JPH03280473A - Manufacture and structure of thin film transistor - Google Patents

Abstract

PURPOSE:To retrain a source and a drain from changing in dimensions by a method wherein a conductor film identical to a gate electrode in shape is formed above the gate electrode, and ions are implanted into a silicon thin film using the conductor film concerned as a mask to form the drain and the source region of the thin film transistor. CONSTITUTION:A conductor film 9 is formed on an insulation protective film 8. A photoresist 10 is formed on a region located above a gate electrode 4, and the disused part of the conductor film 9 is removed by etching to form a conductor film mask 9'. Thereafter, the photoresist 10 is removed, and ions are implanted 11 into a silicon thin film 7 to form a source and a drain by the use of the conductor mask 9' taking advantage of boron fluoride. As a conductor mask is made to serve as a mask, the accuracy of ion implantation depends on the processing accuracy of the conductor mask concerned, and the conductor mask is restrained from changing in dimensions as compared with a photoresist mask. Charge induced due to ion implantation is made to flow through other part, so that an insulating film is protected against breakage.

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to a method for manufacturing a thin film transistor, particularly a thin film transistor disposed directly above a MOS (MOS) transistor formed on the surface of a semiconductor substrate, and a coupling structure of both transistors. r Phi m rrs +k SE 1 In recent years, CMOS integrated circuits have been increasingly used because of their low power consumption and resistance to noise. However, since CMOS has a well structure in order to separate MOS transistors of different types, it has the disadvantage that it occupies a large area. For this reason, various methods have been devised to reduce the occupied area. A method is proposed. An example of the manufacturing method of such a thin film transistor is shown in FIG. 4, and its structure is shown in FIG. 5. In the figure, 41 is a p-type semiconductor substrate, 42 is an n-type diffusion layer, 43 is a gate insulating film, 44 is a gate electrode made of polycrystalline silicon, and 45 is an insulating film formed on the side wall of the gate electrode. The gate electrode 44 of the MOS transistor is formed in common. After forming a thin gate insulating film 46 on the MOS transistor, this gate insulating film 46 is covered with a silicon thin film 47 that will become the substrate of the thin film transistor, and a protective film is formed. For,
Further, an insulating protective film 48 is formed thereon (FIG. 4(b)
)). Next, source/drain regions are formed in the silicon thin film 47 by ion implantation.
), a photoresist mask 49 is formed, and boron fluoride or the like is ion-implanted to a concentration of approximately l x l O cm-. After the ion implantation, the photoresist 49 is removed and a transistor is completed in the silicon thin film 47, as shown in FIG. 4fdl. A plan view of the thin film transistor formed by the above method is shown in FIG. 55 is a drain, and 56 is a channel region of a p-type MOS transistor formed in FIG. 5(b) is an equivalent circuit representation of FIG. 1a). N3 is an n-type MOS transistor made up of 51 to 53, and P3 is a p-type MOS transistor made up of 53 to 56. Note that this figure shows the state before completion of wiring to each electrode.

[Problems to be Solved by the Invention] In the conventional thin film transistor manufacturing method shown in FIG.
Photoresist is used as an implant blocking agent when performing ion implantation into the source and drain of a thin film transistor, but when forming a fine pattern over a wide range, it has the disadvantage that there is a difference in the exposure state near the center and the periphery of the exposed area. In the periphery of the exposed area, as shown in Figure 4 [c], the shape of the photoresist has a size difference between the top and bottom surfaces, and impurities enter the silicon thin film from places where the photoresist is insufficiently thick during ion implantation. The channel length is L for the designed channel length L0 as shown in Fig. 4(d).
E<Lo @ L (Depending on the size of l, there is a risk that the transistor cannot operate due to the short channel effect. Also, since a large amount of ions are implanted into the source and drain, the photoresist becomes charged. In addition, thin film transistors formed using the conventional manufacturing method described above have a floating channel as shown in FIG. The object of the present invention is to provide a method for manufacturing a thin film transistor that eliminates the above-mentioned drawbacks. [Means for Solving the Problems J] The thin film transistor of the present invention has It has a structure in which a MOS transistor formed on the main surface of a substrate is used as a base and a gate electrode is shared on the top thereof.The manufacturing method thereof includes a step of forming a gate insulating film on the base MOS transistor, and a step of forming a gate insulating film on the base MOS transistor. Silicon III on the gate insulating film
a step of forming an insulating protective film on the silicon thin film; a step of forming a conductive film located above the gate electrode and having the same shape as the gate electrode on the protective crotch of the insulating film; The method includes a step of implanting ions into the silicon thin film using a conductive film as a mask to form drain and source regions of a thin film transistor. 1. Effect: When forming a source/drain in a planned region of a silicon thin film by ion implantation, a mask made of a conductive film of the same shape is placed above the gate electrode. This mask is a conductive film. Sources and drains can be formed accurately during ion implantation. Also, unlike a photoresist mask, there is no charge accumulation during ion implantation, and no dielectric breakdown occurs. As will be explained in the embodiments, the conductive film has the effect of keeping the channel of the thin film transistor at a constant potential through the capacitance by appropriately connecting the conductive film.

【Example】

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the manufacturing process of a thin film transistor according to the manufacturing method of this embodiment. FIG. 1(a) shows a cross section of an underlying n-type MOS transistor, for example, where l is a p-type semiconductor substrate, 2 is an n-type source/drain diffusion layer, 3 is a gate insulating film, and 4 is a gate electrode. , 5 are sidewall insulating films. FIG. 1 (bl) shows a state in which a silicon thin film 7, which will become the substrate of a thin film transistor, an insulating film 6, and an insulating protective film 8 have been formed. Here, the insulating film 6 will become the gate insulating film of the thin film transistor. This is the same process as shown in FIG. As shown in d), a photoresist 10 is formed in the region above the gate electrode 4, and unnecessary portions of the conductor film 9 are removed by etching to form a conductor film mask 9'.After this, the photoresist 10 is removed, As shown in FIG. 1(e), using a conductive film mask 9', the silicon thin film 7 is
Ion implantation 11 using, for example, boron fluoride is performed to form sources and drains therein. Since the mask for ion implantation 11 is a conductive film, the accuracy of ion implantation 11 is determined by the processing accuracy of the conductive film, and dimensional changes are suppressed compared to conventional photoresist masks. Further, charges generated by ion implantation flow to other parts, and the insulating film is not destroyed. Note that the conductor film mask 9' is different from a photoresist mask and is not removed after ion implantation (it is used to function so that the channel of the thin film transistor does not become floating), and is used to perform the predetermined connections disclosed in the embodiments below. Figure 2 shows an example of the structure of a thin film transistor obtained by the manufacturing method of the example.
is an equivalent circuit. In FIG. 2 1a), reference numeral 21 is the source of an underlying n-channel MOS transistor, which is supplied with a ground potential. 22 is its drain, 23 is a common gate electrode wiring, 2'4 is a source of a thin film transistor (n-type MOS transistor) formed in the silicon thin film 7, 25 is its drain, 26 is a channel of this transistor, and 27 is an ion. It is connected to the source 21 of the underlying n-channel MOS transistor through a contact 28 through wiring to the conductive film mask 9' of the implantation F shield. In Figure 2+bl, Nl is 21.22 in Figure 1al.
．． 23, an underlying n-type MOS transistor formed by P
I is the n-type M of the thin film transistor formed by 23 to 26
The OS transistor Ct is a capacitor formed between the channel 26 of the p-type MOS transistor and the grounded source 21 of the underlying n-channel MOS transistor. FIG. 3 shows another example of the structure of a thin film transistor obtained by the manufacturing method of the present invention. 3(a) is a plan view, and FIG. 3(b) is an equivalent circuit, 31 to 38, N2. P2.
C2 corresponds to FIG. 21-28, Nl, PI, and CI, respectively. In this embodiment, a contact 38 connects a wiring 33 to a common gate electrode and a wiring 37 to a conductive film. Unfavorable operational phenomena such as the kink phenomenon of thin film transistors can be alleviated by applying a potential indirectly through a capacitive element without applying a direct potential to the channel. C2 corresponds to this, and has the advantage that it can be easily realized by using the conductor film 9 shown in FIG. 1 of the embodiment of the manufacturing method and controlling the thickness of the insulating protective film 8. Effects of the Invention 1 As explained above, the present invention uses a conductive film as a blocking material for ion implantation into the source and drain of a thin film transistor, thereby suppressing dimensional changes in the source and drain compared to photoresist, and reducing dielectric breakdown. It has a preventive effect. Further, by connecting the conductor film to the ground or the common gate electrode, a capacitance is formed between the conductor film and the channel of the thin film transistor, which has the effect of suppressing phenomena such as kink phenomenon that are undesirable for the operation of the IS transistor. In the embodiment, the MOS transistor on the semiconductor substrate as a CMOS transistor is described as an n-type, and the thin film transistor as a p-type, but a combination of opposite conductivity types may also be used. Furthermore, not only CMOS transistors but also a combination of the same conductivity type may be used.

[Brief explanation of the drawing]

FIG. 1 (al to (el) is a cross-sectional view showing an example of the method for manufacturing a thin film transistor of the present invention, FIG. 2 (a) is a plan view showing an example of the structure of a thin film transistor manufactured by the example, 3 is an equivalent circuit diagram, and FIG. 3 is a plan view showing another example of a thin-film transistor. FIG. 5 18) is a plan view showing the structure of a thin film transistor obtained by a conventional manufacturing method;
The same figure (bl is an equivalent circuit diagram. 1.41... Semiconductor substrate, 2.42... Diffusion layer,
3.43...Gate insulating film. 4.44... Gate electrode, 5.45-- Side wall insulating film, 6.46... Gate insulating film, 7.47... Silicon thin film, 8.48...- Insulating protective film, 9.・・Conductor film, 9′・
...Conductor film mask, 21, 31, 51-- Source of n-type MOS transistor, 22, 32, 52-- Drain of n-type MOS transistor, 23.33.53...-Gate electrode, 24. 34.54... Sos of thin film transistor, 25°26°27°28°35.55... Drain of thin film transistor, 36.56-... Channel of thin film transistor, 37... Conductor film. 38--Contact. Figure 2 Cause 3 (a) Cause 5

Claims (1)

[Claims] 1. A MOS transistor formed on the main surface of a semiconductor substrate with a common gate electrode on the base and a MOS transistor formed on the main surface of the semiconductor substrate.
In the manufacturing method for forming a thin film transistor, the steps include forming a gate insulating film on the base MOS transistor, forming a silicon thin film on the gate insulating film, and forming an insulating protective film on the silicon thin film. and a step of forming a conductor film located above the gate electrode and having the same shape as the gate electrode on the insulating film protective film;
A method for manufacturing a thin film transistor, comprising the step of implanting ions into the silicon thin film using the conductor film as a mask to form drain and source regions of the thin film transistor. 2. A thin film transistor obtained by the manufacturing method according to claim 1, characterized in that a conductive film used as a mask of the thin film transistor is connected to a source at a ground potential of an underlying MOS transistor. thin film transistor structure. 3. In the thin film transistor obtained by the manufacturing method according to claim 1 of the claims, the conductive film used as a mask of the thin film transistor is connected to the same potential as the common gate electrode of the underlying MOS transistor and the thin film transistor. A thin film transistor structure characterized by