JPH05286795A - Silicon semiconductor substrate - Google Patents

Abstract

PURPOSE:To provide a silicon semiconductor substrate having an effect to remove a heavy metal impurity represented by iron, nickel and copper which are incorporated during a manufacture of a semiconductor integrated circuit, over the total manufacturing process of the semiconductor integrated circuit. CONSTITUTION:The silicon semiconductor substrate is formed a combined film of a 7-20Angstrom thick silicon oxidized film and a polycrystalline silicon film in a multilayered structure at the rear face of the silicon semiconductor substrate. Thus even after a manufacturing process of the semiconductor integrated circuit was completed, the polycrystalline silicon at the rear side of the silicon semiconductor substrate is kept at a fine state without the formation of coarse grains, so that the silicon semiconductor substrate superior in gettering capacity is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon semiconductor substrate material used for manufacturing semiconductor devices such as integrated circuits. In particular, the present invention is a silicon substrate material for the purpose of enhancing the effect of removing heavy metal impurities received during device manufacturing from the device region within the silicon substrate.

[0002]

2. Description of the Related Art With the high integration of integrated circuits, reduction of a minute leak current in a dynamic memory (DRAM) has become an important issue. This minute leak current is caused by heavy metal impurities represented by iron, nickel, and copper that are mixed in during the semiconductor integrated circuit manufacturing process. A gettering method is used to remove the heavy metal impurities. This gettering method includes a method of forming a polycrystalline silicon film on the back surface of a semiconductor substrate, (Journal of Electrochemical Society 1982
Volume 129, page 1294, JP-A-59-186331, JP-A-0
No. 1-315144) is known. JP-A-59
JP-A-186331 describes a method of forming a polycrystalline silicon film on the back surface of a semiconductor substrate. In this method, the grain boundaries of polycrystalline silicon grains are hard to disappear at high temperatures, so that it is effective through high temperature treatment. It is shown. Japanese Patent Application Laid-Open No. 01-315144 describes a method of forming a polycrystalline silicon film with an oxide film sandwiched on the back surface of a semiconductor substrate, and a gettering ability higher than that of a conventional polycrystalline silicon film forming method is obtained. Has been shown.

[0003]

In the process of manufacturing a semiconductor integrated circuit, with the recent trend toward higher integration represented by 4MDRAM, a temperature of 1150 ° C. to 120 ° C. called a CMOS process is called.
A high temperature and long time heat treatment of 0 ° C. and 6 hours to 10 hours is performed. Among the gettering methods currently used, even in the method of forming a polycrystalline silicon film, which has a high gettering ability, the crystal defect density decreases due to the coarsening of the polycrystalline silicon grains after heat treatment at high temperature for a long time. The deterioration of the ring ability becomes a problem. As a specific example, the 1991 Japan Applied Physics Association Lecture Spring Meeting (Lecture Proceedings 1st Volume 22)
4). It is an object of the present invention to provide a silicon substrate having excellent gettering ability even after a high temperature and long time heat treatment process.

[0004]

The present invention provides the following gettering ability-enhanced single crystal silicon substrate and a method of manufacturing the same for the above-mentioned purpose. A silicon semiconductor, characterized in that, on the back surface side of a silicon semiconductor substrate, two or more layers of a composite film consisting of a silicon oxide film having a thickness of 7Å to 20Å and a polycrystalline silicon film formed on the oxide film are formed. substrate.

[0005]

Function: Oxidation of the silicon semiconductor substrate and the polycrystalline silicon film is usually performed in an oxidizing atmosphere at 500 ° C to 1200 ° C.
It is formed by thermal oxidation in the temperature range of. The formation of a thin oxide film of about 10 Å can also be performed by dipping it in an aqueous solution containing hydrogen peroxide or an aqueous solution containing nitric acid. The silicon oxide film formed by such a method has good adhesion on the silicon semiconductor substrate and a uniform film thickness. Further, a chemical vapor deposition method is used for forming the polycrystalline silicon film. For example, it is possible to uniformly deposit silicon atoms on a silicon semiconductor substrate with good adhesion by a thermal decomposition reaction of silane gas in a temperature range of 600 ° C. to 800 ° C. using silane as a raw material.

A multi-layer structure can be obtained by repeatedly forming a silicon oxide film and a polycrystalline silicon film on the silicon substrate by using the above method. When the silicon substrate formed by the above method is heat-treated at 1150 ° C. for 10 hours, if the thickness of the oxide film is less than 5Å, the oxide film is easily decomposed to cause coarsening of polycrystalline grains and gettering ability. Is reduced. When the oxide film is from 7Å to 20Å, the oxide film becomes an island-shaped oxide, and this oxide prevents coarsening of polycrystalline grains, and fine crystal grains are obtained, and the oxide film dissociates into island-shaped oxide. By so doing, the gettering ability is not lowered because it does not hinder the diffusion of the heavy metal element. If the oxide film is thicker than 20Å, the oxide film is stable and
Although it is possible to prevent coarsening of polycrystalline grains, it becomes a barrier to diffusion of heavy metal impurities and the gettering ability is lowered. Further, the gettering ability is remarkably improved by forming two or more layers of the composite film including the silicon oxide film and the polycrystalline silicon film formed on the oxide film.

[0007]

EXAMPLE FIG. 1 shows a schematic view of the cross-sectional structure of the silicon substrate thus prepared. The oxide film of each layer is heat-treated for 10 minutes in an atmosphere containing oxygen gas at 500 to 800 ° C. for 5Å, 7
Oxide films of Å, 15Å, 20Å and 25Å were formed. The polycrystalline silicon film of each layer was formed by chemical vapor deposition at a substrate temperature of 650 ° C. for 15 minutes using silane gas as a source gas. The thickness of the polycrystalline silicon film is 2000Å. Two layers of a composite film having a polycrystalline silicon film formed on the silicon oxide film were formed.

Next, the gettering ability of the silicon substrate of the present invention was preheated to a sample in which the oxide film thickness of each composite film was changed, then intentionally contaminated with copper, and after the diffusion heat treatment of copper, The amount of copper captured in the polycrystalline silicon film was analyzed by an atomic absorption method and evaluated by the copper recovery rate. The pre-heat treatment condition is 1150 ° C. and a nitrogen atmosphere containing 0.5% oxygen for 10 hours. The intentional contamination of copper was performed by rotating a silicon substrate and dropping an aqueous solution containing copper onto the substrate. According to this method, it is possible to uniformly attach the substrate. The initial surface contamination amount of copper is 10 ¹⁴ / cm ² .

The post-contamination diffusion treatment conditions are 1000 ° C. and 25
It is a partial oxygen atmosphere. The amount of copper gettered on the back surface was obtained by dissolving 0.5 μm from the back surface including the polycrystalline silicon film and the silicon oxide film with a mixed acid of hydrofluoric acid and nitric acid, and analyzing the copper concentration of this solution by atomic absorption spectrometry. It was The recovery rate of contaminated copper was determined by the amount of copper in polycrystalline silicon with respect to the amount of initial surface contamination. Target value of gettering ability The copper recovery rate was 90% or more. The results are shown in Table 1.

[0010]

[Table 1]

The gettering ability of the inventive example is superior to that of the comparative example. Details will be described below. In Comparative Example F, the gettering ability is weak when the composite film is a single layer and there is no first silicon oxide film. In Comparative Example G, the gettering ability is weak when the composite film is a single layer and the thickness of the first silicon oxide film is 7Å. In Comparative Example H, the gettering ability is weak when the composite film is a single layer and the thickness of the first silicon oxide film is 15Å.

In Comparative Example I, the gettering ability is weak when the composite film is a single layer and the thickness of the first silicon oxide film is 20Å. In Comparative Example J, the composite film has two layers, the thickness of the first silicon oxide film is 5Å and the thickness of the second silicon oxide film is 7Å, and the first silicon oxide film is thin and the gettering ability is weak. In Comparative Example K, the composite film has two layers, the thickness of the first silicon oxide film is 5Å and the thickness of the second silicon oxide film is 20Å, and the first silicon oxide film is thin and the gettering ability is weak.

In Comparative Example L, the composite film has two layers and the thickness of the first silicon oxide film is 7Å and the thickness of the second silicon oxide film is 5Å.
In this case, the second silicon oxide film is thin and the gettering ability is weak. In Comparative Example M, when the composite film has two layers and the thickness of the first silicon oxide film is 7Å and the thickness of the second silicon oxide film is 25Å, the second silicon oxide film is thick and the gettering ability is weak. In Comparative Example N, when the composite film has two layers and the thickness of the first silicon oxide film is 20Å and the thickness of the second silicon oxide film is 5Å, the second silicon oxide film is thin and the gettering ability is weak.

In Comparative Example O, the composite film has two layers, the first silicon oxide film has a thickness of 20Å, and the second silicon oxide film has a thickness of 2.
In the case of 5Å, the second silicon oxide film is thick and the gettering ability is weak. In Comparative Example P, the composite film has two layers, the thickness of the first silicon oxide film is 25Å and the thickness of the second silicon oxide film is 7Å.
In this case, the first silicon oxide film is thick and the gettering ability is weak. In Comparative Example Q, when the composite film has two layers and the thickness of the first silicon oxide film is 25Å and the thickness of the second silicon oxide film is 20Å, the first silicon oxide film is thick and the gettering ability is weak.

[0015]

According to the present invention, since two or more composite films of a silicon oxide film and a polycrystalline silicon film are formed on the back surface side of a silicon semiconductor substrate, the crystal grains of the polycrystalline silicon film can be formed even after heat treatment at high temperature for a long time. It becomes possible to miniaturize, and it is possible to maintain high gettering ability throughout the entire semiconductor integrated circuit manufacturing process.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a silicon substrate having a multilayer structure of a polycrystalline silicon film and a silicon oxide film.

Claims (1)

[Claims] 1. A composite film comprising a silicon oxide film having a thickness of 7Å to 20Å and a polycrystalline silicon film formed on the oxide film is formed in two or more layers on the back surface side of a silicon semiconductor substrate. Characteristic silicon semiconductor substrate.