JPH098311A - Method of manufacturing thin film semiconductor device and its structure - Google Patents

Abstract

(57) [Abstract] [Purpose] An inverted staggered thin film transistor having an etching stopper layer, in which the number of manufacturing steps is reduced. [Structure] On a glass substrate 1, a Cr gate electrode 2, a gate insulating film silicon nitride 3, an island-shaped active layer 8 and an etching stopper layer 9 which are collectively patterned are formed. Next, after the n-type amorphous silicon 7 is deposited, it is removed by anisotropic etching to leave the n-type amorphous silicon only on the sidewalls of the active layer 8 and the etching stopper layer 9, and the ohmic contact layer 10 is formed. To form. Then the source-
After forming the drain electrodes 11 and 12, the n-type amorphous silicon remaining between the source and drain electrodes is removed by isotropic etching, and finally the protective film 13 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film semiconductor device, a method of manufacturing a thin film transistor, and its structure.

[0002]

2. Description of the Related Art Generally, the structure of an inverted stagger type thin film transistor having an etching stopper layer is described in the literature (Extended
Abstracts of the 22nd (1990 International)
Conference on Solid State Devices and Mterials: S
-E-23,1027), a gate electrode, a gate insulating film, an active layer made of a semiconductor on an insulating substrate, an etching stopper layer made of an insulating film having an area smaller than the active layer on the upper surface thereof, An ohmic contact layer formed by doping a semiconductor with impurities so as to contact from a part of the upper surface of the etching stopper layer to the end of the active layer,
It is composed of source-drain electrodes.

[0003]

The above-mentioned prior art relates to an inverted stagger type thin film transistor, and dry etching is performed to achieve thinning of an active layer for the purpose of lowering off current and reducing electron excitation by light. An etching stopper layer is partially inserted between the active layer and the ohmic contact layer where the difference in etching rate with respect to gas is not large. Therefore, there is a problem that the number of manufacturing steps is increased to form the etching stopper layer.

An object of the present invention is to reduce the number of thin film transistor manufacturing steps having an etching stopper layer.

[0005]

In order to solve the above problems, a feature of the present invention is that, in a method of manufacturing a thin film transistor, an active layer and an etching stopper layer are collectively patterned in an island shape, and then an impurity-doped semiconductor is formed. It is deposited and anisotropically etched to form an ohmic contact layer only on the side wall of the active layer or the side wall of the active layer and the etching stopper layer, or the active layer and the etching stopper layer are collectively formed into an island shape and a taper shape. Then, after patterning, the active layer protruding from the etching stopper layer is doped with impurities to form an ohmic contact layer.

[0006]

According to the above means, the active layer and the etching stopper layer can be collectively patterned in the shape of an island, so that the number of manufacturing steps for patterning the etching stopper layer in a separate step can be reduced. When this transistor is used as a pixel driving element of a liquid crystal display device, since an ohmic contact layer is provided only on the side wall of the active layer, it is possible to use a transparent conductor for the source-drain electrodes. The number of manufacturing steps can be reduced.

[0007]

EXAMPLE First, a first example in which the present invention is applied to manufacture of a thin film transistor will be described.

FIG. 1 is a sectional view showing a manufacturing process of a thin film transistor in one embodiment of the present invention. Figure 1
As shown in (a), 1,200 Cr is deposited on the glass substrate 1.
Å The gate electrode 2 is formed by depositing by sputtering and patterning. Then, the plasma CVD method uses the source gases SiH ₄ , NH ₃ , and N ₂ , respectively, and the silicon nitride film 3, which is a gate insulating film of 3500Å, and SiH ₄ and H ₂ to form an active layer of 200 to 600Å, which is an amorphous layer. A silicon nitride film 5 serving as an etching stopper layer of 2000 Å is continuously deposited by using the high-quality silicon film 4, SiH ₄ , NH ₃ , and N ₂ . Next, a resist 6 is applied and photolithography is performed to form an island pattern. Then, as shown in FIG. 1B, the silicon nitride 5 and the amorphous silicon 4 are respectively replaced by C
It is sequentially etched by plasma dry etching using F ₄ + O ₂ and BCl ₃ to form an island shape. Then, FIG.
After removing the resist 6 as shown in FIG.
340 Å n-type amorphous silicon 7 is deposited using H ₄ , H ₂ and PH ₃ . Then, this n-type amorphous silicon 7 is anisotropically etched by reactive ion etching using BCl ₃ . Then, as shown in FIG. 1D, the active layer 8 and the etching stopper layer 9 having the largest film thickness in the vertical direction are formed.
Only the n-type amorphous silicon bonded to the sidewall of
The ohmic contact layer 10 is formed only on the sidewalls of the active layer 8 and the etching stopper layer 9. Then, FIG.
2800Å by sputtering method as shown in (e)
Of ITO (Indium Tin Oxide) is deposited and patterned to form the source and drain electrodes 11 and 12, and then the n-type amorphous silicon remaining on the sidewall of the active layer between the source and drain electrodes is formed by using BCl ₃ . It is removed by the isotropic dry etching, and finally the protective film 13 is deposited to complete the thin film transistor.

According to the embodiment, the etching stopper layer 9
Since the active layer 8 is collectively patterned, the number of manufacturing steps is reduced and the manufacturing cost is reduced as compared with the case where the etching stopper layer is individually patterned. Furthermore, since the n-type amorphous silicon is deposited on the active layer by PCVD, the lattice of the active layer 8 and the ohmic contact layer 10 becomes discontinuous, and compared with the case where the ohmic contact layer is formed by ion doping or the like. , The contact resistance between the two layers increases, and as a result, the off current of the transistor decreases.

The active layer is not limited to silicon, and any type of semiconductor such as silicon germanium or germanium can be used. Further, the insulator used for the etching stopper layer is not limited to silicon nitride, and any type may be selected as long as it has sufficient resistance to the etching gas. Further, even if there is no resistance, a semiconductor can be used as long as the film thickness is sufficiently thick, and the use of the semiconductor has an advantage of improving the throughput.

It is also possible to deposit amorphous silicon 4 as an active layer in the embodiment and then irradiate it with an energy beam to form polycrystalline silicon. For example, after depositing the amorphous silicon 4, a 220 mJ / cm ² XeCl laser is irradiated to polycrystallize the silicon film, and the remaining steps are the same as those in the above-described embodiment. It is possible to manufacture a thin film transistor having higher mobility as compared with.

Further, in the embodiment, a p-channel thin film transistor can be manufactured by depositing p-type amorphous silicon instead of n-type amorphous silicon 7.

Next, a second embodiment showing a method of manufacturing a thin film transistor in which an ohmic contact layer forming method is different from that of the first embodiment will be described.

FIG. 2 is a cross-sectional view showing the manufacturing process of the thin film transistor as in FIG. As shown in FIG. 2A, similar to the first embodiment, the gate electrode 2, the gate insulating film silicon nitride 3, the amorphous silicon serving as the active layer 4, the silicon oxide film serving as the etching stopper layer are formed on the glass substrate 1. 5. A resist 6 patterned into an island shape is formed. Here, the difference from the first embodiment is that the etching stopper layer is TEOS.
(Tetra Ethyl Oxide Silan-e) is a silicon oxide film formed by PCVD. Then, as shown in FIG. 2B, the silicon oxide film 5 and the amorphous silicon 4 are collectively isotropically etched by plasma dry etching using CF ₄ + H ₂ . Then, since the etching rate of the silicon oxide film 5 is higher than that of the amorphous silicon film 4, the sidewalls of the processed amorphous silicon film 4 and the silicon oxide film 5 are tapered (inclined), and the amorphous silicon film 4 is formed. Of the silicon oxide film protrudes from the silicon oxide film 5. Then, after removing the resist 6 as shown in FIG.
An end portion of the protruding amorphous silicon is doped with PH ₃ by an ion doping method and is thermally annealed or laser annealed to be activated to be n-type silicon. Then, the ohmic contact layer 10 is formed only on the sidewall of the active layer 8. Then, as shown in FIG. 2D, the remaining steps are the same as those in the first embodiment to complete the thin film transistor. Further, this manufacturing method can also reduce the number of manufacturing steps and the manufacturing cost. Furthermore, in this method, since the lattice of the active layer 8 and the ohmic contact layer 10 are continuous, the contact resistance between the two layers becomes small, and as a result, the on-current of the transistor increases. Note that the active layer is not limited to silicon, and any type of semiconductor such as silicon germanium or germanium can be used.

Also in the second embodiment, it is also possible to deposit amorphous silicon 4 as an active layer and then irradiate it with an energy beam to form polycrystalline silicon. For example, after depositing amorphous silicon 4, 220 mJ / cm ² of XeCl ²
By irradiating a laser to polycrystallize the silicon film, and by making the remaining steps the same as in the second embodiment, a thin film transistor having higher mobility than an amorphous silicon thin film transistor can be manufactured. Furthermore, in the second embodiment, p-channel thin film transistors can be manufactured by doping B instead of doping P at the end of the active layer protruding from the etching stopper layer.

Next, a third embodiment in which a thin film transistor (hereinafter referred to as TFT) manufactured according to the present invention is used as a driving element for a display pixel of an active matrix type liquid crystal display device will be described.

FIG. 3 shows the structure of an active matrix type liquid crystal display device which is an embodiment of the present invention. In the figure,
A TFT is provided for each of a plurality of liquid crystal cells (LC) arranged in a matrix, and each liquid crystal cell is driven by the switching operation of the TFT. Here, a gate voltage is sequentially applied to the gate lines G1 to GM, which are electrodes commonly drawn from the gates of the TFTs arranged in the horizontal direction on the glass substrate 1, and the gates are turned on for each gate line. Go. On the other hand, the drain lines D1 to DN, which are electrodes commonly drawn from the drains of the TFTs arranged in the vertical direction, are sequentially applied with a data voltage for each turned-on gate line and applied to each liquid crystal cell. Go. FIG. 4 shows a planar structure of one pixel composed of one liquid crystal cell and TFT. Further, FIG. 5 shows a sectional structure taken along a broken line XX ′ in FIG. It is composed of a TFT formed near the intersection of the drain wiring D and the gate wiring G and a liquid crystal cell LC connected to the TFT via the source electrode 11.
The cross-sectional structure of the TFT is almost the same as that of the first embodiment. This structure can be obtained by the manufacturing method described in the embodiment, but only the changes from the process are as follows. That is,
The gate line G, the drain line D, and the pixel electrode were formed by simultaneously forming and etching the gate electrode 2, the drain electrode 12, and the source electrode 11, respectively. Other liquid crystal 1
The parts other than the 4th class TFT will be described below. The TN type liquid crystal 14 is sealed between a glass substrate (counter substrate) 15 facing the glass substrate on which the TFT is formed. The black matrix 16 and I for blocking unnecessary light rays are provided on the counter substrate.
A TO17 film is formed. The liquid crystal is IT of the counter substrate
Driven by the voltage between O17 and the pixel electrode ITO of the TFT substrate, the brightness displayed for each pixel is changed to display an image on the pixel matrix. A deflection plate 18 for deflecting light is attached to each of the glass substrates 1 and 15. When the deflection axes of these two deflecting plates are arranged orthogonally or in parallel, the display modes are normally black and normally white, respectively. Although not shown in the drawing, an alignment film 19 for aligning the liquid crystal is formed on the surface in contact with the liquid crystal, that is, on the glass substrate 1 side, on the surface of the protective film 13 and the pixel electrode ITO film 11, and on the counter substrate 15 side. It is applied on the surface of the ITO film. The surface of the alignment film is treated by a rubbing method after coating to give anisotropy for aligning liquid crystal molecules. As described above, when the TFT manufactured according to the present invention is used as a driving element of a display portion pixel of an active matrix type liquid crystal display device, an etching stopper layer and an active layer can be collectively formed, and a pixel electrode and a source / drain electrode are transparent conductors. Since it can be collectively formed by, the number of manufacturing steps can be reduced and the manufacturing cost can be reduced.

Next, a description will be given of a fourth embodiment in which the crystalline thin film transistor according to the present invention is formed on the same substrate as the display section and used as a part of the drive circuit of the active matrix type liquid crystal display device.

FIG. 6 shows the structure of an active matrix type liquid crystal display device using the present invention. In this embodiment, part of the function of the driver circuit is formed over the same glass substrate as the thin film transistor of the pixel. In the figure, thin film transistors are provided for a plurality of liquid crystal cells (LC) arranged in a matrix, and the liquid crystal cells are driven by the switching operation of the thin film transistors. Here, a gate voltage is sequentially applied from the gate drive circuit (driver IC) 20 to the gate lines G1 to GM which are electrodes commonly drawn from the respective gates of the thin film transistors arranged in the lateral direction on the glass substrate 1, The gate is turned on for each gate line. On the other hand, with respect to the drain lines D1 to DN, which are electrodes commonly drawn from the drains of the thin film transistors arranged in the vertical direction, the data driving circuit 21 supplies the data voltage for each gate line turned on to the sampling circuit. It is applied sequentially through 22,
Give each liquid crystal cell. In addition, the sampling circuit 22
As shown in FIG. 7, each drain line has a sampling thin film transistor, and a plurality of voltages φ1 and φ2 are supplied to the gate of the sampling thin film transistor while the pixel thin film transistor gate voltage is on. The two drain lines are grouped together and connected from the sampling circuit 22 to the data driving circuit 21. Since the sampling circuit 22 is formed on the glass substrate 1 like the thin film transistor of the pixel, the number of connections between the sampling circuit 22 and the data driving circuit 21 is halved. The drain lines D1 and D2 are integrated and connected to the data driving circuit as DK1, and as a result, the number of connections between the data driving circuit 21 and the substrate on which the pixel thin film transistors and the sampling circuit 22 are formed is reduced by half, that is, the data driving circuit is configured. The number of driver ICs used can be halved. Since the sampling circuit 22 can be easily formed in the same process as the pixel thin film transistor, the effect of halving the number of driver ICs has an effect of reducing the liquid crystal display cost. The pixel thin film transistor may have an amorphous active layer, or may be a polycrystalline thin film transistor. In this way, if the crystalline thin film transistor according to this embodiment is formed on the same substrate as the display unit as a part of the drive circuit of the active matrix type liquid crystal display device, the number of manufacturing steps is the same as in the third embodiment. Therefore, the manufacturing cost can be reduced.

[0020]

According to the present invention, the number of thin film transistor manufacturing steps can be reduced and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an embodiment in which the present invention is applied to manufacturing a thin film transistor.

FIG. 2 is a cross-sectional view showing a manufacturing process of one embodiment in which the present invention is applied to the manufacture of a thin film transistor.

FIG. 3 is an explanatory diagram of an active matrix type liquid crystal display device using a thin film transistor manufactured according to the present invention as a liquid crystal cell driving element.

FIG. 4 is a plan view of one pixel including a liquid crystal cell and a thin film transistor manufactured according to the present invention.

FIG. 5 is a cross-sectional view of one pixel including a liquid crystal cell and a thin film transistor manufactured according to the present invention.

FIG. 6 is an explanatory diagram of an active matrix type liquid crystal display device using the present invention.

FIG. 7 is an explanatory diagram of a sampling circuit using the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Gate electrode, 3 ... Gate insulating film silicon nitride, 4 ... Amorphous silicon film, 5 ... Etching stopper layer silicon nitride or silicon oxide, 6 ... Resist, 7 ... N-type amorphous silicon, 8 ... Active layer, 9 ... Etching stopper layer, 10 ... Ohmic contact layer, 1
1 ... Source electrode, 12 ... Drain electrode, 13 ... Protective film.

Claims (10)

[Claims] 1. A gate electrode, a gate insulating film, an active layer made of a semiconductor, an insulating film or an etching stopper layer made of a semiconductor, which is formed on an insulating substrate, and an ohmic contact layer formed by doping the semiconductor with impurities. In a method of manufacturing an inverted stagger type thin film transistor having source-drain electrodes, an active layer and the etching stopper layer are collectively patterned in an island shape, and then an impurity-doped semiconductor is deposited and anisotropically etched. And forming an ohmic contact layer only on the side wall of the active layer or only on the side wall of the active layer and the etching stopper layer. 2. A gate electrode, a gate insulating film, an active layer made of a semiconductor, an insulating film or an etching stopper layer made of a semiconductor, an ohmic contact layer formed by doping a semiconductor with an impurity, formed on an insulating substrate. In an inverted stagger type thin film transistor structure having source-drain electrodes, an ohmic contact layer having a discontinuous lattice with the active layer is bonded only to the sidewall of the island-shaped patterned active layer or the sidewalls of the active layer and the etching stopper layer. A thin film transistor which is characterized by: 3. A gate electrode, a gate insulating film, an active layer made of a semiconductor, an etching stopper layer made of an insulating film or a semiconductor, formed on an insulating substrate, an ohmic contact layer formed by doping an impurity into the semiconductor, In a method of manufacturing an inverted stagger type thin film transistor having a source-drain electrode, an active layer and an etching stopper layer are collectively patterned into an island shape and a taper shape, and then the active layer protruding from the etching stopper layer is doped with impurities. A method of manufacturing a thin film transistor, which comprises forming an ohmic contact layer. 4. A gate electrode, a gate insulating film, an active layer made of a semiconductor, an etching stopper layer made of an insulating film or a semiconductor, formed on an insulating substrate, an ohmic contact layer formed by doping an impurity into the semiconductor, In the structure of an inverted stagger type thin film transistor having source-drain electrodes, the ohmic contact layer is a region protruding from the etching stopper layer of the island-shaped and tapered active layer together with the etching stopper layer. . 5. A liquid crystal display device using a thin film transistor as a driving element of a liquid crystal cell constituting a pixel of a display section, wherein the thin film transistor according to claim 2 is used as a liquid crystal cell driving element. . 6. A method of manufacturing a liquid crystal cell driving element of a liquid crystal display device, wherein a thin film transistor is used as a driving element of a liquid crystal cell forming a pixel of a display portion, wherein the method of manufacturing a thin film transistor according to claim 1. A method for manufacturing a thin film transistor for driving a liquid crystal cell of a liquid crystal display device, to which is applied. 7. A liquid crystal display device in which at least a part of a circuit for driving the display unit is formed on the same substrate as the display unit, and the thin film transistor according to claim 2 is used as a drive circuit element. Liquid crystal display used. 8. A method of manufacturing a thin film transistor for driving a display unit of a liquid crystal display device, wherein at least a part of a circuit for driving the display unit is formed on the same substrate as the display unit. A method of manufacturing a thin film transistor for driving a liquid crystal display device, to which the method of manufacturing a thin film transistor described above is applied. 9. A liquid crystal display device in which at least a part of a circuit for driving the display unit is formed on the same substrate as the display unit, and the thin film transistor according to claim 2 or 4 is a device for driving a liquid crystal cell. And a liquid crystal display device used as an element for a display section drive circuit. 10. A method of manufacturing a thin film transistor for driving a liquid crystal cell of a liquid crystal display device and a thin film transistor for driving the display unit, wherein at least a part of a circuit for driving the display unit is formed on the same substrate as the display unit. Item 4. A method of manufacturing a thin film transistor for driving a liquid crystal cell and a display unit of a liquid crystal display device, to which the method of manufacturing a thin film transistor according to Item 1 or 3 is applied.