DE-102022005196-B4 - IMPROVED SEMICONDUCTOR LIGHT SENSOR

DE102022005196B4DE 102022005196 B4DE102022005196 B4DE 102022005196B4DE-102022005196-B4

Abstract

Photosensitive semiconductor structure (2) comprising the following: a substrate (4); a first doped upper region (8) of the substrate (4) which has a first doping type; a second doped upper region (40) of the substrate (4) which is laterally separated from the first doped upper region (8) and has a second doping type; an isolation structure (20) between the first (8) and the second doped upper region (40); a low-resistance path for current flow between the first (8) and the second doped upper region (40), which is arranged below the insulating structure (20) and around an enclosed region (4') of the substrate (4) having a higher resistance; a first implant region (10) which is arranged below the first doped upper region (8) and which is in direct contact with the first upper region (8), wherein the first implant region (10) has the second doping type, such that a pn junction (6) is arranged between the doped upper region (8) and the first implant region (10), wherein the enclosed region (4') is at least partially enclosed on one side by the first implant region (10) and the low-resistance path passes through the first implant region (10); and a second implant area (32) having a second doping type and located below the first implant area (10) and in direct contact with the first implant area (10), wherein the enclosed area (4') is enclosed on one side by the second implant area (32) and wherein the low-resistance path passes through the second implant area (32).

Inventors

Daniel Gäbler
Alexander Zimmer
Robin Weirauch

Assignees

X-FAB Global Services GmbH

Dates

Publication Date: 20260513
Application Date: 20220510
Priority Date: 20210510

Claims (1)

A photosensitive semiconductor structure (2) comprising: a substrate (4); a first doped upper region (8) of the substrate (4) having a first doping type; a second doped upper region (40) of the substrate (4) separated laterally from the first doped upper region (8) and having a second doping type; an insulating structure (20) between the first (8) and the second doped upper region (40); a low-resistance path for current flow between the first (8) and the second doped upper region (40), arranged below the insulating structure (20) and around an enclosed region (4') of the substrate (4) having a higher resistance; a first implant region (10) arranged below the first doped upper region (8) and in direct contact with the first upper region (8) wherein the first implant region (10) has the second doping type, such that a pn junction (6) is arranged between the doped upper region (8) and the first implant region (10), wherein the enclosed region (4') is at least partially enclosed on one side by the first implant region (10) and the low-resistance path passes through the first implant region (10); and a second implant region (32) having a second doping type and located below the first implant region (10) and in direct contact with the first implant region (10), wherein the enclosed region (4') is enclosed on one side by the second implant region (32) and wherein the low-resistance path passes through the second implant region (32).

Description

TECHNICAL AREA The present invention relates to semiconductor light sensors, such as avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs), and methods for manufacturing them. GENERAL STATE OF THE ART A single-photon avalanche diode (SPAD) comprises a pn junction across which a high reverse bias is applied to cause an avalanche event to occur when a charge carrier generated by light enters the multiplication region around the pn junction. One problem with existing SPADs is that the light detection probability is reduced for either shorter or longer wavelengths and is highly dependent on the excessive bias voltage. A well-designed photodiode exhibits stable response over a wide range of reverse bias voltages, and SPADs today require a well-chosen and tightly controlled over-bias to show a similar level of continuity in their response behavior. LÓPEZ-MARTÍNEZ, Juan Manuel [et al.]: Limitation of SPADs quantum efficiency due to the dopants concentration gradient. In: 2020 27th IEEE international conference on electronics, circuits and systems, November 23-25, 2020. Glasgow : IEEE, 2020. pp. 1-4 . investigates the role of doping concentration gradients in the collection of photons in single-photon avalanche diodes (SPADs) and how these can be designed to maximize the collection efficiency. US 2016 / 0 218 236 A1 Disclosing an avalanche photodiode operating in Geiger mode, the device comprises a PN junction formed on a substrate, with a first semiconductor region and a second semiconductor region comprising an anode and cathode. The device further comprises a third semiconductor region, which is in physical contact with the second region but not with the first, and has the same semiconductor type as the first semiconductor region. Additionally, the device includes a diode on the second semiconductor region, the turn-on voltage of which is higher than that of the PN junction. BRIEF SUMMARY OF THE INVENTION The invention provides a photosensitive semiconductor structure as claimed in claim 1. Preferred embodiments of the invention will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS 1 shows a schematic representation of a previous design of a photosensitive semiconductor structure that includes a p-doped implant region;2 shows a graphical representation of the doping profile of the photosensitive semiconductor structure of 1 ;3 shows a schematic representation of a photosensitive semiconductor structure according to an embodiment that includes two p-doped implant regions;4 shows a graphical representation of the doping profile of the photosensitive semiconductor structure of 3 ;5 shows a schematic representation of a photosensitive semiconductor structure that has a low-resistance contact area;6 shows a schematic representation of a light-sensitive semiconductor structure that has an enclosed area;7 shows a schematic representation of a photosensitive semiconductor structure according to an embodiment comprising two p-doped implant regions, a low-resistance contact region and an enclosed region;8 shows a graphical representation of the doping profile of the photosensitive semiconductor structure of 7 ;9 shows a schematic representation of a photosensitive semiconductor structure according to another embodiment, comprising two p-doped implant regions;10 shows a graphical representation of the doping profile of the photosensitive semiconductor structure of 9 ;11a shows a first step in a procedure according to one embodiment;11b shows a second step of the procedure, which includes an initial implantation;11c shows a third step of the procedure, which includes a second implantation;11d shows a fourth step of the procedure;12 shows a schematic representation of a manufacturing step of a building block;13 shows a schematic representation of a manufacturing step of a component using a photoresist mask with a gap;14a shows a photoresist mask before implantation;14b The photoresist mask is shown after implantation;15a shows a different photoresist mask before implantation; and15b The other photoresist mask is shown after implantation. DETAILED DESCRIPTION 1 Figure 1 shows a schematic cross-section of a light sensor 2, enclosed for illustrative purposes. The light sensor 2 comprises a p-doped substrate 4 with a pn junction 6 between an n-doped region 8 and a p-doped region 10. The multiplication region 12 is arranged around the pn junction 6, where charge is built up to a measurable output current. The n-doped region 8 forms part of a cathode, which is connected via a contact 14 to part of a metal layer 16. The p-doped region 10 and the substrate 4 form part of the anode, which is connected via a contact 18 to part of a metal layer 16. Shallow trench insulation (STI) 20 separates the anode and the cathode at the surface. A bias voltage is applied across the anode and cathode (via contacts 14 and 18) so that when a charge carrier generated by light enters the