JPS5945220B2 - CCD manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a CCD.

A typical CCD manufacturing process is shown in FIGS. 1 to 5.
7000-8 which has a shielding effect against diffusion of impurities on the entire surface of a semiconductor substrate of one conductivity type, for example, a P-type silicon substrate 1.
After growing a relatively thick oxide film 2 of 000λ,
Using this oxide film 2 as a mask, N-type impurities are diffused and written into both ends of the substrate 1 to form readout regions 3 and 4 (FIG. 1), and then a region straddles between these regions 3 and 4. Then, a relatively thin gate oxide film 5 is grown on the exposed substrate portion, and then a polycrystalline silicon film 6 that will eventually become a transfer electrode is grown on this gate oxide film 5. (Figure 2). Thereafter, the polycrystalline silicon film 6 is selectively removed using a photolithography method using a mask 7 and a photoresist film 8 (FIG. 3) to form a transfer electrode 9 spanning the writing region 3 and the reading region 4.
, 9... are obtained (Figure 4). Next, a surface protective oxide film 10 is grown on the upper surface of the transfer electrode in a thermal oxidation atmosphere, and finally a write electrode 11 and a read electrode 12 are provided in the write area 3 and read area 4, respectively, and the CCD
complete. According to this method, in the photolithography process shown in FIG.
As a result, the resolution in this photolithography process decreases, and the transfer electrodes 9, 9, etc. with a precision higher than 2μ cannot be obtained, and ultimately, an improvement in transfer efficiency cannot be expected. Nakatsuta.

The present invention was made in view of such problems, and includes:
This will be explained in detail with reference to FIG. 6 and subsequent figures.

The first step of the present invention is as shown in FIG.
Step portions 21, 21 are formed at both ends of 0.
The depth of the stepped portions 21, 2, 1 is at least the thickness of the oxide film that has a shielding effect against the diffusion of impurities, specifically 5000~
It is assumed to be 6000λ. Next, on the entire surface of the substrate 20 having the stepped portions 21, 21, a 500°
An oxide film 22 having a thickness of 0 to 6000 λ is grown, and then impurities are diffused adjacent to the step portions 21, 21 at both ends of the substrate 20 to form a write region 23 and a read region 24 (FIG. T). Thereafter, after removing the oxide film 22 to expose the substrate 20, a gate oxide film 25 with a thickness of about 1000λ and a polycrystalline silicon film 26 with a thickness of 3000 to 4000λ are formed on the exposed substrate 20 (8th figure). Next, as shown in FIG. 9, the polycrystalline silicon film 26 is formed by photolithography using a photoresist film 27 provided on the surface of the polycrystalline silicon film 26 and a mask 28 in close contact with the resist film 27. Transfer electrodes 29 are separated into small areas and span the write area 23 and the read area 24,
Obtain 29... Thereafter, the substrate 20 is placed in a thermal oxidation atmosphere to oxidize the surfaces of the transfer electrodes 29, 29 to obtain a surface film-preservation oxide film 30, and finally write electrodes are formed in the write area 23 and the read area 24, respectively. 31 and readout electrodes 32 are provided to complete the CCD. As is clear from the above description, the present invention involves forming step portions at both ends of the substrate with a depth comparable to the thickness of the oxide film, which has a shielding effect against diffusion of impurities, prior to forming the writing region and the reading region. Because of this, the mask can be brought into close contact with the photoresist film during the photolithography process for forming the transfer electrodes, making it possible to suppress the reduction in resolution and making it possible to manufacture CCDs with high transfer efficiency. I can kami.

[Brief explanation of the drawing]

Figures 1 to 5 are cross-sectional views of main parts showing the rolling process;
11 to 11 are cross-sectional views showing the method of the present invention in the order of steps, and 21 indicates a step, 27 a photoresist film, 28 a mask, and 29 a transfer electrode, respectively.

Claims (1)

[Claims] 1. After forming steps at both ends of the semiconductor substrate with a depth similar to that of the oxide film that has a shielding effect against impurity diffusion, an oxide film with a thickness that has a shielding effect against impurity diffusion is formed. Using this oxide film as a mask, impurities are diffused into the end portion adjacent to the stepped portion to provide a write region and a read region, and then a gate oxide film and polycrystalline silicon are successively deposited over the entire surface of the substrate. Next, the polycrystalline silicon is separated into small regions using a photolithography method using a mask that is in close contact with the substrate to form a transfer electrode that spans both the writing and reading regions, and finally the top surface of the two transfer electrodes is placed in a thermal oxidation atmosphere. C, which is characterized by growing an oxide film for surface protection on
CD manufacturing method.