HK1262789A1 - Plasma reactor having divided electrodes - Google Patents

Description

Plasma reactor with split electrodes

Statement regarding federally sponsored research or development

Is free of

Background

A Chemical Vapor Deposition (CVD) technique used in a process of manufacturing an Integrated Circuit (IC) such as a semiconductor is a technique of applying energy such as heat or electricity to a gaseous raw material including a chemical to increase reactivity of the raw material gas and induce a chemical reaction so that the raw material gas is adsorbed on a semiconductor wafer to form a thin film or an epitaxial layer, and is mainly used for producing a semiconductor, a silicon oxide film, a silicon nitride film, an amorphous silicon thin film.

Generally, during the manufacturing process, if the production is performed at a relatively low temperature, the yield of the semiconductor is improved due to the reduction in the number of product defects. However, the chemical vapor deposition technique causes a chemical reaction by applying energy using heat or light, resulting in an inevitable increase in temperature, making it difficult to improve the yield of semiconductors.

As a method for solving the temperature-induced problem, a Plasma Enhanced Chemical Vapor Deposition (PECVD) method enables chemical vapor deposition even at a low temperature. In the PECVD method, a chemical reaction is induced to deposit a thin film by chemically activating a reactant by using plasma instead of heat, electricity, or light to increase the reactivity of a raw material gas. To achieve this in PECVD, the reactants are converted into plasma by increasing chemical activity by supplying RF power from an RF oscillator to a raw material gas existing in a gaseous state to generate a chemical reaction at a low temperature.

Generally, as the frequency of the RF power becomes higher, a higher deposition rate can be obtained using the PECVD method. The increase in high deposition rate under Very High Frequency (VHF) conditions leads to an increase in productivity, effectively reducing the manufacturing cost in the semiconductor manufacturing process. Thus, PECVD processes are typically performed under VHF conditions to improve manufacturing efficiency. For example, the RF frequency is generally supplied by an RF oscillator at a high frequency of 10MHz or higher, and preferably at a high frequency of 13.56MHz, 27.12MHz, or 40.68 MHz.

PECVD processes, which are performed in typical semiconductor manufacturing, can be performed under high frequency conditions due to the relatively small size of the semiconductor wafer. However, when a semiconductor wafer is large, for example, when the wafer is larger than a semiconductor wafer used in a typical process for manufacturing, such as a solar cell, there arises a problem that it is difficult to constantly maintain a wide plasma corresponding to a large-area wafer. In other words, larger wafers suffer from plasma non-uniformity problems.

The non-uniform plasma is caused by standing waves generated from large area wafers used in solar cell manufacturing processes. The standing wave refers to a wave combination of waves that appear when waves having the same amplitude and frequency move in opposite directions, and refers to a wave that vibrates only in a stopped state without traveling. Therefore, the plasma lacks uniformity due to variations in the magnitude of the RF power on the electrode surface caused by standing waves formed along the surface of the plasma electrode.

Since the non-uniformity of the plasma occurs due to the standing wave in the plasma reactor under the high frequency condition, the characteristics and deposition rate or etching rate of the thin film formed at a position where the density of the plasma is relatively low are different from those formed at a position where the density of the plasma is high, thereby decreasing the productivity of such a large wafer.

Disclosure of Invention

The present invention relates to a plasma reactor, and more particularly, to a plasma reactor for generating plasma used in manufacturing products having a large wafer surface area, such as thin film solar cells. The plasma electrode unit in the plasma reactor is divided into a plurality of sections, and RF power is sequentially applied to the divided plasma electrode sections to solve the standing wave problem on the plasma electrode. Without the split plasma electrode, the high frequency RF power applied to form plasma over a large area corresponding to a large crystal surface area may cause plasma imbalance due to a standing wave phenomenon.

According to an aspect of the present invention, there is provided a plasma reactor for processing plasma, the plasma reactor comprising a plasma electrode unit, a process gas inlet or injection port, a wafer, an RF power unit, and a timing control unit including a timing control circuit, wherein: the plasma electrode unit is divided into a plurality of parts or a plurality of electrodes; the process gas inlet or the injection port is used for injecting process gas to the lower part of the separated plasma electrode unit; the wafer is placed at a lower end of the plasma electrode unit at a time, and the process gas converted into plasma is deposited on the wafer; an RF power unit for supplying RF power; the timing control unit is used to match the split plasma electrodes with a predetermined timing, thereby sequentially applying the RF power to only one plasma electrode at a time.

The timing control unit further includes a voltage dropping unit for selectively dropping a voltage of the RF power applied from the RF power unit, and the timing control unit controls application of the RF power to the separated plasma electrode.

The split plasma electrode unit includes at least a first plasma electrode, a second plasma electrode, a third plasma electrode and a fourth plasma electrode spaced apart from each other. The timing control unit matches each plasma electrode with a timing instance (temporal instance) in the activation timing.

Further, the timing control unit further includes a phase modulation unit for converting the frequency of the RF power by phase modulation.

The divided plasma electrode units or electrodes are spaced apart from each other at the same distance corresponding to the shape of the wafer, the divided plasma electrode units or electrodes are horizontally disposed in the same plane, and the divided plasma electrode units or electrodes are insulated from each other by an insulator.

The plasma reactor may further include a plurality of process gas injection ports for injecting process gases to the divided plasma electrode units or electrodes.

The plasma reactor may further include a chamber including a partition wall extending downward such that the process gas injected to the lower portion of the split plasma electrode unit or the electrode is partitioned, and the chamber is opened downward to deposit the formed plasma on the wafer therebelow, whereby each electrode generates plasma from the corresponding process gas.

It should be understood that different embodiments of the present invention, including those described in accordance with different aspects of the present invention, are intended to be universally applicable to all aspects of the present invention. Any embodiment may be combined with any other embodiment unless it is not appropriate. All examples are illustrative and not restrictive.

The plasma reactor with the split electrodes according to the present invention solves the standing wave problem and the plasma imbalance problem in the plasma reactor, preventing these problems from occurring due to the use of high frequency RF power applied on a large area wafer in the manufacture of, for example, solar cells. The efficiency and productivity of the manufacture of such products are improved even in plasma reactors using large area wafers.

Drawings

Other features and advantages of the present invention will become apparent from the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

fig. 1 shows a portion of a plasma reactor with a split plasma electrode according to an exemplary embodiment of the invention;

FIG. 2 schematically illustrates the application of RF power according to a predetermined timing performed by a timing control unit of the plasma reactor of FIG. 1; and

fig. 3 schematically shows the split plasma electrode of fig. 1 respectively connected to a plurality of output terminals of the timing control unit.

Detailed Description

This application claims priority to U.S. provisional patent application No. 62/329,492, filed 2016, 4, 29, 2016, the entire contents of which are incorporated herein by reference.

The embodiments described in the specification and the configurations shown in the drawings correspond to only exemplary embodiments of the present invention, and do not represent all technical spirit of the present invention.

The present invention relates to a plasma reactor, and more particularly, to a plasma reactor for generating plasma used in manufacturing products having a large wafer area, such as thin film solar cells. The plasma electrode in the plasma reactor is divided into a plurality of electrodes, and RF power is sequentially applied to the plurality of divided plasma electrodes according to a predetermined timing to solve the standing wave problem associated with the plasma electrode of the related art plasma reactor. Without the divided plasma electrode unit, the high frequency RF power applied to form plasma over a large area corresponding to a large wafer surface area may cause plasma imbalance or non-uniformity due to a standing wave phenomenon.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 shows a portion of a plasma reactor with a split electrode according to an embodiment of the invention.

As shown in the drawing, the plasma reactor with split electrodes according to the present invention includes a buffer chamber 40, a process chamber 50, a plasma electrode unit 10, a gas supply unit (not shown), an RF power supply unit 20, and a timing control unit 30, wherein: introducing a process gas into the buffer chamber 40 to generate a plasma; the generated plasma is activated in the processing chamber 50; the plasma electrode unit 10 is divided into a plurality of parts or a plurality of electrodes 11, 12, 13, 14 and forms an upper side of the buffer chamber 40, and the plasma electrode unit 10 serves to convert the process gas into plasma when RF power is applied to the plasma electrode unit 10; a gas supply unit for supplying a process gas into the buffer chamber 40; an RF power supply unit 20 for supplying RF power applied to the plasma electrode unit 10; the timing control unit 30 serves to control the RF power applied to each plasma electrode of the divided plasma electrode unit 10.

The plasma reactor with split electrodes according to the present invention is configured to operate with a wafer substrate 60, wherein a plasma generated from a process gas by the split plasma electrodes 11, 12, 13, 14 in the buffer chamber 40 and activated within the processing chamber 50 is deposited on the wafer substrate 60. The substrate is disposed on a substrate support 70 for supporting the substrate.

In the plasma reactor having the split electrodes according to the present invention, the RF power supplied by the RF power supply unit 20 is supplied to each electrode in the split plasma electrode unit 10 via the timing control unit 30, and the RF power is sequentially supplied to each of the split plasma electrodes corresponding to the sequence of RF power application performed by the timing control unit 30.

As shown in fig. 1, the plasma electrode unit 10 according to an exemplary embodiment of the present invention is divided into four discrete electrodes 11, 12, 13, 14, but the present invention is not limited thereto, and the plasma electrode unit 10 may have a smaller or greater number of electrodes in other embodiments of the present invention. In the embodiments to be described below, an embodiment including the plasma electrode unit 10 divided into four parts (i.e., the first electrode 11, the second electrode 12, the third electrode 13, and the fourth electrode 14) of fig. 2 will be described.

The configuration of the split plasma electrode unit 10 is set to solve the standing wave problem caused by supplying VHF RF power to the large-area electrode corresponding to the large-area wafer 60, and the configurations of the split plasma electrode units 10 are separated from each other to receive power, respectively, and the configuration of the split plasma electrode unit 10 does not cause the standing wave problem compared to the whole electrode unit according to the related art. In an exemplary embodiment of the present invention, the divided plasma electrode unit 10 may be insulated by a known insulator for insulating each electrode 11, 12, 13, 14 from each other.

Furthermore, in another embodiment of the present invention, the process chamber 50 and the buffer chamber 40 may have a plurality of process gas inlets or injection ports corresponding to the number of electrodes of the split plasma electrode unit 10, instead of a single injection port as shown in fig. 1. A plurality of process gas inlets in this embodiment are assigned to each electrode of the plasma electrode unit 10 to inject a respective process gas corresponding to each discrete electrode. To this end, the process chamber 50 and the buffer chamber 40 may include one or more partition walls extending downward between the electrodes such that the process chamber 50 is partially divided into separate gas regions. The lower side of the buffer chamber 40 is opened to deposit plasma on the substrate within the process chamber 50.

The split plasma electrode unit 10 is configured to receive high frequency power from the source 20 via the timing control unit 30 at the plurality of electrodes 11, 12, 13, 14.

The timing control unit 30 is a constituent element for controlling the RF power sequentially applied to each of the four divided plasma electrodes 11, 12, 13, 14. Storing a predetermined timing together with a timing control unit, wherein each of the split plasma electrode units is matched with a timing instance within the timing by the timing control unit. Thus, RF power is sequentially applied to one plasma electrode associated with a corresponding timing instance within a predetermined timing. By performing this timing, RF power is sequentially applied to each plasma electrode. Once the timing control unit sequentially energizes the decoupled plasma electrodes according to the timing, the timing is repeated.

In the illustrated embodiment, there are four plasma electrodes 11, 12, 13, 14, and RF power is sequentially applied to the four electrodes of the separation type plasma electrode unit 10 through the timing control unit 30 according to a predetermined timing. Thereby, the process gas reacts with each of the four electrodes of the split plasma electrode unit 10 to generate plasma corresponding to the entire large area wafer 60. In this case, since plasma is generated by each of the four electrodes of the divided plasma electrode unit 10, respectively, each corresponding reaction region is relatively small. Therefore, it is not necessary to apply the high frequency RF power, thereby solving the problem of non-uniformity of plasma related to the related art and forming uniform plasma corresponding to the large area wafer 60.

The timing control unit 30 of the present invention further includes a voltage reduction unit. As described above, since the plasma electrode unit 10 of the present invention is divided into a plurality of plasma electrodes each for independently generating plasma, it is not necessary to apply RF power of a high voltage such as that used with conventional large-area plasma electrodes. By applying the RF power after the voltage is lowered by the voltage lowering unit to each of the plurality of electrodes 11, 12, 13, 14 of the separated plasma electrode unit 10, the power efficiency is improved.

Furthermore, since the timing control unit 30 enables plasma to be generated via the discrete electrodes of the split plasma electrode unit 10 even at relatively low-frequency RF power, the timing control unit 30 may also be provided with a phase modulator for down-converting the received RF power.

Fig. 2 shows that the RF power is applied according to the sequence performed by the timing control unit 30. Further, fig. 3 schematically shows a separate plasma electrode unit connected to each of a plurality of output terminals of the timing control unit 30.

As shown, in the timing control unit 30, four timing instances sequentially performed, each of which is matched with a corresponding electrode of the divided plasma electrode unit 10, are continuously repeated at preset time intervals.

In the embodiment shown in fig. 2, a first timing example is assigned to the first electrode unit 11, a second example to the second electrode unit 12, a third example to the third electrode unit 13, and a fourth example to the fourth electrode unit 14. As described above, the number of timing instances in the time series corresponds to the number of electrodes. Thus, depending on the implementation, there may be more or less than four timing instances within each timing sequence.

The timing control unit 30 applies voltages to the electrodes of the divided plasma electrode unit 10 designated to the timing instances according to the defined timing.

The timing control unit 30 is constituted by an integrated circuit including a rectifier circuit and a timing control circuit for processing applied power from an RF power supply, and includes a plurality of output terminals each outputting RF power according to a plurality of timing schedules. Therefore, when the RF power is applied to the timing control unit 30, the RF power is applied to one of the divided plasma electrodes corresponding to the timing instance of the predetermined timing.

In one embodiment of the present invention, the timing control unit 30 may further include a phase modulator for varying the frequency of the RF power. With such a phase modulator, before the RF power is applied from the timing control unit 30, the RF power is frequency-converted by phase modulation, and the RF power can be applied at a lower frequency. Since each electrode of the split plasma electrode unit is extremely small compared to the plasma electrode of the related art, the same resultant plasma can be activated by the RF power having a lower frequency.

As shown in fig. 3, in an exemplary embodiment of the present invention, 5KW of RF power having a frequency of 60MHz (relatively low compared to VHF) was applied to the separate plasma electrodes, respectively. The RF power may be supplied through the voltage-decreasing unit of the timing control unit 30. With an arbitrary timing defined within the timing control unit 30, RF power is applied to only one of the split plasma electrodes according to the current timing instance within the timing, and power is not applied to the remaining split plasma electrodes. The RF power applied to each of the separated insulated plasma electrodes generates plasma, but since activation is sequentially and uniformly performed, the same effect as that obtained when a total of 20KW of power is supplied to the conventional electrode can be obtained.

The plasma reactor having the split electrodes according to the present invention solves the standing wave problem and the plasma non-uniformity problem occurring due to the use of the large-area wafer 60 such as in the manufacture of solar cells, by the above configuration. Accordingly, the present invention solves all the disadvantages of the related art plasma reactor and improves the manufacturing efficiency of products even in a plasma reactor using a large area wafer 60, thereby improving productivity.

Although an exemplary embodiment of a plasma reactor with a split electrode according to the present invention has been described in detail, it is only a specific example for illustrating the general concept of the present invention and is not intended to limit the scope of the present invention. It should be clearly understood by those skilled in the art to which the present invention pertains that modifications based on the technical spirit of the present invention may be made in embodiments other than the disclosed embodiments.

Claims (7)

1. A plasma reactor for plasma processing, comprising:

a buffer chamber;

a split plasma electrode unit including a plurality of discrete electrodes and disposed within the buffer chamber;

at least one process gas injection port for receiving a respective process gas and for injecting the respective process gas into the buffer chamber proximate to the discrete electrodes;

a process chamber in which a plasma can be formed by selectively energizing the process gas through the discrete electrodes;

a substrate support provided at a lower end of the process chamber to support a substrate on which the plasma is deposited;

an RF power unit for supplying RF power; and

a timing control unit for associating one discrete electrode with each of a plurality of time intervals within a predetermined timing, and for sequentially applying RF power received from the RF power unit to the plurality of discrete electrodes according to the plurality of time intervals of the predetermined timing.

2. The plasma reactor of claim 1, wherein the timing control unit further comprises a voltage reduction unit for reducing the voltage of the RF power received from the RF power unit before the timing control unit applies the RF power to the plurality of discrete electrodes.

3. The plasma reactor according to claim 2,

the split plasma electrode unit includes a first plasma electrode unit, a second plasma electrode unit, a third plasma electrode unit, and a fourth plasma electrode unit spaced apart from each other in a substantially horizontal plane,

the predetermined timing includes four time intervals, an

The timing control unit associates a time interval within the predetermined timing with a respective one of the plurality of discrete electrodes.

4. The plasma reactor according to claim 1, wherein the timing control unit further comprises a phase modulation unit for converting a frequency of the RF power received from the RF power unit by phase modulation.

5. The plasma reactor according to claim 1, wherein the discrete electrodes of the split plasma electrode unit:

spaced from each other in a substantially horizontal plane;

arranged corresponding to the shape of a wafer to be disposed on the substrate support; and

are insulated from each other by insulators.

6. The plasma reactor of claim 1, wherein the at least one process gas injection port comprises a plurality of process gas injection ports, each process gas injection port associated with a respective one of the plurality of discrete electrodes.

7. The plasma reactor of claim 6, further comprising:

a dividing wall extending downwardly from a top of the buffer chamber and between the plurality of discrete electrodes within the buffer chamber for dividing the process gases from each other, the buffer chamber being downwardly open to allow the process gases to be energized by the respective discrete electrodes and thereby form the plasma within the process chamber.