Control of light-generated load carriers

Abstract

Method for manufacturing a device (400) comprising the following steps: Providing a non-uniform doping profile in a semiconductor substrate (102) such that an electric field with vertical field vector components is generated in at least a part of a light conversion region (112) of the semiconductor substrate (102), and Generating (606) a control electrode structure comprising multiple control electrodes (106, 106b, 106c) above the non-uniform doping profile for steering light-generated charge carriers, wherein the control electrode structure is arranged between two diode structures (114) for accumulating the light-generated charge carriers, where the provision of the uneven doping profile exhibits: Providing (602) a doped layer (202) in the light conversion region (112), wherein the doped layer (202) comprises doping atoms, wherein providing the doped layer comprises generating the doped layer (202) such that the doped layer (202) has a lateral variation of a net doping concentration, wherein the lateral variation of the net doping concentration is symmetrical with respect to a center of the control electrode structure, Performing (604) a migration step to migrate at least some of the doping atoms of the doped layer (202) to an area above the doped layer (202), wherein the non-uniform doping profile in the vertical direction exhibits a local maximum of the net doping concentration in the doped layer (202), wherein the net doping concentration decreases in the vertical direction from the doped layer (202) towards the control electrode structure, so that light-generated charge carriers that are generated within a first depth region are directed towards the control electrode structure, wherein the net doping concentration decreases in the vertical direction from the doped layer (202) away from the control electrode structure, so that the light-generated charge carriers that are generated within a second depth region are directed away from the control electrode structure, where the doped layer (202) is a buried layer, furthermore, at least one additional doped layer (204) is provided at a depth that differs from the depth of the doped layer (202), wherein the further doped layer (204) is spatially separated from the doped layer (202) by the semiconductor substrate, wherein the further doped layer (204) provides a shielding effect for the diode structures (114), so that the light-generated charge carriers may not move directly from within the light conversion region (112) to the diode structures (114), but only under the influence of electric fields generated by the control electrodes (106, 106b, 106c), and wherein the further doped layer (204) extends in a lateral direction at least beyond a defined area to which the light-generated charge carriers are directed.

Description

[0001] Light-sensitive devices, such as imagers, are used in many applications and variations. In addition to solid-state imaging devices, such as charge-coupled devices (CCDs) or complementary metal-oxide-semiconductor (CMOSs), which are capable of providing 2D (two-dimensional) images, 3D imaging devices or depth imaging devices are becoming increasingly popular for several applications. For 3D imaging and depth imaging, optical sensors based on time-of-flight (TOF) hold great promise for future applications ranging from capturing a profile of objects or environments, tracking and recognizing objects and people, detecting the movement of specific parts, or even gesture recognition.

[0002] In applications involving TOF sensors, as well as other optical imaging devices, charge transfer is critical for the operation of the imaging device. For example, for the demodulation of incident light provided by devices based on the time-of-flight principle, the timely transfer of charge carriers to the readout nodes is crucial for the accuracy of depth information and other operating parameters.

[0003] In the publications US 2011 / 0 291 164 A1, US 2011 / 0 089 471 A1, JP 2012– 083215 A and US 4 160 985 A, light-sensitive sensors are proposed.

[0004] The present invention is based on the object of creating an improved concept for controlling light-generated charge carrier transport in imaging devices.

[0005] This object is achieved by a method according to claim 1 and a device according to claim 16.

[0006] According to one aspect, a method for fabricating a device comprises the following steps: providing a non-uniform doping profile in a semiconductor substrate such that an electric field with vertical field vector components is generated in at least a portion of a light conversion region of the semiconductor substrate, and generating a control electrode structure having a plurality of control electrodes above the non-uniform doping profile for directing light-generated charge carriers. The control electrode structure is arranged between two diode structures for accumulating the light-generated charge carriers. Providing the non-uniform doping profile comprises providing a doped layer in the light conversion region. The doped layer comprises doping atoms. Providing the doped layer comprises generating the doped layer such that the doped layer has a lateral variation of a net doping concentration.The lateral variation of the net doping concentration is symmetrical with respect to a center of the control electrode structure. Providing the non-uniform doping profile further comprises performing a migration step for migrating at least a portion of the doping atoms of the doped layer to a region above the doped layer. The non-uniform doping profile has a local maximum of a net doping concentration in the doped layer in the vertical direction. The net doping concentration decreases in the vertical direction from the doped layer toward the control electrode structure, so that light-generated charge carriers generated within a first depth range are directed to the control electrode structure.The net doping concentration decreases in the vertical direction from the doped layer away from the control electrode structure, so that the light-generated charge carriers generated within a second depth range are directed away from the control electrode structure. The doped layer is a buried layer. Furthermore, at least one further doped layer is provided at a depth different from the depth of the doped layer, wherein the further doped layer is spatially separated from the doped layer by the semiconductor substrate. The further doped layer provides a shielding effect for the diode structures, so that the light-generated charge carriers are not allowed to move directly from within the light conversion region to the diode structures, but only under the influence of electric fields generated by the control electrodes.The further doped layer extends in the lateral direction at least beyond a defined area to which the light-generated charge carriers are directed.

[0007] In embodiments, generating the control electrode structure comprises generating a plurality of control electrodes for applying a stepwise electrical potential distribution in the light conversion region.

[0008] In embodiments, a portion of the doping atoms in the range between 1% and 30% migrates to the region above the doped layer.

[0009] The lateral variation of the net doping concentration may, in embodiments, comprise at least a variation of 30% of the maximum net doping concentration of the doped layer.

[0010] Furthermore, at least a first portion of the doped layer may be provided with a first net doping concentration and a second portion of the doped layer may be provided with a second net doping concentration, such that the second net doping concentration is lower than the first net doping concentration.

[0011] The method may further comprise providing a third portion of the doped layer with the first net doping concentration, wherein the second portion of the doped layer lies between the first portion and the third portion of the doped layer. The second portion may lie beneath a central portion of the control electrode structure.

[0012] The second net doping concentration may be equal to a net doping concentration of the light conversion region.

[0013] The net doping concentration of the non-uniform doping profile can increase with increasing depth along a vertical direction from a first doping concentration in the range between 10 12 cm -3 and 10 15 cm -3 to a second doping concentration in the range between 1.1 × 10 15 cm -3 and 10 20 cm -3 gain weight.

[0014] The non-uniform doping profile may be mirror-symmetric with respect to a predefined plane. The non-uniform doping profile may further be provided such that the electric field has vertical and lateral field vector components in at least a portion of the light conversion region.

[0015] By providing the non-uniform doping profile, a stepwise doping profile can be created in the vertical direction. By providing the non-uniform doping profile, a graded doping profile can be created in the vertical direction.

[0016] According to another aspect, a device comprises: a semiconductor substrate having a light conversion region for converting light into light-generated charge carriers, two diode structures for accumulating the light-generated charge carriers, and a control electrode structure between the diode structures having a plurality of control electrodes for generating a potential distribution such that the light-generated carriers are guided to the diode structures to accumulate the light-generated charge carriers based on signals applied to the control electrode structure. A non-uniform doping profile is provided in the semiconductor substrate to generate an electric field with vertical field vector components in at least a portion of the light conversion region. The non-uniform doping profile has a local maximum of a net doping concentration in a doped layer in the light conversion region in the vertical direction.The non-uniform doping profile is created by the migration of at least a portion of doping atoms of the doped layer to a region above the doped layer. The net doping concentration decreases in the vertical direction from the doped layer toward the control electrode structure, so that light-generated charge carriers generated within a first depth range are directed toward the control electrode structure. The net doping concentration decreases in the vertical direction from the doped layer away from the control electrode structure, so that light-generated charge carriers generated within a second depth range are directed away from the control electrode structure.The non-uniform doping profile exhibits a variation in the net doping concentration that is symmetric with respect to a center of the control electrode structure, such that the electric field is mirrored with respect to a plane through a center of the control electrode structure. The doped layer exhibits a lateral variation in the net doping concentration. The doped layer is a buried layer. The device further comprises at least one further doped layer at a depth that is different from the depth of the doped layer. The further doped layer is spatially separated from the doped layer by the semiconductor substrate.The additional doped layer provides a shielding effect for the diode structures, preventing the light-generated charge carriers from moving directly from within the light conversion region to the diode structures, but only under the influence of electric fields generated by the control electrodes. The additional doped layer extends laterally at least beyond a defined region to which the light-generated charge carriers are directed.

[0017] The non-uniform doping profile can provide an electric field for directing light-generated carriers to a predefined section of the control electrode structure.

[0018] The non-uniform doping profile may further provide an electric field such that photogenerated charge carriers generated within a first depth range are directed to the predefined portion of the control electrode structure and photogenerated charge carriers generated within a second depth range are directed away from the control electrode structure.

[0019] The magnitude of the vertical component of the electric field may increase with increasing depth in embodiments.

[0020] The device may further be configured to generate amplitude-modulated light based on a modulation signal to be transmitted to an object, wherein the control electrode structure is configured to receive an electrical signal linked in a temporal relationship to the modulation signal. The non-uniform doping profile may further provide an electric field having lateral and vertical field vector components in at least a portion of the light conversion region.

[0021] In embodiments, the non-uniform doping profile may be a vertically graded or step-wise doping profile.

[0022] Further embodiments are shown in the following detailed description and the attached figures. Fig. 1A shows a device which does not fall within the wording of the patent claims, Fig. Figure 1B shows example potential distributions for the device of Fig. 1A, Fig. Figure 2A shows another device which does not fall within the wording of the patent claims, Fig. Figure 2B shows example potential distributions for the device of Fig. 2A, Fig. 3 shows a further device which does not fall under the wording of the patent claims, Fig. 4 shows a device according to an embodiment, Fig. 5 shows a device according to another embodiment, Fig. 6 shows a flowchart according to an embodiment, Fig. 7 shows a flowchart according to an embodiment, Fig. 8 shows an application of a time-of-flight system according to an embodiment, and Fig. Figure 9 shows examples of stepwise doping profiles.

[0023] The following detailed description explains exemplary embodiments. The description serves to explain the general principles of the embodiments.

[0024] In the exemplary embodiments illustrated in the drawings and described below, any direct connection or coupling between functional blocks, devices, components, or other physical or functional entities illustrated in the drawings or described herein may also be implemented through an indirect connection or coupling. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0025] It is further understood that the features of the various exemplary embodiments described herein may be combined with one another unless specifically stated otherwise.

[0026] In the various figures, identical or similar devices, modules, devices, etc. may be assigned the same reference number.

[0027] The term "vertical" is used in a non-limiting sense to describe, in embodiments, directions that are vertical or substantially vertical to a surface of a substrate, such as a major surface of the substrate. The term "lateral" is used in a non-limiting sense to describe, in embodiments, directions that are parallel or substantially parallel to a surface of a substrate, such as a major surface of the substrate.

[0028] The term substrate used in the embodiments may include, but is not limited to, semiconductor substrates such as a semiconductor die, a stacked die, a semiconductor die with one or more additional semiconductor layers such as epi layers, polysilicon layers, etc.

[0029] Fig. 1 shows an embodiment of a device 100 which does not fall under the wording of the claims, comprising a substrate 102 with a light conversion region 112. The device is designed such that light penetrates the light conversion region 112 and at least a portion of the incident light is converted into charge carriers of both types, i.e., electrons and holes. According to some embodiments, the light could be introduced into the light conversion region from a front side 100a of the device 100. According to other embodiments, the light could be introduced into the light conversion region from the back side 100b of the device 100. The light conversion region can, according to embodiments, extend between 15 µm and 60 µm in the vertical direction into the substrate, wherein each value within this range and each subrange constitutes a specific embodiment.

[0030] The device 100 further comprises a layer 104 of an insulating material, over which a first control electrode 106a, a second control electrode 106b, and a third control electrode 106c are provided. The layer 104 is typically provided as a thin film, for example, a gate layer, and may contain, for example, silicon oxide. Fig. 1A may form a single pixel of multiple pixels. Accordingly, according to some embodiments, the control electrodes may form the modulation gates of a demodulation structure within a pixel of a continuous-wave time-of-flight imaging device. It should therefore be noted that according to some embodiments, multiple pixels may be formed within the device, resulting in a repetition of the Fig. 1A for a single pixel represented structures and elements.

[0031] Structures 108 are formed between the control electrodes 106a, 106b, 106c. The structures 108 may, for example, comprise spacers or coatings produced during the manufacturing process for electrically insulating the control electrodes 106a, 106b, 106c. Other structures formed in Fig. 1A, such as metal layers and through holes, may further be provided in the device 100.

[0032] Furthermore, a cover layer 110 is provided which extends over the semiconductor substrate 102. As Fig. 1A, the cover layer 110 covers the control electrodes 106a, 106b, 106c and the structures 108 provided in the device 100. According to some embodiments, additional elements, such as shielding elements for shielding light-sensitive areas such as readout nodes, may be provided in or above the cover layer 110.

[0033] According to the embodiment of Fig. 1A, which does not fall under the wording of the claims, the second control electrode 106b is arranged between the first control electrode 106a and the third control electrode 106c with respect to a lateral direction (x-direction). According to some embodiments, the second control electrode has a lateral distance between 50 nm and 1 µm to at least one of the first or the second control electrode, wherein each value within this range and each sub-range forms an embodiment. According to some embodiments, the third control electrode has a lateral distance between 0.1 µm and 0.5 µm to at least one of the first or the second control electrode. According to some embodiments, the second control electrode has a lateral distance between 50 nm and 1 µm to both the first and the third control electrode, wherein each value within this range and each sub-range forms an embodiment.According to some embodiments, the second control electrode has a lateral distance between 0.1 µm and 0.5 µm from both the first and third control electrodes.

[0034] According to embodiments, the control electrodes 106a, 106b, and 106c are manufactured such that they are transparent or at least partially transparent to the incident light that generates the charge carriers in the light conversion region 112. This can be achieved by providing a respective thin film for the electrodes and / or using a material that is transparent or partially transparent to the incident light. According to some embodiments, the operating light can be infrared or near-infrared light. According to some embodiments, the operating light can be visible light. As will be described later with reference to Fig. As described in Figure 8, the operating light can be modulated by a modulation signal when emitted by a light source. When used within a demodulation pixel, the control electrodes are then supplied with a signal that has the same frequency as the light modulation signal, but with a predefined time delay relative to it.

[0035] According to embodiments, the control electrodes 106a, 106b, and 106c are electrodes for directing the light-generated charge carriers in a lateral direction based on the potentials present at the respective control electrodes 106a, 106b, 106c. According to embodiments, the potentials at the control electrodes 106a, 106b, 106c cause the generation of space charge regions in semiconductor regions below the respective control electrode. As further described below, the device 100 is capable of generating space charge regions of different extents below the respective control electrodes 106a, 106b, 106c based on the respective electrical potential present at the control electrode.Below each control electrode, the extent of the space charge region and thus the electric potential is essentially constant, while in the region between two adjacent control electrodes with different space charge extents, electric drift fields are generated. This creates a potential distribution for light-generated charge carriers in the semiconductor region near the substrate surface, causing drift fields in the lateral direction depending on the electric potentials present at the control electrodes 106a, 106b, 106c.

[0036] According to one embodiment, the electrical potential of at least one of the control electrodes can be generated primarily by capacitive coupling with other control electrodes. This has the advantage of lower power consumption because the at least one control electrode is not actively controlled, but only by a capacitive divider. By supplying potentials to the control electrodes surrounding the at least one control electrode, a charge redistribution is initiated at the control electrode 106c, which causes the potential of the at least one control electrode to lie between the currently existing potentials of the neighboring control electrodes during operation. If at least one of the actively controlled control electrodes is controlled with a variable electrical potential, a continuous charge redistribution is effected in the at least one control electrode.In contrast to the other control electrodes, whose potentials are supplied by fixed potential sources or time-varying potential sources, the potential of the control electrode is controlled by capacitive coupling with the other control electrodes, which makes it possible to reduce the power consumption for driving the control electrodes.

[0037] Fig. Figure 1B shows a diagram resulting from an example operation of the control electrodes 106a, 106b and 106c of Fig. 1A according to an embodiment which does not fall within the wording of the patent claims. Fig. Figure 1B shows, on the abscissa, the electrical potential distribution as a negative electrical potential generated by the control electrodes 106a, 106b, and 106c in the semiconductor regions below the control gates. The negative electrical potential corresponds to the potential energy seen by light-generated electrons (negative charges), which, according to the described embodiments, are the charge carriers to be transferred by the control electrodes 106a, 106b, and 106c.

[0038] As can be seen, the voltage applied to the first control electrode 106a (in Fig. 1B by “a”) such that a maximum of the potential energy is obtained at time t = 0 and a minimum at time t = T / 2. The second control electrode 106b (in Fig. 1B by "b") is kept constant. It can be seen that at both times t = 0 and t = T / 2, the potential distribution is stepwise, so that for the control electrode 106b arranged between the control electrodes 106a and 106c, the potential of the control electrode 106b is also between the potential of the control electrodes 106a, 106c. The use of two control electrodes driven by time-varying signals while maintaining one control electrode at a constant electrical potential provides the required stepwise potential distribution very efficiently because no time-varying drive signal needs to be applied to the control electrode 106b.

[0039] Note that the number of steps in the potential distribution generated by the control electrode configuration can be increased by adding additional control electrodes. If the number of control electrodes is K, the number of steps in the potential distribution adds up to K + 1.

[0040] In the operation described above, the generated charge carriers can be guided by the electric field generated by the control electrodes to readout nodes arranged laterally to the control electrode structure. In other words, the control electrode arrangement is capable of providing bidirectional transmission to either lateral side once the charge carriers reach the control electrodes' zone of influence. In optical time-of-flight sensors, control of the charge carriers is time-critical because operation depends on the timely transport of the charge carriers to the laterally arranged readout nodes.

[0041] In conventional systems, charge carriers generated within the light conversion region move only by diffusion from the source of charge generation to the zone of influence of the control electrodes 106a, 106b, 106c. Only at the zone of influence of the control electrodes 106a, 106b, 106c are the charge carriers then exposed to an electric field and thereby transferred laterally to the control electrode structure based on the corresponding potential distribution applied to the control electrodes 106a, 106b, 106c. However, this can be a limiting factor in time-critical applications, such as a demodulation pixel for a continuous-wave (CW) time-of-flight system, because it might take too long for the charge carriers to move from within the light conversion region to the zone of influence of the control electrodes 106a, 106b, 106c.Also, when diffusion is the sole mechanism for vertical movement, a certain percentage of the charge carriers are lost and do not reach the zone of influence, and are therefore lost before reaching the readout nodes. This reduces the effectiveness of the system. Because many time-of-flight systems use infrared light, which has a greater penetration depth than visible light, the average distance from the origin of charge generation to the control electrodes 106a, 106b, 106c is even increased.

[0042] Embodiments described herein provide improved and more effective control of photogenerated charge carriers by generating a built-in electric field to produce drift motion.

[0043] The built-in electric field may, according to some embodiments, have a substantially vertical field component, resulting in a vertical field movement from within the light conversion region to the plane in which the control electrodes 106a, 106b, 106c are arranged, as shown in Fig. 1A. As described later, the built-in electric field generates not only a vertical movement but also a lateral movement in some parts of the light conversion region. In other words, according to some embodiments, the built-in electric field may have lateral field components in addition to vertical field components, at least in some regions of the light conversion region. According to some embodiments, the lateral movement caused by the built-in field causes a concentration of charge carriers in predefined sections.

[0044] According to embodiments, the built-in electric field is a static built-in field generated by providing a non-uniform net doping profile in the light conversion region. Fig. 1A shows an example doping profile 122, wherein a region with a specific net doping concentration is shown as a solid line.

[0045] The direction of the acceleration felt by the light-generated electrons in the resulting built-in electric field of the non-uniform doping concentration is Fig. 1A by solid black arrows. The direction of the acceleration felt by the electrons in response to the time-varying control signals applied to the control electrodes 106a, 106b, 106c is shown in Fig. 1A represented by gray solid arrows.

[0046] It should further be noted that the built-in electric field according to the described embodiments is generated by a non-uniform doping profile of only one doping type (n-type doping or p-type doping). Accordingly, the built-in field differs from a built-in field generated in bipolar junctions. In particular, it should be understood that the strength of the built-in electric field is determined by the gradient of the doping concentration. In other words, the more the doping concentration changes per unit length in a direction, the higher the component of the built-in electric field generated in that direction. According to some embodiments, the doping concentration in the light conversion region changes continuously in the vertical direction, so that a built-in electric field with vertical vector components is generated in the light conversion region.Although the described embodiments use built-in fields generated by doping only one type of carrier, it is to be understood that other embodiments may use built-in electric fields generated by bipolar doping profiles instead of these fields or in addition to these fields.

[0047] According to some embodiments, the vertical component of the built-in electric field may be constant. The built-in electric field may be calculated as E = kB * T / q0 d ln(Na) / dz, where kB is the Boltzmann constant, T is the absolute temperature, q0 is the charge of the charge carrier, and d ln(Na) / dz is the change in the natural logarithm of the doping concentration with increasing distance in the vertical direction. Accordingly, a linear built-in field may be achieved by providing a doping profile in which the logarithm of the doping concentration changes linearly in the vertical direction. According to other embodiments, the doping profile may be provided in which the logarithm of the doping concentration changes superlinearly in the vertical direction. Then, a resulting built-in field with a vertical field component that increases in the vertical direction may be obtained.Such embodiments can compensate for the reduced carrier mobility due to the higher doping concentration with increasing depth, for example, to maintain a constant drift velocity of the charge carriers. The above embodiments can enable more efficient transport of charge carriers in the vertical direction because charge carriers generated farther from the control electrodes 106a, 106b, 106c are subjected to a stronger acceleration force by the built-in field than charge carriers generated closer to the control electrodes 106a, 106b, 106c.

[0048] According to some embodiments, the non-uniform doping profile may extend in the vertical direction from the control electrodes at least between 3 µm and 50 µm, wherein each value in this range and each subrange of this range constitutes a specific embodiment.

[0049] The non-uniform doping profile may be created, according to some embodiments, by providing a doped layer containing doping materials in a semiconductor layer, wherein later a migration of at least a portion of the doping atoms of the doped layer to at least one region above the doped layer occurs. Fig. 6 shows an example of a manufacturing process flow 600. At 602, a doped layer is provided, while at 604, a portion of the doping atoms of the doped layer are later migrated to provide the non-uniform doping profile. The migration step may include a heat treatment, according to some embodiments. According to some embodiments, the doped layer prior to the migration step may have a width (full width at half maximum in the vertical direction) between 0.1 and 5 µm, with each value therebetween and each subrange constituting a specific embodiment. According to some embodiments, an activation step may be applied to the doped layer prior to the migration step. The activation step may include a drive-in heat treatment to minimize defects.According to some embodiments, the non-uniform doping profile may extend in the vertical direction from the control electrodes to at least between 30% and 300% of the width (lateral extent) of the lateral extent of the control electrodes in association with an accumulation region, wherein each value in this range and each subrange of this range constitutes a specific embodiment.

[0050] The portion of the doping atoms of the doped layer that migrate into the region above the doped layer may, according to some embodiments, be in the range between 1% and 30% of the doping concentration of the doped layer. Finally, at 606, the control electrode structure is created above the non-uniform doping profile.

[0051] According to some embodiments, the doping profile may be generated by a graded epi-process, wherein the doping profile gradually changes during the epitaxial growth of the material forming the light conversion region. According to some embodiments, a stepwise doping profile may be generated to provide the built-in field. According to some embodiments, a stepwise doping profile may be generated followed by a migration step, wherein a migration of doping atoms of the stepwise doping profile is performed to smooth out the doping steps. Such a migration step may be provided by applying heat. Before the migration step, an activation step may be provided to activate the doping atoms. The activation step may, for example, comprise the application of heat.The stepwise doping profile may include any number of steps, such as two steps, three steps, etc. The stepwise doping profile may include, for each step in the net doping concentration, at least one flat region where the doping profile does not change or changes only slowly in the vertical direction, and a steep region where the change in the doping profile in the vertical direction is much higher than in the flat region. Fig. Figure 9 shows an example of a stepwise doping profile before the migration step. In Fig. 9, the ordinate corresponds to the net doping concentration on a logarithmic scale in arbitrary units and the abscissa corresponds to the vertical axis (z-axis). For the doping profile from Fig. 9, a first flat region 901 with a high net doping concentration is followed by a first step region 902, which is followed by a second flat region 903 with a doping concentration lower than that of the first flat region. At the other end, the second flat region 903 is followed by a second steep region 904, which is followed by a third flat region 905 with a net doping concentration lower than that of the second flat region 903. It should be understood that Fig. 9 shows just one of many examples for implementing a stepwise doping profile. The flat regions of the stepwise doping profile have a greater extent in the vertical direction than the steep regions. According to some embodiments, the vertical extension ratio of the flat region and the steep region is between 3:1 and 10:1. According to some embodiments, each of the flat regions may have an extent in the vertical direction between 3 and 8 µm, each value and each subrange constituting an embodiment. According to some embodiments, each of the steep regions may have an extent in the vertical direction that is between 0.3 and 1.5 µm, each value and each subrange constituting an embodiment. After applying the migration step by heating, the stepwise doping profile is converted into a doping profile.The net doping concentration of the doping profile may vary in the vertical direction from a first doping concentration ranging between 10. 19 and 10 17 cm -3 to a second net doping concentration, which is in the range between 10 13 and 10 15 cm -3 The change in the net doping concentration in cm -3The average slope of the doping profile described per 1 µm may range between 0.6 and 0.3, with each value and each subrange constituting an embodiment. It should be noted that such average slopes may also be achieved by other fabrication and doping techniques. According to some embodiments, a graded epi-process may be used in which a first epi-layer having a first doping concentration and a second epi-layer having a second doping concentration are grown. According to some embodiments, the graded epi-process or the graded epi-process may be combined with a migration step of the doping atoms, thereby enabling efficient and improved specific design of the doping profile.According to some embodiments, a doped layer may be provided in combination with the graded epi process or the step-wise epi process to provide additional specific design of the doping profile.

[0052] Fig. Figure 2A shows a device 200 which does not fall within the scope of the claims and which has a doping profile with a doped layer. Although the device 200 has additional elements which are Fig. 1A, it should be noted that the doping profile explained later also applies to the Fig. 1A, as well as other element configurations and control electrode configurations. According to some embodiments, a region for accumulating the light-generated charge carriers is provided laterally to the control electrodes.

[0053] In contrast to Fig. 1A shows Fig. 2A Diode structures 114, which act as readout nodes, are provided laterally to both ends of the electrode structure. The diode structures 114 cause the accumulation of charge carriers and can be formed, for example, by a doped well within the substrate. The control electrode structure is arranged between the two diode structures 114. The diode structures 114 are electrically connected by connecting structures 118 to provide output signals for further processing. In addition to the control electrodes 106a, 106b, and 106c, additional separation electrodes 106d and 106e, which are maintained at a constant electrical potential, are provided between the diode structures 114 and the control electrodes 106a, 106b, and 106c. The separation electrodes 106d and 106e limit the influences of the control electrodes 106a, 106b, 106c in the manner of a signal coupling with the diode structures 114.Furthermore, a buried channel 206 is provided to improve the lateral transport of charge carriers under the influence of the control electrodes 106a, 106b, 106c. Similarly. Fig. 1B shows Fig. 2B shows, for an example operation, the corresponding potential distributions generated by the control electrodes 106a, 106b, 106c and the separation electrodes 106d and 106e.

[0054] In contrast to Fig. 1A has the doping profile according to Fig. 2A, the built-in electric field in some areas of the light conversion region generates not only a vertical field component but also a lateral field component. The doping profile has a lateral variation of the net doping concentration that is essentially symmetric about a plane passing through the center of the control electrode structure, as shown in Fig. 2A. In addition to the vertical movement, the mirror symmetry also generates a lateral movement to concentrate the charge carriers in a predefined section of the pixel, which may, for example, be the section of highest transfer efficiency of the control electrodes 106a, 106b, 106c.

[0055] In order to achieve the lateral field components, the light conversion region according to the embodiment comprises Fig. 2A, which does not fall under the wording of the claims, has a doped layer 202 which has a lateral variation of the net doping concentration. According to the embodiment of Fig. 2A, which does not fall within the scope of the claims, the doped layer 202 is segmented into a first portion 202a, a second portion 202b, and a third portion 202c. The doped layer 202 may, for example, be provided as a buried layer provided within a manufacturing process.

[0056] The first and third sections 202a, 202c surrounding the second section 202b have a higher net doping concentration than the second section 202b. According to some embodiments, the first and third sections 202a, 202c may have substantially the same net doping concentration. The net doping concentration according to the embodiment of Fig. 2A, which does not fall within the wording of the claims, may be generated by a migration of doping materials of the doped layer 202, as described above with reference to Fig. 6 was declared.

[0057] It can be Fig. 2A that a local maximum of the net doping concentration in the vertical direction is provided by the doped layer 202 in the light conversion region. In other words, the net doping concentration decreases upon movement from the doped layer 202 in the vertical direction toward the control electrodes 106a, 106b, 106c, as well as upon movement from the doped layer 202 in the vertical direction away from the control electrodes 106a, 106b, 106c. This results in the vertical component above and below the doped layer 202 being reversed. With such a doping profile, depth-selective transport of the light-generated charge carriers can be provided.It allows the rejection of photogenerated charge carriers generated deep in the substrate that would not be transported to the influence zone of the control electrodes 106a, 106b, 106c in a timely manner by providing transport in which such photogenerated charge carriers are moved away from the control electrodes 106a, 106b, 106c. In this way, the contrast can be further improved by providing such a depth-selective transport mechanism.

[0058] Similar Fig. 1A, the black solid arrows in Fig. 2A shows the acceleration vector field corresponding to the built-in electric field. It can be observed that the generated built-in field provides the concentration effect due to mirror symmetry, as well as the depth-selective effect, which causes photogenerated electrons generated beneath the doped layer 202 to be directed away from the control electrode structure.

[0059] It should be noted that many variations are possible for the specific design of the built-in electric field. According to some embodiments, the lateral variation of the net doping concentration in the doped layer has a variation of at least 30% of the maximum net doping concentration of the doped layer. Fig. 2A shows a lateral variation of the doping concentration by providing three sections, it is to be understood that other lateral variations, including a doped layer with more than three sections of different doping concentrations or a continuous variation of the doping concentration of the doped layer, can also be implemented.

[0060] The non-uniform doping profile may have a net doping concentration which increases with increasing depth along a vertical direction from a first net doping concentration in the range between 10 12cm -3 and 10 15 cm -3 to a second net doping concentration in the range between 1.1 x 10 15 cm -3 and 10 20 cm -3 increases, with each value in each range and each subrange in each range constituting an embodiment.

[0061] According to some embodiments, the portion of the doped layer 202 having the lowest net doping concentration may be located below a central portion of the control electrode structure, as shown in Fig. 2A. According to some embodiments, the central portion of the control electrode structure may be located midway between the two lateral readout nodes. This provides the concentration effect in the central portion of the control electrode structure, where the modulation efficiency for the charge carriers is highest. However, it should be understood that many variations of the non-uniform doping profile, including asymmetric doping profiles, may be provided.

[0062] According to some embodiments, the doped layer 202 in the lower doped portion 202b may have substantially the same net doping concentration as the substrate 102 before causing the migration of dopant atoms, as described with reference to Fig. 6 is explained. Fig. Figure 3 shows an embodiment of a device 300 with a doping concentration as explained above. The structures of the device 300 essentially correspond to those described with reference to Fig. 2A explained structures. It can Fig. 3 that a part of the doping atoms have migrated from section 202a and section 202c to the central section 202b to form the doping profile in section 202b as well as in other parts of the light conversion region.

[0063] According to some embodiments, another doped layer may be provided in the substrate at a depth (distance from the surface where the control gates are arranged, in the z-direction) that is different from the depth of the other doped layer.

[0064] Fig. 4 shows an embodiment of a device 400 similar Fig. 2A, including a further doped layer 204. The further doped layer 204 may, according to embodiments, extend in the lateral direction at least beyond a predefined region to which the light-generated charge carriers are directed by the control electrodes 106a, 106b, and 106c. In other words, according to some embodiments, the further doped layer may extend at least below and beyond the diode structure 114 to which the light-generated electrons are directed by the control electrodes 106a, 106b, and 106c. As shown in Fig. 4, the doped layer 204, in addition to an increased concentration effect, also provides a shielding effect for the diode structure 114, so that light-generated electrons are not allowed to move directly from within the light conversion region to the diode structure 114, but only under the influence of the electric fields generated by the control electrodes 106a, 106b, 106c.

[0065] According to some embodiments, the doped layer 202 may be provided at or near the backside of the substrate 102, as shown in Fig. 5. The doped layer 202 provided at or near the backside may be provided with a lateral net doping variation, for example, by providing different portions with different net doping concentrations, as explained above. According to some embodiments, the doped layer 202 may not have a lateral doping variation, ie, the net doping concentration may be constant across the doped layer 202. It should be noted that the embodiment of Fig. 5 allows backside illumination to be provided instead of frontside illumination. In other words, light can penetrate the light conversion region from the backside of the substrate 102. A thinning process can be used according to embodiments to provide the substrate with a thickness in the range between 20 µm and 100 µm, with each value of the range and each subrange constituting a specific embodiment.

[0066] Applications of the devices explained above may include photon mixing applications to provide demodulation in time-of-flight systems, wherein the control electrode structure is adapted to receive an electrical signal associated in a temporal relationship (e.g., a phase delay) with the modulation signal.

[0067] Fig. 8 shows an embodiment of a device 800, wherein light generated by a light source 802 is continuously amplitude modulated based on a modulation signal 804 generated by a signal source 806. The modulation signal may have a sine waveform, but other signal waveforms such as a rectangular or triangular waveform may also be used. The modulated light signal is provided to determine the distance to an object 808. The modulated light reflected from the object 808 is directed to an imaging device 810, which has pixels, such as in the embodiments described with reference to FIG. Fig. 1A, Fig. 2A, Fig. 3, Fig. 4 and Fig. 5. In the imaging device 810, a signal 804A corresponding to the modulation signal 804 phase-shifted by a predetermined phase, for example, 0°, 90°, 180°, and 270°, is provided to the control electrodes for mixing and demodulating the reflected light within each pixel. Specific time intervals are assigned for each of the predetermined phases. After integrating the signals in the respective time intervals for each phase 0°, 90°, 180°, and 270°, output signals I0, I1, I2, I3 corresponding to each phase are obtained. From the output signals I0, I1, I2, I3, the phase information corresponding to the transit time can be calculated, as is known to those skilled in the art. It should be noted that the structure of Fig. 2A, which has two readout nodes on both sides, enables the simultaneous reception of phases I0 and I2 or phases I1 and I3.

[0068] When the output signals are further processed, information corresponding to the distance of the object 808 is provided to a user. According to the Fig. In the embodiment illustrated in Figure 8, signal 804A is provided at time intervals that are phase-shifted with respect to modulation signal 804. It should be understood that only the relative phase shift of the modulation signal and the demodulation signal is required. Therefore, according to other embodiments, a system with interchanged signals 804 and 804A may be provided, with the modulation signal 804 for light modulation being phase-shifted at different time intervals with respect to signal 804A, which is provided with no phase change.

[0069] Although the described embodiment has 4-phase calculations, it should be understood that other calculations using 3 phase delays or 5 or more phase delays may be used according to other embodiments.

[0070] With reference to Fig.Figure 7 describes a flowchart of exemplary light demodulation using apparatus 800. In a first step 702, the light source is modulated based on a periodic modulation signal to generate a continuous wave light beam. At 704, the modulated light beam is provided to an object. At 706, the modulated light beam reflected from the object is provided to a light conversion region having a built-in electric field caused by a non-uniform doping profile, as explained above. At 708, time-varying potential distributions are generated based on applied signals through the control electrodes.

Claims

[1] A method for manufacturing a device (400), comprising the following steps: Providing a non-uniform doping profile in a semiconductor substrate (102) such that an electric field with vertical field vector components is generated in at least a part of a light conversion region (112) of the semiconductor substrate (102), and Creating (606) a control electrode structure having a plurality of control electrodes (106, 106b, 106c) above the non-uniform doping profile for directing light-generated charge carriers, wherein the control electrode structure is arranged between two diode structures (114) for accumulating the light-generated charge carriers, wherein providing the non-uniform doping profile comprises: Providing (602) a doped layer (202) in the light conversion region (112), wherein the doped layer (202) comprises doping atoms, wherein providing the doped layer comprises generating the doped layer (202) such that the doped layer (202) has a lateral variation of a net doping concentration, wherein the lateral variation of the net doping concentration is symmetrical with respect to a center of the control electrode structure, Carrying out (604) a migration step for migrating at least a portion of the doping atoms of the doped layer (202) to a region above the doped layer (202), wherein the non-uniform doping profile in the vertical direction has a local maximum of the net doping concentration in the doped layer (202), wherein the net doping concentration decreases in the vertical direction from the doped layer (202) towards the control electrode structure, so that light-generated charge carriers generated within a first depth range are directed to the control electrode structure, wherein the net doping concentration decreases in the vertical direction from the doped layer (202) away from the control electrode structure, so that the light-generated charge carriers generated within a second depth range are directed away from the control electrode structure, wherein the doped layer (202) is a buried layer, wherein at least one further doped layer (204) is provided at a depth different from the depth of the doped layer (202), wherein the further doped layer (204) is spatially separated from the doped layer (202) by the semiconductor substrate, wherein the further doped layer (204) provides a shielding effect for the diode structures (114), so that the light-generated charge carriers may not move directly from within the light conversion region (112) to the diode structures (114), but only under the influence of electric fields generated by the control electrodes (106, 106b, 106c), and wherein the further doped layer (204) extends in the lateral direction at least beyond a defined region to which the light-generated charge carriers are directed. [2] The method of claim 1, wherein generating the control electrode structure comprises: Producing the plurality of control electrodes (106, 106b, 106c) for applying a stepwise electrical potential distribution in the light conversion region (112). [3] The method of claim 1 or claim 2, wherein the portion of the dopant atoms in the range between 1% and 30% migrates to the region above the doped layer (202). [4] The method of any one of claims 1 to 3, wherein the lateral variation of the net doping concentration comprises at least a variation of 30% of the maximum net doping concentration of the doped layer (202). [5] Method according to one of claims 1 to 4, further comprising: Providing at least a first portion (202a) of the doped layer (202) with a first net doping concentration and a second portion (202b) of the doped layer (202) with a second net doping concentration, such that the second net doping concentration is lower than the first net doping concentration. [6] The method of claim 5, further comprising: Providing a third portion (202c) of the doped layer (202) with the first net doping concentration, wherein the second portion (202b) of the doped layer (202) lies between the first portion (202a) and the third portion (202c) of the doped layer (202). [7] The method of claim 6, wherein the second portion (202b) is located below a central portion of the control electrode structure. [8] The method of any one of claims 5 to 7, wherein the second net doping concentration is equal to a net doping concentration of the light conversion region (112). [9] A method according to any one of the preceding claims, wherein the net doping concentration of the non-uniform doping profile increases with increasing depth along the vertical direction from a first doping concentration in the range between 10 12 cm -3 and 10 15 cm -3to a second doping concentration in the range between 1.1 × 10 15 cm -3 and 10 20 cm -3 increases. [10] A method according to any one of the preceding claims, wherein the non-uniform doping profile is mirror-symmetric with respect to a predefined plane. [11] A method according to any one of the preceding claims, wherein the non-uniform doping profile is provided such that the electric field has vertical and lateral field vector components in at least a portion of the light conversion region (112). [12] A method according to any one of the preceding claims, wherein providing the non-uniform doping profile involves generating a stepwise doping profile in the vertical direction. [13] Method according to one of the preceding claims, wherein in providing the non-uniform doping profile a graded doping profile is generated in the vertical direction. [14] Device (400) comprising: a semiconductor substrate (102) having a light conversion region (112) for converting light into light-generated charge carriers, two diode structures (114) for accumulating the light-generated charge carriers, a control electrode structure between the diode structures (114) having a plurality of control electrodes (106, 106b, 106c) for generating a potential distribution such that the light-generated charge carriers are guided to the diode structures (114) to accumulate the light-generated charge carriers based on signals applied to the control electrode structure, and a non-uniform doping profile in the semiconductor substrate (102) to generate an electric field with vertical field vector components in at least a part of the light conversion region (112), wherein the non-uniform doping profile in the vertical direction has a local maximum of a net doping concentration in a doped layer (202) in the light conversion region (112), wherein the non-uniform doping profile is generated by migration of at least a portion of doping atoms of the doped layer (202) to a region above the doped layer (202), wherein the net doping concentration decreases in the vertical direction from the doped layer (202) towards the control electrode structure, so that light-generated charge carriers generated within a first depth range are directed to the control electrode structure, wherein the net doping concentration decreases in the vertical direction from the doped layer (202) away from the control electrode structure, so that the light-generated charge carriers generated within a second depth range are directed away from the control electrode structure, wherein the non-uniform doping profile has a variation in the net doping concentration that is symmetric with respect to a center of the control electrode structure, such that the electric field is mirrored with respect to a plane through the center of the control electrode structure, wherein the doped layer (202) has a lateral variation of the net doping concentration, wherein the doped layer (202) is a buried layer, wherein the device (400) further comprises at least one further doped layer (204) at a depth different from the depth of the doped layer (202), wherein the further doped layer (204) is spatially separated from the doped layer (202) by the semiconductor substrate (102), wherein the further doped layer (204) provides a shielding effect for the diode structures (114), so that the light-generated charge carriers may not move directly from within the light conversion region (112) to the diode structures (114), but only under the influence of electric fields generated by the control electrodes (106, 106b, 106c), and wherein the further doped layer (204) extends in the lateral direction at least beyond a defined region to which the light-generated charge carriers are directed. [15] The device (400) of claim 14, wherein the non-uniform doping profile provides the electric field for directing photogenerated carriers to a predefined portion of the control electrode structure. [16] The device (400) of claim 14 or claim 15, wherein the magnitude of the vertical component of the electric field increases with increasing depth. [17] The device (400) of any one of claims 14 to 16, wherein the device is adapted to generate an amplitude-modulated light to be transmitted to an object (808) based on a modulation signal (804), wherein the control electrode structure is adapted to receive an electrical signal (804A) linked in a temporal relationship to the modulation signal (804). [18] The device (400) of any one of claims 14 to 17, wherein the non-uniform doping profile provides the electric field having lateral and vertical field vector components at least in the portion of the light conversion region (112). [19] The device (400) of any one of claims 14 to 18, wherein the non-uniform doping profile is a vertically graded or step-wise doping profile.

Images