This application claims the priority benefit of Taiwan application serial no. 98129732, filed on Sep. 3, 2009. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Field of the Invention
The present invention relates to a semiconductor apparatus and a method of fabricating a thin film. More particularly, the present invention relates to a plasma apparatus and a method of fabricating a nano-crystalline silicon thin film.
2. Description of Related Art
Plasma is the most widely adopted process for cleaning, coating, sputtering in the semiconductor process, and also used in a plasma chemical vapor deposition (plasma CVD) process, an ion implantation process, a vacuum arc process, a plasma immersion ion implantation (PIII) or etching process.
In conventional technology, plasma is usually used for forming thin films within the semiconductor process, and the products made from the formed thin films may be applied to us as thin films of the solar cells, and various semiconductor devices, such as thin-film transistors (TFT) array, of the liquid crystal display.
However, in the foregoing plasma apparatus disclosed by U.S. Pat. No. 5,952,061, it needs to heat the substrate to a temperature higher than 300° C. for growing the silicon thin film. Therefore, the silicon thin film may not be grown regarding to those substrates vulnerable to heat, such as flexible substrates. As a results, the various semiconductors thin film, such as thin-film transistors (TFT) array, used in the solar cells, and the liquid crystal display may not be successfully produced due to limitation of process.
An embodiment of the present invention provides a plasma apparatus to produce a thin film having an excellent photoconductivity characteristic without applying an additional doping process.
An embodiment of the present invention provides a method of fabricating a nano-crystalline silicon thin film, which has an excellent photoconductivity characteristic.
An embodiment of the present invention provides a plasma apparatus. The plasma includes a chamber, an arc electrode set, and a substrate holder. The arc electrode set is disposed in the chamber, and the arc electrode includes an anode and a cathode, wherein an arc discharging space is formed between the anode and the cathode. The opposite ends of the cathode and the anode opposite to each other respectively has an crystallized silicon target, wherein the resistance of the crystallized silicon targets is smaller than 0.01 Ω·cm. The substrate holder is disposed within the chamber. The substrate holder has a carrier surface facing to the arc discharging space.
In an embodiment of the present invention, each of the above-mentioned crystallized silicon targets has a single crystal structure of silicon, and each of the single crystal structure of silicon grains has dopants with high dopant concentration, wherein the dopant concentration of the dopants in each of the single crystal structure of silicon grains is substantially from 1019 to 1020 atom/cm2. More specifically, a material of the above-mentioned dopants with high dopant concentration in the crystallized silicon targets can be selected from the III-group elements, and the crystallized silicon targets constitute P-type semiconductor targets. Alternatively, a material of the dopants can be also selected from the V-group elements, and thus the crystallized silicon targets constitute N-type semiconductor targets. Certainly, a material of the above-mentioned dopants with high dopant concentration in the crystallized silicon targets can also be selected from the III-group elements and the V-group elements, and thus the crystallized silicon targets constitute intrinsic semiconductor targets.
In an embodiment of the present invention, a resistance of the above-mentioned crystallized silicon targets is greater than 0.005 Ω/cm.
In an embodiment of the present invention, the above-mentioned plasma apparatus can further includes a movable mechanism, wherein the movable mechanism is connected to the arc electrode set. A relative displacement is generated between the anode and the cathode by the movable mechanism.
In an embodiment of the present invention, the above-mentioned plasma can further include a substrate, wherein the substrate is disposed on the carrier surface of the substrate holder. The substrate holder may further include a cooling system, wherein the cooling system is buried inside the carrier surface, so as to force cool the heated substrate during process. Moreover, the cooling system may include a cooling pipe and a coolant, wherein the cooling pipe passes through a trench buried inside the substrate holder, and the coolant flows and circulates in the cooling pipe. At this moment, the above-mentioned carrier surface is forced to cool to a temperature substantially smaller than 0° C. by the cooling system during the process. For example, the above-mentioned coolant includes water or liquid nitrogen.
According to an embodiment of the present invention, the above-mentioned substrate is a flexible substrate.
According to an embodiment of the present invention, a surface of the above-mentioned substrate to be deposited may be a flat surface, a spherical surface or a mirror surface.
According to an embodiment of the present invention, the above-mentioned plasma apparatus may further include a continuous feeding system, wherein the continuous feeding system is connected to the substrate, and the substrate is carried to be disposed on the substrate holder through the continuous feeding system.
According to an embodiment of the present invention, the above-mentioned plasma apparatus may further include a gas pipe, wherein the gas pipe is disposed on the sidewall of the chamber, and the dopant gas passing through the gas pipe includes diborane or phosphine.
Another embodiment of the present invention provides a method of fabricating a nano-crystalline silicon thin film, which is suitable of using the above-mentioned plasma apparatus, and the method of fabricating a nano-crystalline silicon thin film includes the following steps. First, a substrate is provided to dispose on a carrier surface of the substrate holder. Next, a pressure of the gas within the chamber is adjusted to an operation pressure. Then, a voltage is input so as to form a voltage difference between the anode and the cathode. Thereafter, the distance between the anode and the cathode is shorten, so as to form a stable arc plasma between the anode and the cathode. Next, the crystallized silicon target of the anode and the crystallized silicon target of the cathode form a plurality of silicon crystalline grains and silicon atoms by the stable arc plasma. Afterward, a plurality of silicon crystalline grains and silicon atoms deposit to the substrate to form a nano-crystalline silicon thin film.
According to an embodiment of the present invention, the above-mentioned silicon crystalline grains and silicon atoms formed by the stable arc plasma are in a status of high temperature. Meanwhile, the above-mentioned substrate holder may further include a cooling system, wherein the cooling system is buried inside the carrier surface. Before performing the step of forming the silicon crystalline grains and silicon atoms through the stable arc plasma, a coolant passes through the cooling system to force the heated substrate during process to cool, so that the high-temperature silicon crystalline grains and silicon atoms are quenched and deposited to the substrate.
According to an embodiment of the present invention, the above-mentioned nano-crystalline silicon thin film may include a continuous phase of amorphous silicon layer, and a plurality of single crystal of silicon grains dispersed within the amorphous silicon layer.
According to an embodiment of the present invention, a size of each of the above-mentioned single crystal of silicon grains is substantially from 100 nanometers to 5 micrometers.
According to an embodiment of the present invention, the above-mentioned substrate may be a flexible substrate, wherein the substrate is continuously fed, such that a nano-crystalline silicon thin film is continuously deposited on the substrate fed continuously.
Based on the above, by utilizing an arc electrode set having crystallized silicon targets, the plasma apparatus of the present invention is capable of producing high quality nano-crystalline silicon thin films by a simple process. In one embodiment, a cooling system is further installed on the substrate holder, so as to force the heated substrate during process to cool. As such, nano-crystalline silicon thin films can be formed on the substrates which are vulnerable to heat.
To make the aforementioned and other features and advantages of the invention more comprehensible, several embodiments accompanied with figures are described in detail below.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A plasma apparatus of an embodiment of the present invention mainly provides a novel and simple fabricating method to directly form a nano-crystalline silicon thin film having excellent photoconductivity characteristics by installing crystallized silicon targets respectively on the opposite sides of an arc electrode set. When an appropriate voltage is applied between a cathode and an anode of the arc electrode set, silicon crystalline grains of the crystallized silicon targets obtain a sufficient energy through an arc, so that the silicon crystalline grains and silicon atoms are vapored to gas phase. Meanwhile, the silicon crystalline grains and silicon atoms in gas phrase and formed in the solid state are well mixed, and thus forming a nano-crystalline silicon thin film having excellent photoconductivity characteristics with highly dispersing silicon crystalline grains therein.
More specifically, as shown in
It should be mentioned that designers may choose an appropriate material as the dopants according to a product requirements of semiconductor thin films to be formed. For example, a product requirements for forming a structure of the semiconductor thin films may be P-type semiconductor, N-type semiconductor or a structure having a P-N diode. For instance, a material of the dopant can be also selected from the -group elements, and thus the crystallized silicon targets 260 constitute N-type semiconductor targets. Alternatively, a material of the dopants can be also selected from the V-group elements, and thus the crystallized silicon targets 260 constitute N-type semiconductor targets. Certainly, a material of the dopants can be also selected from the III-group elements and the V-group elements simultaneously, and thus the crystallized silicon targets constitute intrinsic semiconductor targets.
Furthermore, designers may adjust the crystalline size of the silicon crystalline grains within the nano-crystalline silicon thin film and the dispersing degree of the silicon crystalline grains spread in the nano-crystalline silicon thin film according to a desired photoconductivity characteristic of the product, such as the wavelength range of an absorb light. Specifically, the design size of the silicon crystalline grains 264 can be further controlled by adjusting the arc discharge energy, the background pressure of the chamber 210, and a distance from the substrate to the center of the arc, etc.
Referring to
As shown in
Consequently, after the silicon atoms 262 in the gas state depositing on the substrate 302, a continuous thin film of amorphous silicon is thus formed. Meanwhile, the silicon crystalline grains 264 in the gas state deposit on the substrate 302 and thus disperse within the amorphous silicon layer of continuous phase, so as to form a nano-crystalline silicon thin film comprising a continuous phase of amorphous silicon layer, and a dispersing phrase of a plurality of micro crystalline structure of silicon grains dispersed therein. In the present embodiment, the size of the single crystal of silicon grains 264 ranges substantially from 100 nanometers to 5 micrometers. A detailed description of the structure of the nano-crystalline silicon thin film is described as follow.
Referring to
Besides, in practice, the substrate may be a glass substrate or a plastic substrate like flexible substrate.
In order to illustrate the method of fabricating a nano-crystalline silicon thin film by utilizing the aforesaid plasma apparatus in the present invention, the plasma apparatus 300 as shown in
Afterward, in the step S30, a voltage is applied so as to form a voltage difference V between the anode 240 and the cathode 250. Thereafter, in the step S40, the distance between the anode 240 and the cathode 250 is shorten, so as to form a stable arc plasma between the anode 240 and the cathode 250. It should be noted that the silicon crystalline grains 264 and silicon atoms 262 formed by the stable arc plasma in this step are in a status of high temperature. Next, in the step S50, the crystallized silicon target 260 of the anode 240 and the crystallized silicon target 260 of the cathode 250 form a plurality of silicon crystalline grains 264 and silicon atoms 262 by the stable arc plasma.
Specially, a step S42 may further be performed before performing the step of forming the silicon crystalline grains 264 and silicon atoms 262. Referring to step S42, the substrate holder 230 may further include a cooling system 310 buried inside the carrier surface 232. A coolant 314 passes through the cooling system 310 to force the heated substrate 302 during process to cool, so that the high-temperature silicon crystalline grains 264 and silicon atoms 262 are quenched and deposited to the substrate 302.
Afterward, in the step S60, the plurality of silicon crystalline grains 264 and silicon atoms 262 deposit to the substrate 302 and thus form a nano-crystalline silicon thin film. In the present embodiment, the nano-crystalline silicon thin film includes a continuous phase of amorphous silicon layer, and a plurality of single crystalline grains 264 dispersed within the amorphous silicon layer, wherein the size of each of the single crystalline grains 264 is substantially from 100 nanometers to 5 micrometers Furthermore, as mentioned above, the substrate 302 may be flexible substrate and is continuously fed, such that a nano-crystalline silicon thin film is continuously deposited on the continuous-fed substrate 302.
In order to illustrate the present invention, an represent embodiment according to the aforesaid plasma apparatus is taken as an example to illustrate the present invention, but the embodiments in the follows are not limit the present invention.
In the following embodiment, the plasma apparatus 300 as shown in
First, a flexible substrate 302 is input to the chamber 210. Next, the pressure of the chamber 210 is extracted to an operation pressure 8×10−6˜5×10−5 torr which is deemed a substantial vacuum state by using a vacuum pump. Next, a coolant 314, such as liquid nitrogen, passes through the cooling pipe 312 of the substrate holder 230, so as to keep the substrate 302 in a low temperature environment. In this present embodiment, the temperature of the substrate 302 is controlled to 77K, for example. Then, a DC voltage power 430 is externally connected to the anode 240 and the cathode 250 of the arc electrode set 220, and an electric current substantial ranging from 20 amperes to 30 amperes is applied to the anode 240 and the cathode 250.
Then, the anode 240 and the cathode 250 are gradually approached to each other by utilizing a linear stepping motor and the a distance therebetween is shortened until an arc discharge is produced in the arc discharge space S between the anode 240 and the cathode 250. Accordingly, the silicon atoms 262 and the silicon crystalline grains 264 of the crystallized silicon targets 260 are vapored through obtaining the heat producing by the arc discharge, so as to generate a silicon source plasma and thus deposit to the substrate 302.
The crystalline ratio of the nano-crystalline silicon thin film fabricated by the above parameters is about 40% to 70%. The structure of the nano-crystalline silicon thin film can be adjusted according to the product requirements, such as P-type semiconductor, N-type semiconductor or a P-N diode structure. Therefore, considering the utility in industry, the nano-crystalline silicon thin film fabricated by the plasma apparatus 300 of one embodiment of the present invention has certain potential to apply to thin film transistors fields and solar cells fields. Compare with an amorphous silicon thin film, the nano-crystalline silicon thin film has better stability and higher electron mobility after chronically irradiated by a light, and thus has an excellent photoconductivity characteristic. Specially, in one embodiment, a nano-crystalline silicon thin film having micro crystalline structures can be directly formed on the low-temperature flexible substrate, such as plastic substrate 302, by the plasma apparatus 300. Accordingly, the application of the nano-crystalline silicon thin film is highly developed and spread to flexible displays and flexible solar cells.
In addition, compare with the prior art, when using the plasma apparatus 300 of one embodiment in the present invention, a nano-crystalline silicon thin film having micro crystalline structures can be directly formed on the substrate 302 by directly using arc discharge to vapor the silicon atoms 262 and the silicon crystalline grains 264 of the crystallized silicon targets 260, rather than taking an additional process to produce crystallization of the silicon atoms 262 deposited to the substrate 302. Besides, since the source of the silicon atoms 262 and the silicon crystalline grains 264 within the thin film are generated from the crystallized silicon targets 260, compare to the prior art that is need to inject an additional medium gas to function as the silicon atoms source within the thin film, the plasma apparatus 300 of one embodiment in the present invention is no need to inject an additional gas containing silicon element, and thus the cost is further saved. On the other hand, the required DC current of the plasma apparatus 300 of one embodiment in the present invention is reduced to lower than 50 amperes. Furthermore, no medium gas is needed to be injected to function as a source to produce plasma. Therefore, compare to the prior art, the plasma apparatus 300 of one embodiment in the present invention has simple and saving cost effect.
In formula (1), Ic represents an integration of the peak of crystal phase, and Ia represents an integration of the peak of disordered silicon phase. As shown in
In addition,
According to the above descriptions, the plasma apparatus and the method of fabricating a nano-crystalline thin film of the present invention have one or a part of or all of the following advantages:
1. A nano-crystalline silicon thin film with excellent quality can be fabricated by a simple process through utilizing an arc electrode set having crystallized silicon target.
2. In one embodiment, the cooling system is installed to the substrate holder to force the heated substrate during process to cool, so that nano-crystalline silicon thin films can be formed on the substrates which are vulnerable to heat.
3. Since the source of the silicon atoms and the silicon crystalline grains within the thin film are generated from the crystallized silicon targets, and thus the plasma apparatus in some embodiment of the present invention is no need to inject an additional gas containing silicon element, and thus the cost is further saved.
4. The required DC current of the plasma apparatus of the present invention is reduced to lower than 50 amperes, and thus the power can be further saved.
5. In some embodiment, the plasma apparatus is no need to inject a medium gas to function as a source to produce plasma, and thus the equipment and the process can be simplify and further saving cost.
Although the invention has been described with reference to the above embodiments, it is apparent to one of the ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed descriptions.
Number | Date | Country | Kind |
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98129732 | Sep 2009 | TW | national |