JP2013214655A - Optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor element which solves a problem in the past technology that it is difficult to control stress accumulated at a boundary surface depending on a deposition condition due to increase in the number of boundary surfaces because occurrence of residual stress is inhibited by stacking a plurality of layers of depositing insulation films.SOLUTION: An optical semiconductor element of the present embodiment having an active layer or a light absorption layer, and having a function of a laser or an optical modulator or an optical amplifier comprises a mesa structure part for waveguiding light to an opposite side to a substrate on which the element is formed. On a part of or the whole of a surface on the side having the mesa structure part, an insulation film is formed. The insulation film is composed of a compound of a silicon oxide (SiO) film and a silicon nitride (SiN).

Description

  The present invention relates to an optical semiconductor element having a step of forming an insulating film.

  An optical semiconductor element has functions such as generation, modulation, and amplification of light, and is an indispensable device for optical communication technology that supports a modern advanced information society. An optical semiconductor device includes (1) epitaxial crystal growth of MOC (Metal-Organic Chemical Vapor Deposition) on mixed crystal compounds having different compositions on a semiconductor substrate such as InP, and (2) optical waveguide pattern formation. Etching, (3) re-growth of crystals to partially fill the etched portion, (4) formation of an insulating film to protect the semiconductor surface from electrical insulation, moisture and air, and (5) electrode formation Therefore, it is manufactured through a very complicated process such as formation of a metal film by vapor deposition.

  As a matter of course, the materials used in the steps (1) to (5) have different substance properties. The process of stacking or vapor depositing these at the atomic or molecular level order is generally performed at a different temperature for each process. After the process, the temperature returns to room temperature, but the substance expands and contracts depending on the temperature, so that repeated stress changes in the manufacturing process generate large stresses and strains at the interface between the different substances and the surrounding area. Become.

The generation and distribution of stress and strain vary depending on the type of laminated material, crystal composition and shape. Of the above (1) to (5), the present invention relates to the formation of the insulating film of (4). Typical examples of the insulating film conventionally used include silicon dioxide SiO ₂ and nitride Si ₃ N ₄ . When SiO ₂ is formed on the semiconductor surface and returned to room temperature, the semiconductor side receives compressive stress and the SiO ₂ film receives tensile stress. On the other hand, when Si ₃ N ₄ is formed on the semiconductor surface and returned to room temperature, the semiconductor side receives tensile stress and the Si ₃ N ₄ film receives compressive stress. It is known that when an optical semiconductor element is operated in a state where stress is inherent, the reliability of the element is deteriorated. By laminating two or more layers of SiO ₂ and Si ₃ N ₄ , it is possible to face each other at the interface. A method for canceling the stress is proposed (see Patent Document 1).

Since materials having different properties are laminated, it is inevitable that stress and strain are inherent therein. In particular, insulating film materials such as SiO ₂ and Si ₃ N ₄ have a large difference in mechanical properties from semiconductors. Under such circumstances, the conventional method has taken an approach of canceling stress in the vicinity of the interface by using two or more insulators. As stress generated at the interface, stresses of opposite signs of compression and tension can occur, so apparent stress can be canceled by forming multiple layers of thin films with the concept of 1 + (-1) +1 + (-1) = 0. can do. However, as the types of interfaces and insulating films increase, there is a problem that it is difficult to stably control the stress accumulated at the interface depending on the film forming conditions of the insulator thin film. The thickness of the insulating film is on the order of submicrons, and from the practical viewpoint of stable control of the ultrathin film, it is most desirable to use a single-layer insulating film.

Japanese Patent No. 4090768

Hideya Yamadera, “Measurement and Control of Thermal Stress in Thin Films”, Toyota Central R & D Review, Vol. 34, no. 1 (1999.3) “Quartz Single Crystals (SiO 2)”, Neotron Co., Ltd. December 28, 2011 search, Internet URL <http://www.neotron.co.jp/crystal/11/SiO2.html>

  As described in the above item of the background art, in the conventional method, the generation of residual stress is suppressed by stacking a plurality of insulating films to be formed. Due to the increase in the number of interfaces, there is a problem that it is difficult to control the stress accumulated at the interface depending on the film formation conditions.

In order to solve the above problems, an optical semiconductor device according to claim 1 of the present invention is an optical semiconductor device having a function of a laser, an optical modulator, or an optical amplifier having an active layer or a light absorption layer. , Having a mesa structure for guiding light on the side opposite to the substrate on which the element is formed, and a part or all of the surface is provided with an insulating film on the surface on the side having the mesa structure, The insulating film is characterized by comprising a compound of a silicon oxide film (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ).

  According to a second aspect of the present invention, in the semiconductor device according to the first aspect, a metal layer for taking an electrode is further formed on the insulating film.

  Further, the invention described in claim 3 is the semiconductor device according to claim 1 or 2, wherein the active layer or the light absorption layer is In (z) Ga (1-z) As (1-w ) A quaternary mixed crystal compound semiconductor such as P (w) or In (1-zw) Al (z) Ga (w) As (where z and w are the composition ratio of the mixed crystal). It is characterized by being.

  According to the optical semiconductor element of the present invention, it is possible to manufacture a semiconductor element with less residual stress inside a semiconductor or metal interface and in the insulating film in contact with the insulating film with one kind of material.

It is a figure which shows the structure of the optical semiconductor element which concerns on the 1st Embodiment of this invention. FIG. 5 is a diagram showing characteristics of linear expansion coefficient and Young's modulus with respect to the composition (x, y) of the insulating film (SiO ₂ ) x (Si ₃ N ₄ ) y in the simulation of stress distribution for the structure of the embodiment of FIGS. It is. It is the figure which showed the center symmetry plane and the depth direction in the structure of the optical semiconductor element which concerns on the 1st Embodiment of this invention. It is a figure which shows the simulation result of the von Mises stress regarding the optical semiconductor element which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the optical semiconductor element which concerns on the 2nd Embodiment of this invention. It is a figure which shows the simulation result of the von Mises stress regarding the optical semiconductor element which concerns on the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a structure of an optical semiconductor device 100 according to the first embodiment of the present invention.
In FIG. 1, an optical semiconductor element 100 has a semiconductor optical waveguide structure called a ridge type. In the optical semiconductor device 100, a p-type InP layer is stacked on a semiconductor active layer or absorption layer 102 stacked on an n-type InP wafer substrate 101, and a protruding mesa shape 103 is formed by etching. The semiconductor surface is covered with a single insulating film 104.

  The semiconductor active layer or absorption layer 102 is made of 4 such as In (z) Ga (1-z) As (1-w) P (w) and In (1-z-w) Al (z) Ga (w) As. An original mixed crystal compound semiconductor can be considered. Here, z and w are composition ratios of mixed crystals.

The insulating film 104 is a single layer film (SiO ₂ ) x (Si ₃ N ₄ ) y according to the present invention, where x is a composition ratio of silicon dioxide SiO ₂ and y is a composition ratio of silicon nitride Si ₃ N ₄ . It is.

  The three-dimensional structure shown in FIG. 1 was constructed on a computer, and the stress distribution applied to each part was obtained by numerical calculation (finite element method). In the calculation, the active layer (absorbing layer) 102 was replaced with InP. Since the mechanical properties of the quaternary mixed crystal are similar to those of InP, the calculation can be performed efficiently without losing generality.

In material design according to the present invention, important physical property data are linear expansion coefficient, Young's modulus, and Poisson's ratio. Linear expansion coefficient of the SiO ₂ actually create the InP wafer was deposited SiO _2, is calculated from the interval of Newton rings was measured warpage of the wafer was determined using the relationship of the warp and the linear expansion coefficient . A similar experiment was performed to calculate the linear expansion coefficient of Si ₃ N ₄ . By linearly interpolating these calculated values of SiO ₂ and Si ₃ N ₄ , linear expansion coefficients were obtained for arbitrary composition ratios x and y of the insulating film (SiO ₂ ) x (Si ₃ N ₄ ) y. The result is shown at 200 in FIG. As can be seen from the figure, the coefficient of linear expansion takes both positive and negative expansion depending on the composition, suggesting that even one type of material can cope with various stress distributions.

210 in FIG. 2 is a graph showing the Young's modulus characteristics with respect to an arbitrary composition ratio x, y of the insulating film (SiO ₂ ) x (Si ₃ N ₄ ) y. This was calculated by linear interpolation from well-known literature data. As a recent numerical value for Si ₃ N ₄ , there is an experimental value of Table 2 on page 22 of Non-Patent Document 1. For SiO ₂ , the values in the characteristic table (76.5 GPa, perpendicular to the Z axis) disclosed in Non-Patent Document 2 are listed. The Poisson's ratio was constant at 0.2 because the fluctuation range depending on the material was small.

FIG. 4 shows a simulation result of the structure of FIG. The structure of FIG. 3 is the same as the structure of FIG. As shown in FIG. 3, the waveguide structure is bilaterally symmetric with respect to a plane (center symmetry plane) surrounded by a dotted line. However, whether or not the structure is symmetrical is irrelevant to the effect of the present invention. FIG. 4 shows the von Mises stress and the composition ratio x when the depth direction is near the center of the active layer (indicated by a white arrow in FIG. 3) and the depth direction is 5 microns from the end face. , Y are calculated results. The composition ratios x and y are taken on the horizontal axis, and the results in the case of the composition of only one of SiO ₂ and Si ₃ N ₄ are also included.

From FIG. 4, by setting the composition ratios x and y of the insulating film (SiO ₂ ) x (Si ₃ N ₄ ) y to x = 0.1 and y = 0.9, the SiO ₂ single layer or Si ₃ N ₄ It can be seen that a low stress that cannot be obtained with a single layer is obtained. The shape of this curve varies depending on the thickness of (SiO ₂ ) x (Si ₃ N ₄ ) y.

Here, the von Mises stress on the vertical axis in FIG. 4 will be described. The unit of von Mises stress is MPa. In the first place, the stress σ is a tensor amount having nine components. For example, σ _xy represents a stress component in the y-axis direction in a plane perpendicular to the x-axis. That is, in a three-dimensional space, these components are

  It is expressed in the matrix form.

Thus, a tensor amount having nine components is projected onto the principal axis of the stress and converted into one scalar value, which is called von Mises stress σ _VM and is defined by the following equation.

The von Mises stress is used as a convenient index because the quantity having the σ _VM direction can be quantitatively expressed by one value. However, since the route is taken, the sign is always positive, so it is not possible to know whether it is compression or tension. The von Mises stress σ _VM is not only convenient, but also a powerful evaluation index in stress evaluation in that it is not preferable that stress is present, whether compression or tension.

σ _VM corresponds to the density of strain energy due to shear stress. In fracture engineering, when this value reaches the yield point (limit of elastic deformation), the structure is considered to yield (transition to plastic deformation state) from there. The part with the largest value is determined to be the most brittle part in terms of dynamics.

  As described above, the stress is a tensor amount and is a complex amount having a direction and a sign. However, by discussing with a scalar amount that takes only a positive value called von Mises stress, how does the magnitude of the stress change? Can be easily and accurately grasped.

  FIG. 5 is a diagram showing a structure of an optical semiconductor element 500 according to the second embodiment of the present invention.

  In FIG. 5, an optical semiconductor element 500 has a semiconductor optical waveguide structure called a ridge type similar to FIG. A difference from the structure shown in FIG. 1 is that gold 505 for electrodes is deposited on the upper surface of the insulating film 504 by 1 micron. As shown in FIG. 5, the waveguide structure is bilaterally symmetric with respect to a plane (center symmetry plane) surrounded by a dotted line. Again, whether or not the structure is symmetrical is irrelevant to the effect of the present invention.

FIG. 6 shows a simulation result of the structure of FIG. FIG. 6 shows the von Mises stress and the composition ratio x at a position where the depth direction is near the center of the active layer (indicated by a white arrow in FIG. 5) and the depth direction is 5 microns from the end face in the left-right symmetry plane. It is the result of calculating the relationship of y. The composition ratios x and y are taken on the horizontal axis, and the results for the composition of only one of SiO ₂ and Si ₃ N ₄ are also included.

The difference between FIG. 4 and FIG. 6 is that the single-layer insulating film (SiO ₂ ) x (Si ₃ N ₄ ) y is subjected to complex stress from the top, bottom, left, and right directions by depositing the gold electrode 505. In the case of the present embodiment, the stress can be minimized by selecting x = 0.2 to 0.3 and y = 0.8 to 0.7. By appropriately selecting the composition of SiO ₂ and Si ₃ N ₄ based on the conditions and shape of gold electrode deposition, stress can be minimized not only on the end face but also on the entire structure. Further, since it is a single-layer insulating film of (SiO ₂ ) x (Si ₃ N ₄ ) y, there is no interface in the insulating film, and the risk of breakdown due to dislocation is further reduced.

  Where the stress concentration or increase occurs depends on the structure of the semiconductor and the shape and thickness of the electrodes. Accordingly, the optimum single-layer insulating film composition x, y corresponding to the change also changes. There is a great advantage that a robust structure with less stress can be realized without searching for an optimum value of a plurality of insulating films.

  As described above, according to the optical semiconductor device of the present invention, since there is one kind of material (x, y), there are fewer interfaces that are the starting points of breakdown or failure, and by changing the composition ratio, the mesa structure or the upper part can be obtained. An element that is strong against the influence of electrodes can be created.

101, 301, 501 InP semiconductor substrate 102, 302, 502 Semiconductor active layer or absorption layer 103, 303, 503 InP semiconductor mesa 104, 304, 504 Insulating film 505 Electrode

Claims (3)

In a semiconductor element having a function of an active layer or a laser or light modulator or optical amplifier having a light absorption layer,
Having a mesa structure for guiding light on the side opposite to the substrate on which the element is formed, and part or all of the surface on the side having the mesa structure has an insulating film;
An optical semiconductor element characterized in that the insulating film is made of a compound of a silicon oxide film (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ).   2. The optical semiconductor element according to claim 1, further comprising a metal layer for forming an electrode on the insulating film.   The active layer or the light absorption layer includes In (z) Ga (1-z) As (1-w) P (w), In (1-z-w) Al (z) Ga (w) As, and the like. The optical semiconductor element according to claim 1, wherein the quaternary mixed crystal compound semiconductor (wherein z and w are the composition ratio of the mixed crystal) is used.

Images