JPH03155136A - Method of gettering - Google Patents

Abstract

PURPOSE:To reduce leakage current through p-n junctions due to heavy-metal precipitation by performing rapid thermal annealing after an IG process and a preprocess to enable gettering of the precipitated heavy metal such as silicide remaining around the wafer surface. CONSTITUTION:A silicon wafer is subjected to the conventional IG process to form a layer having internal defects. Prior to a device process, LOCOS process (for forming field oxide) is performed in which wells are formed by impurity (p-type or n-type) doping. The wafer is then subjected to rapid thermal annealing at 800-1200 deg.C. For example, the wafer is heated to about 1000 deg.C at a rate of 160 deg.C/sec, held at 1000 deg.C for one minute, and cooled rapidly at a rate higher than 100 deg.C/sec, e.g. at about 110 deg.C/sec. The wafer is then subjected to the device process.

Description

[Detailed Description of the Invention] [Summary] This method relates to a gettering method, particularly a method for gettering heavy metal impurities in semiconductor wafers, and is a method for gettering precipitates that are formed and remain in a device active layer due to lack of predetermined gettering. For the purpose of strengthening and improving the gettering ability, an internal defect layer is formed in the semiconductor wafer by intrinsic gettering, a pretreatment process for the device process is performed, and then the annealing temperature is set to 800℃ to 1200℃.
The method includes a step of performing heat treatment at a temperature of 100° C. and rapidly lowering the temperature at a rate of 100° C./second or more.

[Industrial application field]

The present invention relates to a gettering method, and more particularly to a gettering method for heavy metal impurities in semiconductor wafers.

The present invention is a method used in combination with the conventional intrinsic gettering method, and can improve the conventional gettering ability.

[Conventional technology]

In the manufacturing process of semiconductor devices, gettering technology, which is a type of cleaning technology within semiconductor wafers, is a technology that is operated externally (extrinsic gettering technology).
Intrinsic gettering that uses elements intervening inside
ing (hereinafter referred to as IG) method is known.

The IG method has traditionally been effective against heavy metal contamination, but
The method uses Fe introduced during the semiconductor device process by forming an internal defect layer within the semiconductor wafer.
This is to getter heavy metal impurities such as Cu, Ni, and Cr into internal defect layers. These heavy metal impurities are gettered during the cooling process after high-temperature heat treatment during device processing.

[Problem to be solved by the invention]

However, some heavy metals may not be completely gettered to the internal defect layer during the cooling process after high-temperature heat treatment, and precipitates such as silicide may be formed and remain in the device active layer.

The present invention aims to strengthen and improve the gettering ability by gettering precipitates that are formed and remain in the active layer of a device due to a lack of predetermined gettering.

[Means to solve the problem]

According to the present invention, the above problem is solved by forming an internal defect layer in the semiconductor wafer by intrinsic gettering,
Perform a pretreatment process for the device process, then perform heat treatment at an annealing temperature of 800°C to 1200°C,
The problem is solved by a gettering method characterized by including a step of rapidly lowering the temperature at a temperature lowering rate of 100° C./sec or more.

That is, in the present invention, another high temperature heat treatment (RTA: Rap
The heavy metal precipitates are dissolved by thermal annealing and then rapidly cooled to prevent the formation of the precipitates and absorb them into the internal defect layer of the heavy metals.

[For production]

According to the present invention, a pretreatment for a device process after IG is performed, and precipitates mixed in and generated in the pretreatment process are dissolved by high temperature heat treatment (RTA treatment).

During this high-temperature heat treatment, heavy metals are dissolved in solid solution at interstitial positions, and then the temperature is lowered at a high rate of 100° C./sec or higher to suppress the diffusion of the heavy metals dissolved in solid solution.

For reference, Figures 3 and 4 show the solid solubility and diffusion coefficient of heavy metals in Si (Reference: 5solidState).
Communications, Vol. 4(1,
pp, 797-799 (1981) K, Wu'n5t
el and P, Wagner).

The state of heavy metals (Si
A change in the position occupied in a crystal (crystallographic structure) is called DLTS (Deep Level Transi...
This is inferred from the fact that the spectrum changes when measured using the entSpectroscopy method.

In the present invention, the annealing temperature of 800°C to 1200°C is a preferable temperature for melting heavy metal precipitates, and the temperature reduction rate of 100°C/sec or more is used to prevent once-dissolved heavy metal precipitates from precipitating again. This is because gettering occurs in the internal defect layer to prevent it from occurring. In addition, 800-1200
It is preferable to raise the temperature to a temperature of 150°C/second or more.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIGS. 1(a) and 1(b) are a diagram showing a heat treatment method according to an embodiment of the present invention, and a diagram showing the timing of the heat treatment, respectively.

First, the silicon wafer is subjected to conventional IG processing. In this IG process, the wafer is held at a temperature of 1100°C for about 30 minutes, the cooling rate is set to 4°C/min, the temperature is lowered to about 650°C, held for about 360 minutes, then raised to 650°C again, held for 30 minutes, and then gradually I did it cold. Next, as shown in Fig. 1(b), so-called LOCO is performed as a pretreatment for the device process.
In step 3 (element isolation region formation), wells were formed by doping with impurities (p or n type). After that, Figure 1 (a
) The RTA (Rapid Therrna) of the present invention shown in
1 Anneal) treatment was performed. That is, the annealing temperature was increased to approximately 1000°C at a heating rate of 160°C/sec, and after being held at 1000°C for approximately 1 minute, the annealing temperature was increased to approximately 10°C.
RTA treatment was carried out by rapidly cooling the sample at a cooling rate of /second. This RTA
After the gettering process, post-processing of the device process was continued as shown in FIG. 1(b).

When the RTA treatment is performed in this manner, as shown in Table 1, the Fe concentration in the device active region is 1.0×10” or less in the present example (with RTA treatment) and 1.0×10” in the conventional example (without PTA treatment). 0x101012at/cIIl.Also, the dark output signal (DS: Dark Sig
The defective rate (DS defective rate) was reduced to about 1/10.

Table 1 [Effects of the Invention] As explained above, according to the present invention, heavy metals that cannot be removed by intrinsic gettering and remain as precipitates such as silicide near the wafer surface can be gettered, and the heavy metals mentioned above can be gettered. It is possible to reduce the leakage current of the pn junction caused by the precipitates.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are diagrams showing a heat treatment method and the timing of the heat treatment, respectively, in one embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing heavy metals in Si, respectively. FIG. 3 is a diagram showing the solid solubility and diffusion coefficient of .

Claims (1)

[Claims] 1. Form an internal defect layer in the semiconductor wafer by intrinsic gettering, perform a device process pretreatment process, and then increase the annealing temperature to 800°C to 12°C.
Heat treatment is performed at 00℃, and the temperature decrease rate is 100℃/
A gettering method characterized by including a step of rapidly lowering the temperature in seconds or more.