JP2000012666A - Electrostatic chuck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrostatic chuck with large electrostatic attraction and less contamination on an attracted body by forming an insulation layer mainly with zirconia with an oxygen defect and adjusting volume resistivity in a proper range. SOLUTION: In an electrostatic chuck 1, an electrode 2 is provided between upper and lower insulation layers 3 and the electrostatic chuck 1 is fixed on a substrate 4. A DC current 5 is connected to the electrode 2 and a semiconductor wafer W that is placed on an attraction surface 3a of the insulation layers 3 is electrostatically attracted by feeding power to the electrode 2. Then, the insulation layer 3 is formed mainly by zirconia with an oxygen loss, and the volume resistivity of the insulation layer 3 is adjusted to 108-1014 Ωcm. Then, the zirzonia has a high plasma resistance a higher generation free energy in a halogenation reaction than titanium, is stable against such plasma as CF4, and allows the volume resistivity to be adjusted, thus obtaining large attraction without poorly affecting a circuit formed by a semiconductor wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck having an insulating layer on an electrode and applying an electrode to the electrode to electrostatically adsorb an object such as a semiconductor wafer on the insulating layer.

[0002]

2. Description of the Related Art As a jig for fixing an object to be adsorbed such as a semiconductor wafer in a reduced-pressure atmosphere, an insulating layer is provided on an electrode, and a voltage is applied to the electrode to apply the object to the object on the insulating layer. An electrostatic chuck that electrostatically adsorbs the same is used, and as such an electrostatic chuck, one in which an insulating layer is formed of a highly insulating ceramic such as alumina is known.

When a highly insulating material such as alumina is used as an insulating layer of an electrostatic chuck, an electrostatic attraction force (Coulomb force) generated between an electrode and an electric charge induced on an object to be attracted is used. In order to obtain an electroadhesive force, the thickness of the insulating layer must be 0.1 mm or less, and there is a high possibility that the insulating layer will be broken during processing.

Therefore, in order to obtain a high electrostatic attraction force without forming a thin insulating layer, titania is added to an insulating layer such as alumina to lower the volume resistivity of the insulating layer and make it possible to transfer charges. It has been proposed to improve the electrostatic attraction force (JP-A-62-94953, JP-A-2-20).
6147, JP-A-3-147843, JP-A-3-2
No. 04924). That is, by lowering the volume resistivity of the insulating layer, electric charges are induced on the surface of the insulating layer, and an electrostatic attraction force acts between the electric charges induced on the object to be adsorbed. And a high electrostatic attraction force can be obtained.

[0005]

However, when such an electrostatic chuck having an insulating layer to which titania is added is used in plasma, the titania exposed on the surface of the insulating layer is eroded by the plasma, causing the semiconductor wafer to come into contact. In this case, there is a problem that the back surface of the semiconductor wafer is easily contaminated by particles.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an electrostatic chuck having a high electrostatic attraction force and less contamination of the attracted object. .

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found that the insulating layer is mainly made of zirconia having oxygen deficiency and its volume resistivity is adjusted to an appropriate range. As a result, the present inventors have found that an electrostatic chuck having a high electrostatic attraction force can be obtained by the Johnsen-Rahbek force without causing the problem of contamination of the to-be-adsorbed body, and have completed the present invention.

That is, the present invention relates to an electrostatic chuck which has an electrode and an insulating layer provided thereon, and applies a voltage to the electrode to electrostatically adsorb the object to be attracted onto the insulating layer. The insulating layer is mainly made of zirconia having oxygen deficiency, and has a volume resistivity of 10 ⁸ to 10 ¹⁴ Ωc.
m is provided.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 and FIG.
It is sectional drawing which shows the electrostatic chuck which concerns on embodiment of this invention, FIG. 1: shows a monopolar type | mold, FIG. 2: shows a bipolar type.

The single-electrode type electrostatic chuck 1 of FIG. 1 has an electrode 2 provided between upper and lower insulating layers 3 and is fixed on a base 4. A DC power supply 5 is connected to the electrode 2. When power is supplied from the DC power supply 5 to the electrode 2, the semiconductor wafer W, which is an object to be sucked, is placed on the suction surface 3 a of the insulating layer 3 above. Is electrostatically attracted.

In the bipolar electrostatic chuck 1 'shown in FIG. 2, a pair of electrodes 2a and 2b are provided between upper and lower insulating layers 3, and a power source 5 is connected to these electrodes. The electrodes having the opposite polarities are respectively supplied with the electrodes, and the semiconductor wafer W mounted on the suction surface 3a of the upper insulating layer 3 is electrostatically attracted.

The insulating layer 3 is mainly made of zirconia having oxygen deficiency, and has a volume resistivity of 10 ⁸ to 10 ¹⁴ Ω.
cm. Zirconia is used as a material for forming the insulating layer 3 because zirconia has high plasma resistance. Zirconia has a higher free energy of formation in the halogenation reaction than titania and is more stable against plasma such as CF ₄ . The volume resistivity of zirconia can be adjusted by forming oxygen vacancies in the crystal.

As described above, the insulating layer 3 is mainly composed of zirconia having oxygen deficiency and has a volume resistivity of 10 ⁸ to 1.
It is adjusted to 0 ¹⁴ Ωcm, but by adjusting the volume resistivity within this range, a high suction force can be obtained without adversely affecting the circuits formed on the semiconductor wafer.
In other words, if it is less than 10 ⁸ Ωcm, a large leak current may flow through the attracted wafer, and the circuit formed on the wafer may be broken. If it exceeds 10 ¹⁴ Ωcm, the Johnsen-Rahbek force does not work effectively. High electrostatic attraction force cannot be obtained. The volume resistivity in such a range only needs to be obtained at least in the range of -50 to 200C.

The volume resistivity of zirconia can be in the range of 10 ⁸ to 10 ¹⁴ Ωcm by forming oxygen vacancies in zirconia crystals that are essentially high in resistance. The oxygen deficiency in the zirconia crystal can be formed by adding an oxygen deficiency forming agent to zirconia.

As such an oxygen deficiency forming agent, Y ₂
Examples include O ₃ , MgO, CaO, CeO ₂ , Yb ₂ O _3, etc., but are not particularly limited as long as oxygen vacancies can be introduced into the zirconia crystal. Among these, Y ₂ O ₃ is preferable because the range of the addition amount that gives a volume resistivity of 10 ⁸ to 10 ¹⁴ Ωcm is wide. Such an oxygen deficiency forming agent forms a solid solution in the zirconia crystal to introduce oxygen vacancy into the zirconia crystal, thereby lowering the volume resistivity. However, when such an oxygen deficiency forming agent exceeds a certain amount, it does not form oxygen deficiency and penetrates into the crystal lattice, so that the volume resistivity is rather increased.

In this case, the volume resistivity is 10 ⁸ to 10 ¹⁴
Since the addition range of Ωcm varies depending on the type of oxygen deficiency forming agent, the addition amount may be appropriately adjusted according to the type of oxygen deficiency forming agent used. Furthermore, it is desirable to add the oxygen deficiency forming agent so that the ratio of cubic crystals in the zirconia sintered body becomes higher, and more specifically, the amount of the oxygen deficiency forming agent is desirably 60% or more. If the ratio of the cubic crystal is 60% or more, microcracks and the like hardly occur on the surface of the insulating layer even when used at about 200 ° C. for a long time. When Y ₂ O ₃ is added as an oxygen deficiency forming agent,
The addition amount at which the cubic crystal ratio becomes 60% is about 5 mol%.

As described above, the insulating layer of the electrostatic chuck, which applies a voltage to the electrodes and electrostatically attracts the object to be attracted onto the insulating layer,
By mainly using zirconia containing oxygen deficiency, its volume resistivity was adjusted to 10 ⁸ to 10 ¹⁴ Ωcm,
A high electrostatic attraction force based on the Johnsen-Rahbek force can be obtained. In addition, zirconia has high resistance to plasma, and does not cause a problem that titania is eroded by plasma and contaminates the back surface of the object with particles as in the case of using an insulating layer to which titania is added.

The insulating layer mainly composed of zirconia having oxygen deficiency can be obtained by molding and firing a raw material powder according to a conventional method. The structure of the electrostatic chuck is not particularly limited. In addition to the structure shown in FIGS. 1 and 2 in which electrodes are arranged inside an insulating layer made of a zirconia sintered body, electrodes are formed on one surface. Various structures can be adopted, such as a structure in which the zirconia sintered body is attached to a ceramic plate or an Al pedestal with an adhesive. Further, the electrode structure is not particularly limited, and may be a monopolar electrode or a bipolar electrode as described above, and the shape thereof is not particularly limited.

[0019]

Embodiments of the present invention will be described below. (Example 1) ₃ mo of Y ₂ O ₃ powder as an oxygen deficiency forming agent
1% and 97 mol% of ZrO ₂ powder are mixed, and Y ₂ O ₃
After uniformly dispersing the powder in ZrO ₂ powder, φ250 ×
It was molded to 6 ^tmm . Then, in air, at a temperature of 1500 ° C.
After normal pressure sintering in conditions and processed to φ200 × 2 ^t mm
Was produced. The volume resistivity of this sintered body was 8.6 × 10 ¹² Ωcm.

Next, a bipolar electrode is formed on one surface of the zirconia sintered body by printing and baking Ag paste.
The other surface (adsorption surface of the sample) was polished to obtain a surface roughness Ra0.
It was 54 m. Next, the surface on which the electrodes of the zirconia sintered body were formed was adhered to an Al pedestal whose surface was anodized (anodically oxidized) with an adhesive to complete the electrostatic chuck.

(Examples 2 to 6, Comparative Examples 1 to 3) Example 2
In Examples 6 to 6 and Comparative Examples 1 and 2, the type and amount of the oxygen deficiency forming agent were changed.
An electrostatic chuck was manufactured under the same conditions as described above. Comparative Example 3 used TiO ₂ added Al ₂ O ₃ as the insulating layer. Table 1 also shows Example 1 regarding the types and amounts of these oxygen deficiency forming agents, the volume resistivity of the sintered body, and the cubic crystal ratio.

[0022]

[Table 1]

(Evaluation of Electrostatic Chuck) The manufactured electrostatic chuck was incorporated in a plasma etching apparatus, and one electrode of the bipolar electrostatic chuck was +500 V, and the other electrode was −5 V.
00V was applied to investigate whether or not the silicon wafer was adsorbed. Furthermore, it was investigated whether or not the circuit formed on the silicon wafer was damaged. Next, the electrostatic chuck was exposed to CF ₄ + O ₂ plasma for 24 hours (electrostatic chuck surface temperature: 170 ° C.). After the plasma treatment, the silicon wafer was adsorbed, and the number of particles attached to the back surface of the wafer was measured by a particle counter. Further, the surface state of the insulating layer was observed. Table 2 shows the evaluation results. In Table 2, ○ in the column of adsorption indicates that the wafer was adsorbed,
X indicates that the wafer was not adsorbed. In the column of the presence / absence of the destruction of the circuit, ○ indicates that there is no destruction of the circuit formed on the wafer, and X indicates that the destruction has occurred. Further, in the column of the surface state of the insulating layer, ○ indicates that the surface state was good, △ indicates that microcracks occurred, and x indicates that a large number of particles (TiF ₄ ) were observed on the surface. .

[0024]

[Table 2]

As shown in Table 2, Examples 1 to 6 and Comparative Example 2
In No. 3, the silicon wafer was adsorbed, but in Comparative Example 1, no silicon wafer was adsorbed. This is presumably because in Comparative Example 1, the Johnssen-Rahbek force was not obtained because the volume resistivity of the insulating layer was high. The volume resistivity was higher in Comparative Example 1, because the Y ₂ O ₃ too much, Y ₂ O ₃ of remainder without contributing to oxygen vacancies formation, presumably because penetrated into the crystal lattice.

In Examples 1 to 6 and Comparative Examples 1 and 3, no damage was found in the circuit formed on the silicon wafer, but in Comparative Example 2, a damaged circuit was present. In the electrostatic chuck of Comparative Example 2 in which the circuit was broken, the volume resistivity of the zirconia insulating layer was 3.2 × 10 ^7.
It is considered that a large amount of leak current occurred because of the low Ωcm.

Further, in Examples 1 to 6, the number of particles on the back surface of the silicon wafer was less than 50/8 inch wafer, whereas in Comparative Example 3, the number of particles on the back surface of the silicon wafer was 500/8 inch wafer. That was extremely large. In Examples 1 and 5, although there was no problem in practical use, some microcracks were recognized, but in Examples 2 to 4 in which the cubic crystal ratio was 60% or more, no microcracks were recognized on the insulating layer surface. .

[0028]

According to the present invention, zirconia having oxygen deficiency is mainly contained and its volume resistivity is 10 ⁸ to 10 ¹⁴ Ω.
The use of the insulating layer having a thickness of 2 cm makes it possible to obtain an electrostatic chuck having a high electrostatic attraction force based on the Johnsen-Rahbek force without causing the problem of contamination of the object to be attracted.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a monopolar electrostatic chuck to which the present invention is applied.

FIG. 2 is a cross-sectional view showing a bipolar electrostatic chuck to which the present invention is applied.

[Explanation of symbols]

 1, 1 '... electrostatic chuck 2, 2a, 2b ... electrode 3 ... insulating layer 4 ... base 5 ... power supply

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keizo Tsukamoto 1-32-22 Narashinodai, Funabashi-shi, Chiba F-term (reference) 3C016 GA10 5F031 FF03 LL07

Claims (1)

[Claims] 1. An electrostatic chuck having an electrode and an insulating layer provided thereon, wherein a voltage is applied to the electrode to electrostatically attract an object to be attracted onto the insulating layer, An electrostatic chuck characterized in that the insulating layer is mainly made of zirconia having oxygen vacancies in the crystal and the insulating layer has a volume resistivity of 10 ⁸ to 10 ¹⁴ Ωcm.