Patent Application
20100227443
This application claims the benefit of Korean Patent Application No. 10-2009-0018928, filed Mar. 5, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to a method of forming a polycrystalline silicon layer, and more particularly, to a method of forming a polycrystalline silicon layer from an amorphous silicon layer formed using hydrogen gas as a carrier gas, and thus charge mobility of the polycrystalline silicon layer can be improved.
2. Description of the Related Art
Generally, polycrystalline silicon layers are widely used as semiconductor layers for thin film transistors since the polycrystalline silicon layers have high field effect mobility and allow for high-speed operating circuits and formation of complementary metal-oxide-semiconductor (CMOS) circuits. Thin film transistors having the polycrystalline silicon layers are mainly used for active devices of active-matrix liquid crystal display (AMLCD) devices, and switching and driving devices of active-matrix organic light emitting diode (AMOLED) display devices.
Examples of methods of crystallizing amorphous silicon into polycrystalline silicon include solid phase crystallization (SPC), excimer laser crystallization (ELC), metal-induced crystallization (MIC), and metal-induced lateral crystallization (MILC) methods. In the SPC method, an amorphous silicon layer is annealed for several to several tens of hours at a temperature of about 700° C. or less, which is a thermal deformation temperature of glass forming a substrate of a display device using a thin film transistor. In the ELC method, an excimer laser is applied to an amorphous silicon layer to locally heat the amorphous silicon layer for a very short period of time at a high temperature. In the MIC method, a crystallization-inducing metal, such as nickel, palladium, gold, or aluminum, is in contact with or injected into an amorphous silicon layer to induce a phase change to a polycrystalline silicon layer. In the MILC method, silicide, produced by reacting a crystallization-inducing metal with silicon, laterally propagates through the amorphous silicon to sequentially induce crystallization of the amorphous silicon layer.
However, the SPC method requires a long processing time, and may cause deformation of a substrate due to long annealing at a high temperature, and the ELC method requires high-priced laser equipment and has poor interface characteristics between a semiconductor layer and a gate insulating layer due to protrusions occurring on a resultant polycrystalline silicon surface.
Research into methods of crystallizing an amorphous silicon layer using a crystallization-inducing metal has been widely conducted because of faster crystallization at a lower temperature than the SPC method. Examples of these crystallization methods using a crystallization-inducing metal include MIC, MILC, and super grain silicon (SGS) crystallization methods.
In the crystallization methods using a crystallization-inducing metal, an amorphous silicon layer is formed using a source gas including a silicon atom and a carrier gas, such as argon gas. However, when argon gas is used as a carrier gas, charge mobility of a polycrystalline silicon layer is not significantly improved.
Aspects of the present invention provide a method of forming a polycrystalline silicon layer by a crystallization method using a crystallization-inducing metal, in which hydrogen gas is used as a carrier gas to form an amorphous silicon layer, and thus charge mobility of a crystallized polycrystalline silicon layer can be improved.
According to an embodiment of the present invention, a method of forming a polycrystalline silicon layer includes forming an amorphous silicon layer on a substrate using a gas including a silicon atom and hydrogen gas, and crystallizing the amorphous silicon layer into a polycrystalline silicon layer using a crystallization-inducing metal.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “formed on” or “disposed on” another element, it can be disposed directly on the other element, or intervening elements may also be present. In contrast, when an element is referred to as being “formed directly on” or “disposed directly on” another element, there are no intervening elements present.
Subsequently, an amorphous silicon layer 120 is formed on the buffer layer 110. The amorphous silicon layer 120 is formed by chemical vapor deposition (CVD). Examples of CVD may include atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), low temperature CVD (LTCVD), high temperature CVD (HTCVD), and plasma enhanced CVD (PECVD). For example, PECVD may be used.
The amorphous silicon layer 120 is formed by CVD using a gas including a silicon atom as a source gas and hydrogen gas as a carrier gas. The gas having a silicon atom may be monosilane (SiH4) gas, disilane (Si2H6) gas, tetrachlorosilane (SiCl4) gas, dichlorosilane (SiH2Cl2) gas, tetrafluorosilane (SiF4) gas, or difluorosilane (SiH2F2) gas, or combinations thereof.
A flow rate of the hydrogen gas may be 3 to 7 times larger than a flow rate of the gas having a silicon atom. When the flow rate of the hydrogen gas is less than 3 times or more than 7 times larger than the flow rate of the gas having a silicon atom, crystallization may not be properly performed. For example, when the flow rate of the hydrogen gas is less than 3 times larger than the flow rate of the gas having a silicon atom, a coarse amorphous silicon layer may be formed due to a high deposition rate, and nano-sized microcrystalline silicon may be mixed with amorphous silicon. In addition, when the flow rate of the hydrogen gas is more than 7 times larger than the flow rate of the gas having a silicon atom, a micro-sized microcrystalline silicon layer is mainly formed rather than an appropriate amorphous silicon layer.
The nano- and micro-sized microcrystalline silicons are in a metastable state, which have a lower degree of amorphism than the amorphous silicon. The microcrystalline silicon requires a higher energy than the amorphous silicon due to recrystallization of solid-phase silicon, which may adversely affect crystallization via an SGS method, which will be described later. Here, the amorphous silicon layer 120 may be formed to a thickness of 300 to 1000 Å.
The amorphous silicon layer 120 is crystallized into a polycrystalline silicon layer using a crystallization-inducing metal. Examples of crystallization methods using a crystallization-inducing metal include MIC, MILC, and SGS methods.
In the MIC method, a crystallization-inducing metal such as Ni, Pd, or Al is placed in contact with or injected into an amorphous silicon layer to induce a phase change to a polycrystalline silicon layer; and in the MILC method, silicide, produced by reacting a crystallization-inducing metal with silicon, laterally propagates through the amorphous silicon to sequentially induce crystallization of the amorphous silicon layer.
In the SGS method, the size of a grain can be controlled to be several to several hundreds of μm by decreasing the concentration of a crystallization-inducing metal that diffuses to an amorphous silicon layer. In an exemplary embodiment for reducing the concentration of the crystallization-inducing metal that diffuses to the amorphous silicon layer, a capping layer may be formed on the amorphous silicon layer, a crystallization-inducing metal layer may be formed on the capping layer, and the substrate may be annealed to diffuse the crystallization-inducing metal through the capping layer. Alternatively, the concentration of the diffused crystallization-inducing metal may be reduced by forming the crystallization-inducing metal layer at a low concentration without forming the capping layer.
According to the exemplary embodiment of the present invention, rather than the MIC or MILC method, the SGS method which can reduce the concentration of the crystallization-inducing metal diffused to the amorphous silicon layer by forming the capping layer is preferable, which will be described below. Referring to
Subsequently, a crystallization-inducing metal layer 140 is formed by depositing a crystallization-inducing metal on the capping layer 130. Here, the crystallization-inducing metal may be one selected from the group consisting of nickel (Ni), palladium (Pd), titanium (Ti), silver (Ag), gold (Au), aluminum (Al), tin (Sn), antimony (Sb), copper (Cu), cobalt (Co), molybdenum (Mo), terbium (Tb), rubidium (Ru), rhodium (Rh), cadmium (Cd), and platinum (Pt), and may be, for example, Ni. The crystallization-inducing metal layer 140 may be formed to have an areal density of 1011 to 1015 atoms/cm2 on the capping layer 130. When the crystallization-inducing metal layer has an areal density less than 1011 atoms/cm2, an amount of seeds, i.e., crystallization cores, may be too small to crystallize the amorphous silicon layer 120 into a polycrystalline silicon layer by the SGS method. When the crystallization-inducing metal layer has an areal density more than 1015 atoms/cm2, an amount of the crystallization-inducing metals that diffuses to the amorphous silicon layer 120 is large, and thus a grain of the polycrystalline silicon layer may become smaller. Moreover, as an amount of the crystallization-inducing metals remaining in a semiconductor layer is increased, characteristics of a later-formed semiconductor layer may deteriorate.
The crystallization-inducing metal layer 140 may be formed having a uniform thickness and a low concentration by sputtering, vapor phase deposition, ion beam deposition, electron beam deposition, laser ablation, or atomic layer deposition.
Referring to
Thus, the amount of the crystallization-inducing metals reaching the surface of the amorphous silicon layer 120 is dependent on a diffusion-preventing ability of the capping layer 130, which has a close relationship with the thickness or density of the capping layer 130. For example, as the thickness or density of the capping layer 130 increases, the amount of metal that diffuses therethrough is decreased, thereby increasing the size of a grain in the resultant polycrystalline layer. And, as the thickness or density of the capping layer 130 decreases, the amount of metal that diffuses therethrough is increased, thereby decreasing the size of a grain.
The annealing process is performed in the range of about 200 to about 900° C. for about several seconds to hours to diffuse the crystallization-inducing metals. In such temperature and time ranges, deformation of the substrate due to excessive annealing may be prevented, and reduction of production costs and improved yield may be obtained. The annealing process may be performed using one of a furnace process, a rapid thermal annealing (RTA) process, a UV process, and a laser process (i.e., the furnace process, the rapid thermal annealing (RTA) process, the UV process, or the laser process).
Referring to
In
Meanwhile, in the present exemplary embodiment, the crystallization-inducing metal layer 140 is formed on the amorphous silicon layer 120 (i.e., the amorphous silicon layer 120 is formed on the substrate 100 and the crystallization-inducing metal layer 140 is formed on the amorphous silicon layer), but the crystallization-inducing metal layer 140, the capping layer 130, and the amorphous silicon layer 120 may be sequentially formed on the substrate 100 (i.e., the crystallization-inducing metal layer 140 may be formed on the substrate 100, and the amorphous silicon layer 120 may be formed on the crystallization-inducing metal layer 140), and the amorphous silicon layer 120 may be formed into the polycrystalline silicon layer 150 using crystallization-inducing metals diffused from the underlying layers.
Referring to
Referring to
After that, source and drain regions 201 and 202 are formed by doping conductive impurity ions using the gate electrode 220 as a mask. The impurity ion may be a p-type or an n-type impurity. The p-type impurity may be one selected from the group consisting of boron (B), aluminum (Al), gallium (Ga), and indium (In), and the n-type impurity may be one selected from the group consisting of phosphorus (P), antimony (Sb), and arsenic (As). Here, a region, which is not doped with an impurity, between the source and drain regions 201 and 202 is the channel region 203. The doping process may be performed by forming a photoresist before forming the gate electrode 220 but is not limited thereto.
Referring to
Contact holes 240 exposing the source and drain regions 201 and 202 of the semiconductor layer 200 may be formed by etching the interlayer insulating layer 230 and the gate insulating layer 210. Subsequently, source and drain electrodes 251 and 252 connected to the source and drain regions 201 and 202 through the contact holes 240 are formed. The source and drain electrodes 251 and 252 may be formed of one selected from the group consisting of Mo, Cr, W, Al—Nd, Ti, MoW, and Al. Thus, a top-gate thin film transistor having the semiconductor layer 200, the gate electrode 220, and the source and drain electrodes 251 and 252 is completed.
Although, a top-gate thin film transistor is described, a bottom-gate thin film transistor may be formed according to aspects of the present invention.
Hereinafter, experimental examples will be provided to help understanding of the aspects of the present invention. However, these experimental examples are provided only to help with understanding and not to limit the aspects of the present invention.
A substrate having a buffer layer was disposed in a PECVD apparatus. A power of
100W was applied to the PECVD apparatus, SiH4 gas at a flow rate of 400 sccm as a source gas and hydrogen gas at a flow rate of 2000 sccm as a carrier gas were provided to the PECVD apparatus to form an amorphous silicon layer to a thickness of 500 Å. A silicon nitride layer was formed to a thickness of 100 Å as a capping layer on the amorphous silicon layer. Nickel was formed as a crystallization-inducing metal layer to have an areal density of 1×1013 atoms/cm2 on the capping layer. Subsequently, the substrate was annealed to crystallize the amorphous silicon layer into a polycrystalline silicon layer.
The Comparative Example was formed using the same process as the Experimental Example, except that argon gas was used as the carrier gas instead of the hydrogen gas.
Table 1 shows surface roughness of the amorphous silicon layers and charge mobility of the crystallized polycrystalline silicon layers according to Experimental and Comparative Examples.
Referring to Table 1, during formation of the amorphous silicon layer, it can be confirmed that when the amorphous silicon layer was formed using the hydrogen gas, rather than the argon gas, as a carrier gas, the surface roughness of the amorphous silicon layer was decreased by about 53%. In addition, when the amorphous silicon layer was crystallized into the polycrystalline silicon layer using a crystallization-inducing metal catalyst, the charge mobility of the polycrystalline silicon layer formed using the hydrogen gas as a carrier gas was increased by about 28.2 cm2/V·sec compared to that of the polycrystalline silicon layer formed using the argon gas as a carrier gas.
Consequently, in the method of forming a polycrystalline silicon layer using a crystallization-inducing metal, when the hydrogen gas is used as a carrier gas to form an amorphous silicon layer, the charge mobility of the crystallized polycrystalline silicon layer may be significantly increased. When hydrogen gas is used as a carrier gas to form an amorphous silicon layer during crystallization using a crystallization-inducing metal, charge mobility of a crystallized polycrystalline silicon layer can be improved.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2009-0018928 | Mar 2009 | KR | national |
