CN100508311C - Nitride semiconductor device and fabrication method thereof - Google Patents

Nitride semiconductor device and fabrication method thereof Download PDF

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CN100508311C
CN100508311C CN 200510119342 CN200510119342A CN100508311C CN 100508311 C CN100508311 C CN 100508311C CN 200510119342 CN200510119342 CN 200510119342 CN 200510119342 A CN200510119342 A CN 200510119342A CN 100508311 C CN100508311 C CN 100508311C
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nitride
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nitride semiconductor
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CN1770578A (en
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山田英司
神川刚
荒木正浩
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Sharp Fukuyama Laser Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
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    • H01L21/02538—Group 13/15 materials
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/02428—Structure
    • H01L21/0243—Surface structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/02433—Crystal orientation

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Abstract

The invention discloses a nitride semiconductor device and method for manufacturing same. The nitride semiconductor device is provided that prevents development of cracks, that has nitride semiconductor thin films with uniform thicknesses and good growth surface flatness, and is thus consistent in characteristics, and that can be fabricated at a satisfactory yield. In this nitride semiconductor device, the nitride semiconductor thin films are grown on a substrate having an off-angle between a direction normal to the surface of ridges and the crystal direction <0001>. This helps either reduce or intentionally promote diffusion or movement of the atoms or molecules of a source material of the nitride semiconductor thin films through migration thereof. As a result, a nitride semiconductor growth layer with good surface flatness can be formed, and thus a nitride semiconductor device with satisfactory characteristics can be obtained.

Description

Nitride compound semiconductor device and manufacture method thereof
Technical field
The present invention relates to a kind of nitride compound semiconductor device.More specifically, the present invention relates to a kind of use nitride device of the Semiconductor substrate that forms by nitride-based semiconductor of surface at least, and the manufacture method of this nitride compound semiconductor device.
Background technology
Nitride-based semiconductor for example GaN, AlGaN, GaInN and AlGaInN is characterised in that to have than AlGaInAs base or the big band gap Eg of AlGaInP base semiconductor, so also at the direct-gap seminconductor material.Owing to these reasons, nitride-based semiconductor as be used to make light emitting semiconductor device, for example can and cover material at the semiconductor laser luminous from the ultraviolet of spectrum to the shortwave in green district from the ultraviolet of spectrum to the light-emitting diode of the wide emission wavelength scope of red color area, caused a lot of concerns.Like this, people expect that nitride-based semiconductor is used widely in high density compact disc driver, full color display and other equipment and in environment, medical science and the other field.
In addition, nitride-based semiconductor has than GaAs base or the high thermal conductivity of other semiconductors, and therefore can expect to be applied in the device that works in high temperature and high output.In addition, nitride-based semiconductor is without any need for for example being used in the arsenic (As) in the AlGaAs base semiconductor or being used in the material of the cadmium (Cd) in the ZnCdSSe base semiconductor, so they do not need for example arsine (AsH yet 3) source material etc., can expect that like this they are the compound semiconductor materials that help environment.
Yet, routinely, in various types of nitride compound semiconductor devices, extremely low rate of finished products is suffered from the manufacturing of nitride semiconductor laser device, that is, with respect to the total amount of the nitride semiconductor laser device of making on single wafer, flawless quantity is extremely low.A reason of low rate of finished products is considered to the formation of crackle.The reason that causes crackle may be substrate itself or be the nitride-based semiconductor multilayer films that comprise a plurality of nitride semiconductor layers of placing successively (nitride semiconductor film) are placed in the process on the substrate.
Preferably in essence forms the nitride-based semiconductor multilayer film that for example forms, have the crystal mass of getting well and the nitride-based semiconductor multilayer film of defective still less because help like this to produce by GaN by growth on the GaN substrate.Yet, also do not produce the high quality GaN single crystalline substrate that has good lattice match with GaN up to nowadays.Therefore, the SiC substrate often is substituted use because of its relatively little difference on lattice constant.Yet disadvantageously, the SiC substrate is very expensive, is difficult to be fabricated to major diameter, and produces elongation strain.As a result, the SiC substrate is easy to crack.In addition, the substrate of nitride-based semiconductor requires by bearing about 1000 ℃ high growth temperature and forming as fastness (discoloration) in the ammonia environment of source material and erosion-resisting material.
Based on above-mentioned discussion, adopt Sapphire Substrate usually as the substrate of placing the nitride-based semiconductor multilayer film.Yet Sapphire Substrate causes big lattice mismatch (about 13%).Therefore, on Sapphire Substrate, at first form the resilient coating that forms by GaN or AlN by low-temperature epitaxy, then, growing nitride semiconductor multi layer film on this resilient coating.However, still be difficult to eliminate fully strain, the condition of membrane component and thickness for example of therefore depending on has caused the formation of crackle.
The reason that causes this crackle may be substrate other places in addition, will describe below.When making nitride semiconductor laser device, on substrate, place the nitride-based semiconductor multilayer film, and this nitride-based semiconductor multilayer film for example GaN, AlGaN and InGaN form by dissimilar films.Herein, each film of forming the nitride-based semiconductor multilayer film has different lattice constants, therefore demonstrates lattice mismatch, causes the generation of crackle.As the countermeasure of resisting it, proposed to be used to reduce the method for crackle, according to the method, adopt the substrate of handling, make after the nitride-based semiconductor multilayer film is grown on the substrate, the surface of nitride-based semiconductor multilayer film is not smooth, but has depressed area formed thereon (seeing Japanese Patent Application Publication No.2002-246698).By adopting the method that for example is disclosed among the Japanese Patent Application Publication No.2002-246698, may reduce by the crackle that lattice mismatch caused between each layer of forming the nitride-based semiconductor multilayer film that is formed on the substrate.Yet in the disclosed method, the lip-deep depressed area that is formed on the nitride-based semiconductor multilayer film has reduced its evenness in Japanese Patent Application Publication No.2002-246698 disadvantageously.
Countermeasure as the evenness of resisting this reduction nitride-based semiconductor multi-layer film surface, the present inventor has developed such method, according to this method, on the nitride-based semiconductor substrate, form groove (trench) and spine (ridge portion), wherein groove is a form to a plurality of stripe-shaped grooves in each nitride semiconductor laser device, spine each all between two adjacent grooves and have the width of about 100 μ m to 1000 μ m, then, on this nitride-based semiconductor substrate, the nitride-based semiconductor multilayer film is set.Adopt this method, may prevent crackle, and obtain quite improved surface smoothness in ridge surface simultaneously.
When making nitride semiconductor laser device by the said method that the present inventor developed, the nitride-based semiconductor multilayer film is for example constructed as shown in figure 20.
Particularly, the lip-deep nitride-based semiconductor multilayer film 4 of substrate 6 (seeing Figure 19 A and 19B) that is formed on the processing that is formed by the n type GaN of etching etc. has for example following layer, and its order according to name stacks gradually on the surface of handling substrate 6: the n type GaN layer 200 with 0.2 μ m bed thickness; N type Al with 0.75 μ m bed thickness 0.05Ga 0.95N first cover layer (clad layer) 201; N type Al with 0.1 μ m bed thickness 0.08Ga 0.92N second cover layer 202; N type Al with 1.5 μ m bed thickness 0.05Ga 0.95N the 3rd cover layer 203; N type GaN guide layer (guidelayer) 204 with 0.02 μ m bed thickness; Active layer 205 comprises three InGaN trap layers that all have the 4nm bed thickness and all has four GaN barrier layers of 8nm bed thickness; P type Al with 20nm bed thickness 0.3Ga 0.7The N evaporation prevents layer 206; P type GaN guide layer 207 with 0.02 μ m bed thickness; P type Al with 0.5 μ m bed thickness 0.05Ga 0.95 N cover layer 208; P type GaN contact layer 209 with 0.1 μ m bed thickness.Active layer 205 has the following layer that forms successively by its naming order: barrier layer, trap layer, barrier layer, trap layer, barrier layer, trap layer and barrier layer.In being described below, when needs are represented by layer nitride semiconductor layer that is constituted, i.e. the p type Al that stack successively that are doped with Mg 0.3Ga 0.7The N evaporation prevents layer 206, p type GaN guide layer 207, p type Al 0.05Ga 0.95When N cover layer 208 and p type GaN contact layer 209, just adopt term " p layer ".
Like this, nitride-based semiconductor multilayer film 4 is arranged on by MOCVD on the surface of substrate 6 of the processing of being anticipated.Like this, made the nitride semiconductor wafer that the surface at nitride-based semiconductor multilayer film 4 shown in Figure 19 A and 19B has the depressed area.In Figure 19 A and 19B, in-plane is labeled in together.
As the substrate 6 of the processing shown in Figure 19 A and the 19B is the dry etch technique edge＜1-100 that has by for example RIE (reactive ion etching)〉the direction groove that is stripe-shaped 2 formed thereon and the n type GaN substrate of ridge 1.Channel shaped becomes that 5 μ m are wide, 5 μ m are dark and the distance between two adjacent trenches is 350 μ m.On the substrate 6 of etched processing like this, the growing technology by for example MOCVD forms the nitride-based semiconductor multilayer film 4 with stepped construction as shown in figure 20.
When nitride semiconductor laser device by by the actual manufacturing of method that the present inventor developed the time, by using n type GaN substrate as the substrate of handling 6, and subsequently on this n type GaN substrate by MOCVD homepitaxy growing nitride semiconductor multi layer film 4, find that this method is being effectively aspect the minimizing crackle, but can not significantly increase rate of finished products.Particularly, pass through said method, made a plurality of nitride semiconductor laser devices, then from 100 nitride semiconductor laser devices of stochastical sampling wherein and measure the FFP of its horizontal direction and vertical direction half maximum overall with (full width halfmaximum, FWHM).Herein, actual FFP FWHM design load ± nitride semiconductor laser device in 1 scope is thought flawless.The result is that only 30 nitride semiconductor laser devices satisfy the requirement of the FWHM of its FFP, and this demonstrates very low rate of finished products.
This is because the surface of the nitride-based semiconductor multilayer film 4 that forms is smooth inadequately.Have not enough surface smoothness, the bed thickness of each layer is different in nitride-based semiconductor multilayer film 4, causes the variation of characteristic in each nitride semiconductor laser device.This has reduced the number of the device with the characteristic in claimed range.Therefore,, not only need to reduce the generation of crackle, also need to make the more all even film of bed thickness surface more smooth in order to improve rate of finished products.
Find that also when electrode pad is formed on because depressed area and on the very irregular surface time, the electric current that leaks by these depressed areas makes normal current-voltage (C-V) characteristic that can not obtain laser.Basically, SiO for example 2Dielectric film be formed on the depressed area, and above electrode pad further is formed on.Herein, if this surface has for example uneven main plot of depressed area, then the dielectric film that forms thereon can not be formed uniformly.When analyzing this dielectric film, confirmed that it has many such zones, in this region generating crackle and pit and should place's dielectric film as thin as a wafer.Find that also this inhomogeneous dielectric film is the reason that electric current leaks.
In addition, in wafer surface, measured surface smoothness as the nitride semiconductor wafer of Figure 19 A, 19B and formation shown in Figure 20.Edge＜1-100〉measurement result of surface smoothness of direction is shown in Figure 21.This measurement is carried out under the condition below: measure length, 600 μ m; Measuring Time, 3s; Probe pressure, 30mg; Horizontal resolution, 1 μ m/ sampling.In 600 measured μ m width ranges, the level error between the highest and lowermost portion on surface is 30nm, can understand from Figure 21.In this was measured, nitride semiconductor wafer is assumed to be had 0.02 ° or littler inclination angle.
Shown in Figure 19 B, the thickness of each layer that is arranged on the nitride-based semiconductor multilayer film 4 on substrate 6 surfaces of handling changes along with the position in wafer surface, therefore causes the difference of evenness.As a result, the characteristic of nitride semiconductor laser device depend on they be formed on wafer surface where and change, and the p layer thickness of mixing Mg of appreciable impact nitride semiconductor laser device characteristic is (corresponding to p type Al as shown in figure 20 0.3Ga 0.7The N evaporation prevents the gross thickness of the p layer that layer 206 to p type GaN contact layer 209 stack gradually) diverse location alters a great deal in substrate surface.
When the ridge structure as current confinement structure formed, spine remained the wide striped of 2 μ m, and other parts etch away by the dry etch technique that adopts ICP (inductively coupled plasma, inductively coupled plasma) machine.Like this, if the thickness of p layer is in the diverse location difference of wafer surface before etching, so Sheng Xia p tunic is thick, that is, also great changes have taken place at the wafer surface diverse location for the p layer thickness that keeps after etching and therefore influence most the nitride semiconductor laser device characteristic.As a result, not only in different nitride semiconductor laser device layer thicknesses differences, even in same nitride semiconductor laser device, remaining p tunic is thick can be almost nil at some parts, and can be quite big in other parts.When thick variations like this of remaining p tunic, it influences the life-span of nitride semiconductor laser device, and the while also influences for example FFP (far-field pattern, far field pattern) of its characteristic as mentioned above.
The above-mentioned reason that has big layer thickness distribution in wafer surface is that epitaxial growth changes under the influence of the speed of growth at groove of the film on the ridged part of the substrate of the processing that comprises the nitride-based semiconductor substrate, causes inhomogeneity reduction in wafer surface.
Particularly, shown in Figure 22 A and 22B, on the substrate 6 of processing with groove formed thereon 2, when epitaxial growth begins, in the starting stage of growth, shown in Figure 22 A, the groove growth part 222 that is formed by the nitride semiconductor thin film on bottom 224 that is grown in groove 2 and the sidepiece 226 is the part of filling groove 2 only.Simultaneously, the grown on top part 221 that is formed by the lip-deep nitride semiconductor thin film at the top 223 that is grown in ridge 1 keeps the nitride semiconductor thin film surfacing in growth.
The epitaxial growth of nitride semiconductor thin film proceeds to the state shown in Figure 22 B from the above-mentioned state shown in Figure 22 A.Under this state, by the formed groove growth part 222 of the nitride semiconductor thin film of bottom 224 that is grown in groove 2 and sidepiece 226 filling groove 2 almost completely, and be connected to the grown on top part 221 that forms by the top 223 lip-deep nitride semiconductor thin films that are grown in ridge 1 by growth part 225.Under this state, be deposited on the nitride semiconductor thin film surface on the top 223 that grows in ridge 1 as the atom of source material or molecule (for example Ga atom) and under the influence of heat energy, move etc. to move to growth part 225 or groove growth part 222.Take place unevenly by this moving in wafer surface that the migration of atom or molecule causes, and displacement different places in wafer surface are different.As a result, shown in Figure 22 B, the surface smoothness of grown on top part 221 has reduced.
Inhomogeneities at nitride-based semiconductor substrate itself, for example in wafer surface the distribution at inclination angle and in wafer surface substrate curvature distribution or in substrate surface epitaxial growth speed inhomogeneous or under the uneven influence of substrate surface internal channel forming process,＜1-100〉direction, the evenness of nitride semiconductor thin film also reduces.Particularly, required time of filling groove 2 is along with＜1-100〉direction and changing; Like this, fill than place early, the atom of the source material of nitride semiconductor thin film or molecule move or move to growth part 225 or groove growth part 222 from the grown on top part 221 of ridge 1.In the place that they are removed, need form nitride semiconductor thin film for more time, the nitride semiconductor thin film that the result is formed in the groove 2 has bigger thickness.As a comparison, in the place that groove 2 is filled laterly, the atom of the source material of nitride semiconductor thin film or molecule do not move or move to groove 2 from the grown on top part 221 of ridge 1; Even their migrations or mobile also need the less time to form nitride semiconductor thin film.Like this, the nitride semiconductor thin film in these grooves 2 is had littler thickness than groove 2 by more Zao filling place.
Depend in growth rate under the situation of delivery rate, promptly, under the situation of growth rate by the controls such as flow of atom that is fed to wafer surface or molecule of nitride semiconductor thin film, when the atom or the molecular migration of the source material of nitride semiconductor thin film or when moving in the groove 2, because being fed to the atom of source material on entire wafer surface or the flow of molecule is constant, grow in the place on the top 223 of ridge 1 at nitride semiconductor thin film, be that thickness is less in the grown on top part 221.As a comparison, under the atom of the source material of nitride semiconductor thin film or molecule do not move or move to situation in the groove 2, be grown in the place on the top 223 of ridge 1 at nitride film, promptly in the grown on top part 221, thickness is bigger.
Then, the bed thickness in the grown on top part 221 on the top 223 of ridge 1 changes in wafer surface, and the evenness on the surface of nitride semiconductor thin film reduces as a result.Like this, in order to obtain better surface smoothness, need the atom or the grown on top part 221 of molecule from ridge 1 of the source material of prevention nitride semiconductor thin film to move or move to growth part 225 or the groove growth part 22, and therefore stop them to form nitride semiconductor thin film at this place.
The other method that obtains better evenness is that the atom or the molecule of the source material of nitride semiconductor thin film are evenly moved on the entire wafer surface when its grown on top part 221 from ridge 1 is moved or moved to the groove growth part.
Summary of the invention
From above-mentioned angle, the purpose of this invention is to provide such nitride compound semiconductor device, it does not crack, has highly uniform bed thickness, has the nitride-based semiconductor multilayer film of band flat surface, can and not have electric current to leak with the high finished product rate manufacturing.Another object of the present invention provides the manufacture method of this nitride compound semiconductor device.Particularly, the present invention seeks in by the manufacturing that the nitride semiconductor laser device that the nitride-based semiconductor multilayer film makes is set on the substrate that forms by nitride-based semiconductor of surface at least, prevent the generation of crackle, the atom or the molecule of the source material by stoping nitride semiconductor thin film partly move or move to groove and therefore prevent that they are at this formation nitride semiconductor thin film from the top surface that is arranged in ridge surface simultaneously, perhaps the atom of the source material by making nitride semiconductor thin film or molecule on entire wafer equably the top surface from ridge surface partly move or move to the groove, and form nitride-based semiconductor multilayer film with good surface smoothness.
According to crystallographic custom, if the index of expression crystrallographic plane or direction is negative, then this index has the absolute value representation of line by it.In this manual, because this method for expressing is impossible, so negative exponent is had the absolute value representation of minus sign "-" by the front.
" groove " expression forms the depressed area of stripe-shaped as shown in Figure 2 on the nitride-based semiconductor substrate.Fig. 2 is the schematic sectional view of substrate 26 that has groove 22 and form the processing of technology ridge 21 formed thereon by groove.This groove 22 does not need necessarily have rectangular cross sectional shape, but can have triangle or trapezoidal sectional shape, can produce difference in level as long as they are shaped.Groove 2 does not need necessarily to form each and all comprises single depressed area, but can form each all comprise a plurality of have narrow smooth part or between two parties the part the depressed area.
" ridge " expression forms the raised portion with the striped similar shape.Fig. 2 shows the striped arrangement that groove 22 and ridge 21 form along same direction.As selection, also groove 22 and ridge 21 can be formed the arrangement of grid shape, wherein they are formed on two directions that cross one another.Also can on single substrate, groove 22 be formed difformity, different depth or different in width.Also can on single substrate, form groove 22 with the cycle that changes.
" substrate of handling " expression is by on the nitride-based semiconductor or be arranged on the nitride semiconductor thin film surface on the nitride-based semiconductor substrate or the non-nitride-based semiconductor substrate (for example sapphire, SiC, Si or GaAs substrate) that has nitride semiconductor layer is from the teeth outwards gone up and formed the substrate that groove and ridge produce.
" nitride-based semiconductor substrate " expression is at least by Al xGa yIn zThe substrate that N (0≤x≤1,0≤y≤1,0≤z≤1, and x+y+z=1) forms.In the nitride-based semiconductor substrate, comprise wherein nitrogen-atoms about 20% or still less can be by at least a replacement in the following group element: As, P and Sb.The nitride-based semiconductor substrate can be doped with the impurity of n type for example or p type dopant.The example of these impurity comprises: Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg and Be.The preferred total impurities that adds is 5 * 10 16/ cm 3Or it is above but 5 * 10 20/ cm 3Or below.In described impurity, preferred especially is Si, Ge, O, Se or Cl as what provide n type conductivity to the nitride-based semiconductor substrate.As the primary flat direction of nitride-based semiconductor substrate, can adopt C plane { 0001}.
The nitride-based semiconductor multilayer film that is grown on the substrate of handling is known as the nitride-based semiconductor multilayer film.Herein, the nitride-based semiconductor multilayer film is by Al xGa yIn zN (0≤x≤1,0≤y≤1,0≤z≤1, and x+y+z=1) forms.In the nitride-based semiconductor multilayer film, comprise wherein nitrogen-atoms about 20% or still less can be by at least a replacement of a following group element: As, P and Sb.The nitride-based semiconductor multilayer film can be doped with the impurity of n type for example or p type dopant.The example of these impurity comprises: Cl, O, S, Se, Te, C, Si, Ge, Zn, Cd, Mg and Be.The preferred total impurities that adds is 5 * 10 16/ cm 3Or it is above but 5 * 10 20/ cm 3Below.In described impurity, preferred especially is Si, Ge, O, Se or Te as what give that the nitride-based semiconductor multilayer film provides n type conductivity, and that especially preferably offer its p type conductivity is Mg, Cd or Be.
In semiconductor multi layer film, the nitride semiconductor layer that at first is arranged on the substrate of handling is called as nitride-based semiconductor initiation layer (primer layer).The nitride-based semiconductor initiation layer can be formed by for example GaN, AlGaN, AlInGaN, AlGaNP or AlGaNAs.
The active layer system refers to any layer that comprises the trap layer or comprise one or more trap layers and barrier layer.For example, the active layer with single quantum constitutes by single trap layer or by barrier layer, trap layer and barrier layer.On the other hand, the active layer with multi-quantum pit structure is made of a plurality of trap layers and a plurality of barrier layer.
To achieve these goals, according to an aspect of the present invention, nitride compound semiconductor device is provided with: the substrate of handling, and it is by forming groove as at least one depressed area and form spine and form as non-groove on the surface of the nitride-based semiconductor substrate that formed by nitride-based semiconductor of surface at least; With the nitride semiconductor growing layer, it comprises the nitride semiconductor thin film on a plurality of substrates that are arranged on this processing, and this nitride semiconductor growing layer has and { the primary flat direction of 0001} planar alignment.Herein, first vector that extends from the surface portion of ridge along its normal direction be parallel to crystallographic direction＜0,001 second vector that extends between the two angle when hypothesis first vector and second vector start from same point, being the inclination angle, is 0.05 ° or above but at 4 ° or following.
In above-mentioned nitride compound semiconductor device, preferably, the inclination angle of the substrate of handling comprises: first inclination angle, this angle be first vector and by second vector is projected to by mutually perpendicular crystallographic direction＜0001,＜11-20 and＜1-100 in crystallographic direction＜0001 and＜1-100 angle between the 3rd vector that obtains on formed first plane when hypothesis the first and the 3rd vector starts from same point; With second inclination angle, this angle be first vector and by second vector is projected to by mutually perpendicular crystallographic direction＜0001,＜11-20 and＜1-100 in crystallographic direction＜0001 and＜11-20 angle between the four-vector that obtains on formed second plane when hypothesis first and the four-vector start from same point.
In above-mentioned nitride compound semiconductor device, preferably, make that first inclination angle is that the θ a and second inclination angle are θ b, then | and θ a| 〉=| θ b|.
In above-mentioned nitride compound semiconductor device, preferably, 0.09 °≤| θ a| °.
In above-mentioned nitride compound semiconductor device, preferably, 3 * | θ b| °＜| θ a| °＜0.09 °, 0.05 ° simultaneously≤| θ a| °.
In above-mentioned nitride compound semiconductor device, preferably, make that first inclination angle is that the θ a and second inclination angle are θ b, then | and θ a|≤| θ b|.
In above-mentioned nitride compound semiconductor device, preferably, 0.2 °≤| θ b| °.
In above-mentioned nitride compound semiconductor device, preferably, extend with stripe-shaped the depressed area that forms groove, and the bearing of trend of depressed area is parallel to or is basically parallel to crystallographic direction＜1-100 〉.
In above-mentioned nitride compound semiconductor device, extend with stripe-shaped the depressed area that forms groove, and the bearing of trend of depressed area is parallel to or is basically parallel to crystallographic direction＜11-20 〉.
In above-mentioned nitride compound semiconductor device, preferably, the depressed area that forms groove forms grid shape, and in two orthogonal directions that grid extends, one is parallel or be basically parallel to crystallographic direction＜11-20 〉, another is parallel or be basically parallel to crystallographic direction＜1-100 〉.
In above-mentioned nitride compound semiconductor device, preferably, make that first inclination angle is that the θ a and second inclination angle are θ b, it is parallel or be basically parallel to crystallographic direction＜1-100 then to be parallel to the direction of long side of ridge 〉, and | θ a| 〉=| θ b|.
In above-mentioned nitride compound semiconductor device, preferably, make that first inclination angle is that the θ a and second inclination angle are θ b, it is parallel or be basically parallel to crystallographic direction＜11-20 then to be parallel to the direction of long side of ridge 〉, and | θ a|≤| θ b|.
In above-mentioned nitride compound semiconductor device, preferably, first inclination angle square with second inclination angle square root sum square be 0.2 ° or more than.
In above-mentioned nitride compound semiconductor device, preferably, the width that is arranged on the ridge between two adjacent parts of groove is 100 μ m or bigger but at 2000 μ m or following.
In above-mentioned nitride compound semiconductor device, preferably, the nitride semiconductor thin film that contacts with the substrate surface of handling is GaN or the AlGaN with 0.5 μ m or littler thickness.
In above-mentioned nitride compound semiconductor device, preferably, the degree of depth that forms the depressed area of groove be 1.5 μ m or more than.
In above-mentioned nitride compound semiconductor device, preferably, the gross thickness that order is formed on the nitride semiconductor growing layer on the ridge is T, and the degree of depth that then forms the depressed area of groove is T/2 or bigger.
In above-mentioned nitride compound semiconductor device, preferably, the opening that forms the depressed area of groove is 3 μ m or bigger.
In above-mentioned nitride compound semiconductor device, preferably, when the nitride semiconductor growing layer that comprises a plurality of nitride semiconductor thin films forms, at least one nitride semiconductor thin film is to grow under such condition: the substrate surface temperature of handling is 1050 ℃ or lower, and the ratio of mole flow velocity of unit interval that mole flow velocity and the supply of unit interval that supply comprises the source material of V group atom comprises the source material of III family atom is 2250 or bigger.
According to the invention described above, when nitride compound semiconductor device when for example nitride semiconductor laser device is made by on the substrate that formed by nitride-based semiconductor of surface at least the nitride semiconductor growing layer being set, prevented the generation of crackle, hindered the atom of source material of nitride semiconductor thin film or the grown on top of molecule from ridge surface in addition and partly moved or spread or move to the groove, and therefore hindered at this place formation nitride semiconductor thin film.Like this, may form nitride semiconductor growing layer, and therefore obtain nitride compound semiconductor device with desirable characteristics with good surface smoothness.
As selection, according to the invention described above, promote the atom of source material of nitride semiconductor thin film or molecule partly to move or spread or move to groove consciously, make the evenly diffusion or move of the atom of source material of nitride semiconductor thin film or molecule on the whole surface of wafer from the grown on top on the ridge surface.Like this, may form nitride semiconductor growing layer, and therefore obtain nitride compound semiconductor device with desirable characteristics with good surface smoothness.
To achieve these goals, according to a further aspect in the invention, the nitride-based semiconductor initiation layer that at first is formed on the substrate of the processing with groove formed thereon is formed by the compound that comprises GaN.
Adopt this structure, prevented the generation of crackle, after this nitride-based semiconductor multilayer film of Xing Chenging has bed thickness highly uniformly, and obtains flat surface.
Herein, preferably, the bed thickness of nitride-based semiconductor initiation layer is 0.5 μ m or following.Preferably, the ratio of the bed thickness of nitride-based semiconductor initiation layer and total bed thickness of nitride-based semiconductor multilayer film be 15% or below.Preferably, it is 60 ° or bigger perpendicular to the line of the head portion on trenched side-wall surface and perpendicular to the angle between the line on the surface beyond the groove.Preferably, the width of groove is 1 μ m or more, and the cycle of groove is 0.1mm or bigger but at 4mm or following.
Under the situation that above-mentioned nitride-based semiconductor initiation layer is formed by the compound that comprises GaN, when total bed thickness of nitride-based semiconductor multilayer film is 4 μ m or more hour, preferably, the degree of depth of groove is 1 μ m or bigger but be not more than 20 μ m, and the width of groove is 1 μ m or bigger.
Like this, may obtain acceptable surface roughness (300
Figure C200510119342D0012093603QIETU
Or following), and therefore obtain to provide stability characteristic (quality) and long-life device..
According to the invention described above, the substrate that has the processing of groove formed thereon by manufacturing, nitride semiconductor layer at first is set on the substrate of this processing then, may prevents the generation of crackle, and obtain the surface smoothness that highly uniform bed thickness is become reconciled at substrate surface simultaneously.That is, may improve number, improve rate of finished products thus with the device that satisfies zero defect requirement characteristic.
Description of drawings
Fig. 1 is the schematically illustrated schematic diagram that is used in the substrate of the processing with θ a ° inclination angle in the first embodiment of the invention;
Fig. 2 is the sectional view of substrate of the processing of schematically illustrated groove with different shape formed thereon;
Fig. 3 is the schematically illustrated schematic diagram that is used in the substrate of the processing with θ b ° inclination angle in the first embodiment of the invention;
Fig. 4 is the schematic diagram of the substrate of the schematically illustrated processing that does not have an inclination angle;
Fig. 5 illustrates the schematic diagram that concerns between the standard deviation of p layer thickness and the rate of finished products;
Fig. 6 illustrates the schematic diagram that concerns between the standard deviation of tiltangle a and p layer thickness;
Fig. 7 illustrates the schematic diagram that concerns between the standard deviation of tiltangle b and p layer thickness;
Fig. 8 is the drawing of level height deviation of the wafer surface of the nitride semiconductor growing layer on the substrate of the processing that has in the first embodiment of the invention of being arranged on to be adopted, have θ b ° inclination angle;
Fig. 9 A and 9B are the schematically illustrated schematic diagrames that is used in the substrate of the processing in the example 1 to 4 of the present invention;
Figure 10 is the drawing of level height deviation with wafer surface of the nitride semiconductor growing layer on the substrate that is arranged on the processing of being adopted in the example 1 to 4 of the present invention;
Figure 11 A and 11B are the schematic diagrames of the nitride semiconductor laser device in the schematically illustrated example of the present invention 1 to 4;
Figure 12 A is the perspective view that schematically illustrated substrate with processing of nitride-based semiconductor multilayer film formed thereon centers on the part of groove, and Figure 12 B is the sectional view of being got along the line A-A shown in Figure 12 A;
Figure 13 A is the front view of nitride compound semiconductor device, and Figure 13 B is the vertical view of Figure 13 A;
Figure 14 is the sectional view of part B shown in Figure 2;
Figure 15 is the schematic diagram that illustrates along the measurement result of the surface smoothness of the nitride-based semiconductor multilayer film of [1-100] direction;
Figure 16 is the schematic diagram that the nitride-based semiconductor multi-layer film surface roughness that measures when initial GaN layer thickness variation is shown;
Figure 17 A is the sectional view of substrate with processing of nitride-based semiconductor multilayer film with good surface smoothness formed thereon;
Figure 17 B is the sectional view of substrate with processing of the nitride-based semiconductor multilayer film with poor surface smoothness formed thereon;
Figure 18 has the sectional view of substrate of processing of nitride-based semiconductor multilayer film that formed thereon comprising has the initial GaN layer of 0.5 μ m or littler thickness;
Figure 19 A and 19B are schematically illustrated schematic diagrames with wafer of the nitride semiconductor growing layer on the substrate that the conventional treatment of being formed on crosses;
Figure 20 is the sectional view of schematically illustrated conventional nitride semiconductor growing layer;
Figure 21 is the drawing of elevational change with wafer surface of the nitride semiconductor growing layer on the substrate that the conventional treatment of being arranged on crosses; And
Figure 22 A and 22B are the schematic diagrames that the model how evenness that reduces under the regular situation to take place is shown.
Embodiment
First embodiment
The first embodiment of the present invention is described below with reference to accompanying drawings.The description that regards to embodiment down is the example of nitride semiconductor layer as nitride compound semiconductor device, but should be appreciated that the present invention may be embodied as the nitride compound semiconductor device of any other type.Fig. 1 and 3 is the substrate 16 of schematically illustrated usefulness processing in this embodiment and 36 schematic diagram, as viewed when nitride-based semiconductor multilayer film 4 is grown thereon.As shown in figs. 1 and 3, the substrate of handling 16 and 36 each all have fixing inclination angle.Fig. 4 is the schematic diagram of the substrate of the schematically illustrated processing that produces from normally used substrate with 0.02 ° or littler inclination angle.In Fig. 1,3 and 4, in-plane is represented together.In this embodiment, make nitride semiconductor laser device by growing nitride semiconductor multi layer film 4 on the substrate of the processing at the substrate 16 that has and the handled inclination angle similar with 36.
At first, how will to provide from having 0.02 ° or littler inclination angle promptly, the almost description of the substrate 46 crossed of the substrate fabrication process of zero degree, as shown in Figure 4.In this embodiment, suppose that adopting the GaN substrate is the substrate 16,36 and 46 that dealt with.
At first, on the whole surface of n type GaN substrate, pass through sputtering method, SiO 2Deng being 1 μ m thickness by vapor deposition.Then, by common photoetching process, stripe-shaped resist pattern edge＜1-100〉direction forms and makes when along being parallel to＜11-20〉direction is from the center line of a striped during to another stripe centerline measurement, the resist opening has 5 μ m width, and striped is positioned at 350 μ m intervals (after this being called " cycle ").Then, by dry etching technology RIE (reactive ion etching) for example, SiO 2The etched groove 42 that has 5 μ m gash depths and 5 μ m A/Fs with formation of film and n type GaN substrate.Then, by using for example HF (hydrogen fluoride) of etching agent, remove SiO 2Like this, formed the substrate 46 of processing with groove formed thereon 42 and ridge 41.
In this embodiment, SiO 2By vapor deposition on the GaN substrate surface, to form SiO 2Film.Replace ground, another kind of dielectric substance film etc. can be formed on the GaN substrate surface.Above-mentioned SiO 2Film can form by the method beyond the sputter vapor deposition; For example can form by for example electron beam vapor deposition or plasma CVD method.The cycle of resist pattern is not limited to the 350 μ m that mask body is mentioned, but can change according to the width of the nitride semiconductor laser device that will make.In this embodiment, groove 42 forms by dry etching technology; Yet, also can form them by wet etching technique etc.
The substrate of handling 46 can be made by directly form groove 42 on said n type GaN substrate surface, perhaps can by n type GaN substrate or on the nitride-based semiconductor substrate except n type nitride-based semiconductor substrate nitride semiconductor thin films such as growing GaN, InGaN, AlGaN, InAlGaN at first, form groove thereon then and form.
The substrate of handling 16 forms by the method identical with the substrate handled 46 basically with 36.Difference is as follows.The substrate that is used to produce the substrate of handling 16 has about the crystallographic direction＜11-20 as rotating shaft〉rotation or crystallographic direction＜1-100 of cant angle theta a ° and＜0001, and so in crystallographic direction＜0001 and the direction perpendicular to the growing surface on the substrate between have the inclination angle of θ a.On the other hand, the substrate that is used to produce the substrate of handling 36 has about the crystallographic direction＜1-100 as rotating shaft〉rotation or crystallographic direction＜11-20 of cant angle theta b ° and＜0001, and so in crystallographic direction＜0001 and the direction perpendicular to the growing surface on the substrate between have the inclination angle of θ b.On each of these substrates that have θ a and θ b inclination angle respectively, groove 12 and 32 and ridge 11 and 31 form in the same manner as described above.Suppose that each substrate has zero inclination angle and carries out the formation of photoresist pattern, etching and other technology herein.
The inclination angle not only can tilt in a direction, and for example above-mentioned independent θ a or θ b also can tilt with different angles (θ a and θ b) at different directions simultaneously.Particularly, suppose about rotating shaft＜11-20〉direction crystallographic direction＜1-100 and＜0001〉all rotation or cant angle theta a °, make in crystallographic direction＜0001〉and the direction perpendicular to the growing surface of substrate between have the inclination angle of θ a.So, make displacement vector A to start with in before the rotation along crystallographic direction＜0001 unit vector (length is 1) and end at rotation after along crystallographic direction＜0001 the displacement vector of unit vector.In addition, suppose about rotating shaft＜1-100〉direction crystallographic direction＜11-20 and＜0001〉all rotation or cant angle theta b °, make in crystallographic direction＜0001〉and the direction perpendicular to the growing surface of substrate between have the inclination angle of θ b.So, make displacement vector B become starting from before the rotation along crystallographic direction＜0001〉unit vector and end at after the rotation along crystallographic direction＜0001 the displacement vector of unit vector.Then, make that displacement vector C is displacement vector A and B sum, and make resultant vector D for before the rotation along crystallographic direction＜0001 unit vector and displacement vector C sum.Then, the end points direction of this resultant vector D can become the direction that the inclination angle tilts.In this manual, at substrate owing to crystallographic direction＜0001 tilt displacement vector C has in the situation at inclination angle, the two is represented by explaining above-mentioned tiltangle a and θ b.
Determining of inclination angle
As the part of present embodiment explanation, at first with reference to relevant drawings, how the inclination angle that provides substrate influences the growth of the nitride semiconductor thin film on the substrate that is arranged on the processing with groove formed thereon and ridge.
As shown in Figure 4, when employing has 0.02 ° or littler inclination angle, promptly almost during the substrate 46 of the processing of zero degree, be parallel to crystallographic direction＜0001〉perpendicular to the top 43 of ridge 41 and perpendicular to the direction of the bottom 44 of groove 42.In addition, respectively with crystallographic direction＜0001,＜1-100 and＜11-20 three axles aiming at are perpendicular to one another.In this case, the atom and the molecule 15 that are deposited on the nitride semiconductor thin film material at ridge 41 tops 43 are not to spread along specific direction with high probability, but isotropically from its position that is deposited diffusion.As a result, the atom of nitride semiconductor thin film material or molecule 15 isotropically move or spread, and their part moves in the groove 42 and forms nitride semiconductor thin film.
Usually, when groove 12,32 and 42 forms, they are not to be formed uniformly fully on the entire wafer surface, but in the photoetching process that is used to form the photoresist pattern and at the etching technics that is used for carrying out dry etching etc., can be attributable to the fluctuation of technology.The result, not straight fluctuation boundary member 17,37 and 47 may be formed on groove 12,32 and 42 and ridge 11,31 and 41 between the border, and, may form fluctuation projected square part 18,38 and 48 in the sidepiece 19,39 of groove 12,31 and 42 and 49 and bottom 14,34 and 44 out of plumb places.
When groove 12,32 and 42 and ridge 11,31 and 41 because the above-mentioned fluctuation that is attributable to technology and during in the inhomogeneous formation in the whole surface of wafer, the degree that is deposited on the atom of nitride semiconductor thin film source material and molecule 15 migrations or the diffusion of ridge 11,31 and 41 tops 13,33 and 43 or moves to groove 12,31 and 42 is not uniformly on entire wafer, but zones of different is different.Promptly, some zones on wafer, the atom and the molecule 15 that are deposited on the nitride semiconductor thin film source material of ridge 11,31 and 41 tops 13,33 and 43 are more prone to migration or diffusion or move to groove 12,32 and 42, and other zones on wafer, the atom and the molecule 15 that are deposited on the nitride semiconductor thin film source material of ridge 11,31 and 41 tops 13,33 and 43 do not tend to migration or diffusion so or move to groove 12,32 and 42.
As mentioned above, if the degree that is deposited on the atom of nitride semiconductor thin film source material and molecule 15 migrations or the diffusion of ridge 11,31 and 41 tops 13,33 and 43 or moves to groove 12,31 and 42 is not uniform on entire wafer, its influence is grown in the evenness of the nitride semiconductor thin film on ridge 11,31 and 41, the film thickness that the result is grown in the nitride semiconductor thin film on ridge 11,31 and 41 changes on entire wafer, and a district shows different values with another district.
So change if be grown in the thickness of the nitride semiconductor thin film on ridge 11,31 and 41, it has adverse effect to the nitride semiconductor laser device that is formed on ridge 11,31 and 41.Fig. 5 shows the extent of deviation of the p layer thickness on the expression ridge (corresponding to the p type Al that sets gradually shown in Figure 20 0.3Ga 0.7N evaporation prevents that layer 206 is to the gross thickness to the p layer of p type GaN contact layer 209) standard deviation and the relation between the rate of finished products.It is 0.03 μ m or when following that chart among Fig. 5 shows standard deviation when the p layer thickness, has realized 90% or above high finished product rate, but when the standard deviation of p layer thickness be 0.03 μ m or when above, rate of finished products sharply descends.
Above-mentioned standard deviation when the p layer thickness is that 0.03 μ m or rate of finished products sharply descends when above reason are, if p type GaN guide layer 207, p type Al 0.05Ga 0.95The varied in thickness of N cover layer 208 grades is too big, and then when making nitride-based semiconductor substrate devices structure, their electricity and optical characteristics change.In addition, if when nitride semiconductor laser device is made in the p layer thickness shows the zone of big standard deviation, electric current can take place in energising (energization) process leak.This also causes low rate of finished products.
As mentioned above, when making nitride semiconductor laser device,, need to improve the evenness that is grown in the nitride semiconductor thin film on the ridge, comprise the thickness of nitride semiconductor laser device the p layer in manufactured zone in order to realize high finished product rate.For this reason, the present inventor has invented following two kinds of methods: hinder by a kind of method nitride semiconductor thin film source material atom or molecule 15 migrations or diffusion or move to groove; And promote the atom of source material or molecule 15 migrations or the diffusion of nitride semiconductor thin film by a kind of method consciously or move to groove.
In above-mentioned two kinds of methods, hindering atom or molecule 15 migrations or the diffusion of source material of nitride semiconductor thin film or the method that moves to groove relates to by using wherein crystallographic direction＜0001 as shown in Figure 3〉and＜1-100〉all with crystallographic direction＜11-20〉rotate or cant angle theta a ° substrate produces the substrate of handling 16 as rotating shaft, promptly, crystallographic direction＜0001 after the rotation〉about crystallographic direction＜0001 before the rotation〉have the substrate at the inclination angle of θ a, a growing nitride semiconductive thin film on this substrate of handling then.Have been found that, when nitride semiconductor thin film is grown on the substrate 16 of this processing, the atom or the molecule 15 more significant edges that are deposited on the source material of the nitride semiconductor thin film on the top 13 of ridge 11 are basically parallel to＜1-100〉direction, that is, along being parallel to groove 2 bearing of trends rather than edge＜11-20〉the direction migration or the diffusion or mobile of direction.As a result, atom or the molecule 15 that is deposited on the source material of the nitride semiconductor thin film on ridge 11 tops 13 hindered migration or diffusion or moved to groove 12.Like this, on the top 13 of ridge 11, nitride semiconductor thin film is formed with good surface smoothness.
On the other hand, in above-mentioned two kinds of methods, the method that wherein promotes the atom of source material or molecule 15 migrations or the diffusion of nitride semiconductor thin film consciously or move to groove relates to by using as shown in Figure 3, crystallographic direction＜0001〉and＜11-20〉all with crystallographic direction＜1-100〉be the substrate of rotating shaft rotation or cant angle theta b °, i.e. crystallographic direction＜0001 after the rotation〉about crystallographic direction＜0001 before the rotation〉have the substrate at θ b inclination angle and produce the substrate of handling 16, growing nitride semiconductive thin film on this substrate of handling then.Have been found that, when nitride semiconductor thin film is grown on the substrate 36 of this processing, be deposited on the atom of source material of the nitride semiconductor thin film on the top 33 of ridge 31 or molecule 15 more significantly along being basically parallel to＜11-20〉direction of direction, that is, along perpendicular to the groove bearing of trend and be parallel to the direction rather than the edge＜1-100 on the surface at ridge 31 tops 33 the direction migration or the diffusion or mobile of direction.As a result, being deposited on the atom of source material of the nitride semiconductor thin film on ridge 11 tops 13 or molecule 15 is promoted with migration or diffusion or moves to groove 12 by a large amount of.Like this, although have fluctuation boundary member 37 and fluctuation projected square part 38, be deposited on the atom of source material of the nitride semiconductor thin film on the top 33 of ridge 31 or molecule 15 and move equably on the entire wafer surface or spread or move to groove 32.Like this, at the top 13 of ridge 11, nitride semiconductor thin film is formed with good surface smoothness.
Known nitride semiconductor thin film for example GaN base semiconductor film at＜11-20 direction ratio is at＜1-100 direction grows soon.Therefore, when the substrate of handling 16 by using wherein crystallographic direction＜0001 and＜1-100 all with crystallographic direction＜11-20 produce as the substrate of rotating shaft with θ a ° rotation, when nitride semiconductor thin film is grown on the substrate 16 of this processing then, above-mentioned value θ a needs enough greatly to be deposited on promotion the atom or the molecule 15 of the source material of the nitride semiconductor thin film on the top 13 of ridge 11, make it along being basically parallel to＜1-100 direction is promptly along migration of groove 12 bearing of trends or diffusion or move, and prevent to be deposited on the atom of source material of nitride semiconductor thin film at ridge 11 tops 13 or molecule 15 along being parallel to＜11-20〉direction is promptly along perpendicular to the direction migration or the diffusion of groove 2 bearing of trends or move in the groove 12.
Pass between the standard deviation of above-mentioned tiltangle a and θ b and p layer thickness ties up to shown in Fig. 6 and 7.Fig. 6 shows the relation between the standard deviation of tiltangle a measured when nitride semiconductor laser device is made more than or equal to the substrate of the processing of the absolute value of tiltangle b by the absolute value that uses tiltangle a and the p layer thickness on the ridge.Fig. 7 shows the relation between the standard deviation of tiltangle b measured when nitride semiconductor laser device is less than or equal to the absolute value of tiltangle b by the absolute value that uses tiltangle a the substrate of processing is made and the p layer thickness on the ridge.The direction that the wafer that adopts by handle arbitrarily and reality along the symbol of the trunnion axis of Fig. 6 and 7 (+or-) intersects just is used as and is determined; Like this, in the crystallography term, symbol+and-be of equal value, only the absolute value of tiltangle a and θ b is meaningful.
Fig. 6 shows following content.Under the situation of absolute value that adopts tiltangle a more than or equal to the substrate of the processing of the absolute value of tiltangle b, when the absolute value of tiltangle a is 0.09 ° or when bigger, the standard deviation of p layer thickness is 0.03 μ m or following, and nitride semiconductor laser device can be made (see figure 5) with high finished product rate like this.Even when the absolute value of tiltangle a during less than 0.09 °, as long as the absolute value of tiltangle a is greater than three times of tiltangle b absolute value, and the absolute value of tiltangle a is greater than 0.05 ° in addition, and then the standard deviation of p layer thickness is 0.03 μ m or littler.Otherwise the standard deviation of p layer thickness is greater than 0.03 μ m; Like this, good surface smoothness can not be obtained, and therefore high finished product rate can not be realized at growing surface.
Fig. 7 shows following content.Be less than or equal at the absolute value that adopts tiltangle a under the situation of substrate of processing of absolute value of tiltangle b, when the absolute value of tiltangle b is 0.2 ° or when bigger, the standard deviation of p layer thickness is 0.03 μ m or following, and, when the absolute value of tiltangle b during less than 0.2 °, the standard deviation of p layer thickness is greater than 0.03 μ m.That is, when the absolute value of tiltangle b is 0.2 ° or when bigger, the surface smoothness that can obtain at growing surface, and nitride semiconductor laser device can be with the high finished product rate manufacturing.
In by the method for giving the surface quality that big absolute value obtains for tiltangle b, adopt crystallographic direction＜0001〉and＜11-20 all with crystallographic direction＜1-100 be that rotating shaft rotates with θ b ° or the substrate 36 of the processing of inclination, crystallographic direction＜0001 like this〉about perpendicular to the direction at the top 33 of ridge 31 with θ b ° inclination.Like this, atom or molecule 15 are along migration of direction or diffusion or move to groove 32.Like this, as shown in Figure 8, the surface that is grown in the nitride semiconductor thin film on the substrate of handling 36 tilts.Fig. 8 shows and adopts surface level difference in height detector along crossing over the result who is grown in the nitride semiconductor thin film surface scan on the substrate of handling 36 perpendicular to the direction of groove 32 bearing of trends (be arranged essentially parallel to＜11-20〉direction).Nitride semiconductor thin film 32 surfaces that Fig. 8 shows on the top 33 that is formed on ridge 31 tilt along the direction that crystallographic direction tilts.Yet, the height of the core of ridge 31, the raising part that promptly forms the spine of nitride semiconductor laser device on it is uniformly basically, and the p layer thickness also is uniform.Like this, these can not cause problem in the manufacturing of nitride semiconductor laser device.Incidentally, adopting crystallographic direction＜0001〉and＜1-100〉all with crystallographic direction＜11-20〉be that rotating shaft rotates with θ a ° or during the substrate 16 of the processing of inclination, the atom of the source material of nitride semiconductor thin film or molecule 15 are hindered to be moved or is diffused in the groove 12, and like this, when nitride semiconductor thin film is grown on the substrate of handling 16 as mentioned above, the surface that is formed on the nitride semiconductor thin film on ridge 11 tops 13 does not tilt, but the surface is smooth.Like this, more preferably adopt crystallographic direction＜0001〉and＜1-100〉all with crystallographic direction＜11-20〉be the substrate 16 of rotating shaft with θ a ° ° of rotation or inclination.
The crystallographic direction of substrate by the situation of above-mentioned displacement vector C skew under, promptly, under the situation of crystallographic direction with tiltangle a and θ b inclination of substrate, when tiltangle a square with tiltangle b square root sum square be 0.2 ° or when above, the nitride semiconductor thin film that is grown on the substrate of handling has good surface smoothness.
Foregoing description relates to groove 12,32 or 42 along parallel or be basically parallel to＜1-100〉the direction situation of extending, but at groove 12,32 or 42 along parallel or be basically parallel to＜11-20 also can obtain confers similar advantages under the direction situation of extending.Even in the depressed area not only along parallel or be basically parallel to＜1-100 direction forms, as groove 12,32 or 42, and along parallel or be basically parallel to＜11-20〉direction forms, make channel shaped become under the situation of grid shape, also may on ridge, form nitride semiconductor thin film with good surface smoothness.In this case, tiltangle a and θ b preferably being set makes the atom of the source material be deposited on the nitride semiconductor thin film on the ridge or molecule along by the long limit diffusion of the separate ridge of groove or mobile.
The inclination angle of the crystallographic direction by changing substrate as mentioned above may obtain good surface smoothness on the nitride semiconductor thin film that grows on the ridge.
When the inclination of the crystallographic direction of above-mentioned substrate only comprises tiltangle a or θ b or comprises tiltangle a simultaneously and during θ b, even when each inclination angle all is set to less than 0.05 °, also be difficult to actually each substrate is all made the inclination angle that has less than 0.05 °.Usually, adopt cleavage (cleavage) to make the Laser emission end surfaces.Yet cleavage for example occurs in along perpendicular to the { { 11-20} or { in the 1-100} plane, and end surface tilts like this of the direction vector on 0001} plane.Like this, the inclination angle is set to 4 ° or abovely make that chip is difficult to split.Therefore, the preferred angled angle be the inclination angle of the crystallographic direction of substrate be 0.05 ° or more than, but at 4 ° or following.
Example 1
The actual example of first embodiment then, is described with reference to relevant drawings.Should be appreciated that though the example that proposes below relates to the nitride semiconductor laser device as the nitride compound semiconductor device example, the present invention is applicable to the nitride compound semiconductor device of any other type.Figure 11 A is the sectional view of the nitride semiconductor laser device of schematically illustrated example, and Figure 11 B is the vertical view of Figure 11 A.Fig. 9 B is the substrate 90 that is shown schematically in the processing before nitride semiconductor thin film growth thereon in the example of first embodiment, and Fig. 9 A is the vertical view of Fig. 9 B.In Fig. 9 A, 9B and 11A, 11B, in-plane illustrates together, and equals zero in the hypothesis inclination angle.On the substrate 90 of the processing shown in Fig. 9 A and the 9B, the nitride-based semiconductor multilayer film 4 of structure as shown in figure 20 for example is set, to make nitride semiconductor laser device as shown in figure 11.
At first, the substrate of handling 90 is made by the mode identical with the substrate 16,36 and 46 of above-mentioned processing.Yet what be used to make the substrate 90 handled herein is the substrate with-0.35 ° of tiltangle a and-0.02 ° of tiltangle b.Groove 91 is formed with the A/F W of 5 μ m, the cycle of 350 μ m between the degree of depth Y of 5 μ m and the adjacent trenches 91.
On the substrate 90 of the processing of so making,, be provided with the nitride-based semiconductor multilayer film 4 that constitutes by as shown in figure 20 a plurality of nitride semiconductor thin films by the conventional known technology of suitable use MOCVD for example.Herein, at first, n type GaN layer 200 is grown under than (that is the ratio of unit interval molal quantity supply flow velocity and the unit interval molal quantity supply flow velocity of the source material that comprises III family atom that, comprises the source material of V group atom) condition at the source material V/III of 1075 ℃ of growth temperatures and 1200.Then, under 1075 ℃ of growth temperatures, set gradually following layer: n type Al 0.05Ga 0.95First cover layer 201 of N, n type Al 0.08Ga 0.92Second cover layer 202 of N, n type Al 0.05Ga 0.95The 3rd cover layer 203 of N and n type GaN guide layer 204.Then atop, following layer sets gradually by its naming order: active layer 205, p type Al 0.3Ga 0.7The N evaporation prevents layer 206, p type GaN guide layer 207, p type Al 0.05Ga 0.95N cover layer 208 and p type GaN contact layer 209.Herein, active layer 205 is grown under about 800 ℃ of growth temperatures, and p type Al 0.3Ga 0.7The N evaporation prevents layer 206, p type GaN guide layer 207, p type Al 0.05Ga 0.95N cover layer 208 and p type GaN contact layer 209 are grown under about 1030 ℃ of growth temperatures.
Like this, on the substrate 90 of processing, the nitride-based semiconductor multilayer film 4 that comprises a plurality of nitride semiconductor thin films is set with groove formed thereon 91 and ridge 92.Herein, A/F of groove 91 etc. is not limited to the occurrence of above-mentioned proposition.Yet, if the A/F X of groove 91 less than 3 μ m, when nitride-based semiconductor multilayer film 4 formed, groove 91 was filled easily.This not only hinders the release of the strain that appears at nitride-based semiconductor multilayer film 4 inside, and causes atom or the molecular migration or the diffusion of the source material that is deposited on the nitride semiconductor thin film on the ridge 92 or move in the groove 91.Like this, the nitride-based semiconductor multilayer film 4 that is arranged on the ridge 92 has poor surface smoothness undesirably.Similarly, if the degree of depth Y of groove 91 less than 1.5 μ m, when nitride-based semiconductor multilayer film 4 formed, groove 91 was filled undesirably easily.Like this, the A/F X of preferred groove 91 be 3 μ m or more than, and the opening degree of depth Y of groove 91 be 1.5 μ m or more than.In addition, if be formed on the twice of total bed thickness of the nitride-based semiconductor multilayer film 4 on the substrate of handling 90 greater than groove 91 degree of depth Y, when nitride-based semiconductor multilayer film 4 was arranged on the substrate of handling 90, groove 91 was filled undesirably easily.Like this, the degree of depth Y of preferred groove 91 is greater than half of the gross thickness that is formed on the nitride-based semiconductor multilayer film 4 on the substrate of handling 90.
In addition, if along being basically parallel to＜11-20〉on the direction of direction, promptly along perpendicular to the bearing of trend of groove 91 and the width that is parallel to the ridge of being surveyed on the direction on ridge 92 surfaces between adjacent trenches 91 92 less than 100 μ m, the strain that then appears in the nitride-based semiconductor multilayer film 4 is not released, cause the generation of crackle, but also be difficult on ridge 92, make nitride semiconductor laser device.On the other hand, if the width of ridge 92 greater than 2000 μ m, they no longer prevent the generation of the crackle in nitride-based semiconductor multilayer film 4.Like this, the width of preferred ridge 92 is 100 μ m or above but at 2000 μ m or following.
In nitride-based semiconductor multilayer film 4, n type GaN layer 200 (seeing Figure 20) are compared easier migration or diffusion or mobile with AlGaN or other layers.Therefore, if the bed thickness of n type GaN layer 200 greater than 0.5 μ m, is grown in the n type GaN layer 200 easier inflow groove 91 on the ridge 92.And total bed thickness of nitride-based semiconductor multilayer film 4 is bigger subsequently, and groove 91 is filled by nitride-based semiconductor multilayer film 4 easily as a result.Like this, preferably the bed thickness of n type GaN layer 200 is 0.5 μ m or following.Consider migration, the bed thickness of preferred n type GaN layer 200 is 0 μ m, that is, growth is from n type Al 0.05Ga 0.95201 beginnings of N first cover layer.
Have been found that, when the nitride-based semiconductor multilayer film of being made up of a plurality of nitride semiconductor thin films 4 was set, the atom of the source material of nitride semiconductor thin film or molecular migration or diffusion or mobile difficulty or ease were grown residing growth conditions along with each nitride semiconductor thin film and are changed.For the good evenness on the surface that obtains to be grown in the nitride-based semiconductor multilayer film 4 on the ridge 92, each nitride semiconductor thin film need be grown under the condition of the migration of the atom of the source material that prevents nitride semiconductor thin film or molecule.Preferably as this growth conditions be that the surface temperature of the substrate handled is 1050 ℃ or following, and V/III than (ratio of mole supply flow velocity and the mole supply flow velocity of the unit interval of the source material that comprises III family atom of unit interval that comprises the source material of V group atom) be 2250 or more than.
Measured the surface smoothness on surface of the substrate 90 of above-mentioned processing with formation nitride-based semiconductor multilayer film 4 thereon.Along being arranged essentially parallel to＜1-100〉direction is promptly shown in Figure 10 along the measurement result of the measured surface smoothness of the direction that is parallel to groove 91 bearing of trends.Measurement is that the core at ridge 92 carries out.Herein, as what will from the chart of Figure 10, understand, in 600 measured μ m width regions scopes, the highest and difference in level lowermost portion on surface be about 20nm, and so with have the wafer at zero (0.02 ° or littler) inclination angle almost by use at the substrate of handling 6 to make then that the measurement result (300nm) that obtains under the situation of growing nitride semiconductor multi layer film 4 thereon compares be very little.Like this, obtained good surface smoothness.
In addition, by on the substrate of handling 90, forming nitride-based semiconductor multilayer film 4 as mentioned above, made the nitride semiconductor laser device shown in Figure 11 A and the 11B.The SiO that is used for electric current restriction (current constriction) that this nitride semiconductor laser device has as the laser strip 93 of laser waveguide and is arranged to laser strip 93 is clipped in the middle 2Film 94, they are located on the surface of formed nitride-based semiconductor multilayer film 4 on the ridge 92 of the substrate of handling 90, and the substrate 90 of wherein this processing has groove formed thereon 91.Then, at laser strip 93 and SiO 2On the surface of film 94, form p lateral electrode 95, and on the basal surface of the substrate of handling 90, form n type electrode 96.Be formed on the p lateral electrode 95 lip-deep raised portions that are located immediately on the laser strip 93 and be called striped 97.
Nitride semiconductor laser device with ridge structure similar to the above can suitably use conventional known technology make by nitride-based semiconductor multilayer film 4 at first is set on the substrate of handling 90 then, therefore will not provide the detailed description of its manufacture method etc.Then, a plurality of nitride semiconductor laser devices of so making by on the substrate of handling 90 (wafer) nitride-based semiconductor multilayer film 4 being set can be divided into individual devices.Herein, at first, the substrate 90 that a part was handled is removed and makes wafer have about 100 μ m thickness.Then, as n type electrode 96, on substrate 90 basal surfaces of handling, the Hf/Al layer forms by this preface from substrate 90 1 sides of handling.Then, wafer is by along being basically parallel to＜11-20〉direction promptly perpendicular to groove 91 bearing of trends and the direction cleavage that is parallel to ridge 92 surfaces to form resonator surface.Like this, make each and all be provided with bar (bar) (not shown) of a plurality of nitride semiconductor laser devices.In this example, the cleavage surface of nitride-based semiconductor is { 11-20} plane, and tilt with θ a ° of inclination angle.This causes that wafer will be difficult to cleavage and the worry of the cleaved surface that is difficult to obtain.Yet actual proof as long as the inclination angle is 4 ° or following, just can obtain to be enough to be used as the cleaved surface of nitride semiconductor laser device cleavage surface.Herein, the cavity length of preferred nitride semiconductor laser device is 300 μ m or above but at 1200 μ m or following.In this example, cavity length is 600 μ m.In addition, on the resonator surface that forms by the cleavage wafer as mentioned above, SiO 2And TiO 2Dielectric film by electron beam deposition etc. alternately vapor deposition to form the dielectric multilayer film.The material of these dielectric multilayer films is not limited to SiO 2/ TiO 2, but can be SiO 2/ Al 2O 3Deng.The material of n type electrode 96 is not limited to that mask body is mentioned on those, but can be Hf/Al/Mo/Au, Hf/Al/Pt/Au, Hf/Al/W/Au, Hf/Au, Hf/Mo/Au etc.
With similar nitride semiconductor laser device shown in Figure 11 in, p lateral electrode 95 is formed by for example Mo/Au or Mo/Pt/Au from nitride-based semiconductor multilayer film 4 one sides, is perhaps formed by individual layer Au.In this example, SiO 2Film 94 usefulness act on the insulating barrier of electric current restriction; Replace ground, the insulating material that can adopt any other is ZrO, TiO for example 2Or Si 3N 4
The bar of so making is divided into chip to obtain single nitride semiconductor laser device then.Because this cuts apart by conventional known technology and is undertaken, therefore will not provide its detailed description.
In the nitride semiconductor laser device of so making, do not observe the generation of crackle.In addition, from a plurality of nitride semiconductor laser devices of this example of making, randomly draw 100 nitride semiconductor laser devices, and measured their FFP (far field pattern along level and vertical direction, far-fieldpattem) FWHM (half maximum overall with, full width at half maximum).Herein, its actual FFP FWHM design load ± to be can be regarded as is flawless for the nitride semiconductor laser device of 1 degree scope.The result is the requirement that 94 nitride semiconductor laser devices satisfy the FWHM of its FFP, has shown very high rate of finished products.
As mentioned above, form nitride-based semiconductor multilayer film 4 by a plurality of nitride semiconductor thin films of growth on the substrate 90 of processing with θ a and θ b inclination angle, may reduce the variation of p layer thickness and therefore on nitride semiconductor thin film, obtain good evenness, also may suppress the generation of crackle and the nitride semiconductor laser device that therefore has desirable characteristics with the high finished product rate manufacturing.
Example 2
In this example, the substrate of handling is with the method manufacturing identical with example 1.Difference is: the substrate that is used to make the substrate of handling has the tiltangle b of-0.05 tiltangle a and-0.39 °; The A/F of groove is 80 μ m; And the spacing between the adjacent trenches is 300 μ m.In other respects, nitride semiconductor laser device is made in the mode identical with example 1.
In this example, as example 1, be arranged on the substrate of handling at nitride-based semiconductor multilayer film 4 after, measured the surface smoothness on the surface of the nitride-based semiconductor multilayer film 4 that is formed on the ridge.In 600 measured μ m width regions, the difference in level between the highest and lowermost portion on surface is 24nm, and has obtained good surface smoothness like this.
In addition, from a plurality of nitride semiconductor laser devices that this example is made, randomly draw 100 nitride semiconductor laser devices, and measured their FWHM (half maximum overall with) along the FFP (far field pattern) of level and vertical direction.Herein, its actual FFP FWHM design load ± to be can be regarded as is flawless for the nitride semiconductor laser device of 1 degree scope.The result is the requirement that 91 nitride semiconductor laser devices satisfy the FWHM of its FFP, has shown very high rate of finished products.
Example 3
In this example, the substrate of handling is with the method manufacturing identical with example 1.Difference is: the substrate that is used to make the substrate of handling has 0.21 ° tiltangle a and-0.21 ° tiltangle b.In other respects, nitride semiconductor laser device is made in the mode identical with example 1.
In this example, as example 1, be arranged on the substrate of handling at nitride-based semiconductor multilayer film 4 after, measured the surface smoothness on the surface of the nitride-based semiconductor multilayer film 4 that is formed on the ridge.In 600 measured μ m width regions, the difference in level between the highest and lowermost portion on surface is 10nm, thereby has obtained good surface smoothness.
In addition, from a plurality of nitride semiconductor laser devices that this example is made, randomly draw 100 nitride semiconductor laser devices, and measured their FWHM (half maximum overall with) along the FFP (far field pattern) of level and vertical direction.Herein, its actual FFP FWHM design load ± to be can be regarded as is flawless for the nitride semiconductor laser device of 1 degree scope.The result is the requirement that 97 nitride semiconductor laser devices satisfy the FWHM of its FFP, has shown very high rate of finished products.
Example 4
In this example, the substrate of handling is with the method manufacturing identical with example 1.Difference is: the substrate that is used to make the substrate of handling has 0.10 ° tiltangle a and-0.02 ° tiltangle b; In each layer that constitutes nitride-based semiconductor multilayer film 4, n type GaN layer 200, n type Al 0.05Ga 0.95N first cover layer 201, n type Al 0.08Ga 0.92N second cover layer 202, n type Al 0.05Ga 0.95N the 3rd cover layer 203 and n type GaN guide layer 204 are grown under 1030 ℃ growth temperature; And n type GaN layer 200 and n type GaN guide layer 204 at the V/III of source material than being to grow under 4500 the condition.In other respects, nitride semiconductor laser device is made in the mode identical with example 1.
In this example, as example 1, be arranged on the substrate of handling at nitride-based semiconductor multilayer film 4 after, measured the surface smoothness on the surface of the nitride-based semiconductor multilayer film 4 that is formed on the ridge.In the wide zone of 600 measured μ m, the difference in level between the highest and lowermost portion on surface is 28nm, and has obtained good surface smoothness like this.
In addition, from a plurality of nitride semiconductor laser devices that this example is made, randomly draw 100 nitride semiconductor laser devices, and measured them along the FWHM (half maximum overall with) of level with vertical reverse FFP (far field pattern).Herein, its actual FFP FWHM design load ± to be can be regarded as is flawless for the nitride semiconductor laser device of 1 degree scope.The result is the requirement that 90 nitride semiconductor laser devices satisfy the FWHM of its FFP, has shown very high rate of finished products.
As mentioned above, in this example, the inclination angle of substrate little than in the example 1 to 3.Yet, in each layer that constitutes nitride-based semiconductor multilayer film 4, n type GaN layer 200, n type Al 0.05Ga 0.95N first cover layer 201, n type Al 0.08Ga 0.92N second cover layer 202, n type Al 0.05Ga 0.95N the 3rd cover layer 203 and n type GaN guide layer 204 are grown under the condition that hinders migration.This helps to have with the high finished product rate manufacturing nitride semiconductor laser device of desirable characteristics.
Second embodiment
The formation of groove
Figure 12 A is the perspective view of part of the groove of schematically illustrated substrate around the processing with setting nitride-based semiconductor multilayer film thereon, and Figure 12 B is the sectional view of being got along the line A-A shown in Figure 12 A.The substrate that reference number 120 expressions were handled, reference number 121 expression nitride-based semiconductor multilayer films, and reference number 122 expression grooves.
In this embodiment, adopting the surface is the nitride-based semiconductor substrate on C plane (0001).At first, on the whole surface of nitride-based semiconductor substrate, SiO 2Vapor deposition is the thickness with 1 μ m by sputter Deng (not shown).SiO 2Deng film can for example electron beam vapor deposition or plasma CVD form by additive method.
Then, by common photoetching process, resist is set to have along [1-100] direction the marking shape window and the pattern in 250 μ m cycles (representing with T) of 5 μ m width (representing with W) in Figure 12 in Figure 12 B.This period T depends on the width of semiconductor laser chip; Particularly, when chip had 200 μ m width, period T was made as 200 μ m.Then, by ICP (inductive couple plasma, inductively coupled plasma), RIE (reactive ion etching, reactive ion etching) etc., SiO 2Thereby etchedly expose the surface of nitride-based semiconductor substrate, and therefore be formed on the nitride-based semiconductor substrate, forming the SiO of groove with 5 μ m width 2Mask.Then, the nitride-based semiconductor substrate is etched to form groove 122.Like this, the nitride-based semiconductor substrate with formation groove thereon is called as the substrate of handling 120.
The degree of depth of groove 122 (representing with D in Figure 12 B) is for example 5 μ m.Herein, the depth D of preferred groove 122 is 2 μ m or above but at 20 μ m or following.If depth D is less than 2 μ m, groove 122 may be filled by nitride-based semiconductor multilayer film 121.If groove 122 is filled, crackle may produce, and bed thickness may become inhomogeneous in the surface, and produces other problems.Yet, if total the bed thickness of nitride-based semiconductor multilayer film 121 is 4 μ m or following, as long as the depth D that comprises two ends from 1 μ m in 2 mu m ranges, just may prevent crackle and keep smooth.On the other hand, if depth D can have problems in photoetching and glossing greater than 20 μ m.For example, in photoetching process, thickness at the substrate 120 lip-deep resists of handling tends to inhomogeneous, and resist can not kept by abundant exposure place like this, on the other hand, in glossing, when wafer is that chip is cut apart and prepared polishedly when to come attenuate be about 100 μ m, wafer may break.
The width W of preferred groove 122 be 1 μ m or more than.If width W is less than 1 μ m, when 121 growths of nitride-based semiconductor multilayer film, groove 122 is by complete filling.This is because the nitride-based semiconductor multilayer film 121 of growing from groove 122 two edges forms bridge on the groove top, and joins on groove 122.When groove 122 was filled, crackle may produce, and bed thickness may become and owe evenly in the surface, and produced other problems.
Herein, groove 122 to be different from fully in order reducing and to expand to the defect concentration of crystal growth film from the surface and utilize laterally (level) growth effects to form the technology of groove at substrate.In cross growth, in order to obtain the horizontal growth effect, groove forms with the spacing of the thickness of the layer that is approximately equal to or less than formation usually, even and at groove under the situation of groove pitch maximum, form with the spacing that is three times in this thickness approximately.
As a comparison, in this embodiment, groove 122 is not to form for above-mentioned purpose, but in order to prevent the purpose of crackle.Spacing herein is in identical magnitude with the width of nitride semiconductor laser device, and particularly, minimum is about 0.1mm.In addition, form groove 22 simply and cause significantly reduced evenness.Like this, preferred distance (cycle) is 4mm or littler.If spacing (cycle), can not discharge the strain that lattice strain in the present film and thermal expansion coefficient difference cause effectively greater than 4mm, therefore crack.Like this, the spacing (cycle) of preferred groove 122 is 0.1mm or bigger but at 4mm or following.
Then, after etching, SiO 2Removed fully by for example etchant of HF, to finish the substrate processing before 121 growths of nitride-based semiconductor multilayer film.
In the foregoing description, come etching SiO by vapor phase etchant 2With the nitride-based semiconductor substrate; As selection, they can the etching with the etchant that is in liquid phase.Adopting etched groove to form can at first carry out after growing nitride semiconductor layer GaN, InGaN, AlGaN, the InAlGaN etc.That is, also growing nitride semiconductor layer at first forms groove 122 then, and the growing nitride semiconductor multi layer film 121 then.
Under the situation that adopts nitride-based semiconductor substrate substrate (for example sapphire, SiC, Si or GaAs substrate) in addition, at first form nitride semiconductor layers such as GaN, InGaN, AlGaN, InAlGaN, the growing nitride semiconductor multi layer film 121 then.
The epitaxial growth of nitride-based semiconductor multilayer film
Figure 13 A is the front view of nitride compound semiconductor device, and Figure 13 B is the vertical view of Figure 13 A.Figure 14 is the sectional view of part B shown in Figure 13.Now, with reference to Figure 14, will describe nitride compound semiconductor device and how to make.
At first, on the MOCVD machine, use NH 3As group V source material and TMGa (trimethyl gallium) or TEGa (triethyl-gallium) as III clan source material, silane (SiH 4) as making an addition to wherein doped source material, under 1100 ℃ of underlayer temperatures, the initial GaN layer 123 of n type with 0.2 μ m thickness is formed on the substrate of handling 120.Initial GaN layer 123 is examples of nitride-based semiconductor initiation layer; Replace ground, can adopt any other nitride-based semiconductor initiation layer, for example AlGaN, AlInGaN, AlGaNP or AlGaNAs.
Then, under 1050 ℃ of underlayer temperatures, by using group V source material for example TMAl (trimethyl aluminium) or TEAl (triethyl aluminum), the three layers of n type cover layer of growing, it comprises from initial GaN layer 123 1 side: the n type Al with 2.3 μ m bed thickness 0.05Ga 0.95 N cover layer 124, has the n type Al of 0.2 μ m bed thickness 0.08Ga 0.92 N cover layer 125 and n type Al with 1.0 μ m bed thickness 0.05Ga 0.95N cover layer 126.As n type impurity, added 5 * 10 17To 1 * 10 19/ cm 3Silicon.
Then, n type GaN photoconductive layer (has 1 * 10 16To 1 * 10 18/ cm 3The Si impurity concentration) 127 grow into and have 0.2 μ m thickness.
Then, underlayer temperature is reduced to 800 ℃, and comprises the In that all has 4nm thickness in three cycles by following order growth 0.1Ga 0.9N trap layer and the In that all has 8nm thickness 0.01Ga 0.99The active layer (having multi-quantum pit structure) 128 of N barrier layer combination: barrier layer, trap layer, barrier layer, trap layer, barrier layer, trap layer and barrier layer.Preferably between barrier layer and the trap layer or growth interruption between trap layer and the barrier layer 1 second or above but 180 seconds or below because do the evenness that helps to improve each layer like this and therefore reduce light emission FWHM.Can avoid adding SiH arbitrarily herein, 4To barrier layer or barrier layer and trap layer.
Add under the situation of active layer 128 AsH at As 3(arsine) or TBAs (tributyl arsenic) are as source material.Add under the situation of active layer 128 PH at P 3(hydrogen phosphide) or TBP (tributyl phosphorus) are as source material.Add at Sb under the situation of active layer 128, TMSb (trimethylantimony) or TESb (antimony triethyl) are as source material.When active layer 128 forms,, replace NH as the source material of N 3, can adopt any other source material, for example N 2H 4(hydrazine, hydrazine), C 2N 2H 8(Dimethylhydrazine, dimethylhydrazine) or any other contain the source material of N.
Then, underlayer temperature is elevated to 1000 ℃, and the growth successively of following layer: the p type Al with 0.02 μ m thickness 0.2Ga 0.8N charge carrier barrier layer 129, have 0.02 μ m thickness p type GaN photoconductive layer 130, have the p type Al of 5 μ m thickness 0.05Ga 0.95 N cover layer 131 and p type GaN contact layer 132 with 0.1 μ m thickness.As the source material that is used for p type impurity, adopt EtCP 2(diethyl cyclopentadienyl group magnesium, bisethylcyclopentadienylmagnesium), and Mg is with 1 * 10 for Mg 18To 2 * 10 20/ cm 3Concentration add.Preferred p type GaN contact layer 132 has more and more higher p type impurity concentration towards p electrode 133.This helps to reduce the contact resistance that is caused by p electrode 133.In order to remove the remaining hydrogen in p type layer of the activation that hinders the Mg that is used as p type impurity, in the growth of p type layer, can mix the oxygen of trace.
The thickness sum of each nitride-based semiconductor multilayer film 121 of Zhi Zaoing is about 3.58 μ m as mentioned above.Nitride-based semiconductor multilayer film 121 is by initial GaN layer 123, n type Al 0.05Ga 0.95 N cover layer 124, n type Al 0.08Ga 0.92 N cover layer 125, n type Al 0.05Ga 0.95 N cover layer 126, n type GaN photoconductive layer 127, active layer 128, p type Al 0.2Ga 0.8N charge carrier barrier layer 129, p type GaN photoconductive layer 130, p type Al 0.05Ga 0.95 N cover layer 131 and p type GaN contact layer 132 are formed.
After 132 growths of p type GaN contact layer, all gas in the reactor of MOCVD machine is by nitrogen carrier gas and NH 3Replace, and temperature is with the speed reduction of 60 ℃/min.When underlayer temperature becomes when equaling 80 ℃ NH 3Supply stop, this underlayer temperature kept 5 minutes then, underlayer temperature is reduced to room temperature then.Herein, the temperature that preferred substrate kept between 650 ℃ to 900 ℃, and the time that keeps in this temperature place be 3 minutes or above but at 10 minutes or following.In addition, the speed that reduces of preferred temperature be 30 ℃/min or more than.
As above the nitride-based semiconductor multilayer film 121 of manufacturing is measured by Raman (Raman) and is estimated.The result is after wafer takes out from the MOCVD machine, even without the annealing of carrying out the p typeization, still to have observed p type feature (Mg has been activated) at once after growth.In addition, because the contact resistance that formation caused of p electrode 133 is lower.Said method can combine with the annealing of conventional p typeization to realize higher Mg activation rate.
In the above-described embodiments, active layer 128 is made by structure like this and begins and finish with barrier layer with barrier layer; Replace ground, it also can be made by structure like this and begin and finish with the trap layer with the trap layer.The number of trap layer is not limited to three of above-mentioned concrete proposition, but can for ten or below because they provide low thresholding current density and can be in the room temperature persistent oscillation in this case.The special preferable range of trap number of layers is from two to six, because this moment, they provided low especially thresholding current density.Above-mentioned active layer 128 can comprise Al extraly.Do not add the trap layer and the barrier layer 128 of composition active layer herein, to as the Si of impurity; Yet, can add impurity.For example adding, the impurity of Si tends to improve the light emission density to active layer 128.Except Si, such impurity comprises O, C, Ge, Zn and Mg, and these can use separately or two or more being used in combination wherein.The total amount of the preferred impurity that adds is about 1 * 10 17To 8 * 10 18/ cm 3Impurity can add trap layer and barrier layer to or only add trap layer or barrier layer to.
P type Al 0.2Ga 0.8N charge carrier barrier layer 129 can have any other component except above-mentioned concrete proposition.Even have p typeization (p-typification) also take place when the AlGaN that makes an addition to In wherein grows at low temperatures.This helps to reduce the damage that active layer 128 is subjected in crystal growing process, be preferred therefore.Charge carrier barrier layer 129 can be omitted itself, then helps low thresholding current density but it is set.This is because charge carrier barrier layer 129 is used for sealing the charge carrier of active layer 128.P type Al 0.2Ga 0.8Al component in the N charge carrier barrier layer 129 is high more, just has highdensity more charge carrier to be sealed, and is therefore just better.On the other hand, preferably reduce the Al component,,, therefore help to reduce resistance there because do the carrier mobility that helps to improve in charge carrier barrier layer 129 like this as long as can keep charge carrier to be sealed (enclosure).
In the above-described embodiments, n type cover layer 124 to 126 and p type cover layer 131 each all be by Al 0.05Ga 0.95N or Al 0.08Ga 0.92The N crystal forms.Replace ground, can adopt the AlGaN crystal of the Al component that has except 0.05 or 0.08.Al component in these layers is high more, and the difference of their energy gap and refractive index and active layer 128 is just big more.This helps to seal effectively charge carrier and light in (enclose) active layer 128, and helps to reduce the thresholding current density of laser generation.On the other hand, as long as keep charge carrier and light to be sealed, minimizing Al component helps to improve the carrier mobility in cover layer 124 to 126, and helps to reduce the operating voltage of device.
In the above-described embodiments, n type AlGaN cover layer 124 has three-decker to 126.It is unimodal that this allows the vertical transverse pattern to have, and improved photoresistance every efficient, and helped to improve the optical characteristics of laser and reduce laser thresholding current density.The tectal number of n type AlGaN can be other numbers beyond three; That is, can adopt one or more and do not cause any problem.In the foregoing description, cover layer is formed by the element mixed crystal, i.e. AlGaN; Replace ground, can adopt quaternary plain mixed crystal, for example AlInGaN, AlGaNP or AlGaNAs.For low resistance, p type cover layer 130 can have the superlattice structure that comprises p type AlGaN layer and p type GaN layer, perhaps comprises the superlattice layer of p type AlGaN layer and p type AlGaN layer, perhaps comprises the superlattice structure of p type AlGaN and p type InGaN layer.
The characteristic of nitride-based semiconductor multilayer film
In the nitride-based semiconductor multilayer film 121 of present embodiment manufacturing, do not observe crackle.In addition, the surface smoothness in the surface detects on the meter (touch-probe-typelevel difference tester) in touch probe type difference in level and measures.Figure 15 shows the measurement result of nitride-based semiconductor multilayer film 121 at the surface smoothness of [1-100] direction.The result shows that in 600 measured mu m ranges, surface roughness (Ra) is 100
Figure C200510119342D0012093603QIETU
Or below, and show the flat surface that has obtained to have very little surface irregularity.Also in the whole surperficial detailed measurements of substrate Ra, and the result shows and has obtained flat surface.
In addition, under SEM (scanning electron microscopy), measured the distribution of each layer thickness in substrate surface of nitride-based semiconductor multilayer film 121.The result shows, shows that the numerical value of standard deviation of intensity of variation is little of being 5% to the maximum.That is, the thickness of each layer of discovery multilayer film is uniform.
The device division process
Then, the wafer with the nitride-based semiconductor multilayer film 121 that is arranged on the ridge 12 is taken out from the MOCVD machine is the technology description of nitride compound semiconductor device chip then with processing of wafers with providing.
At first, form the vallum line part 134 of serving as the laser wave guide zone.This is by the centre from the epitaxial wafer face side to p type cover layer 131 or bottom and the etching epitaxial wafer makes remaining stripe-shaped part form.Herein, width of fringe is 1 to 3 μ m and preferred 1.3 to 2 μ m.Then, dielectric film 135 is formed on vallum line part 134 place in addition.Herein, dielectric film 135 can be formed by AlGaN.Because the not etched part of maintenance of p shape GaN contact layer 132 exposes,, form p electrode 133 by vapor deposition Pd/Mo/Au successively on this part and on dielectric film 135.
Herein, dielectric film 135 can by except above-mentioned specifically mention material form for example oxide or the nitride of titanium, zirconium, tantalum, aluminium etc.P electrode (216) can be formed by Pd/Pt/Au, Pd/Au or Ni/Au with replacing.
In addition, the basal surface of epitaxial wafer (surface of nitride-based semiconductor substrate) is polished so that wafer is that 80 to 200 μ m are thick, thereby is beneficial to cutting apart of the wafer that carries out later.N electrode 136 forms by set gradually Hf/Al on basal surface 120.N electrode 136 can replace by Hf/Al/Mo/Au, Hf/Al/Pt/Au, Hf/Al/W/Au, Hf/Au, Hf/Mo/Au or these one of in replace the improvement combination of Hf with Ti or Zr.
At last, epitaxial wafer is along Fa Buli-Bo Luo (the Fabry-P é rot) resonant cavity that is had 600 μ m cavity lengths perpendicular to the direction of vallum line direction by cleavage with generation.Preferred cavity length is that 250 μ m are to 1000 μ m.By this technology, wafer is divided into bar, every nitride compound semiconductor device array that links together that all has horizontal expansion.Having edge＜1-100〉resonator surface of the nitride compound semiconductor device of the vallum line part 134 that forms of direction is nitride semiconductor crystal { 1-100} planes.Be substituted in the end face feedback, can adopt by being arranged on inner refraction grating (diffraction gratings) and realize the DFB (distributed Feedback) of feedback, perhaps realize the DBR (distributed Bragg reflector) of feedback by being arranged on outside refraction grating.
After the resonator surface of Fabry-P é rot forms, has the SiO of about 80% reflectivity 2And TiO 2Dielectric film replace vapor deposition at these end faces to form dielectric multilayer reflectance coating (not shown).The dielectric multilayer reflectance coating can be formed by any other dielectric substance.After this, bar is divided into single device to obtain nitride compound semiconductor device shown in Figure 13.This device has setting laser wave guide zone (vallum line part 134) therebetween, and has the transverse width of 250 μ m.
The characteristic of nitride compound semiconductor device
In whole experiment, the confirmation nitride compound semiconductor device was realized 5000 hours or the above laser generation life-span under the condition below: oscillation wavelength 405 ± 2nm; Laser output 60mW; 70 ℃ of ambient temperatures.In addition, obtained to have the flat surfaces of little surface irregularity, and each layer thickness of nitride-based semiconductor multilayer film 121 is highly uniform in substrate surface.Like this, in each device, have the variation of very little characteristic, thereby high reliability is provided.As a result, reduced number, improved rate of finished products with the device that does not satisfy zero defect requirement on devices characteristic.
Relation between surface smoothness and crackle produce
Now, observed relation between surface smoothness and crackle produce when initial GaN layer 123 changes with the depth D of groove 122 and width W will be provided.Figure 16 shows the measurement result of the surface roughness of the nitride-based semiconductor multilayer film 121 that the thickness when initial GaN layer 123 observes when 0 changes to 2.0 μ m.
In the whole experiment of formerly carrying out, the scope of the surface roughness that known variation for device property and device lifetime allows is 300
Figure C200510119342D0012093603QIETU
Or below.This thickness 300
Figure C200510119342D0012093603QIETU
Be equivalent to about 5% of when p type layer has 0.62 μ m thickness device gross thickness.In addition, if surface roughness is 5%, show that comparable (comparable) variation is present in (thickness of p type layer) in each layer thickness herein.The variation of p type layer thickness influences laser characteristics most.When the vallum line part 134 as current confinement structure formed, the wide part of 2 μ m of p layer was remained as vallum line part 134, and remainder is by by for example ICP and etching of vapor phase etchant.Because known appreciable impact laser characteristics is the height of vallum line part 134, i.e. distance from active layer 128 to etched district, if p type layer thickness diverse location place in substrate surface changes, laser characteristics is along with variation.Like this, big surface roughness not only causes low rate of finished products, and influences device lifetime unfriendly.
It is 0.5 μ m or when following, surface roughness is 300 that Figure 16 illustrates thickness when initial GaN layer 123
Figure C200510119342D0012093603QIETU
Or below.Like this, preferably using the thickness of initial GaN layer 123 in this embodiment is 0.5 μ m or following.Under the situation of GaN beyond nitride-based semiconductor multilayer film 121 comprises initial GaN layer 123, preferably the gross thickness of the GaN layer in nitride-based semiconductor multilayer film 121 be nitride-based semiconductor multilayer film 121 total bed thickness 15% or below.
Like this, carried out studying fully, caused big surface roughness as shown in figure 16 what to be found to be when the thickness of initial GaN layer 123 during greater than 0.5mm, in other words, the big layer thickness distribution of appearance in the surface.By this research, each layer thickness variation of finding nitride-based semiconductor multilayer film 121 is because when 121 epitaxial growths of nitride-based semiconductor multilayer film, and initial GaN layer 123 is subjected to its influence.
Figure 17 A is the sectional view of substrate 120 that has the processing of the nitride-based semiconductor multilayer film 121 with good evenness, and Figure 17 B is the sectional view of substrate 120 that has the processing of the nitride-based semiconductor multilayer film 121 with poor evenness.Now, provide the detailed description of growth mechanism model of the varied in thickness of each layer that produces nitride-based semiconductor multilayer film 121 with reference to Figure 12 and 17A, 17B.
Find when during less than 60 °, occurring the variation of each layer thickness of big nitride-based semiconductor multilayer film 121 at the line [0001] on groove shown in Figure 12 122 surface 137 in addition and perpendicular to the angle θ between the line R at the sidewall surfaces 122a on groove 122 tops perpendicular to nitride-based semiconductor multilayer film 121.In this case, shown in Figure 17 B, nitride-based semiconductor multilayer film 121 flows into groove 122.This inflow takes place is because when 121 epitaxial growths of nitride-based semiconductor multilayer film, arrived the source material (mainly being Ga) on surface 137 thus promote to flow into groove 122 by surface migration.
As shown in figure 21, when the thickness of initial GaN layer 123 was 1.0 μ m, the surface smoothness of nitride-based semiconductor multilayer film 121 was such: its highest and difference in level lowermost portion is 300nm, demonstrates the surface and has big surface irregularity.
In addition, the variation of the bed thickness of nitride-based semiconductor multilayer film 121 is estimated on reflection thickness detector in substrate surface.Herein, the reflection peak profile that obtains from reflection thickness detector has been carried out fast fourier transform processing (FFT), and, estimated the p type layer thickness profile in substrate surface based on the reflection peak at interface between p type charge carrier barrier layer 129 that has refringence maximum among each layer therebetween and the p type GaN photoconductive layer 130.Herein, the thickness of p layer is represented following three layers gross thickness: p type GaN photoconductive layer 130, p type AlGaN cover layer 131 and p type GaN contact layer 132.Found that, when the thickness of initial GaN layer 123 is 0.5 μ m or when bigger, the intensity of variation of layer thickness (standard deviation) is 5% or bigger in substrate surface.
In addition, under SEM, observed growth in groove 122 in detail.Observed with reference to Figure 12 and 18 detailed descriptions below.Figure 18 has wherein the sectional view of substrate of processing that initial GaN layer 123 has the nitride-based semiconductor multilayer film 121 of 0.5 μ m or following thickness.Figure 18 shows when initial GaN layer 123 has 0.5 μ m or following thickness, compares the big H of thickness of the flat region E on surface 137 at the thickness of groove 122 upper ends.Thickness difference H is 0.2 to 1.5 μ m.
In addition, in this case, perpendicular to the line [0001] on nitride-based semiconductor multilayer film 121 shown in Figure 12 surface 137 except groove 122 and perpendicular to the angle θ between the line R of the sidewall surfaces 122a on groove 122 tops greater than 60 °.Having angle θ equals 60 ° surface and is considered to the plane corresponding to (11-22).In this embodiment, angle θ is 80 °.Angle θ should be greater than 60 °, and preferred 80 ° or more than.This be because, angle θ is more greater than 60 °, (11-22) plane that takes place easily it on to flow into is not easy appearance more.
Growth model
Based on given result so far, the description of the growth pattern model of the substrate 120 that uses the processing with groove formed thereon 122 will be provided.When the supply of source material gas began and grows beginning, the Ga source material arrived the surface.Then, Ga moves (diffusion into the surface) from the teeth outwards, and when it arrived the position of energy stabilization, its tunicle absorbed.Along with the repetition of this process, film is grown gradually.Simultaneously, become 0.5 μ m or when above, shown in Figure 17 B, the Ga atom is 122 migrations from surface 137 towards groove when the thickness of initial GaN layer 123.In this inflow process, because a variety of causes inhomogeneities in the groove forming process for example, the Ga atom is extremely uneven along the inflow of [11-22] direction.Like this, although in some zones, flow into, be not easy to flow in other zones.
Flow into the place that groove 122 takes place, surface 137 is because the former thereby attenuation relevant with source material efficient.Incident place is not allowed in inflow, surperficial 137 thickenings.Like this, the evenness that has caused difference.Therefore, flow into the evenness that may obtain by suppressing this.A kind of growing method that suppress to flow into be on groove 122 tops to be higher than other local growth rates initial GaN layer 123 of growing, make to form to prevent that the Ga source material from flowing into the barrier rib (the thickness difference H among Figure 18) of groove 122.This evenly is effective for making bed thickness.As discussed previously, when having 0.5 μ m or following bed thickness, initial GaN layer 123 forms such barrier rib.
In addition, as discussed previously, the spacing between the preferred groove 122 is 0.1mm or above but be 4mm or following.The bed thickness of preferred initial GaN layer 123 is 0.5 μ m or following.The bed thickness of preferred initial GaN layer 123 be nitride-based semiconductor multilayer film 121 total bed thickness 15% or below.Angle θ should be greater than 60 °, preferred 80 ° or more than.The depth D of preferred groove 122 is 2 μ m or above but be 20 μ m or following, and the width W of groove 122 be 1 μ m or more than.
Nitride compound semiconductor device according to the present invention has been found to use widely in Laser Devices, light emitting devices, light receiving element etc., and therefore can be suitable for use in optical disc storage/reproducer, laser printer, bar code reader, projecting apparatus, the display device etc.

Claims (1)

1, a kind of nitride compound semiconductor device comprises:
The substrate of handling, form on the surface by the nitride-based semiconductor substrate that forms by nitride-based semiconductor at least one surface as the groove of at least one depressed area and as the spine of non-groove form and
The nitride semiconductor growing layer comprises a plurality of nitride semiconductor thin films on the substrate that is grown in described processing,
The primary flat direction of set described nitride semiconductor growing layer with the 0001} planar alignment,
Inclination angle wherein, promptly first vector that extends from the surface portion of spine along perpendicular direction be parallel to crystallographic direction＜0001 angulation between second vector that extends, when supposing that described first vector and described second vector start from same point, be more than 0.05 ° but below 4 °
The inclination angle of the substrate of wherein said processing comprises:
First inclination angle, its for described second vector with by described first vector is projected to by the crystallographic direction that is perpendicular to one another＜0001, crystallographic direction＜11-20 and crystallographic direction＜1-100 in crystallographic direction＜0001 and crystallographic direction＜1-100 between the 3rd vector that obtains on formed first plane, when supposing that described second vector and described the 3rd vector start from same point angulation and
Second inclination angle, its for described second vector with by described first vector is projected to by the crystallographic direction that is perpendicular to one another＜0001, crystallographic direction＜11-20 and crystallographic direction＜1-100 in crystallographic direction＜0001 and crystallographic direction＜11-20 angulation between the four-vector that obtains on formed second plane, when supposing that described second vector and the described four-vector start from same point
Make wherein that described first inclination angle is that θ a and described second inclination angle are θ b, then | θ a| 〉=| θ b| and 0.09 °≤| θ a|.
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