Manufacturing Method of CMOS Thin Film Semiconductor Device and CMOS Thin Film Semiconductor Device Manufactured Thereby

The present invention relates to a method of manufacturing a CMOS thin film semiconductor device of the type used for a thin film transistor (TFT) type liquid crystal display (LCD), and to a CMOS thin film semiconductor device manufactured thereby.

In TFT-LCDs, a polycrystalline silicon (p-Si) TFT which is formed on a quartz substrate, or an amorphous silicon (a-Si) TFT which is formed on a large size glass substrate, is mostly used. The TFTs in the TFT-LCDs are used in one instance for a TFT matrix in a display portion and in another instance for formation of an outer circumferential circuit on a common substrate for driving such a TFT matrix. In the former instance, an n channel TFT is used, and in the latter instance, a CMOS TFT semiconductor circuit is used for achieving high speed operation.

In order to produce a CMOS TFT semiconductor circuit, it is necessary to form an n channel TFT in which an n type dopant is doped and a p channel TFT in which a p type dopant is doped. A method of forming such CMOS TFT semiconductor circuit is fundamentally based on manufacturing processes of an LSI semiconductor device. Namely, the doping treatments are performed in separate processes while alternatively protecting an n type dopant and a p type dopant with masks.

A conventional method will be explained with reference to FIGS. 9A through 9D which illustrate subject matter disclosed by H. Ohshima et al. "Full-Color LCDs with Completely Integrated Drivers Utilizing Low-Temperature Poly-Si TFTs" in Conference Record of Society for Information Display, pp387-390(1993).

FIG. 9A relates to process (a) and shows a cross sectional view of a coplanar type TFT forming a base body. A backing film 2 consisting of SiO.sub.2 is formed on a glass substrate 1. An active layer silicon film 3 is formed on the backing film 2 and the crystalline quality of the active layer silicon film 3 is improved, such as by laser crystallization and thermal crystallization. On the active layer silicon film 3 a gate insulation film 4 consisting of SiO.sub.2 is formed. Further, a gate electrode 5 consisting of a metal or silicon film, for example is formed on the gate insulation film 4 and is processed so as to work as a gate.

In process (b) shown in FIG. 9B, a dope mask 7b is formed for the TFT on the p channel side and a phosphorus ion beam 8 is irradiated onto the TFT on the n channel side to form a source-drain layer 3a. For the irradiation by the phosphorus ion beam 8, an ion doping method suitable for a large scale substrate which performs no mass separation is used instead of using an ion injector as customary used in an LSI manufacturing process. An acceleration voltage of about 100 keV for the phosphorous ion beam irradiation is necessary because the phosphorous ions have to be accelerated to penetrate through the gate insulation 5. With such high acceleration voltage, ion energy is increased and the temperature of the substrate is raised because of a poor thermal conductivity of the glass. For this reason a heat resistant material, such as polyimide, is used for the dope mask 7b, but further measures for reducing the thermal load are necessary, such as by reducing the ion density and by prolonging the doping time.

In process (c) as shown in FIG. 9C, a dope mask 7a is formed on the TFT on the n channel side and a boron ion beam 6 is irradiated onto the TFT on the p channel side to form a source-drain layer 3b.

In process (d) as shown in FIG. 9D, the source-drain layers 3a and 3b are activated, such as by heat treatment and laser beam heating. Further, a protective insulation layer 9 consisting of SiO.sub.2, for example is formed, and after forming contact holes, source-drain electrodes 10 are formed to complate the element. By connecting the source-drains of the p and n channel TFTs as illustrated, an inverter constituting a base unit of a circuit element is formed.

For a simple TFT semiconductor circuit device, a simple manufacturing process which requires a smaller number of masking times than an LSI semiconductor manufacturing process is required. Thereby, an object of the present invention is to provide a simple and convenient method of manufacturing a CMOS TFT semiconductor circuit device and to provide a CMOS TFT semiconductor circuit device manufactured thereby.

In a method of manufacture of a CMOS TFT semiconductor circuit device according to the present invention, a doping layer of first conductivity type is doped without a mask and then compensated by a dopant of a second conductivity type having a higher density, thereby the conductivity type of the doping layer of first conductivity type is inverted to produce a doping layer of second conductivity type.

Further, in order to carry out easily and reliably the inversion of the conductivity type through the above compensation, the surface dopant density of the doping layer of first conductivity type is reduced before effecting the compensation by the dopant of second conductivity type.

Through the inverting operation of the conductivity type by the compensation, a region of the opposite conductivity type can be formed while reducing the mask doping process, so that the method of manufacture of the CMOS TFT semiconductor circuit device is simplified.

FIGS. 1A through 1D are diagrams for explaining a method of manufacturing a coplanar type CMOS TFT according to the present invention;

FIGS. 2A through 2D are density distribution diagrams for boron and phosphorus in the manufacturing processes in FIGS. 1B and 1C;

FIGS. 3A through 3D are diagrams for explaining another method of manufacturing a coplanar type CMOS TFT according to the present invention;

FIGS. 4A through 4E are diagrams for explaining still another method of manufacturing a coplanar type CMOS TFT according to the present invention;

FIGS. 5A through 5F are density distribution diagrams for boron and phosphorus in the manufacturing processes in FIGS. 4B, 4C and 4D;

FIGS. 6A through 6D are diagrams for explaining a method of manufacturing an inverted stagger channel etching type CMOS TFT according to the present invention;

FIGS. 7A through 7D diagrams for explaining a method of manufacturing an inverted stagger channel protection type CMOS TFT according to the present invention;

FIGS. 8A through 8D are diagrams for explaining a method of manufacturing a normal stagger type CMOS TFT according to the present invention; and

FIGS. 9A through 9D are diagrams for explaining a conventional method of manufacturing a coplanar type CMOS TFT.

An embodiment according to the present invention will be explained with reference to FIGS. 1A through 1D.

FIG. 1A relates to process (a) and is a cross sectional view of a coplanar type TFT forming a base body. A backing film 2 consisting of SiO.sub.2 is formed on a glass substrate 1. An active layer silicon film 3 is formed on the backing film 2 and the crystalline quality of the active layer silicon film 3 is improved, such as by laser crystallization and thermal crystallization. On the active layer silicon film 3 a gate insulation film 4 consisting of SiO.sub.2 is formed. Further, a gate electrode 5 consisting of a silicon film is formed on the gate insulation film 4 and is processed so as to work as a gate.

In process (b) shown in FIG. 1B, boron ion beam 6 is irradiated onto the substrate to form source-drain layers 3b. For the irradiation of the boron ion beam 6, an ion doping method is used which effects no mass separation. The doping operation is performed for about 10 seconds with an acceleration voltage from 3 keV to 7 keV using 1% diborane gas at ion density of 0.5 mA/cm.sup.2.

In process (c) shown in FIG. 1C, a resist doping mask 7b is formed on a TFT on the p channel side and a phosphorus ion beam 8 is irradiated onto a TFT on the n channel side to form a source-drain layer 3a. The irradiation conditions are substantially the same as in process (b) except that the irradiation time is prolonged to 30.about.60 seconds so as to increase the density of the phosphorus. Because of the low acceleration voltage and the corresponding low ion energy, a customary resist can be used as a mask.

FIGS. 2A through 2D show density distributions of boron and phosphorus in the depth direction of the coplanar type TFT. FIGS. 2A and 2B show density distributions of boron and phosphorus in the process (b) as shown in FIG. 1B and FIGS. 2C and 2D show density distributions of boron and phosphorus in the process (c) as shown in FIG. 1C. As shown in FIG. 2C, the conductivity type of the layer is changed to the opposite conductivity type by increasing the density of phosphorus, whereby the conductivity type of the doping layer in the n channel TFT is inverted to form an n type source-drain layer 3a, and in the p channel TFT, the original p type source-drain layer 3b remains.

In process (d) shown in FIG. 1D, the source-drain layers 3a and 3b are activated, such as by heat treatment and laser beam heating. Further, a protective insulation layer 9 consisting of SiO.sub.2, for example is formed, and after forming contact holes, source-drain electrodes 10 are formed to complete an inverter constituting a base unit of the circuit element. Further, the active layer silicon film 3 can be p-Si or a-Si.

FIGS. 3A through 3D show another embodiment according to the present invention. The manufacturing method of the present embodiment is substantially the same as in the embodiment explained in connection with FIGS. 1A through 1D except that the order of the doping operations of phosphorus and boron is reversed.

In process (b) shown in FIG. 3B, phosphorus of high density is at first doped into the n channel region while using the resist doping mask 7b, and in the process (c) shown in FIG. 3C, boron of a low density is doped over the entire surface. In the n channel region the doped boron is compensated by the phosphorus, thereby, an n channel is formed therein. With the present method, a CMOS element also can be produced through a single masking operation.

FIGS. 4A through 4E show still another embodiment according to the present invention. The manufacturing method of the present embodiment is substantially the same as in the embodiment explained in connection with FIGS. 1A through 1D, except that the acceleration voltages for phosphorus and boron doping are modified in order to carry out the conductivity type inverting operation more easily and reliably.

In process (b) shown in FIG. 4B, boron ion beam 6 is irradiated onto the substrate to form source-drain layers 3b. For the irradiation of the boron ion beam 6, an ion doping method is used which effects no mass separation. The doping operation is performed for about 10.about.30 seconds with an acceleration voltage from 500 eV to 3 keV using 1% diborane gas at an ion density of 0.5 mA/cm.sup.2. The features of the present embodiment, in comparison with the embodiment shown in FIGS. 1A through 1D are that the acceleration voltage is low and the source-drain layer 3b is shallow.

In the process (c) shown in FIG. 4C, a resist doping mask 7b is formed on the TFT on the p channel side. Thereafter, an oxygen ion beam 11 is irradiated by a reactive ion ashing, thereby, the high density boron layer on the surface of the shallow source-drain layer 3b is removed.

In the process (d) shown in FIG. 4D, the phosphorus ion beam 8 is irradiated onto the TFT on the n channel side to form the source-drain layer 3a in the same manner as in the process (c) in FIG. 1C. The irradiation conditions are substantially the same as in the process (c) in FIG. 1C, however, if the irradiation time is prolonged to about 10.about.30 seconds as in the above process (b), the conductivity type can be sufficiently inverted because of the lower surface density of boron.

FIGS. 5A through 5F show the density distributions of boron and phosphorus in the depth direction of the coplanar type TFT manufactured according to the method shown in FIGS. 4A through 4D. FIGS. 5A and 5B show the density distributions of boron in the process (b) shown in FIG. 4B, FIGS. 5C and 5D show the density distributions of boron in the process (c) shown in FIG. 4C, and FIGS. 5E and 5F show the density distributions of boron and phosphorus in the process (d) shown in FIG. 4D. As shown in FIGS. 5C and 5E, through the oxygen ion beam treatment, the surface density of boron is reduced, thereby the inversion of the conductivity type can be easily effected.

In the process (e) shown in FIG. 4E, substantially the same element as in the previous embodiment can be obtained. Further, in place of the oxygen ion beam 11 by the irradiation of reactive ion ashing another treatment, by inert gas or active gas having low energy is also effective.

FIGS. 6A through 6D show a further embodiment of the present invention which is applied to an inverted stagger channel etching type TFT. In the present embodiment, after forming the gate electrodes 5, the gate insulation films 4 and the active layer silicon film 3, the doping operation is performed in substantially the same manner as in the embodiment shown in connection with FIGS. 4B through 4E.

In the process (a) shown in FIG. 6A, a boron ion beam 6 is irradiated over the entire surface of the substrate to form a shallow source-drain layer 3b.

In the process (b) shown in FIG. 6B, a resist doping mask 7b is formed on the TFT on the p channel side. Thereafter, an oxygen ion beam 11 is irradiated by a reactive ion ashing, thereby, the high density boron layer on the surface of the shallow source-drain layer 3b is removed.

In the process (c) shown in FIG. 6C, the phosphorus ion beam 8 is irradiated onto the TFT on the n channel side to form the source-drain layer 3a in the same manner in the process (c) in FIG. 4D.

In the process (d) as shown in FIG. 6D, after forming the source-drain electrodes 10 and etching the back face channel, a surface protective film 12 consisting of SiN, for example is formed to complete an inverter constituting a base unit of the circuit element. Further, the active layer silicon film 3 can be p-Si or a-Si.

FIGS. 7A through 7D show a still further embodiment of the present invention which is applied to an inverted stagger channel protective type TFT. In the present embodiment, after forming the gate electrodes 5, the gate insulation films 4, the active layer silicon film 3 and a channel protective film 13, the doping operation is performed in substantially the same manner as in the embodiment shown in connection with FIGS. 6A through 6D.

In the process (a) shown in FIG. 7A, a boron ion beam 6 is irradiated over the entire surface of the substrate to form a shallow source-drain layer 3b.

In the process (b) shown in FIG. 7B, a resist doping mask 7b is formed on the TFT on the p channel side. Thereafter, an oxygen ion beam 11 is irradiated by a reactive ion ashing, thereby, the high density boron layer on the surface of the shallow source-drain layer 3b is removed.

In the process (c) shown in FIG. 7C, the phosphorus ion beam 8 is irradiated onto the TFT on the n channel side to form the source-drain layer 3a in the same manner as in the process (c) in FIG. 4D.

In the process (d) shown in FIG. 7D, after forming the source-drain electrodes 10, an inverter constituting a base unit of the circuit element is completed.

FIGS. 8A through 8D show a still further embodiment of the present invention which is applied to a normal stagger type TFT. In the present embodiment, after forming source-drain electrodes 10a and 10b, the doping operation is performed in substantially the same manner as in the embodiment shown in connection with FIGS. 1B through 1C.

In the process (a) shown in FIG. 8A, a boron ion beam 6 is irradiated over the entire surface of the substrate to form a shallow source-drain layer 3b.

In process (b) as shown in FIG. 8B, a resist doping mask 7b is formed on a TFT on the p channel side and a phosphorus ion beam 8 is irradiated onto a TFT on the n channel side to form a source-drain layer 3a.

In the process (c) shown in FIG. 8C, the active layer silicon films 3, the gate insulation films 4 and the gate electrodes 5 are formed.

In the process (d) shown in FIG. 8D, the protective insulation films 9 and the source-drain electrodes 10 are formed, thereby, an inverter constituting a base unit of the circuit element is completed.

According to the present invention, the doping process for manufacturing the CMOS TFTs can be realized in a single masking operation.