JPH0529240A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To avoid the deterioration in electrical characteristics by a method wherein the direct thermal oxidation of a silicon substrate surface is avoided after finishing the ion implantation step for restraining the development of oxidation induced defect. CONSTITUTION:Boron ions are implanted in a silicon substrate 1 using a photoresist film 3 and a silicon oxide film 2 so as to form a P<+> region 4. Next, after the removal of the photoresist film 3, a silicon oxide film 2A is formed using ozone or oxygen plasma. Later, the whole body is annealed in an inert gas atmosphere so as to form a P well region 4A at specific depth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of reducing crystal defects caused by ion implantation.

[0002]

2. Description of the Related Art As an example of a conventional method for manufacturing a semiconductor device, a P well forming step of a CMOS structure will be described with reference to FIG.

First, as shown in FIG. 3A, a silicon oxide film 2 having a thickness of about 500 nm is formed on a silicon substrate 1 by a thermal oxidation method. Next, a photoresist film 3 is applied on this silicon oxide film 2, and an opening is formed in the photoresist film 3 in the P well forming region by photolithography. Next, using the photoresist film 3 as a mask, the silicon oxide film 2 in the P well forming region is removed by etching to form an opening.

Next, as shown in FIG. 3B, boron ions are implanted to form a P well by using the photoresist film 3 and the silicon oxide film 2 as a mask to form a P ⁺ region 4.

Next, as shown in FIG. 3 (c), in order to diffuse the P ⁺ region to a predetermined depth after removing the photoresist film 3, a high temperature ( Annealing is performed at 1000 ° C. or higher) to form the P well region 4A.

[0006]

In recent years, as the degree of integration of semiconductor devices has increased, in the case of a semiconductor device having a CMOS structure, for example, in order to improve the latch-up resistance, the impurity concentration in the well region is increased. There is a need to. Therefore, the dose amount of impurity ions such as boron is increased, and a crystal defect due to ion implantation becomes a problem.

In the conventional method of manufacturing a semiconductor device, impurity ions are directly implanted into a silicon substrate, and thereafter annealing is performed at a high temperature. At this time, if annealing is performed in a complete inert gas atmosphere, the surface of the silicon substrate becomes rough, so a method of adding a small amount of oxygen is used.
Therefore, in the process of annealing, the surface of the silicon substrate is directly oxidized by oxygen in the atmosphere to form a silicon oxide film. At this time, excess silicon at the interface between the silicon oxide film and the silicon substrate is supplied to the inside of the silicon substrate from the site where the crystal defects have been generated by the ion implantation, and oxygen interstitial oxygen-induced defects grow. This oxygen-induced defect is
Impurities (heavy metal ions) in the semiconductor device manufacturing process can be trapped and become carriers generation centers, so that there is a problem that characteristics of the semiconductor device are deteriorated such as increase of reverse leakage current of the diffusion layer.

A method of implanting ions through an oxide film in order to prevent oxygen-induced defects is also conceivable. In this case, oxygen in the silicon oxide film is knocked on into the silicon substrate and removed even after an annealing step. However, there is a problem that dislocations are induced in the silicon substrate without causing deterioration of the characteristics of the semiconductor device.

[0009]

A method of manufacturing a semiconductor device according to the present invention comprises a step of forming a first silicon oxide film on a silicon substrate and then patterning the same to form an opening, and the step of forming the opening. A step of ion-implanting impurities into the silicon substrate using the first silicon oxide film as a mask to form an ion-implanted region; and a step of forming a second silicon oxide film on the ion-implanted region by ozone or oxygen plasma. It includes.

[0010]

The present invention will be described below with reference to the drawings. 1A to 1D are cross-sectional views of a semiconductor chip shown in the order of steps for explaining an embodiment of the present invention. FIG. 2 is a graph showing the effect of this embodiment. The difference from the conventional example is that a silicon oxide film is formed by ozone or oxygen plasma before annealing after ion implantation.

First, as shown in FIG. 1A, a silicon oxide film 2 of about 500 nm is formed on a silicon substrate 1 by a thermal oxidation method, and a photoresist film 3 is applied on the silicon oxide film 2. A photoresist film 3 having an opening in the P well formation region is formed by photolithography. Next, using the photoresist film 3 as a mask, the silicon oxide film in the P well forming region is etched to form the opening 5
To form.

Next, as shown in FIG. 1B, boron is ion-implanted into the P well forming region using the photoresist film 3 and the silicon oxide film 2 as a mask to form a P ⁺ region 4.

Next, as shown in FIG. 1C, after removing the photoresist film 3, the silicon substrate 1 is placed in an ozone atmosphere to oxidize the surface of the silicon substrate 1 to form a silicon oxide film 2A. Form. The film thickness of the silicon oxide film 2A at room temperature is about 3 nm. The ozone is formed by turning on a low pressure mercury lamp in an oxygen atmosphere.

Next, as shown in FIG. 1D, the P ⁺ region 4
To a predetermined depth to form a P-well region 4A, and annealing at 1000 ° C., for example, in a complete inert gas atmosphere to recover crystal defects generated in the surface layer portion of the silicon substrate 1 by ion implantation. Do.

As described above, according to the present embodiment, ion implantation is performed with the silicon substrate exposed, and a silicon oxide film is formed at room temperature after the ion implantation process, and thereafter, a complete inert gas atmosphere is formed. Since annealing is performed at a high temperature, it is possible to prevent the generation of crystal defects due to knock-on of oxygen, and to prevent the growth of oxygen-induced defects caused by excess silicon that occurs when exposed to an oxidizing atmosphere at a high temperature. Therefore, impurities, especially heavy metal ions, in the manufacturing process of the semiconductor device are not trapped in the element active region, and deterioration of electrical characteristics such as increase of reverse leakage current in the diffusion layer of the semiconductor device can be prevented. it can.

FIG. 2 shows the diffusion layer leakage currents of the example and the conventional example. According to this example, it is found that the crystal defects can be suppressed, the carrier generation center density is reduced, and the reverse leakage current of the diffusion layer is significantly reduced.

In the above embodiment, the case where the silicon oxide film is formed by ozone has been described, but oxygen plasma may be used. In this case, the silicon substrate 1 is placed in the chamber to generate oxygen plasma, and a positive potential equal to or lower than the plasma potential is applied to the silicon substrate to collect active charged oxygen on the silicon substrate to form an oxide film. Form. The temperature of the silicon substrate is about 200 ° C,
The film thickness of the silicon oxide film 2A to be formed is about 3 nm as in the case of ozone.

The method using oxygen plasma has the advantages of high throughput and the use of existing plasma processing equipment.

[0019]

As described above, according to the present invention, since the ion implantation is performed with the silicon substrate exposed, it is possible to prevent the generation of crystal defects due to the knock-on of oxygen. In addition, since a silicon oxide film is formed by ozone or oxygen plasma after the ion implantation step and annealing is performed thereafter, the growth of oxygen-induced defects due to excess silicon can be suppressed. Further, even when high temperature annealing is performed in a complete inert gas atmosphere, the surface of the silicon substrate can be prevented from being roughened. Therefore, it is possible to prevent the deterioration of the electrical characteristics of the semiconductor device due to the capture of impurities (heavy metal ions) during the manufacturing process of the semiconductor device, and it is possible to improve the manufacturing yield and reliability of the semiconductor device. Have.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor chip for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing leak currents of an example and a conventional example.

FIG. 3 is a cross-sectional view of a semiconductor chip for explaining a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

1 Silicon Substrate 2, 2A Silicon Oxide Film 3 Photoresist Film 4 P ⁺ Region 4A P Well Region 5 Opening

Claims (1)

Claim: What is claimed is: 1. A step of forming a first silicon oxide film on a silicon substrate and then patterning the first silicon oxide film to form an opening, and the step of forming the opening in which the first silicon oxide film is formed. A semiconductor including a step of ion-implanting impurities into the silicon substrate as a mask to form an ion-implanted region, and a step of forming a second silicon oxide film on the ion-implanted region by ozone or oxygen plasma. Device manufacturing method.