System in Package (SiP) with an integrated In-situ 3D wafer level monitoring and control unit

FIELD OF THE INVENTION

The present invention relates to a System in Package

{SiP) with an integrated In-situ 3D wafer level monitoring and control unit arranged to monitor and control performance and reliability of a LED, system on substrate ( SoS ) comprising said control unit, a BiCMOS process for making said IC, and a device comprising said SiP.

BACKGROUND OF THE INVENTION

The present invention is in the field of Light Emitting Diodes (LEDs) . A light-emitting diode (LED) is a semiconductor light source. It typically relates to a diode having a single p-n junction. The diode emits light when an electrical

current/voltage is provided to the diode. This effect is referred to as electroluminescence. The colour (or wavelength, and likewise energy) of the light emitted by the diode may vary depended on a specific p-n junction involved and may be varied as well by changing properties of said junction. LEDs can be in a red range (620-645 nm) , red-orange (610-620 nm) , green (520-550 nm) , cyan (490-520 nm) , blue (460-490 nm) , violet (400-450 nm) and even ultra-violet (100-400 nm) . The LED can be made in a semiconductor process. As a result the LED can be relatively small in area (typically less than 1 mm ² ) and still provide a relatively large amount of light, such as 500 Lumen [lm] . The power consumption of a LED may vary from a few mW up to tens of W at a current of 10-500 mA. The amount of lumen per watt depends a bit on the colour of the LED and is on the order of 10-200 lm/W) .

For making white light two options exist. The first is to combine a red (R) , a green (G) , and a blue (B) LED, mix the light of these three (RGB) and thereby form white light. The second is to use a specific (monochromatic) LED, such as a blue or UV LED, and use a medium, such as yellow phosphor, and have as combined effect of the LED and activated phosphor white light. This option may be referred to as dichromatic (e.g. blue and yellow) . This approach is also referred to as phosphor based white method; it produces white light by a single typically short wavelength LED, such as blue or UV, combined with a yellow phosphor coating. It is considered that the blue or UV photons, respectively, generated by the LED either travel through the phosphor layer without shift, or they are converted into yellow photons in the phosphor coating layer. The combination of the yellow light with the unabsorbed blue light appears as a white light in the human eyes. A remote phosphor layer may be used in which the phosphor layer is placed at a sufficiently large enough distance from the LED chip. It offers much better colour rendering than RGB white, often similar to the florescent sources. Furthermore, phosphor converted white light is also much more efficient than RGB white. Because of its high efficiency and acceptable colour rendering and lifetime, phosphor white is the most common approach of producing white light for general illumination. Two specific examples of the second option are a near UV or UV-LED in combinations with RGB phosphor, and a blue LED with yellow phosphor. Phosphor can be used as such and more

typically in combination with other materials, such as metals.

It is noted that LEDs in general do not provide one single colour (monochromatic) but rather a colour distribution, or distribution of intensities over a wavelength range, with a main peak in the distribution being considered indicative for the "colour" (or wavelength) of the LED, e.g. R, G or B. The wavelength having the main peak is considered to be the "main" wavelength.

LEDs can be divided into high-power (e.g. 200 mA-lOA) , midrange power (50-200 mA) , and low power (1-20 mA) .

LEDs suffer from various drawbacks. Mostly occurring phenomena are that a LED over time has a gradual lowering of light output, loss of efficiency, and colour shifting. In addition LED performance depends on a temperature thereof.

Specifically, an exact shade or colour temperature of dichromatic white light is considered to be determined by the dominant wavelength of the (blue) LED and the composition and thickness of a phosphor coating. Manufacturers therefore attempt to minimize the colour variations by controlling the thickness and composition of the phosphor layer during manufacturing. The LEDs are in general suffering from light intensity decay in stress tests. Their light intensity decays during a long operation time and/or at a high working

temperature. Another drawback of phosphor based white method is colour shifting due to degradation of the blue LED die and the yellow phosphor over time. It also happens when the device operates at a different current or operating temperature. It is noted that the LED performance decays critically over time, up to failure typically.

Some documents relate to partial integration of various LED components. For instance, Kim et al. in "MSM Photo

detector on a Polysilicon Membrane for a Silicon-Based Wafer- Level Packaged LED", IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 25, NO. 24, DECEMBER 15, 2013, describe the use of an improved metal-silicon-metal photo detector for measuring light output of a LED which is placed on a membrane. Said detector is somewhat complicated to produce, and further the performance in terms of responsivity (mA/W) at a given wavelength is somewhat low (e.g. below 50 mA/W at a wavelength of 450 nm) , albeit much better than previously constructed MSM sensors.

More background documents, showing some integration are for instance Lau in "3D LED and IC wafer level packaging", Microelectronics International, 27/2 (2010) p. 98-105, and Chang et al . , in "A Novel Silicon-Based LED Packaging Module With an Integrated Temperature Sensor", IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, VOL. 4, NO. 5, MAY 2014.

A document relevant for improved sensing is of Pauchard et al., "A silicon blue/UV selective stripe-shaped

photodiode", in Sensors and Actuators 76 1999 172-177. The responsivity of this sensor is also relatively low (e.g. below 150 mA/W at a wavelength of 450 nm) , albeit better than the above MSM sensor of Kim.

Other background documents are for instance WO

2010/012999 A2 which recites a tunable colour LED module comprises at least two sub-modules, each comprising an LED, a wavelength converting element (WCE) and a reflector cup. The total light emitted by the module comprises light generated from each LED and WCE and the module is configured to emit a total light having a predefined colour chromaticity when activation properties of the LEDs are managed appropriately. The total light may have a broad white emission spectrum. The module comprises two LED sub-modules, which may be considered somewhat complex. The integration is at electrical board level. It may be considered as relative complex in term of fabrication, as it does not relate to full system integration. As it has two LEDs amongst others for mutual compensation there is no need for further compensation in intensity of wavelengths by other means. The control of the LEDs is

performed externally.

EP 2 048 718 Al recites an emitter package comprising a light emitting diode {LED) emitting light at a wavelength within a wavelength range and a plurality of phosphors. Each of the phosphors absorbs at least some light from the LED and re-emits a different wavelength of light. The package emits a combination of light from the LED and the plurality of

phosphors, with the phosphors having excitation

characteristics such that for an LED emitting at any

wavelength within the wavelength range, the emitter package emits light having color-point coordinates lying within a one standard deviation Macadam ellipse centred on a target color. Each of the LEDs are arranged in a respective package with a plurality of conversion materials so that at least some light from each of the LEDs is absorbed and re-emitted by its corresponding conversion materials. The plurality of

conversion materials have excitation characteristics that compensate for different LED emission wavelengths within the LED range of wavelengths such that each of the LED packages emits light within a standard deviation from a target color. So it is aimed to compensate the variation of the wavelength shift within the tolerable range with combination of different phosphorous conversion materials.

US 2015/257232 Al recites a a planar lighting apparatus, a liquid crystal display apparatus, and a planar light source. The planar lighting apparatus includes a planar light source including light emitting elements, a first housing, a light emitting surface divided into light emitting regions, and a first temperature sensor disposed inside of the first housing. The planar lighting apparatus further includes a second housing covering the planar light source; a second temperature sensor disposed outside of the first housing and inside of the second housing; a light-source drive circuit including light- source drive section each driving and controlling the light emitting elements belonging to the corresponding light

emitting region; a memory section; and a computing section calculating a driving condition of each light-source drive section and correcting the driving condition on the basis of measurement values of the first temperature sensor and the second temperature sensor, and setup information in the memory section. This document is not considered very relevant for the present invention.

So there is a need for improved sensors for measuring performance of a LED, as well as an improved control of the LED performance over time in a cost effective manner.

The present invention therefore relates to a package comprising a LED and further aspects thereof, which overcomes one or more of the above disadvantages, without compromising functionality and advantages.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more limitations of the devices of the prior art and at the very least to provide an alternative thereto. The present invention relates to a system in package with a LED, a remote layer, and a system on substrate (SoS) comprising an

integrated circuit, a BiCMOS method for making said SoS for the system in package with the integrated circuit, an

integrated circuit for use in such a system in package, and specific devices making use of and incorporating said system in package.

In a first aspect, the invention relates to a System in package (SiP) with In-situ 3D wafer level monitoring and control unit arranged to monitor and control performance and reliability of a LED. The present system relates to highly integrated components, comprising a LED, a remote layer arranged to generate light complementary to the dominant wavelength of the LED light, in order to provide "combined white light", such as in a so-called phosphor converted white LED, located at a distance of e.g. 0.1-5 mm from the LED, such as a phosphor layer, and a system on substrate (SoS)

manufactured typically in a BiCMOS process; a "phosphor" is considered to be a substance capable of luminescence, by . phosphorescence or fluorescence; fluorescent materials are common used in white LEDs; phosphors may be transition metal compounds or rare earth compounds of various types; examples are cerium doped yttrium aluminium garnet, Eu-based

phosphores, copper and aluminium-doped zinc sulphide, and ZnSe; for applications wherein only one colour light is provided, the remote layer may relate to a UV-protection layer. In the description the term "IC" may relate to all electrical components that can be made on a substrate with for example the present process. The SoS comprises at least one improved high responsive colour selective semiconductor photo- diode, having a responsivity of above 100 mA/W at a wavelength range of 300-800 nm, and above 200 mA/W at a wavelength range of 380-650 nm, which is a factor higher than prior art

integrated sensors. Even further the responsivity is above 250 mA/W at a wavelength range of 410-580 nm, which is the most relevant range for blue and UV LED's. The performance is even better than commercial external and non-integrated sensors, typically some 100 mA/W in the most relevant range; only at higher wavelengths, typically above 550 nm, said commercial sensor performance better, and between 550nm-600 nm slightly better. The information obtained by the improved photo-diode is used to monitor wavelength specific LED output light intensity distribution, which may be referred to as wavelength responsivity, that is a light intensity as a function of wavelength is determined and compared to at least one initial intensities. Therewith a change in intensity and a change in colour distribution can be established. The established change is if present used as feedback to control the LED and to obtain at least a same or similar distribution, by changing a LED drive current. Thereto a power transistor for switching is used, typically providing a high current. For integration purposes the LED is located on a space (which may also

referred to as "cavity") for receiving the LED made available on the IC. On or near the space electrical contacts for the LED are provided. In addition a reflector for the LED is present .

The present system in package, as well as the present method, the integrated circuit, and devices provide various advantages as indicated throughout the description. For instance a simple 5 or 7 mask step BiCMOS process is provided, having a low cost which provides a smart package wafer level fabrication. Multi-functional SoS blocks including different sensors, analogue and digital circuits were integrated in the package. The process optimization was done for whole system operation. For the process specific and optimized temperature and light sensors for online scanning of LED array performance were designed, fabricated and tested. It was found that an example of the present photo-diode with a p-n junction at 330nm depth exhibited a very high selectivity to blue light. A maximum responsivity was found at 480nm, which matched with a blue LED's illumination almost ideally. In addition power switches for supplying a high current, an analogue light feedback control loop and a digital sensor readout system could also be integrated. In the present process an advanced lithographic defined wiring was developed. So in summary a 3D package with multiple function was designed and introduced.

The present method and SiP have relatively low costs, integration can take place at a relatively higher scale, the process gives superior yields and a higher accuracy and a highest density integration for electronic and heterogeneous applications is made available. It is noted that using SiP for high accuracy multi-domain applications is considered quite a challenge .

It is noted that for e.g. the transistor the doping profiles may be reversed, e.g. from n to p for the well, etc. So the term "n-doped" encompasses "p-doped" as well, and vice versa. The examples given in the description however relate to the most preferred embodiment.

The present system is considered to be especially

applicable for any kind of UV/blue/phosphor based LED package, such as a white light package, such as for medical

application, when a high reliability is required, for light based therapies wherein a specific wavelength is used, for a UV light sanitizer for killing microorganisms, and for smart lighting systems with automated application, amongst others.

The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art .

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In view of the above the present inventors were motivated to develop a system monitoring unit. Although not all the performance falloffs can be compensated, a smart integrated LED power control with light and temperature sensors can compensate for light intensity decay, monitor colour shifting and protect for over-temperature problems and hence prevent or limit degradation of the LED and the remote layer. It is noted that the term layer may refer to a

relatively thin 3-dimensional structure, such as a film or layer, to a structure provided on top of the LED or at a distance, such as a transparent dome, etc. Decay may refer both to phosphor and LED chip performance over the time. While a phosphor working mechanism is typically related to a

manufacturing process thereof, the LED aging and adjustment of its light intensity are compensated for by changing a drive current. There are two strategies considered to alter the current: 1- Feed a forward control based on the lifetime prediction: Increasing current based on the correction values stored in a memory. Such is typically done in prior art devices. 2- Using output light feedback: Including blue light sensors and a control loop circuit. Such is considered for the present invention.

A smart package with an output light feedback is found to compensate for brightness variation by changing the drive current of a LED. Light sensing provides information on both colour (distribution) and intensity of the LED. Using a for UV or blue light selective photodiode that is integrated in a package also comprising the LED is found to be an advantageous solution.

The present inventors made use of silicon based wafer level packaging (WLP) . This technology is found to be cost effective and having an appropriate thermal design. It provides batch fabrication and component integration; it is compatible with CMOS technology and may include further components as micro electromechanical systems (MEMS) as well. Applying these technologies, a smart LED package is produced that resolves the brightness problems associated with LED intensity decay. There are at least two categories of silicon- wafer-based wafer level packaging (WLP) LEDs; a so-called surface-mounted type, in which electrodes are formed on a silicon wafer and then the LED chip is attached to the wafer; and a so-called cavity type, in which cavities are formed prior to the electrodes. Generally, the cavity is fabricated using KOH wet etching with a (100) silicon wafer. The present cavity acts both as a reflector and a holder.

Inventors firstly designed and implemented a colour

(UV/blue) selective photodiode, which can selectively monitor the led output light, in a process. Secondly a switch power and analogue control and feedback loop was designed and implemented in the same process. In the present package photodiode data is used as an input to the analogue feedback loop. The output of the control loop is a voltage of a power switch. Therein the switch can keep the output light intensity at a desired wavelength in a predefined level by changing the driving current of the LED. Figure 1 shows the schematics of the concept .

Inventors designed a photo sensor appropriate for the target wavelength and compatible to a planar and cavity type WLP process and monolithic integration. In this respect it is found that basic silicon photo detectors generally have a poor responsivity to blue and UV light, because these spectra absorb very close to the surface while the active sensing regions of these devices are usually situated at a certain depth below a device surface. Different structures for silicon photodiodes are used to tune wavelength selectivity. The basic structure used is a p-n-p dual-j unction photodiode; the active region of the p-n photodiode is limited by a second n-p junction situated below the first one. The detector doping profile of the photodiode is adjusted in a way to have a sharp and high potential barrier thereof, which is found to generate a strong built-in drift field in which photo-generated

carriers (e.g. electrons) are separated efficiently. This type of detector structure can typically only be fabricated in a dedicated sensor process, that is not compatible with standard CMOS processing, unfortunately. An alternative sensor relates to a stripe shaped photodiode, compromising shallow P layers implanted in an N-well. The geometry was optimized for better UV/blue responsivity. These devices show a promising

selectivity for blue light. Inventors have further optimized a size and features of these sensors to better fit process and application requirements. All structures are also simulated and the efficiencies of the devices have been thoroughly investigated before fabrication. Fig. 2 demonstrates the schematic of the designed photo detector and the equivalent circuit .

The present photodiode may be fabricated in a 5 mask BiCMOS process, which can be extended to a 7 mask process (or more) if e.g. further interconnect layers are required. For the interconnects High Aspect Ratio (HAR) Lithography may be applied by using a conventional CMOS interconnect toolset and processes combination with multi-level lithography. The aim could be for a "wire bond"-like interconnect structure and a HAR interconnect. The process may include deposition of a metal film and patterning a "wire-like" trace with high aspect ratio lithography. Use can be made of a multi-step Imaging module on an ASML stepper. HAR lithography is found to be a potential key technology for heterogeneous integration. The present inventors used a photo-selective diode which can selectively detect the output (blue) light intensity in a very accurate and efficient way. This provides brightness information of a in a package mounted LED. Typically a control block is also implemented in the same process used for fabrication the photo-selective diode. An example of a circuit schematics can be found in Fig. 3. The items shown in the central square are the designed unit in wafer level and the remainder shows the items e.g. for further test and

measurement on PCB level.

The BiCMOS process was developed in the TU Delft Else Kooi Laboratory and comprises a 5-7 masks process that

involves both Bipolar and CMOS elements such as transistors. These are e.g. used for feedback and control circuits. It exhibits the two outstanding features; simplicity and

cheapness. Although it has a limited performance, it is sufficient to be implemented for the present LED WLP and some simple SoS designs. The present process can implement a smart LED driver platform for the cost of even less than l$/cm ² . The process advantage of integrating both types of (bipolar junction (BJT) and CMOS) transistors, but the disadvantage of having a trade-off between the two optimum settings for each type. Figure 4 shows a first 5 lithography steps for this process. The core of the process may consist of 7 mask steps.

In an exemplary embodiment of the present package a light emitting diode (LED) having a main or dominant wavelength in the range of 100-750 ran was used; preferably a blue or UV LED is used in a wavelength range of 250-550 rati, more preferably 350-500 nm, such as 450-470 nm. An example of such a LED is a Bridgelux blue power LED of about 1 mm ² , with a DC forward current of maximum 700 mA, a reversed voltage of 5V, and optical power of 340 mW, and a dominant wavelength of 450-470 nm. For making white light a remote layer arranged to provide light complementary to dominant wavelength of the LED light, located at a distance from the LED, such as at a distance of 0.1-5 mm, preferably 0.2-2 mm, such as 0.3-1 mm. The remote layer may be a phosphor type layer, which may be combined with further typically metallic elements, in order to improve performance thereof. The remote layer may also protect the LED and also the SoS of the present SiP from environmental

influences . In an exemplary embodiment of the present package an internal temperature sensor arranged to measure a temperature of the LED, or likewise scan a temperature thereof online, preferably located close to or adjacent to the LED, such as in the space for receiving the LED. The temperature sensor can be fully integrated in the IC. The temperature differences caused by the temperature variation between the surface and back side of the LED chips can be measured accurately and with good resolution. Inventors found a good consistency of the measured values by the present thermal sensors and TI results. In addition it is found that the temperature under the LED dies is compatible with electronics enabling stacking LED die on driver electronics. The integration provides a reduced footprint and cost. Measurements were performed at e.g. 100 mA, 300 mA and 500 mA forward current, and measured

temperature were 28.78 °C, 37.41 °C, and 57.52 °C,

respectively.

In an exemplary embodiment of the present package the space arranged to receive the LED has an area slightly larger than the footage of the LED, such as 10%-100% larger. The space area is typically in the order of 1-10 mm ² .

In an exemplary embodiment of the present package the first reflector covers the space partly (10-95%, preferably 20-90%, more preferably 30-85%, such as 40-75%) or fully.

Therewith more light is provided to especially the present photo-diode, which improves the control and feedback.

In an exemplary embodiment of the present package the space for receiving the LED is a cavity, the cavity having a depth of 1 urn- 1500 um, preferably 10 pm- 500 μπι, more

preferably 20 um- 300 μπι, most preferably 50 μπϊ- 250 um.

In an exemplary embodiment of the present package the power consumption of the individual LED is from 0.001-20 W, preferably 0.05- 6 W, such as 0.5-3 W. If a package comprises more (a multitude of) LEDs the total power consumption can clearly be much higher, typically a multitude of the above.

In an exemplary embodiment of the present package the cavity comprises the at least one colour selective photo-diode incorporated in at least one side thereof and the LED at a bottom thereof. It is preferred to use two or more photo- diodes, such as at every side of the cavity, e.g. four.

In an exemplary embodiment of the present package 50-100% of a remainder of the cavity forms part of the first

reflector, preferably 60-90%, such as 70-80%. Typically the reflector material is Al, preferably having a thickness of 50- 1500 nm, such as 100-750 nm.

In an exemplary embodiment of the present package the control and feedback loop comprises at least one bipolar junction transistor and at least one CMOS transistor. The use of the BJT provides various advantages, such as a high power may be provided. The control and feedback loop, as well as the at least one power transistor for switching, typically control a LED drive current in a single individual and independent mode. Typically one LED is present. If an array of n by m LEDs is present, each LED may have its own control and feedback loop including at least one power transistor, or one or more control and feedback loops may be used to drive the current of more than one LED, albeit still in a single individual and mutually independent mode. In other words, the control and feedback of the LED module is performed by integrated

electronics .

In an exemplary embodiment of the present package the photo-diode is a dual junction photodiode, hence having a pn- and an np-junction. These two junctions inherently perform different, but it has been found that the combined photo-diode provides further advantages as mentioned and further optional features can easily be added, such as filters, which further improve the sensitivity and feedback.

In an exemplary embodiment of the present package the photo-diode is stripe shaped comprising a P-substrate, an N- well, and at least one shallow stripe shaped P layer implanted in an N-well, and arranged to measure a wavelength intensity distribution in a range of 50-1000 nm, hence a slightly broader range than a wavelength distribution range or dominant wavelength of the LED is envisaged; in this respect see also figure 6 being indicative of such a broader range. T is noted that typically the substrate is a Si-substrate, such as Si (100); however, it may also relate to glass, a ceramic, GaN, SiC, a suitable polymer, etc.

In an exemplary embodiment of the present package the N- well depth preferably is 1200-1700 nm, more preferably 1400- 1600 nm. Such improves the performance of e.g. the present sensor .

In an exemplary embodiment of the present package the shallow n- and p-layers respectively preferably have a depth of 250-450 nm, more preferably 300-400 nm, even more

preferably 320-360 nm, which in turn also improves the performance of the present sensor, especially in terms of harvesting charge carriers.

In an exemplary embodiment of the present package wherein the distance (d _P ) between the P-layers is 1-10 um, preferably 2-7 μιη, more preferably 3-5 um, which in turn also improves the performance of the present sensor, especially in terms of harvesting charge carriers.

In an exemplary embodiment the present package further comprises at least one shallow N-layer, preferably an N-layer surrounding the shallow P-layers.

In an exemplary embodiment the present package further comprises at least one shallow P-layer located in the p- substrate .

In an exemplary embodiment of the present package further comprises one shallow p-layer, adjacent to the photo-diode.

In an exemplary embodiment of the present package the p- layers have a width (w _P ) of 1-10 pm, preferably 2-7 μιη, more preferably 3-5 μπι.

In an exemplary embodiment of the present package a ratio between the width (w _P ) of the shallow layers and the combined width (w _P ) and distance (d _P ) between the P-layers ( (w _E +dp/w _P ) is in the range of 2.5-2.8, preferably 2.6-2.7, such as 2.64- 2.66. Such a range between total area and "active" sensor area is found to be optimal in terms of obtainable responsivity .

In an exemplary embodiment of the present package the p- layers (and likewise n-layers) have a length from 0.5-500 μιη, preferably 1-400 μιη, more preferably 20-300 pm, more

preferably 50-250 pm, such as 100-150 pm. The length may be varied somewhat, with respect to available space and amount of photons captured.

The dimensions and characteristics of the diode sensor may be tuned to a wavelength to be monitored.

In an exemplary embodiment the present package further comprises a second reflector, such as located above the LED and reflecting light back towards a photo-diode. Said photo- diode is then preferably located adjacent to the present space for receiving the LED.

In an exemplary embodiment of the present package at least one colour selective photo-diode is arranged to measure reflected LED light, such as indicated above.

In a second aspect the present invention relates to a BiCMOS process according to claim 14. The process comprises the steps of providing a silicon wafer, forming at least one bipolar junction transistor (BJT) , forming at least one CMOS transistor, forming electrical contacts for a LED, forming at least one colour selective photo-diode, forming an analogue light intensity control and feedback loop in contact with the transistors, and forming a space for receiving the LED.

In an example the present process comprises the steps of providing a p-doped substrate, patterning and n-doping an N- well for a pMOS transistor and a collector for the BJT, annealing, patterning and n-doping an n-drain for an nMOS transistor, an emitter for the BJT, a low resistance collector contact, and an n-type guard ring for the colour sensitive- diode, patterning and p-doping a p-type source and drain for a pMOS transistor, a base of the BJT, and at least one p-type stripe for the colour sensitive-diode, activating dopants at an elevated temperature, forming a gate oxide, patterning and forming contact openings, forming interconnects (that is forming contacts and connecting them using a metal layer and patterning the metal layer accordingly), and forming gates. It is noted that if the present photo-diode is located at a side of the present cavity doping may be under an angle in view of the diode location, such as under an angle of about 50 degrees relative to the substrate surface.

In an example the present process further comprises forming a further dielectric layer, patterning and forming vias in the further dielectric layer, and forming a metallic interconnect layer.

In an example the present process further comprises the step of forming a cavity, such as by KOH etching.

In a third aspect the present invention relates to an integrated (IC) for use in a package according to the

invention. In the SoS the space for receiving a LED is a cavity, the cavity having a depth of 1 pm- 1500 μπι. The cavity comprises the at least one colour selective photo-diode incorporated in at least one side thereof and electrical contacts for the LED at a bottom thereof. 50-100% of a remainder of the cavity forms part of the first reflector. The SoS clearly can be used for monitoring a LED, but is also suitable for other applications.

In an example of the present SoS the internal

temperature sensor is located at a bottom of the cavity.

In a fourth aspect the present invention relates to a device comprising the present system in package or the present IC, selected from one or more of a chemical sensor, such as an 0 ₂ sensor, a CO sensor, a smoke sensor, a light source, as a detector in a combustion device, and a device for killing microorganisms .

The present system in package may comprise an array of n by m LEDs, wherein ne [1,100] and me [1,100], preferably ne[2,50] and me [1,10], and further comprising at least one of an AD-converter, an encoder, a comparator, a booster, a resistor, a divider, a voltage source, a rectifier, a diode for mitigating electro-static discharge (ESD) , an amplifier, a flip-flop, a memory, a calibration curve, a sensor read-out circuit, a further sensor, a humidity sensor, software, and an inverter .

The invention will hereafter be further elucidated through the following examples which are exemplary and

explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

FIGURES

Figure 1. Schematic of Monitor/Control unit for the LED chip .

Figure 2. Schematic striped-shape photodiode and

equivalent circuit.

Figure 3. Schematic of the total circuit.

Figure 4. Process overview of the core mask steps in the BICM0S5 process.

Figure 5: Photodiode structures.

Figure 6: Measured responsivity vs wavelength for the multi-stripe photodiode.

Figure 7: Photodiode - Performance test.

Figure 8: 3D LED package .

Figure9: Prototype chip layout (10x10 mm2).

DETAILED DESCRIPTION OF FIGURES

The present invention, as well as further embodiments and details thereof, is also described in a scientific paper by Kolahdouz, van Zeijl, Zhang et al., submitted to Phys . Rev. Applied, entitled "Monolithically Integrated Light Feedback

Control Circuit for Blue/UV LED Smart Package", which document and its content is incorporated by reference in the present application. The paper provides various experimental results and characterizations of the present device. It concludes that a successful monolithic integration of light output feedback control circuit in a blue/UV LED package was established, which may likewise be applicable for packaging a phosphor- based white LED module. For sensing blue/UV light in the package, optical sensors with peak responsivity at 480nm wavelength were successfully implemented. For controlling functions, a feedback circuit with a power transistor for driving the LED current was monolithically integrated. The opamp functionality was successfully tested having a 47 dB gain. The power transistor provides up to 700 mA current. The whole feedback circuit regulates light output based on a reference voltage with removing power supply ripples up to 680 kHz. Robustness of the feedback system was tested against changes in LED current/voltage to light intensity characteristics. Considering a tight error tolerance of 1%, the system was able to handle up to a 150 mA and 0.6 V change in current and voltage characteristic of the LED while

providing the same light intensity. Furthermore, the system is considered to demonstrate a functionality of a Si-based smart LED packaging with stable light output; the solution can also be applied to other systems, such as an interposer for high level electronics, a MEMS, etc.

Figure 1. Schematic example of Monitor/Control unit for the LED chip. The UV/ blue selective photodiode 130 can

selectively monitor the LED 100 output light. The photodiode data is then used as an input to the analogue feedback loop 110. The output of control block is the voltage of power switch 120. The power switch can keep the output light

intensity as desired by changing the driving current of the LED.

Figure 2. Schematic example of a striped-shape photodiode 130and equivalent circuit. The basic sensor structure consists of a stripe-shaped shallow P+ layer SP/160 implemented in an N well 150, in a p-type substrate 140. The distance between two adjacent striped (D) is 5 μιη; the width of the stripes (W) is 3 um, the length L is about 150 μπι. The stripe-shaped structure is used to minimize the dead layer area to increase the responsivity. Also striped shape N layers 170 are shown.

Figure 3. Schematic example of the total circuit. The items shown in the orange square {The thermal sensors, the photo-diodes, the LED chips, the analogue feedback control loop and the power switch) are the designed unit on a wafer level and the remainder shows items for further test and measurement on PCB level. For each LED die, two sets of photodiodes are used for output light measurements.

Figure 4. Exemplary process overview of the core mask steps in the BICMOS5 process. The photodiode and the control block are fabricated in a 5-7 mask BiCMOS process.

1. N-well: the N-well is formed using either diffusion or ion implantation of phosphorus into the p-substrate. N-type area for the PMOS transistor and the collector for the bipolar npn are defined through lithography. 2. Shallow N: n-type source-drain for the NMOS transistor and the emitter of the bipolar transistor is made. Diffusion or ion implantations are used to create n-diffusion regions.

3: Shallow P: p-type source-drain for the PMOS transistor and for the base of the bipolar transistor is made. Diffusion or ion implantations are used to create p-diffusion regions.

4: Contact opening: Defines contacts holes.

5: Interconnect: Defines metal connections for wiring.

Annealing is done after each implantation to repair the broken bonds.

Figure 5: Example of a cross-sectional dopant profile (dopants/cm3) view of a photodiode structure (depth in μπι) . The basic photodiode structure in our work is a P-N-P dual junction photodiode. The P-N junction is at 0.35 urn and the N -P transition is at 1.5 μιτι from the surface. The dopant concentration in the p-region is about 3*10 ²⁰ dopants/cm ³ , in the N-well region about 1*10 ¹⁷ dopants/cm ³ , and in the p- substrate about 2*10 ¹⁶ dopants/cm ³ . A dopant pileup is found to occur in an interfacial layer between Si0 ₂ and Si. This layer acts as a sink for photo generated electrons in this region.

In the present striped version inventors minimized the effect.

Figure 6: Measured responsivity (A/W) versus wavelength (nm) for a multi-stripe photodiode. Responsivity of this work (multi stripe photodiode) has a peak of 0.34 A/W at 480nm, matched with the blue LED' s illumination, while the photodiode in Pauchard et al./1999 has a peak of about 0.15 A/W at 400nm. So an increase in quantum efficiency is measured in our work {0.34 A/W} compared to the same previous device (0.15 A/W) (Pauchard et al . /1999) . The line having a peak of 0.37 A/W at about 700 nm represents performance of a commercially

available S1226-188Q external (hence not integrated) sensor.

In a further example a maximum responsivity was found at λ= 480nm with 342 mA/W. In comparing 2 structures, namely a single anode photodiode and the present multi-strip

photodiode, an improvement in responsivity for the multi- stripe photodiode as predicted in the simulation results is found. Also a dramatic fall for IR range is found which contributes to a high selectivity for the target λ: a selectivity of 42 for 470nm compared to lOOOnm is found.

Figure 7: Photodiode - Performance test. A remarkable consistency can achieved for our photodiode output (blocks) compared to the LED data sheet (points) amounts in terms of relative luminous intensity (normalized at 1=350 mA, hence at 350 mA=l)vs. LED forward current in mA.

Figure 8: Example of a 3D LED package 180. Reflector cavity: In an exemplary process flow of the present 3D LED package, first the silicon wafer is etched with KOH etchant to form the cavity 190, and then coated with Al to form the reflector cup to improve output light efficiency. A

temperature sensor is provided at the bottom and an optical diode sensor on the sidewall of cavity: Several temperature sensors may be implemented beneath the LED chip and at the cavity bottom to monitor the working temperature of the LED. Light sensor is implemented at the cavity sidewall to

selectively monitor the LED output light; at such location no reflector is typically present. Litho defined wiring and reflection layer: The cavity sidewall is patterned both for wiring to the LED chip and active sensing devices (photodiode) .

LED chip placement: The LED chip is located at the bottom of the package.

Remote phosphor plate: A remote phosphor layer is used which is placed at sufficiently large distance from the LED chip to produce combined white light.

Figure9: Example of prototype chip layout 200 {10x10 mm ² ) . LED Feedback control loop circuit, 4 LED package sites with temperature and light sensors, photodiode readout system and test circuits (e.g. for monitoring data and digital control) are all shown in the prototype chip layout. In an example 4 photodiodes in LED package are shown. For each LED die, two sets of photodiodes (at every right top and bottom side of the LED} were used for output light measurement. In addition external power source contacts are provided.

Experimental

Process details For photoresist coating of normal equipment recipes, HMDS (hexamethyldisilazane) with nitrogen as a carrier gas is used for surface treating of a semiconductor wafer. A resist film with a thickness of 1.4 um is formed by spin coating of a Shipley SPR3012 positive resist, dispensed by a pump. The wafer is then soft baked at 95 °C for 90 seconds. It is noted that the relative humidity of (48 ± 2 %) is maintained in the room during coating.

For a photoresist coating of 3D and cavity formation steps, HMDS with nitrogen as a carrier gas is used for surface treating of a semiconductor wafer. 8 layers of a resist film are formed by spraying with positive diluted AZ9260 resist. The wafer is then soft baked at 110 °C for 1-5 minutes.

Process details on exposure are as follow: Projection printing 5x, with an I-line stepper, on an ASML PAS 5500/80, typical NA: 0.48, mask type: binary as well as grayscale. For

developing the resist, the sample receives a post-exposure bake at 115 °C for 90 seconds and is developed with Shipley MF322. At a final stage, the sample is hard baked at 100 °C for 90 seconds.

The blanket N-well region is formed by implanting phosphorus ions to a dosage of 6. Ox 10 ¹² ions/cm ² . The process is executed with 150 KeV ions at an angle of 0 degree (relative to an axis perpendicular to the surface of the wafer) , performed on a Varian E500HP implanter.

The NPN-emitter (shallow N) and source/drain of the NMOS is formed by implanting Arsenic ions to a dosage of 6.00x 10 ¹⁵ ions/cm ² . This process is executed with 40KeV ions at angle of 0 degree, and is also performed on the Varian E500HP

implanter.

The intrinsic base (shallow P) and source/drain of the PMOS could is formed by implanting Boron ions to a dosage of 3. Ox 10 ¹⁴ ions/cm ² . This process is executed with 20 KeV ions at angle of 0 deg (and 55 deg for the cavity sidewalls) .