CN103871855B - A kind of preparation method of integrated circuit Dual Gate Oxide - Google Patents

Abstract

The invention relates to the technical field of semiconductor integrated circuits, and discloses a method for preparing an integrated circuit double gate oxide, comprising: forming a field oxide layer on the surface of the substrate in the field region; forming a first layer of polysilicon on the surface of the field oxide layer in the field region; Form a thick gate oxide layer on the substrate surface of the active area of the MOS tube and the active area of the low-voltage MOS tube; coat photoresist on the surface of the semi-finished integrated circuit that has completed the above steps; expose and develop the semi-finished integrated circuit coated with photoresist The surface of the first layer of polysilicon is covered with a layer of photoresist in the field area, and the surface of the thick gate oxide layer in the active area of the high voltage MOS transistor is covered with a layer of photoresist in the active area. By adopting the technical scheme of the present invention, when the thick gate oxide layer of the low-voltage MOS transistor is etched away, the field photoresist can effectively protect the field oxide layer under the first layer of polysilicon from being etched laterally, avoiding voids, and greatly improving product reliability.

Description

A kind of preparation method of integrated circuit double gate oxide

technical field

The invention relates to the technical field of semiconductor integrated circuits, in particular to a method for preparing integrated circuit double gate oxides.

Background technique

In integrated circuits, due to the different withstand voltage conditions of the respective gates of the low-voltage MOS transistor and the high-voltage MOS transistor, the thickness of the gate oxide layer corresponding to the two is also different. Usually, the gate voltage is 5V, and the corresponding gate oxide layer thickness is 15V. ~20nm, so the thickness of the gate oxide layer corresponding to the high-voltage MOS transistor is larger. If there are gate oxide layers of two thicknesses in the integrated circuit, it is called double gate oxide.

According to the functional requirements of integrated circuits, in addition to low-voltage MOS tubes and high-voltage MOS tubes, high-value resistors (referred to as high-resistance) and capacitors need to be designed. The gate of the MOS tube, the upper and lower plates of the high resistance and the capacitor can be made of polysilicon.

In the prior art, when making double gate oxides for integrated circuits, a thick gate oxide layer is formed first; then the thick gate oxide layer in the area where a thin gate oxide layer needs to be formed is etched away; and a thin gate oxide layer is formed again. As shown in Figure 1, using the existing technology, when the thick gate oxide layer is etched away, the field oxide layer 2 covered with the first layer of polysilicon 5 will be etched laterally, and then a thin gate oxide layer 4 will be prepared, as shown in Figure 1. A schematic diagram of an integrated circuit with double gate oxides produced by existing technologies, the substrate 1 is covered with a field oxide layer 2, a thick gate oxide layer 3 and a thin gate oxide layer 4, and the field oxide layer 2 under the first layer of polysilicon 5 A cavity 8 is produced.

The defect of the prior art is that in the process of etching away the thick gate oxide layer, the field oxide layer under the first layer of polysilicon will be etched laterally, resulting in voids, which eventually lead to product defects and affect the reliability of the product.

Contents of the invention

The purpose of the present invention is to provide a method for preparing integrated circuit double gate oxide, which is used to improve the problem of voids caused by lateral etching of the field oxide layer under the first layer of polysilicon in the prior art, and improve product reliability.

The preparation method of integrated circuit double gate oxide of the present invention comprises:

forming a field oxide layer on the surface of the substrate in the field region;

forming a first layer of polysilicon on the surface of the field oxide layer in the field region;

Form a thick gate oxide layer on the surface of the substrate in the active area of the high-voltage MOS tube and the active area of the low-voltage MOS tube;

Coating photoresist on the surface of the integrated circuit semi-finished product after completing the above steps;

Expose and develop the semi-finished integrated circuit coated with photoresist, so that the surface of the first layer of polysilicon is covered with a layer of field photoresist, and the surface of the thick gate oxide layer in the active region of the high-voltage MOS tube is covered with a layer of photoresist in the active region. Engraving.

The preparation method of the integrated circuit double gate oxide also includes:

Etching away the thick gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor;

removing the photoresist in the field region and the photoresist in the active region;

Form a thin gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor;

A second layer of polysilicon is formed on the surface of the thin gate oxide layer and the thick gate oxide layer in the active region of the high voltage MOS transistor.

Preferably, each side of the photoresist in the field region exceeds the corresponding side of the first layer of polysilicon by 0.5-2.0 microns.

Preferably, the first layer of polysilicon serves as a high-resistance and/or lower plate of a polysilicon capacitor.

In the method for preparing integrated circuit double gate oxide of the present invention, since the first layer of polysilicon is covered with a field photoresist, when the thick gate oxide layer of the low-voltage MOS transistor is etched away, the field photoresist can effectively Protect the field oxide layer under the first layer of polysilicon from being etched laterally, avoid voids, and greatly improve product reliability.

Description of drawings

FIG. 1 is a schematic diagram of a double gate oxide structure of an integrated circuit in the prior art;

2 is a schematic flow chart of a method for preparing an integrated circuit double gate oxide of the present invention;

3a to 3e are process schematic diagrams of a specific embodiment of the method for preparing integrated circuit double gate oxides according to the present invention.

Reference signs:

1-substrate 2-field oxide layer 3-thick gate oxide layer 4-thin gate oxide layer

5-First layer of polysilicon 6-High resistance 7-Double polycrystalline capacitor lower plate 8-Void

9-The second layer of polysilicon 10-Active area photoresist 11-Field area photoresist

21-field area 22-high voltage MOS tube active area 23-low voltage MOS tube active area

detailed description

In order to solve the technical problem in the prior art that the field oxide layer under the first layer of polysilicon is etched laterally, voids are easily generated, and product defects are caused, the invention provides a method for preparing an integrated circuit double gate oxide.

As shown in Figure 2, the schematic flow chart of the preparation method of the integrated circuit double gate oxide of the present invention includes:

Step 101, forming a field oxide layer on the surface of the substrate in the field region;

Step 102, forming a first layer of polysilicon on the field oxide layer in the field region;

Step 103 , forming a thick gate oxide layer on the surface of the substrate in the active region of the high-voltage MOS transistor and the active region of the low-voltage MOS transistor.

Step 104, coating photoresist on the surface of the semi-finished integrated circuit after the above steps;

Step 105, exposing and developing the photoresist-coated integrated circuit semi-finished product, so that the surface of the first layer of polysilicon is covered with a layer of field photoresist, and the surface of the thick gate oxide layer in the active region of the high-voltage MOS transistor is covered with a layer Active area photoresist.

In the technical solution of the present invention, since the surface of the first layer of polysilicon is covered with a layer of field photoresist, in the subsequent etching step, the lateral etching of the field oxide layer under the first layer of polysilicon is avoided, thus The generation of voids is reduced, and the reliability of the product is improved.

The method for preparing the integrated circuit double gate oxide of the present invention, after step 105, further includes:

Etching away the thick gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor;

Remove the photoresist in the field area and the photoresist in the active area;

Form a thin gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor;

A second layer of polysilicon is formed on the surface of the thin gate oxide layer and the thick gate oxide layer in the active region of the high voltage MOS transistor.

Preferably, the first layer of polysilicon is used as a high-resistance and/or lower plate of a polysilicon capacitor, and the first layer of polysilicon can be used to prepare different devices according to the needs of integrated circuit design.

Preferably, each side of the photoresist in the field region exceeds the corresponding side of the first layer of polysilicon by 0.5-2.0 microns.

In the preferred solution of the present invention, the photoresist in the field area covers the first layer of polysilicon, and each side of the photoresist in the field area exceeds the corresponding side of the first layer of polysilicon by 0.5 to 2.0 microns. When the thick gate oxide layer on the substrate surface of the region is used, it can more effectively prevent the lateral etching of the field region oxide layer under the first layer of polysilicon, and improve the reliability of the product.

As shown in Figure 3a to Figure 3e is a specific embodiment of the preparation method of integrated circuit double gate oxide of the present invention, its main production process is as follows:

As shown in FIG. 3a, a high-voltage MOS transistor active region 22, a low-voltage MOS transistor active region 23, and a field region 21 are artificially divided on the substrate 1, and a field oxide layer 2 is formed on the surface of the substrate 1 in the field region 21;

According to the design of the integrated circuit, the first layer of polysilicon 5 is formed on the field oxide layer 2 of the field region 21 of the polysilicon device, and the first layer of polysilicon 5 can be used as the lower plate 7 of the high resistance 6 and the polysilicon capacitor;

A thick gate oxide layer 3 is formed on the surface of the substrate 1 in the active region 22 of the high voltage MOS transistor and the active region 23 of the low voltage MOS transistor.

As shown in Figure 3b, photoresist is coated on the surface of the integrated circuit semi-finished product after completing the above steps;

Expose and develop the photoresist-coated integrated circuit semi-finished product, so that the surface of the first layer of polysilicon 5 is covered with a layer of field photoresist 11, and the surface of the thick gate oxide layer 3 of the high-voltage MOS tube active region 22 is covered with a A layer of active region photoresist 10, wherein the field region photoresist 11 covers the first layer of polysilicon 5, preferably, each side of the field region photoresist 11 exceeds the corresponding side of the first layer of polysilicon 5 by 0.5 to 2.0 microns .

As shown in Figure 3c, the thick gate oxide layer 3 on the surface of the substrate 1 in the active region 23 of the low-voltage MOS transistor is etched away, and the field oxide layer 2 in the field region not covered by the photoresist is also etched to a certain thickness , the thickness is generally equal to 1.05 to 1.25 times the thickness of the thick gate oxide layer 3, and a small part of the field oxide layer 2 under the photoresist 11 in the field area is also laterally etched away, generally less than 0.2 microns.

As shown in Figure 3d, remove the field region photoresist 11 on the surface of the first layer of polysilicon 5 and remove the active region photoresist 10 on the surface of the thick gate oxide layer in the active region of the high-voltage MOS transistor. After removing the photoresist, the first A layer of polysilicon 5 and field oxide layer 2 will not produce voids, and the surface of the field oxide layer is a smooth step, which avoids the reliability risk of the final product;

Forming a thin gate oxide layer 4 on the surface of the substrate 1 in the active region 23 of the low-voltage MOS transistor;

As shown in Figure 3e, a second layer of polysilicon 9 is formed on the surface of the thin gate oxide layer 4 and the thick gate oxide layer 3 in the active region of the high-voltage MOS transistor, and this layer of polysilicon can be used to form the gates of the low-voltage MOS transistor and the high-voltage MOS transistor .

In this embodiment, adopt the first layer of polysilicon to make the lower plate of high resistance and capacitance, but the present invention is not limited to this embodiment, the device that the first layer of polysilicon is made and its position in the field area can be according to the integrated circuit The design is different. For example, the first layer of polysilicon is only used to make high resistance or the lower plate of the capacitor. Similarly, the second layer of polysilicon is not limited to just making the gate of the MOS, and can also be used to make capacitors. of the upper plate. As long as the double gate oxide of the integrated circuit is prepared after the first layer of polysilicon, it is applicable to the present invention.

It can be seen that in the technical solution of the present invention, since the first layer of polysilicon is covered with field photoresist, when the thick gate oxide layer of the low-voltage MOS transistor is etched away, the field photoresist can effectively protect the first layer of polysilicon. The field oxide layer under the polysilicon layer is not etched laterally, avoiding voids, reducing product defects, and greatly improving product reliability.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (3)

1. A method for preparing an integrated circuit double gate oxide, characterized in that, comprising: forming a field oxide layer on the surface of the substrate in the field region; forming a first layer of polysilicon on the surface of the field oxide layer in the field region; Form a thick gate oxide layer on the substrate surface of the active area of the high-voltage MOS tube and the active area of the low-voltage MOS tube; Coating photoresist on the surface of the integrated circuit semi-finished product after completing the above steps; Expose and develop the photoresist-coated integrated circuit semi-finished product, so that the surface of the first layer of polysilicon is covered with a layer of field-region photoresist, and the surface of the thick gate oxide layer in the active region of the high-voltage MOS transistor is covered with a layer of The photoresist in the source region, each side of the photoresist in the field region exceeds the corresponding side of the first layer of polysilicon by 0.5-2.0 microns. 2. The preparation method of integrated circuit double gate oxide according to claim 1, characterized in that, after exposing and developing the semi-finished integrated circuit product coated with photoresist, further comprising: Etching away the thick gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor; removing the photoresist in the field region and the photoresist in the active region; Form a thin gate oxide layer on the substrate surface of the active region of the low-voltage MOS transistor; A second layer of polysilicon is formed on the surface of the thin gate oxide layer and the thick gate oxide layer in the active region of the high voltage MOS transistor. 3. The method for preparing integrated circuit double-gate oxides according to claim 1, wherein the first layer of polysilicon is used as a high-resistance and/or lower plate of a polysilicon capacitor.