafer,
As shown in Figure 3, two power supplies with the same characteristics are connected directly to one another.
, set the same output value, and connect the middle to ground. At this time, the wafer is at ground potential and the above-mentioned problem does not occur.

(Other examples) FIG. 4 shows another embodiment.

In Examples 1 and 2, the outer periphery of the metal holder 5 is exposed to the plasma space. In that case, if this exposed surface is sputtered, particles may be generated.
This causes metal contamination of the wafer.

Therefore, in the case of wood, the surface of the outer periphery of the metal holder exposed to plasma is coated with an insulating film, thereby making it possible to prevent such contamination.

Note that it has been confirmed that even if such an insulating film is coated, it does not affect the cooling or heating of the wafer.

On the other hand, instead of being covered with an insulating film, the metal holder 5 may be roughly housed in an insulating holder.

Note that if a coolant flow path for cooling is provided in the metal holder 5, or if a heater is embedded in the metal holder 5, more effective and accurate temperature control of the wafer becomes possible.

[Effects of the Invention] As explained above, the present invention has a simple structure in which an electrode with an insulated surface is housed in a metal holder.
Even when used in plasma-based film formation and etching processes, there is no variation in the temperature of the C wafer over time, making it possible to perform microfabrication on the wafer.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a Kuehasa Sebuta according to Embodiment 1 of the present invention. FIG. 2 is a structural diagram and an equivalent circuit diagram of a wafer susceptor according to a second embodiment of the present invention. FIG. 3 is an equivalent circuit diagram showing a modification of the second embodiment. FIG. 4 is a diagram showing the composition of a Kuehasasa-seibuta according to another embodiment of the present invention. FIG. 5 is a configuration diagram of the low voltage side electrode in diagram N1. FIG. 6 is a block diagram of a conventional wafer susceptor. FIG. 7 is a diagram schematically showing the reaction between a conventional wafer susceptor and plasma. Figure (Explanation of symbols) 1... Wafer, 2... High voltage side electrode, 3... Low voltage side electrode, 4... Insulating film, 5, 5a, 5b... High voltage side electrode holder 6...Low voltage side electrode holder 7...Wiring, 8...Wiring, 9...Support stand, 1o
...Field through 11...Low pass filter 12...DC high voltage power supply for adsorption, 13...DC bias power supply, 14...Matching circuit, 15...High frequency power supply, 16...Insulation for holder Film, 17... Coil spring, 19... Insulating film. Figure 2 Figure 3 Figure (b) Figure 4 Figure 5 Figure 3

Claims (3)

[Claims] (1) A pair of electrodes, the surface of at least one of which is covered with an insulating film, a means for applying a voltage between the pair of electrodes, and at least a portion that contacts the wafer is covered with an insulating film. 1. An electrostatic adsorption type wafer susceptor, comprising: a metal holder; and at least an electrode covered with the insulating film is housed in the metal holder. (2) The electrostatic adsorption type wafer susceptor according to claim 1, wherein the outer periphery of the metal holder is coated with an insulating film. (3) The electrostatic adsorption type wafer susceptor according to claim 1, wherein the metal holder is further housed in an insulating holder.