JPH0444274A - Thin film semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To stably operate a thin film semiconductor device associated with a liquid crystal display, an image sensor, etc., for a long period irrespective of an aging change in a display image quality, a read signal by composing an insulating film of a silicon oxide nitride (SiOxNy), and so forming it as to reduce a nitrogen content while increase an oxygen content continuously from the silicon semiconductor layer side toward a gate electrode. CONSTITUTION:A gate electrode G is formed on a glass board 1, and a gate insulating film 2 made of silicon oxide nitride (SiO2Ndy) is formed on the surface. In this method, a plasma CVE device 10 is used, mixture gas for forming silicon oxide nitride is supplied into a film forming chamber 11, and the flow rate of the mixture gas is varied in an aging manner by a mass flow controller 12. Accordingly, the film 2 of the composition represented by an atomic composition ratio, i.e., in which the nitrogen content is continuously reduced from an emorphous silicon semiconductor layer 3 side toward the electrode G, while its oxygen content is continuously increased from the layer 3 side toward the electrode G side, is formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a thin film semiconductor device used for driving various devices such as linear image sensors and liquid crystal displays, and in particular, the present invention relates to a thin film semiconductor device that is used for driving various devices such as linear image sensors and liquid crystal displays. This invention relates to improvements in thin film semiconductor devices that do not easily change over time.

[Conventional technology]

As shown in FIGS. 11 and 12, this type of thin film semiconductor device includes a glass substrate (a) and a glass substrate (a).
), a gate insulating film (b) covering the second gate electrode (G), and a thin silicon film provided on the gate insulating film (b) and acting as an active layer. Semiconductor layer (C) and this silicon semiconductor layer (C)
r inverted stagger type 1, which constitutes its main part with a source electrode (S) and a drain electrode (D) connected to both ends of the
As shown in FIGS. 13 and 14, there is a MOS type thin film transistor called a glass substrate (a) and a thin silicon semiconductor layer (C) provided on the glass substrate (a).
and a source electrode (S) connected to both ends of this silicon semiconductor layer (C), a drain electrode (D), and a gate electrode provided on the silicon semiconductor layer (C) via a gate insulating film (b). A MOS type thin film transistor called "r stagger type" whose main part is composed of (G) and (G) is known.

In these MOS type thin film transistors, a drain voltage (V, ) is applied between the source electrode (S) and the drain electrode (D), and the gate electrode (G)
A channel is formed in the silicon semiconductor layer (C) by applying a predetermined gate voltage (v6) to r threshold voltage VTHJ
If it is set below, a channel will not be formed in the silicon semiconductor layer (C), the transistor will be in an OFF state, and the drain current (I,) will not flow, and it will not be used for driving the various devices mentioned above. It is something that

By the way, in this type of thin film semiconductor device, the gate insulating film (
Conventionally, b) is composed of a SiO2 film formed by thermal oxidation treatment of a silicon layer formed on a substrate.

However, when forming a gate insulating film using a Si film using this thermal oxidation method, the insulating substrate is exposed to high temperatures of about 1000°C, so there is a drawback that it cannot be applied to inexpensive glass substrates with poor heat resistance. Si by this thermal oxidation method
In recent years, low pressure CVD method and plasma CVD method have been used instead of O□ film.
A silicon oxide gate insulating film, a silicon nitride gate insulating film, etc. formed by a film deposition method that does not require high temperature conditions, such as the D method, are used.

That is, the gate insulating film made of silicon oxide is made of, for example, 5i14 (silane) gas, - (oxygen) gas,
Furthermore, low pressure CVD using a mixed gas consisting of Nt (nitrogen) gas added to suppress the explosive reaction of both gases.
It is an electrically insulating film formed by a method such as a method or an atmospheric pressure CVD method, and its chemical structure is represented by a structural formula such as SiO.The other gate insulating film made of silicon nitride is, for example, S+H+( silane) gas and Nus (ammonia)
It is an electrically insulating film formed by plasma CVD using a mixed gas, and its chemical structure is 3i.
It was shown by the structural formula of Nx.

[Problem to be solved by the invention]

When the gate insulating film is composed of these compounds, the thermal conditions during film formation are relaxed and an inexpensive insulating substrate such as a glass substrate can be used.
On the other hand, the gate insulating film is made of silicon oxide (5iO2).
), the silicon oxide bulk itself has the advantage of having fewer trap levels (1), but there is a gap between the silicon oxide and the adjacent silicon semiconductor layer (the area indicated by α in the energy band diagram in Figure 15). Since there are many interface states 1 (portions indicated by β in the energy band diagram of FIG. 15), there is a problem that the determined threshold voltage VTH of the thin film semiconductor device tends to change over time.

On the other hand, when the gate insulating film is made of silicon nitride (SiN), there is an advantage that the r-interface level 1 between the silicon semiconductor layer and the silicon nitride is small, as opposed to when silicon oxide is used. Since there are many C trap levels 1 in the bulk of silicon itself, there is a problem in that the threshold voltage V7H tends to change over time, similar to when silicon oxide is used.

For this reason, when these thin film semiconductor devices are incorporated into the above-mentioned liquid crystal display, image sensor, etc., there is a problem that the display image quality and read signals change over time, making it impossible to expect stable operation over a long period of time.

[Means to solve the problem]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thin film semiconductor device in which the threshold voltage does not easily change over time, and a method for manufacturing the same.

In other words, the invention according to claim 1 provides the following: an insulating substrate, a thin silicon semiconductor layer provided on this substrate and forming an active layer, a source/drain electrode connected to this silicon semiconductor layer, and a gate insulating film interposed therebetween. Assuming a thin film semiconductor device comprising a gate electrode disposed opposite to the silicon semiconductor layer, the gate insulating film is composed of silicon nitride oxide (SiOxNy), and the silicon nitride oxide (SiO,N,) While the nitrogen component in the film continuously decreases from the silicon semiconductor layer side to the gate electrode side, the oxygen component, on the contrary, continuously increases from the silicon semiconductor layer side to the gate electrode side. On the other hand, the invention according to claim 2 is based on the method for manufacturing a thin film semiconductor device according to claim 1, and the gate insulating film made of silicon nitride oxide (SiOXNF) is Chemical veins - Devotion solution (
During the film formation process of this gate insulating film, the nitrogen component ratio of the silicon nitride oxide (SiOxNy) composition gas supplied into the film formation chamber changes over time. The present invention is characterized in that the composition ratio of the mixed gas is continuously changed and supplied so that the ratio of the oxygen component increases or decreases while the ratio of the oxygen component decreases or increases.

In the invention according to claim 1 as described above, as the insulating substrate, a glass plate, a quartz plate, etc. can be used as in the past, and on the other hand, as the silicon semiconductor constituting the active layer, intrinsic amorphous silicon, 3 value or 5
Amorphous silicon into which valence ions are introduced, polysilicon, or the like can be used.

Furthermore, the silicon nitride oxide (Si) constituting the gate insulating film is
O□N,), while the nitrogen component in the film continuously decreases from the silicon semiconductor layer side to the gate electrode side (that is, the value of y in the above structural formula decreases continuously),
On the contrary, the oxygen component is characterized by continuously increasing from the silicon semiconductor layer side toward the gate electrode side (that is, the value of X in the structural formula increases continuously).

In the gate insulating film, the oxygen component on the side adjacent to the silicon semiconductor layer is small, and silicon nitride (
Silicon nitride oxide (SIO-NF), which has the same or similar structure to SiN, ), is adjacent to the silicon semiconductor layer, and silicon oxide (5iO3) is not directly adjacent to it. Since the interface level 1 decreases and the composition of silicon nitride oxide (SiOfNF) in the gate insulating film changes continuously, making it difficult to form an interface therein, the gate insulating film is composed of multiple materials. The increase in the r-interface level 1 in this gate insulating film is suppressed despite the fact that the r-trap level in this gate insulating film is ) Since the nitrogen component in the composition decreases continuously from the silicon semiconductor layer side to the gate electrode side, the "trap quasi" decreases as the ratio of silicon nitride (SiN, ) in the gate insulating film decreases. 1 will also be reduced.

Therefore, in the thin film semiconductor device according to claim 1, the "interface level" and r-trap level 1 of the gate insulating film are reduced, so that the conventional change in threshold voltage VTH over time can be prevented. have.

Next, the invention according to claim 2 provides the silicon nitride oxide (Si
As a means of forming a gate insulating film composed of (OxNy), a CVD (chemical vapor deposition) method such as a plasma CVD method, a photoCVD method, or a normal pressure or low pressure CVD method is applied. It is characterized by:

The silicon nitride oxide (SiOfNF) constituent gas supplied into the film formation chamber of this CV [device] includes, for example,
StH+ (silane) gas as a gas for silicon component, 5
iC14 (silicon chloride) gas, 5itHs (disilane) gas, etc. can be applied, while Ol (oxygen) gas, CO! (carbon dioxide) gas,
Also, as the gas for the nitrogen component, NH, (ammonia) gas, etc. can be used.

Note that N containing hydrogen atoms is used as the gas for the nitrogen component mentioned above.
11 (ammonia), etc., hydrogen atoms contained in this gas saturate the silicon dangling bonds (broken bonds) on the surface of the silicon semiconductor layer during film formation, so that the silicon semiconductor layer and silicon nitride oxide (SiOXNF
) has the advantage of further reducing the T-interface level 1 between them.

Further, during the film formation process of the gate insulating film, as means for continuously changing the composition ratio of the mixed gas for forming silicon nitride oxide (StO, N,) supplied into the film formation chamber, for example, the above-mentioned method can be used. A method can be adopted in which the flow rate ratio of the mixed gas is adjusted using a mass flow controller that controls the supply amount of each component gas supplied into the film forming chamber. In other words, when forming a gate insulating film on the gate electrode surface, the composition ratio of the mixed gas is continuously adjusted so that the ratio of nitrogen component increases over time, while the ratio of oxygen component decreases. In addition, when forming a gate insulating film on a silicon semiconductor layer, the mixed gas is supplied so that the ratio of nitrogen component decreases over time, while the ratio of oxygen component increases over time. It is supplied by continuously changing the composition ratio.

[Effect]

According to the invention according to claim 1, the gate insulating film is made of silicon nitride oxide (S+0-Ny), and the nitrogen component in this silicon nitride oxide (StO-Ny) film is distributed from the silicon semiconductor layer side to the gate electrode side. On the other hand, the oxygen component continuously increases from the silicon semiconductor layer side to the gate electrode side. Silicon nitride (SiN,
) is adjacent to the silicon semiconductor layer, so that the r-interface level j between these adjoining layers is reduced, and the silicon nitride oxide in the gate insulating film is The composition of the gate insulating film changes continuously and it is difficult to form an interface within it. Therefore, even though the gate insulating film is made of multiple materials, the increase in the interface level 1 in the gate insulating film is suppressed. On the other hand, regarding the "trap level 1" in this gate insulating film, the nitrogen component in the silicon nitride oxide (S+0-Ny) composition constituting it continues from the silicon semiconductor layer side to the gate electrode side. As the ratio of silicon nitride (SiN) in the gate insulating film decreases, the
It is also possible to reduce the trap level 1.

Further, according to the invention according to claim 2, the gate insulating film made of silicon nitride oxide (Sho-Ny) is formed by chemical vapor deposition (CVD).
) method, and during the film-forming process of this gate insulating film, the ratio of nitrogen component of the mixed gas for forming silicon nitride oxide (SiOfNr) supplied into the film-forming chamber decreases or decreases over time. Since the composition ratio of the mixed gas is continuously changed and supplied so that the ratio of the oxygen component increases or decreases while the ratio of the oxygen component increases or decreases, the nitrogen component in the silicon nitride oxide (SiO, N,) film increases. While the oxygen component continuously decreases from the silicon semiconductor layer side to the gate electrode side, the oxygen component increases continuously from the silicon semiconductor layer side to the gate electrode side. It becomes possible to form.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

◎First Embodiment In this embodiment, the present invention is applied to an "r inverted stagger type" MOS transistor.

That is, this thin film MOS transistor is shown in FIGS.
As shown in Fig. 2, there is a glass substrate (1), a gate electrode (G) formed on the glass substrate (1) and made of 500% Cr, and a coating covering the gate electrode (G). A gate insulating film (2) made of silicon nitride oxide (SJO) with a thickness of 3000 μm and a gate insulating film (2)
500mm thick amorphous silicon layered on top (
a-3i:H) A semiconductor layer (3) and a protective layer formed of SiN with a thickness of 1500 nm and provided on the amorphous silicon semiconductor layer (3) at a portion corresponding to the gate electrode (G). 4), an ohmic contact forming layer (5) formed of n+ amorphous silicon (n''a-3i) with a thickness of 1000 nm and provided on both end sides of the amorphous silicon semiconductor layer (3), and this ohmic contact. The amorphous silicon semiconductor layer (3) is formed through the formation layer (5).
) connected to the source electrode (S) formed of 1 μm thick AI and the drain electrode (D), the main part of which is connected to the silicon nitride oxide ( As for SiO(N), its nitrogen component continuously decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side, while its oxygen component conversely decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side. The film is formed so as to continuously increase from the side toward the gate electrode (G) side.

In this MOS transistor, the gate insulating film (2) is made of silicon nitride oxide (SiOfNF), and the nitrogen component in this silicon nitride oxide (SiOfNF) film is transferred from the amorphous silicon semiconductor layer (3) side to the gate electrode. On the other hand, the oxygen component decreases continuously toward the (G) side, whereas the oxygen component decreases in the amorphous silicon semiconductor layer (3).
) side toward the gate electrode (G) side, in this gate insulating film (2), the oxygen component on the side adjacent to the amorphous silicon semiconductor layer (3) is small, and the silicon nitride Silicon nitride oxide having the same structure as (SiN) or similar to this is adjacent to the amorphous silicon semiconductor layer (3), so that the "interface level 1" between these adjacent layers is reduced, and the gate The composition of silicon nitride oxide in the insulating film (2) changes continuously, making it difficult to form an interface within it. While the increase in the r-interface level in the gate insulating film (2) is suppressed, the trap level 1 in the gate insulating film (2) is
Since the nitrogen component in the composition of OfN, ) continuously decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side, silicon nitride (SiN, ) decreases in proportion to its [
The trap level J is reduced.

Therefore, in the MOS l-transistor according to this example, the r-interface level 1 and the r-trap level 1 of the gate insulating film (2) are reduced, so that the threshold voltage VT8 changes over time. It has the advantage of being difficult.

"Manufacturing Process of MOS Transistor" Hereinafter, the manufacturing process of the MOS l-transistor according to this embodiment will be explained in detail with reference to the drawings.

First, as shown in FIG. 3(A), a gate electrode (G) with a thickness of 500 mm is made of Cr on a glass substrate (1).
A gate insulating film (2) made of silicon nitride oxide (Si, xNy) is formed to a thickness of 3000 nm on this surface (see FIG. 3B).

In this case, the gate insulating film (2) is formed by the following method. That is, using a plasma CVD apparatus (10) as shown in FIG.
11) SiH, + as a gas for forming silicon nitride oxide
By supplying a mixed gas of NH+++N2O and changing the flow rate ratio of the mixed gas over time as shown in Fig. 5 using a mass flow controller (12) that controls the supply amount of each constituent gas. , the gate insulating film (2) has the composition shown by the atomic composition ratio in FIG. 6, that is, its nitrogen component continuously decreases from the amorphous silicon semiconductor layer (3) side toward the gate electrode (G) side. on the other hand,
On the contrary, the oxygen component is in the amorphous silicon semiconductor layer (
A gate insulating film (2) was formed which continuously increases from the 3) side toward the gate electrode (G) side. The film forming conditions at this time were: glass substrate temperature: 350°C, pressure crab: 0.
2 Torr and RE power: 100W.

Next, only the gas was switched without breaking the vacuum to form an amorphous silicon (a-3i:H) semiconductor layer (
3) and a nitride film (4゛) with a thickness of 1,500 yen (see Figure 3C), and then a positive resist layer (
r) was formed into a film (see the third diagram).

Then, as shown in FIG. 3(E), the glass substrate (1
) side to change the resist layer (r) in the exposed area to a property that can be dissolved by a developer, and then remove the resist layer (r) in the exposed area with the developer (see Figure 3C). On the other hand, the exposed nitride film (4') is dissolved and removed with buffered hydrofluoric acid to form a protective layer (4) as shown in Figure 3 (G).
form.

Next, a film with a thickness of 100 mm is formed on this surface by plasma CVD method.
An ohmic contact forming layer (5) is formed by depositing 0 n+ amorphous silicon (n" a-5i), and further,
After forming a 1 μm aluminum (AI) film (6) on this surface (see Figure 3C), this aluminum film (6)
are patterned to form a source electrode (S) and a drain electrode (D) as shown in FIG. 3(I), and an ohmic contact forming layer (5) exposed from these electrodes.
3 (J) was removed by dry etching.
) was obtained.

Note that silicon nitride oxide (
Regarding the composition of SiOxNy), as shown in FIG. 7, the composition on the gate electrode (G) side is 5iO0, and the composition on the amorphous silicon semiconductor layer (3) side is SiNx.
Further, the composition between these may be S+0-Ny in which the nitrogen atoms and oxygen atoms change continuously.

◎Second Embodiment In this embodiment, the present invention is applied to a 1-brainer type MOS transistor.

That is, this thin film MOS l-transistor is
As shown in the figure, the glass substrate (1) and this glass substrate (
1) Consisting of an amorphous silicon semiconductor layer (3) with a thickness of 2000 nm provided above and silicon nitride oxide (SiO□N) laminated on this amorphous silicon semiconductor layer (3) with a thickness of 3000 nm. A gate insulating film (2), a gate electrode (G) formed on the gate insulating film (2), and a gate electrode (G) formed on the amorphous silicon semiconductor layer (3) at both ends of the amorphous silicon semiconductor layer (3). AI connected to the source electrode (S) and drain electrode (D) through the source electrode (S) and drain electrode (D) and the contact hole (7) provided in the gate insulating film (2). The main part is constituted by the wiring part (8), and
Silicon nitride oxide (Si) constituting the gate insulating film (2)
Regarding O, N,), the nitrogen component continuously decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side, while the oxygen component decreases conversely from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side. Gate electrode (G) from the side
) The film is formed so as to continuously increase toward the side.

Also in this Brehner-type JMOS transistor, the gate insulating film (2) is made of silicon nitride oxide (StO
This silicon nitride oxide (Si
O, N,) While the nitrogen component in the film decreases continuously from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side, the oxygen component, on the contrary, decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side. Since the oxygen component increases continuously from the side to the gate electrode (G) side, in this gate insulating film (2), the oxygen component on the side adjacent to the amorphous silicon semiconductor layer (3) is small, and the silicon nitride ( Silicon nitride oxide having the same or similar structure to SiN, ) is adjacent to the amorphous silicon semiconductor layer (3), so that the "interface level 1" between these adjacent layers is reduced, and the gate insulation film(
The composition of silicon nitride oxide in the silicon nitride oxide layer (2) changes continuously, making it difficult to form an interface therein. ) is suppressed, while the r-trap level 1 in the gate insulating film (2) is suppressed by the silicon nitride oxide (Si) constituting the gate insulating film (2).
Since the nitrogen component in the composition of OfNF continuously decreases from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side, silicon nitride (SiN, ) in the gate insulating film (2) As the ratio of
Trap level 1 is reduced.

Therefore, in the Brehner-type JMOS transistor according to this embodiment, the threshold voltage VTH also decreases over time because the interface level and trap level 1 of the gate insulating film (2) decrease. It has the advantage of being difficult to change.

"Manufacturing Process of MOS Transistor" Hereinafter, the manufacturing process of the MOS transistor according to the second embodiment will be explained in detail with reference to the drawings.

First, as shown in FIG. 9(A), an amorphous silicon semiconductor layer (3) is formed on a glass substrate (1), and then silicon nitride oxide (SxO-Ny) is formed to a thickness of 3000 nm using the plasma CVD method. After forming the gate insulating film (2) (see FIG. 9B), as shown in FIG. Further, a resist layer (r) is formed in a pattern on this upper surface.

Regarding the atomic composition in the gate insulating film (2),
As in the first embodiment, by changing the flow rate ratio of the constituent gas mixture over time, the nitrogen component decreases continuously from the amorphous silicon semiconductor layer (3) side to the gate electrode (G) side. On the other hand, the oxygen component flows from the amorphous silicon semiconductor layer (3) side to the gate electrode (
G) It is adjusted so that it increases continuously toward the side.

Next, the Cr film (G) exposed from the resist layer (r) is removed by an etching method to form a gate electrode (G) as shown in FIG. 9(D), and as shown in FIG. 9(E). As shown in Figure 2, p+ ions of 2 x 10" 1ons/crl are implanted into both end portions of the amorphous silicon semiconductor layer (3) from above through the gate insulating film (2) by an ion implantation method to form a source electrode (S). ) A drain electrode (D) was formed.

Then, a contact hole (
7) and form an aluminum wiring part (8) connected to the source electrode (S) and drain electrode (D) through this contact hole (7), as shown in FIG. 9(F). A MOS transistor as shown was obtained.

◎Third Embodiment In this embodiment, the present invention is applied to one stagger type MOS transistor.

That is, as shown in FIG. 1O(A), a glass substrate (1
) on sputtering method (sputtering conditions are power...
1. A 1,000-layer tantalum layer (91) was deposited on this surface using a 1000 kW, a pressure of 8 mTorr, and a glass substrate temperature of 150°C, and low-pressure CVD was performed on this surface.
method (glass substrate temperature...600℃, pressure...0.3
-Torr, gas flow rate...SiH<2PH, :H,
1000 nm thick amorphous silicon layer doped with phosphorus (92)
After forming a film, it is patterned and shown in Figure 1θ (
A source electrode (S) and a drain electrode (D) as shown in B) were formed.

Next, as shown in FIG.
, gas flow rate...SiH,=lOOSCCM) to form a film of amorphous silicon (3゛), and annealing at 600° C. for 12 hours in a nitrogen atmosphere to form a polysilicon semiconductor layer (3). As shown in Fig. 1θ (D), plasma CVD method (glass substrate temperature: 350°C)
, Pressure + 0.2 Torr, RF power: 100
Silicon nitride oxide (SiOI) with a thickness of 1000
A gate insulating film (2) made of NF) was formed. As for the atomic composition in the gate insulating film (2), by changing the flow rate ratio of the constituent gas mixture over time as in the first embodiment, the nitrogen component is changed to the polysilicon semiconductor layer (3). The oxygen component is adjusted so that it continuously decreases from the polysilicon semiconductor layer (3) side toward the gate electrode (G) side, while the oxygen component increases continuously from the polysilicon semiconductor layer (3) side toward the gate electrode (G) side. has been done.

Next, as shown in FIG. 10(E), a gate electrode (G) made of aluminum with a thickness of 1 μm is formed on the gate insulating film (2) to form a "staggered JMOS".
I asked for a lungister.

Also in this "stagger type JMO5" transistor, the gate insulating film (2) is made of silicon nitride oxide (SiO,N
), and this silicon nitride oxide (SiO□N
,) While the nitrogen component in the film decreases continuously from the polysilicon semiconductor layer (3) side to the gate electrode (G) side, the oxygen component decreases from the polysilicon semiconductor layer (3) side to the gate electrode (G) side. Since the oxygen component continuously increases toward the electrode (G) side, in this gate insulating film (2), the oxygen component on the side adjacent to the polysilicon semiconductor layer (3) is small, and silicon nitride (SiN, ) Since silicon nitride oxide having the same or similar structure is adjacent to the polysilicon semiconductor layer (3), the T interface level 1 between these adjacent layers is reduced, and the gate insulating film (2) is adjacent to the polysilicon semiconductor layer (3). ) The composition of silicon nitride oxide changes continuously, making it difficult to form an interface within the gate insulating film (2), even though the gate insulating film (2) is composed of multiple materials. While the increase in the r-interface level 1 in the gate insulating film (2) is suppressed, the trap level J in the gate insulating film (2) is
Since the nitrogen component in the composition (O, N, ) continuously decreases from the polysilicon semiconductor layer (3) side to the gate electrode (G) side, the silicon nitride ( As the ratio of SiN, ) decreases, the r-trap level is reduced.

Therefore, in the r-stagger type J MOS transistor according to this embodiment, the threshold voltage VTH also decreases over time because the "interface level j" and the "trap level J" of the gate insulating film (2) are reduced. It has the advantage of being difficult to change.

〔Effect of the invention〕

According to the invention according to claim 1, in the gate insulating film, the oxygen component on the side adjacent to the silicon semiconductor layer is small, and silicon nitride (SiN,
) with a structure similar to or similar to this is adjacent to the silicon semiconductor layer, the "interface level 1" between these adjoining layers is reduced, and the silicon nitride oxide in the gate insulating film is The composition of the gate insulating film changes continuously and it is difficult to form an interface therein, so even though the gate insulating film is composed of multiple materials, the increase in the r-interface level 1 in the gate insulating film is suppressed. On the other hand, regarding one trap level 1 in this gate insulating film, the nitrogen component in the silicon nitride oxide (3i0.N,) composition constituting it is continuous from the silicon semiconductor layer side to the gate electrode side. As the ratio of silicon nitride (SiN) in the gate insulating film decreases,
It is also possible to reduce the trap level 1.

Therefore, this has the effect of making it difficult for the threshold voltage in the thin film semiconductor device to change over time.

Further, according to the invention according to claim 2, the nitrogen component in the silicon nitride oxide (SiO,N) film decreases continuously from the silicon semiconductor layer side to the gate electrode side, while the oxygen component decreases continuously from the silicon semiconductor layer side to the gate electrode side. On the other hand, since it is possible to reliably form a gate insulating film that continuously increases from the silicon semiconductor layer side to the gate electrode side, the thin film semiconductor device according to claim 1 can be manufactured easily. have.

[Brief explanation of the drawing]

Figures 1 to 1O show embodiments of the present invention.
The figure is a schematic perspective view of an inverted staggered JMOS transistor according to the first embodiment, and Figure 2 is a cross-sectional view of Figure 1.
3(A) to 3(J) are process explanatory diagrams showing the manufacturing process of this MOS transistor, FIG. 4 is a schematic configuration diagram of the plasma CVD apparatus used for manufacturing this MOS transistor,
Fig. 5 is a graph showing the change in gas flow rate over time of each constituent gas supplied into this plasma CVD apparatus, and Fig. 6 is a graph showing the atomic composition ratio in the film thickness direction of the gate insulating film formed. 7 is a graph showing the atomic composition ratio in the film thickness direction of the gate insulating film according to the modified example, and FIG. 8 is a cross-sectional view of the r-brainer type J MOS transistor according to the second embodiment.
9(A) to (F) are process explanatory diagrams showing the manufacturing process of this MOS transistor, and FIGS. 10(A) to (E) are process explanatory diagrams showing the manufacturing process of the r stagger type J MOS transistor according to the third embodiment. FIGS. 11 to 14 show conventional examples, and FIG. 11 is a schematic perspective view of a conventional MOS type thin film transistor called r inverted stagger type 1, and FIG. 11 is an xn-xn plane sectional view, FIG. 13 is a schematic perspective view of a conventional MOS type thin film transistor called "r stagger type", and FIG. 14 is an XI of FIG. 13.
FIG. 15, a sectional view taken along the V-XIV plane, is an energy band diagram between the gate insulating film and the silicon semiconductor layer adjacent thereto. [Explanation of symbols] (G)...Gate electrode (S)...Source electrode (D)...Drain electrode...Glass substrate...Gate insulating film...Polysilicon semiconductor layer Patent application Person Fuji Xerox Co., Ltd. Patent Attorney Tomohiro Tsunakamura (2 others) Fig. Fig. Fig. Fig. Fig. Time Fig. Fig. Fig. Fig. Fig. 10 Figure 10 Figure 11 ↓・ 12 Figure 13 Figure 14 Figure 15

Claims (2)

[Claims] (1) An insulating substrate, a thin silicon semiconductor layer provided on this substrate and forming an active layer, a source/drain electrode connected to this silicon semiconductor layer, and facing the silicon semiconductor layer through a gate insulating film. In a thin film semiconductor device comprising a gate electrode disposed as a gate insulating film, the gate insulating film is made of silicon nitride oxide (SiO_xN_y).
This silicon nitride oxide (SiO_xN_
y) While the nitrogen component in the film continuously decreases from the silicon semiconductor layer side to the gate electrode side, the oxygen component, on the contrary, continuously increases from the silicon semiconductor layer side to the gate electrode side. A thin film semiconductor device characterized by: (2) In the method for manufacturing a thin film semiconductor device according to claim 1, the gate insulating film made of silicon nitride oxide (SiO_xN_y) is formed by chemical vapor deposition (C).
During the film formation process of this gate insulating film, the nitrogen component ratio of the mixed gas for forming silicon nitride oxide (SiO_xN_y) supplied into the film formation chamber changes over time. A method for manufacturing a thin film semiconductor device, characterized in that the composition ratio of the mixed gas is continuously changed and supplied so that the ratio of the oxygen component increases or decreases while the ratio of the oxygen component decreases or increases.