JPH0642494B2 - Method of manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) In recent years, research and development of thin film transistors used as driving devices for liquid crystal flat panel displays, electroluminescent displays, and the like have been actively conducted. This thin film transistor requires (1) it can be formed on a transparent insulating substrate, (2) a large ON current and a sufficiently small OFF current, and (3) a process for forming a large capacity transistor array. As a semiconductor thin film, polycrystalline Si or amorphous S is mentioned.
A thin film transistor using i as an active layer has been researched and developed (for example, Society of Information Display, Digest of Technical Piper (Soc
iety of lnformation Display, Digest of Technical Pa
per) p312, 1984). However, since the carrier mobility of polycrystalline Si or amorphous Si is relatively small at 1 to ²⁰ cm ² / v · sec, a peripheral drive IC for driving this thin film transistor is required. Therefore, it is necessary to connect terminals between the large-capacity thin film transistor array and the peripheral driving IC, which has brought about an increase in size, cost, and reliability of the device.

On the other hand, single-crystal Si has the above-mentioned conditions as a transistor.
Since the requirements of (2) and (3) are satisfied and the mobility is high and the peripheral drive circuit can be formed on the same substrate at the same time when the transistor array is formed, there is an advantage that terminal connection with the peripheral drive circuit is unnecessary (for example, , Society of Information Display, Digest of Technical Paper
Technical Paper), p150-p151, 1983). However, since the transistor array with peripheral circuits using this Si single crystal substrate uses opaque single crystal Si as the substrate, it is unsuitable for driving a liquid crystal display using light transmitted through the substrate. It was

On the other hand, as a technique for reducing the thickness of single crystal Si, a transfer technique is known in which a single crystal Si substrate on which a device is formed is attached to a supporting substrate, then polished to form a thin film, and attached again to a desired substrate. (Japanese Journal of
Applied Physics (Jpn.J.Appl.Phys.) 23, L815
~ 817, 1984). A thin film transistor array with a peripheral drive circuit that does not require a terminal connection technique can be obtained by simultaneously forming a transistor portion for driving a liquid crystal and a peripheral drive circuit using this technique.

However, when a single crystal Si transistor is used as a switching element for driving a liquid crystal, it has a high photosensitivity, and therefore it is necessary to provide a light shielding film to reduce the photosensitivity. There is a problem that the process becomes complicated because it needs to be left in the array section.

(Problems to be Solved by the Invention) An object of the present invention is suitable for driving a liquid crystal when a peripheral drive circuit is configured by a single crystal Si drive circuit by using the technique of thinning the single crystal Si. It is to provide a method of manufacturing a thin film transistor by a simple process.

(Means to be Solved by the Invention) According to the present invention, a step of forming an insulating layer for selective polishing on a Si substrate, a polycrystalline Si thin film is formed on the insulating layer, and the unnecessary polycrystalline Si thin film is removed. Island-shaped step, a step of forming a TFT including source and drain regions in the island-shaped polycrystalline Si layer, a step of adhering a transparent insulating substrate to the formed TFT side, and a Si substrate Remove by polishing
A step of thinning the selective polishing insulating layer, the TFT and the transparent insulating substrate, and forming a hole in the selective polishing insulating layer T
A method of manufacturing a thin film transistor, which comprises at least a step of forming source and drain electrodes so as to make electrical contact with the source and drain layers of FT.

(Operation) As can be seen from the above-described configuration, the device transfer performed twice in the transistor of the planer structure in the conventional technique can be performed once in the present invention, and the process is simplified. In addition, since the thin film transistor manufactured by this manufacturing method has a structure in which the entire device is bonded to the transparent insulating substrate by the transparent adhesive layer, light incident from the transparent insulating substrate hardly absorbs, and the transmissive liquid crystal It is the most suitable structure for a display.

In addition, a thin film transistor array in which the drain wiring and the gate wiring are easily multilayered by a flat element isolation insulating film which is relatively thick as compared with the conventional polycrystalline Si thin film transistor, and there is less risk of pixel defects such as short circuit between electrodes. can get.

(Example) The Example of this invention is described using drawing. Figure 1 (a) ~
An example of the method of manufacturing a thin film transistor of the present invention is shown in (e). In FIG. 1, a p-type Si substrate 1 was formed with a 700 nm thermal oxide film as an insulating layer 2 for selective polishing.
The polycrystalline Si film 3 is formed by a low pressure CVD method using H ₄ gas.
It is formed to a thickness of 50 nm and patterned in an island shape (Fig. 1
(a)). Then, a thermal oxide film is formed as a gate insulating film 4 on the polycrystalline Si film 3 to a thickness of 150 nm, and a polycrystalline Si film is formed to a thickness of 300 nm on the thermal oxide film 4 to form an island pattern to form a gate electrode. 5 is formed. Further 160K
Phosphorus of 5 × 10 ¹⁵ cm ^-2 was injected into the polycrystalline Si film 3 by using the gate electrode as a mask at an accelerating voltage of V, and the temperature was set to 900 ° C. for 2 hours.
Anneal for 0 minutes to form the source and drain regions 6 and 7. Further, 0.3 nm of Al is formed as the gate electrode 7 and patterned. Then, a SiO ₂ film 8 having a thickness of 500 nm is formed as a protective layer by the CVD method and annealed at 800 ° C. for 30 minutes to form a MOSFET structure (FIG. 1 (b)).

Furthermore, using a transparent adhesive 9 (for example, epoxy resin)
The Si substrate on which the MOSFET is formed is bonded so that the gate electrode 4 can be bonded to the transparent insulating substrate 10 such as glass (FIG. 1 (c)). After that, the Si substrate 1 is removed by chemical polishing to form a thin film (FIG. 1 (d)). Quartz grains with a diameter of 20 nm and organic ammonia were used as abrasives during chemical polishing. As a result, the polishing speed of the Si crystal 1 is about 10 times faster than that of the insulating layer 2 for selective polishing, and polishing is automatically completed with the thickness of the insulating layer 2 for selective polishing. Further, after forming a contact hole in the insulating layer 2 for selective polishing by dry etching, Al is formed to a thickness of 800 nm, patterned into an island shape, and annealed at 400 ° C. for 30 minutes. As a result, the source and drain electrodes 11 and 12 are formed, and at the same time, the source and drain regions 6 and 7 are electrically connected (first
(Figure (e)). Further, when forming a thin film transistor array for a liquid crystal display, as shown in FIG. 2, indium oxide (ITO) is formed to a thickness of 100 nm as a transparent electrode 13 by a sputtering method so as to be connected to the source electrode 12.
A pixel electrode is formed by patterning, and a thin film transistor for display (FIG. 2) is completed.

(Effects of the Invention) As a result of investigating the characteristics of the thin film transistor according to the present invention, a thin film transistor having a mobility of 10 cm ² / v · sec, an OFF current of 0.8 to 4 × 10 ⁻¹² A and sufficient performance for a liquid crystal display can be obtained by a simple process. Obtained, and also ordinary SiFET
It was confirmed that single crystal Si can be used as a peripheral drive circuit because the process is similar. Also,
A high performance thin film transistor having a light transmittance of 80% or more was obtained.

The present invention is not limited to the embodiment and is effective for transistors having other structures.

[Brief description of drawings]

1 (a) to 1 (e) are process diagrams showing an embodiment of a method of manufacturing a thin film transistor of the present invention. FIG. 2 is a schematic view of a thin film transistor obtained by the manufacturing method of the present invention. In the figure, 1 ... Single crystal Si substrate, 2 ... Insulating layer for selective polishing, 3 ...
... Polycrystalline Si film, 4 ... Gate insulating film, 5 ... Gate electrode, 6 ... Drain region, 7 ... Source region, 8 ... Protective layer, 9 ... Adhesive layer, 10 ... Glass transparent Insulating substrate, 11 ... Drain electrode, 12 ... Source electrode, 13
...... Indicates transparent pixel electrodes, respectively.

Claims (1)

[Claims] 1. A step of forming an insulating layer for selective polishing on a Si substrate, a step of forming a polycrystalline Si thin film on the insulating layer and removing an unnecessary polycrystalline Si thin film to form islands, A step of forming a TFT including a source / drain region on an island-shaped polycrystalline Si layer; a step of adhering a transparent insulating substrate to the formed TFT side; and a step of removing the Si substrate by polishing, A step of thinning the selective polishing insulating layer, the TFT and the transparent insulating substrate, and a source / drain electrode for making a hole in the selective polishing insulating layer to make electrical contact with the source / drain layer of the TFT. And at least a step of forming a film.