Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2002-07-05
2004-02-17
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S237200, C356S237600, C356S635000
Reexamination Certificate
active
06693707
ABSTRACT:
Japanese Patent Application No. 2001-208892, filed on Jul. 10, 2001, is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a method of inspecting a surface-emitting semiconductor laser and an inspection device for a surface-emitting semiconductor laser.
A surface-emitting semiconductor laser is a light-emitting element capable of integration in two dimensions, whose application is a wide range of fields is anticipated, for example as a high-speed and large capacity light source for optical communications.
As a means of increasing the efficiency of a surface-emitting semiconductor laser, a current blocking structure has been proposed in which an AlAs layer or an AlGaAs layer having an extremely high content of aluminum is formed on a pillar portion formed on at least a part of a resonator, using the oxidized current blocking layer obtained by oxidizing this layer from the side, and is widely adopted. Such a current blocking layer is constructed from, for example, an oxide aperture formed from an AlAs layer, and an oxidized portion formed around this oxide aperture. This oxidized portion is formed from a layer including aluminum oxide. The layer including this aluminum oxide is formed by oxidizing an AlAs layer from the side. The diameter of the oxide aperture (also referred to below as the “oxide aperture diameter”) forming this current blocking layer greatly affects the light emission efficiency of the element and the light emission pattern and the like, and therefore measurement of the diameter and shape of the oxide aperture is extremely important. Normally this current blocking layer is formed within an upper mirror forming the pillar portion. Alternatively, an active layer is formed at a lower portion of the upper mirror, and the current blocking layer is formed at a part of the upper mirror closer to the active layer.
On the other hand, as the semiconductor layer constituting the upper mirror is commonly used an AlGaAs material. However, the properties of this AlGaAs material are such that it absorbs light at visible wavelengths, and therefore attempts to confirm the diameter and shape of the oxide aperture using a conventional microscope or the like are difficult, because light is absorbed by the upper mirror, and the diameter and shape of the oxide aperture cannot easily be confirmed.
Here, there is the method of irradiating with infrared radiation passed by the AlGaAs material, to confirm the diameter of the oxide aperture. For example, Japanese Patent Application Laid-Open No. 2000-332355 discloses a method of measuring the oxide aperture diameter using an infrared radiation microscope.
However, an infrared source generates a large amount of heat, and therefore it is difficult to obtain a large light source, and in particular when the dispersion ratio is increased, since a sufficient quantity of light cannot be obtained, it is often difficult to obtain a clear image. Since the heights of the upper surface of the pillar portion and the oxidized current blocking layer are different, it is difficult to bring both of these into focus, and therefore accurate analysis of the diameter and shape of the oxide aperture is commonly not possible. Furthermore, not only is the wavelength of infrared radiation longer than that of visible light, but also a conventional infrared source such as a halogen lamp or the like includes a variety of wavelength components, and therefore the resolution of the image obtained is often low.
BRIEF SUMMARY OF THE INVENTION
The present invention may provide a method of inspecting a surface-emitting semiconductor laser and an inspection device for a surface-emitting semiconductor laser, enabling to accurately measure a diameter and shape of an oxide aperture.
Method of Inspecting Surface-emitting Semiconductor Laser
According to the present invention, there is provided a method of inspecting a surface-emitting semiconductor laser having a resonator which is formed in the vertical direction on a semiconductor substrate, wherein:
the surface-emitting semiconductor laser includes a pillar portion in at least a part of the resonator, the pillar portion having an oxidized current blocking layer which has an oxide aperture and an oxidized portion formed around the oxide aperture; and
the surface-emitting semiconductor laser is irradiated with laser light from the side on which the pillar portion is formed, in a direction perpendicular to a surface of the semiconductor substrate to measure the shape of the oxide aperture based on the amount of reflected light from the oxidized current blocking layer.
The surface of the semiconductor substrate refers to a surface of the surface-emitting semiconductor laser on which the resonator is provided.
According to this inspection method, the shape of the oxide aperture is detected on the basis of the amount of reflected light obtained by irradiating the surface-emitting semiconductor laser with the laser light, so that the influence of noise components such as ambient light or the like is low, and therefore the shape of the oxide aperture can be accurately measured.
The method of inspecting a surface-emitting semiconductor laser may have following features (1) to (8).
(1) The shape of the oxide aperture may be measured on the basis of the difference between the amount of reflected light from the oxide aperture of the oxidized current blocking layer and the amount of reflected light from the oxidized portion of the oxidized current blocking layer.
(2) The laser light may have a wavelength shorter than the wavelength of light emitted by the surface-emitting semiconductor laser. In particular, when the diameter or shape of the oxide aperture is measured by measuring the difference between the amount of reflected light from the oxide aperture and the amount of reflected light from the oxidized portion, measurement is possible with a very small amount of reflected light. Therefore, measurement is possible even when a laser light of short wavelength is used and it is difficult to obtain a high intensity because the light is absorbed within the laser element. Since the resolving power can be increased by using the laser light of the shorter wavelength, the diameter or shape of the oxide aperture can be accurately measured.
(3) The laser light may be focused at a predetermined position of the oxidized current blocking layer by an optical element. This makes it possible to limit the amount of reflected light from unfocused portions such as light reflected from the surface of the semiconductor substrate, so that the diameter or shape of the oxide aperture can be measured even more accurately.
(4) Two-dimensional scanning may be done for the laser light reflected by at least a cross-section of the pillar portion in a plane parallel to the surface of the semiconductor substrate. This makes it possible to accurately determine the entire shape of the oxidized current blocking layer.
In this case, two-dimensional scanning may be done for the laser light reflected by a region which is larger than the cross-section of the pillar portion and includes the cross-section of the pillar portion in the plane parallel to the surface of the semiconductor substrate. This makes it possible to more accurately determine the shape of the oxidized current blocking layer in the resonator.
(5) Two-dimensional scanning may be done for the laser light reflected by a plane parallel to the surface of the semiconductor substrate; the distance between the surface-emitting semiconductor laser and the optical element being used to focus the laser light may be varied; and the distance may be fixed at a point at which the difference between the amount of reflected light from the oxidized portion and the amount of reflected light from the oxide aperture is maximum to measure the amounts of reflected light. This makes it possible to accurately focus on a predetermined position of the oxidized current blocking layer. By irradiating the laser light and capturing the difference in the amount of the reflecte
Font Frank G.
Oliff & Berridg,e PLC
Punnoose Roy M
Seiko Epson Corporation
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