JP3446495B2 - Method for manufacturing compound semiconductor epitaxial wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] FIELD OF THE INVENTION The present invention relates to a method of forming at low temperatures.
Equipped with a thin film buffer layer made of gallium nitride based compound semiconductor
Related to compound semiconductor epitaxial wafers
Obtain compound semiconductor epitaxial wafer with excellent surface condition
Semiconductor epitaxy with thin film buffer layer suitable for
Related to a shallow wafer. [0002] 2. Description of the Related Art Gallium nitride-based compound semiconductor epitaxy
Al wafer is Al_x Ga_y In_z N (x + y + z =
1, 0 ≦ x, y, z ≦ 1) etc. as a constituent layer
Is used as a base material. This laminated structure is
Conventionally, generally, sapphire (α-alumina single crystal)
Etc. are formed on a crystal substrate. Silicon carbide (SiC)
And zinc oxide (ZnO) are used as substrate materials
In some cases. However, the constituent layers that make up the laminated structure are not
They do not lattice match with the substrate material. For example, GaN and
The degree of lattice mismatch with fire is considered even if mutual orientation is considered.
About 13.8% ("Journal of Japan Society for Crystal Growth",Vo
l. 20, No. 4 (1993), pp. 28-36). Obedience
Therefore, when forming a constituent layer directly on these substrates,
Is due to the misfit (mis-f
it) A large amount of crystal defects such as dislocations
Is introduced into the semiconductor component layer. Also, the lattice mismatch
A continuous film with excellent surface flatness on a substrate
It is not easy, the constituent layers lack continuity and surface
This results in a film with poor topology. Quality with a large amount of crystal defects
Excellent characteristics from a laminated structure composed of inferior constituent layers
Semiconductor device cannot be obtained. A gallium nitride-based compound semiconductor according to the prior art
The problem in the laminated body will be explained more concretely.
For example, if GaN is grown directly on a sapphire substrate,
Only isolated growth islands are scattered and occur.
Is known to be a film lacking continuity
FIG. 1 (p. 30)).
When forming a film with a discontinuous film as the underlying layer, the constituent layers to be formed
Are also discontinuous. Use discontinuous membrane
In compound semiconductor devices manufactured by
Is uneven, hindering uniform distribution of device operating current.
Is caused. Therefore, the laminated structure including the discontinuous film
The structure obtains a semiconductor element with excellent uniformity of electrical characteristics, etc.
Make it difficult. Recently, compound semiconductor epitaxial wafers have been developed.
Of the old problems in the formation of laminated structures used for EHA
100-500 angstroms (Å) for avoidance
Insert a thin buffer layer between the substrate and component layer
(JP-A-2-229476)
Gazette). These thin film buffer layers are made of Al_x Ga_1-x N (0
.Ltoreq.x.ltoreq.1).
JP-A-2-229476, JP-A-4-297923
JP, JP-A-5-41541 and JP-A-6-15
1962). Thin film buffer layers are also generally
00 ° C to 900 ° C (JP-A-2-229476) and
400 ° C to 800 ° C (JP-A-6-151962)
Because it is grown at a relatively low temperature, it is especially called a low-temperature buffer layer.
It is called. The low-temperature buffer layer is composed of the substrate and
By alleviating the lattice mismatch with
Also form a continuous gallium nitride-based compound semiconductor film
It is placed with the intention of doing so. [0005] The low temperature buffer layer also covers the substrate surface.
It is arranged as a base layer to be formed. This underlayer
(Low-temperature buffer layer) allows the growth of the layers constituting the laminated structure
It is said that sometimes uniform generation and formation of growth nuclei can be promoted.
In addition, the presence of the underlayer allows two-dimensional growth in the lateral direction.
Because the process proceeds preferentially, the membrane expands and develops flatly
No. That is, it is advantageous for obtaining a constituent layer having continuity. Advantageous in obtaining a continuous film as described above
The low-temperature buffer layer that provides
The higher the (coverage), the more the function can be exhibited.
Ideally, the entire surface of the substrate should be covered.
You. Low is said to increase the possibility of achieving continuous film formation
The temperature buffer layer is mainly composed of amorphous
(JP-A-2-229476, JP-A-2-229476)
JP-A-6-151962). The layer thickness is as described above.
Low, at most, hundreds of angstroms.
You. [0007] In the growth of a thin film, an adsorbing surface on the substrate surface is used.
Selective or local deposition on site
Is by no means rare. If the desired thin film is thin,
This is manifested as non-uniformity of the layer thickness. Low temperature relaxation of substrate surface
The pattern of distribution of the stratum is an electron microscope that can obtain high resolution,
Analysis method using atomic force microscope, laser interference roughness meter, etc.
And measurement methods. 1 and 2 show amorphous
The thickness of the layer mainly composed of high quality GaN is about 5 nm.
It is a schematic diagram of a plane and a section of a conventional low-temperature buffer layer. one
Generally, when the low temperature buffer layer (102) is thin, the low temperature buffer layer (1)
02) completely and uniformly covers the entire surface of the substrate (101)
I can't. As a result, it is composed mainly of amorphous
Growth islands (103) do not exist close to each other
Area where there is no growing island (103) between Nagashima (103)
The region remains as a groove (104). By observing the cross section
The low temperature buffer layer is extremely
Area that is thin or the surface of the substrate (101) is exposed.
(See FIG. 2). The thickness of the growing island (103) (high
Is not always uniform (see FIG. 2). [0008] If amorphous, the phase of the atoms constituting it
The bonds between them are not as strong as in single crystals. This
In the case of an amorphous low-temperature buffer film having a small thickness as described above,
Disappears due to sublimation during the process of raising the temperature to high temperatures,
Alternatively, the thickness of the layer decreases. The disappearance of the low-temperature buffer film reduces the layer thickness
The larger the area, the more pronounced, resulting in the width of the groove (104).
(Indicated by the symbol w in FIGS. 1 and 2)
Means that the substrate surface is exposed. Lattice mismatch between deposited layer and substrate
There is a low-temperature buffer layer as an underlayer that plays a role of relaxation
In the area where the substrate is exposed (the above groove), abnormal
The long happens. FIG. 3 shows the pattern of abnormal growth occurring in the groove.
The growth is shown in contrast to the normal growth mode with the growth island as the core.
It is a schematic diagram of a long layer surface. The surface of the substrate (101) is exposed
From the groove (104) that led to the growth, pyramidal growth grains (1
05) occurs. On the other hand, from the growing island (103)
Hexagonal or polygonal flattened parts
Long grains (106) are generated. But the remaining cold buffer
Growth grains due to the different layer thickness of each layer
The height (thickness) of (106) is not uniform. These grown grains form the surface morphology of the growth layer.
The pyramidal growth grains are pyramids.
May be formed on the surface of the growth layer (deposited layer).
You. On the other hand, from the growth grains that have expanded
The flat plate portion provides a flat growth layer surface. Substrate surface
Where the grooves are dominant, ie, the substrate surface is almost
Low temperature buffer layer does not remain in the whole area, and the substrate surface is exposed
When in the state, the planar shape of the growth layer surface is approximately hexagonal.
It is known that a large number of protrusions occur (Jpn.
J. Appl. Phys. ,30(10A) (199
1), L1705 to L1707. ). Also, low temperature buffer layer
Does not disappear and the entire surface of the substrate is ideally covered
In the state, a continuous film having a flat surface is obtained.
FIG. 4 shows an intermediate state between these conditions, that is, a groove or a turtle having a large width.
Substrate crystal surface partially exposed due to crack generation
Diagram schematically showing the growth layer surface obtained in the state of
It is. In this case, the projection (1) whose planar shape is substantially hexagonal
07) and a region lacking flatness and almost flatness
The surface is a mixture of the maintained area. pyramid
The projections (107) are generated from the grooves (104).
Things. In areas where flatness is ensured,
This corresponds to the area where the opposing layer (102) remains. Ma
The reason that the thickness of the flat portion differs from region to region is that
It depends on the degree of reduction in the thickness of the temperature buffer layer (102).
You. [0010] The details of the region where the protruding portion and the flat portion coexist are shown
5 is a schematic sectional view. In the area where the low-temperature buffer layer has disappeared,
In the projection generated from the corresponding groove (104), for example, the product
The layer structure constituting layers ((110) to (112)) are sequentially deposited.
As it is stacked, the distance between the top and bottom of the projection (108)
(Depth) is further increased. For this reason, the area between the protrusions
The pores increase in depth as the thickness of the deposited layer increases.
And remain as pits (109).
On the other hand, flat portions having different thicknesses (indicated by symbol d in FIG. 5)
Step (114) formed at the junction of (113) is laminated
It remains after deposition of the constituent layer. After all, the laminated structure constituent layer
Surface has pits (109) and steps (114)
It becomes uneven. For example, using the laminated structure illustrated in FIG.
Thus, a pn junction type compound semiconductor light emitting device is manufactured. this
In this case, the structure of the laminated structure is assumed for forming a pn junction.
The layer (111) is an n-type semiconductor layer, and the constituent layer (112) is
It is a p-type layer. In terms of the operation of this light-emitting element, an electrode
The supply current from (115) is divided into the constituent layers ((111) and
Via a pn junction formed at the interface between (112))
Flow into lower constituent layers ((110) to (111))
There is a need. However, the pit (109) as above
If present, the pit will be deeper each time the constituent layers are layered
((108) in FIG. 5), for example, the electrode (11
5) increases the chance of direct contact with the constituent layer (111).
Let The consequence of this situation is that the electrode (115)
Of short-circuited n without passing through the pn junction
It is the flow into the shaped component layer (111). This defect is shown in FIG.
The current-voltage characteristics (IV characteristics) shown in FIG.
Appears as a lack of use. For pn junction type light emitting element
Lack of rectification means no light emission or weak light emission,
This results in poor electrical characteristics such as lack of withstand voltage. That is,
The presence of large-width grooves creates pits and eventually
It spreads to the deterioration of electrical characteristics of compound semiconductor devices
It is. Also, the presence of the step (114) causes the step
In the region where (114) exists on both sides, the laminated structure
Discontinuity of ((110)-(112)) of layer occurs
Therefore, a pit (109) is formed. This discontinuity
In the region where the occurrence occurred, the formation of a good pn junction was also inhibited.
You. Also, discontinuity of the electrode (115) occurs. In particular,
The device operating current supplied from the electrode is applied to almost the entire area of the light emitting layer.
Ultra-thin, transparent conductive as electrode to diffuse
Gully nitride with transparent electrode or translucent electrode
Compound semiconductor light emitting device, such a step
The occurrence immediately deteriorates the electrical characteristics of the light emitting device.
Specifically, the input resistance increases and the operating current spreads sufficiently.
This results in a reduction in the light emitting area that occurs because it is not achieved. For this reason, in the prior art, the pit portion
Intended to prevent short-circuit current flow through
The pits with an insulating material that impedes the flow of current
And other measures have been implemented. For example, using gallium nitride
Anodize the laminated structure made of compound semiconductor and
The technique of coating the coating with an insulating film such as aluminum oxide
This is one example (JP-A-57-62579). I
However, this technique uses an insulating film to cover the surface of the pit.
Is difficult to precisely control the film thickness. For example, if the depth is small
Even if the pit with a narrow opening is buried,
In a pit with a wide opening, the opening surface is thin.
In some cases, it is only coated. A big pit
Sufficient time to form enough coating to be buried
Conversely, the thickness of the coating in the small pits buried the pits
The thickness becomes larger than the thickness
You. In other words, the surface irregularities are reduced by the insulation treatment of the pits.
It can lead to encouraging results. [0014] SUMMARY OF THE INVENTION The present invention provides a gallium nitride
Low temperature in epitaxial wafers
The peaks found on the surface of the laminated component layer deposited on the buffer layer
The growth of gallium nitride based compound semiconductor crystal growth
Constrains essentially in light of the nature of the style. Also low temperature buffer
The gallium nitride-based
Suppress surface step on compound semiconductor epitaxial wafer
Control or reduce. [0015] SUMMARY OF THE INVENTION The present invention relates to a compound semiconductor.
In an epitaxial wafer, a nitride gas
Thin layers composed of growing islands made of a lithium-based compound semiconductor
A film buffer layer, wherein the growing islands are located between adjacent growing islands.
Is 45 nm or less. Also, in particular,
In the above compound semiconductor epitaxial wafer,
The height difference (Δh) of each of the growing islands constituting the membrane buffer layer is 4
The thickness is set to 0 nm or less. The distance between the growing islands according to the present invention is defined as
Between the growing islands. As an example
In FIG. 7, the distance between the growing islands is indicated by the symbol L. FIG. 8 shows low temperature
The pit density on the surface of the growth layer deposited on the buffer layer
It shows the distance dependence between growing islands. Adjacent
That the distance between the growing islands is 0 means that the growing islands
Represents a continuous film. Pit density
Tend to increase with increasing distance between adjacent growing islands
Show. In particular, the distance between adjacent growing islands exceeds 45 nm
Then it increases sharply. The distance between pits is also adjacent
When the distance between the growing islands exceeds approximately 45 nm, it suddenly increases.
You. In other words, since the distance between the pit tops increases,
The probability of occurrence of a larger pit increases. [0017] 9 and 10 show the (0001) plane.
Average distance between growing islands grown on sapphire substrate is 1
1050 ° C. on a low-temperature buffer layer made of GaN with a thickness of 2 nm
Surface morphology of a GaN growth layer with a thickness of about 2 μm
FIG. 6 is a schematic diagram showing a change in the chemistry according to a layer thickness. FIG.
Is the surface condition when the thickness of the GaN growth layer is about 0.5μm
State. In the early stage of growth, it is generated in the groove (104) on the substrate surface.
The generated fine pyramidal growth grains (105) are
03) The top plate part developed two-dimensionally with the nucleus as the core
Is almost buried inside the growth grain (106) that flattens
It is in a state of being left. At this point the surface is partially flat
Small corresponding to the incompleteness of coalescence of the growing grains (106)
Pit (109) remains, but already flat
I have. This is a gallium nitride based compound semiconductor such as GaN
The layer is perpendicular to the substrate surface with the low-temperature buffer layer as the underlying layer.
It is understood that it grows two-dimensionally dominantly. this
Especially when the distance between adjacent growing islands is small.
Growing grains that develop preferentially in area fill gaps
Is more likely to occur, and will be superior to ensuring surface flatness.
Will be interpreted. As film formation progresses and the layer thickness increases to about 1 μm
The opening of this small pit (109) gradually narrows.
The pit density decreases (see FIG. 10).
See). Furthermore, the pits disappear almost completely as the layer thickness increases.
A flat surface is formed. That is, a low-temperature buffer layer is formed.
The distance between the growing islands is equal to or less than the value specified by the present invention.
Already at the relatively early stage of growth,
The loss of the pits that hinder the maintenance is achieved. On the other hand, the distance between adjacent growing islands is about 60 to
Low temperature relaxation with growth islands arranged sparsely to 120 nm
The surface morphology of the growth layer on the impact layer increases as the layer thickness increases.
It is not a steady improvement. 11, 12, and 1
3 is a GaN low-temperature buffer having a groove width exceeding the specification of the present invention.
Surface of the GaN growth layer formed on the layer with increasing layer thickness
It is the schematic diagram which showed the change of the state. FIG. 11 shows that the layer thickness is approximately
Surface at the time of 0.5 μm, so to speak, at the beginning of growth
Show morphology. Groove (1) on the surface of the substrate (101)
04), pyramidal growth grains (10
5) occurs. Almost no underlayer exists in this region
Growth in the direction perpendicular to the surface of the substrate (101)
Become. In addition, since the interval between the grooves (104) is large,
The top plate developed flat with Nagashima (103) as the core
Growing grains (106) filling the groove (104)
This will take more time. During this time the groove
The pyramidal growth grains (105) generated from (104) are
In the meantime, the height is increased in the vertical direction and flat growth grains (10
The difference in height from (6) becomes more significant. Growth time
When the layer thickness increases to about 1.5 μm with the progress of
(104) is filled with flat growth grains (106).
Pyramidal growth with increasing height during that time
The grain (105) is the surface of the united flat growth grain (106)
Will remain as pyramid-shaped projections
(See FIG. 12). In addition, a pin
A cut (109) is formed. Furthermore, the layer thickness increases
The height of the projection increases because the projection grows further upward
At the same time, the depth of the pit (109) with a large opening
(See FIG. 13). As described above, the groove width is regulated by the present invention.
If the thickness is larger than the specified value,
As a result, the pits will not be filled, and the depth will increase
You. That is, when a groove width exceeding the stipulation of the present invention is present, flattening is performed.
Many pits and protrusions that hinder the formation of
Therefore, it is difficult to obtain a growth layer with excellent surface morphology.
Become. In the present invention, the distance between adjacent growing islands and
Means the adjacent growth during low temperature buffer layer growth
Refers to the distance between islands. Low temperature buffer layer is a continuous film (distance = 0)
Consisting of a collection of growing islands with some or some spacing
The irrigator is an atomic force microscope (abbreviation: AFM) as described above.
And a laser interference roughness meter. Between growing islands
Distance can also be obtained by using a scanning electron microscope with high resolution.
It can be easily measured using In order to deposit a growth layer on the low temperature buffer layer,
After exposure of low temperature buffer layer in high temperature deposition environment
May increase the distance between adjacent growing islands.
Adjacent to the transition of conventional low-temperature buffer film to high-temperature environment
The increase in the distance between the growing islands indicates that the growing islands are
It was caused by the fact that it was mainly composed of
One way to prevent the growth island from disappearing due to such sublimation
As a method, a low-temperature buffer made of gallium nitride-based compound semiconductor is used.
Considering that the temperature of the impact layer is increased in an atmosphere containing nitrogen (atoms).
available. For example, a gallium nitride-based compound such as GaN
Heating of the conductor is carried out using ammonia (NH), which is a hydride of nitrogen.
_Three ) Is carried out in an atmosphere containing
It is said to have the effect of preventing. But magnesium
Intended to electrically activate acceptor impurities such as (Mg)
If ammonia (NH_Three Temperature rise in an atmosphere containing
Is produced by insufficient ammonia thermal decomposition
A fragment in which nitrogen and hydrogen are bonded (NH bond).
Is taken into the gallium nitride-based compound semiconductor film and p
To obtain a gallium nitride-based compound semiconductor layer
There was a case. Therefore, in the prior art, nitrogen
Heat treatment in an atmosphere containing gas has also become common. Only
However, it is difficult to thermally decompose nitrogen molecules into atomic nitrogen.
That is a fact that has been known for a long time. For this reason,
Temperature rise under nitrogen gas atmosphere is a low temperature buffer made of amorphous
It is sufficient to suppress the alteration of the
There is no. Increasing the distance between adjacent growing islands at high temperatures
In addition, it is necessary to change the constituent requirements of the growth island that forms the low-temperature buffer layer.
And can be avoided. For example, compared to amorphous
In other words, from a single crystal that has stronger mutual bonding between constituent atoms
Low temperature buffer layer is composed of growing islands at high temperature
This is one means for preventing the buffer layer from disappearing. That is, one
General formula Al_x Ga_y In_z N (where x + y + z = 1,
0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) and other than nitrogen
General formula Al containing group V element_x Ga_y In_zN_a P_1-a
 (0 <a ≦ 1) or the general formula Al_x Ga_y In_z N_a A
s_1-a Gallium nitride based compound represented by (0 <a ≦ 1)
The growth island is composed mainly of the single crystal of the oxide semiconductor.
You. Aggregate of growing islands mainly composed of single crystal grains with low temperature buffer layer
The first advantage obtained by constructing from
The growing island's resistance to the This is low
Because the temperature buffer layer is made of single crystal, it is
This is because the mutual bonding power of the constituent atoms is strong. Therefore,
In high temperature environment, contains nitrogen such as ammonia
Even if you don't create an atmosphere composed of molecules,
Alteration due to thermal dissociation of the stratum can be suppressed. Such properties
The growth island that forms the low-temperature buffer layer composed of
Ear, silicon carbide (SiC), zinc oxide (ZnO), etc.
Conventional substrate materials and metal substrates such as hafnium (Hf)
Sheet material, lithium containing gallium and aluminum (L
i) Forming on a substrate made of an oxide substrate material such as an oxide
Can be In the present invention, the low-temperature buffer layer is particularly high and low.
A growth island having a difference (Δh) of 40 nm or less
I do. This is to make the height of the growing island uniform. FIG.
Is G composed of growing islands mainly composed of single crystal GaN.
aN Low temperature buffer layer growth island height difference and
FIG. 4 is a diagram illustrating a relationship with a surface roughness of a GaN growth layer. here
In this case, the thickness of the growth layer is about 2.5 μm. Surface roughness is
PV (Peak-to-Vally) value
This indicates the maximum height difference of the surface irregularities.
You. In FIG. 14, the boundary is that Δh is 40 nm.
Thus, the PV value is rapidly increasing. That is, the concave surface
The protrusion (difference in height) increases. For example, Δh is about 60 nm
Of the GaN growth layer formed on the GaN low temperature buffer layer
PV values can reach about 40-50 nm. FIG.
5 is composed of GaN single crystal growth islands having Δh of about 60 nm.
Of the GaN growth layer formed on the formed GaN low temperature buffer layer
It is a schematic diagram which shows an example of a surface state. The surface of the growing island
Smooth fish-scale projections corresponding to the height difference (Δh)
It has unevenness present. In this case, the PV value is about 5
Reaches 0 nm. Others such as aluminum nitride (AlN)
In the case of a gallium nitride based compound semiconductor growth layer, the surface P
V value exhibits almost the same dependence on Δh as in GaN.
I do. Field-effect transistors and visible light emitting dies such as blue
In the case of Ode, a gallium nitride system with a layer thickness of around 100 nm
Compound semiconductor layer is a channel layer or light emission
It is used as an active layer such as a layer. Such a relatively thin
Active layer with a surface smoothness with PV value around 50nm
Forming with inferior layers is disadvantageous. Large PV value
Means that there is non-uniformity of the layer thickness.
As a result, a layer having a layer thickness not much
Unevenness of electrical characteristics such as unevenness of sheet resistance
Is brought about. In obtaining the low-temperature buffer layer according to the present invention,
First, to form a growth island consisting of a single crystal, the growth temperature
Is required. Growth temperature generally exceeds 400 ° C
It is important to set the temperature to about 480 ° C or less.
You. If the growth temperature exceeds about 500 ° C, the growth island will be united
It is easy to be composed of crystals. But on the other hand, the growing island surface
This causes the formation of protrusions. Therefore, at relatively high temperatures,
When trying to obtain a growth island with a flat surface, the following V / III
The ratio of the conventional example (see, for example, JP-A-7-312350)
There is a restriction that the ratio is set to a much smaller range on the lower ratio side.
Wrong. It does not require precise setting of the V / III ratio
In order to obtain stable growth islands, the
Although there is some variation in the optimal temperature range, the growth temperature
It is preferable to be in the range of about 450 ° C or more and about 480 ° C or less.
No. In other words, to form a single crystal growth island with excellent surface condition
Is a conventional example (see, for example, JP-A-7-312350).
200) to 900 ° C., as in the case of “T.
Even a wide temperature range of 400 ° C to 800 ° C is acceptable
Not. In addition, a group V element with respect to a group III element raw material
The raw material supply ratio, so-called V / III ratio, is
It is an important factor affecting spacing. Therefore, a single crystal
To control the distance between growth islands, the deposition temperature must be
In addition to having to set within a limited temperature range,
It is necessary to precisely control the V / III ratio. Preferred
The V / III ratio depends on the growth temperature. For example, film formation
Growth reaction is carried out under almost atmospheric pressure, which is an example of the method
The sapphire C surface ((00
01) plane) The gallium nitride (G
aN) growing the low temperature buffer layer at a growth temperature of about 400 ° C. to about 480 ° C.
The preferred V / III ratio when growing in the range is approximately 7 ×
10^Three That is all. Increase the growth temperature to, for example, 500 ° C.
When set around, the preferred V / III ratio is generally about 2
× 10^Three About 4 × 10^Three Limited to a relatively narrow range of
Is done. Both the growth temperature and the V / III ratio are set in a preferable range.
By setting to, growth islands can be constructed from single crystals,
Further, the distance between the growing islands can be set to 45 nm or less.
Wear. The distance between adjacent growing islands can increase the V / III ratio
It tends to be shortened. That is, the raw material of the group III element
Creation of a growth environment in which the raw materials for Group V elements are excessive compared to
It is effective in shortening the interval between growing islands. The distance between the adjacent growing islands is a rule according to the present invention.
And the height difference (Δh) of the growing island is 40 nm.
In order to make the following, the growth temperature and the V / III
Set within the preferred range of
Stores the flow rate of raw materials and carrier gas to be supplied in the preferred range
Need to be done. The preferred range is to supply into the growth system
The total amount of gas to be deposited
Simple linear flow velocity expressed by the value divided by the area cross-sectional area
Thus, it is generally in the range of 10 cm / sec to 50 cm / sec.
More specifically, a quantitative example will be described. (A) Growth temperature = 460
° C, (b) V / III ratio = 9.6 × 10^Three , (C) hydrogen and
Supply amount of Group V element raw material (ammonia) into the growth system
(Total amount of gas supplied to the reaction system) = 9 liters / minute,
(D) Hydrogen: Group V element source gas supply ratio = 8: 1, etc.
Under long conditions, the linear velocity near the surface of the sediment
Preferably, it is about 35 cm. Linear flow velocity
By setting it within the preferable range, the height difference (Δh) is 4
A single crystal growth island having a thickness of 0 nm or less can be formed. The present invention
In order to facilitate understanding of the linear flow velocity described in FIG.
The following is an example of the configuration of the long device. An example of a growth device is a raw material
Carrier gas accompanying gas is applied to the surface of the substrate (101).
A so-called nozzle (123) for spraying is connected to the reactor (1).
24). Source gas and carrier gas
Is the inlet hole (125) provided at the upper end of the nozzle (123).
And supplied to the inside of the nozzle (123). The cross-sectional area is S (simple
Rank: cm^TwoBelow the nozzle (123)
Substrate support (susceptor) made of graphite etc.
(126) The substrate (101) placed on the
I have. Nozzle (123) is installed and supplied inside
Concentrate and spray raw material gas on the surface of substrate (101)
Configuration. Supplied inside the nozzle (123)
The total amount of gas used is Q per second (unit: cm^Three(Cc))
Then, a very simple linear flow velocity just above the substrate (101) is
Q / S (unit: cm)^Three / Sec). Linear flow velocity
With Q / S, passed through the area near the substrate (101)
Raw material gas and the like are discharged from the discharge hole (127) to the reaction furnace (124).
It is discharged outside. [0026] [Function] Gallium nitride based compound semiconductor with excellent surface condition
Layers are provided. [0027] DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, gallium nitride-based compounds will be described using the present invention.
Example of manufacturing light-emitting element composed of semiconductor laminate
State. FIG. 17 shows the structure of the laminate. Figure 17
The substrate (101) has (0001) sapphire C-plane
It was used. The substrate (101) is cleaned and the mirror-polished surface is cleaned.
After cleaning, a low-temperature buffer layer (102) made of GaN is formed.
Done. The low temperature buffer layer (102) is a bird for the semiconductor industry.
Methylgallium ((CH_Three )_Three Ga) to gallium (G
a) As a source, ammonia (NH_Three ) As the nitrogen (N) source
And grown by atmospheric pressure MOCVD. Figure 1 for growth
An apparatus having the same configuration as shown in FIG. 6 was used. Low temperature
The opposing layer (102) is formed at a growth temperature of 450 ° C.
Was. Prior to film formation, a flow rate of 1 liter / min
Nozzle of ammonia gas (see figure number (123) in Fig. 16)
Into the growth furnace (reactor) (Fig.
24)) on the surface of the substrate (101) placed in
It was supplied for. Start supplying ammonia gas
After the gas flow in the growth reactor becomes steady,
Of trimethylgallium molecules bubbled with lium
Growing hydrogen bubbling gas with a flow rate of 5 cc / min
Supply into the furnace to start growth of GaN low temperature buffer layer (102)
Started. V / III ratio (ammonia / trimethylgallium
Ratio) is about 1 × 10^FourSet to. Also, low temperature buffer layer
At the time of film formation of (102), a carrier composed of hydrogen
The gas flow was 8 liters per minute. That is, the hydrogen carrier
The supply flow ratio between the gas and the ammonia gas is 8: 1.
Was. The cross-sectional area of the nozzle is about 6.25cm^TwoWas
The linear flow rate was about 24 cm / sec. Substrate (101)
Supply of ammonia and trimethylgallium source gas to
Feeding is continued for 20 minutes to obtain an average film thickness of about 20 nm.
A low temperature buffer layer (102) was obtained. GaN low temperature buffer formed under the same conditions as above
Measure the roughness of the layer surface with a general laser interference roughness meter.
Was. From the measurement results, the growth island has a planar shape of approximately hexagonal shape.
Or polygonal thin plates are considered to be united with each other.
Refused. Where there is a step measured by a roughness meter
Due to the width of the region, the distance between adjacent growing islands is up to 11 nm.
Was. Also, from the size of the step, the growing island has the maximum height
205 nm and the minimum value is 180 nm.
Was. That is, Δh described in the text was 25 nm. Change
Then, the GaN low-temperature buffer layer formed
Thinned by ion-thinning technique
Later, using a normal transmission electron microscope (TEM),
The surface was observed. Accelerating voltage of incident electron beam is 200 kB
(KV), an enlarged imaging magnification sufficient for cross-sectional observation was obtained.
In the state, when the components of the growing island were identified,
It turned out that it is mainly composed of a single crystal. this
In the cross section observation by TEM, the width of the groove existing between the growing islands is
It was found to be a maximum of 13 nm, and the distance between adjacent growing islands was
The maximum value of separation is measured by the laser interferometer described above.
Nearly consistent results were obtained. The maximum value of the distance between the adjacent growing islands is
Consists of single crystal grown islands of 45nm or less
After the formation of the low-temperature buffer layer, the ammonia: hydrogen flow ratio
Of substrate in an atmosphere containing ammonia with a ratio of 1: 8
Was raised to the film forming temperature of the layer constituting the laminate. After that, low
The following constituent layers are sequentially deposited on the temperature buffer layer and used for LEDs.
To form a laminate. (A) Carrier concentration 3 × 10¹⁸cm^-3, About 2 μm thick
A silicon (Si) doped n-type GaN high temperature buffer layer (116),
(B) Carrier concentration 2 × 10¹⁶cm^-3, Layer thickness 0.1μm
Of zinc (Zn), magnesium (Mg) and indium
(In) doped n-type GaN light emitting layer (117),
(C) Carrier concentration 8 × 10¹⁶cm^-3, Layer thickness 0.2μm
Mg-doped p-type Al_0.05Ga_0.95N upper cladding layer
(118), (d) carrier concentration 2 × 10¹⁷cm^-3,layer
0.2 μm thick Mg-doped p-type GaN contact layer (1
19). These laminated body constituent layers ((116) to (11)
9)) was formed at a temperature of 1000 ° C. Laminate Constituent Layer ((116) to (119))
Surface morphology by differential interference light microscopy and
Each layer was observed with a scanning electron microscope (SEM).
As a result, the pits are deposited on the first bank on the cold buffer layer (102).
On the surface of the stacked GaN high temperature buffer layer (116)
Already, it was almost unrecognizable. From this example
Even if pits are generated at the beginning of growth, it will increase the layer thickness.
Interpreted as having a small opening so that it disappears with
Was done. In addition, the gradual fish scale due to the height difference of the growing island
No ridges (see FIG. 15) were also present. as a result,
The contact layer (119) which is the outermost layer of the laminate is a continuous film
The PV value is 2.8 nm, and the RMS (R
oot Mean Square; one representing the degree of unevenness
The square of the linear distance from the virtual reference plane (the next power)
It is the square root value of the average value (root mean square value). )
Was about 0.3 nm. Known photolithography is applied to the above-mentioned laminate.
After patterning using technology,
Area marked with argon (Ar) / methane (CH_Four )
/ H_Two General microwave plasma using mixed gas
It was etched by the method. This plasma etching
Stacked structure below the region where the n-type electrode (120) is to be formed
The layers ((116) to (119)) are removed, and the constituent layer (1) is removed.
16) After exposing the surface layer portion, aluminum (Al)
Was applied in vacuum to form an n-type electrode (120). p
The shape-shaped electrode (121) is located on the periphery of the constituent layer (119).
In some places, a low-resistance titanium nitride (TiN) thin film electrode (12
Installed via 2). FIG. 18 is a plan view of the formed LED.
FIG. 19 is a schematic view, and FIG. 19 is a schematic sectional view thereof. The flow of the forward current to the light emitting element is
And blue-violet light emission was obtained. Light output is about 0.9mm
Watts (mW). 20 mA of forward current
A (mA), the forward voltage (the so-called V_f ) Is
It was about 3.8 to 4.0 volts (V). FIG.
From the current-voltage characteristics shown in FIG.
Means that the reverse breakdown voltage is 4.5 V or more (＠ 10 microamps)
A (μA)). [0033] Industrial Applicability For compound semiconductor epitaxial wafer
With excellent surface condition with few pits and protrusions
Since it can be composed of a continuous film, it is a compound semi-conductor with excellent electrical properties.
There is an effect that a conductor element can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view showing a surface state of a conventional low-temperature buffer layer made of GaN. FIG. 2 is a schematic cross-sectional view of the conventional low-temperature buffer layer illustrated in FIG. FIG. 3 is a diagram schematically showing that a growth mode changes depending on whether or not a low-temperature buffer layer remains on a substrate surface. FIG. 4 is a diagram schematically showing a surface state of a growth layer corresponding to the presence or absence of a low-temperature buffer layer. FIG. 5 is a diagram schematically showing a cross section of the laminated structure in a region where pits and flat regions are mixed. FIG. 6 is an example of a current-voltage characteristic when rectification is lacking based on imperfection of a pn junction due to generation of a pit. FIG. 7 is a schematic diagram for explaining a distance between growth islands (a maximum width of a groove between adjacent growth islands). FIG. 8 is a diagram showing the relationship between the pit density on the GaN growth layer surface and the distance between adjacent growth islands of the growth islands forming the low-temperature buffer layer. FIG. 9 shows GaN having a groove width between growth islands according to the present invention.
FIG. 3 is a schematic diagram showing the surface morphology of a GaN growth layer having a thickness of about 0.5 μm formed on a low-temperature buffer layer. FIG. 10 shows Ga having a groove width between growth islands according to the present invention.
FIG. 3 is a schematic diagram showing the surface morphology of a GaN growth layer having a thickness of about 1.0 μm formed on an N low-temperature buffer layer. FIG. 11 shows a film thickness of about 0.5 μm formed on a GaN low-temperature buffer layer having a groove width between growth islands exceeding the regulation of the present invention.
FIG. 3 is a schematic diagram showing a surface morphology of a GaN growth layer where m is a number. FIG. 12 shows a film thickness of about 1.5 μm formed on a GaN low-temperature buffer layer having a groove width between growth islands exceeding the regulation of the present invention.
FIG. 3 is a schematic diagram showing a surface morphology of a GaN growth layer where m is a number. FIG. 13 is a schematic diagram showing the surface morphology of a GaN growth layer having a layer thickness of about 2 μm formed on a GaN low-temperature buffer layer having a groove width between growth islands exceeding the provisions of the present invention. FIG. 14 is a diagram showing the relationship between the PV value on the surface of a GaN growth layer and the height difference (Δh) of a growth island constituting a low-temperature buffer layer. FIG. 15 is a diagram showing an example of the surface morphology of a GaN growth layer formed on a GaN low-temperature buffer layer composed of growth islands having a height difference (Δh) exceeding the regulation of the present invention. FIG. 16 is a schematic diagram showing a configuration of a growth apparatus. FIG. 17 is a diagram showing a structure of a stacked body of a gallium nitride-based compound semiconductor according to an example of the present invention. FIG. 18 shows a compound semiconductor device (LED) according to the present invention.
FIG. FIG. 19 is a schematic cross-sectional view of the LED shown in FIG. 18 taken along a broken line AA ′. FIG. 20 shows a compound semiconductor device (LED) according to the present invention.
5 is an example of the current-voltage characteristic of the present invention. [Description of Reference Numerals] (101) Substrate (102) Low-temperature buffer layer (103) Growth island (104) Groove (groove) (105) Pyramidal growth grain (106) Planar growth growth grain (107) Projection (108) Distance (depth) from the bottom to the top of the protrusion (109) Pit (110) Laminated structure constituent layer (111) Laminated structure constituent layer (112) Laminated structure constituent layer (113) Flat surface part ( 114) step (115) electrode (116) n-type GaN high-temperature buffer layer (117) n-type GaN light emitting layer (118) p-type AlGaN upper cladding layer (119) p-type GaN contact layer (120) n-type electrode (121) P-type electrode (122) Titanium nitride (TiN) thin film electrode (123) Nozzle (124) Reactor (125) Gas inlet (126) Substrate support (susceptor) (127) Discharge hole

──────────────────────────────────────────────────続 き Continued on the front page (56) References X. H. Wu, D .; Kapolnek, E .; J. Tarsa, B .; Heying, S .; Keller, B .; P. Keller, U.S.A. K. Misra, SP. Den Baars, "Nucleation layer evolution in metal-organic chemical vapor deposition growth GAN", Applied Physics Letters, Applied Physics Letters, March 3, 1996, Applied Physics Letters. 68, no. 10, pp. 1371 -1373 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/20 H01L 21/205 H01L 33/00 H01S 5/30-5/347 Web of Science

Claims (1)

(57) [Claim 1] A low-temperature buffer layer made of a gallium nitride-based compound semiconductor is formed on a crystal substrate, and a laminated body constituent layer made of a gallium nitride-based compound semiconductor is formed on the low-temperature buffer layer. In the method for producing a compound semiconductor epitaxial wafer, a low-temperature buffer layer is formed at a growth temperature exceeding 400 ° C.
C. or lower, a V / III ratio of 7 × 10 ³ or more, and a linear flow rate of the raw material gas and the carrier gas supplied to the surface of the substrate in the range of 10 cm / sec to 50 cm / sec.
The low-temperature buffer layer is composed of an aggregate of single crystal growth islands, the distance between adjacent growth islands is 45 nm or less, and the height difference (Δh) of each growth island is 4
A method for producing a compound semiconductor epitaxial wafer, wherein the thickness is set to 0 nm or less.