JP2001319879A - Thin film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film transistor having stabilized characteristics. SOLUTION: The thin film semiconductor device has an active layer 207 of a crystalline semiconductor film formed on an insulation film 202 containing oxygen, argon, halogen elements or phosphorus wherein the concentration of a metallic element accelerating crystallization of silicon contained in the crystalline semiconductor film is lower than that of a metallic element in the insulation film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD [0001] The invention disclosed in the present specification is:
The present invention relates to a semiconductor device using a crystalline silicon thin film and a manufacturing method thereof. In particular, the present invention relates to a thin film transistor using a crystalline silicon thin film and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, active research has been made on lowering the temperature of semiconductor device processes. The main reason is that
This is because a semiconductor element needs to be formed on an inexpensive and highly processable insulating substrate such as glass. This is largely due to the necessity of forming a thin film transistor used for an active matrix type liquid crystal display device on a glass substrate. In addition, there is a demand accompanying miniaturization of elements and multilayering of elements.

In a semiconductor process, it is necessary to crystallize an amorphous component or an amorphous semiconductor material contained in a semiconductor material, and it is necessary to further improve the crystallinity. There is. Conventionally, thermal annealing has been used for such a purpose. In the case where silicon is used as a semiconductor material, 600 ° C.
By performing annealing at a temperature of 100 ° C. for 0.1 to 48 hours or more, amorphous crystallization, improvement in crystallinity, and the like have been performed.

[0004] Generally, the higher the temperature, the shorter the processing time of the thermal annealing. However, 500
There was almost no effect at temperatures below ° C. For example, C
When the amorphous silicon film formed by the VD method is crystallized by heating, when the heat treatment temperature is 600 ° C., a time of 10 hours or more is required. At a heat treatment temperature of 550 ° C., a heat treatment time of 100 hours or more was required. However, in general, when a glass substrate is subjected to a heat treatment at 600 ° C. for 10 hours or more, distortion and deformation of the substrate become apparent. This distortion or deformation of the substrate does not cause a serious problem if the substrate is small (generally 10 cm square or less). However, when the size of the substrate is increased, a serious problem occurs. In addition, when a heat treatment is performed for 100 hours or more even at a temperature of about 550 ° C., the problem of distortion and deformation becomes significant.

In order to solve this problem, a special glass substrate or quartz substrate that can withstand heat may be used. However, such a substrate has a high unit price and is not suitable for production of a liquid crystal display aiming at cost reduction. That is, it is difficult to use it industrially.

[0006]

As for a technique for crystallizing an amorphous silicon film formed on a glass substrate by heating, a technique described in Japanese Patent Application Laid-Open No. 6-244103 by the present applicant is known. is there. In this technique, an amorphous silicon film is crystallized by a heat treatment at about 550 ° C. for about 4 hours by using a metal element which promotes crystallization of silicon. If this technology is used, a crystalline silicon film can be obtained without any problem even when an inexpensive glass substrate is used.

However, when a thin film transistor is formed using a crystalline silicon film formed by using this technique, the electrical characteristics of the thin film transistor may be affected by the influence of a metal element that promotes crystallization of silicon. I am concerned.

Further, variations in the characteristics of the thin film transistor, which are considered to be affected by the metal element, have been observed. In an active matrix type liquid crystal display device, several hundreds ×
It has a configuration in which a thin film transistor is arranged in each of several hundred pixels arranged in a matrix. Therefore,
Variations in characteristics of individual thin film transistors cause unevenness and unnaturalness of a displayed image.

Therefore, an object of the invention disclosed in this specification is to provide a technique for obtaining a thin film transistor in which the influence of a metal element that promotes crystallization of silicon is eliminated.

[0010]

According to the invention disclosed in this specification, when an element such as a thin film transistor is formed using a crystalline silicon film obtained using a metal element which promotes crystallization of silicon, Moving the metal element to a vicinity of a region (a region made of silicon containing the metal element) constituting the element,
The concentration of the metal element in the element region or a part of the element region is reduced.

The metal elements that promote crystallization of silicon include Fe, Co, Ni, Ru, Rh, Pd, Os, and I.
One or a plurality of elements selected from r, Pt, Cu, and Au can be used. Among these elements, in particular, N
The use of i is very useful in terms of its effect and reproducibility. Next to Ni, Pd, Pt,
Further, it is Cu.

In order to move the metal element to the vicinity of the element region, a silicon oxide film or a silicon nitride film having a lattice defect region is present in contact with a region constituting the element, and heat treatment is performed. Can be realized. This heat treatment also serves as a step of crystallizing the element region.

The lattice defect region has a high concentration of defects and dangling bonds that are difficult to anneal, and has a property of strongly trapping the metal element that promotes the crystallization of silicon. Therefore, by performing the heat treatment, the metal element existing in the element region diffuses into the lattice defect region and is strongly trapped.

The lattice defect region is formed by adding oxygen, argon, or the like to a region where the lattice defect region is to be formed, such as a silicon oxide film.
It can be formed by implanting ions of one or more kinds of elements selected from chlorine, fluorine, phosphorus, and boron by an ion implantation method or a plasma doping method and giving bombardment of the ions.

The outline of the invention disclosed in this specification will be described below. One of the inventions disclosed in this specification is a step of forming a lattice defect region for trapping a metal element that promotes crystallization of silicon, and an element formed of an amorphous silicon film in contact with the lattice defect region. Forming a region, contacting and holding the metal element in contact with the amorphous silicon film forming the element region, and crystallizing the element region by performing a heat treatment. Features.

FIG. 2 shows a specific example of the above configuration. FIG.
In (D), reference numeral 207 denotes an active layer (element region) constituting a thin film transistor. In the example shown in FIG.
In the step shown in FIG. 2A, phosphorus ions are implanted into the silicon oxide film 202 to make the silicon oxide film 202 a lattice defect region. Then, an active layer 204 made of an amorphous silicon film is formed thereon as shown in FIG.

Then, a nickel acetate salt solution 205 is applied using a spinner 206 and spin-dried, so that a nickel element which is a metal element for promoting crystallization of silicon is held in contact with the active layer 204. And

Next, as shown in (D), the active layer 204 is crystallized by performing a heat treatment to obtain an active layer 207 made of a crystalline silicon film. At this time, the nickel element diffuses from the active layer into the silicon oxide film 202 serving as a lattice defect region and is trapped.

According to another aspect of the invention, a step of forming an insulating film on a substrate and implanting ions of at least one element selected from oxygen, argon, a halogen element, and phosphorus into the insulating film. Forming a lattice defect region, forming an amorphous silicon film on the insulating film, and holding a metal element in contact with the amorphous silicon film to promote crystallization of silicon. Performing a heat treatment to crystallize the amorphous silicon film.

Another embodiment of the invention has a structure in which a crystalline silicon thin film is formed on an insulating film, and the crystalline silicon film contains 1 × 10 ¹⁶ metal elements for promoting crystallization of silicon. Atoms / cm ^{3 to} 5 × 10 ¹⁹ atoms / cm ³ , and the insulating film contains at least one element selected from oxygen, argon, a halogen element, and phosphorus. The insulating film has a lattice defect region as a whole, and the insulating film contains the metal element at a higher concentration than that contained in the crystalline silicon film. And

In the above structure, the concentration of the metal element contained in the crystalline silicon film is 1 × 10 ¹⁶ atoms / cm ^{3 to} 5 × 1.
It is limited to a concentration of 0 ¹⁹ atoms / cm ³ . This is because if the concentration of the metal element is lower than this concentration, it is one of the features of the invention disclosed in the present specification.
This is because a crystalline silicon film cannot be obtained by a certain degree of heat treatment. (That is, a crystalline silicon film containing a metal element at a concentration lower than the above concentration is not a constituent feature of the present invention.)

Further, when the metal element is contained at a concentration higher than the above concentration, the influence of the metal element is too strong and the characteristics as a semiconductor are impaired.

FIG. 2D shows a specific example of the above configuration. In the structure shown in FIG. 2D, silicon oxide film 20 having lattice defect regions formed by phosphorus ion implantation
2 further shows an active layer 207 made of a crystalline silicon film formed on the silicon oxide film 202.

In the structure shown in FIG. 2D, the entire silicon oxide film 202 can be regarded as a lattice defect region.
Further, since the silicon oxide film 202 contains phosphorus which is an element for gettering a metal element which promotes crystallization of silicon, in the heat treatment step for forming the active layer 207, The metal element is a silicon oxide film 20
2 is trapped or gettered by the phosphorus element in the silicon oxide film 202. Then, in a final state, the concentration of the metal element in the silicon oxide film 202 is higher than the concentration of the metal element in the active layer 202. This is because traps and elements for retaining the metal element exist in the silicon oxide film.

When the trapping or gettering action of the metal element by the silicon oxide film 202 proceeds extremely effectively, the concentration of the metal element in the active layer 207 is 1 × 10 ¹⁶ atoms / cm ³ or less. However, when the crystallization is performed effectively, a concentration higher than the above value is generally observed in the active layer.

The concentration of the element shown in this specification is S
It is defined as the maximum value obtained by IMS (secondary ion analysis).

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] In this embodiment, a metal element which promotes the crystallization of silicon is introduced into an amorphous silicon thin film, and the silicon film is given crystallinity by heat treatment. Shows a technique for removing the unnecessary metal element outside the crystalline silicon film.

Here, Ni is used as a metal element that promotes crystallization of silicon. First, a silicon oxide film 102 is formed as a base film on a glass substrate (for example, Corning 7959 glass substrate) 101 to a thickness of 3000 °.
This silicon oxide film is formed by plasma CV using TEOS as a raw material.
The film is formed by the method D.

Next, ion doping or plasma
Oxygen or silicon is added to the silicon oxide film 102 by the
Implants argon ions. The dose is 10¹⁶~
10 ^{twenty one}Pieces / cm^TwoChoose between In this way, oxidation
A lattice defect region is formed in the silicon film 102, and a silicon oxide film
Reference numeral 102 mainly comprises a lattice defect region. This
In the step, the silicon oxide film 102 is
It is important to configure as a defective area. Also, a large amount
Dose (generally 10¹⁸Pieces / cm^TwoAbove)
Repaired by annealing, by driving on
It can be a lattice defect region that is difficult to be formed. (Figure 1
(A))

Next, an amorphous silicon film (amorphous silicon film) 103 is formed by a plasma CVD method.
Here, a plasma CVD method is used.
Method may be used. Further, the thickness of the amorphous silicon film 103 is set to 500 °. Of course, this thickness may be a required thickness. However, as will be described later, laser light irradiation is also used, and a metal element (here, Ni
In order to lower the concentration of the element and simultaneously improve its crystallinity, the thickness of the amorphous silicon film needs to be 500 ° or less.

Next, the substrate is immersed in aqueous ammonia at 70 ° C.
For 5 minutes, an oxide film (not shown) is formed on the surface of the amorphous silicon film 103. This oxide film is formed to improve the wettability in a later step of applying a nickel acetate solution. Further, a nickel acetate solution is applied to the surface of the amorphous silicon film by spin coating. The Ni element functions as an element that promotes crystallization when the amorphous silicon film is crystallized.

Next, by maintaining the temperature at 450 ° C. for one hour in a nitrogen atmosphere, hydrogen in the amorphous silicon film is released. This is because a dangling bond is intentionally formed in the amorphous silicon film to lower the threshold energy at the time of subsequent crystallization. Then, the amorphous silicon film 103 is crystallized by performing a heat treatment at 550 ° C. for 4 to 8 hours in a nitrogen atmosphere. The temperature at the time of this crystallization could be set to 550 ° C.
This is due to the action of the Ni element.

The crystallized silicon film contains hydrogen at a ratio of 0.001 to 5 atomic%.
During the heat treatment, the Ni element moves through the silicon film,
The crystallization of the silicon film is promoted. Further, the Ni element moves toward the lattice damage region formed in the amorphous silicon film 102 as indicated by 104.

The heat treatment at a temperature of about 550 ° C. does not repair the lattice defect region formed in the silicon oxide film. In addition, due to the large number of lattice defect regions, the final concentration distribution is higher in the silicon oxide film 102 than in the silicon film 103.

Thus, the glass substrate has crystallinity,
In addition, a crystalline silicon film having a low concentration of Ni element can be obtained. (FIG. 1 (B))

Next, the active layer 105 of the thin film transistor is formed by patterning. Further, a silicon oxide film 106 functioning as a gate insulating film is formed to a thickness of 1000 °. Further, a gate electrode 107 is formed by forming an aluminum film containing a small amount of scandium to a thickness of 6000 ° and performing patterning. Then, anodization is performed in an electrolytic solution using the gate electrode 107 as an anode to form an aluminum oxide layer 108 to a thickness of 2000 °. This oxide layer 108 functions as a mask for forming an offset gate region in a later step of implanting impurity ions. (Fig. 1 (C))

In this state, P (phosphorus) ions are implanted by a plasma doping method or an ion implantation method. Then, the gate electrode 107 and the surrounding oxide layer 108 serve as a mask, and the active layers 109 and 11 are used as masks.
2 and P ions are implanted. And 110 and 1
No P ions are implanted into the region 11. As a result, the regions 109 and 112 are configured as source / drain regions. The region 110 is configured as an offset gate region. The region 111 is configured as a channel formation region. (Fig. 1 (D))

After the step shown in FIG. 1D, an interlayer insulating film is formed, and further, a contact hole is formed. Then, a contact electrode to the source / drain region and a contact electrode to the gate electrode are formed. Finally,
By performing heat treatment for one hour in a hydrogen atmosphere at 350 ° C., a thin film transistor is completed.

In the thin film transistor manufactured in this embodiment, a crystalline silicon film can be obtained by heat treatment at a low temperature (meaning that the glass substrate can withstand). In addition, the concentration of the nickel element in the active layer of the obtained thin film transistor can be reduced. In this manner, a thin film transistor with low production cost and without deterioration or change in characteristics can be obtained.

[Embodiment 2] In this embodiment, the silicon film produced in Embodiment 1 is made to have better crystallinity, and the concentration of a metal element for promoting crystallization of silicon is further reduced. Related to the configuration.

First, a crystalline silicon film is obtained by performing a heat treatment as shown in the step shown in FIG. Then, laser light irradiation is performed in two stages. Here, laser light irradiation is performed by irradiating the linearly processed laser beam while operating it. As a laser beam, a KrF excimer laser is used. The irradiation conditions of the laser beam are as follows.
00 mJ / cm ² , then 200-500 m for main irradiation
J / cm ² two-stage irradiation. The number of pulses is 30 pulses / s. Here, the two-stage irradiation is performed in order to minimize the deterioration of the film surface uniformity due to the irradiation of the laser beam.

In the crystalline silicon film crystallized only by the heat treatment shown in the first embodiment, many amorphous components remain in the film. In such a case, uniform laser energy is not absorbed in the entire film, and the surface of the film becomes rough due to the irradiation of the laser light. Therefore, the amorphous portion remaining in the film is crystallized by the first irradiation, and the entire crystallization is promoted by the second irradiation. By doing so, the overall crystallinity is high,
In addition, a crystalline silicon film with less roughness on the film surface can be obtained.

The effect of the two-step irradiation is very high, and the characteristics of the completed semiconductor device can be remarkably improved. In particular, in the case of manufacturing a thin film device having a thickness of 1000 ° or less, the surface condition of the thin film semiconductor to be used greatly affects the characteristics of the device. Is very effective.

The laser beam irradiation is performed while maintaining the substrate temperature at 500.degree. This is performed in order to moderate the rate of rise and fall of the substrate surface temperature due to the irradiation of the laser beam. Generally, it is known that a sudden change in the environment impairs the uniformity of a substance. Therefore, by keeping the substrate temperature high, it is possible to minimize deterioration of the uniformity of the substrate surface due to the irradiation of the laser beam. In this embodiment, the substrate temperature is set to 500 ° C.
The temperature can be selected from ℃ to the strain point of the substrate.
For example, when a Corning 7059 glass substrate is used, its strain point is 593 ° C., so that the temperature can be selected from a temperature lower than this temperature and higher than 450 ° C.

In the case where the thickness of the silicon film is about 500 ° or less, when the above laser light irradiation is performed, the nickel element is further diffused into the underlying silicon oxide film 102, so that the silicon film Can be reduced. This effect is greater when the thickness of the silicon film is thinner, but care must be taken when the thickness is less than 100 ° C., since it becomes difficult to form the film by a general CVD method. Therefore, it is generally appropriate to set the thickness of the silicon film to about 100 to 500 °. In addition, irradiation with laser light increases the crystallinity of the film, and thus is very useful in that sense.

[Embodiment 3] In this embodiment, a lattice defect region is artificially formed adjacent to a region constituting an active layer (also referred to as an element region) of a thin film transistor. And trapping the metal element in the active layer to reduce the concentration of the metal element in the active layer.

FIG. 2 shows a part of the manufacturing process of the semiconductor device shown in this embodiment. First, a silicon oxide film 202 as a base film is formed on a glass substrate 201 to a thickness of 3000 ° by plasma CV.
The film is formed by the D method or the sputtering method.

Then, phosphorus ions are implanted into the silicon oxide film 202 by a plasma doping method or an ion implantation method. The dose is 10 ¹⁶ to 10 ²¹ / cm ² . In this step, the silicon oxide film 202 becomes a phosphorus glass state like a PSG film. The entire film is formed as a lattice defect region. In this step, it is necessary to devise such that defects are formed at a high density in the entire silicon oxide film.
(Fig. 2 (A))

The surface of the silicon oxide film 202 becomes rough as a result of the ion implantation. Therefore, wet etching using buffered hydrofluoric acid is performed, and the surface is removed with a thickness of about several tens to several hundreds of mm, and the surface is planarized.

Next, the amorphous silicon film 203 is formed by plasma CVD.
The film is formed to a thickness of 500 ° by a low pressure method or a low pressure thermal CVD method.
(FIG. 2 (B))

Next, the active layer 204 of the thin film transistor is formed by patterning the amorphous silicon film 203 into a predetermined pattern. Then, Ni, which is a metal element that promotes crystallization of silicon, is introduced. Here, a sample is placed on the spinner 206, and a nickel acetate solution adjusted to a predetermined Ni concentration is first applied. In this state, FIG.
A water film 205 is formed as shown in FIG. (Fig. 2 (C))

Then, by spinning the spinner 206 to perform spin drying, excess nickel acetate solution is blown off. Thus, a state where the nickel element is held in contact with the amorphous silicon film 204 patterned into the shape of the active layer is realized.

Here, an example of introducing a nickel element using a solution containing a nickel element has been described.
A nickel thin film or a thin film containing a nickel element may be formed on the surface of the amorphous silicon film by an evaporation method, a sputtering method, or a plasma CVD method.

Next, as shown in FIG.
By performing the heat treatment for 4 hours, the active layer 204 made of an amorphous silicon film is crystallized. As a result, an active layer 207 made of a crystalline silicon film is formed. At this time, arrow 20
As shown by 8, the nickel element diffuses from the active layer into the silicon oxide film 202 which is entirely a lattice defect region. (FIG. 2 (D))

Generally, the strain point of a glass substrate is about 600 ° C., so that the heat treatment at 550 ° C. for 4 hours does not cause any problem of deformation or distortion. In the structure shown in this embodiment, nickel is diffused and trapped in the silicon oxide film 202, so that the concentration of nickel element in the active layer can be reduced. In particular, in this embodiment, in addition to the lattice defect region for trapping the nickel element in the silicon oxide film, phosphorus having an action of gettering nickel is contained, so that the nickel element can be effectively converted to silicon oxide. It can be moved into the membrane 202.

Further, as shown in the second embodiment, further irradiating a laser beam after the heat treatment improves the crystallization of the active layer 207 and further increases the concentration of the nickel element contained in the active layer 207. Can be lowered.

[0057]

According to the technology disclosed in this specification, a crystalline silicon film can be obtained in a heat treatment at a temperature at which a glass substrate can be used.
In addition, since the concentration of the metal element in the crystalline silicon film can be reduced, a thin-film semiconductor device obtained without deterioration or change in characteristics can be obtained.

In particular, utilizing the invention disclosed herein,
When a thin film transistor array used for an active matrix type liquid crystal display device is manufactured, variation in characteristics of each thin film transistor can be suppressed, so that a TFT liquid crystal panel having high display characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 illustrates a manufacturing process of a thin film transistor described in an example.

FIG. 2 illustrates a manufacturing process of a thin film transistor described in an example.

[Explanation of symbols]

Reference Signs List 101, 201 glass substrate 102, 202 silicon oxide film 103, 203 amorphous silicon film 105, 207 active layer 106 gate insulating film (silicon oxide film) 107 gate insulating film containing aluminum as a main component 108 aluminum anodic oxide layer Reference Signs List 109 Source region 110 Offset gate region 111 Channel forming region 112 Drain region 205 Water film of nickel acetate solution 206 Spinner

Claims (4)

[Claims] 1. A thin-film semiconductor device having an active layer made of a crystalline semiconductor film on an insulating film, wherein the insulating film contains oxygen, argon, a halogen element or phosphorus, and is contained in the crystalline semiconductor film. A thin-film semiconductor device, wherein a concentration of a metal element that promotes crystallization of silicon contained therein is lower than a concentration of the metal element in the insulating film. 2. The method according to claim 1, wherein the metal element for promoting crystallization of silicon is Fe, Co, Ni, Pd, Ir, P
A thin-film semiconductor device comprising t, Cu or Au. 3. The thin film semiconductor device according to claim 1, wherein said thin film semiconductor device is a thin film transistor. 4. A liquid crystal display device using the thin-film semiconductor device according to claim 1.