JP2000200752A - Preparation of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of preparing a semiconductor device exhibiting excellent performance. SOLUTION: This preparation method comprises the steps of forming a silicon oxide film using TEOS (tetraethoxysilane) on a substrate, forming an amorphous silicon film on the silicon oxide film, and crystallizing the amorphous silicon film. In this case, the silicon oxide film and the amorphous silicon film are successively formed in a film-forming apparatus having two or more chambers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for performing laser annealing for obtaining a crystalline semiconductor used for a thin film device such as an insulated gate field effect transistor by irradiating a laser beam.

[0002]

2. Description of the Related Art Conventionally, in fabricating a thin film device such as a thin film type insulated gate field effect transistor (TFT), an ion implantation method, a plasma doping method, or the like is used to form an impurity region such as a source and a drain. Impurities are introduced into the silicon semiconductor thin film using energy ions, and as a result, the crystallinity is deteriorated, and the impurity-doped silicon film is recrystallized by light energy of a laser, a lamp or the like, and the activity of the impurity element is reduced. A method for performing the conversion is known. In particular, a method using a laser is known as a laser annealing method, and is excellent in mass productivity. In particular, laser annealing using a pulsed laser is excellent in productivity,
It has been regarded as a promising technology because thermal energy can be effectively applied only to the surface of an object to be irradiated.

[0003]

However, in the conventional pulse laser annealing (laser activation) step, the temperature changes rapidly, so that sufficient crystallization is not performed during laser irradiation, and the crystallinity is partially increased. Poor parts remain, deteriorating the reliability of the TFT obtained. The present invention has been made in view of the conventional problems, and has an object to improve uniformity of crystallization at the time of laser annealing, thereby improving overall crystallinity, and thereby improving reliability of a thin film transistor. And

[0004]

According to the present invention, a silicon film having impurities is formed at a temperature of 100 ° C. or higher, preferably 100 to 50 ° C.
This is a laser annealing method characterized in that impurity atoms are activated by heating to a temperature of 0 ° C. and irradiating it with a pulsed laser beam. Here, the impurities are phosphorus or boron, or both, and
The energy density of pulsed laser light is 200-400m
It is preferably J / cm ² . Irradiating too much energy is not preferable because it may damage the silicon film instead.

Further, according to the present invention, a step of forming a gate insulating film covering an island-shaped crystalline silicon film formed on a substrate; a step of forming a gate electrode portion on the gate insulating film; After forming the gate electrode portion, a step of introducing phosphorus or boron into the crystalline silicon film using the gate electrode portion as a mask;
The present invention also provides a method for manufacturing a semiconductor device, which comprises irradiating a pulsed laser beam while being heated to 00 to 500 ° C.

As a laser, an excimer laser is preferable from the viewpoint of mass production. However, the configuration of the present invention does not limit the kind of laser at all, and it goes without saying that any laser may be used.

The first effect obtained by the present invention is to improve the crystallinity of a silicon semiconductor and increase the reliability. As described above, when laser activation is performed after introducing impurities into a silicon semiconductor by means of high-energy ion irradiation or the like, especially in the case of a pulsed laser, the temperature rise due to light absorption and heat radiation The accompanying temperature drop was so steep that the doped impurities migrated, causing the temperature to drop before reaching the position needed to impart conductivity to the semiconductor, causing the impurity movement to freeze. . As a result, a large number of defects exist due to the forced entry of impurities into the silicon semiconductor, which results in a change with time and non-uniformity, thereby causing a significant decrease in reliability.

The effect of heating to an appropriate temperature as in the present invention during laser annealing is to mitigate such rapid temperature changes. That is, if the substrate is 100
By heating to ~ 500 ° C, part of the energy coming and going due to the laser irradiation is partially absorbed, and the temperature changes more slowly than in the case without heating (particularly in the case of falling).
Becomes For this reason, the position of the impurity in the silicon crystal becomes stable, and the number of defects decreases.

[0009] This also means that a smaller amount of doping can be performed as compared with the related art in order to obtain required characteristics of the silicon semiconductor (for example, conductivity, sheet resistance, etc.). Therefore, the doping time can be reduced, and the productivity is improved. In addition, a small doping amount means that the silicon semiconductor is less damaged, which also improves the reliability of silicon.

A second effect of the present invention is an effect of reducing the energy density of laser annealing. This is because, by irradiating the laser in a pre-heated state, it is not necessary to raise the temperature of the silicon semiconductor to that temperature. By this effect, mass productivity of laser annealing is improved. That is, if the laser having the same energy is used by reducing the energy density of the laser to be used, a wider area can be simultaneously processed.

The third effect of the present invention is particularly remarkable in the production of thin film semiconductor devices such as TFTs. However, when impurities are introduced in a self-aligned manner, laser annealing is performed. This is to improve the reliability of the semiconductor device. That is, in a top gate TFT or the like, usually, a gate insulating film is provided on a silicon semiconductor, and a gate electrode or a structure including the gate electrode (these are referred to as gate electrode portions) is provided. Impurity is introduced by means such as irradiation. Thereafter, activation is performed by irradiating a laser from above. However, in this case, since the gate electrode portion becomes a shadow, the temperature of the portion irradiated with the laser is significantly different from that of the lower portion of the gate electrode portion, and a difference in thermal expansion, a difference in activation, etc. Various stresses are generated near the boundary between the impurity region and the channel formation region, and defects are generated along with the stresses. It goes without saying that the defects generated in this way cause the reliability of the semiconductor device to be reduced.

This problem can be solved by a method of irradiating the laser beam not from above but from the substrate side. However, for that purpose, the laser beam and the substrate are restricted. For example, if the substrate is quartz, Xe
Light from a Cl excimer laser (wavelength 308 nm) or a KrF excimer laser (wavelength 248 nm) can be sufficiently transmitted. However, a quartz substrate is expensive, and a glass substrate containing borosilicate as a main component such as Corning 7059, which is inexpensive, absorbs these laser beams. In order to use a glass substrate containing borosilicate as a main component, it is desirable that the wavelength of the laser be 400 nm or more.
There are few lasers having a wavelength of 0 to 650 nm that are excellent in productivity. Also, if the wavelength is infrared or longer, the absorption in the silicon film is not sufficient, heat reaches the substrate,
Laser energy may be wasted, and the film may peel off due to a difference in thermal expansion or the like.

On the other hand, according to the present invention, the temperature gradient between the impurity region and the channel formation region (below the gate electrode portion) at that time can be reduced by heating the silicon film in advance, even if laser irradiation is performed from above. Can be moderate. Therefore, stress is reduced, defects are reduced, and reliability is improved as compared with the related art. In addition to the above, the effects associated with the improvement in crystallinity, the decrease in the dose, and the decrease in the laser energy density are added. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0014]

[Embodiment 1] FIG. 3 shows an embodiment of the present invention. The substrate used was Corning 7059. An underlying silicon oxide film having a thickness of 2000 mm was deposited on the substrate by a sputtering method, and an amorphous silicon film was deposited to a thickness of 1200 mm by a plasma CVD method. Then, after patterning this, a silicon oxide film having a thickness of 1000 ° was deposited again by the sputtering method.

Then, by plasma doping,
Doping with phosphorus (P) and boron (B) was performed. Phosphine (PH ₃ ) and diborane (B ₂ H ₆ ) were used as doping gases. The acceleration voltages were 80 kV and 65 kV, respectively. The dose was 4 × 10 ¹⁵ cm ⁻² .

Thereafter, the sample is heated from room temperature to 450 ° C., and KrF of 200 to 350 mJ / cm ² is applied in a nitrogen atmosphere.
Excimer laser light (wavelength 248 nm, pulse width 30
nsec) for two shots to activate the silicon film. An electrode was formed on the silicon film thus obtained, and the sheet resistance was measured. The result shown in FIG. 3 was obtained.

FIG. 3 clearly shows that a significant decrease in sheet resistance was observed when the sample was heated, preferably to 300 ° C. or higher. For example, when activating a silicon film doped with phosphorus, a laser having an energy density of 250 mJ / cm ² or more was required at room temperature to obtain a sheet resistance of 300 Ω / □ or less. 4
By heating to 50 ° C., a sufficient energy density of 200 mJ / cm ² could be achieved. Indeed 20
% Could reduce the laser energy density.

Similarly, when activating a boron-doped silicon film, a laser having an energy density of about 250 mJ / cm ² is required at room temperature to obtain a sheet resistance of 400 Ω / □ or less. However, heating the sample to 300 to 350 ° C.
/ Cm ² could be achieved satisfactorily.

FIGS. 4 and 5 show the results of similar experiments. Here, the substrate temperature is maintained at 300 ° C., and the dose amount is 1 to
The sheet resistance was examined by changing the sheet resistance to 4 × 10 ¹⁵ cm ⁻² . 4 shows the case where the thickness of the silicon film is 500 °, and FIG. 5 shows the case where the thickness of the silicon film is 1500 °. 4 and 5, the sheet resistance decreases as the dose increases,
It was also found that the thicker the silicon film, the lower the sheet resistance.

In order to improve the characteristics of the TFT, it is desired that the sheet resistance is 500 Ω / □ or less. However, the silicon film has a thickness of 1500 °, the substrate temperature is 300 ° C., and the laser energy density is 300 mJ / cm ² . Then 1
It has been found that this condition can be achieved with a dose of × 10 ¹⁵ cm ^-2 .

Embodiment 2 An example of manufacturing a TFT using the present invention will be described with reference to FIGS. Substrate (Corning 7
059) A silicon oxide film 12 as an underlayer was deposited at 500 to 2500 ° by a plasma CVD method. Plasma C
Tetraethoxysilane (TEOS) and oxygen were used as source gases for VD. Next, plasma CVD
By the method, a substantially intrinsic amorphous silicon film was deposited at 1500 °. The formation of the base silicon oxide film and the amorphous silicon film is preferably performed continuously without exposing the substrate to the air in a film forming apparatus having two or more chambers. Then, at 430 ° C, 30 ~
After the dehydrogenation treatment for 60 minutes, the amorphous silicon film was changed to a crystalline silicon film by annealing at 600 ° C. for 24 to 48 hours. Then, this silicon film was patterned into island-shaped silicon regions 13, and a silicon oxide film 14 having a thickness of 1000 ° functioning as a gate insulating film was deposited by a plasma CVD method.
Further, an aluminum film having a thickness of 5
000Å deposited and patterned to form a gate electrode 1
5 was formed. (Fig. 1 (A))

Thereafter, the substrate was immersed in a 3% solution of tartaric acid in ethylene glycol, and anodization was performed by passing an electric current using the platinum electrode as a negative electrode and the aluminum gate electrode 15 as an anode. At this time, the voltage was increased to 220 V while keeping the current constant. As a result, a thickness of about 2500
The anodic oxide 16 of Å was formed around the gate electrode.
Hereinafter, the anodic oxide and the gate electrode are collectively referred to as a gate electrode portion. (FIG. 1 (B))

Then, by the plasma doping method,
An impurity element, for example, phosphorus was introduced into the silicon region using the gate electrode as a mask. The conditions of the plasma doping were as follows. Dose amount: 1 × 10 ¹⁵ cm ⁻² Acceleration voltage: 80 kV RF plasma power: 10 to 20 W As a result, source / drain regions (impurity regions) 17 were formed. (Fig. 1 (C))

Next, the silicon oxide film 14 other than that existing under the gate electrode was removed by etching with hydrofluoric acid. Then, a KrF excimer laser was irradiated in this state to activate the laser. The conditions for laser activation are as follows. Laser energy density: 200 mJ / cm ² Number of shots: 5 Substrate temperature: 300 ° C. Atmosphere: 100% nitrogen Laser energy density was as small as 200 mJ / cm ² , but was sufficiently activated because the silicon film was exposed. Was able to do. The dose is 1 /
Typically between 300 and 500, even though it is less than 4
A sheet resistance of Ω / □ was obtained. (Fig. 1 (D))

Thereafter, a silicon oxide film having a thickness of 2000 to 3000 ° was deposited as an interlayer insulator 18 by a plasma CVD method, a contact hole was provided in the silicon oxide film, and source and drain electrodes 19 were formed. In this way,
The TFT is completed. (FIG. 1 (E))

The typical mobility of the obtained TFT (N-channel) was 50 to 90 cm ² / Vs. In addition, the TFT manufactured in this manner and a conventional method (dose amount: 4
× 10 ¹⁵ cm ^-2 , laser energy: 250 mJ / c
m ² , substrate temperature: room temperature, other conditions were the same)
For the purpose of comparing the reliability with T, the source of each TFT was grounded, and a voltage of 25 V was applied to the drain and the gate for 1 hour. And the ON current decreases by 60
%, But in the case of this embodiment, the former is 0.1%.
V or less, and the latter was also 10% or less, confirming that the reliability was improved.

Embodiment 3 An example of manufacturing a TFT using the present invention will be described with reference to FIGS. Substrate (Corning 7
059) An underlying silicon oxide film 22 was deposited on 21 by 500 to 2500 ° by sputtering. The sputtering atmosphere was oxygen and argon, and the oxygen concentration was 50% or more. Furthermore, a weak (~ 2
0W) Sputtering was performed by nitrogen plasma for 1 to 5 minutes, and a substantially intrinsic amorphous silicon film was deposited at 1500 ° by a plasma CVD method. In this series of steps, it is preferable to perform the process continuously in a device having three or more chambers without exposing the substrate to the atmosphere. Then, at 430 ° C, 3
After the dehydrogenation treatment for 0 to 60 minutes, the amorphous silicon film was changed to a crystalline silicon film by annealing at 550 ° C. for 2 to 4 hours. Then, this silicon film was patterned into island-like silicon regions 23, and a silicon oxide film 24 having a thickness of 1000 ° functioning as a gate insulating film was deposited by a plasma CVD method.
Further, an aluminum film having a thickness of 5
2,000 deposited and patterned to form a gate electrode 2
5 was formed. (Fig. 2 (A))

Thereafter, the substrate was immersed in a 3% solution of tartaric acid in ethylene glycol, and anodic oxidation was performed by passing a current using the platinum electrode as a negative electrode and the aluminum gate electrode 25 as an anode. At this time, the voltage was increased to 220 V while keeping the current constant. As a result, a thickness of about 2500
An anodized oxide 26 was formed around the gate electrode.
Hereinafter, the anodic oxide and the gate electrode are collectively referred to as a gate electrode portion. (FIG. 2 (B))

Then, by the plasma doping method,
An impurity element, for example, phosphorus was introduced into the silicon region using the gate electrode as a mask. The conditions of the plasma doping were as follows. Dose: 2 × 10 ¹⁵ cm ⁻² Acceleration voltage: 80 kV RF plasma power: 10 to 20 W As a result, source / drain regions (impurity regions) 27 were formed. (Fig. 2 (C))

Next, a KrF excimer laser was irradiated to activate the laser. The conditions for laser activation are as follows. Laser energy density: 250 mJ / cm ² Number of shots: 5 Substrate temperature: 300 ° C. Atmosphere: Nitrogen 100% Despite the dose amount is 以下 or less of the conventional, the sheet resistance is typically 300 to 500 Ω / □. was gotten.
(FIG. 2 (D))

Thereafter, a silicon oxide film having a thickness of 2000 to 3000 ° was deposited as an interlayer insulator 28 by a plasma CVD method, a contact hole was provided in the silicon oxide film, and a source / drain electrode 29 was formed. In this way,
The TFT is completed. (FIG. 2 (E))

The typical mobility of the obtained TFT (N-channel) was 70 to 140 cm ² / Vs. Example 2
As in the case of the above, when a reliability test was performed on the TFT manufactured according to this embodiment and the TFT manufactured according to the conventional method, it was found that the TFT according to this embodiment was superior.

[0033]

The effects of the present invention, directly and indirectly, are as follows: (1) In the pulse laser activation of a silicon semiconductor doped with impurities by means of high energy ion irradiation or the like, crystal defects are reduced and reliability is improved. (2) Improve mass productivity by reducing dose, (3) Improve reliability by reducing dose, (4) Reduce energy density required for laser activation. (5) In manufacturing a thin film semiconductor device such as a TFT, stress is reduced when laser is activated in a portion where impurities are introduced in a self-aligned manner (self-alignment). Therefore, it is to improve reliability. As described above, the present invention has many effects, and has a great industrial value.

[Brief description of the drawings]

FIG. 1 shows a manufacturing process diagram (cross-sectional view) of a TFT in Example 2.

FIG. 2 shows a manufacturing process diagram (cross-sectional view) of a TFT in Example 3.

FIG. 3 shows the substrate temperature dependence of the sheet resistance of a silicon film.

FIG. 4 shows the dose dependence of the sheet resistance of a silicon film.

FIG. 5 shows the dose dependence of the sheet resistance of a silicon film.

[Explanation of symbols]

 11, 21 ... substrate (Corning 7059) 12, 22 ... base film (silicon oxide) 13, 23 ... island-like silicon film 14, 24 ... gate insulating film (silicon oxide) 15, 25 ..Gate electrodes (aluminum) 16, 26 ... anodized oxide (aluminum oxide) 17, 27 ... impurity regions (source, drain) 18, 28 ... interlayer insulator (silicon oxide) 19, 29 ..Source and drain electrodes

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[Procedure amendment]

[Submission date] March 6, 2000 (200.3.6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

4. A silicon oxide film is formed on a substrate by using TEOS, an amorphous silicon film is formed on the silicon oxide film, the amorphous silicon film is dehydrogenated, and the amorphous silicon film is crystallized. a crystalline silicon film, an insulating film is formed on the crystalline silicon film, said insulating film a gate electrode formed on said gate electrodes a method for manufacturing a semiconductor device you introduce impurities as a mask A method of manufacturing a semiconductor device, wherein the silicon oxide film and the amorphous silicon film are continuously formed in a film forming apparatus having two or more chambers. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 6, 2000 (200.3.6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroyuki Zhang 398 Hase, Hase, Atsugi-shi, Kanagawa Inside the Semi-Conductor Energy Laboratory Co., Ltd. Inside

Claims (4)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: forming a silicon oxide film on a substrate by using TEOS; forming an amorphous silicon film on the silicon oxide film; and crystallizing the amorphous silicon film. A method for manufacturing a semiconductor device, wherein a silicon film and the amorphous silicon film are continuously formed in a film forming apparatus having two or more chambers. 2. A silicon oxide film is formed on a substrate using TEOS, an amorphous silicon film is formed on the silicon oxide film, the amorphous silicon film is dehydrogenated, and the amorphous silicon film is crystallized. A method for manufacturing a semiconductor device, wherein the silicon oxide film and the amorphous silicon film are continuously formed in a film formation apparatus having two or more chambers. 3. A silicon oxide film is formed on a substrate by using TEOS, an amorphous silicon film is formed on the silicon oxide film, and the amorphous silicon film is crystallized into a crystalline silicon film. Forming an insulating film on the film; forming a gate electrode on the insulating film; introducing impurities into the crystalline silicon film using the gate electrode as a mask; and forming an interlayer insulating film on the gate electrode and the insulating film. Wherein the silicon oxide film and the amorphous silicon film are continuously formed in a film forming apparatus having two or more chambers. 4. A silicon oxide film is formed on a substrate using TEOS, an amorphous silicon film is formed on the silicon oxide film, the amorphous silicon film is dehydrogenated, and the amorphous silicon film is crystallized. Forming a crystalline silicon film, forming an insulating film on the crystalline silicon film, forming a gate electrode on the insulating film, introducing impurities using the gate electrode as a mask, on the gate electrode and on the insulating film. A method for manufacturing a semiconductor device, comprising: forming a silicon oxide film and an amorphous silicon film continuously in a film forming apparatus having two or more chambers. Method.