JPS6329824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor manufacturing process, and more specifically, to a heat treatment process for intrinsic gettering in the process of manufacturing a semiconductor device using a Czyochralski silicon single crystal. Regarding inspection methods.

With the increasing density and large-scale integration of integrated circuits,
The influence of crystal defects generated in silicon substrates on the characteristics and yield of devices is increasing. Impurities that induce crystal defects include oxygen, carbon, heavy metals, etc., and oxygen is said to have a particularly large influence. Czyochralski silicon crystals currently used in silicon device manufacturing contain approximately 1.0×10 ¹⁸ cm ^-3 of oxygen. During the device manufacturing process, this supersaturated oxygen becomes an oxide of SiOx (x=2) and precipitates. The precipitates thus generated cause lattice distortion and generate dislocations, stacking faults, etc. These crystal defects, oxygen precipitates, dislocations, and stacking faults cause significant deterioration of device characteristics.

Intrinsic gettering is a technique for removing these crystal defects and further gettering. For example, 1250 in a 0.5% Hcl atmosphere
When thermal oxidation is carried out for 4 hours at °C, a so-called denuded zone (DZ) is formed in the depth direction from the wafer surface in which no crystal defects are found. Moreover, many crystal defects occur only within the wafer. A similar DZ also occurs during heat treatment at 1050°C in a _N2 atmosphere. These DZ
The width varies depending on the heat treatment conditions, but is 10 to 100 μm.
Formed to a degree. If a device is manufactured after forming this DZ, the characteristics and manufacturing yield of the device will be significantly affected, both because there are no crystal defects on the surface and because the crystal defects generated inside act as gettering sinks for heavy metals. improves.
Therefore, intrinsic gettering technology is becoming an important process in device manufacturing.

On the other hand, a problem when forming a DZ in a heat treatment process for intrinsic gettering is that it is not possible to form a DZ with good reproducibility on many silicon wafers from different lots. The presence or absence of DZ formation depends on factors such as the oxygen concentration in the ingot. Therefore, it is necessary to determine the appropriate wafer by evaluating the presence or absence of DZ formation after the heat treatment process.
The presence or absence of DZ formation is usually evaluated by cleaving the wafer and observing the pit distribution in the cross section using an etching method. This method is a destructive method and cannot be used for inspection of semiconductor manufacturing processes.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide an inspection method capable of evaluating the normality of a heat treatment process for intrinsic gettering without destroying the silicon single crystal after the process.
According to the present invention, this purpose is to generate crystal defects inside a silicon single crystal, create a defect-free layer in the surface region, and use the internal defects as a gettering center for intrinsic gettering. In a method for inspecting a heat treatment process for intrinsic gettering, the recombination characteristics of minority carriers in a silicon single crystal are measured by an optical attenuation method after the heat treatment process for intrinsic gettering is completed, and recombination occurs at the measured recombination center. a first recombination center that has a characteristic that recombination occurs earlier; and a first recombination center that is formed at a deeper level than the first recombination center due to crystal defects and has a characteristic that recombination occurs later than the first recombination center. This is achieved by providing an inspection method for a semiconductor manufacturing process, characterized in that the normality of the heat treatment process is inspected based on whether or not two or more types of attenuation characteristics due to the second recombination center appear. .

The principle and one embodiment of the present invention will be explained in detail below with reference to the drawings. Figures 1 and 2 are diagrams for explaining the principle of the present invention, and show the minority carriers of a silicon single crystal before and after the heat treatment process for intrinsic gettering, as measured by an optically attenuated microwave method. Demonstrates recombination (lifetime) properties.

In other words, Figure 1 shows the measurement results of the lifetime of minority carriers when a silicon single crystal is received before the heat treatment process for intrinsic gettering. This is the result of observing the time change of the microwave detection output using an oscilloscope (CRT).
As shown in Figure 1, in a crystal without crystal defects, the decay curve is given in the form e ^-t/ 〓, and the lifetime τ is determined. In this example, τ100μs is found. FIG. 2 shows the results of the same measurements as in FIG. 1 after the same silicon single crystal was subjected to a heat treatment process for intrinsic gettering. The heat treatment process was conducted at 700℃ for 12 hours.
Heat treatment was carried out twice in a N ₂ atmosphere and at 1200° C. for 3 hours in an N ₂ atmosphere. The characteristics of the decay curve in Figure 2 are: (i) a rapid decay occurs at the beginning, corresponding to a decrease in the lifetime of minority carriers (t = 0 to 10 μs);
(ii) The subsequent decay is gradual and corresponds to a long time constant (20 μs to 80 μs or more). This phenomenon is caused by crystal defects, in addition to the first recombination center (i) (which has a fast recombination process) that ordinary silicon single crystals have.
This is due to the presence of a second recombination center (ii) (having a slow recombination process) formed at a deep level. This decay curve changes in a way that cannot be expressed by a single exponential decay l ^-t/ 〓. Therefore, the formation of DZ and the occurrence of internal defects due to the heat treatment process for intrinsic gettering can be nondestructively inspected using changes in the attenuation characteristics, that is, changes in the lifetime of minority carriers.

In accordance with the above-mentioned principle, the present invention measures the recombination characteristics of minority carriers in a silicon single crystal using an optical attenuation method after the heat treatment process for intrinsic gettering is completed, and uses the measurement results to determine whether the heat treatment process is normal or not. This is to inspect whether a defect-free layer DZ has been formed and whether or not internal defects have occurred. FIG. 3 is a block diagram of an embodiment for measuring the lifetime of minority carriers by the optical attenuation method, and this example is an example of the optical attenuation method using the microwave reflection phenomenon. In FIG. 3, the subject is irradiated with microwaves through an aperture waveguide, and only strongly reflects the microwaves when irradiated with light from an excitation light source. When the irradiation of the excitation light source is stopped, the reflected microwaves decay exponentially. Therefore, by guiding this reflected wave to a cathode ray tube (CRT) through a crystal detector made of gallium arsenide (GaAs) or silicon (Si), it is possible to observe the attenuation characteristics of the reflected wave. Since the characteristics depend on the lifetime of the minority carrier, the lifetime of this minority carrier can be measured. Note that the tuner has a function of reducing reflected light to zero when no excitation light is irradiated. The other configurations are well known and therefore need not be explained.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining the principle of the present invention, and FIG. 3 is a diagram showing the configuration of an embodiment for measurement using the optical attenuation method.

Claims (1)

[Claims] 1. A heat treatment process for intrinsic gettering in which crystal defects are generated inside a silicon single crystal, a defect-free layer is created in the surface region, and the internal defects are used as a gettering center. In this method, the recombination characteristics of minority carriers in a silicon single crystal are measured by an optical attenuation method after the heat treatment process for intrinsic gettering is completed, and the measured recombination characteristics indicate that recombination occurs quickly. a first recombination center having a characteristic, and a second recombination center having a characteristic that the recombination center is formed at a deeper level than the first recombination center due to crystal defects and recombination occurs later than the first recombination center. A method for inspecting a semiconductor manufacturing process, characterized in that the normality of the heat treatment process is inspected based on whether or not two or more types of attenuation characteristics due to recombination centers appear.