JPH0417341A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device in buried channel type CCD structure using a thin gate insulation film without losing a maximum transfer charge quantity by using an ONO film as a gate insulation film. CONSTITUTION:A title item has a first semiconductor region 101 of a first conductive type, a second semiconductor region 102 of a second conductive type which is formed on the first semiconductor region 101, a third semiconductor region 107 of first conductive type which is formed near a surface of the second semiconductor region 102, gate insulation films 103 and 105 in ONO (SiO2/Si3N4/SiO2) structure which is formed on a surface of the third semiconductor region 107, and gate electrodes 104 and 106 which are formed on the gate insulation films 103 and 105 as main entities. For example, an ONO (SiO2/Si3N4/ SiO2) film in three-layer structure using an SiO2 film with a film thickness where current constituents within film under a high electric field directly become tunnel current as gate insulation films 103 and 105 of charge transfer elements.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to the structure of a semiconductor device that realizes a CCD in which the gate insulating film is scaled without impairing dynamic range characteristics (maximum charge transfer characteristics). It is.

Conventional technology Embedded channel CCD is the most popular signal charge transfer circuit for solid-state image sensors used in consumer video cameras (Reference: C0H1 Sequin
(Sequin) & M, F, Tompsett.

“Charge transfer device (Ch.
transfer device)”,
Akatemi 7ri 7°less (Academic
Press) 1975) LL As shown in FIG. 3, an n region 302 formed on the top of a p substrate 301,
Gate oxide film with thickness Tox (approximately 1000 5i02)
A first layer polysilicon gate electrode 304 formed on 303 and a gate oxide film (SiOa) 305
A typical example is a second layer of polysilicon gate electrode 306 formed at a distance from the second layer of polysilicon gate electrode 306 .

An energy band diagram in a thermal equilibrium state (thermal equilibrium state when no voltage is applied) along the AA' cross section in FIG. 3 is shown in FIG. 4(a). In the main operating state of the CCD in FIG. 3, a positive voltage (15 to 20
v) is applied to the n region 302, so the energy band diagram becomes as shown in FIG. 4(b). At this time, the voltage of the polysilicon gate electrode is Ov. If the voltage of the gate electrode increases in the positive direction, the signal charge is accumulated, and if it increases in the negative direction, the signal charge is not accumulated.

At present, representative CCD-type image sensors (image sensors that use a CCD as a signal charge transfer circuit) include the 1/2-inch 400,000-pixel CCD for consumer use and the 2/3-inch 400,000-pixel CCD for commercial use. .

-J, "Broadcast Satellite B" scheduled to be launched in 1990-91
Satellite broadcasting began in earnest from ``5-3 (3 channels)''.
Broadcasting satellite B5- scheduled to be launched after 1997
It is expected that satellite broadcasting will become more important than terrestrial broadcasting if multiple commercial broadcasters become possible with ``4 (8 channels)''. Be captivated by 2 million pixel CC
Development of high-definition video cameras using D is progressing.

When it comes to a 2 million pixel CCD, the DR of semiconductor memory
As with AM, the application of scaling (miniaturization) is essential. In particular, miniaturization of gate insulating film thickness (calculation result in Figure 5)
Maximum transfer charge amount N51g and gate electrode voltage V when human
As shown in (relationship g), it can be seen that the smaller the thickness of the insulating film, the smaller the amplitude of the drive pulse applied to the gate electrode while handling the same dynamic range, which is advantageous in lowering the voltage.

Problems to be Solved by the Invention A well-known phenomenon in thin gate oxide films (SiC2) is that positive charges (
As a result, Fowler-Nordheim) tunnel current (current generated when carriers flow in the gate oxide film according to the electric field after being injected into the gate oxide film by the tunnel effect) This increased current causes a positive feedback effect in which the trapped positive charges (holes) increase again, so that dielectric breakdown occurs even at voltages below 10 V. 500 thin SiC people shown in Figure 5
2 cannot be used.

Therefore, in DRAM, etc., which is a scaling driver, ON○ has better dielectric breakdown characteristics than thin SiC2.
A film (three-layer film with Si○2/Si*N-/Sioa configuration) is used.

Therefore, 5iOa in Figure 4(a) is
Thermal equilibrium state when replacing with ONO film equivalent to 02 film (
The energy in the thermal equilibrium state when no voltage is applied
A band diagram is shown in FIG. 6(a).

Figure 6(b) shows the energy band diagram when the CCD is in the main operating state and the voltage applied to the gate electrode is Ov.
Shown below.

As shown in Figure 6(b), the lower part 5 from the n-type silicon side
Holes 1 injected into the i02 film 601 by direct tunneling (a tunnel effect phenomenon in which carriers penetrate through a gate oxide film);! , Poole- in the 5isNa film
Flows as a Frenkel current (a current that flows according to the electric field because carriers in the conduction band or valence band of the nitride film do not move back and forth between the trap level and the trap level) and directly tunnels through the thin upper 5i02 film 603 to form the gate electrode. Exit to the 604 side. In this case, the surface of the Jun-type silicon tends to become more n-type.Even if the voltage of the gate electrode 604 is changed in the negative direction, a large amount of holes only flow from the silicon side to the gate electrode, and the accumulation state Because of this phenomenon, simply using a thin ONO film as the gate insulating film will reduce the maximum transfer charge amount of the CCD.

The present invention ζ focuses on these issues and aims to improve the maximum transfer charge amount (
The purpose of the present invention is to provide a semiconductor device having a buried channel type CCD structure using a thin gate insulating film without impairing dynamic performance.

Means for Solving the Problems The present invention (in order to achieve the above objects) After forming a hole accumulation region on the surface of the n-type region on the upper part of silicon, which will serve as a charge transfer region, a thin ○No film is used as gate insulator. A buried channel type CCD structure is used as a film.

Effects of the present invention (According to the above-described structure, the gate insulating film on the silicon surface of the CCD can be scaled by using an ONO film as a thin gate insulating film without adversely affecting the maximum transfer charge amount, which is the main characteristic of the CCD. becomes possible.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the structure of a semiconductor device according to an embodiment of the present invention. As can be seen from the figure, there is an n region 102 formed on the upper part of the p substrate 101, a p+ region 107 formed on the upper surface of the n region 102, and a thickness T which becomes the gate insulating film.
A first layer polysilicon gate electrode 104 formed on the ono ○No film 103 and an oxide film (SiO2)
Alternatively, it is composed of a second layer polysilicon gate electrode 106 formed with a NO film 105 in between. The structural feature is that a p-domain region 107 is formed on the silicon surface.

FIG. 2(a) shows an energy band diagram in a thermal equilibrium state (thermal equilibrium state when no voltage is applied) along the AA' cross section in FIG. 1. In the main operating state of the CCD in FIG. 1, a positive voltage (15 to 20
When V) is applied to the n region 102, the energy band diagram becomes as shown in FIG. 4(b). At this time, the voltage of the polysilicon gate electrode is Ov. p ten area 1
Due to the presence of 07, the energy on the silicon surface does not become very high. ○The electric field at both ends of the NO film is smaller than that of an oxide film of equivalent thickness. Therefore, as in the case of a thick gate oxide film, if the voltage of the gate electrode is increased in the positive direction, the signal charge will be accumulated, and if it is increased in the negative direction, the signal charge will not be accumulated.

The reason why the embodiment of the present invention exhibits the same effect as the thick gate oxide film shown in FIG. 4 is because the nitride film (Si3N4)
The valence band and trap level of 202 are in the p+ region 107
Since the energy is higher than the valence band of
This is due to the lack of tunnel injection into the NO film.

SiO constituting the ○No film as a gate insulating film
Since the trapping of holes in the two layers causes dielectric breakdown at low voltages, rF
It is also effective to set a film thickness such that a "direct tunnel current" flows before a "owler-Nordheim tunnel current" flows.

Effects of the Invention The present invention makes it possible to use an ONO film as a thin gate insulating film without adversely affecting the maximum amount of transferred charge, which is the operating performance of the charge transfer region. It becomes possible to scale the insulating film. As a result, the insulating film of the CCD becomes thinner and the amplitude of the transfer pulse becomes smaller, making it possible to reduce the power supply voltage resulting from scaling, which is a design guideline for increasing the number of pixels. The effect is extremely strong

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional diagram showing the structure of a CCD type semiconductor device according to an embodiment of the present invention. FIG. Figure 4 is an energy band diagram along the A-A' cross section of the conventional example in Figure 3. Figure 5 shows that the thickness of the insulating film depends on the gate voltage and the maximum amount of transferred charge. Graph doctor showing the results of calculating the influence on the relationship of
The figure shows an energy band diagram along the AA' cross section of the conventional example of FIG. 3 when a NO film equivalent to a thin oxide film is used. p-substrate・101, 301. n area・102, 302, p
Ten areas...107, Gate insulating film...River 03.104
．． 303.304, first layer polysilicon gate electrode
...104.304, second layer polysilicon gate electrode...106.306゜Name of agent: Patent attorney Shigetaka Awano iOz alyst N S/ f (tt −, 500) φ−−−(d−Sρ’s N5il (Ko−/riρO) φ, (Da rattan lρρρ)

Claims (2)

[Claims] (1) A first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type formed above the first semiconductor region, and a second semiconductor region formed near the surface of the second semiconductor region. a third semiconductor region of the first conductivity type, and an ONO (SiO_2/Si_3) formed on the surface of the third semiconductor region.
A semiconductor device comprising, as main components, a gate insulating film having a N_4/SiO_2) structure and a gate electrode formed on the gate insulating film. (2) Three-layer ON using a SiO_2 film with a thickness such that the current component in the film under a high electric field becomes a direct tunnel current
2. The semiconductor device according to claim 1, wherein an O (SiO_2/Si_3N_4/SiO_2) film is used as a gate insulating film of a charge transfer element.