JP3820212B2 - Method for conditioning a CVD chamber after CVD chamber cleaning - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to chemical vapor deposition (CVD) processing. In particular, the present invention relates to a method for conditioning a chamber after cleaning the CVD chamber and prior to the next CVD process.
[0002]
[Prior art]
CVD is widely used in the semiconductor industry, for example, to deposit films of various materials on substrates, such as intrinsic and doped amorphous silicon, silicon oxide, silicon nitride, silicon oxynitride and other similar compounds. ing. Modern semiconductor CVD processes are typically performed in a vacuum chamber by heating a precursor gas that dissociates and reacts to form the desired film. In order to deposit the film at a low temperature and at a relatively high deposition rate, a plasma can be formed from the precursor gas in the chamber during deposition. Such a process is known as plasma enhanced chemical vapor deposition or PECVD.
[0003]
Current technology CVD chambers are made of aluminum and include a substrate support to be processed and a gas inlet port which is the required precursor. When plasma is used, the gas inlet and / or substrate support is connected to a power source, such as a radio frequency (RF) power source. A vacuum pump is also connected to the chamber to control the pressure in the chamber and remove various gases and particles generated during deposition.
[0004]
As the semiconductor devices on the substrate become smaller and closer together, the particles in the chamber must be kept to a minimum. During the deposition process, the deposited film not only deposits on the substrate but also forms on the walls and various fixtures such as shields in the chamber, substrate support, etc. Is done. Further, during subsequent deposition, the film on the wall or the like may crack or peel off, allowing contaminant particles to fall on the substrate. This causes problems and damages to certain devices on the substrate. When individual devices or dies are cut from, for example, a silicon wafer, it can happen that damaged devices, such as transistors, must be discarded.
[0005]
Similarly, when a large glass substrate is processed to form a thin film transistor for use as a computer screen or the like, as many as one million transistors are formed on a single substrate. In this case, the presence of contaminants in the processing chamber is also a serious problem. This is because computer screens do not work if they are damaged by particles.
[0006]
Therefore, the CVD chamber must be periodically cleaned to remove particles between one deposition process and the next. Cleaning is generally accomplished by passing an etching gas, particularly a fluorine containing gas such as nitrogen trifluoride, through the chamber. Next, plasma is generated from the fluorine-containing gas. The gas reacts with the coating produced on the chamber walls and fixtures by previous deposition, i.e., coating of amorphous silicon, silicon oxide, silicon nitride, etc. and any particles in the chamber to form a gaseous fluorine-containing product. . The product can be exhaled through the chamber exhaust system. In general, a nitrogen purge is then performed.
[0007]
[Problems to be solved by the invention]
However, it has been found that after this cleaning step, residual fluorine remains in the chamber and, more importantly, the particles are not completely removed from the chamber. The residual fluorine can adversely affect the film quality of amorphous silicon on subsequently deposited films, particularly silicon nitride films, and shifts the threshold voltage of devices created therefrom. The presence of particles can damage the device on the substrate.
[0008]
In this way, the CVD chamber is conditioned or conditioned between deposition steps using a nitrogen-containing gas, and then any residual fluorine remaining in the chamber is removed, while remaining in the chamber at the same time. There has been a need for a process that can prevent particles from falling onto a substrate.
[0009]
[Means for Solving the Problems]
We have found a multi-step conditioning process for CVD chambers after cleaning and removing unwanted deposits from the chamber using a fluorine-containing gas. The process removes residual fluorine from the chamber and reduces the number of particles in the chamber that can subsequently fall onto the substrate being processed.
[0010]
In the preceding cleaning process, fluorine flows into the chamber where it reacts with unwanted deposits and particles. In the first conditioning step of the present invention, a plasma is generated from hydrogen in the chamber, which reacts with the fluorine residue remaining in the chamber. These are wiped out. In the second conditioning step, the plasma is formed from the deposition gas mixture, forming a layer of solid compound on the chamber walls and fixtures, and any particles remaining on the interior surface of the chamber. Wrap effectively.
[0011]
Silane can be used as the deposition gas mixture, and a co-reactant may be added to form a solid silicon compound such as silicon oxide or silicon nitride in the chamber. Alternatively, the deposition gas mixture may be tetraethoxysilane (TEOS) and oxygen, which forms a silicon oxide compound. In general, the deposition gas mixture used in the conditioning process uses some of the same gases used to deposit the film on the substrate.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
U.S. Pat. No. 5,366,585, granted to Robertson et al., Discloses a PECVD chamber suitable for processing large area glass plates. Referring now to the figure, the vacuum chamber 113 surrounded by the reactor housing 112 includes a hinged lid. A gas manifold 132 is positioned above and parallel to the susceptor 116, and a substrate is mounted on the susceptor during processing. The gas manifold 132 includes a face plate 192 that has a plurality of orifices 193 for supplying process and purge gases therein. The RF power supply 128 creates a plasma from the supplied gas.
[0013]
A set of ceramic liners 120, 121, 122 adjacent to the housing 112 insulate the metal walls of the housing 112 to prevent arcing between the housing 112 and the susceptor 116 during plasma processing. These ceramic liners 120, 121, 122 can also withstand fluorine-containing etch cleaning gases. A ceramic ring 123 is attached to the face plate 192 and provides electrical insulation for the face plate 192. These ceramic components also do not attract the plasma, thus helping to confine the processing plasma near the substrate and help reduce the amount of deposition that accumulates on the walls of the housing 112.
[0014]
After the last substrate on which a layer is to be deposited has been removed from the chamber, a standard fluorine-containing gas cleaning is first performed in the chamber in a conventional manner. An 800 sccm flow of nitrogen trifluoride is established by wide opening the gas inlet valve, creating a pressure of 200 millitorr in the chamber. At this time, the susceptor and the gas manifold are placed at an interval of 1600 mils. A 1600 watt RF power source is used in the gas manifold to generate the plasma. The cleaning plasma is continued for about 1 minute per 2000 angstroms of amorphous silicon film previously deposited in the chamber. The cleaning plasma is additionally continued for about 1 minute per 4000 angstroms of silicon nitride film previously deposited on the substrate in the chamber.
[0015]
The two-step conditioning process continues with a thin inert solid compound film on the fixture and walls in the chamber to remove residual fluorine remaining after the CVD chamber cleaning step and to encapsulate the particles. Used to deposit.
[0016]
As an example of the process, in the first conditioning step, hydrogen plasma was formed in the chamber by flowing 1200 sccm of hydrogen into the chamber for 30 seconds and creating a plasma using 300 watts of power. Hydrogen plasma that reacted with the fluorine present in the chamber formed hydrogen fluoride (HF), which could be easily removed through the chamber exhaust system. The chamber was maintained at the temperature used for subsequent deposition and at a pressure of 1.2 Torr. The spacing between the substrate support and the gas manifold was 1462 mils.
[0017]
In the second conditioning step, a thin film of silicon nitride was deposited under the same spacing, temperature and pressure conditions, except that the power was increased to 800 watts and the gas was changed. A silicon nitride film was deposited by flowing 100 sccm silane, 500 sccm ammonia and 3500 sccm nitrogen for an additional 30 seconds into the chamber.
[0018]
In this way, the total time required to condition the chamber for subsequent deposition processes is only about 1 minute. A thin silicon nitride film covers the chamber walls and fixtures, thereby enclosing and sealing any particles that remain in the chamber after the cleaning process so that they do not fall on the substrate being processed. . The deposited silicon nitride layer also reduces gas emissions from the wall material and reduces residual fluorine-containing material from the chamber.
[0019]
The two-step adjustment process described above is used in conjunction with a standard cleaning process including cleaning stabilization, plasma cleaning with a fluorine containing gas, followed by a nitrogen purge. After the silicon deposition and hydrogen plasma treatment of the conditioning process, the chamber may be purged with nitrogen.
[0020]
The above process is preferred in that it removes fluorine-containing residues and reduces the number of particles in the chamber while minimizing system throughput degradation.
[0021]
Other single-step conditioning processes that use the same length of processing time have been attempted so far, but they are not as efficient as the process of the present invention. A single 60 second silicon nitride deposition process is effective in reducing particles, but is less effective in reducing fluorine residues. It also creates a thicker wall deposit that must be etched away in a subsequent cleaning step. A single 50 second process to form a hydrogen plasma is effective for reducing fluorine residues, but is less effective for reducing particles. A single 60 second step of amorphous silicon deposition, formed by adding silane to the hydrogen plasma process, is effective in reducing fluorine residues. It is because of high hydrogen atom production. However, particle reduction is not as effective as silicon nitride deposition. Again, it is necessary to remove amorphous silicon deposits in subsequent cleaning steps.
[0022]
Another two-step conditioning process that uses the same length of processing time is also not effective. 30 second amorphous silicon deposition plus 30 second silicon nitride deposition is effective in reducing fluorine residue and particles. However, the added amorphous silicon wall deposition needs to be removed in a subsequent cleaning process.
[0023]
The multi-step cleaning and conditioning process described above is used with a conventional stabilization treatment of the reaction chamber between the cleaning steps and the nitrogen cleaning step after the fluorine cleaning step and after the silicon nitride deposition step. A purge can be used. It is done in preparation for the subsequent CVD process.
[0024]
FIG. 2 is a flowchart showing a preferred sequence of steps for the CVD chamber cleaning and conditioning process of the present invention. The plasma CVD chamber is first cleaned with a fluorine-containing gas, a hydrogen plasma is formed in the chamber to remove fluorine residues, a silicon compound precursor gas plasma is formed, and a solid silicon compound is deposited inside the chamber. Finally, the chamber is purged with an inert gas prior to inserting the substrate into which the material is to be deposited into the chamber.
[0025]
Although the process has been described with respect to specific examples, it will be apparent to those skilled in the art that various modifications can be made to the gas, reaction conditions, etc., and that these are also included therein. .
[0026]
Furthermore, while specific CVD chambers have been described herein, many CVD chambers are commercially available and can be cleaned and adjusted according to the process. The present invention is limited only by the claims.
[0027]
【The invention's effect】
As described above, according to the present invention, fluorine residue and particles can be effectively removed, and the CVD chamber can be effectively adjusted.
[Brief description of the drawings]
FIG. 1 is a cross-sectional plan view of a PECVD chamber useful for depositing thin films on large area glass substrates.
FIG. 2 is a flowchart illustrating a preferred processing step of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 112 ... Housing, 113 ... Vacuum chamber, 116 ... Susceptor, 120, 121, 122 ... Ceramic liner, 123 ... Ring, 132 ... Gas manifold, 192 ... Face plate.

Claims (11)

A method for cleaning and conditioning a chemical vapor deposition chamber having an inner surface comprising:
a) cleaning the inner surface with a fluorine-containing gas;
b) a hydrogen plasma forming step of forming hydrogen plasma by flowing hydrogen gas into the chamber and removing fluorine residues in the chamber generated in the cleaning step;
c) Conditioning by depositing a thin film of a silicon-containing compound on the inner surface with a suitable silicon-containing gas, on the inner surface, which generates particles in the chamber and can contaminate the deposited film, Wrapping, conditioning step,
d) purging with nitrogen gas .   The method according to claim 1, wherein the fluorine-containing gas is nitrogen trifluoride. The conditioning method of claim 1 performed for about 30 seconds. The method of claim 1 , wherein the silicon-containing compound is silicon nitride.   The method according to claim 4, wherein the silicon nitride is generated by simultaneously flowing a mixed gas of silane gas, ammonia gas, and nitrogen into the chamber.   The method according to claim 5, wherein the mixed gas includes silane gas 100 sccm, ammonia gas 50 sccm, and nitrogen 3500 sccm. The method of claim 1 , wherein the silicon-containing compound is silicon oxide.   The method according to claim 7, wherein the silicon oxide is generated by simultaneously flowing a mixed gas containing tetraethoxysilane and oxygen into the chamber.   The method according to claim 3, wherein the depositing operation is further performed for 30 seconds. The method of claim 1 film containing silicon, which is deposited in the chamber after the cleaning. The method of claim 10 , wherein the same film is deposited in the conditioning step and the deposition step.

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