JPS607123A - Photo heating method - Google Patents

Abstract

PURPOSE:To maintain the stable strength of incidence regardless of the thickness of a protection film by a method wherein a film of a reflectance smaller than that of the interface, with respect to the wavelength of a ray emitted from a light source, is interposed at the interface between an object covered with a transparent film over the surface and the transparent film. CONSTITUTION:The transparent protection film 2 is provided by sandwiching the film 7 to make a semiconductor 1 to reduce the interface reflectance, where the film 2 contacts air 3. An interface 8 exists between the surface of the substrate 1 and the film 7, and an interface 9 between the film 7 and the protection film 2. Further, an interface 5 exists between the film 2 and the air. The incidence light 6 comes in through the interface 5 to the direction of an arrow.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of heating an object, and in particular to a method of heating an object using light with a narrow emission spectrum.

A heating method using light is widely used for activating impurity ions in an ion-implanted layer of a semiconductor.

When heating semiconductor crystals to high temperatures, prevent surface contamination,
In order to prevent the semiconductor from scattering or changing its shape, a protective film is applied to the surface. Since this film is heated using light, it naturally needs to be transparent, but in this case, the incident intensity will vary depending on the film thickness due to the interference of reflected light from the surface interface between the protective film and the air, and between the protective film and the semiconductor. The problem is that it varies greatly depending on the situation.

On the other hand, when considering applications to LSI and the like, semiconductor crystals use disk-shaped wafers with a diameter of several centimeters, but it is difficult to form a film with a uniform thickness over such a wide area. Currently, the method used is to make the film thickness much thinner than the emission wavelength of the light source to reduce the effect of changes in film thickness. However, a certain degree of mechanical strength is required to prevent the shape of the semiconductor from changing, and the thin films used in the conventional method tend to change shape, and the films of arbitrary thickness are prone to variations in film thickness. The intensity of light incident on the semiconductor varies greatly depending on the location. Normally, in the case of the optical heating method used in semiconductor processes, a slight change in the temperature of the sample can greatly change the properties of the crystal, so such variations in incident intensity affect the reproducibility and uniformity of the optical heating method. However, this is a major hindrance to practical application.

The present invention solves the above problems, and includes a method of heating an object whose surface is covered with a transparent film using a light source whose main emission wavelength exists in one narrow wavelength range. It is characterized in that a film having a reflectance smaller than that of the interface with respect to the wavelength of the light beam emitted from the light source is interposed at the interface with the film.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is a cross-sectional view when a transparent protective film is attached to the surface of a semiconductor. In the figure, 1 is the semiconductor, 2 is the transparent protective film, 3 is air,
4 is an interface between 1 and 2, 5 is an interface between transparent protective film 2 and air 3, and 6 is incident light. Semiconductor 1, transparent protective film 2, air 3
Let the refractive index of each be 111 it, the thickness of the ns p transparent protective film 2 be tl, the wavelength of the incident light 6 be λ, and rl*r
ltδ as rx = (nt − ns)/(ng ”ns)
(1) rfi = (n, -ng)/ (ns ”nt
) (2) δ-2πn,t,/λ (3) Then, the reflectance R is expressed by the following formula.

In FIG. 2, λ is the wavelength at which the maximum intensity of the argon laser occurs, 0.5145 μm, silicon with a refractive index of 4.21 is used as the semiconductor 1, and 810 μm with a refractive index of 1.46 is used as the protective film 2. It shows the change in reflectance due to change in film thickness d when
It can be seen from FIG. 2 that the reflectance varies greatly depending on the film thickness. In this case, the reflectance at the internal interface 5 is lr
, l'', and its value is 0.235.

FIG. 3 is a diagram showing a structure for implementing the method of the present invention. In the figure, 7 is a film for reducing the interface reflectance of the present invention, 8
9 is the interface between the semiconductor 1 and the film 7, and 9 is the interface between the film 7 and the transparent protective film 2. The same parts as in FIG. 1 are given the same numbers.

Figure 4 shows a case where a Si, N4 film with a thickness of 0.062 μm is used as the film 7, and the reflectance at the interface 9 is set to 0.0455. Rate 2.
5) Consider the film and set the reflectance at interface 9 to 0.0010.
4, the reflectance for light with λ = 0.5145 μm and S10! It is a figure showing the relationship with film thickness. As is clear from the figure, it can be seen that the reflectance decreases and the amplitude with respect to the film thickness also decreases. That is, it can be seen that the relative fluctuation in the intensity of the incident light is greatly reduced.

Assuming that the reflectance at the internal interface 9 is a river and the reflectance at the interface 5 between air and the transparent protective film is 4, the maximum value RmaX% and the minimum value Rim of the surface reflectance, which changes depending on the film thickness, is expressed as follows. Ru.

Figure 6 shows Sin, and the reflectance R8 at the interface with air is 0 on the left.
．． 035, the internal reflectance angle and Rmaxlo
,R,! 11 shows the relationship between reflectance and amplitude U.

In the figure, 13 indicates the internal reflectance according to the conventional method. It can be seen from the figure that if the surface reflectance is lower than 0.235, the fluctuation range of the reflectance is reduced and more stable heating can be performed. The film structure for reducing the reflectance at the internal interface is not limited to the single-layer film as described above, but may also be a multi-layer film. In addition, the object is semiconductor silicon, the transparent film is StO,
9 has been explained using an example, but it is clear from the explanation that it can be applied to objects other than semiconductors and other types of transparent films.

As described above, the method of the present invention eliminates the conventional drawbacks, maintains a sufficiently stable incident intensity even when the thickness of the surface protective film changes greatly, does not change the properties of the sample, and produces a uniform product. It has the effect that can be obtained.

[Brief explanation of drawings]

Figure 1: Schematic cross-sectional diagram when heating an expanded object using light,
Figure 2 shows the StO reflectance when an 810W film is attached to the silicon surface for light with a wavelength of 0.5145 μm. FIG. 3 is a cross-sectional view of a heated object according to the present invention, and FIG. 4 is a diagram showing film thickness dependence. FIG. Figure 5 is a diagram showing the relationship between the reflectance of light with a wavelength of 0.5145 μm and the stow film thickness for a film made of a material with a thickness of 0.049 μm and a refractive index of 2.5. FIG. 3 is a diagram showing the relationship between internal interface reflectance and surface reflectance when using sio. 1... Semiconductor, 2... Transparent protective film, 3... Air,
6... Incident light, 7... Film, 5, 8.9... Interface Patent applicant NEC Corporation Figure 1 Oxide film thickness (blade ■) Oxide film thickness (pm) Oxide film thickness (door) )

Claims (1)

[Claims] (1) In a method of heating an object whose surface is covered with a transparent film using a light source whose main emission wavelength exists in one narrow wavelength range, the light source is emitted at the interface between the object and the transparent film. An optical heating method characterized in that a film having a reflectance smaller than that of the interface is interposed with respect to the wavelength of the light beam.