TWI527500B - Heater with independent center zone control - Google Patents

Description

Heater with independent central zone control

[Reciprocal Reference Related Applications]

The present application claims priority to U.S. Patent Application Serial No. 61/334,386, filed on May 13, 2010, the disclosure of which is hereby incorporated by reference.

The present invention is generally directed to the field of substrate processing equipment. In particular, the present invention relates to apparatus and methods for controlling the temperature of substrates (such as semiconductor substrates) used in the fabrication of integrated circuits.

Modern integrated circuits (ICs) contain millions of individual components that are formed by patterning materials such as germanium, metal, and/or dielectric layers that make up the integrated circuit up to a few microns in size. Many of the steps associated with the fabrication of integrated circuits include accurately controlling the temperature of the semiconductor substrate on which the IC is formed.

One challenge semiconductor manufacturers face in such steps is to evenly control the temperature of the substrate across the entire surface of the substrate. Even the temperature difference between the various locations of the substrate can cause undesired differences in physical properties of one or more layers formed at these locations on the substrate.

One type of heater that is particularly useful in high temperature substrate processing is the base design using a ceramic substrate support. A resistive heating element is buried beneath the upper surface of the ceramic substrate support, and an electronic feedback member for the resistive heater is positioned within the base, the base being attached to the bottom of the heater and lifting the substrate to the substrate processing chamber Above the floor of the room. Figure 1 is an example of a previously known base heater 2 comprising a ceramic substrate support 4 to which a hollow column or base 6 is attached. Embedded in the ceramic support 4 are an RF electrode 8 and a resistive heater 10. The electrical connecting rods 12 and 14 provide power to the RF electrode 8 and the resistive heater 10, respectively. Some base heaters also include a vacuum line (not shown) that allows the substrate to be clamped to the base by vacuum pressure.

The challenge of temperature control discussed above often appears for base heaters (such as heater 2): it is slightly cooler at the center of the substrate heater than the rest of the heater. This is because the electrical connections of the heater and RF electrodes are generally close to the center of the base, providing a smaller area of resistive heating elements (comparable to other areas of the heater).

Therefore, although the substrate heater shown in Fig. 1 is quite practical in many substrate processing operations, it is expected that there will be new and improved substrate heaters and methods for precisely controlling the substrate temperature.

Some embodiments of the present invention provide a substrate heater comprising two separately controllable heating systems, the systems comprising a first primary heater and a second auxiliary heater, the first primary heater being embedded in a substrate support The substantially auxiliary upper surface is positioned within the hollow base coupled to the back surface of the substrate support. The primary heater can be, for example, a resistive heater embedded in the substrate support and spread in a two-dimensional pattern to cover the footprint of the substrate support. The auxiliary heater is operatively coupled to the substrate support such that the auxiliary heater is capable of changing the temperature in a central region of the upper surface of the substrate support.

In accordance with one embodiment of the present invention, a substrate heater is provided that includes a ceramic substrate support having a substantially flat upper surface to support a substrate during processing of the substrate. A resistive heater is embedded in the substrate support, and a heater shaft is coupled to a back surface of the substrate support. The heater shaft can have an internal cavity extending along its longitudinal axis and terminating at a bottom central surface of the substrate support. The substrate heater can further include an auxiliary heater separate from the ceramic substrate support and positioned within the interior cavity of the heater shaft, the bottom of the substrate support A portion of the central surface is in thermal contact such that the auxiliary heater is capable of changing the temperature of a central region of the upper surface of the substrate support.

A substrate heater according to another embodiment comprises a ceramic substrate support having a substantially flat upper surface to support a substrate during processing of the substrate. a resistive heater embedded in the substrate support and spread in a two-dimensional pattern adapted to heat the upper surface of the substrate support in a substantially uniform manner, and a heater shaft coupling A back surface of the substrate support is attached. The heater shaft includes an internal cavity extending along a longitudinal axis thereof and terminating at a bottom central surface of the substrate support. a detachable auxiliary heater positioned in the cavity, and an air gap surrounding the auxiliary heater located on an inner surface of the heater shaft defining the cavity and an outer peripheral surface of the auxiliary heater between. A biasing mechanism is operatively coupled to force the auxiliary heater to be in thermal contact with a portion of the bottom center surface of the substrate support such that the auxiliary heater can change the substrate support The temperature of a central region of the upper surface.

The various advantages and benefits that can be achieved by these and other embodiments of the present invention are described below in conjunction with the drawings.

2 is a simplified cross-sectional view of a substrate heater 20 in accordance with an embodiment of the present invention. The heater 20 includes a ceramic (e.g., AlN, BN, SiC, SiN) substrate support 22 having RF electrodes 24 and resistive heating elements 26 embedded therein and with a shaft or base 28. The heating element 26 is the primary source of heat for the substrate support and may be a two-dimensionally patterned resistive heating coil that is positioned slightly below the surface of the substrate support and designed to provide a traverse across the substrate support Substantially uniform heating at the substrate support surface on the ground. The base 28 can be made of the same ceramic material as the substrate support 22, including an internal cavity 30 that allows a metal rod (not shown) to extend within the cavity 30 and couple the electrode 24 and the heating element 26, providing power to each of the electrodes and the heating elements. As shown in Fig. 2, the substrate heater 20 also includes an auxiliary heater 40 that fits within the cavity 30 of the base 28 to provide an additional source of heat in the central region of the substrate support. The auxiliary heater can be any suitable compact heat source that fits within the cavity 30. In a particular embodiment, the heater 40 is a ceramic block (e.g., aluminum nitride) having a second resistive heating element embedded therein, the second heating element being controlled independently of the heating element 26. In another embodiment, the heater 40 includes a cartridge heater that slides into a cavity that is machined into a heater block.

The auxiliary heater 40 is fitted within the cavity 30 and is positioned adjacent the bottom surface 32 of the substrate support 22 to provide good thermal contact between the heater 40 and the substrate support. According to an embodiment of the invention, the heater 40 is a separate component from the substrate support 22 and is not integrated or bonded to the substrate support. This allows the auxiliary heater to be attached, removed, and replaced as needed during the life of the substrate processing tool. Moreover, the fact that the two components are not bonded together in a fixed manner reduces or eliminates the chance of cracking at the interface between the surface 32 and the auxiliary heater 40 due to the relationship between the heater 40 and the substrate support 22. The difference in thermal expansion coefficient is related to the stress. Some embodiments of the invention include a biasing mechanism (not shown in Figure 2) that urges the heater 40 into thermal contact with the substrate support (as described below), and which also causes the auxiliary heater to be in need It is easy to get rid of.

When the heater 20 is positioned within the substrate processing chamber, the cavity 30 is isolated from the substrate processing region (not shown) of the chamber. In general, the cavity 30 is at atmospheric pressure and the substrate processing area is evacuated to sub-atmospheric pressure or near vacuum pressure. Therefore, the heater 40 is not exposed to the environment within the processing chamber (which is often corrosive). Although not shown in FIG. 2, in a particular embodiment, the heater 40 includes four terminals that run through the shaft 30 to the substrate support, the terminals including two heater terminals , RF terminals, and thermocouple terminals.

Embodiments of the present invention allow for an additional margin of temperature control at the center of the substrate heater 20 such that the substrate positioned on the surface 21 can see a more uniform temperature across the overall surface. As previously mentioned, without this additional temperature control, the central region of the substrate may sometimes be cooler than the surrounding region, which may result in non-uniform processing of the substrate. For example, a centrally cold heater temperature profile will result in film deposition having a higher central region during deposition of thick films or films of various SACVD cerium oxides. The inventors have determined that this problem is caused in part by the lack of a heater coil at the center, which is due to the area occupied by the desired connection of the heater to the RF electrode. However, even if the heater coil design of the heating element 26 is optimized such that a particular heater delivers a uniform temperature profile at a particular temperature (eg, 480 ° C or 540 ° C) across the surface of the overall substrate, the conductivity of the AlN will still follow temperature change. Thus, as the heater set point decreases, the AlN thermal conductivity of the base 28 and the substrate support 22 increases, thereby increasing heat loss through the base. Even a temperature difference of 0.5% between the center and the periphery (for example, 500 ° C at the periphery and 497.5 ° C at the center) may cause unacceptable performance in terms of film uniformity.

Embodiments of the present invention compensate the temperature drop in the center of the heater with an auxiliary heater 40 that is operatively coupled to the lower surface of the substrate support 22 at the interface 32 within the cavity 30 of the shaft 28. . In one embodiment (shown in FIG. 3), the auxiliary heater is a metal block 50 (eg, aluminum, copper, nickel, or some combination, or alloy of the foregoing, etc.) that is in contact with the back surface of the substrate support 22 . The air gap 58 surrounds the periphery of the heater block 50 such that the heater block does not directly contact the sidewall of the base shaft 28. The heater block 50 can be heated by a suitable mechanism such as a resistive heater or a rake heater. The thermocouple 52 monitors the temperature of the auxiliary heater, and the desired set point of the heater block 50 can be based on whether a temperature sensor (not shown) at each radius of the substrate support 22 indicates that the center of the substrate is relative to the periphery. Set by temperature difference. End rods (e.g., nickel rods) run through ceramic conduits 54 and 56 to provide power to the embedded RF electrodes and resistive heating elements embedded in substrate support 22 (all not shown in Figure 3). As mentioned above, the substrate support 22 includes one or more temperature sensors or thermocouples (not shown) that are distinct from the thermocouple 52, which measure the temperature of the substrate support at different locations. And operatively coupled to a resistive heater (such as heater 26 shown in FIG. 2, which is the primary source of heat to support 22).

4 is a simplified perspective view of a substrate heater in accordance with another embodiment of the present invention, wherein the auxiliary heater 60 is mounted within the cavity 30 and is operatively coupled to the substrate support 22 within the cavity. The lower surface. As shown in Fig. 4, the heater 60 is separated from the inner surface of the shaft 28 by an air gap 58. The heater 60 can be made of a metal or ceramic block, such as aluminum nitride, and includes a heater cartridge 61 that fits within a dimension-matched cavity. The thermocouple 62 monitors the temperature of the substrate support in a manner similar to that described above for the thermocouple 52. Lines 64a, 64b provide power/signal to heater 匣 61 and thermocouple 62. The heater 匣 61 may comprise, for example, a standard resistive tungsten heater element.

A ceramic cap 63 is secured to the end of the heater 60 to hold the heater 匣 61 in place. The ceramic cap 63 may be made of an insulative ceramic material, such as alumina, having a lower thermal conductivity than aluminum nitride to isolate the components within the shaft 30 and below the heater 60 from its heat. Separate from the ceramic cap 63 is a high temperature ceramic (e.g., Al ₂ O ₃ ) plate 65 that is operatively attached to the spring 66 proximate the center point of the plate 65. In other embodiments, the plate 65 can be made of a high temperature plastic or similar material.

One or more ceramic conduits 67 are positioned between the plate 65 and the cap 63 such that the heater and RF terminals are allowed to travel through the conduits to the substrate support 22. Spring 66 biases the assembly of plate 65, line 67 and cap 63 such that, in operation, the upper surface of heater 60 is in thermal contact with the lower surface of substrate support 22. The spring 66 is positioned against the aluminum heater base plate 68, which is fixedly attached to the base 28.

In another embodiment, shown in Figure 5, the auxiliary heater 70 is positioned within the cavity 30 of the base 28 and is coupled to a spring loaded mechanism 72 that allows the heater 70 to move or move between the first positions. Entering a second position that is where the heater is operatively engaged with the substrate support when additional heat control is desired, and the second position is where the heater 70 does not physically contact the substrate support . Heater 70 includes one or more apertures 71 through which end bars 73 (e.g., electrodes 24 and end bars of RF heater 26) extend. The hole 71 allows the heater 70 to slide up and down within the base cavity. If desired, corrugated foil (eg, Al, Cu, BeCu, etc.) or ceramic foil or similar components can be positioned in heater 70 (and heaters 40, 50, 60 or 80 shown in other embodiments) and base Between the interfaces of the material support members to effect heat transfer between the two bodies.

In yet another embodiment of FIG. 6, the auxiliary heater 80 is operatively coupled to the spring such that the heater can engage the inner surface 81 of the base shaft 28 that is coupled to the bottom of the substrate support 22. To engage the surface 81, the heater 80 is capable of radially expanding along the line 85. Once engaged, heat from the heater 80 is transmitted through the shaft 28 to the annular region at the bottom of the support 22. As shown in FIG. 7A, which is a simplified cross-sectional view of the shaft 28, in some embodiments, the cross-section of the shaft 28 is circular at the outer surface 83, but has a rectangular, rounded rectangle at the inner surface 81. Or oval. This asymmetrical shape in the case of a circular substrate is particularly useful when the substrate support 22 includes a vacuum chuck (not shown) that is operatively coupled to the vacuum line 84. The heater 80 can be designed to compensate for the asymmetrical shape by providing a higher temperature at portions of the shaft 28, the portions of the shaft 28 contacting the bottom of the substrate support 22 having a surface area that is more than the shaft 28 other There are few areas. In other embodiments, both the outer and inner surfaces of the shaft 28 have a circular cross-section as shown in FIG. 7B and are therefore symmetrical about the circular substrate being treated on the support 22.

Figures 8 and 9 depict test results showing the efficiency of the present invention compared to previously known substrate supports. In particular, Figure 8 shows that embodiments of the present invention can be used to improve wafers processed over a substrate heater in accordance with the present invention as compared to previously known heaters ("baseline" tests) Temperature uniformity on the surface. Note that at 0% power, the temperature uniformity of the particular 550 °C process is worse than previously known heaters because the heater acts as a heat sink to transfer heat away from the center of the wafer, at which point the wafer center It has been colder than the perimeter at 550 °C in this heater design. Although the auxiliary heater is energized by 50%, the average temperature difference across the substrate is reduced and the temperature is more uniform, as compared to those without the present invention. Figure 9 shows the true temperature of the test power level plotted in Figure 8 at different substrate radii.

In some instances, the substrate support can be designed to have a center temperature that is indeed hotter than the perimeter at some or all temperature ranges. Embodiments of the present invention are also capable of improving the non-uniformity of the substrate supports by disabling the heaters within the auxiliary heater or by driving the auxiliary heaters at a set point that is lower than the substrate temperature. In these cases, the auxiliary heater having a relatively large mass functions as a heat absorbing body, and heat is extracted from the center of the substrate, thereby cooling the center of the substrate with respect to the periphery.

2. . . Base heater

4. . . supporting item

6. . . Base

8. . . electrode

10. . . Resistive heater

12, 14. . . Electric connecting rod

20. . . Substrate heater

twenty one. . . surface

twenty two. . . Substrate support

twenty four. . . RF electrode

26. . . Heating element

28. . . Base

30. . . Cavity

32. . . Bottom surface

40. . . Auxiliary heater

50. . . Heater block

52. . . Thermocouple

54, 56. . . Pipeline

58. . . Air gap

60. . . Heater

61. . . Heater匣

62. . . Thermocouple

63. . . cap

64a, 64b. . . line

65. . . board

66. . . spring

67. . . Pipeline

68. . . Base plate

70. . . Auxiliary heater

71. . . Hole

72. . . Spring loaded mechanism

73. . . End rod

80. . . Auxiliary heater

81. . . The inner surface

83. . . The outer surface

84. . . Vacuum line

85. . . line

Figure 1 is a simplified cross-sectional view of a substrate heater in accordance with the prior art;

2 is a simplified cross-sectional view of a substrate heater in accordance with an embodiment of the present invention;

Figure 3 is a simplified perspective view of a substrate heater in accordance with another embodiment of the present invention;

Figure 4 is a simplified perspective view of a substrate heater in accordance with still another embodiment of the present invention;

Figure 5 is a simplified cross-sectional view of a substrate heater in accordance with another embodiment of the present invention;

Figure 6 is a simplified cross-sectional view of a substrate heater in accordance with still another embodiment of the present invention;

7A and 7B are simplified cross-sectional views of a heater shaft in accordance with various embodiments of the present invention;

Figures 8 and 9 depict test results showing the efficiency of the present invention compared to previously known substrate heaters.

28. . . Base

30. . . Cavity

58. . . Air gap

60. . . Heater

61. . . Heater匣

62. . . Thermocouple

63. . . cap

64a, 64b. . . line

65. . . board

66. . . spring

67. . . Pipeline

68. . . Base plate

Claims (11)

A substrate heater comprising: a substrate support having a substantially flat upper surface to support a substrate during processing of the substrate; and a resistive heater embedded in the substrate support a heater shaft coupled to a back surface of the substrate support, the heater having an internal cavity extending along a longitudinal axis thereof and terminating at a bottom central surface of the substrate support An auxiliary heater that is separate from the ceramic substrate support and positioned within the interior cavity of the heater shaft in thermal contact with a portion of the bottom central surface of the substrate support such that the auxiliary The heater is capable of changing a temperature of a central region of the upper surface of the substrate support; and a biasing mechanism operatively coupled to bias the auxiliary heater to the substrate support This portion of the bottom central surface is in thermal contact. The substrate heater of claim 1, wherein the auxiliary heater comprises a first cavity and a second cavity, a heater can be inserted into the first cavity, and a thermocouple can be inserted In the second cavity. The substrate heater of claim 1, wherein the substrate support comprises a ceramic material. The substrate heater of claim 1 wherein the biasing mechanism comprises a spring. The substrate heater of claim 4, wherein the biasing mechanism further comprises a biasing plate and a ceramic conduit positioned between the biasing plate and the heater, and wherein a force from the spring passes through the bias A pressure plate and the ceramic pipe are delivered to the auxiliary heater. The substrate heater of claim 1, wherein an air gap is formed around the auxiliary heater and is located on an inner surface of the heater shaft defining the cavity and an outer peripheral surface of the auxiliary heater. between. The substrate heater of claim 1, further comprising: a thermocouple operatively coupled to measure a temperature of the substrate support; an RF electrode embedded in the substrate support And wherein the auxiliary heater comprises: a ceramic block having a bottom surface and a top surface, the top surface thermally contacting a portion of the bottom central surface of the substrate support; and a plurality of through holes The bottom surface extends to the top surface to allow a first terminal to operatively couple the resistive heater, to allow a second terminal to operatively couple the RF electrode, and to allow a third terminal to The thermocouple is operatively coupled. The substrate heater of claim 7, wherein the ceramic block further comprises a first cavity and a second longitudinally aligned cavity that does not extend through the top surface, wherein the first cavity is sized to accept A heater is sized and the second cavity is sized to receive a thermocouple suitable for measuring the temperature of the auxiliary heater. A substrate heater comprising: a ceramic substrate support having a substantially flat upper surface to support a substrate during processing of the substrate; and a resistive heater embedded in the substrate support And being spread in a two-dimensional pattern adapted to heat the upper surface of the substrate support in a substantially uniform manner; a heater shaft coupled to a back surface of the substrate support, The heater defines an internal cavity extending along a longitudinal axis thereof and terminating at a bottom central surface of the substrate support; an auxiliary heater detachable from the ceramic substrate support and positioned In the inner cavity of the heater shaft, an air gap is formed around the auxiliary heater and is located on an inner surface of the heater shaft defining the cavity and an outer peripheral surface of the auxiliary heater a biasing mechanism operatively coupled to urge the auxiliary heater to be in thermal contact with a portion of the bottom center surface of the substrate support such that the auxiliary heater can change the base The upper part of the material support The temperature of a central region of the plane. The substrate heater of claim 9, wherein the biasing mechanism comprises a spring. A substrate heater comprising: a ceramic substrate support having a substantially flat upper surface to support a substrate during processing of the substrate; and a resistive heater embedded in the substrate support And being spread in a two-dimensional pattern adapted to heat the upper surface of the substrate support in a substantially uniform manner; a heater shaft coupled to a back surface of the substrate support, The heater defines an internal cavity extending along a longitudinal axis thereof and terminating at a bottom central surface of the substrate support; an auxiliary heater separated from the ceramic substrate support and positioned The inner cavity of the heater shaft; and a biasing mechanism operatively coupled to urge the auxiliary heater to heat the inner surface of one of the heater shafts defining the cavity contact.