JP2000269133A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a homegeneous and high-quality crystalline semiconductor film by forming a silicon oxide film which will be a base protective film, on a substrate, and forming a semiconductor film mainly made of silicon on the base protective film, and then casting the pulse laser light having a wavelength within a specified range on the semiconductor film. SOLUTION: A silicon oxide film is deposited on a substrate 101 by a plasma chemical vapor phase deposition method to form a base protective film 102. On the base protective film 102, an intrinsic amorphous silicon film is deposited. Second higher harmonic waves of the pulse laser light having a wavelength between 370 nm and 710 nm which is pulse-oscilated is cast on the amorphous silicon film to melt and recrystallize it into a crystalline silicon film. The crystalline silicon film is patterned to form an island 103 of a semiconductor film. Then, the island 103 of the semiconductor film is coated by a silicon oxide film 104. Immediately before this, the oxygen plasma is cast to deposit an oxide film, which is formed into a gate electrode 105 by a sputtering method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a polycrystalline semiconductor film having excellent crystallinity at a relatively low temperature of about 600 ° C. or less, preferably about 425 ° C. or less. In particular, the present invention relates to a manufacturing method for significantly improving the performance of a thin film semiconductor device represented by a polycrystalline silicon thin film transistor by using this technique.

[0002]

2. Description of the Related Art Polycrystalline silicon thin film transistors (p-Si
TFTs) are manufactured at a low temperature of about 600 ° C. or less, at which a general-purpose glass substrate can be used, or at a low temperature of about 425 ° C. or less, which is about the same as the manufacturing temperature of an amorphous silicon thin film transistor (a-Si TFT). In such a case, the following manufacturing method has conventionally been adopted. First, an amorphous silicon film serving as a semiconductor film is deposited on a substrate to a thickness of about 50 nm by low pressure chemical vapor deposition (LPCVD). Next, the amorphous film is irradiated with a XeCl excimer laser (wavelength 308 nm) to form a polycrystalline silicon film (p-Si film). XeCl
Absorption coefficient in amorphous silicon and polycrystalline silicon in the excimer laser light其s 0.139Nm ^-1 and 0.149nm ^-1
90% of the laser light incident on the semiconductor film is absorbed within 15 nm from the surface. Also, the absorption coefficient of amorphous silicon is about 7% smaller than that of polycrystalline silicon. Thereafter, a silicon oxide film serving as a gate insulating film is formed by chemical vapor deposition (CVD) or physical vapor deposition (PCVD).
VD method). Next, a gate electrode is made of tantalum or the like to form a field effect transistor (MOS-FET) composed of a metal (gate electrode) -oxide film (gate insulating film) -semiconductor (polycrystalline silicon film). Finally, an interlayer insulating film is deposited on these films, a contact hole is opened, and wiring is formed with a metal thin film, thereby completing a thin film semiconductor device.

[0003]

However, in the conventional method of manufacturing a thin film semiconductor device, it is difficult to control the energy density of the excimer laser light, and the semiconductor film can be formed on the same substrate even by a slight change in the energy density. Even in this case, there was great variation. In addition, even when the irradiation energy density is slightly larger than the threshold determined according to the film thickness or the hydrogen content, the semiconductor film is severely damaged, and the semiconductor characteristics and the product yield are remarkably reduced. In order to obtain a homogeneous polycrystalline semiconductor film in the substrate from such a thing,
It was necessary to set the energy density of the laser beam to be considerably lower than the optimum value. Therefore, in order to obtain a good polycrystalline thin film, it was inevitable that the energy density was insufficient. Further, even if laser irradiation is performed at an optimum energy density, it is difficult to increase the crystal grains constituting the polycrystalline film, and in fact, many defects remain in the film. In accordance with such a fact, in order to stably manufacture a thin film semiconductor device such as a p-Si TFT by a conventional manufacturing method, there is a problem that the electric characteristics of a completed thin film semiconductor device must be sacrificed. Had it.

Accordingly, the present invention has been made in view of the above-mentioned circumstances and aims at a temperature of about 600 ° C. or less, ideally 425 ° C.
It is an object of the present invention to provide a method for stably manufacturing an excellent thin film semiconductor device in a low-temperature process at a temperature lower than the order.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a thin film semiconductor device using a crystalline semiconductor film mainly composed of silicon (Si) formed on a substrate as an active layer.
A base protection film forming step of forming a silicon oxide film serving as a base protection film on the substrate; a first step of forming a semiconductor film mainly containing silicon (Si) on the base protection film;
A second step of irradiating a pulsed laser beam having a wavelength of 70 nm or more and 710 nm or less. At this time, if the wavelength of the pulse laser beam is λ (nm) and the thickness of the semiconductor film is d (nm), the wavelength λ is 440 nm.
In the case where the wavelength is not less than 710 nm, the wavelength λ and the film thickness d are 9.8 × 10 ^{αL2 (λ-440)} <d <53 × 10
^{αH2 (λ-440)} However, it is preferable that the relational expression of αL2 = 4.9 × 10 ⁻³ nm ^{−1 and} αH2 = 5.4 × 10 ⁻³ nm ⁻¹ be satisfied. Further, the film thickness d
And λ are 9.8 × 10 ^{αL2 (λ-440)} <d <32 × 10
^{αM2 (λ-440)} However, it is more preferable to satisfy the relational expression of αL2 = 4.9 × 10 ⁻³ nm ^{−1 and} αM2 = 5.2 × 10 ⁻³ nm ⁻¹ . Nd: YAG is the most excellent type of pulsed laser light.
It is the second harmonic of laser light (abbreviated as YAG2ω; its wavelength is 532 nm). When the wavelength λ is 370 nm or more and 440 nm or less, the wavelength λ and the film thickness d are 2.4 × 10 ^{αL1 (λ-370)} <d <11.2 × 1
0 ^{αH1 (λ-370)} where αL1 = 8.7 × 10 ⁻³ nm ^{−1 It} is desirable that the relational expression of αH1 = 9.6 × 10 ⁻³ nm ⁻¹ be satisfied. More preferably, the wavelength λ and the film thickness d are 2.4 × 10 ^{αL1 (λ-370)} <d <6.0 × 10
^{αM1 (λ-370)} where αL1 = 8.7 × 10 ⁻³ nm ⁻¹ αM1 = 1.04 × 10 ⁻² nm ⁻¹ . The more preferable wavelength of the pulse laser beam is about 450 nm or more and about 650 nm or less, and ideally about 532 nm.

It is desirable that the pulse laser light is formed by a solid-state light emitting element, and the second harmonic of Nd: YAG laser light is suitable. In order to manufacture an excellent thin film semiconductor device, when the pulsed laser light is irradiated on the semiconductor film, the fluctuation of the irradiation energy density of the laser light on the semiconductor film is about 5% of its average value. It is required to be less than.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glass having a strain point temperature of 55.
Method for manufacturing thin-film semiconductor device using crystalline semiconductor film formed on various transparent substrates such as low heat-resistant glass substrate at about 0 ° C. to 650 ° C. or high heat-resistant plastic substrate as active layer And an underlying protective film forming step of forming a silicon oxide film serving as an underlying protective film on the substrate; a first step of forming a silicon (Si) -based semiconductor film on the underlying protective film; Irradiating a pulsed laser beam to the semiconductor film formed in the same manner as above.
The feature is achieved by being less than 0 nm. Among such pulse laser beams, the absorption coefficient μ _pSi of the pulse laser beam in polycrystalline silicon is not less than 10 ⁻³ nm ^{−1 and not} more than 10 ₋₁₀ nm.
^-2 nm ^-1 or less is more preferable.

In the first step, silicon (Si) is formed on the underlying protective film.
A semiconductor film mainly composed of is formed. Silicon film (Si) or silicon germanium film as a semiconductor film _(Si x G
e _1−x : A semiconductor material represented by 0 <x <1 is used, and silicon is used as a main constituent element (silicon atomic composition ratio is 80%).
Degree or more). As the substrate, a transparent non-alkali glass used for a liquid crystal display device, or an insulating substrate such as plastic or ceramic is usually used. However, as long as the substrate has a heat resistance of about 550 ° C. or more, the type is not limited. On the surfaces of these substrates, a silicon oxide film is deposited as a base protective film for the semiconductor film on the order of 100 nm to 10 μm. The silicon oxide film as a base protective film not only provides electrical insulation between the semiconductor film and the substrate, or prevents diffusion of impurities contained in the substrate into the semiconductor film, but also prevents the base oxide film from being crystalline. The interface with the semiconductor film is made of good quality. In the present invention, the semiconductor film of the thin-film semiconductor device has a thickness of about 10 nm to about 200 nm, and the energy band is bent over the entire region in the thickness direction of the semiconductor film (corresponding to a fully depleted SOI model). Is the main target. In such a situation, the interface between the underlying protective film and the semiconductor film, as well as the interface between the gate insulating film and the semiconductor film, has a considerable effect on electric conduction. Since a silicon oxide film is a substance that can reduce the interface trap level when forming an interface with a semiconductor film, it is suitable as a base protective film. The semiconductor film is formed on the underlying protective film. Therefore, as a base protective film, an interface with the semiconductor film is 10 ¹² cm.
It is desired in the present application to use a silicon oxide film having an interface state of about ^-2 or less. Further, in the present invention, the lower part of the semiconductor film is more likely to be heated to a high temperature than in the prior art, so that impurity diffusion from the substrate easily occurs. In order to prevent this and to produce an excellent thin film semiconductor device using a high-purity semiconductor film in the present invention, it is essential to use a dense silicon oxide film having a high density as a base protective film. Such a silicon oxide film has an etching rate of 1.5 n in an aqueous solution of hydrofluoric acid (HF) having a liquid temperature of 25 to 5 ° C. and a concentration of 1.6 to 0.2%.
m / s or less. Usually, the underlayer protective film is formed by a vapor deposition method such as a plasma enhanced chemical vapor deposition (PECVD), a low pressure chemical vapor deposition (LPCVD), or a sputtering method. Among them, in order to prepare a base protective film particularly suitable for the present invention, among the PECVD methods, an electron cyclotron resonance PECVD method (ECR-PECVD) is used.
Method), a helicon PECVD method, or a remote PECVD method. Also, the industrial frequency (13.56
MHz) or a general-purpose PECV using an integer multiple of that frequency
To obtain a silicon oxide film suitable for the present invention by the D method, TEOS as a raw material _{(Si- (O-CH 2 CH} 3) 4)
And oxygen (O ₂ ), and the oxygen flow rate was set at 5 times the TEOS flow rate.
It is sufficient to deposit the silicon oxide film by setting it to twice or more. Alternatively, monosilane (SiH ₄ ) and nitrous oxide (N ₂ O) are used as raw materials, and helium (He) is used as a diluent gas.
Alternatively, using a rare gas such as argon (Ar), the proportion of the rare gas in the total gas flow is about 90% or more (that is, the proportion of the raw material in the total gas flow is less than about 10%), and the silicon oxide film is used. Should be deposited. At that time, the substrate temperature was 280 ° C.
It is hoped that this is the case. When the substrate is made of high-purity quartz, the underlying protective film and the quartz substrate can be used in combination. It is preferable to form a base protective film.

A semiconductor film in an amorphous state or a polycrystalline state is formed on a base protective film by a chemical vapor deposition method (CVD method), preferably a higher order silane (Si _n H _{2n + 2} : n = 2,3,3).
4) is used as a source gas to form a deposit.
Plasma chemical vapor deposition (PECVD) is used for semiconductor film deposition.
), Low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), and sputtering, but various types of vapor deposition are possible. From the standpoint of deposition, low pressure chemical vapor deposition (LPCVD) is particularly suitable. The low pressure chemical vapor deposition method is performed in a high vacuum type low pressure chemical vapor deposition apparatus. This is to increase the purity of the semiconductor film and minimize the generation of crystal nuclei due to impurities so that the crystalline semiconductor film finally obtained by the present invention is composed of high purity and large crystal grains. It is for the purpose. In particular, in the present invention, since the semiconductor film is relatively uniformly heated in the thickness direction in the second step to promote the crystal growth in the lateral direction, the generation of crystal nuclei due to impurities is minimized. A polycrystalline semiconductor thin film composed of crystal grains can be easily obtained. The high-vacuum type is an apparatus in which the degree of background vacuum in a film forming chamber immediately before semiconductor film deposition can be reduced to about 5 × 10 ⁻⁷ Torr or less. Such a high-vacuum type low-pressure chemical vapor deposition apparatus not only has excellent airtightness in the film forming chamber, but also has a pumping speed in the film forming chamber of 100 sccm / mTorr (inert gas of 1 inert gas).
The equilibrium pressure obtained when flowing into the 00 sccm deposition chamber is 1
It is further desired to have a pumping capacity of at least about (a pumping speed of mTorr). In such a device having a high pumping capacity, the degas flow rate from the substrate or the like can be sufficiently reduced in a relatively short time of about one hour, and high-purity semiconductor thin film can be deposited while maintaining high productivity. Because it is.

It is preferable that a semiconductor film mainly composed of silicon typified by an amorphous silicon film is deposited using high order silane (Si _n H _{2n + 2} : n is an integer of 2 or more) as a kind of source gas. In consideration of price and safety, disilane (Si ₂ H ₆ ) is most suitable as the higher order silane. When disilane is applied to low-pressure chemical vapor deposition, a high-purity amorphous silicon film can be obtained at a relatively low deposition rate of about 0.5 nm / min or more at a low temperature of about 425 ° C. or less. In order to obtain a high-quality amorphous semiconductor film suitable for the present invention, it is important to control the deposition temperature and the deposition rate. Deposition temperature is 430
It is necessary to determine the flow rate of disilane and the pressure at the time of film formation so that the temperature is about not higher than about ° C and the deposition rate is about 0.6 nm / min or more.

When a large substrate having a substrate area of about 2000 cm ² or more is used, it becomes difficult to use the LPCVD method. Under such circumstances, the plasma box type PE
A semiconductor film is deposited by a CVD device. In a plasma-box-type PECVD apparatus, a film formation chamber for performing a plasma treatment is installed in another vacuum chamber larger than the chamber, so that the background vacuum degree in the film formation chamber is not more than about 1 × 10 ⁻⁶ Torr. And Although the degree of background vacuum is inferior to that of a high-vacuum LPCVD apparatus, the deposition rate of the semiconductor film can be increased to about 3 nm / min or more. As a result, a high-purity semiconductor film in which generation of crystal nuclei due to impurities is minimized is obtained. Can be PECVD method to adapt to the present invention, the background vacuum degree in the deposition chamber as more than about 1 la ¹⁰ -6 Torr,
In addition, the semiconductor film is deposited under the condition that the deposition rate of the semiconductor film is about 3 nm / min or more. The substrate temperature during the deposition of the amorphous film is between about 350 ° C. and 450 ° C. 35
If the temperature is higher than about 0 ° C., the amount of hydrogen contained in the amorphous film can be reduced to about 8% or less, and the crystallization in the second step can be performed stably. If the temperature is lower than about 450 ° C., the amorphous grains constituting the amorphous film become large, and the crystal grains constituting the polycrystalline film obtained when the amorphous film is crystallized become large. To stably promote laser crystallization in the second step, the amount of hydrogen in the amorphous semiconductor film is preferably set to less than about 5% with respect to silicon. Such a silicon film having a small hydrogen content is formed at a deposition rate of 25 nm / min or less. When the PECVD method is applied, monosilane can be used as a raw material gas in addition to disilane.

After the amorphous semiconductor film or the polycrystalline semiconductor film is thus obtained, the semiconductor film is irradiated with a pulsed laser beam as a second step to crystallize the amorphous semiconductor film.
Alternatively, recrystallization of the polycrystalline semiconductor film is advanced. A continuous wave laser beam can be used as the laser beam, but a pulsed laser beam is more preferably used. That is, as will be described later, the present invention promotes the lateral growth of the crystal. In this case, the pulse oscillation that can move an appropriate distance for each irradiation is larger than the continuous oscillation, This is because a polycrystalline semiconductor thin film made of When the semiconductor film is irradiated with laser light, pulse laser light having a wavelength λ of 370 nm or more and 710 nm or less is used. FIG. 1 shows the absorption coefficients of these lights in amorphous silicon and polycrystalline silicon. The horizontal axis in FIG. 1 is the wavelength of light, and the vertical axis is the absorption coefficient. Dashed line (Amorp
hous Silicon) represents amorphous silicon, solid line (Polysilicon)
Represents polycrystalline silicon. As can be seen from FIG.
In the wavelength range from 0 nm to 710 nm, the light absorption coefficient is larger in amorphous silicon than in polycrystalline silicon. For example, the absorption coefficient μ _{aSi of} YAG2ω light having a wavelength of 532 nm in amorphous silicon and the absorption coefficient μ of polycrystalline silicon
_Each of _pSi has μ _aSi (YAG2ω) = 0.01723 nm ⁻¹ _μpSi (YAG2ω) = 0.00426 nm ^−1, which means that the absorption coefficient of amorphous silicon is 4 times higher than that of polycrystalline silicon. More than twice as large. The polycrystalline film is microscopically composed of a crystalline component and an amorphous component.
A crystal component is a portion in a crystal grain where defects such as stacking faults are extremely small, and can be said to be a portion in a substantially single crystal state. On the other hand, the amorphous component is a portion where the structural order is disturbed, such as a crystal grain boundary or a defect portion in the crystal grain, and can be said to be a portion in a so-called amorphous state. In melt crystallization in which crystallization is promoted by irradiating a laser beam, a non-melted portion serves as a nucleus for crystal growth in a cooling and solidifying process. When a crystal component having a high structural order becomes a crystal growth nucleus, a crystal grown therefrom becomes a high-quality crystallized film having a high structural order. On the other hand, if the disordered structural order becomes the crystal growth nucleus, stacking faults etc. will grow from there during the cooling and solidification process, and the finally obtained crystallized film will have low quality including defects etc. It becomes something. Therefore, in order to obtain an excellent crystallized film, it is only necessary to melt the amorphous component preferentially without using the crystal component in the polycrystalline film as a nucleus for crystal growth. In the present invention, since the absorption coefficient of the irradiation laser light in amorphous silicon is larger than the absorption coefficient in polycrystalline silicon, the amorphous component is heated preferentially over the crystalline component. Specifically, the crystal grain boundaries and defect portions are easily melted, and a high-quality crystal component in a substantially single crystal state serves as a crystal growth nucleus. Also, corresponding grain boundaries with high structural order are dominant. This has the effect of significantly reducing the trap level density near the center of the forbidden band in the energy band diagram in view of the electrical characteristics of the semiconductor film. Further, when such a semiconductor film is used as an active layer (source region, drain region, channel formation region) of a thin film semiconductor device, the off-state current value is small, and a sharp sub-threshold characteristic is exhibited (the sub-threshold hold swing value is reduced). (Small) transistor having a low threshold voltage. The reason that such an excellent thin film semiconductor device could not be easily manufactured by the conventional technology is that laser light having a wavelength suitable for melt crystallization is not used, and both the crystalline component and the amorphous component are used together. It can be said that it had been melted. The principle of the present invention described here works most effectively when the ratio (μ _pSi / μ _aSi ) of the absorption coefficient of polycrystalline silicon to the absorption coefficient of amorphous silicon is large. Referring to FIG. 1, the wavelength of light is about 450 nm to 65 nm.
It can be seen that the above ratio becomes large at about 0 nm. Therefore, it can be said that the most preferable wavelength of the pulsed laser beam irradiated in the second step of the present invention is from about 450 nm to about 650 nm. The absorption coefficient μ _pSi of light having a wavelength of 450 nm in polycrystalline silicon is 1.127 × 10 ⁻² nm.
⁻¹ , the absorption coefficient μ _pSi of light having a wavelength of 650 nm in polycrystalline silicon is 8.9 × 10 ⁻⁴ nm ⁻¹ . Therefore, in the second step of irradiating a pulse laser beam having a wavelength of about 450 nm or more and about 650 nm or less, the absorption coefficient μ _pSi in polycrystalline silicon is approximately 1 as the pulse laser light.
An object having a size of from 0 ⁻³ nm ^{−1 to} 10 ⁻² nm ⁻¹ is used.

In order to obtain a high-quality polycrystalline semiconductor film, oscillation stability of laser light is the most important. Therefore, it is desirable that pulsed laser light is formed by a solid-state light emitting device. (In the present application, this is abbreviated as a solid-state laser.) In a conventional excimer gas laser, it depends on non-uniformity of gas such as xenon (Xe) or chlorine (Cl) in a laser oscillation chamber, deterioration of gas itself or halogen. Due to corrosion in the oscillation chamber and the like, the variation in oscillation intensity was about 5%, and the variation in oscillation angle was also about 5%. Variations in the oscillation angle lead to variations in the area of the irradiation region, and as a result, the energy density on the semiconductor film surface (energy value per unit area)
Fluctuated by more than 10% in total, which was one of the hindrance factors in manufacturing an excellent thin film semiconductor device. Further, the laser oscillation lacks long-term stability, causing lot-to-lot variation of thin film semiconductor devices. On the other hand, since such a problem cannot exist in the solid-state laser, the laser oscillation is extremely stable, and the fluctuation of the energy density on the surface of the semiconductor film is less than about 5% of its average value. It is possible. In order to more effectively use the present invention, the fluctuation of the laser energy density on the surface of the semiconductor film is 5%.
It is required to use a solid-state laser that is less than the degree. Furthermore, the use of solid-state lasers has the effect of minimizing lot-to-lot variations during thin-film semiconductor device manufacturing, and frees the production of thin-film semiconductor devices from the cumbersome gas exchange work that has been frequently performed in the past. This has the effect of leading to an improvement in productivity and a reduction in price when manufacturing a thin film semiconductor device. The requirement of the wavelength and the absorption coefficient and the requirement of the solid-state laser can be simultaneously satisfied by the second harmonic (YAG) of the Nd: YAG laser light.
2ω light, wavelength 532 nm). Therefore, in the second step of the present invention, the fluctuation of the energy density is 5% of the average value.
It is most suitable to irradiate the semiconductor film with YAG2ω light of less than about%.

Now, light is absorbed in the semiconductor film, and the intensity of the incident light is attenuated exponentially. Now, let the incident light intensity be I ₍₀₎ , the distance from the surface in the silicon-based polycrystalline semiconductor film be x (nm), and the intensity at location x be I _{(0).
Assuming (x)} , the following relationship is established between them using the absorption coefficient μ _pSi .

I _(x) / I ₍₀₎ = exp ( _−μpSi · x) (Equation 1) When the absorption coefficient _μpSi is 10 ⁻³ nm ⁻¹ and 10 ⁻²
In the case of nm- ^1, the case of the second harmonic (YAG2ω light) of the Nd: YAG laser beam which is the most excellent pulse laser beam of the present invention, and the case of the XeCl excimer laser beam of the prior art, FIG. 2 shows the relationship. In order for the silicon film to be efficiently heated, at least 10
Since about% needs to be absorbed by the semiconductor film, a horizontal dotted line is drawn at a position of 0.9 which satisfies the condition in FIG. Further, the light intensity means the amount of heat applied to the silicon as it is, and therefore FIG. 2 also shows the temperature distribution in the silicon film during laser light irradiation. According to the research conducted by the applicants, the surface of the semiconductor film is severely damaged by the conventional excimer laser irradiation, while a low-quality semiconductor layer remains under the semiconductor film, thereby obtaining an excellent polycrystalline semiconductor film. The reason for this is due to the large temperature difference existing between the surface and the lower part. The damage to the surface does not occur, and the whole is melted in the thickness direction of the semiconductor film when the light intensity at the lower part of the semiconductor film is about half or more of the incident light intensity. When this condition is satisfied, the temperature difference between the surface and the lower part becomes small. Therefore, in FIG. 2, a horizontal dotted line is also drawn at a position of 0.5 where the light intensity is half of the surface. Therefore, the condition that the semiconductor film mainly composed of silicon is effectively heated, and the favorable crystallization proceeds over the entire film thickness without damaging the semiconductor film is 0.9 in FIG.
And an area between the horizontal dotted line of 0.5 and the horizontal dotted line of 0.5. Since most of the incident light of the conventional XeCl excimer laser light is absorbed on the surface of the semiconductor film, it is understood that the semiconductor film thickness suitable for laser crystallization is limited to 1 nm to 4 nm. On the other hand, under the conditions of the present invention, good crystallization is performed in a wide film thickness range.

In melt crystallization using laser light, a crystal grows along a temperature gradient regardless of which laser light is used. On the other hand, the thickness of a semiconductor film used in a thin film semiconductor device is usually about 30 nm to about 100 nm. As described above, in conventional crystallization using XeCl excimer laser light, most light is absorbed within about 4 nm of the semiconductor film surface, and only the vicinity of the surface is heated. In this case, a steep temperature gradient occurs in the vertical direction (FIG. 3, a-1). For this reason, the crystals grew from the lower part of the semiconductor film toward the surface, and the polycrystalline film obtained after laser irradiation had a strong tendency to be composed of small crystal grains (FIG. 3, a-2). (As described above, in the prior art, since a large number of small crystal grains grew from the bottom to the top, the presence of crystal nuclei due to impurities in the semiconductor film was not a very important problem.) On the other hand, in the present invention, the semiconductor film is uniformly heated in the film thickness direction because a laser beam having an absorption coefficient most suitable for melt crystallization is irradiated. As a result, at the end of the laser irradiation area, a temperature gradient is generated in the lateral direction (FIG. 3, b-1), and the crystal grows more easily in the lateral direction than in the vertical direction. That is, large crystal grains grow at the end of the irradiation area (FIG. 3, b-2). Since the temperature difference in the vertical direction is small even at locations other than the ends in the irradiation region, the probability of generating crystal nuclei at the lower portion of the semiconductor film is significantly reduced as compared with the conventional case, and the crystal constituting the polycrystalline semiconductor film on average The grains are larger than before. Lateral crystal growth is promoted when the light intensity between the surface and the lower part does not change so much. According to experiments, the light intensity at the lower part of the semiconductor film is about one third or more of the incident light intensity. This is the case. In FIG. 2, a horizontal dotted line is drawn at a position of 0.667 under the condition that horizontal growth is likely to occur. Therefore, the conditions under which the semiconductor film mainly composed of silicon is effectively heated and the lateral growth occurs to form a polycrystalline semiconductor film composed of large crystal grains are shown in FIG. And the area between the horizontal dotted lines.
Needless to say, in order to enlarge the crystal grains, it is necessary to suppress the crystal nuclei based on impurities in addition to the temperature gradient. Therefore, the above-mentioned consideration is required also for the formation of the base protective film and the semiconductor film in the first step.

Referring to FIG. 2, the absorption coefficient is 10 ⁻³ nm.
^It can be seen that even if the thickness is not less than ^{-1 and not} more than 10 ⁻² nm ⁻¹ , an excellent polycrystalline film cannot be obtained with all semiconductor film thicknesses. For example, YAG2ω light (absorption coefficient μ _pSi = 4.2
In the case of 6 × 10 ⁻³ nm ⁻¹ ), the silicon film is effectively heated when the thickness of the semiconductor film is about 25 nm or more.
The entire film thickness is substantially melted without any damage on the surface when the thickness of the semiconductor film is about 165 nm or less. Also, the lateral growth occurs and the crystal grains become large when the semiconductor film thickness is about 95 nm or less. Therefore, when the YAG2ω laser beam is applied to the semiconductor film mainly composed of silicon, the preferable thickness of the semiconductor film is about 25 nm to about 165 nm, and ideally about 25 nm to about 95 nm. The optimum semiconductor film thickness varies depending on the wavelength and absorption coefficient of the laser light used in polycrystalline silicon as described above. Specifically, the silicon film is effectively heated, and the entire film thickness is substantially melted without surface damage. In Equation 1, x is defined as the thickness d of the semiconductor film, and I _(d) / I ₍₀₎ is set to 0.1. Since it is between 5 and 0.9, it is expressed as 0.5 <I _(d) / I ₍₀₎ <0.9 (Equation 2). When Equation 2 is solved for d using Equation 1, a relational expression of 0.105 · μ _pSi ⁻¹ <d <0.693 · μ _pSi ^-1 (Equation 3) is obtained. Similarly, the silicon film is effectively heated and lateral growth occurs to increase the crystal grain size.
_{(D) Since} / I ₍₀₎ is between 0.667 and 0.9, the relationship with 0.405 · μ _pSi ⁻¹ <d <0.693 · μ _pSi ^-1 (Equation 4) An expression is obtained. When the thickness d of the semiconductor film and the absorption coefficient μ _{pSi of} the pulsed laser beam applied to the semiconductor film in the polycrystalline silicon satisfy the above-mentioned formulas 3 and 4, an excellent polycrystalline semiconductor thin film must be obtained. As a result, an excellent thin film semiconductor device is manufactured.

The relationship between the above equations 3 and 4 is redrawn into the relationship between the wavelength and the thickness of the silicon-based semiconductor thin film in consideration of the relationship between the wavelength of light and the absorption coefficient shown in FIG. The thing is in FIG. The semiconductor thin film is heated in a region above the triangle in FIG. 4, and an irradiation energy density can be present in a region below the circle without causing surface damage and melting in the entire thickness of the semiconductor film. Further, in the region below the square mark, the temperature difference between the upper and lower portions becomes smaller, so that the lateral growth of the crystal is promoted. In FIG. 4, circles, squares, and triangles are further approximated by straight lines. Using this approximate straight line, the wavelength λ is 440
In the case of not less than nm and not more than 710 nm, the wavelength λ and the film thickness d are 9.8 × 10 ^{αL2 (λ-440)} <d <53 × 10
^{αH2 (λ-440)} where αL2 = 4.9 × 10 ⁻³ nm ⁻¹ If the relational expression of αH2 = 5.4 × 10 ⁻³ nm ⁻¹ is satisfied, a semiconductor thin film mainly composed of silicon is obtained. It is possible to heat the thin film in the thickness direction of the semiconductor film efficiently without being heated efficiently and without damaging the surface. For example, when YAG2ω light is used as laser light, the wavelength is 532 nm, and the semiconductor film thickness that satisfies this condition is from 28 nm to 166 nm. Further, the film thickness d and the wavelength λ are 9.8 × 10 ^{αL2 (λ-440)} <d <32 × 10
^{αM2 (λ-440)} where αL2 = 4.9 × 10 ⁻³ nm ⁻¹ If the relational expression of αM2 = 5.2 × 10 ⁻³ nm ⁻¹ is satisfied, the semiconductor thin film mainly composed of silicon is This is more preferable because it is efficiently heated and promotes the lateral growth of the crystal. If YAG2ω light is used as the laser light, the semiconductor film thickness should be 9 nm to 9 nm.
At 6 nm, this condition is satisfied.

Similarly, the wavelength λ is 370 nm or more and 440 nm.
In the following case, the wavelength λ and the film thickness d are 2.4 × 10^{αL1 (λ-370)}<D <11.2 × 1
0^{αH1 (λ-370)} However, αL1 = 8.7 × 10−³ nm^-1 αH1 = 9.6 × 10^-3 nm^-1 If the relational expression is satisfied, silicon-based semiconductors
The film is heated efficiently and is half-finished without surface damage.
Almost the entire thin film can be melted in the thickness direction of the conductor film.
You. The wavelength λ and the film thickness d are 2.4 × 10^{αL1 (λ-370)}<D <6.0 × 10
^{αM1 (λ-370)}  However, αL1 = 8.7 × 10^-3 nm^-1 αM1 = 1.04 × 10^-2 nm^-1 If the relational expression is satisfied, silicon-based semiconductors
The thin film is efficiently heated, and the crystal grows in the lateral direction.
It is more preferable because it is accelerated.

Embodiment 1 FIGS. 5A to 5D show MOS transistors.
FIG. 4 is a cross-sectional view showing a manufacturing process of a thin-film semiconductor device for forming a field-effect transistor. In the first embodiment, the substrate 1
As No. 01, non-alkali glass having a glass strain point of 650 ° C. was used. However, even with other substrates, if they can withstand the maximum temperature during the thin film semiconductor device manufacturing process,
The type and size are of course not questioned. First, a silicon oxide film serving as a base protective film 102 is deposited on a substrate 101. When the substrate is a ceramic substrate or the like and contains undesirable impurities in the semiconductor film, a first underlayer protective film such as a tantalum oxide film or a silicon nitride film may be deposited before the silicon oxide film is deposited. In Example 1, a silicon oxide film having a thickness of about 200 nm was deposited on the substrate 101 by a plasma enhanced chemical vapor deposition (PECVD) method to form a base protective film 102. Silicon oxide film is EC
It was deposited under the following deposition conditions by R-PECVD.

Monosilane (SiH ₄ ) flow rate: 60 sccm Oxygen (O ₂ ) flow rate: 100 sccm Pressure: 2.40 mTorr Microwave (2.45 GHz) output: 2250 W Applied magnetic field: 875 Gauss Substrate temperature ... 100 ° C Film formation time ... 40 seconds The etching rate of this oxide film in a hydrofluoric acid aqueous solution having a solution temperature of 25 ° C and a concentration of 1.67% is 0.5 nm / s.
It was.

As a first step, an intrinsic amorphous silicon film was deposited to a thickness of about 50 nm on the thus formed base protective film by a high vacuum LPCVD apparatus. High vacuum LPCVD
The device is a hot wall type with a capacity of 184.5 l,
Total area of depositable area after substrate insertion is about 44000cm
^{It is 2} . The maximum pumping speed in the deposition chamber is 120 scc
m / mTorr. The deposition temperature was 425 ° C., and the substrate was heated and dried at this temperature for 1 hour and 15 minutes before depositing the semiconductor film. During the drying heat treatment, helium (He) having a purity of 99.9999% or more was 200 (sccm) and the purity was 99.99 in the film formation chamber in which the substrate was installed.
Hydrogen (H ₂ ) of 99% or more was introduced at 100 (sccm), and the pressure in the film formation chamber was maintained at about 2.5 mTorr. After the drying process is completed, the background degree of vacuum in the film forming chamber immediately before the deposition of the semiconductor film is 2.5 l
^-7 Torr. When depositing an amorphous silicon film, disilane (Si ₂ H ₆ ) having a purity of 99.99% or more
At a flow rate of 00 sccm and a deposition pressure of about 1.1 T
kept at orr. Under these conditions, the deposition rate of the silicon film is 0.77 nm / min.

Next, as a second step, the intrinsic amorphous silicon film obtained in the first step was irradiated with the second harmonic of Nd: YAG laser light that oscillates in a pulsed manner to perform melting and recrystallization. The time half-width of the pulse laser beam was about 60 ns, and the transmission frequency was 200 Hz. The laser light was condensed in a linear form having a width of 270 μm and a length of 5 mm, and the linear light was shifted by 2.5% in the width direction for each irradiation to scan the substrate.
Therefore, any one point on the semiconductor film has been subjected to about 40 laser irradiations. Laser beam irradiation energy density is 7
It is 50 mJ · cm ⁻² . The variation of the irradiation energy density on the semiconductor film surface with respect to the average value was about 4%. In the YAG2ω laser beam used in the first embodiment, the energy density for melting only the outermost surface of the semiconductor film of 50 nm is about 200 mJ · cm ⁻² , and the energy density for completely melting the semiconductor film is about 800 mJ · cm ^−2. Therefore, about 92% of the semiconductor film is melted. The crystalline silicon film thus obtained was patterned to form a semiconductor film island 103. (FIG. 5-a) Next, a silicon oxide film 104 was formed by ECR-PECVD so as to cover the island 103 of the semiconductor film subjected to patterning. This silicon oxide film functions as a gate insulating film of the semiconductor device. The conditions for depositing the silicon oxide film as the gate insulating film are the same as the conditions for depositing the silicon oxide film as the base protective film, except that the deposition time is reduced to 24 seconds. However, immediately before the deposition of the silicon oxide film, the substrate was irradiated with oxygen plasma in an ECR-PECVD apparatus to form a low-temperature plasma oxide film on the surface of the semiconductor. The plasma oxidation conditions are as follows.

Oxygen (O ₂ ) flow rate: 100 sccm Pressure: 1.85 mTorr Microwave (2.45 GHz) output: 2000 W Applicable magnetic field: 875 Gauss Substrate temperature: 100 ° C. Processing time: An oxide film of about 3.5 nm is formed on the semiconductor surface by plasma oxidation for 24 seconds. After the oxygen plasma irradiation ends,
An oxide film was deposited continuously while maintaining the vacuum. Therefore, the silicon oxide film serving as the gate insulating film was composed of a plasma oxide film and a vapor deposition film, and had a thickness of 122 nm. Thus, the deposition of the gate insulating film was completed. (FIG. 5-b) Subsequently, the gate electrode 105 is formed by a sputtering method using a metal thin film. The substrate temperature during sputter is 150 ° C
It was. In the first embodiment, α having a thickness of 750 nm
A gate electrode was formed from tantalum (Ta) having a structure, and the sheet resistance of the gate electrode was 0.8Ω / □. Next, using the gate electrode as a mask, an impurity ion 106 serving as a donor or an acceptor is implanted, and a source / drain region 107 and a channel formation region 108 are formed in a self-aligned manner with respect to the gate electrode. In the first embodiment, the CMOS
A semiconductor device was manufactured. When fabricating an NMOS transistor, the PMOS transistor portion is made of aluminum (A
l) After covering with a thin film, 5%
Phosphine (PH ₃ ) diluted at a concentration of 7 × 10 3
^At a concentration of ¹⁵ cm ^-2 , the source of the NMOS transistor
Driven into the drain region. Conversely, when fabricating a PMOS transistor, after covering the NMOS transistor portion with an aluminum (Al) thin film, diborane (B ₂ H ₆ ) diluted in hydrogen at a concentration of 5% is selected as an impurity element and accelerated. 5x total ions containing hydrogen at a voltage of 80 kV
It was implanted into the source / drain region of the PMOS transistor at a concentration of 10 ¹⁵ cm ⁻² . (FIG. 5-c) The substrate temperature at the time of ion implantation is 300 ° C.

Next, TEOS (Si- (O
Using CH ₂ CH ₃ ) ₄ ) and oxygen as source gases, an interlayer insulating film 109 was deposited at a substrate temperature of 300 ° C. The interlayer insulating film was made of a silicon dioxide film, and its thickness was about 500 nm. After the deposition of the interlayer insulating film, a heat treatment was performed at 350 ° C. for 2 hours in a nitrogen atmosphere to bake the interlayer insulating film and activate the impurity element added to the source / drain regions. Finally, a contact hole was opened, aluminum was deposited at a substrate temperature of 180 ° C. by a sputtering method, and a wiring 110 was formed to complete a thin film semiconductor device. (FIG. 5
-D) The transfer characteristics of the thin film semiconductor device thus prepared were measured. The length and width of the channel formation region of the semiconductor device measured were 10 μm each, and the measurement was performed at room temperature. 4
The average mobility of the NMOS transistors obtained from the saturation region at Vds = 8 V is 117 cm ² · V ^-1 ·
s ⁻¹ , the average threshold voltage is 3.41 V, the average sub-threshold hold swing is 0.260 V, and the average acceptor-type trap state density determined from the threshold voltage and the flat band voltage is 2.09. × 10 ¹⁶ cm ⁻³ . Also, Vds = −8 of the four PMOS transistors
The average mobility determined from the saturation region at V is 62 cm
² · V ⁻¹ · s ⁻¹ and the average threshold voltage is −0.8
1V, average sub-leash hold swing is 0.
368 V, the average donor-type trap state density determined from the threshold voltage and the flat band voltage is 1.66 × 10 ¹⁶ cm
^-3 . The characteristics of these semiconductor devices hardly fluctuated within the substrate, and high-performance semiconductor devices were manufactured uniformly. On the other hand, the average mobility of the NMOS transistor is 33 cm ² · V ^-1 · in the comparative example in which an amorphous silicon film is deposited and crystallized by an excimer laser in the prior art.
s ⁻¹ , average threshold voltage 3.70 V, average sub-threshold hold swing 0.646 V, average acceptor-type trap level density 2.62 la 10 ¹⁶ cm ^−3.
And the average mobility of the PMOS transistor is 16 cm ²
V ^-1 s ^-1 , average threshold voltage is -7.06 V, average sub-threshold hold swing is 0.617
V, the average donor-type trap level density is 6.52 × 10 ¹⁶
cm ^-3 . As this example shows, according to the present invention, N
Both the P-type and P-type semiconductor devices have a high mobility and a low threshold voltage, and a good thin-film semiconductor device exhibiting a steep sub-threshold hold characteristic can be easily and simply manufactured in a low-temperature process where a general-purpose glass substrate can be used. It can be easily and stably made. In particular, as can be seen from the sub-leash hold swing value, it has a tremendous effect of significantly reducing the trap level density near the center of the forbidden zone and the trap level density called donor type trap level density. Low-voltage driving of a circuit using a semiconductor device is made possible. Further, in the prior art, the threshold voltage and the trap level density are increased when the mobility is high. However, according to the present invention, the high mobility and the low threshold voltage and the low trap level density can be realized at the same time. The effect is also recognized.

[0026]

As described above in detail, a crystalline semiconductor film having a low quality and a large variation in the prior art can be changed to a uniform and high quality crystallographic film by devising a film forming method and a crystallization process in the present invention. Semiconductor film. This has the effect of significantly improving the electrical characteristics of the thin film semiconductor device represented by the thin film transistor, operating the thin film semiconductor device at a low voltage, and stably manufacturing such a thin film semiconductor device. Is recognized.

[Brief description of the drawings]

FIG. 1 is a view for explaining the relationship between the wavelength of light and the absorption coefficient of a semiconductor.

FIG. 2 illustrates a relationship between a semiconductor film thickness and light intensity in the film.

FIG. 3 is a diagram illustrating the principle of the present invention.

FIG. 4 is a diagram illustrating a relationship between wavelength and semiconductor film thickness for explaining the scope of the present invention.

FIG. 5 is a diagram illustrating a manufacturing process of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Substrate 102 ... Underlying protective film 103 ... Semiconductor film island 104 ... Silicon oxide film 105 ... Gate electrode 106 ... Impurity ions 107 ... Source / drain region 108 ...・ Channel forming region 109 ・ ・ ・ Interlayer insulating film 110 ・ ・ ・ Wiring

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/336 (72) Inventor Tetsuya Ogawa 2-3-2 Marunouchi 2-chome, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Hidetada Tokioka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Yukio Sato 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric ( 72) Inventor Mitsuo Inoue 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsui Electric Co., Ltd. (Reference) 4K030 AA06 AA14 AA16 AA17 BA29 BB12 DA09 FA02 FA10 5F045 AA06 AB03 AB04 AC01 AD08 AE09 AF07 BB07 BB16 BB18 CA15 DA61 DA63 DA67 HA18 5F052 AA02 BA07 BB02 BB0 3 CA07 DA02 DA10 DB01 DB02 DB03 DB07 EA12 JA01 JA10 5F110 AA08 AA17 BB04 CC02 DD01 DD02 DD07 DD12 DD13 DD14 DD17 DD24 EE04 EE11 EE23 EE44 FF02 FF09 FF25 FF29 GG01 GG02 GG13 GG16 J04 GG25 GG43 GG43 GG43 GG43 HGG NN23 NN35 NN40 PP03 PP04 PP23 QQ11

Claims (17)

[Claims] In a method of manufacturing a thin film semiconductor device using a crystalline semiconductor film mainly composed of silicon (Si) formed on a substrate as an active layer, a silicon oxide serving as a base protective film on the substrate is provided. A step of forming a base protective film for forming a film, a first step of forming a semiconductor film mainly composed of silicon (Si) on the base protective film, and a pulsed laser beam having a wavelength of 370 nm or more and 710 nm or less on the semiconductor film. And a second step of irradiating the thin film semiconductor device. 2. The pulse laser beam has a wavelength of 450 n.
2. The method according to claim 1, wherein the thickness is not less than about m and not more than about 650 nm. 3. The method according to claim 1, wherein the pulse laser beam has a wavelength of about 532 nm. 4. The method for manufacturing a thin film semiconductor device according to claim 1, wherein said pulsed laser light is formed by a solid light emitting element. 5. The method according to claim 4, wherein the pulsed laser light is a second harmonic of Nd: YAG laser light. 6. The thin-film semiconductor device according to claim 1, wherein a variation in an irradiation energy density of the pulse laser light on the semiconductor film is less than about 5%. Manufacturing method. 7. Mainly silicon (Si) formed on a substrate
Thin film using crystalline semiconductor film as active layer
In a method of manufacturing a conductor device, a silicon oxide film serving as a base protective film is formed on a substrate.
Forming a protective film, and forming a semiconductor film mainly composed of silicon (Si) on the base protective film.
A first step of forming a film having a thickness of d (nm), and a wavelength λ of 440 nm or more and 710 nm or less
Second step of irradiating a pulse laser beam having (nm)
The film thickness d and the wavelength λ are 9.8 × 10^{αL2 (λ-440)}<D <53 × 10
^{αH2 (λ-440)}  However, αL2 = 4.9 × 10^-3 nm^-1 αH2 = 5.4 × 10^-3 nm^-1 Thin film semiconductor device characterized by satisfying the relational expression
Manufacturing method of the device. 8. A method for manufacturing a thin-film semiconductor device using a crystalline semiconductor film mainly composed of silicon (Si) formed on a substrate as an active layer, the method comprising the steps of: A first step of forming a semiconductor film mainly composed of silicon (Si) on the base protective film so as to have a thickness of d (nm); and forming a film of 440 nm on the semiconductor film. Wavelength λ not less than 710 nm
(Nm), and the film thickness d and the wavelength λ are 9.8 × 10 ^{αL2 (λ-440)} <d <32 × 10
^{αM2 (λ-440)} where αL2 = 4.9 × 10 ⁻³ nm ⁻¹ αM2 = 5.2 × 10 ⁻³ nm ⁻¹ Method. 9. The pulse laser beam has a wavelength of 450 n.
9. The method for manufacturing a thin film semiconductor device according to claim 7, wherein the thickness is not less than about m and not more than about 650 nm. 10. The pulse laser beam has a wavelength of about 532 nm.
9. The method for manufacturing a thin-film semiconductor device according to claim 7, wherein: 11. The method for manufacturing a thin film semiconductor device according to claim 7, wherein said pulsed laser light is formed by a solid state light emitting device. 12. The pulsed laser beam is Nd: YAG.
2. The method according to claim 1, wherein the second harmonic is a laser beam.
2. The method for manufacturing a thin film semiconductor device according to claim 1. 13. The thin-film semiconductor device according to claim 7, wherein a variation of an irradiation energy density of the pulsed laser beam on the semiconductor film is less than about 5%. Manufacturing method. 14. A method of manufacturing a thin film semiconductor device using a crystalline semiconductor film mainly composed of silicon (Si) formed on a substrate as an active layer, wherein silicon oxide serving as an underlayer protective film on the substrate is provided. A step of forming an underlayer protective film for forming a film; a first step of depositing a semiconductor film mainly composed of silicon (Si) on the underlayer protective film so as to have a thickness of d (nm); Wavelength λ not less than 440 nm
(Nm), and the film thickness d and the wavelength λ are 2.4 × 10 ^{αL1 (λ-370)} <d <11.2 × 1
0 ^{αH1 (λ-370)} where αL1 = 8.7 × 10 ⁻³ nm ⁻¹ αH1 = 9.6 × 10 ⁻³ nm ⁻¹ Production method. 15. A method for manufacturing a thin-film semiconductor device using a crystalline semiconductor film mainly composed of silicon (Si) formed on a substrate as an active layer, the method comprising the steps of: A step of forming an underlayer protective film for forming a film; a first step of depositing a semiconductor film mainly composed of silicon (Si) on the underlayer protective film so as to have a thickness of d (nm); Wavelength λ not less than 440 nm
(Nm), and the film thickness d and the wavelength λ are 2.4 × 10 ^{αL1 (λ-370)} <d <6.0 × 10
^{αM1 (λ-370),} where αL1 = 8.7 × 10 ⁻³ nm ⁻¹ αM1 = 1.04 × 10 ⁻² nm ⁻¹ Method. 16. The method according to claim 14, wherein the pulsed laser light is formed by a solid-state light emitting element. 17. The thin-film semiconductor device according to claim 1, wherein a variation of an irradiation energy density of the pulse laser beam on the semiconductor film is less than about 5%. Manufacturing method.