JPH0362526A - Manufacture of thin film transistor - 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 thin film transistor.

[Summary of the invention]

In a method for manufacturing a thin film transistor, the present invention forms an inverted star-type thin film transistor having a channel region on a gate electrode via a gate insulating film, and then introduces hydrogen atoms into the channel region by ion implantation. This is intended to improve transistor characteristics by reducing crystal defects (dangling bonds) at the interface between the gate insulating film and the channel region.

Furthermore, by forming the gate insulating film by high-temperature, short-time oxidation, it is possible to improve the gate breakdown voltage and avoid thermal effects on the underlying layer.

Furthermore, by forming the gate insulating film by high-temperature, short-time oxidation after forming the CVD oxide film, a gate insulating film with good flatness and quality is obtained, thereby improving gate breakdown voltage.

[Background Art] In recent years, research on thin film transistors has been actively conducted. In order to improve the characteristics of thin film transistors using polycrystalline silicon thin films, hydrogen is introduced into the polycrystalline silicon thin film that serves as the channel region to eliminate crystal defects (so-called dangling bonds) that exist at grain boundaries.
A method to reduce this, ie, a hydrogenation method, is essential.

The commonly used hydrogenation method uses a hydrogenated plasma silicon nitride (plasma SiN:H) film as a passivation film, and heats it at about 400'C to diffuse hydrogen from this film through the glabella insulating film into the channel region. has become common.

In order to manufacture thin film transistors, as shown in FIG. 6, a gate insulating film (3) of SiO□ or the like is deposited on a polycrystalline silicon thin film (2) on an insulating substrate (1), as shown in FIG.
) A so-called top gate structure is adopted in which a gate electrode (4) is formed through a gate electrode (4). (2s) is the source region, (
2D) indicates a drain region, and (2C) indicates a channel region. A hydrogenated plasma silicon nitride film (5) as a passivation film is deposited on this thin film transistor, and by heat treatment, hydrogen (6) in the film (5) is transferred to the channel region (2C) and the channel region (2C) and gate. Insulating film (
3) can be easily introduced into the interface with

As a hydrogenation method, a method has also been experimentally proposed in which hydrogenation is carried out by exciting plasma from the cervical vertebrae of hydrogenated amorphous silicon (a-5i:H).

Furthermore, as a hydrogenation method for thin film transistors with a top gate structure, a method has been proposed in which hydrogen atoms are introduced into the silicon thin film from above the gate electrode by ion implantation after forming the gate electrode (Japanese Patent Laid-Open No. 60-1643
(See Publication No. 63).

On the other hand, as the gate insulating film of the thin film transistor, a SiO□ film formed by thermal oxidation or a 5iOz film formed by CVD (chemical vapor deposition) method (hereinafter referred to as CVD5iOz film) is used.

[Problem to be solved by the invention]

As mentioned above, in a top-gate structure thin film transistor, the gate insulating film (3) and channel region (3), which are important for transistor characteristics, are removed by the usual hydrogenation method shown in FIG.
Hydrogen easily reaches the interface with 2C). However,
Recently, p-channel MOS transistors have been added to n-channel MOS transistors.
A completely CMO3 type SRAM (static RAM) that uses memory cells made by stacking O3 thin film transistors has been proposed, but such so-called stacked SR
As shown in Figure 7, thin film transistors applied to AM etc. are mainly due to manufacturing process requirements such as flattening.
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 of an insulating substrate or the like. In this case, even if a hydrogenated plasma silicon nitride film (5) is deposited and heat-treated as a passivation film, hydrogen (6) from the hydrogenated plasma silicon nitride film (5) is slightly removed from the polycrystalline silicon thin film (2). ), but the hydrogenation effect cannot be obtained because the hydrogenation does not reach the interface between the gate insulating film (3) and the channel region (2C).

Note that in the top gate structure, when hydrogen atoms are introduced by ion implantation, it is difficult to uniformly introduce hydrogen atoms into the channel region because the hydrogen atoms are actually in the shadow of the gate electrode.

On the other hand, regarding the gate insulating film of a thin film transistor, when a StO□ film formed by thermal oxidation of the surface of a silicon thin film is used, a gate insulating film with good breakdown voltage can be obtained because it is a dense and high quality film. However, since the furnace oxidation method requires a high-temperature process, so-called three-dimensional LS such as stacked SRAM
I cannot be applied because it causes re-diffusion of the source and drain regions of the underlying LSI MOS transistor. Further, even on quartz, it takes a long time, for example, about 60 minutes. This furnace oxidation can be expected to have the effect of densifying the polycrystalline silicon thin film at the same time as forming the oxide film, and this densification reduces the trap density in the polycrystalline silicon thin film. Reducing trap density reduces leakage current.

Characteristics of thin film transistors can be improved, such as by increasing hyperactivity μ and decreasing gate voltage swing.

The higher the oxidation temperature, the more effective the trap density reduction effect is, but the above-mentioned problems occur when the oxidation temperature is high, and when the base is a quartz substrate, oxidation at 1000° C. or higher in a furnace becomes difficult due to the softening of the quartz. Furthermore, when a gate insulating film is formed using a CVD5iOz film, it has drawbacks such as a sparse film quality with many pinholes and variations in breakdown voltage.

In view of the above-mentioned points, the present invention provides a method for manufacturing a thin film transistor that enables good hydrogenation in an inverted staggered transistor.

The present invention also provides a method for manufacturing a thin film transistor that makes it possible to form a high-quality gate insulating film without thermally affecting the underlying layer.

[Means to solve the problem]

The method for manufacturing a thin film transistor of the present invention includes forming an inverted staggered thin film transistor having a channel region on a gate electrode via a gate insulating film, and then introducing hydrogen atoms into the channel region by ion implantation.

Further, the gate insulating film is formed by high-temperature, short-time oxidation using, for example, lamp irradiation, laser irradiation, or the like.

Alternatively, after forming the CVD oxide film, a gate insulating film is formed by high temperature short time oxidation.

[Effect]

In the above manufacturing method, after forming an inverted staggered thin film transistor, hydrogen atoms are introduced into the channel region by ion implantation, so that hydrogen atoms can be easily and uniformly introduced into the channel region and the interface between the channel region and the gate insulating film. will be introduced in

As a result, the inverted staggered thin film transistor is hydrogenated, crystal defects in the channel region and at the interface with the gate insulating film are reduced, and the transistor characteristics are improved.

On the other hand, when forming a gate insulating film using a thermal oxide film obtained by oxidizing the semiconductor/body film surface at high temperature and for a short period of time, a gate insulating film with a denser film quality and good breakdown voltage can be obtained, and at the same time, it is possible to There is no thermal effect on the

In particular, in three-dimensional LSIs in which thin film transistors are stacked, stacked SRAMs, etc., re-diffusion of the source and drain regions of the underlying MO3I transistors is avoided.

In addition, when forming a CVD oxide film on the surface of a semiconductor film and then oxidizing it at high temperature for a short time to form a gate insulating film, the gate insulating film is flattened by the CVD oxide film, and the gate insulating film is flattened by the CVD oxide film, and a dense thermal oxide film is formed by heat treatment. Since it is formed of a dense CVD film, a gate insulating film with good breakdown voltage can be obtained, and as mentioned above, there is no thermal influence on the underlying region.

[Example] Hereinafter, an example of a method for manufacturing a thin film transistor according to the present invention will be described with reference to the drawings.

In this example, first, as shown in FIG.
1) After forming a gate electrode (12) on the gate electrode (12), a polycrystalline silicon thin film (14) is formed on the gate electrode (12) via a gate insulating film (13) made of, for example, SiO□, and impurities are introduced. Then, a source region (14S) and a drain region (140) are formed to form an inverted staggered thin film transistor (15).

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

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

In recent thin film transistors, polycrystalline silicon thin films (14
The film thickness d is becoming smaller, for example, to about 1000 people. Therefore, hydrogen can be easily introduced into the interface between the channel region (14C) and the gate insulating film (13) with low implantation energy. Furthermore, since the implantation dose can be effectively reduced due to the low implantation energy, there is little damage to the polycrystalline silicon thin film (14).
Note that hydrogen ions have a small mass number, so the damage is inherently small.)

After the ion implantation, the ions are heated at 400° in an inert gas atmosphere such as forming gas (N2 gas containing 2 to 3% H).
Perform annealing treatment before and after C.

After that, a passivation film (
17) is deposited and formed. The passivation film (17) is a hydrogenated plasma silicon nitride film or other Si0
A g film can also be used.

According to the above manufacturing method, hydrogen atoms are introduced by ion implantation after the inverted staggered thin film transistor (15) is formed, so that the hydrogen atoms are introduced into the channel region (14C) of the polycrystalline silicon thin film (14) and the channel region. (14G)
It can be easily and uniformly introduced into the interface between the film and the gate insulating film (13). At this time, ion implantation is possible with low implantation energy, so polycrystalline silicon thin film (14
) damage is small. Further, by hydrogen ion implantation and subsequent annealing treatment, it is possible to easily perform hydrogenation on an inverted stagger type thin film transistor, which was previously impossible, and the characteristics of the thin film transistor can be improved. Furthermore, since hydrogen atoms are introduced by ion implantation, an insulating film other than the conventionally commonly used hydrogenated plasma silicon nitride (plasma SiN) film may be used as the passivation film (17). This makes it possible to improve the degree of freedom in the passivation film formation process.

Next, an example of a method for forming a gate insulating film will be described.

This invention can be applied to both bottom gate structure (inverted stagger type) and top gate structure thin film transistors.

In the case of a bottom gate structure, for example, as shown in FIG. 2, after forming a gate electrode (12) made of a polycrystalline silicon film on a substrate (11) (A in the same figure), a lamp beam, e.g. For example, 110
Gate electrode (12) was subjected to oxidation treatment at 0°C for 530 seconds.
For example, there is a thermal oxide film (SiOx) on the surface of the
A gate insulating film (13,) is formed using a film (FIG. 1B). Thereafter, a polycrystalline silicon thin film (14) is formed to surround the gate electrode (12), and impurities for source and drain are ion-implanted to form a source region (14S) and a drain region (140) (the same figure). C).

In this way, the gate insulating film (1
3), a gate insulating film with dense film quality and good withstand voltage can be obtained, and the underlying substrate (11) will not be thermally affected. That is, for example, three-dimensional LS I
In stacked SRAMs, etc., the source and drain regions of MOS transistors formed on the base substrate (11) are not re-diffused, making it possible to manufacture high-performance three-dimensional LSIs and stacked SRAMs. . Furthermore, these 3
Dimensional LSI.

In a stacked SRAM or the like, the high-temperature, short-time oxidation shown in FIG. 3B also serves to activate the source and drain regions of the underlying MOS transistor. Furthermore, when forming a thin film transistor LSI on a quartz or glass substrate, for example, a high-performance LSI can be manufactured without softening the quartz or glass substrate constituting the base substrate (11).

In addition, due to such high-temperature, short-time oxidation, the gate insulating film (
131), it becomes possible to manufacture fine-sized thin film transistors. Furthermore, high-temperature, short-time oxidation also has a densifying effect, and can be expected to improve the breakdown voltage and flatness of the gate insulating film (13,).

In the case of a top gate structure, for example, as shown in FIG. 3, an island-shaped polycrystalline silicon thin film (22
) (A in the same figure), at the same time as described above, e.g. arc lamp light is irradiated in an oxygen atmosphere to e.g. 1100°.
A polycrystalline silicon thin film (2
2), for example, a thermal oxide film (Si) of about 100 layers thick.
A gate insulating film (13,) is formed using a n2 film (FIG. B). Next, a gate electrode (23) made of polycrystalline silicon is formed on the gate insulating film (13,), impurities for source and drain are ion-implanted, and annealed to form a source region (22S) and a drain region (22D). ) to form (
Figure C). After that, the usual process is to deposit a passivation film and open a contact window.

A top gate structure thin film transistor is obtained through processes such as Al vapor deposition and hydrogen annealing.

In this example, the same effect as in the case of the bottom gate structure can be obtained, and in addition, during high-temperature, short-time oxidation (step B in Figure 4), the polycrystalline silicon thin film (22) is densified and the trap density is reduced. Fewer thin film transistors can be obtained.

In addition, in Figures 2 and 3, high-temperature, short-time oxidation was performed using lamp light, but the same effects and results can be obtained by performing high-temperature, short-time oxidation by irradiating, for example, an excimer laser pulse instead of lamp light. It will be done. As the excimer laser, one whose energy density has been made uniform by a beam homogenizer is used, such as excimer laser (XeC1),
80 Hz and energy of about 280 mJ/c+fl can be used. Before forming the polycrystalline silicon thin film (22) into an island form, the polycrystalline silicon thin film (22) may be formed into an island form after being irradiated with an excimer laser to form a gate insulating film (131). Source area (22S),
The drain region (22D) is annealed at 600° C. or less or by excimer laser.

FIGS. 4 and 5 show other examples of the method of forming the gate insulating film. In the case of a bottom gate structure, as shown in FIG. 4, a gate electrode (
12) (FIG. 1A), a 5VDSiO□ film (25) with a thickness of about 200, for example, is formed on the gate electrode (12).
(B). Next, in an oxygen atmosphere, a lamp beam, for example, an arc lamp beam is irradiated to
A CVD5iOz film (2
5) and the gate electrode (12) by thermal oxidation.
A gate insulating film (13) consisting of a CVD5iOz film (25) and a thermally oxidized SiO□ film (26) is formed.
□) (Figure C). After that, the gate electrode (1
2) A polycrystalline silicon thin film (14) is formed so as to surround the top, and impurity ions for source and drain are implanted to form a source region (14S) and a drain region (140) (FIG. 3D).

According to such a gate insulating film (13□), CVD5i
The flatness of the gate insulating film (13□) is obtained by the O□ film (25), and the CVD5iO□ film (25) is densified by the heat treatment when the thermally oxidized Si0g film (26) is formed, so that the gate insulating film (13□) as a whole is The film quality of the insulating film becomes dense, and a gate insulating film with good breakdown voltage can be obtained. Incidentally, when forming a gate insulating film using the conventional thermal oxidation method, the flatness of the gate insulating film deteriorates because the oxidation occurs along the grain boundaries of polycrystalline silicon, but the flatness of the gate insulating film becomes better with the thermal oxidation method. . Further, in this example, as in the case above, it is possible to manufacture thin film transistors with fine dimensions, and there is no thermal influence on the underlying substrate (11).

In the case of the top gate structure, as shown in Fig. 5, after forming an island-shaped polycrystalline silicon thin film (22) on the substrate (11) (Fig. A CVD5iO □ film (2
5) is deposited and formed (B in the same figure). Next, in an oxygen atmosphere, e.g., arc lamp light is irradiated to e.g. 1100°C.
After 5 seconds of oxidation treatment, Si was formed by thermal oxidation at the interface between the CVD 5iOz film (25) and the polycrystalline silicon thin film (22).
n, a gate insulating film (13) consisting of a CVD 5iOz film (25) and a thermally oxidized 5ift film (26), which forms the film (26).
g) is formed (C in the same figure). Next, the gate insulating film (13
g) Form a gate electrode (23) made of polycrystalline silicon on top, ion-implant impurities for source and drain, and annealing to form a source region (22S) and a drain region (22S).
D) is formed (D in the same figure). Thereafter, a top gate structure thin film transistor is obtained through the usual steps of forming a passivation film, opening a contact window, AI vapor deposition, and hydrogen annealing.

In this example as well, it is possible to form a flat gate insulating film (13□) with good breakdown voltage, as in FIG. 4, and there is no thermal influence on the base substrate (11).

Furthermore, the top gate structure is advantageous because a thermally oxidized Si0g film (26) of good quality exists at the most important interface between the gate insulating film (13□) and the channel region (22C). Also, during the high temperature short time oxidation in Figure 6C,
Since the underlying polycrystalline silicon thin film (22) is densified, the trap density is reduced and a thin film transistor with higher performance can be manufactured.

Note that in the high-temperature, short-time oxidation shown in FIGS. 5 and 6, laser irradiation may be used instead of lamp irradiation.

[Effects of the Invention] According to the present invention, hydrogen atoms are introduced into the channel region by ion implantation after forming the inverted stagger type 7ij and the film transistor. Hydrogenation is easily and uniformly introduced into the interface between the hydrogen and the channel region, and therefore an inverted staggered thin film transistor with good characteristics can be manufactured.

In addition, when forming the gate insulating film of a thin film transistor by high-temperature, short-time oxidation, it is possible to obtain a gate insulating film with good withstand voltage, and there is no thermal effect on the underlying region. . Furthermore, when forming a gate insulating film by oxidizing at high temperature for a short time after forming a CVD oxide film, it is possible to obtain a gate insulating film with good flatness and withstand voltage, and it also avoids thermal effects on the underlying region. Never. Therefore, especially the three-dimensional L
SI, stacked SRAM, or LSI on an insulating substrate
This makes it suitable for application to the manufacture of thin film transistors for applications such as the following.

[Brief explanation of drawings]

FIGS. 1A-C are process diagrams showing an example of the method for manufacturing a thin film transistor according to the present invention, FIGS. 2A-C and 3A-C are process diagrams showing other examples of the thin film transistor according to the present invention, respectively,
4A-D and 5A-D are process diagrams showing other examples of thin film transistors according to the present invention, respectively, and FIG. 6 is a cross-sectional view showing an example of a hydrogenation method for a conventional thin film transistor with a top gate structure. , and FIG. 7 are cross-sectional views showing an example of a hydrogenation method for a conventional bottom-gate structure thin film transistor. (11) is the substrate, (12) is the gate electrode, (13),
(13,). (13□) is a gate insulating film, (14) is a polycrystalline silicon film, (16) is hydrogen, (25) is a CVD5iOz film, (
26) is a thermally oxidized Si0g film. Agent Hidemori Matsukuma 11... - Master grade 12... Gate electrode 13... Gate Zetsu hIII 14... Rare crystal silicon III @ 15... - The leader is snowing' Tsukizo transistor 16...
・Hydrogen high ion master 17--Noma Tsunba-geon 1 1--Curtain board 12--Kate electric cover 13r--Gate clear kll odor 14--Introduction to silicon book membrane 2 2nd Figure 11--Basic source 131...Gate support line 22...Recrystalline silicon 225--Sor and tilt d 22D-...Drain 4iz years old'' 22C...Character@area 23- --ke; Todenmei 7l-31 edition 12 --- Kate 1 piece IJF--Date has 91 Monthly bag I4-Eleven Chin Shaojing silicon book pus 25--CVD5i (h Monthly fee 26- --Gongga 1~11 Igo, 5iOz order 2 11-11 act class 131-・ke;tof?!#pus 22---Ne bucket hair ^ Silicon thin film 22S--・Source 4 pieces or 22D・Bottom Ray〉Now Q Castle' 22C--・Sudenel 1 East 23 ・--Ke"-to Electrical 2S---CVD5i (h Tsukihana 26---11M conversion 5t (hR 1-Base 2・-iI) Shao crystal silicon 4 call J---Ge F Zetsu #pus 4-1-date electronic book 5・-・red, t+hyphrasma nitrogen 4 do silicon> membrane 6--
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Claims (1)

[Claims] 1. A thin film transistor characterized in that, after forming an inverted staggered thin film transistor having a channel region on a gate electrode via a gate insulating film, hydrogen atoms are introduced into the channel region by ion implantation. manufacturing method. 2. A method for manufacturing a thin film transistor, characterized in that a gate insulating film is formed by high-temperature, short-time oxidation. 3. A method for manufacturing a thin film transistor, characterized in that a gate insulating film is formed by high-temperature, short-time oxidation after the formation of a CVD oxide film.