RU2318272C1 - METHOD FOR PRODUCING HIGH-SPEED MULTICOMPONENT PHOTODETECTORS BUILT AROUND EPITAXIAL STRUCTURES InGaAs/InP - Google Patents

Abstract

FIELD: laser location systems, laser radiation detection, infrared spectrometry, multiple-spectrum fiber-optic communication lines, new-generation night viewing systems.

SUBSTANCE: photodetector producing method includes coating of n-InP/n-In_0.53 Ga₀₄₇ As/n⁺-InP epitaxial wafer incorporating epitaxial layers n-InP/n-In_0.53 Ga_0.47 As and substrate n⁺-InP with silicon nitride film both on n-InP epitaxial layer end and on n⁺-InP one. Diffusion windows are covered with photolithographic layer by way of plasmochemical etching in silicon nitride film on end of n-InP/n-In_0.53 Ga_0.47 As epitaxial layers and marks are formed for further alignment of photomask patterns on n⁺-InP substrate end. Local p-n junction is formed in n-InP/n-In_0.53 Ga_0.47 As epitaxial layers by cadmium diffusion in soldered exhaust ampoule from Cd₃P₂ source. Epitaxial wafer n-InP/n-In_0.53 Ga₀₄₇ As/n⁺-InP is coated with second layer of Si₃N₄ film on end of n-InP/n-In_0.53 Ga_0.47 As epitaxial layers. Contact windows are opened in second layer of Si₃N₄ film and Au/Ti ohmic contacts are made for p⁺ regions. Contact windows are opened in Si₃N₄ film on n⁺-InP substrate side for n⁺-InP region by way of photolithography and plasmochemical etching. Si₃N₄ film remains above p-n junction region in this case that functions as clearing coating. Titanium-sublayer gold is evaporated in vacuum so that metal plating is formed for n⁺-InP substrate contacts. Pattern that affords ohmic contact for n⁺-InP substrate on one end and forms diaphragm limiting shading region by spatial charge region of multicomponent photodetector only on other end is etched in titanium-sublayer gold by photolithographic method.

EFFECT: enhanced speed of photosensitive component due to eliminating non-depleted n-region shading when using planar technology for multicomponent photodetector manufacture.

1 cl, 5 dwg

Description

The invention relates to the manufacturing technology of semiconductor photodetectors and can be used to create multi-element arrays of pin photodiodes based on InGaAs / InP heterostructures intended for use in laser location systems, laser detection, IR spectrometry, multispectral fiber optic lines, as well as a new generation of night-time systems visions. In addition, the invention can be used in the manufacture of multi-element matrix pin-photodiodes with any number of elements based on compounds A ₃ B ₅ .

A known method of manufacturing an InGaAs multi-element photodetector (Marshall J. Cohen et al. Commercial and Industrial Applications of Indium Gallium Arsenide Near Infrared Focal Plane Arrays described in Part of the SPIE Conference on Infrared Technology and Applications XXV Orlando, Florida, April 1999 SPIE Vol. 3698), no mesa-planar technology using the n-InP / n-In _0.53 Ga _0.47 As / n ⁺ -InP epitaxial structure, developed by Sensor Unlimited, Inc. (USA). Single photodiodes are planar, and all diffusion processes are carried out with a mask of a passivating film of silicon nitride (Si ₃ N ₄ ). The photodiode array is isolated by mesa etching the epitaxial layers of n-InP and n-In _0.53 Ga _0.47 As to the n ⁺ -InP substrate, and an electrical contact is formed to n ⁺ -InP, the so-called general conclusion. The manufacturing method technology includes the following processes:

- the plate is covered with a film of Si ₃ N ₄ ^. for good passivation of the surface;

- photolithographic method in the film open the window under diffusion using plasma-chemical etching;

- the pn junction is formed by diffusion of zinc in a closed pipe from a source of ZnAs. The time and temperature of diffusion are chosen so that the diffusion front is at a depth of about 2500 A in the InGaAs active layer;

- the plates are coated with a second layer of a Si ₃ N ₄ film;

- in the second layer of Si ₃ N ₄ open contact windows and create ohmic contacts by metallization of gold / zinc (Au / Zn);

- the photodiode array is isolated by mesa-etching, and n ⁺ -InP substrate contact is formed;

- the ohmic contact gold / germanium (Au / Ge) is applied to the substrate and, thus, form both contacts on the plate;

- on the reverse side apply an antireflection coating;

- metallization of gold / titanium (Au / Ti) is applied as the upper layer both on the ohmic contacts to the p-region and on the ohmic contacts to the n ⁺ -InP substrate;

- indium columns are applied to the contacts as to the p-region, and to the contacts to the substrate n ⁺ -InP;

- the plates are rejected and cut into crystals.

The disadvantages of this method are:

- the formation of the contact system at two levels of the relief plate, which is fraught with a break in the metallization on the step, which in turn leads to a decrease in the yield and reliability of the photosensitive element;

- when the crystal is illuminated from the back side (during operation as part of the photoelectronic module), there is a high probability of lateral illumination outside the space charge region (SCR), which leads to a decrease in the speed of the photosensitive element due to the diffusion component of the collection time of the charge carriers generated by light.

In the general case, the pin-PD photoresponse rate (τ) is limited by three factors:

- the time constant of the RC circuit (τ _RC );

- time of flight, which is determined by the drift of the photocarriers generated in the SCR structure (τ dr);

- the delay associated with the diffusion of photocarriers generated in the quasineutral p- and n-regions of the pin structure (τ diff).

The time constant of the RC circuit τ _RC = Rn × C,

where Rн is the load resistance, C is the capacity of the pn junction.

Given that in high-speed systems, the load resistance Rn is usually 50 Ohms, the series PD resistance (determined mainly by the resistance of ohmic contacts) is Rs << Rn, and the pn junction capacitance for the site is 60 × 60 μm and carrier concentration the charge in the heterostructure of less than 2 × 10 ¹⁵ cm ^-3 does not exceed 1 pF, τ _RC = 50 × 1 × 10 ^-12 = 50 × 10 ^-12 s = 50 ps.

The collection time of the photocarriers is determined by the drift time of the carriers generated in the SCR through this region, τdr, as well as the diffusion time of the photocarriers generated outside the SCR, τdif. The carrier drift velocity at a field strength of 10 ⁴ V / cm (created by a bias voltage of ~ 5-10 V) is limited by scattering and is ~ 10 ⁷ cm / s in In _1-X Ga _X As _1-Y P _Y compounds [1]. Then, at Wopz = 2 μm, τdr = 20 ps.

For electrons diffusing to the SCR through the p-region of the active layer, the diffusion time:

where Ln is the diffusion length of electrons (in our case, when the thickness of the p-region h _{p1 is} less than the diffusion length of electrons [1], Ln is replaced by h _p1 ).

At h _p1 = 0.5 μm and Dn = 259 cm ² / s

τdif n = (0.5 × 10 ^-4 ) ² / (2.4 × 259) = 4 × 10 ^-12 s = 4 ps.

It should be noted that for a planar structure with backlight, expression (2) is valid only in the absence of exposure to an undepleted n-region adjacent to the SCR. When radiation is absorbed in the n-region, the even more inertial component of the hole current can lead to a significant limitation of the device performance.

For holes diffusing to the SCR through a nondepleted n-region:

Lp = Ln = 1-2 microns - the diffusion length of holes [2],

Dp = 13 cm ² / s is the diffusion coefficient of holes [2].

τdif p = (1 × 10 ^-4 ) ² / (2.4 × 13) = 321 × 10 ^-12 s = 321 ps

Hence,

τdif = τdif n + τdif p = 325 ps

Thus performance

τ = √ (50 ² +20 ² +325 ² ) = 329.4 ps for the first case, and

τ = √ (50 ² +20 ² +4 ² ) = 54.1 ps for the second case.

The objective of the invention is to increase the speed of the photosensitive element by eliminating the possibility of exposure to the peripheral undepleted n-region with planar technology for manufacturing a multi-element photodetector.

The technical result is achieved by the fact that the inventive method of manufacturing a high-speed multi-element photodetector based on InGaAs / InP heterostructures includes the following processes:

- the n-InP / n-In _0.53 Ga _0.47 As / n ⁺ -InP epitaxial plate is coated with a silicon nitride film, both from the epitaxial layer of n-InP and from the side of the n ⁺ -InP substrate;

- open the diffusion windows using the photolithographic method by plasma-chemical etching in a Si ₃ N ₄ film from the side of the n-InP / n-In _0.53 Ga _0.47 As epitaxial layers and form marks for further alignment of the patterns of the photo masks from the side of the substrate n ⁺ -InP;

- in the epitaxial layers of n-InP / n-In _0.53 Ga _0.47 As form a local pn junction by diffusion of cadmium;

- the n-InP / n-In plate _0.53 Ga _0.47 As / n ⁺ -InP is coated with a second layer of a Si ₃ N ₄ film on the side of the epitaxial layers of n-InP / n-In _0.33 Ga _0.47 As;

- open the contact windows in the second layer of Si ₃ N ₄ and create ohmic contacts of gold with a titanium sublayer to the p + regions;

- by a photolithographic method, in the silicon nitride film from the side of the n ⁺ -InP substrate, windows are opened to contact the n ⁺ -InP region by plasma-chemical etching, while a silicon nitride film remains over the region of pn junctions, which serves as an antireflection coating;

- sprayed in vacuum Au / Ti so that metallization is formed for contact n ⁺ -InP to the substrate;

- by a photolithographic method, a pattern is etched in a gold film with a titanium sublayer, which, on the one hand, is contact and provides ohmic contact to the n ⁺ -InP substrate, and on the other hand forms a diaphragm that limits the illumination region only to the space charge region of the multi-element photodetector.

Such a sequence of operations ensures that radiation during the illumination through the substrate to the space charge region is precisely exposed and, thus, the diffusion of holes into the n-region from the periphery is eliminated and, therefore, the response time of a planar multi-element photodiode is increased, while maintaining a completely planar structure. With this manufacturing method, the possibility of metallization breaks on the step is eliminated, as is the case with the mesa-planar technology described above.

Figures 1-5 show the manufacturing technology of a high-speed multi-element photodetector based on InGaAs epitaxial structures.

The n-InP / n-In _0.53 Ga _0.47 As / n ⁺ -InP epitaxial plate containing the n-InP / n-In _0.53 Ga _0.47 As epitaxial layers and the n ⁺ -InP substrate are coated with a film silicon nitride (Si ₃ N ₄ ), both from the side of the n-InP epitaxial layer and from the side of the n-InP substrate (Fig. 1). Using a photolithographic method, the diffusion windows are opened by plasma-chemical etching in a silicon nitride film from the side of the n-InP / n-In _0.53 Ga _0.47 As epitaxial layers and marks are created for further alignment of the photo masks from the side of the n ⁺ -InP substrate . In the epitaxial layers of n-InP / n-In _0.53 Ga _0.47 As, a local pn junction is formed by diffusion of cadmium in a sealed pump-out ampoule from a Cd ₃ P ₂ source. The n-InP / n-In plate _0.33 Ga _0.47 As / n ⁺ -InP is coated with a second layer of silicon nitride (Si ₃ N ₄ ) film on the side of the epitaxial layers of n-InP / n-In _0.53 Ga _{0, 47} As (Fig. 2). Contact windows are opened in the second layer of silicon nitride and create ohmic contacts of gold with a titanium sublayer (Au / Ti) to the p ⁺ regions (Fig. 3). Using a photolithographic method, in the silicon nitride film from the side of the n ⁺ -InP substrate, windows are opened to contact the n ⁺ -InP region by plasma-chemical etching, while a silicon nitride film remains over the region of pn junctions, which serves as an antireflection coating (Fig. .four). Gold is sprayed in a vacuum with a titanium sublayer, so that metallization is formed to contact n ⁺ -InP substrate (Fig. 4). In a photolithographic method, a pattern is etched in a gold film with a titanium sublayer, which, on the one hand, is contact and provides ohmic contact to the n ⁺ -InP substrate, and on the other hand forms a diaphragm that limits the illumination region only to the space charge region of the multi-element photodetector (Fig. 5 )

Thus formed on the substrate side n ⁺ -InP aperture eliminates the possibility of lateral illumination of the peripheral undepleted n-region with planar technology for manufacturing a crystal of a multi-element photodetector. In turn, with planar technology, the possibility of a metallization break on the step is eliminated.

The proposed method was tested at the applicant enterprise when developing the technology of uncooled high-speed FEM of the spectral range of 0.8-1.55 μm FUK 7L (product documentation BUTI.432234.060).

The authors experimentally established that when using the developed method for manufacturing a multi-element line of photosensitive elements, which is part of an uncooled high-speed FEM, a spectral range of 0.8-1.55 μm with 128 elements with a unit size of 60 × 60 μm, the measured value of τ does not exceed 100 ps. To measure the impulse characteristics at a wavelength of 1.55 μm, we used an experimental semiconductor laser with a radiation wavelength of 1.548 μm, which was triggered by rectangular current pulses of the G5-84 generator. The photocurrent pulses were recorded with a C1-122 oscilloscope. Load resistance Rn = 50 Ohm, operating voltage Up = -5V.

As a result of using the proposed method, planar multi-element photodiodes (arrays and arrays) with any number of elements suitable for integration with silicon amplification and signal processing microcircuits can be manufactured. This method can be applied to other heterostructures of the A ₃ B _{5 system} .

Literature.

1. Optical communication technology. Photodetectors / F.Capasso and others; under the editorship of W. Tsanga: Per. from English under the editorship of M.A. Trishenkova. - M .: Mir, 1988 .-- 526 p.

2. Forrest S. Performance of InGaAsP photodiodes with dark current limited by diffusion, generation-recombination and tunneling // IEEE Journal of Quantum Electronics. - 1981. QE-17. - N2. - P.217-226.

Claims (1)

A method of manufacturing a high-speed multi-element photodetector based on n-InP / n-In _0.53 Ga _0.47 As / n ⁺ -InP epitaxial structures, the n-InP / n-In _0.53 Ga ₀ epitaxial plate _{, 47} As / n ⁺ -InP is coated with a silicon nitride film, both from the side of the n-InP epitaxial layer and from the side of the n ⁺ -InP substrate, the diffusion windows are opened by the photolithographic method using plasma-chemical etching in the silicon nitride film from the epitaxial side layers of n-InP / n-In _0.53 Ga _0.47 As and form labels for further pattern matching s on the n + -InP substrate side, in the epitaxial layers of n-InP / n-In _0.53 Ga _0.47 As, a local pn junction is formed by diffusion of cadmium, the n-InP / n-In _0.53 Ga ₀ plate ₄₇ As / n ⁺ -InP cover the second layer of silicon nitride film on the side of the epitaxial layers of n-InP / n-In _0.53 Ga _0.47 As, open the contact windows in the second layer of the silicon nitride film and create ohmic contacts of gold with the titanium sublayer a p + region, a photolithographic method in the silicon nitride film from the n + -InP substrate under the contact windows opened to the field n ⁺ -InP via plasma-chemical etching, thus on The region of pn junctions remains a silicon nitride film, which serves as an antireflective coating, gold is sprayed in a vacuum with a titanium sublayer, so that metallization is formed to contact the n + -InP substrate, and a pattern is etched in a gold film with a titanium sublayer that on the one hand, it is contact and provides ohmic contact to the substrate, n + -InP, and on the other hand forms a diaphragm restricting the illumination region to only the space charge region of the multi-element photodetector.

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