JP2945032B2 - Manufacturing method of thin film transistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a thin film transistor.

[Summary of the Invention] The present invention relates to a method of manufacturing a thin film transistor, in which, after forming an inverted staggered thin film transistor, hydrogen atoms are introduced into the channel region from the semiconductor thin film side by ion implantation, thereby forming a gate insulating film between the channel region and the channel region. A crystal defect (dangling bond) at an interface with a film is reduced, damage to a polycrystalline semiconductor film is reduced, and transistor characteristics are improved.

According to the present invention, in a method of manufacturing a thin film transistor, a gate electrode made of a semiconductor film is formed on a base region which is easily affected by heat, and the surface of the gate electrode is oxidized at a high temperature for a short time to form a gate insulating film made of a thermal oxide film. Thereafter, an inverted staggered thin film transistor is formed by forming a semiconductor thin film having a channel region, and hydrogen atoms are introduced into the channel region from the semiconductor thin film side by an ion implantation method, whereby the inverted staggered film having a good gate breakdown voltage and improved characteristics is provided. Type thin film transistor while avoiding thermal effects on the base
It is designed to be easily formed on a base region which is easily affected by heat.

The present invention relates to a method for manufacturing a thin film transistor, which comprises forming a gate electrode of a semiconductor film on a base region which is easily affected by heat, forming a CVD oxide film on the gate electrode, and then oxidizing at a high temperature for a short time to form a CVD oxide film. After forming a gate insulating film by a thermal oxide film, a semiconductor thin film having a channel region is formed to form an inverted staggered thin film transistor,
By introducing hydrogen atoms into the channel region from the semiconductor thin film side by ion implantation, a high-quality gate insulating film with good flatness is obtained, the gate withstand voltage is improved, and an inverted staggered thin film transistor with further improved characteristics is formed on the underlayer. Is easily formed on a base region which is easily affected by heat while avoiding the influence of heat.

[Related Art] In recent years, research on thin film transistors has been actively conducted. In a thin film transistor using a polycrystalline silicon thin film, in order to improve the characteristics, hydrogen is introduced into the polycrystalline silicon thin film serving as a channel region to remove crystal defects (so-called dangling bonds) existing at crystal grain boundaries and the like. A method for reducing the amount, that is, a hydrogenation method, is essential.

A common hydrogenation method is to use a hydrogenated plasma silicon nitride (plasma SiN: H) film as a passivation film and diffuse it from this film into the hydrogen channel region through an interlayer insulating film by heat treatment at about 400 ° C. It has become common.

In order to manufacture a thin film transistor, a gate insulating film made of SiO ₂ or the like is usually formed on a polycrystalline silicon thin film (2) on an insulating substrate (1) as shown in FIG.
A so-called top gate structure in which a gate electrode (4) is formed through the gate electrode is adopted. (2S) is the source area, (2D)
Indicates a drain region, and (2C) indicates a channel region. A hydrogenated plasma silicon nitride film (5) as a passivation film is formed on the thin film transistor, and hydrogen (6) in the film (5) is converted into a channel region (2C) by heat treatment.
And it is easily introduced into the interface between the channel region (2C) and the gate insulating film (3).

As a hydrogenation method, a method has been proposed in which hydrogen is excited by plasma excitation experimentally based on analogy with hydrogenated amorphous silicon (a-Si: H).

Further, as a hydrogenation method for a thin film transistor having a top gate structure, a method has been proposed in which after forming a gate electrode, hydrogen atoms are introduced into the silicon thin film from above the gate electrode by an ion implantation method (JP-A-60-164363). Reference).

On the other hand, as a gate insulating film of a thin film transistor, a SiO ₂ film formed by thermal oxidation or an S ₂ film formed by a CVD (chemical vapor deposition) method is used.
An iO ₂ film (hereinafter referred to as a CVD SiO ₂ film) or the like is used.

[Problems to be Solved by the Invention] As described above, in a thin film transistor having a top gate structure, a gate insulating film (3) and a channel region (2C), which are important for transistor characteristics, are formed by a normal hydrogenation method shown in FIG. Hydrogen easily reaches the interface with. However,
In recent years, memory cells have been adopted by stacking p-channel MOS thin-film transistors on n-channel MOS transistors.
CMOS type SRAMs (static RAMs) have been proposed. However, as thin film transistors applied to such a so-called stacked type SRAM, as shown in FIG. In addition, a bottom gate structure (that is, an inverted stagger type) in which a polycrystalline silicon film (2) is formed on a gate electrode (4) via a gate insulating film (3) is advantageous. (7) is a lower semiconductor element region or a base region such as an insulating substrate. In this case, even if the hydrogenated plasma silicon nitride film (5) as a passivation film is formed and heat-treated, the hydrogenated plasma silicon nitride film (5) is formed.
Hydrogen (6) from the source only slightly reduces traps (crystal defects) in the polycrystalline silicon thin film (2), and does not reach the interface between the gate insulating film (3) and the channel region (2C), and the hydrogen No effect.

Note that in a top gate structure, a method of introducing hydrogen atoms by an ion implantation method actually makes it difficult to uniformly introduce hydrogen atoms into a channel region because the method is behind a gate electrode.

On the other hand, regarding a gate insulating film of a thin film transistor, when a SiO ₂ film is formed by thermal oxidation of the surface of a silicon thin film, a dense and high quality film can be obtained, and a gate insulating film with good withstand voltage can be obtained. However, since the furnace oxidation method requires a high-temperature process, it cannot be applied to a so-called three-dimensional LSI such as a stack type SRAM because the source and drain regions of the MOS transistor of the underlying LSI occur. Also, a long time of about 60 minutes is required on quartz. This furnace oxidation can be expected to have the effect of densifying (densifying) the polycrystalline silicon thin film simultaneously with the formation of the oxide film, and the densification reduces the trap density in the polycrystalline silicon thin film. Reducing the trap density can improve the characteristics of the thin film transistor, such as reducing the leak current, improving the mobility μ, and decreasing the gate voltage swing. The effect of reducing the trap density is more effective as the oxidation temperature is higher. However, when the temperature is increased, the above-described problem occurs, and when the base is a quartz substrate, oxidation at 1000 ° C. or higher in a furnace becomes difficult due to softening of the quartz. In addition, when a gate insulating film is formed by a CVD SiO ₂ film, it has disadvantages such as many pinholes, sparse film quality, and variation in breakdown voltage.

In view of the above, the present invention provides a method of manufacturing a thin film transistor which enables favorable hydrogenation in an inverted staggered transistor and also enables formation of a high quality gate insulating film without thermally affecting a base. Things.

[Means for Solving the Problems] In a method of manufacturing a thin film transistor according to the present invention, a thermal oxide film is formed by forming a gate electrode of a semiconductor film on a base region which is easily affected by heat, and oxidizing the surface of the gate electrode at high temperature for a short time. , A semiconductor thin film having a channel region is formed to form an inverted staggered thin film transistor, and hydrogen atoms are introduced into the channel region from the semiconductor thin film side by an ion implantation method.

In the method of manufacturing a thin film transistor of the present invention, a gate electrode made of a semiconductor film is formed on a base region which is easily affected by heat, and a CVD oxide film is formed on the gate electrode, and then oxidized at a high temperature for a short time to form a CVD oxide film. After forming a gate insulating film of an oxide film, an inverted staggered thin film transistor in which a semiconductor thin film having a channel region is formed is formed, and hydrogen atoms are introduced into the channel region from the semiconductor thin film side by an ion implantation method.

[Operation] In the above-described manufacturing method, after an inverted staggered thin film transistor is formed, hydrogen atoms are introduced into the channel region from the semiconductor thin film side by an ion implantation method, so that the hydrogen atoms are introduced into the channel region and the channel region and the gate insulating film. Easily and uniformly at the interface with Thus, hydrogenation is performed on the inverted staggered thin film transistor, and crystal defects in the channel region and at the interface with the gate insulating film are reduced, so that the transistor characteristics are improved. Since implantation energy can be achieved with a low implantation energy such that hydrogen can be introduced into the interface between the channel region and the gate insulating film, ion implantation with a small implantation dose and little damage to the polycrystalline semiconductor film can be performed.

On the other hand, when a gate insulating film is formed using a thermal oxide film obtained by oxidizing the surface of a semiconductor film at a high temperature for a short time, a gate insulating film having a denser film quality and a high withstand voltage can be obtained, and the thermal conductivity of the underlying region can be improved. Has no effect.
In particular, in a three-dimensional LSI or a stacked SRAM in which thin film transistors are stacked, re-diffusion of the source and drain regions of the underlying MOS transistor is avoided.

When a gate insulating film is formed by oxidizing at a high temperature for a short time after forming a CVD oxide film on the surface of the semiconductor film, the gate insulating film is flattened by the CVD oxide film, and a dense thermal oxide film and heat treatment are performed. Since the gate insulating film is formed with a dense CVD film, a gate insulating film with good withstand voltage can be obtained, and thermal influence cannot be exerted on the underlying region as described above.

Example An example of a method for manufacturing a thin film transistor according to the present invention will be described below with reference to the drawings.

In this example, first, as shown in FIG. 1A, after a gate electrode (12) is formed on a substrate (11), a gate insulating film such as SiO ₂ is formed on the gate electrode (12). A polycrystalline silicon thin film (14) is formed, and an impurity is introduced to form a source region (14S) and a drain region (14D) to form an inverted staggered thin film transistor (15).

The substrate (11) corresponds to an insulating substrate made of quartz, glass, or the like, or a base region in which transistors and the like are formed in the case of, for example, a three-dimensional LSI or a stacked SRAM. As the gate electrode (12), a polycrystalline silicon film, a metal silicide,
It can be formed of polycide, a metal film, or the like.

Next, as shown in FIG. 1B, the polycrystalline silicon thin film (1
Hydrogen (16) is ion-implanted into 4). By this hydrogen ion implantation, hydrogen atoms are easily and uniformly introduced into the polycrystalline silicon thin film (14) into the channel region (14C) and the interface between the channel region (14C) and the gate insulating film (13).

In recent thin film transistors, the thickness d of the polycrystalline silicon thin film (14) has become smaller due to demands for higher performance (that is, lower leakage current, lower threshold voltage V _th , and smaller gate voltage swing). For example, it is less than about 1000 mm. Therefore, hydrogen can be easily introduced into the interface between the channel region (14C) and the gate insulating film (13) with low implantation energy. Since the implantation dose can be effectively reduced by the low implantation energy, damage to the polycrystalline silicon thin film (14) is small. (Because hydrogen ions have a small mass number, damage is originally small.)

After the ion implantation, annealing is performed at about 400 ° C. in an atmosphere of an inert gas such as a forming gas (N ₂ gas containing ₂ to 3% of H).

Thereafter, as shown in FIG. 1C, a passivation film (17) is deposited. As the passivation film (17), a hydrogenated plasma silicon nitride film or another SiO ₂ film can be used.

According to the above-described manufacturing method, hydrogen atoms are introduced by ion implantation after forming the inverted staggered thin film transistor (15), so that the hydrogen atoms are transferred to the channel region (14C) and the channel region of the polycrystalline silicon thin film (14). It can be easily and uniformly introduced into the interface between (14C) and the gate insulating film (13). At this time, since ion implantation can be performed with low implantation energy, damage to the polycrystalline silicon thin film (14) is small. In addition, hydrogenation of the inverted staggered thin film transistor, which has been impossible in the related art, can be easily performed by hydrogen ion implantation and subsequent annealing treatment, and the characteristics of the thin film transistor can be improved.
In addition, since hydrogen atoms are introduced by ion implantation, as a passivation film (17), conventionally used hydrogenated plasma silicon nitride (plasma SiN:
H) An insulating film other than the film can be used, and the degree of freedom in the process of forming the passivation film can be improved.

Next, an example of a method for forming a gate insulating film will be described. This method can be applied to both the thin film transistors having the bottom gate structure (inverted stagger type) according to the embodiment and the top gate structure according to the reference example.

In the case of the bottom gate structure, for example, after a gate electrode (12) made of a polycrystalline silicon film is formed on a substrate (11) as shown in FIG. 2 (A in FIG. 2), a lamp beam such as an arc lamp is formed in an oxygen atmosphere. Irradiate with light, for example 1100 ℃, 3
A 0 second oxidation process is performed to form a gate insulating film (13 ₁ ) of a thermal oxide film (SiO ₂ film) having a film thickness of about 100 ° on the surface of the gate electrode (12) (FIG. B). Thereafter, a polycrystalline silicon thin film (14) is formed so as to surround the gate electrode (12), and source and drain impurities are ion-implanted to form a source region (14S) and a drain region (14D). C).

As described above, when the gate insulating film (13 ₁ ) is formed by high-temperature and short-time thermal oxidation, a dense gate insulating film with good withstand voltage can be obtained, and thermal influence on the underlying substrate (11) can be obtained. I will not give. That is, for example, in a three-dimensional LSI, a stacked SRAM, or the like, the MOS formed on the underlying substrate (11) is used.
It is possible to manufacture a high-performance three-dimensional LSI or stacked SRAM without re-diffusion of the source and drain regions of the transistor. In addition, this 3D LSI, stack type SR
In the case of AM, etc., when the high-temperature short-time oxidation shown in FIG.
It also serves to activate the source and drain regions of the transistor. Further, for example, when an LSI of a thin film transistor is formed on a quartz or glass substrate, a high-performance LSI can be manufactured without softening the quartz or glass substrate constituting the base substrate (11). Further, by forming the gate insulating film (13 ₁ ) by such high-temperature short-time oxidation, it becomes possible to manufacture a thin-film transistor having a fine size. Furthermore, the high-temperature short-time oxidation also has a densifying effect, and can expect flatness as well as withstand voltage of the gate insulating film (13 ₁ ).

In the case of a top gate structure, for example, as shown in FIG. 3, an island-like polycrystalline silicon thin film (22) is formed on a substrate (11).
(FIG. 3A), and at the same time as described above, an arc lamp is irradiated in an oxygen atmosphere, for example, and an oxidation treatment is performed, for example, at 1100 ° C. for 30 seconds to form a film on the surface of the polycrystalline silicon thin film (22). A gate insulating film (13 ₁ ) is formed from a thermal oxide film (SiO ₂ film) of about 100 ° (FIG. B). Next, a gate electrode (2) made of polycrystalline silicon is formed on the gate insulating film (13 ₁ ).
3) is formed, and source and drain impurities are ion-implanted and annealed to form a source region (22S) and a drain region (22D) (FIG. 3C). After that, normal passivation film deposition, contact window opening, Al evaporation,
Through a process such as hydrogen annealing, a thin film transistor having a top gate structure is obtained.

In this example, the same operation and effect as in the case of the bottom gate structure can be obtained, and further, at the time of high-temperature short-time oxidation (step B in FIG. 3), the polycrystalline silicon thin film (22) is densified to reduce the trap density. A small number of thin film transistors can be obtained.

In FIGS. 2 and 3, high-temperature and short-time oxidation is performed by a lamp beam. However, similar effects can be obtained by irradiating an excimer laser pulse instead of the lamp beam to perform high-temperature and short-time oxidation. An excimer laser having a uniform energy density by a beam homogenizer is used. For example, an excimer laser (XeCl), 80 Hz,
Energy of about 280 mJ / cm ² can be used. After the polycrystalline silicon thin film (22) forming a gate insulating film is irradiated with an excimer laser (13 ₁₎ before islanded may islanded.
60 for source region (22S) and drain region (22D)
Anneal at 0 ° C. or lower or excimer laser.

4 and 5 show another example of a method for forming a gate insulating film. In the case of a bottom gate structure, as shown in FIG.
After forming a gate electrode (12) made of a polycrystalline silicon film on a substrate (11) (A in the figure), a CVD SiO ₂ film (25) having a thickness of, for example, about 200 mm is formed on the gate electrode (12). (B in the figure). Then, irradiating the example 1100 ° C. The lamp light for example an arc lamp light in an oxygen atmosphere, CVD SiO ₂ film (25) is subjected to oxidation treatment 5 seconds and SiO ₂ by interfacial thermal oxidation of the gate electrode (12) A film (26) is formed and a CVD SiO ₂ film (2
5) and gate insulation film (13 ₂ ) consisting of thermally oxidized SiO ₂ film (26)
Is formed (FIG. C). Thereafter, a polycrystalline silicon thin film (14) is formed so as to surround the gate electrode (12), and source and drain impurities are ion-implanted to form a source region (14S) and a drain region (14D) ( FIG. D).

According to such a gate insulating film (13 _2), heat treatment when the flatness of the gate insulating film (13 ₂₎ with obtained was formed a thermal oxide SiO ₂ film (26) by CVD SiO ₂ film (25) Thus, the CVD SiO ₂ film (25) is densified, so that the film quality of the gate insulating film becomes dense as a whole, and a gate insulating film with good withstand voltage can be obtained. Incidentally, when the gate insulating film is formed by the conventional thermal oxidation method, the flatness of the gate insulating film is deteriorated because the gate insulating film is oxidized along the crystal grain boundaries of the polycrystalline silicon. Get better. Further, in this example, similarly to the above example, it is possible to manufacture a thin film transistor having a small size, and there is no thermal influence on the underlying substrate (11).

In the case of the top gate structure, as shown in FIG. 5, an island-like polycrystalline silicon thin film (22) is formed on a substrate (11) (FIG. 5A), and then, as shown in FIG. On the thin film (22), a CVD SiO ₂ film (25) having a thickness of about 200 ° is deposited (FIG. B). Next, for example, irradiating an arc lamp in an oxidizing atmosphere, for example, performing an oxidation treatment at 1100 ° C. for 5 seconds.
At the interface between the CVD SiO ₂ film (25) and the polycrystalline silicon thin film (22), a SiO ₂ film (26) is formed by thermal oxidation, and the CVD SiO ₂ film (2
5) and gate insulation film (13 ₂ ) consisting of thermally oxidized SiO ₂ film (26)
Is formed (FIG. C). Next, a gate insulating film (13 ₂₎ forming a gate electrode (23) by the polycrystalline silicon on the source, the impurity for the drain by ion implantation, the source region is annealed (22S) and drain region (22D) Is formed (FIG. D). Thereafter, a thin film transistor having a top gate structure is obtained through processes such as formation of a normal passivation film, opening of a contact window, Al deposition, and hydrogen annealing.

In this example, it is possible to form the Figure 4 as well as flat and withstand good gate insulating film (13 _2), is not the thermal effect on the underlying substrate (11). In yet a top-gate structure, the most important gate insulating film (13 ₂₎ and the film quality good thermal oxidation at the interface between the channel region (22C) S
Advantageously, an iO ₂ film (26) is present. In addition, since the underlying polycrystalline silicon thin film (22) is densified during the high-temperature short-time oxidation in FIG. 5C, the trap density is reduced, and a higher-performance thin film transistor can be manufactured.

In the high-temperature short-time oxidation shown in FIGS. 4 and 5, laser irradiation can be used instead of lamp beam irradiation.

[Effects of the Invention] According to the present invention, after a reverse staggered thin film transistor is formed, hydrogen atoms are introduced into the channel region by ion implantation from the semiconductor thin film side.
Hydrogenation is performed easily and uniformly at the interface between the gate insulating film and the channel region. At the same time, ion implantation can be performed with low implantation energy, the implantation dose can be reduced, and damage to the polycrystalline semiconductor film can be reduced. In addition, since implantation energy is low, hydrogen atoms can be uniformly introduced only into the thinner polycrystalline semiconductor film region. Therefore, an inverted staggered thin film transistor having good characteristics can be manufactured.

Then, a gate electrode made of a semiconductor film is formed on a base region which is easily affected by heat, and the surface of the gate electrode is oxidized at a high temperature for a short time to form a gate insulating film made of a thermal oxide film. To form a reverse staggered thin film transistor, and when hydrogen atoms are introduced into the channel region from the semiconductor thin film side by ion implantation, a gate insulating film with good withstand voltage can be obtained and a reverse staggered thin film transistor with good characteristics can be obtained. It can be easily formed on the underlying region without thermally affecting the underlying region.

In addition, a gate electrode made of a semiconductor film is formed on a base region that is easily affected by heat, a CVD oxide film is formed on the gate electrode, and then oxidized at high temperature for a short time to form a gate insulating film made of the CVD oxide film and the thermal oxide film. After the formation, a semiconductor thin film having a channel region is formed to form an inverted staggered thin film transistor, and when hydrogen atoms are introduced into the channel region from the semiconductor thin film side by an ion implantation method, a gate insulating film having good flatness and good withstand voltage is formed. An inverted staggered thin film transistor having a film and good characteristics can be easily formed on the underlying region without thermally affecting the underlying region.

Therefore, the present invention can be suitably applied particularly to the manufacture of a thin film transistor applied to a three-dimensional LSI, a stacked SRAM, or an LSI on an insulating substrate.

[Brief description of the drawings]

1A to 1C are process diagrams showing an example of a method for manufacturing a thin film transistor according to the present invention, FIGS. 2A to 2C are process diagrams showing another example of a thin film transistor according to the present invention, and FIGS. Process diagram showing a reference example applied to a gate structure, FIG. 4A
5D are process diagrams showing another example of the thin film transistor according to the present invention, FIGS. 5A to 5D are process diagrams showing a reference example applied to a top gate structure, and FIG. FIG. 7 is a cross-sectional view illustrating an example of a hydrogenation method of a conventional bottom-gate thin film transistor. (11) is the substrate, (12) is the gate electrode, (13), (1
3 _1), (13 ₂₎ is a gate insulating film, (14) is polycrystalline silicon film, (16) is hydrogen, (25) is CVD SiO ₂ film, (26) is a thermally oxidized SiO ₂ film.

Claims (2)

(57) [Claims] A gate electrode formed of a semiconductor film on a base region which is easily affected by heat; a surface of the gate electrode is oxidized at a high temperature for a short time to form a gate insulating film formed of a thermal oxide film; Forming an inverted staggered thin film transistor by forming a semiconductor thin film having: and introducing hydrogen atoms into the channel region from the semiconductor thin film side by an ion implantation method. 2. A method of forming a gate electrode of a semiconductor film on a base region which is easily affected by heat, forming a CVD oxide film on the gate electrode, and then oxidizing the CVD oxide film at a high temperature for a short time. Forming a semiconductor film having a channel region, forming an inverted staggered thin film transistor, and introducing hydrogen atoms into the channel region from the semiconductor thin film side by an ion implantation method. Manufacturing method of thin film transistor.