KR102029180B1 - Method for manufacturing of tin sulfide (II)(SnS) thin film - Google Patents

Abstract

The present invention relates to a high quality tin sulfide (SnS) thin film free of impurities on a substrate, a method of synthesizing the thin film, and a method of synthesizing a tin sulfide (SnS) thin film having two-dimensional crystals through process temperature control.

Description

Method for manufacturing of tin sulfide (II) (SnS) thin film}

The present invention relates to a thin film synthesized by chemical vapor deposition using a tin precursor having a controlled oxidation value and a method of synthesizing the thin film.

The two-dimensional material has a property that cannot be obtained from the existing bulk material, and since the physical properties can be controlled in a desired direction according to the number of layers, the two-dimensional material is greatly attracting attention in various fields requiring new material properties.

In particular, two-dimensional materials with band gaps have been studied as alternative materials that can overcome the limitations of miniaturization of existing silicon-based transistors. However, since most two-dimensional materials (tungsten sulfide, molybdenum sulfide) have a very high melting point, a very high process temperature of 600 ° C. or more is essential for thin film synthesis. Exfoliation method at room temperature has also been studied, but has a disadvantage in that reproducibility is very poor. Therefore, it is required to develop a two-dimensional thin film and a method for manufacturing the thin film which can be stably synthesized even at a low temperature process temperature lower than 300 ° C.

Tin sulfide (SnS _x ) is a layered material having characteristics such as p-type semiconductor for SnS and n-type semiconductor for SnS ₂ depending on the oxidation value of tin. It is particularly noteworthy that the melting point (SnS: 882 ℃ & SnS ₂ : 600 ℃) is significantly lower than other layer structure materials, there is an advantage that can form a high quality thin film through a low temperature process. Tin sulfide (SnS _x ) can be applied not only as a two-dimensional transistor channel material but also as an absorption material for solar cells and photo detectors, and has potential as a low-power gas sensor material.

However, sulfide tin (IV), as is well known (SnS ₂₎ the sulfide tin (II) as not normal compared to the (SnS) implementation of the n-type semiconductive characteristics sulfide tin has a relatively easy one, p-type semiconductive characteristics ( The formation of II) is hardly known, and the thin film synthesis method reported so far has a disadvantage that the process temperature is higher than 300 ° C. or the process window is very narrow. In addition, there was a difficulty in effectively suppressing the impurity concentration in the thin film and the composition of SnS ₂ and Sn ₂ S ₃ .

Since Sn atoms are thermodynamically stable in the presence of +4 in the thin film, a new method is required to synthesize only the tin (II) sulfide thin film by suppressing the formation of tin (IV) sulfide in the thin film. In conclusion, there is a need for a technique for forming a stoichiometric SnS thin film with controlled impurities in a wide process window in a low temperature region.

Korea Patent Registration 10-1512749

The present invention has been made to solve various problems including the above problems, and an object of the present invention is to provide a high quality two-dimensional tin sulfide (II) (SnS) thin film. Another object of the present invention is to provide a method for synthesizing a tin (II) sulfide (SnS) thin film having a reproducible two-dimensional structure in a wide process window in a low temperature region of 300 ° C or lower. However, these problems are exemplary, and the scope of the present invention is not limited thereby.

According to an aspect of the present invention, a method of forming a tin (II) sulfide (SnS) thin film by chemical vapor deposition using a tin precursor and a sulfur precursor is provided on a substrate.

In this case, the tin precursor is a metal organic compound having an oxidation value of +2 valent tin, and the temperature of the substrate for forming the tin sulfide (II) (SnS) thin film is in the range of 90 ° C to 300 ° C, preferably 90 ° C to It is characterized by having a 240 ℃ range.

In the method of forming the tin sulfide (II) (SnS) thin film, the metal precursor includes Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II).

In the method of forming the tin sulfide (II) (SnS) thin film, the chemical vapor deposition method may include an atomic layer deposition method.

In the method of forming the tin sulfide (II) (SnS) thin film, the tin sulfide (II) (SnS) thin film, a cubic SnS (π-SnS) and tetragonal SnS (o-SnS) is mixed with each other It may have a phase or may have a phase in which tetragonal SnS (o-SnS) is present alone.

In addition, when the tetragonal SnS (o-SnS) has a phase present alone, the tetragonal SnS (o-SnS) may have a structure in which the crystal plane 040 is arranged parallel to the substrate. .

According to another aspect of the present invention, as a method of manufacturing a semiconductor transistor device having a tin (II) sulfide (SnS) thin film channel, the tin (II) sulfide (SnS) thin film channel according to any one of the methods described above. A semiconductor transistor device manufacturing method is provided.

According to another aspect of the present invention, a method of manufacturing a gas sensor having a tin (II) sulfide (SnS) thin film as a sensing material, wherein the tin (II) sulfide (SnS) thin film is any one of the methods described above. To be formed, there is provided a gas sensor manufacturing method.

The present invention can provide a tin sulfide (II) (SnS) thin film free of impurities in a wide range of low process temperatures, and a method of forming the thin film. In addition, it is possible to provide a method of controlling the crystal phase or thickness (number of layers) of tin sulfide desired by the user through controlling the process temperature and the number of cycles. By using the tin sulfide (II) (SnS) thin film, a low-power gas sensor can be manufactured, and p-type transistor technology having high mobility can be expected.

1 is a series of processes for synthesizing a tin (II) sulfide (SnS) thin film of the present invention.
FIG. 2A is Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II), an oxidation-controlling precursor used to synthesize tin (II) sulfide (SnS) thin films in the present invention. Figures 2b, 2c and 2d is a oxidized tetravalent tin of a commercial precursor, which is different from the divalent precursor used in the present invention.
FIG. 3A shows that the thickness of a tin sulfide (II) (SnS) thin film according to the number of cycles can be accurately controlled using atomic layer deposition in chemical vapor deposition. 3b shows that a very even thin film was deposited on a large area as a result of synthesizing tin sulfide (II) (SnS) on a 4 inch silicon dioxide substrate using the method of the present invention.
Figure 4a shows the results of measuring the crystallinity of the tin (II) sulfide (SnS) thin film according to the process temperature by GIXRD. Figure 4b is the result of measuring the crystallinity of the thin film through theta-2theta mode XRD to observe the preferred orientation of the crystal.
5A is a TEM image of a tin (II) sulfide (SnS) thin film synthesized at 90 ° C, and FIG. 5B is a TEM image of a tin (II) sulfide (SnS) thin film synthesized at 240 ° C.
FIG. 6A is a result of measuring WDXRF that tin sulfide (II) having a composition of Sn: S 1: 1 (SnS) was formed at 90-240 ° C., and FIG. 6B shows tin (II) sulfide (SnS). It shows Raman coupling vibration according to the temperature of the thin film.
7A, 7B, 7C and 7D show the XPS spectra of Sn 3d, S 2p, O 1s and C 1s, respectively.
8 is an AES analysis result of a tin (II) sulfide (SnS) thin film synthesized at 120 ° C.
9 is an output curve of a thin film transistor fabricated from the synthesized tin sulfide (II) (SnS) thin film.
10A and 10B show NO ₂ and NH ₃ gas sensing of tin (II) sulfide (SnS) thin film gas sensors, respectively.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms, and the following embodiments are intended to complete the disclosure of the present invention, to those skilled in the art It is provided to inform you completely. In addition, the components may be exaggerated or reduced in size in the drawings for convenience of description.

Throughout the specification, when referring to one component, such as a layer or region, being located "on" another component, said one component directly "contacts" the other component, or between It may be interpreted that there may be other intervening components. On the other hand, when referring to one component located directly on another component, it is interpreted that there are no other components intervening therebetween.

Based on the accompanying drawings, the physical properties of the tin (II) sulfide thin film provided in the present invention and a method of synthesizing the tin (II) sulfide (SnS) thin film will be described.

According to the present invention, a tin sulfide (II) (SnS) thin film is formed on a predetermined substrate by chemical vapor deposition (CVD) using a tin precursor and a sulfur precursor as a deposition source. The chemical vapor deposition method is a tin (II) sulfide (SnS) on the substrate through a chemical reaction in the gas phase state by introducing a tin precursor containing tin and a sulfur precursor containing sulfur to a substrate maintaining a predetermined temperature The method of forming a thin film is generically described. The chemical vapor deposition method is a method of injecting precursor gases into a chamber having a predetermined space, as well as LPCVD (plasma enhanced CVD), plasma enhanced CVD (PECVD), atmosphere pressure CVD (APCVD) as well as spaced apart from each other precursor gas in time And atomic layer deposition (ALD) which alternately input into a substrate to form a thin film at the atomic layer level.

In the present invention, it is a technical feature to use a tin precursor as a metal organic compound whose oxidation value of +2 is controlled, rather than a conventional commercial tin precursor, as a deposition source for providing tin. As an example, Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II) may be used as the tin precursor having an oxidation value of +2.

2A discloses a molecular structure of Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II). On the contrary, FIGS. 2B to 2D are tin precursors having a tetravalent tin oxide, which are conventionally used, such as SnCl ₄ , SnI ₄ , [(CH ₃ ) ₂ N] ₄ Sn (Tetrakis (dimethylamino) tin (IV), TDMASn) The molecular structure of is shown respectively (H in combination with C is omitted in the molecular structure of Figures 2a and 2d).

The inventors of the present invention use Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II), which has an oxidation value of tin controlled to +2, as a precursor, thereby making it possible to use a precursor having an oxidation value of +4. It has been found that metastable tin sulfide (II) (SnS) thin films can be formed with high quality as compared to when used. Particularly, in the case of using a tin precursor whose tin oxide is controlled to +2 valence, tin (II) sulfide (II) having excellent characteristics even at a low temperature of 300 ° C. or lower, for example, 90 to 240 ° C. SnS) thin film was possible to manufacture.

Meanwhile, hydrogen sulfide (H ₂ S) may be used as the sulfur precursor, but is not limited thereto.

FIG. 1 illustrates a synthesis process of a tin sulfide (II) (SnS) thin film using an atomic layer deposition method as an embodiment of the present invention. The precursor of tin was s (1-dimethylamino-2-methyl-2-propoxy) tin (II) and hydrogen sulfide was used as the precursor of sulfur. The temperature of the substrate was selected in the range of 90 to 24 ° C. while the deposition was performed. A silicon oxide (SiO ₂ ) wafer was used as the substrate.

Referring to FIG. 1, a deposition method according to an embodiment of the present invention includes supplying a tin precursor on a substrate provided (S1), purging the tin precursor (S2), and hydrogen sulfide on the substrate. Supplying (S3) and purging the hydrogen sulfide. Steps S1 to S4 form one cycle and may be repeatedly performed one or more times.

When tin oxides having an oxidation value of +4 is shown in FIGS. 2b, 2 and 2d, they are basically synthesized in the form of tin (IV) sulfide (SnS ₂ ) and form tin (II) sulfide (SnS). Process conditions are very demanding, such as high temperatures, and are formed in the form of a mixture with tin (IV) sulfide. In particular, when the process temperature is 300 ° C. or less during deposition as in the embodiment of the present invention, almost no tin sulfide (II) (SnS) is produced.

However, in comparison with the embodiment of the present invention, it was possible to prepare a stoichiometric tin sulfide (II) (SnS) thin film having excellent physical properties. Hereinafter, the microstructure and properties of the tin sulfide (II) (SnS) thin film prepared according to the embodiment of the present invention will be described.

In FIG. 3A, it can be seen that the thickness of the thin film increases linearly with the number of cycles of the atomic layer deposition method. This indicates that the thickness of the tin sulfide (II) (SnS) thin film is effectively controlled by atomic layer deposition.

FIG. 3B shows the result of synthesizing a tin (II) sulfide (SnS) thin film by atomic layer deposition on a 4 inch silicon oxide wafer, one of the substrates used in the present invention, for 125 cycles. As a result of calculating the uniformity by the thickness of the five thin films, it can be seen that a very uniform thin film was deposited at a large area of 98%.

4A and 4B show the crystallinity of tin (II) sulfide (SnS) thin films synthesized at process temperatures of 90 ° C, 120 ° C, 150 ° C, 180 ° C, 210 ° C, and 240 ° C by X-ray diffraction (XRD). Shows one result. The peaks of tin disulfide (SnS ₂ ) were not detected at all process temperatures, indicating that stoichiometric tin sulfide (SnS) thin films were synthesized over the entire process temperature range.

It can be seen from the GIXRD results of FIG. 4A that the tin sulfide (II) (SnS) thin film was well crystallized and synthesized even at a low process temperature of 90 ° C. Show that they exist together. In the case of the tin sulfide (II) (SnS) thin film synthesized at a relatively low range of 90 to 180 ° C among the process temperature conditions provided by the present invention, the thin film is synthesized in such a manner that the o-SnS phase and the π-SnS phase coexist.

It can be seen that as the process temperature increases, the composition of the π-SnS phase in the synthesized tin sulfide (II) (SnS) thin film decreases, and in contrast, the composition of the o-SnS phase increases. Furthermore, from the process temperature of 210 ° C., the 2D van der Waals plane of the tin (II) sulfide (SnS) thin film is arranged in parallel with the substrate. Theta-2theta mode XRD of FIG. This can be confirmed from. When synthesizing a tin (II) sulfide (SnS) thin film at a process temperature of 240 ° C., it is precisely arranged parallel to the substrate such that it cannot be detected by GIXRD of FIG. 4A and can only be observed by θ-2θ mode XRD of FIG. 4B. Two-dimensional van der Waals planes were detected, and transmission electron microscopy (TEM) analysis was performed to more accurately identify them.

5A and 5B show TEM analysis of cross-sections of tin (II) sulfide (SnS) thin films synthesized at 90 ° C., and tin (II) (SnS) thin films synthesized at 240 ° C. One result is shown.

As already confirmed in FIGS. 4A and 4B, at 90 ° C., where the process temperature is low, very small grains are randomly distributed with various orientations. In contrast, the TEM cross-section of tin (II) sulfide (SnS) synthesized at 240 ° C. of FIG. 5B shows that the two-dimensional van der Waals plane is well aligned in parallel with the substrate and exhibits very good crystallinity. The two-dimensional van der Waals interplanetary distance of 0.28 nm shows the Orthorhombic (040) plane, which corresponds to the XRD results of FIG. 4B.

Therefore, the present invention not only provides a tin (II) sulfide (SnS) thin film and a method for synthesizing the thin film under a wide process temperature condition, but also suppresses π-SnS in the thin film through precise control of temperature conditions to thereby suppress two-dimensional o-SnS. A method for synthesizing two-dimensional tin sulfide (II) (SnS) in which only a phase is present can be provided. Through the process temperature conditions and the cycle time, it is possible to provide a method of controlling the crystallinity, orientation, thickness (or two-dimensional surface layer number) of the thin film desired by the user.

In order to confirm the quality of the tin sulfide (II) (SnS) thin film provided in the present invention and a method of synthesizing the thin film, thin film analysis such as WDXRF, RAMAN, XPS, and AES was further performed.

FIG. 6A is a result of analyzing the composition of tin (Sn) and sulfur (S) of a tin (II) sulfide (SnS) thin film synthesized by varying process temperature conditions through WDXRF. It was confirmed that a tin sulfide (II) (SnS) thin film having an accurate stoichiometry was synthesized with an S composition of about 50% in all growth temperature conditions.

RAMA analysis was performed to confirm whether the fine SnS ₂ phase was detected, which was not detected by the XRD results of FIGS. 4A and 4B. As shown in FIG. 6B, no SnS ₂ phase was detected through RAMAN analysis.

In addition to XRD and RAMAN analysis, no SnS ₂ phase was detected, indicating that only pure tin sulfide (II) (SnS) was distributed in the thin film. Corresponding to the results of TEM, the peak intensity was detected the most because of the best crystallinity at 240 ° C, which is the high process temperature, and exactly matches the Raman shift position of the tetragonal tin sulfide (SnS).

FIG. 7 shows XPS analysis results of tin sulfide (II) (SnS) synthesized under all process temperature conditions, and shows the impurity concentration in the thin film and the atoms in the thin film. In FIG. 7A, it was confirmed that a core level binding energy of Sn 3d was detected at 485.7 eV. As a result, Sn in the thin film may be distributed with an oxidation value of +2. In FIG. 7B, the core level binding energy of S 2p was detected only at 161.2 eV, which is a peak resulting from the binding of Sn and S of tin sulfide (SnS). 7C and 7D show core level binding energies of oxygen (O) 1s and carbon (C) 1s, respectively. It can be seen from FIG. 7C that the binding energy peak of Sn and O was not detected and the detected O 1s peak was caused from the silicon oxide substrate. In addition, it can be seen from FIG. 7B that no carbon impurities are present in the thin film.

FIG. 8 shows AES results of analyzing atoms existing in a thin film with a depth profile. The Sn and S compositions of the thin film are 1: 1 and the impurities of carbon and nitrogen oxygen are present at concentrations below the detection limit. It appears that the carbon composition is large near the surface because carbon contamination is inevitably present on the surface of the thin film exposed to air, and there is no carbon at the interface between the thin film and the thin film and the substrate.

9 is a result of fabricating a thin film transistor through an additional semiconductor process using a tin sulfide (SnS) thin film manufactured according to the embodiment of the present invention as a channel material and measuring the characteristics thereof. It can be seen that the drain current value is accurately controlled according to the gate voltage.

10A and 10B illustrate the results of fabricating and measuring a gas sensor device using a tin sulfide (II) (SnS) thin film as a sensing material. In the graphs of FIGS. 10A and 10B, the reaction gas was flowed during the section indicated by <G>, and the other section was air flowed. In addition, all measurements were performed at room temperature without additional heating. In the case of Figure 10a, NO ₂ is adsorbed on the thin film to act as an electron acceptor (Electron acceptor) serves to lower the electron concentration inside the tin (II) sulfide (SnS) thin film of the p-type semiconductor. Where (R _a -R _g ) / R _g The response value was 121%, which was relatively high at room temperature. In the case of FIG. 10B, as NH ₃ is adsorbed, it acts as an electron donor to increase the electron concentration in the thin film or decrease the concentration of the hole to increase resistance. At this time, the response value obtained by the formula (R _{g -} R _a ) / R _a is 38.6%, which is also relatively high at room temperature.

As a result, the present invention can provide not only a tin (II) sulfide (SnS) thin film, but also a method of synthesizing and crystallizing the thin film, as well as a method of applying the thin film to a transistor and a gas sensor.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (7)

A method of forming a tin (II) sulfide (SnS) thin film by chemical vapor deposition using a tin precursor and a sulfur precursor on a substrate,
The tin precursor is a metal organic compound having an oxidation value of +2 valence of tin,
The tin sulfide (II) (SnS) thin film is formed stoichiometric,
The temperature of the substrate for forming the tin sulfide (II) (SnS) thin film has a range of 210 ℃ to 240 ℃,
The tin sulfide (II) (SnS) thin film has a phase in which tetragonal SnS (o-SnS) exists alone, and the tetragonal SnS (o-SnS) has a crystal plane 040 arranged in parallel with the substrate. With the structure to become,
Tin sulfide (II) (SnS) thin film formation method. The method of claim 1, wherein the tin precursor,
Containing Bis (1-dimethylamino-2-methyl-2-propoxy) tin (II),
Tin sulfide (II) (SnS) thin film formation method. The method of claim 1,
The chemical vapor deposition method includes an atomic layer deposition method,
Tin sulfide (II) (SnS) thin film formation method. delete delete delete A method of manufacturing a gas sensor having a tin (II) sulfide (SnS) thin film as a sensing material,
The tin sulfide (II) (SnS) thin film is formed by any one of claims 1 to 3,
Gas sensor manufacturing method.

Images