1. FIELD OF THE INVENTION
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, a thin film semiconductor device formed on an insulating substrate and a method of manufacturing the same.
2. DESCRIPTION OF THE RELATED ART
Semiconductor devices such as transistors can be formed on an insulating substrate such as a glass plate or a silicon substrate coated with a passivation layer. It is not possible to apply epitaxial growth onto the insulating substrate in a usual manner. Thus, a thin film semiconductor layer of polycrystalline or amorphous state is first formed on the insulating substrate and a semiconductor device is then formed on the thin film semiconductor layer.
For example, a matrix of cells together with active elements such as transistors are formed on a transparent substrate, thereby forming an active matrix. In the field of liquid crystal displays, a high attention is directed to an active matrix liquid crystal display panel in which a matrix of transparent electrodes for exciting a liquid crystal material and thin film transistors (TFTs) serving as switching elements are formed on a glass substrate. Such a TFT can be made in the form of either a p-channel insulated gate (IG) or an n-channel IGTFT. In the case of making the n-channel IGTFT, n.sup.+ -type source/drain regions are formed by doping a thin film of highly resistive i-type or p-type silicon (of polycrystalline or amorphous state) with an n-type impurity, and source/drain electrodes are disposed on the n.sup.+ -type source/drain regions in contact therewith. In the case of making the p-channel IGTFT, p.sup.+ -type source/drain regions are formed in a thin film of i-type or n-type silicon with a p-type impurity, and source/ drain electrodes are disposed on the p.sup.+ -type source/drain regions in contact therewith.
Lepselter and Sze have proposed an IGTFT using Schottky barrier contacts for a source and a drain (see Proceedings of the IEEE, Proceedings Letters, Aug. 1968, pp. 1400-1402). In the proposed IGFET, source and drain electrodes made of platinum silicide PtSi are brought in contact with a &lt;100&gt; oriented n-type silicon substrate having a resistivity of 1 .OMEGA..multidot.cm. When a negative voltage is applied to a gate electrode, a channel inverted to be of p-type is produced between the source electrode and the drain electrode. In the case where the electrodes of PtSi are disposed on the n-type silicon substrate, the barrier height of 0.85 V is established. But, in the case of electrodes of PtSi disposed on a p-type silicon substrate, the barrier height is 0.25 V so that a drain current flows.
Taking account of the fact that when the source and drain regions are formed with Schottky junctions, a short-channel effect can be improved but a restriction is imposed on an ability of current supply from the source region, Mizutani has proposed an MOSFET having a source region formed through impurity diffusion and a drain region formed with a Schottky junction (see JP-A-58-182871).
For driving the liquid crystal display (LCD) panel, there are required various peripheral circuits including a shift register, a matrix circuit, an inverter circuit, etc. If it is possible to incorporate these peripheral circuits into the LCD panel, the number of parts required can be reduced, thereby allowing improved reliability and greatly lowered cost.
When it is desired to make a limitation of power consumption , complementary insulated gate thin film transistors (C-IGTFTs) must be used for a part of such peripheral circuits. Namely, it is necessary to simultaneously fabricate a p-channel IGTFT and an n-channel IGTFT. The fabrication of C-IGTFTs requires both doping with an n-type impurity and doping with a p-type impurity. This increases the number of process steps for manufacture of the device, which provides a great factor of increasing the cost. For example, in spite of the fact that switching elements necessary for ah active matrix type of LCD panel can be formed by only either p-channel IGTFTs or n-channel IGTFTs, the requirements for incorporation of the peripheral circuits into the panel necessitate the use of both p-channel IGTFTs and n-channel IGTFTs and hence the doping with both p- and n-type impurities, thereby resulting in remarkable increase of the number of photomasks to be used and of the number of process steps to be carried out.