JP2002184697A - Method of manufacturing clearer silicon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality and reliability of a thin-film transistor(TFT). SOLUTION: A method of reducing contamination in polycrystalline silicon regions on a display substrate comprises a step (a) of depositing a base coating on the display substrate, a step (b) of annealing the base coating, having an upper surface, a step (c) of decontaminating the upper surface of the base coating, a step (d) of depositing amorphous silicon on the decontaminated base coating and step (e) of crystallizing the amorphous silicon, to form polycrystalline regions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to semiconductor technology, and more particularly, to a method for forming polycrystalline silicon in an amorphous silicon film.

[0002]

2. Description of the Related Art Polycrystalline silicon thin film transistors (TF)
T) for a variety of microelectronic applications, especially active matrix liquid crystal displays (LCDs),
Can be used.

A thin film transistor (TFT) used for a liquid crystal display (LCD) or a flat display of the active matrix display type is manufactured on a silicon film deposited on a transparent substrate. The most widely used substrate is glass. Amorphous silicon is easily deposited on glass. Amorphous silicon limits the quality of TFTs that can be formed. If the switches and driver circuits and other components associated with each pixel are formed on a display panel, crystalline silicon is preferred.

[0004] Amorphous silicon can be crystallized to form crystalline silicon by solid-phase crystallization. Solid phase crystallization is performed by high temperature annealing. However, glass substrates cannot withstand the temperatures required to melt and crystallize silicon. Quartz substrates can withstand high temperature annealing, but are too expensive for most LCD applications.

[0005] Low temperature crystallization (preferably below 550 ° C) is used for solid-state processing of silicon on glass because the glass deforms when exposed to temperatures above 600 ° C. Low temperature processing requires a long annealing time (at least several hours). Such processing is inefficient and
A relatively low field effect mobility and threshold voltage unstable polycrystalline silicon TFT is produced. Polycrystalline silicon produced by solid-phase crystallization of amorphous silicon as deposited on glass has the disadvantage of small crystal size and high density of defects in the crystal.

Excimer laser annealing (ELA)
Has been actively studied as an alternative to low-temperature solid-state crystallization of amorphous silicon on glass. In excimer laser annealing, a high-energy pulsed laser is irradiated toward a selected region of a target film to expose the silicon to ultra-high temperature for a short time. Typically, each laser pulse is applied to only a small area (a few millimeters in diameter).
And the substrate or laser is moved into small knurls through the illumination pattern of the overlap illumination, as is known in the art.

[0007]

SUMMARY OF THE INVENTION In order to produce good TFT characteristics and improve reliability, a base coat is deposited on a glass substrate. The base coat is typically a silicon oxide material. In order to reduce the defect density, the base coat film needs to have as few Si—OH bonds as possible in the film. In a typical poly-Si process, the base coat is a TEOS or silane oxide film deposited by a conventional PECVD process. After deposition, the base coat is annealed in a nitrogen atmosphere to remove Si-OH bonds and water from the film. Although the annealing process removes the Si-OH, the basecoat is easily contaminated during or during the annealing process. After annealing, a layer of amorphous silicon is deposited on the base coat and any contamination present. Contaminants can diffuse into the silicon film from the amorphous silicon or the interface between silicon and the basecoat during silicon deposition. Contaminants can diffuse further into the silicon during subsequent laser crystallization. Such contamination of the silicon reduces the quality and reliability of the TFT.

The present invention has been made in view of such problems, and has as its object to improve the quality and reliability of a TFT.

[0009]

SUMMARY OF THE INVENTION The present invention is a method for reducing contamination in a polycrystalline silicon region on a display substrate, comprising: a) depositing a base coat on the display substrate; The base coat has an upper surface; c) removing contamination of the upper surface of the base coat; and d) depositing amorphous silicon on the removed base coat. And e) crystallizing the amorphous silicon to form a polycrystalline region, thereby solving the above-mentioned problems.

According to one embodiment of the present invention, the display substrate may be glass, plastic, or metal foil.

According to one embodiment of the present invention, the step of removing the contamination on the upper surface may include a step of dry-etching the upper surface.

According to one embodiment of the present invention, removing the contamination on the upper surface may include counter-sputtering the upper surface.

Further, the present invention is a method for reducing contamination in a polysilicon region on a display substrate, comprising:
a) depositing a base coat on the display substrate; b) annealing the base coat, wherein the base coat has an upper surface; c) removing contamination of the upper surface of the base coat. D) depositing amorphous silicon on the base coat from which the contamination has been removed, wherein the vacuum is not impaired during the transition from the step of removing the contamination of the upper surface to the step of depositing the amorphous silicon. And e) crystallizing the amorphous silicon to form a polycrystalline region.
This solves the above problem.

According to one embodiment of the present invention, the step of removing the contamination of the base coat may include a step of dry etching the display substrate in a dry etching chamber.

According to one embodiment of the present invention, the dry etching chamber is mounted on a deposition chamber, whereby the display substrate may be transferred to the deposition chamber without breaking vacuum.

According to one embodiment of the present invention, the step of removing the contamination of the base coat may include counter sputtering in a sputtering chamber.

According to one embodiment of the present invention, the step of depositing the amorphous silicon is performed by sputtering in the same sputtering chamber used for the counter sputtering during the step of removing the contamination. May be performed.

Prior to depositing the amorphous silicon layer, a method is needed to reduce or eliminate contamination on the basecoat.

Accordingly, a method is provided for reducing or eliminating contamination on a display substrate, which prevents contamination of subsequently produced polysilicon. A base coat is deposited on the display substrate. The display substrate is preferably a glass, plastic, or metal film. The base coat is annealed. During the annealing process and during subsequent transfer between processing stations, a contaminant layer forms on the basecoat upper surface.

Next, the contaminant layer is removed before further processing. The contamination layer is removed by dry etching or counter sputtering. Once the contamination is removed, if the amorphous silicon is formed without breaking the vacuum, the display substrate can be suitably used for the subsequent processing without further exposing the display substrate to the contamination.

If dry etching is used to remove contamination, the dry etching chamber is joined to a sputtering chamber to allow transfer of the display substrate without further exposing the display substrate to contamination.

[0022] Countersputtering is preferred for removing contaminant layers because the same sputtering chamber is used for countersputtering with argon and sputter deposition of amorphous silicon. This allows the current processing equipment to be used without any significant changes.

With the contamination reduced or removed, the amorphous silicon is crystallized using laser annealing to produce polycrystalline silicon.

After processing according to the method of the present invention, to produce a finished display, such as an active matrix LCD or other integrated circuit, the clean polycrystalline material is
It can be further processed.

[0025]

DETAILED DESCRIPTION OF THE INVENTION With reference to FIGS. 1-5 (prior art), the contamination problem associated with the prior art method is illustrated. The figures are illustrative and do not follow a uniform scale. Fig. 1 (Prior art)
In the display 10 during processing, the glass substrate 1
2 and a base coat 14 deposited on the glass substrate 12. A base coat is typically formed using a conventional PECVD process to deposit a layer of TEOS or silane oxide.

FIG. 2 (Prior Art) shows the display 10 after annealing of the base coat 14.

FIG. 3 (Prior Art) shows the formation of a contaminant layer 16 formed on a base coat 14. Display 10
This contaminant layer 16 forms as the display 10 is annealed or removed from the controlled vacuum environment during transfer to a later process.

FIG. 4 (Prior Art) shows the display 10 after an amorphous silicon layer 18 has been deposited on the base coat 14. The amorphous silicon layer 18 also overlaps the contamination layer 16. The amorphous silicon layer 18
Manufactured by sputtering in a vacuum chamber.

FIG. 5 (prior art) shows the display 10 after the silicon layer 18 has been laser crystallized to form a polycrystalline layer 20. It is this polycrystalline layer 20 that is used to form the active elements of the display 10. Region 22 shows the diffusion of contamination from contamination layer 16 to polycrystalline layer 20. This contamination reduces the performance and reliability of the manufactured finished display device.

Following the above steps, subsequent processing may be performed to fabricate active and passive device structures on polycrystalline layer 20.

Next, a processing sequence related to the embodiment of the present invention will be described with reference to FIGS. The figure is for illustration,
Does not follow a uniform scale. In FIG. 6, the display 1
Reference numeral 00 denotes a glass substrate 112 and a base coat 114 deposited on the glass substrate 112. The base coat is suitably formed using a conventional PECVD process to deposit a layer of TEOS or silane oxide.

FIG. 7 shows a display 100 having an annealed base coat 114. The process of annealing the base coat 114 or the substrate transfer is as follows.
Contaminants can be introduced to the upper surface 115 of the basecoat. By way of illustration, the contamination on the top surface 115 of the basecoat is shown to form a contamination layer 116, as shown in FIG. This contaminant layer 116 forms when the display 100 is annealed or when the display 100 is removed from the controlled vacuum environment during transfer to later processing. Although mechanisms have been described that may cause the formation of this contamination layer, the actual means by which the contamination is formed is irrelevant to the present disclosure and should not be construed as limiting the claims.

FIG. 9 shows the display 100 after the contamination layer 116 has been removed. In a preferred embodiment of the method of the present invention, the contamination layer 116 is removed by counter sputtering. After annealing the base coat 114, the display 100 is transferred and placed in a sputtering chamber (not shown). The contamination layer 116 is removed by counter sputtering using bombardment with argon ions. Bombarding the contaminated layer 116 with inert argon ions removes the contaminated layer and exposes the uncontaminated base coat 114.

An amorphous silicon layer is deposited on the display by sputtering without compromising the sputtering chamber vacuum. FIG. 10 shows the display 100 after the amorphous silicon layer 118 has been deposited on the base coat 114.

Although sputtering of amorphous silicon after countersputtering is preferred, other methods of practicing the present invention are within the scope of the present invention. Another preferred embodiment uses a dry etch process to contaminate layer 116.
Is to be removed. Dry etching has the advantage of higher etching rates than counter sputtering. However, etching gases or by-products produced can adversely affect the properties and reliability of the TFT. In order to remove the contaminant layer 116 without unduly reducing the characteristics and reliability of the TFT, the process gas must be carefully selected. To avoid recontaminating the basecoat 114, the dry etching chamber is preferably connected to a deposition chamber for amorphous silicon deposition. Display 100
Is preferably transferred from the dry etch chamber to the deposition chamber without breaking vacuum.

Although countersputtering is slower than dry etching, it is preferred. This is because it offers several advantages during processing. First, countersputtering utilizes inert argon to reduce or eliminate problems associated with etching gases and by-products. Counter-sputtering is also preferred because amorphous silicon is usually deposited by sputtering in a sputtering chamber. By counter sputtering, the contaminant layer 116 can be removed just before depositing amorphous silicon, preferably using the same sputtering chamber. This improves the process flow and prevents inadvertent exposure that could recontaminate the basecoat 114.

FIG. 11 shows the display 10 after the polycrystalline layer 120 is formed by laser crystallization of the silicon layer 118.
Indicates 0. It is this polycrystalline layer 120 that is used to form the active elements of the display 100. As shown, contamination is reduced or eliminated.

Following the above steps, subsequent processing is performed to produce active and passive device structures on the polycrystalline layer 120 and to provide a functional display device, preferably an active matrix LC.
D can be manufactured.

Thus, according to the present invention, there is provided a method for producing polycrystalline silicon on a display substrate with reduced contamination. A base coat is formed on a display substrate, which is preferably glass. The basecoat can become contaminated during annealing of the basecoat or in contact with the atmosphere. This contamination is removed by dry etching or counter sputtering. Next, the vacuum is maintained until the amorphous silicon sputtering is completed. If dry etching is used, the dry etching chamber is coupled to the sputtering chamber, so that the display substrate can be transferred without exposing the substrate to potential contaminants.
In the case of counter sputtering, the same sputtering chamber is preferably used for both counter sputtering and amorphous silicon sputtering. After the deposition of the amorphous silicon, the amorphous silicon is crystallized using laser annealing.

Still other embodiments are possible within the scope of the present invention. Other variations within the scope of the invention are:
Those skilled in the art will be reminded. Accordingly, the above disclosure and description of the invention is illustrative only and is not intended to limit the invention. The invention is defined by the claims, as construed by the rules of the claims.

[0041]

As described above, according to the present invention, the contamination on the base coat is removed before the deposition of the amorphous silicon layer. Therefore, the quality and reliability of the TFT can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing steps in a conventional method.

FIG. 2 is a cross-sectional view showing steps in a conventional method.

FIG. 3 is a sectional view showing steps in a method of the prior art.

FIG. 4 is a cross-sectional view showing steps in a conventional method.

FIG. 5 is a cross-sectional view showing steps in a method of the prior art.

FIG. 6 is a sectional view showing a step in the method of the present invention.

FIG. 7 is a sectional view showing a step in the method of the present invention.

FIG. 8 is a cross-sectional view showing steps in the method of the present invention.

FIG. 9 is a cross-sectional view showing a step in the method of the present invention.

FIG. 10 is a sectional view showing a step in the method of the present invention.

FIG. 11 is a sectional view showing a step in the method of the present invention.

[Explanation of symbols]

 10, 100 Display 12, 112 Glass substrate 14, 114 Base coat 16, 116 Contamination layer 18, 118 Amorphous silicon layer 20, 120 Polycrystalline layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Apostroth Boutousus United States 97217, Portland, North Hayden Bay Drive 157 F-term (reference) 4K029 AA09 BA35 BB10 BD01 CA05 FA04 GA00 5F052 AA02 AA11 AA17 BB07 CA02 DA02 EA11 EA15 JA01 5110 AA17 AA26 BB01 DD01 DD02 DD13 GG02 GG13 GG43 GG57 PP03 QQ09

Claims (9)

[Claims] 1. A method for reducing contamination in a polysilicon region on a display substrate, the method comprising: a) depositing a basecoat on the display substrate; and b) annealing the basecoat.
C) removing contaminants from the upper surface of the basecoat; d) depositing amorphous silicon on the decontaminated basecoat; and e) crystallizing the amorphous silicon. Forming a polycrystalline region. 2. The method according to claim 1, wherein the display substrate is glass, plastic, or metal foil. 3. The step of removing contamination on the upper surface,
Including a step of dry etching the upper surface,
The method of claim 1. 4. The step of removing contamination of the upper surface,
The method of claim 1, comprising countersputtering the upper surface. 5. A method for reducing contamination in a polysilicon region on a display substrate, the method comprising: a) depositing a base coat on the display substrate; and b) annealing the base coat.
The base coat having an upper surface; c) removing contaminants on the upper surface of the base coat; d) depositing amorphous silicon on the contaminated base coat; A method that does not break vacuum during the transition from removing contamination to depositing the amorphous silicon; and e) crystallizing the amorphous silicon to form a polycrystalline region. 6. The method of claim 5, wherein removing the basecoat contamination comprises dry etching the display substrate in a dry etching chamber. 7. The method of claim 6, wherein the dry etching chamber is attached to a deposition chamber, such that the display substrate is transferred to the deposition chamber without breaking vacuum. 8. The method of claim 5, wherein removing the contamination of the base coat comprises counter sputtering in a sputtering chamber. 9. The method of claim 8, wherein depositing the amorphous silicon is performed by sputtering in the same sputtering chamber used for the counter sputtering during the step of removing the contamination. the method of.