JPH0719831B2 - Electrostatic check - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has an insulating film on the surface of a support plate made of a conductor or a semiconductor, and a sample made of a conductor or a semiconductor is placed on the insulating film surface.
The present invention relates to an electrostatic chuck that attracts and fixes the sample to the support plate by using an electrostatic force generated by applying a potential difference between the support plate and the sample.

[Conventional technology]

In recent years, attempts have been made to apply an electrostatic chuck to attachment / detachment of a semiconductor element substrate (hereinafter referred to as a wafer) and adsorption / fixation during a semiconductor element manufacturing process that frequently uses a vacuum apparatus.

FIG. 5 shows a sectional view of the basic structure of the electrostatic chuck. This electrostatic chuck is provided with an insulating film 3 on the upper surface of a support plate 2 made of a conductor or a semiconductor, and a sample 1 made of a conductor or a semiconductor is made to face the insulating film 3 and a DC power supply 4 is used to support the sample 1 By applying a potential difference between the plate 2 and the plate 2, the sample 1 is chucked by the electrostatic force generated between the sample 1 and the support plate 2.

In this case, the magnitude of the electrostatic force is ideally proportional to the square of the potential difference and inversely proportional to the square of the thickness of the insulating film 3, that is, the square of the electric field strength (potential difference / insulating film thickness). It is believed to be proportional to.

Therefore, as the electric field strength of the insulating film 3 is higher, the thickness of the insulating film 3 can be made thinner, and a large electrostatic force, that is, a chucking force can be obtained at a low applied potential. Therefore, an insulating film having a high electric field strength can be formed. Was thought to affect the performance of the electrostatic chuck.

Alumina (Al ₂ O ₃ ) based and silicon oxide (SiO ₂ ) based inorganic materials are used for this type of insulating film. Plasma spraying, firing, electron beam evaporation, sputtering or vapor phase epitaxy It is possible to form an insulating film that can withstand high electric field strength. However, when actually applied to an electrostatic chuck using such a high-voltage film, no electrostatic force is obtained, or even if an electrostatic force is obtained, it is extremely small and unstable. Later, a low response phenomenon such that the electrostatic force gradually increased or gradually decreased, and was not satisfactory as an electrostatic chuck.

As described above, it has not been possible to realize an electrostatic chuck having a large electrostatic force by simply using an insulating film having a high withstand voltage as has been conventionally considered.

In addition, the conventional electrostatic chuck also has a poor response of electrostatic force.

〔Purpose〕

An object of the present invention is to provide an electrostatic chuck having a large electrostatic force.

Another object of the present invention is to provide an electrostatic chuck having a high response of electrostatic force.

[Means for solving problems]

The present invention depletes oxygen in an oxide-based high insulator or nitrogen in a nitride-based high insulator from a stoichiometric composition and increases one conductor or semiconductor composition combined with them. In general, an insulating film that has been reduced in film resistance by mixing conductors, semiconductors, or low-resistivity materials with a high-insulator that cannot avoid an increase in film resistance proportional to volume resistivity due to dense homogenization Is an electrostatic chuck configured by being used instead of the insulator of the electrostatic chuck having the structure of.

Still another aspect of the present invention is an electrostatic chuck having a structure in which minute protrusions are provided on the surface of the insulating film.

[Operation] The present invention has been made by elucidating the reason why an ideal electrostatic force is not obtained when a conventional high breakdown voltage insulating film is used, and improving the cause.

Therefore, the mechanism of electrostatic force generation will be described first.

FIG. 4 shows the mechanism of the electrostatic force generation based on the observation result of the electrostatic force of the electrostatic chuck having the conventional structure. The adsorption plate 5 (corresponding to the sample 1 in FIG. 5) and the insulating film 6 (corresponding to the sample 5 in FIG. 5) are shown. There is always a minute space 8 between the two (corresponding to the insulating film 3 in the figure) based on the surface roughness of both and the processing accuracy. For this reason,
The circuit configuration between the electrode 9 (corresponding to the support plate 2 in FIG. 5) and the adsorption plate 5 is the same as the series connection of the capacitor 10 having the insulating film 6 and the space 8 as an insulating layer. Therefore, the electrostatic force acting on the attraction plate 5 is the charge Coulomb force between the attraction plate 5 and the surface of the insulating film 6 (hereinafter referred to as the attraction surface) and between the attraction plate 5 and the electrode 9 (hereinafter referred to as the attraction plate-electrode). Is the sum of By the way, compared with the film resistance 11 of the insulating film 6 in FIG.
If 12 is small and the space resistance 13 between the adsorption surfaces is infinite, the contact resistance 15 at the contact point 14 is almost zero,
The current flows on the surface of the insulating film 6 and is concentrated at the contact point 14. As a result, the negative charges 16 are accumulated on the surface of the insulating film 6. Therefore,
Since the electrostatic force is due to the Coulomb force between positive and negative charges, the electrostatic force acts on the surface of the insulating film 6 but does not act on the adsorption plate 5. In addition, since the membrane resistance 11, the surface resistance 12 and the space resistance 13 are all finite, the resistance values change the potential gradient between the adsorption plate 5 and the electrode 9 and determine the amount of accumulated charge. The effect of these resistance values on the electrostatic force cannot be ignored.

On the other hand, the low responsiveness of the electrostatic force is due to the charging / discharging time of the charge stored between the adsorption surfaces having the minute space 8 as the insulating layer. Since the space 8 is very small, the capacitance C between the adsorption surfaces is
Becomes large and is charged / discharged through the insulating film 6, so that the product of the electrostatic capacitance C and the resistance value R of the film resistor 11, that is, the so-called time constant R · C increases, and it takes time to charge / discharge. is there.
Therefore, the low response of the electrostatic force is based on the charge Coulomb force between the adsorption surfaces. However, the charge Coulomb force between the adsorption plate and the electrode has a small electrostatic capacity and a resistance value of almost zero, and thus has a high response. Incidentally, 17 is a positive charge.

As described above, the instability and low responsiveness of the electrostatic force are caused by the insulating film 6
This is because the value obtained by dividing the surface resistance 12 by the film resistance 11 (hereinafter, referred to as surface / membrane resistance ratio) is small and the electrostatic capacity between the adsorption surfaces is large. Further, due to the surface resistance 12 becomes smaller in the former, the air in the molecule on the insulating film 6 side, in particular conductive hydroxyl molecules (OH ^-) and water vapor molecules (H
_This is because ₂ O) is adsorbed.

Since this is a phenomenon that usually occurs, it is desirable to reduce the film resistance in order to increase the surface / film resistance ratio.

In the present invention, by using an oxide-based insulating film with less oxygen, a nitride-based insulating film with less nitrogen, or an insulating film mixed with a low-resistance material as the insulating film, it has a volume resistivity of 10 ¹³ Ω · cm or less. An electrostatic chuck having an insulating film is realized. As a result, the above-mentioned surface / film resistance ratio can be increased, so that an electrostatic chuck having a high electrostatic force can be obtained.

Further, the surface of the insulating film is made uneven to increase the space between the insulating film and the sample surface. As a result, the capacitance between the insulating film and the sample surface can be reduced and the response of the electrostatic force can be improved.

[Embodiment 1] FIG. 1 shows one of the embodiments of the present invention. An insulating film is formed on the surface of a supporting plate 102 made of a ceramic substrate 101 having a sheet electrode 100 on its surface so as to cover the sheet electrode 100.
103 is formed. A power supply 104 is connected to the sheet electrode 100 so that a positive voltage is applied. A feature of the present invention is that as the insulating film 103, an insulating film having a volume resistivity of 10 ¹³ Ω · cm or less and a relatively low resistance is used.

In one embodiment of this embodiment, the insulating film 103 is formed with SiO _x (x <
2) is used. In order to form this SiO _x (x <2), for example, when electron beam evaporation is performed with Si as a target, the flow rate of oxygen in the oxygen atmosphere is controlled so that a film of x <2 is obtained. By controlling in this way, the composition amount of SiO which is a semiconductor substance in SiO _x can be increased,
SiO _x having a desired film resistance can be obtained.

Further, according to another aspect of this embodiment, the insulating film 103 is made of alumina mixed with a resistance reducing material. That is, the insulating film 10
For example, an alumina film formed by mixing ultrafine particles of metal titanium into alumina and firing as a resistance reducing material having a smaller resistance value than alumina (Al ₂ O ₃ ) and well mixed with alumina as a main material Good.

FIG. 2 shows the electrostatic force and electric field in each of the above-mentioned baked alumina (Al ₂ O ₃ ) film 18, baked silicon oxide (SiO ₂ ) film 19, electron beam vapor-deposited silicon oxide film 20, and titanium-mixed baked alumina film 21. It is an experimental value obtained by obtaining the relationship with the strength in a vacuum. As shown in FIG. 2-B, a calcined alumina (Al ₂ O ₃ ) film 18 and a calcined silicon oxide (SiO ₂ ) film 1 formed by a conventional method.
9 and an electron beam evaporated silicon oxide film 20 formed by this method
Comparing the magnitude of the electrostatic force with the sintered alumina film 21 mixed with titanium at the same electric field strength, this method is larger by one or two orders of magnitude.
In No. 21, high electrostatic force can be obtained with low electric field strength.

In this way, the effect of this method, in which the film resistance is optimized by the deficiency method and the mixing method, is clear, and the appropriate value of the volume resistivity to obtain this effect is 10 ¹³ Ωcm or less. It's obvious.

The above experimental data only show one example of the result of applying the insulating film forming method of the present method to the insulating film of alumina (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ) and are not limited to this. Without
It suffices to achieve both high electric field strength and appropriate film resistance, for example, alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), beryllia (BeO) with high volume resistivity and high insulation. , Barium titanate (BaTiO ₃ ) or tantalum pentoxide (Ta
O ₅ ), depletion methods, semiconductor materials typified by various pure metals and silicon (Si), and low resistance ceramics such as titania (TiO ₂ ), titanium carbide (Ti
It goes without saying that the mixing method combined with C), silicon carbide (SiC), zirconia (ZrO ₂ ) and the like can be applied.

On the other hand, the low responsiveness of the electrostatic force is due to the small space 8 shown in FIG.
This is due to the large electrostatic capacitance between the adsorbing surfaces with the insulating layer as an insulating layer, and because of the charge Coulomb force between the adsorbing surfaces, by increasing the space 8 between the adsorbing surfaces so as not to be a minute space, It suffices to reduce the electrostatic capacity and use the charge Coulomb force between the adsorption plate and the electrode with high response.

[Embodiment 2] FIG. 3 shows one embodiment in which the surface of the insulating film of the present invention described in Embodiment 1 (hereinafter referred to as "the present insulating film") is uneven. FIG. 3-A is a plan view of an embodiment in which minute convex portions are formed on the surface of the insulating film, and FIG. 3-B is an explanatory view of forming minute convex portions on the surface of the insulating film.

The insulating film 103 and the support plate 102 are configured as described in the first embodiment. The second embodiment is characterized in that the insulating film 103 of the first embodiment is provided with the minute convex portions 22. In order to form this minute convex portion, for example, it is formed as follows. That is, as shown in FIG. 3-B, the diameter of the rotary grindstone 24 may be appropriately determined, but the width of the grindstone 40 is made to match the width of the concave groove 23 between the minute convex portions 22 to be formed. First, while cutting the insulating film 103 to a desired depth of the concave groove 23, the arrow A2 in FIG.
The insulating film 103 is scanned in the direction of 5 at equal intervals. in this case,
The feed pitch of the rotary grindstone 24 is a value obtained by adding the width of the grindstone 24 to the desired width of the minute convex portion 22. Next, if the relative position between the rotary grindstone 24 and the insulating film 103 is rotated by 90 ° and the same processing is performed, it means that the rotary grindstone 24 is scanned in the direction of arrow B26 in FIG. 3-A. On the insulating film 103, the rectangular small convex portions 22 arranged at regular intervals in the orthogonal direction are left. As described above, by changing the width, the cutting depth and the feed pitch of the rotary grindstone 24, it is possible to easily form the minute convex portions 22 having a desired size and arrangement on the insulating film 103. The scanning of the rotary grindstone 24 is shown at 90 ° so that the minute protrusions 22 have a square shape, but the triangular or hexagonal minute protrusions 22 can be easily processed by changing the scanning angle. It is needless to say that this is also possible because it is possible, and if the concave groove is processed in one direction, it becomes a linear rectangle and the convex portion has a small area.

The above is an example of forming a convex portion on the insulating film 103, and the present invention is not limited to this. If the convex portion is formed by processing the concave portion, it can be formed by melting and evaporating the concave portion by, for example, a laser engraving method, On the contrary, it goes without saying that the convex portion may be directly formed on the insulating film 103 by a means such as a screen printing method used for forming a poster.

In any case, if a step is formed on the insulating film 103 so that the area of the convex portion is smaller than that of the concave portion, the adverse effect of dust adhesion and electrostatic force in the flatness correction of the wafer are proportional to the area ratio. The low responsiveness can be improved.

〔The invention's effect〕

As described above, the insulating film of the present invention shown in the examples has an advantage that a large electrostatic force can be obtained with a low electric field strength in any atmosphere-vacuum atmosphere. This means that the electrostatic chuck can be operated at a low voltage due to the low electric field strength and high electrostatic force, and the insulating film can be formed thick. Being able to operate the electrostatic chuck at a low voltage can reduce obstacles such as dielectric breakdown to the element when applied to the semiconductor element manufacturing process, and also can easily configure the applied power source. On the other hand, being able to thicken the insulating film makes it possible to form a step made up of a concave portion and a convex portion on the insulating film, which makes it possible to make a high response to the generation and disappearance of the electrostatic force associated with the application and stop of voltage, and thus the electrostatic chuck. It is possible to speed up the attachment and detachment of the wafer, and to prevent the influence of dust in correcting the flatness of the wafer stochastically.
In addition, the electrostatic chuck is the only means capable of chucking a conductor or a semiconductor material in a vacuum atmosphere, so that a semiconductor device manufacturing process using a vacuum apparatus frequently, for example, exposure / transfer of a circuit pattern using an electron beam or If it is used as an inspection device, a chuck for wafer adsorption and fixation in dry etching or dry coating, or an ion implantation device, or a chuck for transferring between air and vacuum, production by miniaturization of circuit patterns and improvement of element quality or automation It can exert a direct or indirect effect in improving the sex.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an insulating film and a supporting plate of the present invention, and FIG. 2 is experimental data of volume resistivity and electric field strength of an insulating film formed by the conventional method and the present method and formed by the conventional method and the present method. Experimental data of electrostatic force and electric field strength of insulating film, FIG. 3-A,
FIG. 3-B is a plan view of an embodiment in which a minute convex portion is processed on an insulating film surface, FIG. 4 is a principle diagram for explaining a mechanism of electrostatic force generation, and FIG. 5 is a basic structure of an electrostatic chuck. 1 is a sample material, 2 is a support plate, 3 is an insulating layer, 4 is a DC power supply,
5 is an adsorption plate, 6 is an insulating film, 8 is a space, 9 is an electrode, 10 is a capacitor, 11 is a film resistance, 12 is a surface resistance, 13 is a space resistance,
14 is a contact point, 15 is a contact resistance, 16 is a negative charge, 17 is a positive charge,
Reference numeral 18 is a conventional fired alumina film, 19 is a conventional fired silicon oxide film, 20 is a vapor deposited silicon oxide film according to the present invention, 21 is a titanium mixed fired alumina film according to the present invention, 22 is a minute convex portion, and 23 is a concave groove. 24 is a rotary grindstone, 25 is an arrow A, 26 is an arrow B, 100 is a sheet electrode, 101 is a ceramic substrate, 102 is a support plate, 103 is this insulating film, and 104 is a DC power supply.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seitaro Matsuo 3-1, Morinosato Wakamiya, Atsugi City, Kanagawa Pref. Atsugi Telecommunications Research Laboratories, Nippon Telegraph and Telephone Corporation (56) Reference JP-A-58-137536 (JP, A) Kai-sho 58-223670 (JP, A)

Claims (6)

[Claims] 1. An electrode having an insulating film on at least a surface, wherein the insulating film is an oxide or a nitride, and oxygen of the oxide or nitrogen of the nitride is less than a stoichiometric composition. Characteristic electrostatic chuck. 2. The electrostatic chuck according to claim 1, wherein the insulating film is SiO _x (x <2). 3. The electrostatic chuck according to claim 1, wherein the insulating film is Si ₃ N _y (y <4). 4. The electrostatic chuck according to claim 1, wherein a step formed of a concave portion and a convex portion is provided on the insulating film. 5. An electrode having an insulating film on at least the surface, wherein the insulating film has a volume resistivity of 10 ¹³ Ω, which is a mixture of an insulator material having a high volume resistivity with a conductor, a semiconductor or a low resistance material.
An electrostatic chuck characterized by being an insulating film of cm or less. 6. The electrostatic chuck according to claim 5, wherein a step formed of a concave portion and a convex portion is provided on the insulating film.