JP3181006B2 - Electrostatic chuck - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chuck for processing and transporting a wafer by electrostatically attracting and holding it in a semiconductor manufacturing apparatus or the like.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor manufacturing apparatus, it has been necessary to hold a silicon wafer or the like while forming and etching a semiconductor such as a silicon wafer while maintaining the flatness of the silicon wafer. Type, vacuum suction type, and electrostatic suction type have been proposed. Among these holding means, an electrostatic chuck capable of electrostatically holding a silicon wafer can easily realize the flatness and flatness of a processing surface required when processing a silicon wafer. Since silicon wafers can be processed in a vacuum, they are most frequently used in semiconductor manufacturing.

A conventional electrostatic chuck has an insulating layer made of alumina, sapphire, etc. formed on an electrode plate (Japanese Patent Laid-Open No. 60-261377). A conductive layer is formed on an insulating substrate, and a conductive layer is formed on the insulating layer. Having an insulating layer formed thereon (Japanese Unexamined Patent Publication No.
No. 4953) and a device in which a conductive layer is incorporated inside an insulating substrate (Japanese Patent Application Laid-Open No. 62-94953).

In recent years, as the degree of integration of integrated circuits of semiconductor devices has increased, the precision of electrostatic chucks has become higher, and a ceramic electrostatic chuck having excellent corrosion resistance, wear resistance and thermal shock resistance has been required. It has become In particular, since aluminum nitride has excellent plasma resistance, an electrostatic chuck using the same has been studied.

In general, the volume resistivity of an insulator decreases with temperature. For example, in the case of aluminum nitride, the temperature decreased from 10 ¹⁶ Ω-cm at room temperature to 9 ⁷ Ω-cm or less at 600 ° C., and a stable operation was impossible, and the operating temperature was limited. Therefore, Japanese Patent Application Laid-Open No. 2-160444 discloses a structure in which two or more insulating layers are laminated, and an electrode layer, an electric circuit, and a switching corresponding to each layer are provided to withstand use from room temperature to 400 ° C. Proposed. In Japanese Patent Application Laid-Open No. 4-300137, a temperature detector such as a heater and a thermocouple is mounted in an electrostatic chuck, and a control unit is provided outside to control a power supply unit in accordance with a temperature change to stabilize an attraction force. It has also been proposed to extend the operating temperature range.

[0006]

Problems to be Solved by the Invention Aluminum nitride, alumina and the like have been mainly studied as a dielectric insulator for forming the surface of an electrostatic chuck. However, as described above, the structure of the electrostatic chuck has been changed, and an attempt has been made to expand the usable temperature range by electrical control. However, when the electrode layer is increased by laminating two or more insulating layers as described above, the electric circuit is complicated, and the structure of the electrostatic chuck itself is complicated, so that the manufacturing process is complicated. There are drawbacks such as reduced product reliability and increased cost.

Also, in a method for controlling the applied voltage by detecting the temperature of a built-in heater, a temperature detector such as a thermocouple is built in the electrostatic chuck, so that it cannot be used if the detector fails. In this method, the characteristics of the ceramic material are not essentially changed, and the range of use is naturally limited.

[0008]

Means for Solving the Problems The present inventors have repeatedly studied the above problems with respect to the ceramic resistor forming the surface of the electrostatic chuck, particularly from the viewpoint of the material constituting the electrostatic chuck. By allowing oxygen to be contained in the aluminum nitride crystal and controlling its lattice constant to a specific range, the volume resistivity at room temperature (25 ° C.) is 10%.
^It has a resistance of ⁷ to 10 ¹³ Ω-cm and is 4
The inventors have found that a resistor having a stable resistance can be obtained in a temperature range up to 00 ° C., and have reached the present invention.

That is, the electrostatic chuck according to the present invention includes a thin layer made of a ceramic resistor having an aluminum nitride crystal phase as a main phase on a predetermined substrate surface.
The aluminum nitride crystal has a lattice constant of 3.107 to 3.116 ° in the a-axis,
4.976 to 4.988 ° on the c-axis, and 25
It is characterized in that the volume resistivity at 10 ° C. is 10 ⁷ to 10 ¹³ Ω-cm. In addition, the ceramic resistor
The resistance change of the antibody to a temperature change of 25 to 400 ° C. is 3
It is preferable that it is within the order of magnitude. Further, the substrate is nitrided.
A sintered body mainly composed of aluminum is preferred.
No.

Hereinafter, the present invention will be described in detail. In the electrostatic chuck of the present invention, as shown in FIG. 1, an electrode layer 2 to which a voltage is applied is formed on the surface of a substrate 1 made of an insulator having a volume resistivity of 10 ¹⁴ Ω-cm or more at room temperature. On the electrode layer 2, a thin layer 3 (hereinafter, referred to as a ceramic resistor layer) made of a ceramic resistor is formed. The ceramic resistor layer 3 is formed on at least the mounting surface of the silicon wafer 4 or the entire base surface exposed in the semiconductor manufacturing apparatus. The heater 5 may be built in the base 1 without any problem.

In the present invention, the ceramic resistor layer 3
Is mainly composed of aluminum nitride and contains 0.01% of oxygen atoms.
-20 atomic%. This is because if the oxygen atomic weight is less than 0.01 atomic%, it is not enough to lower the volume resistivity, and if it exceeds 20 atomic%, the characteristics as aluminum nitride change, and for example, plasma resistance is deteriorated and In particular, a change in the coefficient of thermal expansion affects the adhesion to the substrate, which is not preferable.

The lattice constant of the aluminum nitride crystal constituting the ceramic resistor layer is 3.107 ° -a-axis.
It is important that the angle be 3.116 ° and 4.950 ° to 4.985 ° on the c-axis. Accordingly, a volume resistivity of 10 ⁷ to 10 ¹³ Ω-cm at a temperature of 25 ° C. can be realized. If this lattice constant deviates from the above range, 25
Volume resistivity at a temperature of 10 ° C. 10 ⁷ to 10 ¹³ Ω-cm
The following are not achieved:

In terms of the characteristics of the electrostatic chuck, if the resistance of the ceramic resistor layer is smaller than 1 × 10 ⁷ Ω-cm, the leakage current becomes large, and 1 × 10 ¹³ Ω-cm.
If it is larger than the above range, a residual adsorption force may be generated. Therefore, the volume resistivity at the operating temperature range of the electrostatic chuck, that is, 25 ° C. to 400 ° C., is 1 × 10 ⁷ Ω-c over the temperature range.
It must be in the range of m to 1 × 10 ¹³ Ω-cm. Among them, 1 × 10 ^{8 to} 5 × 10 ¹² Ω-cm is most preferable in consideration of the response to leakage current and voltage application, and 1 × 10 ^{9 to} 5 × 10 ¹¹ Ω-cm is more preferable in consideration of withstand voltage. . The change in the volume resistivity has a correlation with the lattice constant. To obtain the respective resistance characteristics, the lattice constant may be controlled as shown in Table 1 below.

[0014]

[Table 1]

That is, the lattice constant is 3.116 ° on the a-axis,
If the angle exceeds 4.988 ° on the c-axis, the concentration of carriers contributing to electric conduction is low, and the volume specific resistance changes rapidly with temperature, so that stable electrostatic adsorption characteristics cannot be obtained. On the other hand, if the angle is less than 3.107 ° on the a-axis and 4.976 ° on the c-axis, the electric resistance is low, and the leakage current becomes large as an electrostatic chuck, which is not practical.

Further, in order to perform a stable operation as an electrostatic chuck, the change of the volume resistivity in the temperature range of 25 ° C. to 400 ° C. is preferably within three digits, and more preferably within two digits.

The ceramic resistor layer made of aluminum nitride according to the present invention has, as a structure, an aluminum nitride crystal in which oxygen is dissolved as a main phase, but is oxidized by oxygen which cannot be completely dissolved in the aluminum nitride crystal. In some cases, a phase of aluminum and / or aluminum oxynitride is present as a subphase.

As described above, it is difficult to manufacture a ceramic resistor layer having a solid solution of oxygen and having the above-mentioned electrical characteristics by a powder sintering method, but it is easy to manufacture it by a gas phase synthesis method. it can. As a specific film forming method,
Physical vapor phase synthesis (PVD) such as sputtering and ion plating, plasma CVD, photo CVD, M
It is formed by a chemical vapor synthesis method (CVD method) such as O (Metal-organic) CVD. Among them, the CVD method is preferable.

For example, in order to form the ceramic resistor layer by the CVD method, for example, N ₂ gas, NH ₃ gas, NO ₂ and AlCl ₃ gas are used as raw material gases.
The flow rate of these gases _{N 2 / AlC 13 = 5~70,} N
O ₂ / NH ₃ = 0.005 to 1, NH ₃ / AlCl ₃ =
It can be manufactured by setting the film formation temperature to a relatively high value of 850 ° C. or more, with the range being 1 to 10.

Meanwhile, as a substrate for forming a ceramic resistive layer, though not particularly limited, in particular Al ₂ O
₃ , AlON, Si ₃ N ₄ , diamond, mullite,
A ceramic material mainly composed of ZrO ₂ or the like can be mentioned, and among these, a sintered body mainly composed of aluminum nitride is most desirable because of its excellent plasma resistance during semiconductor production.

Further, a well-known metal material can be applied to the electrode layer 2 to which a voltage is applied, for example, W, Mo, Mo-M
Any of n and Ag can be used. In addition, a conductive ceramic material, for example, TiN, SiC, WC, carbon, or a Si semiconductor material (n-type or p-type) can also be used as the electrode material. In addition, there is a case where the electrode layer 2 is not present and the base itself has an electrode function. In this case, the base 1 is made of a conductive ceramic mainly composed of SiC, TiN, WC, or the like; What is necessary is just to form with these alloys. In that case, static electricity is generated by directly applying a voltage to the conductive substrate itself. When a heater is built in the base, Mo, W, Mo-Mn, TiC, TiN, or the like is used as a heater material.

In order to electrostatically adsorb a silicon wafer by the electrostatic chuck having the above-described structure, a voltage of about 0.2 to 2.0 kV is applied to the electrode layer 2 or the conductive substrate 1 to thereby electrostatically hold the silicon wafer. Adsorption can be performed.

According to the present invention, the case where the ceramic resistor is used as the ceramic resistor layer formed on the surface of the substrate of the electrostatic chuck has been described. However, the ceramic resistor of the present invention additionally generates static electricity. As a component for prevention, for example, in addition to a wafer transfer arm and a wafer handling jig in a semiconductor manufacturing apparatus, it can be used for a heater material, a vacuum tube outer tube, and the like.

[0024]

[Action] Normally, aluminum nitride has a volume resistivity of 10 ¹⁴
Although it is a high insulator of Ω-cm or more, if oxygen is dissolved in the aluminum nitride crystal to replace nitrogen with oxygen, one extra electron becomes available, which contributes to conductivity and increases the conductivity of the crystal. It is considered to act. The solid solution of oxygen in the aluminum nitride crystal can be determined by a change in the lattice constant. For example, the lattice constant of oxygen-free aluminum nitride is 3.120 ° on the a-axis and 4.99 on the c-axis.
Although it is 4 °, both the a-axis and the c-axis become smaller as the oxygen atoms are dissolved. And the lattice constant is 3.107-
When 3.116 ° and 4.976 to 4.988 ° on the c-axis, the volume resistivity at room temperature can be controlled to 10 ⁷ to 10 ¹³ Ω-cm. In addition, the resistance change of the resistor layer with respect to the temperature is small, for example, the resistance change with respect to the temperature change from 25 ° C. to 400 ° C. is three digits or less. As a result, the wafer chucking characteristics in this temperature range are stabilized, and an electrostatic chuck free of residual suction force can be obtained.

Further, according to the present invention, it is not necessary to take a particularly complicated structure as the electrostatic chuck, and the use of the material of the present invention simplifies the structure of the electrostatic chuck itself, thereby reducing the cost and the cost. The device can be used in the temperature range, the device itself including the electric circuit can be simplified, and the reliability and long-term stability of the electrostatic chuck are guaranteed.

[0026]

【Example】

Example 1 After an alloy of Mo and Mn was metallized as an electrode layer on the surface of a substrate made of an aluminum nitride sintered body, an AlN film was formed on the surface of the substrate including the electrode by chemical vapor deposition. To form the AlN film, the substrate was placed in a furnace heated to 900 ° C. by an external heating method, the nitrogen gas was kept constant at 8 SLM, the ammonia gas was kept constant at 1 SLM, and N ₂ O gas, dry-air and steam ( H ₂ O) was changed to a flow rate shown in Table 2 in the range of 0~200SCCM were the furnace pressure and 40 torr. Then, the reaction was started by flowing aluminum chloride (AlCl ₄ ) at a flow rate of 0.3 SLM, and a ceramic resistor layer having a thickness of 400 μm was formed by the reaction for 6 hours.

With respect to the obtained resistor layer, the amount of oxygen atoms in the layer is measured by neutron activation analysis, the angle is corrected by X-ray diffraction using Si (SRM640b) as a standard sample, and the lattice is formed by the pictop method. Constants were calculated.
The measurement plane index is (100), (002), (101),
(102), (110), (103), (112),
(004). Further, at 25 ° C. and 4 ° C.
The volume resistivity at 00 ° C. was measured.

After polishing the surface of the ceramic resistor layer after the vapor phase growth so that the surface roughness Ra becomes 0.02 mm, the chucking force as an electrostatic chuck when a voltage of 400 V is applied to the electrode. Then, a voltage was applied for 30 minutes, and the presence or absence of the residual adsorption force immediately after stopping the voltage application was measured in vacuum. Further, in the change of the adsorption force from room temperature to 400 ° C., the case where the rate of change was within 10% was evaluated as 、, and the case where the change rate was more than 10% was evaluated as ×.

[0029]

[Table 2]

[0030]

[Table 3]

As is clear from the results in Tables 2 and 4, the oxygen atomic weight and the lattice constant of the resistor layer change depending on the flow rate of the oxygen-containing gas. In the case of 0.0001 atomic%, the resistance value was also high insulating property of 9 × 10 ¹⁵ Ω-cm, but when the flow rate of air such as N ₂ O and H ₂ O was gradually increased, And the volume resistivity at room temperature also decreased to 9.7 × 10 ⁷ Ω-cm.

The obtained resistor layer was an AlN film oriented to (002) by X-ray diffraction measurement. However, observation with a transmission electron microscope revealed that a small amount of an alumina (Al ₂ O ₃ ) crystal phase was present, and a slight crystal phase in which aluminum, oxygen and nitrogen were detected was also found.

FIG. 2 shows the measurement result of the temperature dependence of the volume resistivity value of the sample No. 4, and FIG. 3 shows the measurement result of the temperature dependence of the attraction force. As is clear from FIGS. 2 and 3, in the temperature range from room temperature to 400 ° C.,
Volume specific resistance value is 1 × 10 ^{12 to} 1.4 × 10 ¹⁰ Ω · cm
, And the adsorptive power was almost constant in this temperature range, showing a stable adsorptivity.

On the other hand, in the case of the electrostatic chuck A in which the AlN film contains oxygen only at the impurity level, the measured temperature is 2.
With the change from 00 ° C to 400 ° C, the volume resistance becomes 10 ¹⁶
It rapidly changed from Ω-cm to 10 ¹⁰ Ω-cm. Therefore, at 150 ° C. and 200 ° C., the time until the adsorption force was stabilized was long, and residual adsorption force was observed.

[0035]

As described above in detail, according to the present invention, as the surface layer of the electrostatic chuck, a controlled oxygen amount and the lattice constant of aluminum nitride, the volume resistivity of 10 at 25 ° C. ⁷ to 10 ¹³ Ω-cm resistance and 40
By forming a ceramic resistor having a small resistance change due to temperature up to 0 ° C. and using it as an electrostatic chuck, it has stable adsorption characteristics at least in a temperature range from room temperature to 400 ° C. in a semiconductor manufacturing process, and has no residual adsorption force. An electrostatic chuck having a large suction force can be provided. Therefore, excellent reliability and long-term stability can be obtained as an electrostatic chuck, and the manufacturing cost of the electrostatic chuck can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of an electrostatic chuck according to the present invention.

FIG. 2 is a diagram showing temperature dependence of a volume resistance value of a ceramic resistor layer manufactured in an example.

FIG. 3 is a diagram showing the temperature dependence of the attraction force of an electrostatic chuck manufactured in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Electrode 3 Ceramic resistor layer 4 Silicon wafer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-3956 (JP, A) "NONMETALLIC CRYSTALS WITH HIGH THE THE RMAL CONDUCTIVITY" Phys. Chem. Solids, 1973, Vol. 34, pp 321-335 (issued in 1973) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/68 B23Q 3/15

Claims (3)

(57) [Claims] 1. A thin layer comprising a ceramic resistor having an aluminum nitride crystal phase as a main phase on a predetermined substrate surface,
Oxygen is present in the thin layer at a rate of 0.02 to 20 atomic%, and the lattice constant of the aluminum nitride crystal is 3.
107-3.116 °, 4.976-4.988 on the c-axis
、 And the volume resistivity at 25 ° C. is 10
An electrostatic chuck having a resistance of ⁷ to 10 ¹³ Ω-cm. 2. The method according to claim 1, wherein said ceramic resistor has a temperature of 25 to 400.degree.
Characteristic is that resistance change to temperature change is within 3 digits
The electrostatic chuck according to claim 1, wherein 3. The method according to claim 1, wherein the base is mainly composed of aluminum nitride.
3. The static electricity according to claim 1, wherein the static electricity is a sintered body.
Electric chuck.