KR20060064967A - Method for forming aluminum silicate thin film - Google Patents

Abstract

The present invention relates to a method for forming an aluminum silicate (aluminum and silicon oxide) thin film using plasma atomic layer deposition (PEALD), wherein the deposition cycles of aluminum oxide and silicon oxide are as follows: 1: 1, 1: 2, 1: 3. By controlling with a small water ratio, the deposition rate can be improved by the intercatalysis and the silicon content can be adjusted according to the cycle bar. It exhibits excellent properties even at low temperatures below 150 ° C, less residual stress between the plastic substrate and the inorganic thin film than the case of using aluminum oxide, and also has a low coefficient of thermal expansion. In addition, since the etching rate is faster than that of the alumina oxide, it has a high etching selectivity with respect to polysilicon or a metal thin film.

Aluminum silicate, plasma atomic layer deposition, cycle, deposition rate, residual stress

Description

Method for forming aluminum silicate thin film

1 is a process chart for explaining a method for forming an aluminum silicate thin film according to the present invention.

Figure 2 is a graph showing the thickness change of the aluminum oxide film and aluminum silicate thin film according to the number of cycles.

3 is a graph showing the change in deposition rate and etching rate of the aluminum silicate thin film according to the cycle ratio.

4 is a graph showing the deposition rate change of the aluminum silicate thin film according to the cycle ratio.

Figure 5 is a glyph showing the change in the silicon content of the aluminum silicate thin film with a cycle ratio.

6A and 6B are cross-sectional views illustrating residual stresses of an aluminum oxide film and an aluminum silicate thin film deposited on a plastic substrate.

The present invention relates to a method for forming an aluminum silicate (aluminum and silicon oxide) thin film applied to a semiconductor device, a display device or a bio device, and more particularly, to an aluminum silicate using plasma enhanced atomic layer deposition (PEALD). It relates to a thin film formation method.

Recently, a technology for implementing a semiconductor device, a display device, or a bio device that can be bent or bent using a plastic substrate and attached to a garment has been developed.

If a plastic substrate is used, the process must be carried out at a temperature below 150 ° C. to deposit an inorganic insulating film on the substrate [see “Thin Solid Films”, 430, pp 15 (2003)]. Even when the thin film is grown at a low temperature of less than 150 ℃, residual stress occurs due to the difference in thermal expansion coefficient between the plastic substrate and the inorganic insulating film. Therefore, there is a need for a thin film formation method that can reduce the residual stress.

Generally, at low temperatures, the overall properties of the thin film are reduced, and the density of the thin film is reduced. In the case of using a plastic substrate, such deterioration occurs very rapidly because deposition must be performed at a low temperature of 150 ° C. or lower. In the case of the insulating film, as the deposition temperature decreases, the leakage current rapidly increases, the dielectric constant decreases, and the deposition rate also decreases.

US Patent No. 6,723,642 (JW Lim et al., 2004) formed an aluminum oxide film (Al ₂ O ₃ ) exhibiting excellent properties at low temperatures by atomic layer deposition (PEALD) using plasma. However, it has been reported that the formation of aluminum oxide films on plastic substrates has some residual stress [see Electrochemical and Solid State Letters, 7, pp C13, 2004].

Although atomic layer deposition has been reported to be very difficult to deposit a silicon oxide film, especially at temperatures below 200 ° C., there have been reports of forming silicon oxide films using organic or ammonia catalysts [SCIENCE, 278, pp. 1934, 1997]. It is known that formation of a silicon oxide film is almost impossible without a catalyst.

In the case of silicates (compounds of silicon and other oxides), precursors containing silicon and other metals are developed to allow deposition of thin films, but it is difficult to control the composition, and there is a problem in that the composition changes with temperature [S. W. Rhee et al., US Patent 2003/0203126, 2003]. In addition, a method of forming a silicate using a seed layer has also been proposed, but it is difficult to finely control the composition [J. Ramdani et al., US Pat. No. 2002/0197881, 2002].

An object of the present invention is to provide a method for forming an aluminum silicate thin film that can be deposited at a low temperature, low residual stress, easy to control the composition.

The present invention for achieving the above object includes a first step of mounting a substrate in the chamber, a second step of depositing aluminum oxide on the substrate, a third step of depositing silicon oxide on the aluminum oxide; In this case, the second step and the third step are characterized in that the alternating progress in the ratio of m: n.                         

The first step includes supplying an aluminum precursor into the chamber, first purifying the interior of the chamber, supplying an oxygen plasma to the chamber to deposit the aluminum oxide, and secondly depositing the interior of the chamber. Purifying, wherein the second step includes supplying a silicon precursor into the chamber, first purifying the interior of the chamber, and supplying an oxygen plasma into the chamber to deposit the silicon oxide. And purifying the inside of the chamber.

The present invention provides a method for forming an aluminum silicate thin film that can be usefully applied, particularly when using a plastic substrate requiring a low temperature process of less than 150 ℃.

In the case of the atomic layer deposition method, one cycle consists of several pulses, and each reaction gas is supplied in time division, so that silicon oxide (SiO ₂ ) may be alternately supplied with aluminum oxide. The present invention enables the silicon content to be controlled by controlling the number of deposition cycles of aluminum oxide and silicon oxide using plasma enhanced atomic layer deposition (PEALD). By controlling the content of silicon, the residual stress between the plastic substrate and the inorganic thin film can be reduced, and the coefficient of thermal expansion can be reduced. Also, the etching rate can be improved to improve the etching selectivity.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below. .

1 is a process chart for explaining a method for forming an aluminum silicate thin film according to a preferred embodiment of the present invention.

The sub-cycles for depositing aluminum oxide and silicon oxide consist of four pulses each. That is, it consists of precursor injection, purge using an inert gas, oxygen plasma supply, and purge process.

Assuming that aluminum oxide is deposited by m subcycles and silicon oxide is deposited by n subcycles, where m and n are integers, one cycle consists of m + n subcycles. If it is expressed as (m, n), it means that (1, 2) consists of one aluminum oxide deposition subcycle and two silicon oxide subcycles in one cycle.

First, a plastic substrate is mounted in a chamber of a plasma atomic layer deposition apparatus, and then aluminum (Al) precursor is supplied into the chamber. After purifying the inside of the chamber using an inert gas, oxygen (O ₂ ) plasma is supplied into the chamber to deposit aluminum oxide on the substrate, and then the inside of the chamber is purged.

Next, the silicon (Si) precursor is supplied into the chamber and the inside of the chamber is purified. Then, oxygen (O ₂ ) plasma is supplied into the chamber so that silicon oxide is deposited on the aluminum oxide, and then the inside of the chamber is purified.

As described above, the aluminum oxide deposition step (m) and the silicon oxide deposition step (n) are alternately performed at a ratio of m: n. At this time, m: n is preferably such that a small integer ratio, such as 1: 1, 1; 2, 1; 3.

Trimethyl Aluminum (TMA) may be used as the aluminum (Al) precursor, and TEOS, Tetramethyl Silicon (TMS), Tetraethyl Silicon (TES), Tetradimethylamino Silicon (TDMAS) or Tetraethylmethylamino Silicon (TEMAS) may be used as the silicon (Si) precursor. ). The purification process is performed using an inert gas such as argon (Ar), and the oxygen (O ₂ ) plasma is generated using a reaction gas containing oxygen, nitrogen, and argon.

2 is a graph showing the deposition thickness change of the aluminum silicate thin film (line 1) and the aluminum oxide film (line 2) according to the number of cycles, the slope of the aluminum silicate thin film (line 1) was large. Initially, the aluminum oxide film is deposited thicker at the same number of cycles, but when a predetermined number of cycles (about 200 cycles) elapse, the deposition thickness increases, indicating that the aluminum silicate thin film is deposited thicker.

3 is a graph illustrating changes in deposition rates and etching rates of aluminum oxide and silicon oxide films according to cycle ratios.

In the graph, a cycle ratio of 0.5 is (2,1), 1.0 is (1,1), 2.0 is (1,2), and 3.0 is (1,3), and deposition is performed at a temperature of 150 ° C. At the initial value (cycle ratio 0, 0), only aluminum oxide was deposited without depositing silicon oxide. As the cycle ratio increased, that is, as the deposition cycle ratio of silicon oxide increased, the deposition rate increased. In the case of depositing only silicon oxide, the deposition rate was almost close to zero, which means a mutual catalysis.

Etching was performed by wet etching with hydrofluoric acid solution. As the number of deposition cycles of the silicon oxide increases, the etching rate also increases. However, when the leakage current was measured, the leakage current decreased slightly as the number of silicon oxide deposition cycles increased. Therefore, it was found that the electrical properties were not deteriorated and the etching rate was increased, and the etching selectivity for the relatively other thin films, for example, polysilicon or aluminum metal, was relatively improved.

4 is a graph showing a change in deposition rate according to a cycle ratio at different deposition temperatures.

It can be seen that as the deposition temperature is lowered, the deposition rate is improved. This change was observed even when aluminum oxide films were deposited [J.W. Lim et al., US Pat. No. 6,723,642, 2004].

5 is a graph showing a change in the content of silicon according to the number of cycles, the silicon content also increases as the number of deposition cycles of silicon increases. Therefore, by adjusting the cycle ratio, it is possible to control the content of silicon.

Further, more silicon was contained under the conditions of (1, 1) when comparing the conditions of (1, 1) with the same cycle ratio and (10, 10). Therefore, it can be seen that the number of cycles is more actively catalyzed at a small integer ratio such as 1: 1, 1: 2, 1: 3, and the deposition rate at the condition of (1, 1) is (10, 10). Higher than in

6A and 6B are experiments for checking the residual stress, by depositing an aluminum oxide film (Al ₂ O ₃ ) (FIG. 6 a) and an aluminum silicate thin film (AlSiO) (FIG. 6 b) on a plastic substrate at a temperature of 150 ° C., respectively. , And shows a state in which the bending is performed at room temperature and the size of the bending is measured.

Due to the difference in thermal expansion coefficient, banding occurs as much as stress. If the distance from the center of the substrate surface to the center of the curved arc of the plastic substrate and the thin film is d, the stress is proportional to d. Experimental results showed that the aluminum silicate thin film had a stress reduction of about 20 to 30% under the conditions of (1, 1).

As described above, the preferred embodiment of the present invention has been disclosed through the detailed description and the drawings. In the above embodiment, only the aluminum silicate thin film has been described, but the present invention may be applied to the formation of a metal silicate thin film using a metal such as titanium (Ti). The terms are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the present invention controls the deposition cycles of aluminum oxide and silicon oxide in a small integer ratio such as 1: 1, 1: 2, 1: 3 during the aluminum silicate thin film formation process using plasma atomic layer deposition (PEALD). Therefore, firstly, the deposition rate is improved by the mutual catalysis and the content of silicon can be adjusted according to the cycle ratio. Second, it exhibits excellent characteristics even at a low temperature of less than 150 ℃, less residual stress between the plastic substrate and the inorganic thin film than the case of using aluminum oxide, and also has a low coefficient of thermal expansion. Third, since the etching rate is faster than that of the alumina oxide, it has a high etching selectivity for polysilicon or a metal thin film.

In addition, by controlling the silicon content according to the present invention, the aluminum silicate thin film of the present invention can be used as a dielectric layer of a buffer layer or a capacitor as well as a gate insulating film. In particular, when used as an insulating layer to form amorphous silicon to be crystallized, the characteristics of the silicon layer are determined according to the characteristics of the insulating layer that acts as a buffer layer. In the case of aluminum oxide, the thermal expansion coefficient is relatively large and is different from that of silicon or silicon oxide. Due to the separation process of the thin film is caused or peeling occurs in the thermal process, by using the aluminum silicate thin film of the present invention it is possible to prevent such a phenomenon by reducing the thermal expansion coefficient and to reduce the stress.

Claims (8)

A first step of mounting the substrate inside the chamber, A second step of depositing aluminum oxide on the substrate, And depositing silicon oxide on the aluminum oxide, wherein the second and third steps are alternately performed at a ratio of m: n. The method of claim 1, wherein the substrate is a plastic substrate. The method of claim 1, wherein the first step comprises: supplying an aluminum precursor into the chamber; First purifying the interior of the chamber, Supplying an oxygen plasma into the chamber to deposit the aluminum oxide; And purifying the inside of the chamber. The method of claim 3, wherein the aluminum precursor is Trimethyl Aluminum (TMA). The method of claim 1, wherein the second step comprises: supplying a silicon precursor into the chamber; First purifying the interior of the chamber, Supplying an oxygen plasma into the chamber to deposit the silicon oxide; And purifying the inside of the chamber. The method of claim 5, wherein the silicon precursor is any one of TEOS, Tetramethyl Silicon (TMS), Tetraethyl Silicon (TES), Tetradimethylamino Silicon (TDMAS) and Tetraethylmethylamino Silicon (TEMAS). 6. The method of claim 3 or 5, wherein a reaction gas comprising oxygen, nitrogen, and argon is used to generate the oxygen plasma. The method of claim 1, wherein m: n is 1: 1, 1: 2, 1: 3.

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