JPS62282480A - Formation of electrode - Google Patents

Abstract

PURPOSE:To form a platinum stripe electrode to enable continuous oscillation at a high temperature, and to enhance the characteristic of an element by a method wherein after a part of a dierectric film is removed in a stripe type to expose the surface of a semiconductor, platinum is evaporated on the whole surface, alloying treatment is performed, and then a platinum layer on the dielectric film is removed. CONSTITUTION:A clad layer 6, an active layer 5, a clad layer 4 and a cap layer 3 are grown in order on a substrate 7, an SiO2 oxide film is laminated thereon, and photolithography is performed using a mask to form stripe type grooves. The wafer and ZnP2, ZnAs2, InP are put in a quartz ampoule to be sealed in a vacuum, Zn is diffused up to the middle of the p-type clad layer 4, and the SiO2 film is removed. An SiO2 film is adhered again, stripe type grooves of two pieces are formed performing positioning of a mask, and mesa etching is performed using a Br2-CH3OH solution. Then an SiO2 film 10 is adhered again, positioning of a mask is performed, and stripes are formed. Pt is evaporated thereon, and after alloying is performed, the platinum layer on the dielectric film is removed.

Description

[Detailed description of the invention] Detailed description of the λ invention (Industrial application field) The present invention relates to a method for forming electrodes of semiconductor devices.

(Prior Art) A number of structures have been invented for semiconductor lasers in order to improve their characteristics such as high output, low power operation, high temperature operation and long life.

In visible light semiconductor lasers that emit red light in the visible range, the greatest goal is to shorten the oscillation wavelength.

However, in semiconductor lasers with short oscillation wavelengths, the bandgap energy of the active layer increases, making it difficult to create a sufficient bandgap difference with the cladding layer, and the composition of the active layer approaches the indirect transition region, resulting in a decrease in luminous efficiency. However, the injected carriers tend to leak from the active region. For this reason, there was a problem in that the oscillation threshold current increased, making it difficult to cause continuous rooting at room temperature. Therefore, device structures that make it possible to reduce the threshold current Ith, the threshold current density J'th, and the thermal resistance Rth have been studied.

Conventional structures of visible light semiconductor lasers include S10° oxide film stripes and Zn diffused planar stripes, which have been prototyped since the early stages of development. These are relatively easy to manufacture and are effective when it is desired to know the oscillation wavelength, etc. But 1.
In these conventional structures, when the current constricted inside the stripe spreads within the cladding layer and Ith increases, in the former structure, the current is transferred to an oxide film with poor thermal conductivity, resulting in poor heat dissipation and continuous operation. The temperature does not get high. Furthermore, even in a buried structure or a self-aligned structure in which reverse bias regions are created on both sides to confine current, the existence of leakage current cannot be ignored, and there is also the problem that crystal growth must be performed more than once.

A mesa stripe structure laser was developed to solve these problems. Figure 2 shows an actual example. n-G
a As (11 Pll, 4/A
The entire uZn layer 10 is alloyed. and the width in the center is 5
The Au-Zn layer is removed by making two stripes using a mask with stripes of 5 μm on both sides of the 1 μm layer, and then etched with a bromine-methanol solution to form a mesa groove 20 squares 21.

The grooves 20, 21 should not reach the active layer 5.

The photoresist is removed and a Ti/Au electrode 1 is placed on top of it.
Deposit. After polishing the substrate, the n-side electrode 8 is deposited,
Complete the mesa stripe structure.

The characteristics of this structure are that the grooves 20 and 21 are formed to limit the area where the current flows, and that the effect is further strengthened by Zn diffusion and AuZn alloy, and that the grooves 20 and 21 are formed with an oxide film with low thermal conductivity. By layering unalloyed metals without adding metal, the threshold current density does not increase even if the stripe width is narrow and the threshold current is low, making it possible to realize an element with good heat dissipation. . With this structure, we achieved continuous oscillation at room temperature with a threshold current density of 4.5 kg/att (Japanese Journal of Applied Fixtures, (Japanese J,
Appl.

Phys, 'l 4, L 163.1985)).

(Problems to be Solved by the Invention) The structure shown in FIG. 2 effectively constricts the current, and the active layer 5
The heat generated in can be efficiently dissipated to the outside,
This made continuous oscillation possible at room temperature, but its lifetime was short enough to measure device characteristics, and the optical output was also short.
~2 mW.

In addition to the still high thermal resistance, a major cause of this deterioration is considered to be deterioration at the electrodes. [AuZn alloy has been used as the P-side ohmic electrode, but AuZn
has a high contact resistance and relatively good ohmic contact (<<, and tends to short-circuit when a large current is applied. Au/Sn is used as the heat sink, and during high-temperature operation, Sn may enter the crystal. There is also a risk that deterioration (solder ! migration y m S M ) may occur.Such deterioration of the electrode
This phenomenon has also been observed in semiconductor lasers, and is a major problem in improving the stability of semiconductor lasers.

(Means for Solving the Problems) The present invention provides means for solving the above-mentioned problems by forming a dielectric film on the semiconductor surface and forming a part of this dielectric film into stripes. After exposing the surface of the semiconductor, platinum (Pi) is deposited on the entire surface, alloying treatment is performed on the platinum, and then the platinum layer on the dielectric film is peeled off to form a platinum stripe electrode. 'This is a method of forming starch.

・(Function) PT has low contact resistance with semiconductors (, A u Z n e
Compared to Cr/Au, Ti/Au, etc., it is stable even at high temperatures and large currents and has a low degree of deterioration. Also, the electrode on pt (
It has the function of preventing special KAu) from entering the crystal. T
t/pt, /Au is used as the P-side electrode, but in the present invention, KPt is selectively deposited (in stripes) and alloyed, and the other regions are not alloyed and are simply layered with metal. The current is constricted. In other words, the effect of changing the electrodes to PT in the conventional structure shown in FIG. 2 is added.

(Example) The embodiment shown in FIG. 1 will be described below.

Figure 1(a) is a completed diagram, in which AuZn1iLO in Figure 2 is replaced with platinum Pt2. However, there are some differences in the manufacturing method as shown below.

n-type GaAs QP by hydride-vPE method
IC on aa/Ga composition graded substrate 7
An 8e-doped n-type InGaP clad GaAsP active layer 5, a Zn-doped PPinGaP cladding layer 4, and an undoped n-type InGaAsP cap layer 3 are successively grown. A 1/C3iO, oxide film was laminated by 2,000 layers using a thermal C'VD method, and photolithography was performed using a negative resist using a 7 μm wide mask.
Form stripe grooves. Wafer and ZnPl#
ZnAs! e InP is vacuum sealed in a quartz ampoule and diffused to the middle of the Znt-P shaped rad layer 4 by thermal diffusion, 810. It should be removed. S10 again. A film is applied, two stripe grooves each having a width of 5 μm and an interval of 5 μm are opened by mask alignment, and mesa etching is performed using a Br, -CH30H solution. In general, the grooves 20.11 do not reach the active layer 5 (although they may do so, as will be described later).

And S10. Figure 1 (1
)).

Next, Sin! The entire film 10 is now aligned with a 4 μm mask to form stripes (FIG. 1(C)).

P is sputter-deposited thereon and alloyed at 460° C. (FIG. 1(d)). The part where Pt2 is laminated on the cap layer 3 of the central stripe is alloyed and has strong adhesive strength, but the surrounding parts are on the Sin film 10 and have very poor adhesive strength. Then, after applying adhesive tape ttt from above and peeling it off, Sin! The Pt 2 on the film 10 is easily peeled off, leaving only the central portion (FIG. 1(e)).

To remove the membrane 10 (FIG. 1(f)),
After depositing "pt L", the substrate 7 is polished to about 100 μm, and uGaNi/Au 8 is deposited and alloyed (350"C) on the n side, and finally Ti/P is deposited on the p side for fusion.
t/Au is completed by vapor deposition (Fig. 1 (g) and (a)
)).

Note that without removing the Sin and oxide film 10, T is formed on it.
If the i/Pt/Au capacitor 1 is laminated, the current confinement can be more effectively achieved, and even if mesa etching is performed below the active layer 5, the current will not be short-circuited, so that the threshold current Ith can be further increased. Can be lowered. However, in this case, Sin has a low thermal conductivity.

Since the heat dissipation is worsened by the film, which causes problems during continuous operation and high temperature operation, the thickness of the film should be approximately 500~
We need to reduce the number to 600 people.

A semiconductor laser was manufactured using this method and the device characteristics were measured, but the deterioration at the electrode part that was observed conventionally was improved.
Good characteristics could be obtained.

(Effects of the Invention) As described above, by using platinum instead of the conventionally used ohmic electrode using AuZn, continuous oscillation at a higher temperature is possible, and device characteristics are improved. By adopting a method of selectively removing platinum on a dielectric film, it is possible to easily and effectively form an electric stripe b.
′-I can.

[Brief explanation of drawings]

Figure 1 shows an InGaAs film using a platinum electrode according to the present invention.
1 is a cross-sectional view of a P/InGaP visible light semiconductor laser, in which figure (a) is a completed view, and figures (b) to (g) sequentially show the manufacturing process from the middle (after mesa etching). FIG. 2 is a cross-sectional view of a similar semiconductor laser using conventionally used AuZntli. Agent Patent Attorney Nobu Honjo PTT Figure 1 (a) Figure 1 (1)) Figure 1 (e) Figure 1 Busy)
Figure 1 (f) Figure 1 (d) Figure 1 (9) Figure 2

Claims (1)

[Claims] A dielectric film is formed on a semiconductor surface, a part of this dielectric film is removed in a striped form to expose the semiconductor surface, and then platinum is deposited on the entire surface, and this platinum is subjected to an alloying treatment,
Next, a platinum stripe electrode is formed by peeling off the platinum layer on the dielectric film.