JPH0714052B2 - Method for forming electrode of charge coupled device - Google Patents

Description

The present invention relates to a method for forming electrodes of a charge-coupled device (CCD), and more specifically, when the pattern size is miniaturized by increasing the device density. The present invention relates to a method of forming a transfer electrode that can preferably separate adjacent electrodes.

[Prior art]

Generally, the CCD transfer electrode has a multi-layer structure in which oxidized polysilicon is superposed as shown in FIG. 2, for example.

In the production of such a transfer electrode having a multilayer structure, for example, if the alignment of the mask pattern used in the lithographic process is misaligned, one end of one electrode is separated from the adjacent electrode, resulting in a so-called misaligned structure. Therefore, in the conventional device, a margin is provided in the overlapping portion of the mask, and the electrodes have an overlap of, for example, about 1 μm.

However, with such an overlap, it has been difficult to miniaturize the pattern size to achieve high density of devices.

An electrode structure finally made of single-layer polysilicon as shown in FIG. 3 has been considered as one that can cope with high density. Such an electrode structure has the same effect as an electrode with a conventional mating structure, so that the distance between adjacent electrodes is 0.2μ.
They must be separated at minute intervals of about m to 0.5 μm.

Further, in the final step of manufacturing the electrodes, an oxide film is provided between the electrodes separated by the etching of the polysilicon into the minute intervals to insulate the electrodes.

[Problems to be solved by the invention]

However, it is difficult to embed a PSG (Phospho-Silicate Glass) oxide film in the above-mentioned minute interval, and air encapsulation occurs, and the minute interval of polysilicon has a defect that mechanical strength and thermal strain are weak. Therefore, a problem occurs in the passivation film formed in the final stage, which causes cracks and the like.

The object of the present invention was made based on the above circumstances,
Transfer electrodes having a single-layer polysilicon structure are formed at minute intervals,
Another object of the present invention is to provide a method for forming an electrode of a charge-coupled device in which the distance can be suitably insulated.

[Means for solving problems]

That is, the above object of the present invention is to provide a gate oxide film and a gate oxide film on a semiconductor substrate in an electrode forming method of a charge-coupled device in which a plurality of electrodes made of a single-layer polysilicon layer are arranged along a direction intersecting a charge transfer direction. A polysilicon layer is sequentially formed, and a polysilicon oxide film is grown to a predetermined thickness on the surface of the remaining polysilicon layer after patterning the polysilicon layer at a predetermined interval, and then a photoresist is applied to the entire area to cover at least the polysilicon layer surface. Charge coupling is characterized by performing planarization etching until it is exposed, removing the photoresist and the polysilicon layer, depositing polysilicon on the entire area, and performing oxidation after doping to complete insulation between polysilicons. This is achieved by the method of forming electrodes of the device.

〔Example〕

Hereinafter, embodiments of the electrode forming method according to the present invention will be described in detail with reference to the drawings.

In one embodiment shown in FIG. 1, in (a), a gate oxide film (SiO ₂ film) 1 is sandwiched on an N-type channel impurity layer (not shown) formed on the surface of a P-type silicon crystal substrate 10. Polysilicon 2 is deposited. The gate oxide film 1 is formed to a thickness of 250 Å by thermal oxidation. Also,
The polysilicon 2 has conductivity by adding phosphorus,
Formed by CVD with a thickness of 2000Å. In (b), the polysilicon 2 is arranged at a predetermined interval, for example, one cell has a width of 3 μm, and a plurality of polysilicon 2 are arranged along a direction intersecting the charge transfer direction (direction indicated by an arrow in the figure). To be patterned. This patterning is performed by the usual lithography, and the description here is omitted.
In (c), a polyoxide film 3 is grown on the surface of the polysilicon 2 by a thermal oxidation method to a predetermined thickness. The film thickness is 0.2 μm to 0.5 μm, and the wall portion of the polyoxide film 3 serves as an insulating layer between separated electrodes, which will be described later.
In (d), a low-viscosity resist 4 is applied to the entire area to fill the steps, and then planarization etching is performed by reactive ion etching (RIE). At this time, the planarization etching is performed until at least a part of the polysilicon 2 is removed together with the polyoxide film 3 corresponding to the eaves part on the polysilicon 2. In (e), the low viscosity resist 4 is peeled off,
Further, the polysilicon 2 is also etched to remove the poly oxide film 3
Only form a vertical wall. In (f), the polysilicon 5 is again deposited over the entire area, and after doping (g), the polyoxide film 3a is grown on the surface of the polysilicon 5. At this time, the upper portion of the poly-Si in FIG. 6 (f) may be oxidized up to the line shown by the dotted line to complete the insulation of the adjacent poly-Si electrode, or planarization etching may be performed before the oxidation step.

This planarization etching is performed at least until the top of the vertical wall of the polyoxide film 3 is exposed.

〔The invention's effect〕

As described above, according to the method of the present invention, it is possible to fabricate a charge-coupled device in which polysilicon is a single layer and is separated by minutely spaced poly oxide films. Further, in the final step, since the surfaces of the polysilicon and the polyoxide film are provided flat, troubles such as cracks do not occur when the passivation film is formed. In the present invention, the electrodes are separated only by the polyoxide film.

[Brief description of drawings]

FIG. 1 is a process diagram for explaining one embodiment of the present invention, FIG. 2 is a sectional view for explaining a CCD transfer electrode having a conventional laminated polysilicon structure, and FIG. 3 is for explaining a single-layer polysilicon structure. FIG. 1 ... Gate oxide film, 2,5 ... Polysilicon, 3,3a ...
Poly oxide film, 4 ... Low viscosity resist, 10 ... P type silicon crystal substrate

Claims (1)

[Claims] 1. A method for forming an electrode of a charge-coupled device, wherein a plurality of electrodes made of a single-layer polysilicon layer are arranged along a direction intersecting a charge transfer direction, wherein a gate oxide film and a polysilicon layer are formed on a semiconductor substrate. Sequentially formed, after patterning the polysilicon layer at a predetermined interval, a poly oxide film is grown to a predetermined thickness on the remaining polysilicon layer surface and sidewalls,
After applying photoresist to the entire area and performing planarization etching until at least the surface of the polysilicon layer is exposed, the photoresist and the polysilicon layer are removed, and then polysilicon is again deposited on the entire area. A method for forming an electrode of a charge-coupled device, which comprises performing oxidation until polysilicon insulation isolation is completed.