JPH03185735A - Manufacturing method of semiconductor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a semiconductor device.

[Prior Art] Conventionally, a thin film transistor on an insulating substrate (hereinafter referred to as TPT) has an insulating substrate 3 made of glass or the like, as shown in FIG.
1, a semiconductor thin film 32 is formed on top of the semiconductor thin film 32, and elements are built therein.

Furthermore, in recent years, crystalline semiconductor thin films are often used as semiconductor thin films in order to improve the characteristics of TPT. The term "crystalline semiconductor" as used herein refers to a single-crystal semiconductor, which has more defects than a normally used single-crystal wafer, or a polycrystalline semiconductor, which has one or more internal crystal grain boundaries.

[Problems to be Solved by the Invention] However, in the above conventional example, as shown in FIG. There are interface levels 34.35 in the crystalline semiconductor thin film 32,
For example, when a MOSFET is formed as shown in the figure, due to the influence of this interface state, carriers in the channel part reach the interface state 3.
4°35, forming a so-called back channel, resulting in deterioration of device characteristics such as fluctuations in threshold voltage and reduction in signal ON10ff ratio.

Further, polycrystalline silicon thin films are often used as crystalline semiconductor thin films, but there are many interface states 37 in the crystal grain boundaries 36 that exist within the polycrystalline silicon thin film, and these are carriers. By trapping
This reduces carrier mobility in the channels and channels.

In addition, if an inexpensive material such as glass with a high alkali ion content is used for the substrate, alkali ions such as Na3 contained in the substrate material will migrate toward the semiconductor thin film due to heat treatment during the manufacturing process. They exist as mobile ions at the interface with silicon and in the silicon thin film, causing deterioration of device characteristics and reliability problems.

As a method to solve these problems, for example, after the device is formed, a silicon nitride film is formed as a protective film of the device by plasma CVD method, and hydrogen passivation by this protective film is used to improve localized levels within the silicon thin film. reduce,
Efforts have been made to increase mobility. Additionally, in order to prevent alkali ion contamination, a method of using high-purity quartz, alkali-free glass, or the like as a substrate has been used.

However, even with the above method, the passivation of the grain boundaries and the passivation of the interface with the substrate are not perfect. That is, in the above method, a process in which hydrogen is introduced into the semiconductor thin film and a process in which hydrogen is released from the semiconductor thin film coexist. Hydrogen diffuses even in areas with good properties, and there remains much room for further improvement in order to effectively passivate grain boundaries and interfaces.

Further, substrates made of high-purity quartz or non-alkali glass are expensive, and one of the inherent advantages of TPT, which is employed to form inexpensive elements on large-area substrates, is lost.

[Means for Solving the Problems] A method for manufacturing a semiconductor device of the present invention is a method for manufacturing a semiconductor device comprising forming a crystalline semiconductor thin film on an insulating substrate. forming first and second insulating films that serve as barriers to hydrogen diffusion; and forming an amorphous semiconductor thin film containing hydrogen on at least one of the semiconductor thin film and the insulating film. , and then performing at least one of heat treatment and light irradiation.

[Function] The function of the present invention will be explained below together with the detailed structure of the present invention.

(Insulating Film) In the present invention, first and second insulating films that serve as barriers to hydrogen diffusion are formed on both upper and lower sides of a crystalline semiconductor thin film, respectively.

By forming an insulating film that acts as a barrier against hydrogen diffusion on the crystalline semiconductor thin film, out-diffusion of hydrogen diffused from the amorphous semiconductor thin film into the crystalline semiconductor thin film by heat treatment, which will be described later, can be prevented. be able to.

Here, the first insulating film and the second insulating film which serve as a barrier against the hydrogen diffusion may be formed by, for example, low pressure CVD method,
Alternatively, a silicon nitride film or silicon nitride oxide film formed by plasma CVD may be used.

In addition, by forming a silicon nitride film as an insulating film between the substrate and the crystalline semiconductor thin film, it is possible to have a blocking effect against alkali ions such as Na+ from the substrate such as glass. The reliability of child characteristics can be improved.

(Crystalline semiconductor thin film) As a crystalline semiconductor thin film, for example, polycrystalline silicon formed by sputtering, low pressure CVD, or plasma CVD, or amorphous silicon formed by sputtering or CVD, can be annealed. Use recrystallized silicon or large-grain polycrystalline silicon obtained by the effect of adding hydrogen halide gas such as HCf to the formation atmosphere in the plasma CVD method proposed separately by the applicant. (Japanese Patent Application No. 62-73630). The large-grain polycrystalline silicon thin film proposed by us is most suitable for the present invention from the viewpoints of lower process temperatures and electrical properties.

(Amorphous semiconductor thin film) In the present invention, an amorphous semiconductor thin film containing hydrogen is formed on at least one of the semiconductor thin film and the insulating film.

Here, as the amorphous semiconductor thin film material, for example, RF
Amorphous silicon formed by a glow discharge method may be used. The hydrogen content in the amorphous semiconductor thin film is preferably several atomic percent to several tens of atomic percent.

Note that when an amorphous semiconductor thin film containing hydrogen is formed particularly between the substrate and the crystalline semiconductor thin film, there is a conductive layer in the amorphous semiconductor thin film opposite to that of the source/drain of TPT. By introducing relatively high-concentration type impurities, it is possible to more effectively suppress the formation of back channels during TPT operation, thereby reducing threshold voltage fluctuations and signal on10.
A decrease in the ff ratio can be more effectively prevented, and a TPT with even more excellent electrical characteristics can be realized.

(Heating Treatment) In the present invention, the above-described amorphous semiconductor thin film and crystalline semiconductor thin film are heated.

Due to this heat treatment, hydrogen in the amorphous semiconductor thin film diffuses into the crystalline semiconductor thin film, and the diffused hydrogen diffuses into the interface states existing in the crystalline semiconductor thin film, defect levels in the crystalline semiconductor thin film, It is possible to terminate levels existing at grain boundaries in a crystalline semiconductor thin film, suppress the generation of back channels, reduce the potential of grain boundaries, and increase carrier mobility.

The heating temperature varies depending on the material of the amorphous semiconductor thin film or crystalline thin film, but for example, in the case of silicon, it is
600°C is preferred. If the temperature is less than 300°C, hydrogen diffusion is difficult to occur, and if the temperature exceeds 600°C, the hydrogen in the crystalline semiconductor thin film will diffuse out again.

The heating atmosphere is preferably an inert atmosphere such as N2, Ar, N2, or a mixed gas thereof.

The heat treatment may be performed by holding the substrate on which the crystalline semiconductor thin film is formed in a heating furnace or by irradiating it with irradiation light. This is preferable for the following reasons.

In the case of light irradiation, it is possible to selectively heat only the vicinity of grain boundaries, the vicinity of defects, or the vicinity of the interface between the crystalline semiconductor thin film and the substrate in the crystalline semiconductor thin film, and trap units existing in these places can be heated. It can be effectively terminated with hydrogen.

In addition, in the case of light irradiation, only crystal grain boundaries, defects, or interfaces between semiconductor thin films and other thin films are selected without changing the spatial position of impurities introduced into the source and drain of TPT. Since it is possible to heat the device in a controlled manner, manufacturing of fine transistors becomes easier.

Furthermore, in the case of light irradiation, since only the semiconductor thin film can be heated, it is possible to prevent alkali ions such as Na'' from entering from a substrate such as glass, and an improvement in reliability can be expected.

When heating is performed by irradiating irradiation light, it is preferable to use near-infrared light as the irradiation light.
) etc. are suitable. When irradiated with light having a wavelength of about 0.8 μm, electron-hole pairs are generated in the semiconductor thin film. Electrons and holes generated by light irradiation travel in the conductive band and valence band, respectively, with a relatively long life in the crystal of the semiconductor thin film. Of these, those that reach grain boundaries, defects, or interfaces cause recombination via trap levels caused by Dougson bonds and the like that exist there. The energy of electrons and holes lost through recombination is converted into lattice vibration, that is, thermal energy. In other words, grain boundaries, defects, or interfaces contained in the crystalline semiconductor thin film are selectively heated by heat due to electron/hole recombination. This thermal energy causes trap levels at grain boundaries, defects, or interfaces to
Can be terminated with hydrogen already present in the film,
Crystal defects can be recovered.

Here, light with a wavelength of 0.8 μm corresponds to 1.5 keV when converted into energy, the absorption coefficient is about I x 10'am-' in the case of crystalline silicon, and the penetration depth is 1 / from the surface. The intensity of e is approximately 10 μm. 0
．． Light with a wavelength sufficiently shorter than 8 μm (for example, visible light, infrared light, etc.) has high energy, so
Electrons generated by light irradiation now exist in one high-energy direction of the conductive band, and the collision of electrons in the conductive band heats the entire thin film, causing heating of the substrate, desorption of hydrogen, and doping. This causes the diffusion of impurities.

Conversely, for light with a wavelength sufficiently longer than 0.8 μm (e.g., light with a wavelength of 1 to several μm), if the film is thick, the light will penetrate considerably deep from the surface, thereby causing not only the surface but also Even at great depths, electron-hole pairs are generated, causing recombination and heating the entire thin film. therefore,
There is a possibility that only the vicinity of the surface of the thin film, which is necessary for device operation, cannot be efficiently heated.

From the above, light irradiation with near-infrared light having a wavelength greater than 0.7 μm and smaller than 1.0 μm, preferably about 0.8 μm, is most preferred in the present invention.

Note that in order to set the heating temperature to 300 to 600°C, the amount of irradiation light may be adjusted.

[Example] Embodiments of the present invention will be described in detail using the drawings.

FIG. 1 is a schematic cross-sectional view of a MOSFET manufactured according to the present invention, and FIG. 2 is a schematic cross-sectional view showing the manufacturing process thereof.

(Example 1) SiH4 was deposited on a glass substrate 21 by plasma CVD as a first insulating film that acts as a barrier against hydrogen diffusion.
/NH3 mixed gas system to convert silicon nitride@22 to 10
00 people were deposited (Figure 2(a)).

The deposition conditions were a parallel plate plasma CVD device, SiH4 (10% H2 dilution) flow rate of 15 SCCms.
Deposition was carried out for 35 minutes under the following conditions: NH2 flow rate of 10105e, pressure of 0.16 Torr, discharge power of 3.5 W, and substrate temperature of 300.degree.

Next, by the RF Dougu discharge plasma method, St)! Amorphous silicon 23 was deposited by 200 people using a 4-gas system (FIG. 2(b)).

The deposition conditions were 100% S i H4 gas at a flow rate of 5.
~10105c, pressure 50mTorr, RF frequency 4~
13.5MHz%RF power 0.01~0, 03
Deposition was performed at W/am', a cathode-anode distance of 40 mm, and a substrate temperature of 150°C.

As a result of IR (infrared spectroscopy) analysis, it was found that the amorphous silicon deposited under these conditions contained about 25% hydrogen. The amount of hydrogen in amorphous silicon depends on the substrate temperature of the deposition conditions ti! It depends on the L feeling, and generally the amount of hydrogen tends to increase at low temperatures. Under these deposition conditions, the effects of the present invention are more pronounced than at a deposition temperature of about 250° C., which is commonly used.

Next, 1000 polycrystalline silicon thin films 24 were deposited on the amorphous silicon jlj23 using a SiH2Cj22/HC12/H2 mixed gas system using the RF plasma CVD method (FIG. 2(C)).

The deposition conditions are 5iHz CJ12: 0.9s
ecm, HCl2: 130secm, N2:2
00sec, pressure crab 2.0Torr%RF power: 6
0W, substrate temperature: 230°C.

Next, by sputtering, 5iOz was deposited as a gate insulating film.
tl! After depositing 500 Å of Al25, Al1 was deposited by sputtering and patterned to form a gate electrode FiA2.
6 was formed (Fig. 2(d)).

Next, P" is implanted into predetermined positions of the polycrystalline silicon thin film 24 by ion implantation, and the source/drain regions 27 are
was formed (Fig. 2(e)).

Next, 5000 silicon nitride films 28 were deposited by plasma CVD in the same manner as the first insulating film 22 as a second insulating film to serve as a barrier against hydrogen diffusion (see Fig. 2(f)). )).

Next, N2. Heat treatment was performed in an atmosphere of Ars N2 or a mixed gas thereof at a temperature higher than the temperature at which the nitrogen silicon film was formed as the first insulating film that acts as a barrier against hydrogen diffusion (300 t: to 600° C.).

Next, contacts were opened in desired regions, and Al1 was deposited and patterned to form source/drain electrodes 29 and gate electrodes 30 (FIG. 2(g)).

In this example, we measured and compared the electrical characteristics of a MOSFET formed on a polycrystalline silicon thin film directly formed on a glass substrate and a MOSFET created according to this example. The degree is more than twice as high,
The fluctuation width of the threshold voltage was reduced to 1/2 or less.

This means that due to the heat treatment, hydrogen diffuses from the amorphous silicon film 23 into the polycrystalline silicon thin film 1i24, and this hydrogen diffuses into the polycrystalline silicon thin film interface and the crystal grain boundaries in the polycrystalline silicon thin film @24. terminating the interface states existing in
This is considered to be because the number of levels decreased, the generation of back channels at the base interface was suppressed, and the potential barrier at the grain boundary was lowered. This is clear from the fact that the density of dangling bonds in the polycrystalline silicon thin film was reduced by more than one order of magnitude as a result of the heat treatment, as a result of ESR (II electron spin resonance measurement).

In addition, silicon nitride, which acts as a barrier to hydrogen diffusion,
Regarding the effect of ff122.28, for example, depending on the presence or absence of this silicon nitride film 28, the polycrystalline silicon thin film 24
Since the density of hydrogen present in the film has decreased from the order of 1 x 10"cm-3 to below the order of 1 x 101gam-3, this film
It was found that it acts as a barrier against iffusion.

Further, in a reliability test of an element formed on this crystalline semiconductor thin film, there was almost no change in electrical characteristics even in high-temperature tests, and the reliability was sufficient.

This is considered to be because the silicon nitride film 22 blocks the diffusion of alkali ions from the glass substrate.

Furthermore, in this example, it was revealed from the measurement of electrical characteristics that the heat treatment for 550 t makes it possible to diffuse hydrogen and activate the source/drain regions at the same time.

(Example 2) In this example, the heat treatment step was carried out by irradiating a xenon lamp with a wavelength of O and a power of 1000 W in a μm from a distance of about 10 cm in an N2 gas atmosphere. At this time, the effective power of the xenon lamp is 40
It is thought to be approximately W/c+m'.

Other steps were performed in the same manner as in Example 1.

In this example as well, the effect of the silicon nitride film 22, 28, which acts as a barrier against hydrogen diffusion, depends on the presence or absence of the silicon nitride film 28, for example.
The density of hydrogen present in I
This decreases the hydrogen out-division from the order of 1 x 10 cm to below the order of 1
It was found that it acts as a barrier against fusion.

Further, in the reliability test, there was almost no change in the electrical characteristics even in the high-temperature test, and the reliability was also sufficient as in Example 1.

This is considered to be because the silicon nitride film 22 blocks the diffusion of alkali ions from the glass substrate.

Furthermore, in this example, it was revealed from the measurement of electrical characteristics that it was possible to diffuse hydrogen and activate the source/drain regions by light irradiation at the same time.

Furthermore, it was confirmed that impurity diffusion in the source/drain region 27 did not occur because the vicinity of the interface state was selectively heated at this time.

(Example 3) In this example, the 5i of the gate insulating film 24 described in Example 1 is
As a third embodiment, instead of 500 oz of silicon nitride oxide film was formed by plasma CVD method as a gate insulating film and as an insulating film that acts as a barrier against hydrogen diffusion.
00 people were deposited. As is well known, a silicon nitride oxide film can have the properties of both a silicon nitride film and a silicon oxide film by appropriately selecting the composition ratio of nitrogen and oxygen in the film. Here, S i H
By reoptimizing the deposition conditions using a 4/NH3/N20 mixed gas system, the composition ratio of the film was set to 3.0 to 2 of N to Si.

Other steps are the same as in Example 1.

In this example, even if a silicon nitride oxide film is used as the second insulating film that resists hydrogen diffusion, the density of hydrogen in the polycrystalline silicon thin film is completely the same as when a silicon nitride film is used. There was no change.

Further, although a silicon nitride oxide film was used as the gate insulating film, almost no deterioration in electrical characteristics was observed compared to the case where a SiO3 film was used.

Moreover, the same effect was obtained even when the light irradiation described in the second example was performed instead of the heat treatment.

(Example 4) When depositing the amorphous silicon thin film 23 described in Example 1, as a fourth example, approximately 11000 pp of 82Ha gas is mixed in SiH gas to form an amorphous silicon film 23. A quality silicon thin film 23 was deposited.

Other steps are the same as in Example 1. As mentioned earlier, the amorphous silicon formed by the RF dougling discharge method contains a large amount of hydrogen in its film, but since structural defects such as dougling bonds are terminated with this hydrogen, It is known that P-type control can be achieved by introducing an acceptor-type impurity such as boronate, and that N-type control can be achieved by introducing a donor-type impurity such as ferrode.

In this embodiment, by mixing B2H6 gas into SiH< gas, the amorphous silicon thin film 23 exhibits P-type conductivity type. As a result, Po of the source/drain region 27
A P-type region of the opposite conductivity type is formed between the crystalline semiconductor thin film 24 and the insulating film 22, which has the effect of further suppressing the formation of a back channel.

Also at this time, the amorphous silicon thin film 23 is
Hydrogen inside acts as a barrier to hydrogen diffusion11
It effectively diffuses into the amorphous silicon thin film 23 surrounded by i22, 25 and the crystalline silicon thin film 24, and causes defect levels in the amorphous silicon thin film and crystalline silicon thin film. , it is possible to terminate the interface states existing at grain boundaries and reduce the number of trap levels.

In this example, the same effects as in the first example were obtained in terms of improving the electrical characteristics of the MOSFET, and in particular, with regard to the OFF characteristics, even better results were obtained due to the suppression of the formation of the cut channel. An improvement effect was obtained.

Moreover, the same effect was obtained even when the light irradiation described in Example 2 was performed instead of the heat treatment.

Incidentally, in this embodiment, there is wood in the area where the amorphous silicon thin film 23 having a conductivity type opposite to that of the source/drain region '27 is deposited. Therefore, when the conductivity type of the source/drain region 27 is N type, the conductivity type of the amorphous silicon thin film may be set to P type. For example, when depositing the amorphous silicon thin film 23, SiH4
This can be achieved by mixing about 11,000 pp of PH4 gas into the gas and depositing a thin layer of amorphous silicon 1123.

[Effects of the Invention] According to the present invention, semiconductor fifM! The interface state at the base interface can be reduced and the back channel effect can be suppressed.
In addition, it was possible to reduce the levels existing in the silicon thin film, and as a result, it was possible to improve the electrical characteristics of the TPT, such as reducing the fluctuation width of the threshold voltage and improving carrier mobility.

Further, in the present invention, since an amorphous semiconductor thin film containing hydrogen is formed as a hydrogen introduction source, hydrogen can be easily introduced without damaging the semiconductor thin film.

As a result, electrical properties and (
It has become possible to easily form TPT with excellent X-reliability.

Note that by using a silicon nitride film as an insulating film that acts as a barrier against hydrogen diffusion, Na
It is possible to block the invasion of alkali ions such as ``TPT'', thereby improving the reliability of TPT.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a MOSFET produced according to the present invention, FIG. 2 is a schematic cross-sectional view showing steps in an embodiment of the present invention, and FIG. FIG. (Explanation of symbols) 21.31...Substrate, 22...Hydrogen diffusion)
The t-th absolute H1i, which acts as a barrier, t 2, 24...
Semiconductor thin film, 23... Amorphous semiconductor thin film containing hydrogen, 25... Gate insulating film, 27... Source/drain, 2B... Serving as a barrier against hydrogen diffusion;
2 insulating film, 29.30...electrode. Figure (a) (e) (b)

Claims (8)

[Claims] (1) In a method for manufacturing a semiconductor device in which a crystalline semiconductor thin film is formed on an insulating substrate, a first layer, which serves as a barrier to hydrogen diffusion, is provided on both upper and lower sides of the crystalline semiconductor thin film.
, a step of forming a second insulating film, a step of forming an amorphous semiconductor thin film containing hydrogen on at least one of the semiconductor thin film and the insulating film, and then at least heat treatment or light irradiation. A method of manufacturing a semiconductor device, comprising: a step of performing one of the steps. (2) The step of forming the first and second insulating films is performed by low pressure CV
2. The method of manufacturing a semiconductor device according to claim 1, wherein the step is to form a silicon nitride film by a D method or a plasma CVD method. (3) The method of manufacturing a semiconductor device according to claim 1, wherein the step of forming the first and second insulating films is a step of forming a silicon nitride oxide film by a plasma CVD method. (4) The method of manufacturing a semiconductor device according to any one of claims 1 to 3, wherein the crystalline semiconductor thin film material is silicon. (5) The method of manufacturing a semiconductor device according to any one of claims 1 to 4, wherein the amorphous semiconductor thin film material is amorphous silicon formed by an RF glow discharge method. (6) The method of manufacturing a semiconductor device according to any one of claims 1 to 5, wherein the temperature of the heat treatment is in a range of 300°C to 600°C. (7) The method of manufacturing a semiconductor device according to any one of claims 1 to 6, wherein the heat treatment is performed by irradiating with irradiation light. (8) The method for manufacturing a semiconductor device according to claim 7, wherein the irradiation light is near-infrared light.