JP7517852B2 - Ceramic heater and its manufacturing method - Google Patents

Description

The present invention relates to a ceramic heater, which is a component for semiconductor manufacturing equipment, and a method for manufacturing the same.

Patent Document 1 discloses a method for manufacturing a ceramic heater in which a heater electrode layer is formed on a substrate made of sintered aluminum nitride, in which a conductive paste containing tungsten carbide particles is used to form a heater electrode layer on an aluminum nitride green sheet, and then a heat treatment step is performed in which the green sheet is heated in a non-oxidizing atmosphere at a temperature range lower than that during main firing, followed by a main firing step in which the green sheet is completely sintered.

Patent Document 2 discloses a method for producing a ceramic sintered body, which includes a film-forming step of forming a metal film on the surface of a heat-resistant metal material, the metal film being made of a metal material whose standard free energy of formation of metal carbide is smaller than that of the heat-resistant metal material, a molding step of arranging the heat-resistant metal material on which the film has been formed in the film-forming step at a predetermined position in a powder, which is the raw material of the ceramic base, and pressurizing and molding the material into a ceramic molded body, and a sintering step of sintering the ceramic molded body molded in the molding step to produce a ceramic sintered body.

Patent Document 3 discloses a method for manufacturing a ceramic heater, which includes a process for producing a molded body by embedding a heating element and a metal member surrounding the heating element in ceramic raw material powder, which is the raw material for the ceramic base, with raw material powder having the same main component as the ceramic raw material powder between the heating element and a process for producing a ceramic base and a reaction layer by sintering the molded body so that the metal member is carbonized or oxidized preferentially to the heating element.

Patent Document 4 discloses a method for producing a ceramic heater that includes a ceramic sintered body and a resistance heating element that is arranged so as to be in contact with the ceramic sintered body, in which a ceramic powder compact is brought into contact with a resistance heating element and a dummy member made of a metal that contains one or more metal elements selected from elements in Groups 4a, 5a, and 6a of the periodic table, and then the compact is sintered to obtain the ceramic sintered body.

JP 2000-012194 A JP 2012-096948 A JP 2009-295960 A JP 2003-288975 A

The ceramic heater manufacturing methods in Patent Documents 1 to 4 aim to reduce the volume resistivity of the heater electrodes (increase electrical conductivity) and reduce variation in volume resistivity by suppressing carbonization of the heating element such as W or Mo embedded in the AlN ceramics. However, these methods have the problem that the volume resistivity of the heater electrodes is partially reduced, causing variation in volume resistivity, resulting in non-uniform heating temperatures.

The present invention was made with a focus on these problems, and aims to provide a ceramic heater in which heater electrodes containing W and Mo are embedded in a substrate containing AlN ceramics, and in which the volume resistivity of the heating element is stable and the heating temperature is highly uniform, as well as a method for manufacturing the same.

To achieve the above object, the ceramic heater of the present invention is a ceramic heater in which a heater electrode is embedded in a substrate containing AlN ceramics, and the heater electrode contains Mo and C, and is characterized in that the ratio of the number of C atoms to the sum of the number of Mo atoms and the number of C atoms is 0.20 or more.

In the ceramic heater according to the present invention, the substrate contains a Y component, YAG is formed around the heater electrode in the substrate, and in an X-ray diffraction chart of the substrate around the heater electrode, when the peak intensity of YAG at a position where 2θ is 54.978° is A and the peak intensity of AlN at a position where 2θ is 36.041° is B, it is preferable that the relationship (A/B) ≧ 0.11 is satisfied.

The method for producing a ceramic heater according to the present invention is the above-mentioned method for producing a ceramic heater, and includes the steps of: preparing a first precursor and a second precursor which contain a binder and form the base material; and firing the laminate obtained by stacking the first precursor and the second precursor with a mesh made of Mo wires which form the heater electrodes sandwiched between them, while applying a predetermined pressure in the stacking direction, and is characterized in that, when the pressure is P (MPa) and the diameter of the Mo wire is φ (m), the relational expression (P/φ)≦5× ¹⁰⁴ is satisfied.

Another method for manufacturing a ceramic heater according to the present invention is the above-mentioned method for manufacturing a ceramic heater, characterized in that it includes a step of preparing a first precursor and a second precursor that form the base material, a carbonization step of carbonizing the Mo material that forms the heater electrode, and a firing step of firing the laminate obtained by sandwiching the Mo material after the carbonization step between the first precursor and the second precursor while applying a predetermined pressure in the stacking direction.

The present invention provides a ceramic heater having a heater electrode containing Mo embedded in a substrate containing AlN ceramics, in which the volume resistivity of the heating element (for heater) is stable and the heating temperature is highly uniform, and a method for manufacturing the same can be provided.

FIG. 2A is an upper perspective view, and FIG. 2B is a lower perspective view of the ceramic heater according to the embodiment. FIG. 2 is a lamination process diagram of the ceramic heater of the embodiment. 1 is an element mapping image showing a cross section of an electrode of a ceramic heater according to Example 3 of the present invention. 1 is an element mapping image showing a cross section of an electrode of a ceramic heater of Comparative Example 1. FIG. 1 is an intensity spectrum diagram of Mo and C in the cross section of the electrode of the ceramic heater of Comparative Example 1. 1 is an X-ray diffraction chart of the AlN ceramic of the ceramic heater of Example 3. 1 is an X-ray diffraction chart of the AlN ceramic of the ceramic heater of Comparative Example 1. 1A is a SEM image of a cross section of a Mo electrode, (B) a Y element map, and (C) an O element map of Example 3. FIG. 11 is an explanatory diagram showing a state in which a mesh-shaped Mo material is placed in a carbon storage container in Test Example 2.

The ceramic heater according to an embodiment of the present invention is a ceramic heater in which a heater electrode is embedded in a substrate containing AlN ceramics, and the heater electrode contains Mo and C, and the ratio of the number of C atoms to the sum of the number of Mo atoms and the number of C atoms is 0.20 or more.

In the ceramic heater according to the embodiment of the present invention, the entire cross section of the heater electrode through which the current passes is mainly _Mo2C , and the volume resistivity of the heater electrode is stable at a high value. As a result, the volume resistivity can be prevented from becoming too low compared to conventional heater electrodes made of Mo alone. In addition, when part of Mo becomes _Mo2C , the heater electrode has a mixture of areas with low and high volume resistivities, which causes non-uniformity in the resistance of the heater electrode and deteriorates the temperature uniformity. However, in the ceramic heater according to the present invention, this is suppressed and the temperature uniformity is improved.
That is, a heater electrode in which the reaction 2Mo+C→Mo ₂ C has progressed sufficiently maintains a high volume resistivity and a stable resistance value of the heater electrode.

In this case, the ratio of the number of atoms constituting the heater electrode is 0.20 or more, i.e., the ratio of the total number of atoms of C and Mo to Mo. If the value is smaller than this, the C component is relatively small, and Mo that has not sufficiently reacted with C is mixed, reducing the resistivity of the electrode and preventing the heater from achieving a uniform temperature distribution effect. If the heater is completely converted to _Mo2C , the theoretical atomic ratio is 0.333, which is the upper limit.

In the ceramic heater according to the embodiment of the present invention, the substrate contains a Y component, YAG is formed around the heater electrode in the substrate, and in an X-ray diffraction chart of the substrate around the heater electrode, it is preferable that the relationship (A/B) ≧ 0.11 is satisfied, where A is the peak intensity of YAG at a position where 2θ is 54.978° and B is the peak intensity of AlN at a position where 2θ is 36.041°.

_It was found that in the ceramic heater according to the embodiment of the present invention, when the reaction of forming _Mo2C is progressing, a large amount of _YAG ( _Y3Al5O12 ) component is formed at the grain boundaries of the AlN ceramic around the electrodes. _{Y2O3 is} added to the AlN ceramic as a sintering aid, and Y-based oxide particles consisting of _at least one component of YAG ( _Y3Al5O12 ), YAP ( _YAlO3 ), and YAM ( _Y4Al2O9 ) are formed _{at the} grain _boundaries .
It was found that electrodes with a high ratio of _Mo2C generation and small drop in resistance have a high ratio of YAG generation at the grain boundary of the AlN sintered compact near the interface between Mo and AlN. It was also found that the variation in resistance is small when the YAG peak intensity A and the AlN peak intensity B at the position where 2θ is 36.041° satisfy the relational expression (A/B) ≥ 0.11.

A method for producing a ceramic heater according to an embodiment of the present invention is the method for producing a ceramic heater described above, and includes the steps of preparing a first precursor and a second precursor which contain a binder and form the base material, and a firing step of firing a laminate obtained by stacking the first precursor and the second precursor with a mesh made of Mo wires which form the heater electrodes sandwiched between them while applying a predetermined pressure in the stacking direction, wherein the pressure is P (MPa) and the diameter of the Mo wires is φ (m), and the relational expression (P/φ)≦5× ¹⁰⁴ is satisfied.

In the manufacturing method of the ceramic heater according to the embodiment of the present invention, the cross section of the Mo wire forming the heater electrode is prevented from forming a region where the C component is relatively small and the Mo component is relatively large, and the Mo and C react sufficiently to form an electrode that is converted into Mo ₂ C. As a result, the volume resistivity of the electrode can be suppressed from being reduced, and the resistivity is partially reduced, which suppresses the occurrence of non-uniformity in the resistance of the heater electrode, thereby improving the temperature uniformity of the heater. The inventor discovered that this reaction is caused by the wire diameter and pressure. That is, it was discovered that a region where the C component is relatively small is formed along the direction in which pressure is applied in the cross section of the wire, and that this region is likely to be formed when the pressure is equal to or higher than a certain level. This region is particularly noticeable near the intersection of the wires. The formation of the above region can be suppressed by setting the pressure during firing to a certain value or less.

The method for manufacturing a ceramic heater according to another embodiment of the present invention is the method for manufacturing a ceramic heater described above, and includes the steps of preparing a first precursor and a second precursor that form the base material, a carbonization step that carbonizes the Mo material that forms the heater electrode, and a firing step that sandwiches the Mo material after the carbonization step between the first precursor and the second precursor and fires the laminate while applying a predetermined pressure in the stacking direction.

In another embodiment of the method for manufacturing a ceramic heater according to the present invention, the Mo material forming the heater electrode is carbonized in advance, so that the Mo in the Mo material is transformed into Mo ₂ C. By manufacturing a heater using this Mo material for the heater electrode, it is possible to prevent the formation of an area in the wire cross section where the C component is relatively small and the Mo component is relatively large, and it is possible to form a heater electrode in which Mo and C have sufficiently reacted to form Mo ₂ C. As a result, the temperature uniformity of the heater is improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in Fig. 1, the heater has one end 2a of a cylindrical shaft 2 made of AlN ceramics that supports the heater plate 1, which is vertically joined to the center of one surface 1a of the heater plate 1, which has a diameter of 12 inches and a thickness of about 15 to 30 mm. Furthermore, a metal terminal 3 for power supply is inserted into the heater from the other end 2b of the shaft 2 to electrically connect it to an electrode, and one end of the terminal 3 is electrically connected to an electrode buried inside the heater plate 1 via a brazing material (not shown). The heater plate 1 and the shaft are made of a material containing AlN ceramics.

The heater plate 1 was made by the following process. As shown in FIG. 2, 5 wt% of _Y2O3 as a sintering aid and a _binder were added to the AlN raw material and molded to prepare AlN ceramic precursors 11 and 12 (1. Precursor preparation). An electrode embedding recess 12a was provided on the upper surface of one of the molded precursors 12 (2. Precursor processing). The precursors 11 and 12 were degreased (3. Precursor degreasing). A Mo mesh electrode 13 was placed in the electrode embedding recess 12a on the upper surface of the degreased one of the precursors 12, and the precursor 11 was laminated on the precursor 12 (4. Lamination), and the Mo mesh electrode 13 was embedded in the precursors 11 and 12. This was hot-press fired (5. Hot-press firing) to produce the AlN ceramic heater plate 1.

(Heater electrode resistance)
The embedded Mo mesh electrode was cut to a predetermined shape in accordance with the wire diameter and mesh size (number of wires per inch) constituting the mesh so that the heater resistance value after firing would be 4.1 Ω.
The resistance value of the AlN ceramic heater was obtained by measuring the resistance between the terminals with a commercially available tester.

(Temperature distribution measurement)
The manufactured AlN ceramic heater was placed in a vacuum chamber, electricity was passed between the terminals, and a thermocouple was separately placed in the center of the back surface of the heater plate. The AlN ceramic heater was heated so that the temperature measured by the thermocouple reached 550°C.
After the heater temperature reached a steady state, the AlN ceramic heater was photographed through a sapphire transmission window with an infrared camera (manufactured by FLIR Corporation), and the difference between the maximum and minimum temperatures on the substrate mounting surface of the heater was measured as the temperature distribution (°C). Note that the input power during the measurement was about 3 kW.

(Quantitative analysis of elements)
The cross section of the fired body was subjected to elemental mapping analysis by FE-EPMA (field emission electron probe microanalyzer) to quantify C and Mo and calculate the C/(C+Mo) ratio, as shown in Figures 3 and 4. Also, the intensity spectrum diagram of Mo and C of the cross section of the heater electrode of the ceramic heater of Comparative Example 1 is shown in Figure 5.

In the case of the electrode cross section of the ceramic heater of Example 3 shown in Figure 3, it is considered that the distribution of elements is uniform overall and conversion to Mo ₂ C has progressed. In the case of the electrode cross section of the ceramic heater of Comparative Example 1 shown in Figure 4, as shown in Figure 5, it is clear that conversion _to Mo ₂ C has progressed at measurement point 1 but has not progressed at measurement point 2.

(Test 1)
By changing the electrode shape and the firing pressure, AlN ceramic heaters of Examples 1 to 8 and Comparative Examples 1 and 2 were manufactured and tested by the above-mentioned method. Table 1 shows the conditions and measurement results.
As shown in Table 1, when the ratio of the number of atoms in the wire cross section is C/(C+Mo) 0.20 or more, the heater resistance value is maintained high. The heater temperature distribution in this case is 10°C or less, and it is found that the heating uniformity is high. Furthermore, when the C/(C+Mo) ratio is 0.26 or more, particularly 0.29 or more, it is shown that the heater resistance value is maintained higher and the heater temperature distribution can be further reduced to within 6°C.
It was also shown that if the ratio P/φ (MPa/m) of the pressure P during sintering to the wire diameter φ of Mo is P/φ≦5×10 ⁴ , the C/(C+Mo) ratio is 0.24 or more.
It is preferable that P/φ is 1×10 ⁴ or more (as in the first embodiment). Also, P/φ is 0.333 or less.

(X-ray diffraction of AlN ceramics)
For the AlN ceramic heaters of Examples 1 and 3 and Comparative Examples 1 and 2, X-ray diffraction was performed on a localized region (diameter of about 100 μm) by μ-XRD (micro X-ray diffraction).
The ratio of the peak intensity of YAG corresponding to a diffraction angle 2θ of 54.978° on the JCPDA card (PDF #04-006-4052) to the peak intensity of AlN corresponding to a diffraction angle 2θ of 36.041° on the JCPDS card (PDF #00-025-1133) was measured.
The results are shown in Table 2.

It is apparent from Table 2 that when the ratio of the YAG peak intensity to the AlN peak intensity is 0.11 or more, the production ratio of Mo ₂ C increases.

X-ray diffraction charts of the AlN ceramics surrounding the AlN ceramic heaters of Example 3 and Comparative Example 1 are shown in FIG. 6 and FIG.
6 and 7 show that the ratio of the YAG peak intensity to the AlN peak intensity is greater in Example 3 than in Comparative Example 1.
FIG. 8 shows (A) an SEM image of the cross section of the Mo electrode, (B) a Y element map, and (C) an O element map of Example 3. In FIG. 8, the electrode 21 can be seen sandwiched between the AlN ceramic heater plates 22. In FIG. 8 (B) and (C), the white areas indicate that there are a lot of Y and O elements. This shows that the Y and O elements are concentrated around the electrode 21.

(Test 2)
A mesh-shaped Mo material for forming a heater electrode was carbonized to _Mo2C in advance.
9, a mesh-shaped Mo material 24 was placed in a carbon storage container 23 and heat-treated in a specified atmosphere (nitrogen or inert gas) to produce a mesh made of Mo ₂ C. Using the Mo ₂ C mesh, the AlN ceramic heaters of Examples 9 and 10 were produced according to the manufacturing method of Example 1.

The mesh specifications were wire diameter φ0.1 mm, mesh size #50, and plain weave.
The heat treatment conditions are shown in Table 3, with a temperature of 1300° C. or higher, a holding time of 0.1 hour or more (1 hour in the following examples), and a nitrogen atmosphere.
Table 3 shows the C/(C+Mo) ratio after heat treatment, the C/(C+Mo) ratio after firing, the heater resistance, and the temperature distribution for each example.
As shown in Table 3, it was shown that by previously performing a heat treatment to carbonize the Mo electrode to Mo ₂ C, the heater resistance was stabilized and the temperature distribution was reduced.

The present invention is not limited to the above-described embodiment, and may be embodied in various forms without departing from the scope of the present invention.
Although the present invention has been described with reference to electrodes for heaters, the present invention can also be applied as is to electrodes for electrostatic attraction embedded in AlN and electrodes for high frequency to stabilize the volume resistivity of the electrodes, and can also be applied to heaters equipped with an electrostatic chuck function and a high frequency electrode function.

REFERENCE SIGNS LIST 1 heater plate 2 shaft 3 terminal 11, 12 AlN ceramic precursor 12a electrode embedding recess 13 Mo mesh electrode 21 electrode 22 AlN ceramic heater plate 23 carbon storage container 24 mesh-shaped Mo material

Claims (3)

A ceramic heater having a heater electrode embedded in a substrate containing AlN ceramics, the heater electrode containing Mo and C, and a ratio of the number of C atoms to the sum of the number of Mo atoms and the number of C atoms is 0.20 or more and 0.325 or less,
The substrate contains Y, YAG is formed around the heater electrode in the substrate, and in an X-ray diffraction chart of an interface between the heater electrode and the substrate, when the peak intensity of YAG at a position where 2θ is 54.978° is defined as A and the peak intensity of AlN at a position where 2θ is 36.041° is defined as B, the relationship (A/B) ≧ 0.11 is satisfied . A method for producing a ceramic heater according to claim 1, comprising the steps of:
providing a first precursor and a second precursor that comprise a binder and form the substrate;
and a firing step of firing the laminate obtained by stacking the first precursor and the second precursor with a mesh made of Mo wires forming the heater electrode sandwiched between them while applying a predetermined pressure in a stacking direction, wherein the pressure is P (MPa) and the diameter of the Mo wire is φ (m),
A method for manufacturing a ceramic heater, characterized in that the relational expression (P/φ)≦5× ¹⁰⁴ is satisfied. A method for producing a ceramic heater according to claim 1, comprising the steps of:
providing a first precursor and a second precursor for forming the substrate;
a carbonization step of carbonizing the Mo material forming the heater electrode;
and a firing step of firing the laminate obtained by sandwiching the Mo material after the carbonization step between the first precursor and the second precursor while applying a predetermined pressure in a stacking direction.