JPH0454964B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a method for heating a sample such as a semiconductor wafer by irradiating an infrared beam with a rod-shaped infrared lamp.

(b) Background of the technology For example, an insulating film such as silicon dioxide (SiO ₂ ) is formed on a silicon wafer, a polycrystalline silicon layer is formed on top of it, and this is annealed using a laser beam or lamp. BACKGROUND ART The technology for forming single-crystal silicon layers is becoming important in the production of three-dimensional (stereoscopic) integrated circuits constructed by laminating multiple single-crystal silicon layers.

At this time, a polycrystalline silicon layer is formed on the entire surface of the wafer, and by scanning and annealing a rod-shaped heater (lamp) large enough to cover the entire wafer surface, a large area of polycrystalline silicon with uniform crystal orientation is formed. is obtained.

(c) Conventional technology and problems Figure 1 shows a conventional lamp annealing process.

As shown in FIG. 2(a), a linear beam 2 from an infrared lamp scans in the direction of the arrow over a wafer 1 on which a polycrystalline silicon layer is formed. As a result, the polycrystalline silicon layer is heated, melted, and then solidified to become a single crystal.

Conventionally, the intensity and scanning speed of the beam 2 were kept constant. The scanning position of the beam on the wafer at this time and the temperature of the scanning area corresponding to it are shown in Figure b.
Shown below.

The temperature of the wafer 1 is mainly represented by a temperature distribution component due to beam radiation (broken line 4) and a temperature distribution component due to heat conduction within the wafer (including polycrystalline silicon) (dotted chain line 3).

The temperature distribution component due to beam radiation is a component brought about by direct irradiation with the beam,
If the beam scans a flat wafer,
Theoretically, the distribution is almost uniform. However, in reality, the side edges of the wafer are heated by beam radiation just before and after the wafer is scanned by the beam, so the area near the edge of the wafer is slightly heated compared to other areas where only the wafer surface is heated. The temperature increases.

Further, the temperature distribution component due to heat conduction is a component that takes into consideration heat conduction from the scanning area by the beam.
Since heat conduction continues to occur centering around the region scanned by the beam, the temperature at the end B, which is the end point of the beam scan, is the highest during the beam scan compared to other regions.

Due to the two types of temperature distribution components described above, the temperature of the region within the wafer during beam scanning has a distribution shown by the solid line 5.

In other words, the temperature increases in the direction of the scanning end position on the wafer, and the wafer is subjected to excessive heating.

If such excessive annealing is performed, the silicon layer that should be single-crystalized in the latter half of the wafer may peel off, or
Furthermore, in the case of a tertiary circuit, the lower layer LSI that has already been completed
This may impair the device characteristics of the device. Conversely, if the radiation intensity is lowered to prevent this from happening, sufficient annealing will not be performed in the first half of the wafer. Therefore, uniform annealing is not possible with constant radiation intensity and constant speed scanning.

(d) Object of the Invention The object of the present invention is to provide a heating method that can eliminate these conventional drawbacks and uniformly heat a wafer.

(e) Structure of the Invention To achieve the above object, the present invention provides a method for heating a sample by scanning a linear beam from one end of the sample to the other end. It is characterized in that the beam irradiation amount per unit time is gradually increased along the direction of the other end and then decreased.

(f) Embodiment of the invention FIG. 2 is a diagram illustrating an embodiment of the invention.
In the embodiment of FIG. 1, the intensity of the beam is gradually decreased along the direction of the edge B of the wafer, as shown by the solid line 6 in FIG.

As a result, it is possible to compensate for the bias in the temperature distribution shown by the solid line 5 in FIG. 1, and to obtain a uniform temperature distribution.

In a second embodiment, the scanning speed of the beam is gradually increased along the direction of the end B, as shown by the broken line 7 in FIG.

In other words, in these first and second embodiments, the amount of beam irradiation per unit time per unit area of the wafer is initially slightly increased along the direction of the edge B of the wafer, and then gradually decreased. . Thereby, the temperature distribution within the wafer surface can be made uniform.

(g) Effects of the Invention As explained above, according to the present invention, the temperature distribution within the wafer can be made uniform, and therefore, when polycrystalline silicon is made into a single crystal, the temperature distribution is uniform over the entire surface of the wafer. A homogeneous single crystal silicon layer is obtained. Furthermore, since the amount of irradiation can be kept to the minimum necessary throughout the wafer, there is no risk of thermally damaging the underlying LSI elements of the three-dimensional circuit.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the conventional heating method.
FIG. 2 is a diagram for explaining an embodiment of the present invention. In the figure, 1 is a wafer, 2 is a beam, 6 is a line showing the intensity distribution of the beam on the wafer, and 7 is a line showing changes in the scanning speed of the beam on the wafer.

Claims (1)

[Claims] 1. A method of heating a sample by scanning a linear beam from one end of the sample to the other end of the sample,
A method for heating a sample, characterized in that the amount of beam irradiation per unit area and per unit time to the sample is gradually increased along the direction of the other end and then decreased so that the sample is heated uniformly. .