JPH0537027A - Led array - Google Patents

Abstract

PURPOSE:To prevent a GaAs layer from being destructed or contaminated by forming an electrode layer on the surface of the GaAs layer and by extracting the electrode layer onto a different kind of substrate for external connection. CONSTITUTION:An SiO film is formed on the surface of a silicon substrate 2 and then it is partially etched to make a window. Nextly, a GaAs layer 6 is formed on the window, the SiO film is etched and the whole surface is protected with an SiN protective layer 14. Then, an electrode 16 is formed by sputtering, vacuum evaporation or other method. Under the condition that the GaAs layer 6 is heated together with the silicon substrate 2, ultrasonic vibration is applied between a gold wire 20 and an external connection layer 18 of the electrode 16 and the gold wire 20 is wire-bonded to the external connection layer 18 with the pressure applied to the gold wire 20 and the ultrasonic vibration. By this method, the GaAs layer 6 is prevented from being destructed or contaminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array used for an LED printer head, a display, an image sensor or the like. More specifically, the present invention is an LE in which a GaAs layer is epitaxially grown on a heterogeneous substrate such as silicon.
It relates to the electrode connection of the D array.

[0002]

PRIOR ART GaAs on a silicon or germanium substrate
An LED array in which layers are epitaxially grown has been proposed (for example, JP-A-53-74,895). In this LED array, a GaAs layer is epitaxially grown on the entire surface of the substrate, an electrode is also formed on the GaAs layer, and Ga is formed.
The As layer is connected to the outside by wire bonding or the like.

However, since the GaAs layer is fragile, if the wire bonding is performed in this portion, defects frequently occur, and, for example, the GaAs layer frequently breaks. GaAs on silicon
Epitaxially growing layers is directly linked to obtaining high density LED arrays. At least, increasing the density of LED arrays is the trend of the times. The higher the density of the LED array, the higher the density of bonding. Here, if wire bonding is performed on a thin and brittle GaAs layer, the electrode becomes thin and thin as the density increases, so the pressure applied during bonding must be increased. When the pressure is increased, cracks are generated in the fragile GaAs layer,
The layer is destroyed. Similarly, densification of LED arrays results in increased bonding density. And this is G
It increases damage to the aAs layer and increases the frequency of destruction.

In addition to wire bonding, there are various types of bonding such as bump connection, all of which are Ga.
There is no change in that mechanical stress is added to the As layer or many steps are performed on the GaAs layer, which causes deterioration and contamination of the GaAs layer. For example, when forming solder bumps, barrier film formation and underlying conductive metal film formation, mask of resist other than bump formation part, bump formation by solder plating, resist removal, base conductivity of parts other than bumps It requires a long process such as etching of the conductive metal film and etching of the barrier film. Exposing the GaAs layer to these steps causes contamination of the GaAs layer.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide an expensive and fragile G
This is to prevent the GaAs layer from being destroyed or contaminated by avoiding external connection on the aAs layer.

[0006]

The LED array of the present invention comprises a heterogeneous substrate made of a material different from that of GaAs, and the GaAs of the light emitting layer.
In an LED array in which layers are epitaxially grown,
It is characterized in that an electrode layer is formed on the surface of the GaAs layer, and the electrode layer is drawn onto the different type substrate and externally connected here.

[0007]

According to the present invention, the electrode layer is drawn out on a heterogeneous substrate such as silicon and is externally connected here. As a result, the impact, load, and pollution on the GaAs layer during external connection are eliminated,
External connection is possible without damaging or contaminating the expensive GaAs layer. In addition, a heterogeneous substrate such as silicon is stronger than GaAs and does not break when externally connected.

[0008]

EXAMPLE FIG. 1 shows a first example. In the figure, 2
Is a silicon substrate, and in addition to this, a silicon-on-sapphire substrate in which a silicon film is grown on a sapphire plate, a simple sapphire substrate, or a germanium substrate may be used. The substrate 2 may be any one that can epitaxially grow a GaAs layer. 4 is a GaAs layer and a silicon substrate 2
A strained superlattice layer having an intermediate lattice constant for relaxing the strain due to the difference in the lattice constant between the and, and has a thickness of, for example, 1 atom to 10 atom layers. The strained superlattice layer 4 is, for example, InG.
For example, it is assumed that the aAs atomic layer and the GaAs atomic layer are alternately laminated in five layers. Reference numeral 6 is a GaAs layer which is laminated on the superlattice layer 4 by epitaxial growth. The GaAs layer 6 includes, for example, an n-type GaAs layer 8, an n-type GaAlAs layer 10, and Ga.
P-type GaAlA obtained by introducing p-type impurity Zn into AlAs
The s-Zn layer 12 comprises three layers, a GaAs layer 8 and an n-type G layer.
The p-type GaAlAs-Zn layer 12 is formed by continuing epitaxial growth of the aAlAs layer 10 and the p-type GaAlAs-Zn layer 12, or by implanting Zn after forming the GaAs layer 8 and the n-type GaAlAs layer 10. n
-Type GaAlAs layer 10 and p-type GaAlAs-Zn layer 12
The interface becomes the light emitting layer. The thickness of the n-type GaAs layer 8 is, for example, 2 to 3 μm, and the thickness of the n-type GaAlAs layer 10 is 1 to 2 μm.
The p-type GaAlAs-Zn layer 12 has a thickness of about 1 to 2 μm,
The total film thickness is, eg, about 7 μm. Note that the structure of the GaAs layer 6 shown here is an example, and can be changed to any structure of the GaAs layer that can be used as a light emitting diode.
The type of impurities is arbitrary. 14 is a protective layer of SiN, SiO, etc., 16 is an electrode layer of gold, Al, etc., and is p-type GaAlA
It is formed on the s-Zn layer 12 and is drawn out onto the silicon substrate 2. The electrode layer on the silicon substrate 2, especially the external connection layer 1
Call it 8. Reference numeral 20 is, for example, a wire-bonded gold wire having a wire diameter of about 20 to 30 μm. Two
2 is a common electrode layer provided on the back surface of the silicon substrate 2,
It is used as a common electrode for many LEDs provided on the As layer 6. Further, 24 is an external substrate on which the silicon substrate 2 is mounted. As a result, the n-type GaAlAs layer 10 and the p-type G
The light emitting layer at the interface of the aAlAs-Zn layer 12 is connected to the electrode 16 and the common electrode 22. LED per array
Is 40 to 120, for example.

The LED array of FIG. 1 is manufactured as follows. As shown in FIG. 6, the surface of the silicon substrate 2 is thermally oxidized to form the SiO film 30. This is partially etched to provide a window. Then, a GaAs layer 6 is formed in the window portion by epitaxial growth, the SiO film 30 is etched, and the surface is protected by the SiN protective layer 14. Si
The O film 30 may be replaced with a SiN film, a SiO ₂ film, or the like.
After these, the electrode 16 is provided by sputtering or vacuum deposition. Here, as shown in the figure, if the end portion of the GaAs layer 6 is not perpendicular to the silicon substrate 2 but is inclined, the height of the surface changes continuously, so that the electrode 16 is easily formed. When it is difficult to form the electrode 16 due to the difference in surface height between the GaAs layer 6 and the silicon substrate 2, for example, Ga
SiO or SiN or the like is deposited on the portion other than the As layer 6 to make the surface height uniform, or a resist is applied to the portion other than the GaAs layer 6 and the height is made uniform with the GaAs layer 6 by lapping and hardened to this portion. The electrode 16 may be formed.
The LED density of the LED array is, for example, 400 dpi.

Wire bonding is performed as follows, for example. Gold wire 20 having a wire diameter of about 20 to 30 μm, especially wire diameter 2
A gold wire 20 having a thickness of 5 to 30 μm is prepared, and the gold wire 20 and the electrode 16 are heated with the GaAs layer 6 being heated together with the silicon substrate 2.
Ultrasonic vibration is applied between the external connection layer 18 and the
The gold wire is connected to the external connection layer 18 by the applied pressure and ultrasonic vibration.
Wire bond to. Here, the silicon substrate 2 is G
If the silicon substrate 2 is stronger than the aAs layer 6, is less damaged by impact or pressure during bonding, and the silicon substrate 2 is not physically destroyed even if damage occurs, LE is used.
It does not affect the performance of the D array. Also, in the example,
The exposed area of the silicon substrate 2 is extremely wider than the area of the GaAs layer 6, and since wire bonding can be performed on the wide silicon substrate 2, mutual contact of the gold wires 20 can be prevented and the external connection layer 18 of the wire bonding portion is locally formed. Since it can be made wider and larger, bonding becomes easier. On the other hand, if the electrode 16 is directly wire-bonded on the GaAs layer 6, the GaAs layer 6 is frequently broken due to the pressure or impact of the bonding. It should be noted that the type of wire bonding may use not only ultrasonic waves and heat but also heat and ultrasonic waves only.

FIG. 2 shows a second embodiment. The manufacturing method itself of the LED array is similar to that of FIG. In the figure, 26 is an IC for controlling an LED array, for example, and bumps 30 such as gold, tin, and solder provided on the external connection layer 18 and I
The bumps 32 provided on C26 are connected to make an external connection. Since the silicon substrate 2 is inexpensive and a large substrate can be used, the play portion of the silicon substrate 2 is used as a substrate for a control IC or the like. The bump 30 is provided, for example, by bonding a gold wire or a tin wire to the external connection layer 18 while applying ultrasonic waves and heat as in the wire bonding, and then cutting the root of the wire. Alternatively, like a normal solder bump, after forming a barrier film, a plating electrode as a base conductive metal film is formed, a portion other than the bump formation portion is covered with a resist, and solder plating is performed to form a bump. Then, the resist is removed, and the barrier film and the plated electrode other than the bumps are removed. Such a process is performed on the GaAs layer 6 when the bumps are formed from a gold wire or a tin wire by a method similar to the wire bonding, the GaAs layer 6 is destroyed, and the solder bumps are formed. There is a risk of contaminating the GaAs layer 6. On the other hand, if the bumps 30 are formed on the surface of the silicon substrate 2, the GaAs layer 6 is not affected when the bumps are formed by a method similar to the wire bonding of gold wires or tin wires. However, it is only necessary to protect the GaAs layer 6 with a resist.

FIG. 3 shows a third embodiment. The manufacturing method itself of the LED array is similar to that of FIG. In the figure, 17 is an electrode layer arranged so as to vertically cross the surface of the GaAs layer 6, 34 is a glass substrate of the LED printer head, and 36 is a data wiring provided on the glass substrate 34. It is preferable that the data wiring 36 is not provided on the light emitting layer to prevent light scattering by the data wiring 36. The total thickness of the bumps 30 and 32 is set to be slightly larger than the thickness of the GaAs layer 6, and the light emitting layer of the LED array faces the glass substrate 34. By doing this, the LED array can be externally connected without wire bonding.
It is possible to eliminate a short circuit between the gold wires 20 due to the high density.
Further, the heights of the light emitting layers are made uniform with respect to the glass substrate 34, and the variation in the heights of the light emitting layers due to the variation in the thickness of the silicon substrate 2 or the like can be eliminated, and the focus performance can be improved.

In FIG. 3, the electrode 17 is formed so as to cross the GaAs layer 6 vertically. The reason for this is shown in FIG. What is shown in the figure is the connection relationship between the data wiring 36 and the electrode layer 17. In the LED printer head, a large number of LED arrays are used, and each array is operated by time-division drive, for example. Therefore, the data wirings 36 are also formed, for example, by the number of one array (for example, 64). And for the convenience of wiring,
The data wiring 36 is arranged so as to be folded back for each array. Further, the data wiring 36 is not provided near the light emitting layer of the LED array in order to prevent light scattering. Here, the electrode layer 17 bypasses the data wiring 36 to complete the wiring. If this is not done, the data wiring 36 will also be provided in front of the light emitting layer, and the light from the LED array will be scattered and the efficiency will decrease.

FIG. 5 shows a fourth embodiment. This embodiment is a modification of the embodiment of FIG. 2, in which a part of the silicon substrate 2 on the right side of the drawing is provided with a power supply for the LED array, a control IC, etc. 18 is connected. In this way, the GaAs LED array and the control circuit can be incorporated in one silicon substrate 2.

[0015]

According to the present invention, the Ga of the LED array is not damaged or destroyed due to wire bonding or bump formation.
The electrode of the As layer can be connected to the outside. For example, in the case of wire bonding, destruction of the GaAs layer due to pressing force or ultrasonic waves can be avoided, and in the case of bumps, steps such as barrier film formation, plating electrode formation, solder plating, etc. can be performed with the exception of the GaAs layer. Can be done in part
The contamination of the GaAs layer can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a sectional view of a second embodiment.

FIG. 3 is a sectional view of a third embodiment.

FIG. 4 is a diagram showing an electrode configuration of a third embodiment.

FIG. 5 is a sectional view of a fourth embodiment.

FIG. 6 is a cross-sectional view showing a manufacturing process of an example.

[Explanation of symbols]

 2 Silicon substrate 6 GaAs layer 16 Electrode layer 18 External connection layer 30 Bump 32 Bump 34 Glass substrate 36 Data wiring 38 Control IC formation area

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location H04N 1/036 A 9070-5C 1/04 101 7251-5C

Claims (1)

Claim: What is claimed is: 1. In an LED array in which a GaAs layer as a light emitting layer is epitaxially grown on a heterogeneous substrate made of a material different from GaAs, an electrode layer is formed on the surface of the GaAs layer, and An LED array, wherein an electrode layer is drawn onto the different type substrate and externally connected thereto.