# Patent

## Title
Chemical vapor deposition apparatus having a susceptor with a grounded lift pin

## Abstract

A chemical vapor deposition apparatus includes a ground voltage source, a susceptor for placing a substrate, a center pin passing through the susceptor for lifting the substrate, and a ground member for connecting the center pin to the ground voltage source.

## Background
The present invention claims the benefit of Korean Patent Application No. P2001-27128 filed in Korea on May 18, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus, and more particularly to a chemical vapor deposition apparatus for creating a uniform electric field.
2. Description of the Related Art
In general, a liquid crystal display (LCD) controls a light transmittance of liquid crystal cells that are arranged in a matrix array on a liquid crystal display panel. Accordingly, the liquid crystal cells receive data signals, thereby displaying an image (picture). The LCD includes electrodes for supplying an electric field to a liquid crystal layer, a thin film transistor (TFT) for switching the data signals provided to the liquid crystal cells, a lower substrate having signal wiring for supplying the data signals to the liquid crystal cells and signal wiring for supplying control signals of the TFT, an upper substrate having a color filter, a spacer formed between the upper substrate and the lower substrate for providing a predetermined cell gap, and liquid crystal molecules disposed within a space provided between the upper substrate and the lower substrate.
During fabrication of the liquid crystal display device, a channel portion in an active layer of the TFT and a protective layer protecting the TFT are formed during plasma enhanced chemical vapor deposition (PECVD) processing. During PECVD processing, a gas is injected into a vacuum chamber. Then, at a specific pressure and substrate temperature, the injected gas decomposes into a plasma by use of a radio frequency (RF) voltage, thereby depositing materials onto a surface of the substrate. A quality of the deposited material is dependent upon the deposition conditions, such as the vacuum, the RF voltage, the RF voltage frequency, substrate temperature, reaction gas, and reaction pressure, for example. In addition, the deposited materials includes insulating films, semiconductor films, gate insulating films, protective films, and etch stopper films. The semiconductor films include amorphous silicon (a-Si:H) that form an active layer, and doped amorphous silicon (n+a-Si:H) that form a contact protective layer.
FIG. 1 is a cross sectional view of a plasma enhanced chemical vapor deposition (PECVD) apparatus according to a related art. In FIG. 1, the PECVD apparatus includes a gas jet 9 for releasing a gas to be deposited onto a substrate 7, and a chamber 1. The chamber 1 includes a susceptor 5 for applying heat via a heating coil to the substrate 7, a shadow frame 10 for securing the substrate 7, and a center pin 12 for separating the susceptor 5 from the substrate 7.
During processing, the substrate 7 is placed upon the susceptor 5 within the chamber 1, and the susceptor 5 applies heat to the substrate 7 and functions as a lower electrode for generating a plasma. A temperature of the susceptor 5 averages about 370° C. In addition, the susceptor 5 includes various pins formed to penetrate the susceptor 5.
The shadow frame 10 secures the substrate 7 within the chamber 1, and the center pin 12 rises by a pin plate 16 to prevent any drooping of the substrate 7. In addition, the center pin and pin plate 16 prevents formation of any scratches between a robot arm 14 and the substrate 7 during loading and unloading of the substrate 7. The pin plate 16 includes a center pin-supporting portion 18 having the center pin 12 passing through it.
FIGS. 2A to 2D show a process for loading a substrate into a chamber according to the related art.
In FIG. 2A, the substrate 7 is loaded into the chamber 1 by the robot arm 14, and the substrate 7, the susceptor 5, and the center pin 12 are not mutually contacting each other.
In FIG. 2B, the pin plate 16 rises to mount the center pin-supporting portion 18 in center pin mount portions 20 and 21 equipped on a rear surface of the susceptor 5, and each of corner pins 22 and 23 and the center pin 12 rise by a power driver (not shown) to lift the substrate 7.
In FIG. 2C, the robot arm 14 is separated from the substrate 7 by the power driver (not shown).
In FIG. 2D, the susceptor 5 rises by a susceptor-lifting portion 24 to make the susceptor 5 lift the substrate 7 and the center pin 12. Then, the susceptor 5 raises the substrate 7 close to the shadow frame 10. Accordingly, the substrate 7 is safely placed into a deposition position.
FIG. 3 is a cross sectional view representing an inside of a chamber according to the related art. In FIG. 3, the chamber 1 includes the substrate 7 safely placed upon the susceptor 5, and an upper electrode 30 that faces the substrate 7 with a predetermined gap therebetween. The center pin 12 raises the substrate 7 upon loading, and the susceptor 5 rises. Accordingly, the substrate 7 sustains a predetermined gap from the upper electrode 30, and the center pin 12 lowers into a center pin hole 19 formed on the susceptor 5. The center pin 12 is made of ceramic material that has a low coefficient of thermal expansion.
FIG. 4 is a cross sectional view of a center pin according to the related art as shown in FIG. 3. In FIG. 4, an insulating film Al2O3 is formed upon a head portion 3 of the center pin 12, thereby preventing electrical arcing during plasma processing. Accordingly, the center pin 12 is not ground to the susceptor 5. However, the heating coil (not shown) formed inside the susceptor 5 is ground with an external ground voltage source GND.
In FIG. 3, a radio frequency (RF) voltage source 32 is connected to the upper electrode 30. Accordingly, an electric field is generated between the upper electrode 30 and the substrate 7, whereby an insulating film or a semiconductor film is deposited upon a surface of the substrate 7. When depositing the insulating film or the semiconductor film on the substrate 7, the electric field emanating from the upper electrode 30 is bowed in a region of the center pin 12. Accordingly, an electric field density in a region of the center pin 12 is relatively low, thereby a thickness of the deposition film in the region of the center pin 12 will be thinner than surrounding regions.
FIG. 5 shows a defect resulting from the center pin according to the related art. In FIG. 5, a thickness of the deposition film in an area A of the substrate 7, which corresponds to a region of the center pin 12 (in FIG. 3), is different from a thickness of the deposition film in other regions.
FIG. 6 is a spectrum photograph showing the defect on a substrate illustrated in FIG. 5 according to the related art. In FIG. 6, the thickness of the deposition film in the area A of the substrate 7, which corresponds to the region of the center pin 12 (in FIG. 3), is relatively thinner than the thickness of the deposition film in the other regions.
FIG. 7 is a graph showing thickness distribution of a deposition film of the substrate 7 (in FIG. 5) taken along I–I′ of FIG. 6. In FIG. 7, the graphical distribution of deposition thickness of the deposition film on the substrate indicates that a defect is generated in a region corresponding to the center pin 12 (in FIG. 3). Accordingly, the defect degrades image quality of the liquid crystal display device.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a chemical vapor deposition apparatus that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a chemical vapor deposition apparatus generating a uniform electric field, thereby forming a deposition film having a uniform thickness.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a chemical vapor deposition apparatus includes a ground voltage source, a susceptor for placing a substrate, a center pin passing through the susceptor for lifting the substrate, and a ground member for connecting the center pin to the ground voltage source.
In another aspect, a chemical vapor deposition apparatus includes a chamber, a ground voltage source, a susceptor within the chamber, a substrate on the susceptor, a center pin passing through the susceptor for lifting the substrate, a plate for driving the center pin, and a ground member for connecting the center pin to the ground voltage source.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a cross sectional view of a chemical vapor deposition apparatus according to a related art;
FIGS. 2A to 2D show a process for loading a substrate into a chamber according to the related art;
FIG. 3 is a cross sectional view of an inside of a chamber according to the related art;
FIG. 4 is a cross sectional view of a center pin according to the related art, as shown in FIG. 3;
FIG. 5 shows a defect resulting from the center pin according to the related art;
FIG. 6 is a spectrum photograph showing the defect on a substrate illustrated in FIG. 5 according to the related art;
FIG. 7 is a graph showing thickness distribution of a deposition film of the substrate taken along I–I′ of FIG. 6;
FIG. 8 is a cross sectional view showing an exemplary chamber according to the present invention;
FIG. 9 is a cross sectional view of an exemplary center pin according to the present invention; and
FIG. 10 is a cross sectional view of another exemplary center pin according to the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
FIG. 8 is a cross sectional view showing an exemplary chamber according to the present invention. In FIG. 8, a chemical vapor deposition apparatus may include a chamber 50 for performing a deposition process on a substrate 37. The chamber 50 may include a susceptor 45 contacting the substrate 37, a center pin 42 for lifting the substrate 37, and an upper electrode 40 facing the substrate 37 and having a predetermined gap therebetween for generating an electric field.
The substrate 37 may be placed onto the susceptor 45 within the chamber 50. A heating coil (not shown) may be formed within the susceptor 45 to supply heat to the substrate 37. The susceptor 45 may also function as a lower electrode for generating a plasma discharge. During the deposition process, a temperature within the susceptor 45 may average about 370° C. The susceptor 45 may include various pins (not shown) that pass through the susceptor 45 for chemical vapor deposition.
The center pin 42 may be elevated by means of a pin plate 36 to prevent any drooping of the substrate 37. The pin plate 36 prevents any of the substrate 37 by a robot arm (not shown) during loading and unloading of the substrate 37. In addition, the pin plate 36 functions to raise the center pin 42 via a power driver (not shown).
FIG. 9 is a cross sectional view of an exemplary center pin according to the present invention. In FIG. 9, the center pin 42 may include a head portion 53, a head supporter 54, and a grounding terminal 52. The head portion 53 may include a conductive segment 53a formed of aluminum (Al), for example, and an insulating segment 53b such as aluminum oxide (Al2O3), for example. The insulating segment 53b may prevent electrical arcing between the substrate 37 and the susceptor 45 when the electrical field is applied between the susceptor 45 and the upper electrode 40 (in FIG. 8).
The head supporter 54 may be formed of a ceramic material, for example, having a low coefficient of thermal expansion. A ground line 56 may be formed at one side of the head supporter 54. The ground line 56 may be formed of an electrically conductive metal such as aluminum (Al), for example, inserted into a groove formed at one side of the head supporter 54 and electrically interconnected to the conductive segment 53a of the head portion 53.
The ground terminal 52 may be electrically connected to the conductive segment 53a of the head portion 53 via the ground line 56, thereby grounding the center pin 42 to an external ground voltage source GND. The grounding the center pin 42 may be accomplished by electrically connecting a lower part of the center pin 42 to the ground terminal 52 after removing a portion of the ground terminal 52 that has been coated with the insulating segment 43b. Then, the ground terminal 52 may be connected to a metal line that extends from a lower part of the susceptor 45, thereby electrically grounding the center pin 42 to the external ground voltage source GND.
In FIG. 8, the upper electrode 40 may receive a voltage from a radio frequency voltage source 38 to form a deposition film on the substrate 37. Accordingly, since the center pin 42 is grounded to the ground voltage source GND via the ground line 56, a uniform electric field is generated between the susceptor 45 and the upper electrode 40. This form electric field results in a deposition film have a uniform thickness across a surface of the substrate 37, and prevents formation of any defects within a region of the center pin 42.
FIG. 10 is a cross sectional view of another exemplary center pin according to the present invention. In FIG. 10, the center pin 42 may include a head portion 53, a head supporter 54, and a grounding terminal 52. The head portion 53 may include a conductive segment 53a formed of aluminum (Al), for example, and an insulating segment 53b such as aluminum oxide (Al2O3). The insulating segment 53b may prevent electrical arcing between the substrate 37 and the susceptor 45 when the electrical field is applied between the susceptor 45 and the upper electrode 40 (in FIG. 8).
The head supporter 54 may be formed of a ceramic material, for example, having a low coefficient of thermal expansion. A ground line 56 may be formed passing through a center part of the head supporter 54, and may be formed of an electrically conductive metal, for example, and may electrically interconnect the conductive segment 53a of the head portion 53 to an external ground voltage source GND via the grounding terminal 52.
The ground terminal 52 may be electrically connected to the conductive segment 53a of the head portion 53 via the ground line 56, thereby grounding the center pin 42 to an external ground voltage source GND. The grounding the center pin 42 may be accomplished by electrically connecting a lower part of the center pin 42 to the ground terminal 52 after removing a portion of the ground terminal 52 that has been coated with the insulating segment 43b. Then, the ground terminal 52 may be connected to a metal line that extends from a lower part of the susceptor 45, thereby electrically grounding the center pin 42 to the external ground voltage source GND.
In FIG. 8, the upper electrode 40 may receive a voltage from a radio frequency voltage source 38 to form a deposition film on the substrate 37. Accordingly, since the center pin 42 is grounded to the ground voltage source GND via the ground line 56, a uniform electric field is generated between the susceptor 45 and the upper electrode 40. This uniform electric field results in a deposition film have a uniform thickness across a surface of the substrate 37, and prevents formation of any defects within a region of the center pin 42.
It will be apparent to those skilled in the art that various modifications and variations can be made in the chemical vapor deposition apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

## Claims

1. A chemical vapor deposition apparatus, comprising:
a ground voltage source;
a susceptor for placing a substrate, the susceptor being connected to the ground voltage source via a metal line;
a center pin passing through the susceptor configured to lift the substrate; and
a ground member electrically connecting the center pin to the metal line,
wherein the ground member extends along and is attached to an entire axial length of the center pin.

2. A chemical vapor deposition apparatus, comprising:
a ground voltage source;
a susceptor for placing a substrate, the susceptor being connected to the ground voltage source via a metal line;
a center pin passing through the susceptor configured to lift the substrate; and
a ground member electrically connecting the center pin to the metal line,
wherein the ground member extends along and is attached to an entire axial length of the center pin, and the center pin includes a head portion connected to the substrate and a head supporter for supporting the head portion.

3. The apparatus according to claim 2, wherein the ground member is formed between the head portion and the head supporter.

4. The apparatus according to claim 2, wherein the ground member passes through a center portion of the head supporter.

5. The apparatus according to claim 2, wherein the ground member is formed along one side of the head supporter.

6. The apparatus according to claim 1, wherein the ground member includes an electrically conductive metal.

7. The apparatus according to claim 2, wherein the head portion includes aluminum.

8. The apparatus according to claim 2, wherein the head supporter includes a ceramic material.

9. The apparatus according to claim 1, further comprising a heating coil within the susceptor.

10. A chemical vapor deposition apparatus, comprising:
a chamber;
a ground voltage source;
a susceptor within the chamber, the susceptor being connected to the ground voltage source via a metal line;
a substrate on the susceptor;
a center pin passing through the susceptor configured to lift the substrate;
a plate for driving the center pin; and
a ground member electrically connecting the center pin to the metal line,
wherein the ground member extends along and is attached to an entire axial length of the center pin.

11. A chemical vapor deposition apparatus, comprising:
a chamber;
a ground voltage source;
a susceptor within the chamber, the susceptor being connected to the ground voltage source via a metal line;
a substrate on the susceptor;
a center pin passing through the susceptor configured to lift the substrate;
a plate for driving the center pin; and
a ground member electrically connecting the center pin to the metal line,
wherein the ground member extends along and is attached to an entire axial length of the center pin, and the center pin includes a head portion contacting the substrate and a head supporter for supporting the head portion.

12. The apparatus according to claim 11, wherein the ground member is formed between the head portion and the head supporter.

13. The apparatus according to claim 12, wherein the ground member passes through a center portion of the head supporter.

14. The apparatus according to claim 12, wherein the ground member is formed along one side of the head supporter.

15. The apparatus according to claim 12, wherein the ground member includes an electrically conductive metal.

16. The apparatus according to claim 10, wherein the head portion includes aluminum.

17. The apparatus according to claim 13, wherein the head supporter includes a ceramic material.

18. The apparatus according to claim 10, further comprising a heating coil within the susceptor.

19. The apparatus according to claim 1, wherein the ground member is directly connected to the center pin.

20. The apparatus according to claim 10, wherein the ground member is directly connected to the center pin.

21. A chemical vapor deposition apparatus, comprising:
a ground voltage source;
a susceptor having a surface for placing a substrate, the susceptor being connected to the ground voltage source via a metal line such that the surface of the susceptor is grounded during chemical vapor deposition;
a T-shaped center pin passing through the susceptor configured to lift the substrate, the center pin including a head portion and a head supporter; and
a ground member electrically connecting the center pin to the metal line, wherein the head supporter has a groove formed along its entire axial length, and the ground member extends along and is attached to the entire axial length of the center pin within the groove.

22. The apparatus according to claim 21, wherein the head portion is formed with a conductive material, and the head supporter is formed with a material having a low coefficient of thermal expansion.

23. The apparatus according to claim 22, wherein the conductive material includes aluminum, and the material having a low coefficient of thermal expansion includes ceramic.

24. The apparatus according to claim 21, wherein the head portion is coated with an insulating material.

25. The apparatus according to claim 24, wherein the insulating material includes aluminum oxide.

26. The apparatus according to claim 21, wherein the susceptor and the center pin are commonly grounded such that a uniform electric field is generated over the first and second surfaces of the susceptor and the center pin, respectively.