Integrated semiconductor chip with lateral thermal insulation

An integrated semiconductor with lateral thermal insulation is disclosed. In one embodiment, the chip has, on a common substrate, at least one power semiconductor circuit region and, laterally adjacent to the power semiconductor circuit region, at least one further temperature-sensitive semiconductor circuit region, interspaces being maintained between the circuit regions. At least one thermally insulating trench is provided at least in each interspace in each case between power semiconductor circuit region(s) and temperature-sensitive semiconductor circuit region(s), which at least one thermally insulating trench extends into the depth of the chip right into the substrate and in the longitudinal direction of the chip at least over a lateral side of the at least one power semiconductor circuit region and/or the temperature-sensitive semiconductor circuit region and is either unfilled or filled with a thermally insulating filling material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority to German Patent Application No. DE 10 2006 031 539.1 filed on Jul. 7, 2006, which is incorporated herein by reference.

BACKGROUND

One aspect of the invention relates to an integrated semiconductor chip having, on a common substrate, at least one power semiconductor circuit region and, laterally adjacent to the power semiconductor circuit region, at least one further temperature-sensitive semiconductor circuit region, interspaces being maintained between the circuit regions.

Such integrated semiconductor chips which are constructed e.g., using high-voltage CMOS or BCD technology contain e.g., a plurality of power output stages together with a logic circuit region and/or an analog circuit region and/or, if appropriate, a flash memory. The power output stages are generally positioned at the chip edge in order to keep the resistances of the bonding connections as small as possible. The flash memory, which is generally the most sensitive to temperature, must for the most part lie in direct proximity to the output stages. Owing to the high electrical powers switched in the output stages, a very large amount of heat is developed here and thermally loads adjacent components, that is to say components of the temperature-sensitive semiconductor circuits. These thermal loadings essentially arise during switching operations and are therefore temporally limited. In the case of repetitive clamping, the switching operations last for 50 to 500 μs. If these operations last longer, the thermal switching losses generated are not as high. Generally, the temperature-sensitive components lying e.g., in the flash memory alongside the power output stages must not be exposed to temperatures higher than 150° C. By virtue of the advancing miniaturization of the CMOS transistors, in particular the PMOS transistors therein become more sensitive to temperature. Their voltage-temperature characteristic (VT) starts to shift.

In previously developed, commercially available integrated semiconductor chips, primarily to heat dissipations heat sinks are a tried and tested means for enabling the temperature of the entire semiconductor chip not to rise excessively. This was possible since the high-voltage processes had not yet been miniaturized to an extent such that temperature problems arose. High-voltage CMOS or BCD processes in the range of less than 250 nm will be developed in the future, however. For this reason, lateral thermal insulation measures on the integrated semiconductor chip at least between in each case the temperature-sensitive semiconductor circuit regions and the power semiconductor circuit region(s) are desirable or necessary.

SUMMARY

One embodiment includes an integrated semiconductor with lateral thermal insulation. In one embodiment, the chip has, on a common substrate, at least one power semiconductor circuit region and, laterally adjacent to the power semiconductor circuit region, at least one further temperature-sensitive semiconductor circuit region, interspaces being maintained between the circuit regions. At least one thermally insulating trench is provided at least in each interspace in each case between power semiconductor circuit region(s) and temperature-sensitive semiconductor circuit region(s), which at least one thermally insulating trench extends into the depth of the chip right into the substrate and in the longitudinal direction of the chip at least over a lateral side of the at least one power semiconductor circuit region and/or the temperature-sensitive semiconductor circuit region and is either unfilled or filled with a thermally insulating filling material.

DETAILED DESCRIPTION

One aspect of the invention specifies an integrated semiconductor chip of the generic type such that it enables an effective lateral thermal insulation between the power semiconductor circuit region(s) and the temperature-sensitive semiconductor circuit region(s).

In accordance with one embodiment, an integrated semiconductor chip is characterized by the fact that at least one thermally insulating trench is provided at least in each interspace in each case between power semiconductor circuit region(s) and temperature-sensitive semiconductor circuit region(s), which at least one thermally insulating trench extends into the depth of the chip right into the substrate and in the longitudinal direction of the chip at least over a lateral side of the at least one power semiconductor circuit region and/or the temperature-sensitive semiconductor circuit region and is either unfilled or filled with a thermally insulating filling material.

By using such thermally insulating trenches which are either filled with a material having high thermal resistance or which are alternatively empty, i.e. unfilled, the heat-generating chip regions can be thermally decoupled from the thermally sensitive chip regions. The depth of the thermally insulating trenches is at least approximately one third of the chip thickness. The thermally insulating trench or the thermally insulating trenches can reach as far as the silicon surface of the chip. However, they can also be buried below the silicon surface of the chip. In the latter case, however, there should be a very small distance between the upper edge of the thermally insulating trench and the silicon surface. The heat usually arises in the depth of 2 to 6 μm in such an integrated semiconductor chip.

In one embodiment, a plurality of thermally insulating trenches can be formed alongside one another in the interspace or interspaces between the power semiconductor circuit region(s) and the temperature-sensitive semiconductor circuit region(s) for the purpose of even better thermal insulation, the thermally insulating trenches being constructed identically and running approximately parallel alongside one another.

In the case of the thermally insulating trenches filled with a filling material, the filling material can be either electrically insulating or electrically conductive and, in the latter case, produce e.g., a substrate contact to the silicon surface of the chip. In the case of the electrically conductive filling material, the latter includes polysilicon and the sidewalls of the thermally insulating trench are then lined with an insulating oxide.

The conduction type of the polysilicon filling the thermally insulating trench or the thermally insulating trenches is identical to the conduction type of the substrate.

As a further measure, the semiconductor chip according to one embodiment additionally has an electrical insulation layer having good thermal conductivity on the chip rear side between the substrate and a rear side metallization, the electrical insulation layer including e.g., SiC or diamond. In this case, the depth of the thermally insulating trenches is chosen such that it reaches as far as the electrical insulation layer.

In the case where the power semiconductor circuit region(s) have a vertical power transistor, e.g., a vertical DMOS, the electrical insulation layer is cut out below the or each power semiconductor circuit region.

As an additional thermal insulation measure, a void can be provided between the substrate and an overlying silicon epitaxial layer, the void extending over the area of the respective temperature-sensitive semiconductor circuit region.

In one embodiment of the integrated semiconductor chip, the plurality of power semiconductor circuit regions are spatially combined to form at least one power block and the plurality of temperature-sensitive semiconductor circuit regions are spatially combined to form at least one second (temperature-sensitive) circuit block. In this case, at least one such thermally insulating trench in each case is situated in the interspace between each power block and each second (temperature-sensitive) circuit block.

The semiconductor chip according to one aspect can be present in a plurality of exemplary embodiments in which the power semiconductor circuit region(s) or the at least one power block can be equipped with bipolar high-voltage transistors in one example, with DMOS high-voltage transistors in an alternative example, and wherein the DMOS high-voltage transistors can be either vertical or lateral MOS transistors.

In further embodiments of the semiconductor chip according to aspects of the invention, the temperature-sensitive semiconductor circuit region(s) or the second temperature-sensitive circuit block are equipped with a low-voltage semiconductor circuit, which may have a logic circuit and/or an analog circuit and/or a memory circuit.

In the case of an integrated semiconductor chip realized with the above features, the lateral thermal diffusion can be greatly restricted by the thermally insulating trenches that are unfilled or filled with oxide, oxide/polysilicon. By way of example, 1 μm of oxide has a thermal resistance corresponding to 300 μm of silicon. Since, on account of the thermally insulating trenches whose depth is at least approximately one third of the wafer thickness, the heat cannot propagate toward the side, it propagates toward the rear side of the chip. On the chip rear side it is possible to provide effective heat dissipating layers that dissipate the heat e.g., toward a heat sink. High but short heat pulses such as arise in power transistors (including NPN, vertical, lateral DMOS, etc.) can be kept away from the temperature-sensitive semiconductor circuit regions on the semiconductor chip by using the thermally insulating trenches according to embodiments of the invention.

The layout views—illustrated schematically inFIGS. 1A,1B and1C—of integrated semiconductor chips configured according to embodiments of the invention illustrate customary partitionings with a plurality of power semiconductor circuit regions11-15positioned at the chip edge in order to keep the resistances of the bonding connections as small as possible, and additionally with a plurality of temperature-sensitive semiconductor circuit regions21,22,23(FIGS. 1A and 1B) and21-25(FIG. 1C). By way of example, the temperature-sensitive semiconductor circuit region21is a logic circuit region, the circuit region22contains e.g., analog circuits, and the circuit region23has e.g., a flash memory. The circuit regions24and25in accordance withFIG. 1Cmay represent e.g., logic and/or analog and/or flash memory areas. The flash memory (e.g., the circuit region23) is usually the most sensitive to temperature and lies in direct proximity to the power semiconductor circuit regions12,13,14,15. As can be seen fromFIGS. 1A-1C, the plurality of semiconductor circuit regions are combined to form circuit blocks (in this case to form two circuit blocks10A and10B), while the temperature-sensitive semiconductor circuit regions likewise form a circuit block20. In the case of the exemplary embodiments illustrated inFIGS. 1A-1C, a first thermally insulating trench WIG1lies in an interspace Z1between the power block10A and the temperature-sensitive circuit block20. A second thermally insulating trench WIG2extends in interspaces Z2and Z3between the second power block10B with the power semiconductor circuit regions14and15and the temperature-sensitive circuit block20, the second thermally insulating trench being embodied doubly in accordance withFIG. 1B, that is to say that two parallel thermally insulating trenches WIG2and WIG3of identical type are formed in the interspaces Z2and Z3.

In the schematic layout illustration illustrated inFIG. 1C, a thermally insulating trench WIG4is additionally formed in an interspace Z4between temperature-sensitive semiconductor circuit regions22,23, on the one hand, and24,25, on the other hand. Consequently, the thermally insulating trenches WIG1-WIG3provided according to an embodiment of the invention extend in the lateral direction in the respective interspaces Z1, Z2, Z3at least over a longitudinal side of a power semiconductor circuit region or a power block10A,10B and/or over a longitudinal side of the temperature-sensitive semiconductor region, e.g.,21, or a longitudinal side of the temperature-sensitive circuit block20. As is explained even more clearly below with reference to the cross-sectional illustrations, the depth of the thermally insulating trenches reaches right into the substrate and is at least approximately one third of the chip thickness. Moreover, the thermally insulating trenches WIG1-WIGn can either be unfilled or be filled with thermally insulating filling material, e.g., with an oxide lining and with polysilicon.

The integrated semiconductor chip illustrated in cross section inFIG. 2Arepresents a section e.g., through the regions15,23and13in accordance withFIG. 1A. The illustration reveals thermally insulating trenches WIG1, WIG2, WIGn reaching right into the substrate P-SUB, in the case of which trenches only the walls are lined with insulating oxide O and which trenches are filled with P-type polysilicon P-POLY and thus produce a conductive connection of the substrate P-SUB to the silicon surface, that is to say to the surface of an N-type epitaxial layer N-EPI. The depth—designated by t1—of the thermally insulating trenches WIG1, WIG2, WIGn is at least one third of the chip thickness, which, in the example, is composed of the thickness t2of the P-type substrate P-SUB and the thickness t3, where the thickness t3is the sum of the thicknesses of the epitaxial layer N-EPI and a buried layer N-BL (t1>⅓ (t2+t3)). A thermal coupling TA to a heat sink (not illustrated) is situated on the rear side of the chip.

The cross-sectional illustration illustrated inFIG. 2Brepresents a section e.g., through the power semiconductor circuit regions13,15and the temperature-sensitive semiconductor circuit region23and differs from the exemplary embodiment illustrated in the cross-sectional illustration ofFIG. 2Aby virtue of the fact that the thermally insulating trench in the interspace Z2between the power semiconductor circuit region15and the temperature-sensitive semiconductor circuit region23is embodied doubly, that is to say includes two thermally insulating trenches WIG2and WIG3of identical type that lie parallel alongside one another (cf.FIG. 1B). The other regions and measures of the exemplary embodiment illustrated inFIG. 2Bare identical to the corresponding features inFIG. 2Aand designated by the same reference symbols. The parallel arrangement of a plurality, i.e. two in this example, of parallel thermally insulating trenches improves the thermal insulation between the power semiconductor circuit region15and the temperature-sensitive semiconductor circuit region23, i.e. for example a flash memory, in comparison with the exemplary embodiment illustrated inFIG. 2A. In addition, what is common to the two exemplary embodiments illustrated inFIGS. 2A and 2Bis that the thermally insulating trenches WIG1, WIG2, WIGn enable a substrate contact GND on the silicon surface by virtue of their polysilicon filling that produces a connection to the P-type substrate P-SUB.

FIGS. 3A and 3Billustrate further exemplary embodiments of integrated semiconductor chips in which the thermally insulating trenches WIG2, WIG3(FIG. 3A) and WIG1, WIG2(FIG. 3B) are completely insulated.FIG. 3Aillustrates that the substrate connection GND including polysilicon P-POLY is situated between the two parallel thermally insulating trenches WIG2and WIG3. Otherwise, the construction of the integrated semiconductor chip is similar to that illustrated inFIG. 2B. While the thermally insulating trenches WIG2, WIG3in accordance withFIG. 3Areach as far as the silicon surface, that is to say as far as the surface of the epitaxial layer N-EPI, the thermally insulating trenches WIG1and WIG2in accordance withFIG. 3Bare completely buried. In this case, the remaining region of the silicon, that is to say of the epitaxial layer N-EPI between the upper edge of the thermally insulating trenches WIG1, WIG2and the surface of the epitaxial layer N-EPI should be as small as possible. 0 μm would be best. The filling of the thermally insulating trenches WIG1, WIG2, WIG3lined completely with oxide can be polysilicon in the case of the exemplary embodiments illustrated inFIGS. 3A,3B. This need not necessarily be the case, however, since the filling material can also be a different thermally insulating material, e.g., oxide, which need not have electrical conductivity. There is also the possibility of leaving the thermally insulating trenches lined with oxide O in accordance withFIGS. 3A and 3Bunfilled, that is to say empty, since an air filling also forms a good thermal insulator. By way of example, 1 μm of oxide has a thermal resistance corresponding to 300 μm of silicon.

FIG. 4Aillustrates a cross section e.g., through the semiconductor circuit regions15,23,25and13in accordance withFIG. 1C, the semiconductor circuit regions13and15of which are power semiconductor circuit regions in the example. The power semiconductor circuit region15has a vertical power DMOS transistor, the gate of which is connected to a gate voltage V-GATE, the source of which is connected to a source voltage V-SOURCE and the drain of which, formed by the rear side metallization MR+TA, is connected to a drain voltage V-DRAIN. Consequently,FIG. 4Aillustrates an integrated semiconductor chip in common-drain technology, the substrate of which is an N+-type substrate and the epitaxial layer of which is an N-type epitaxial layer. Situated in a P-type well in the temperature-sensitive semiconductor circuit region23are for example CMOS or bipolar circuit parts (not illustrated) in a P-type well. Here, too, the depth of the thermally insulating trenches WIG1, WIG3, WIG4lined with oxide O is at least one third of the chip thickness composed of t2+t3. The rear side metallization MR+TA simultaneously also forms a heat-dissipating connection to a heat sink (not illustrated).

FIG. 4Billustrates a cross-sectional view of yet a different exemplary embodiment. In the exemplary embodiment illustrated inFIG. 4B, the power transistor technology in the power semiconductor circuit region15is a lateral power DMOS technology, wherein source voltage V-SOURCE is applied to a source electrode of the lateral power DMOS, gate voltage V-GATE is applied to a gate electrode of the lateral power DMOS and drain voltage V-DRAIN is applied to a drain electrode of the lateral power DMOS. As illustrated, the thermally insulating trenches WIG1, WIG3and WIG4are lined with oxide and filled with n+-type polysilicon inFIG. 4B, too. In contrast to the exemplary embodiment illustrated inFIG. 4A, the exemplary embodiment ofFIG. 4Bhas a layer TL that has good thermal conductivity but is not electrically conductive on the rear side of the chip, which layer can be used to produce completely electrically insulating circuit blocks. SiC, for example, is appropriate as the material of the layer TL. However, the material can also be diamond. If possible, the semiconductor wafer should be as thin as possible in order to save etching costs when etching the thermally insulating trenches. The substrate is an N−-type substrate N−-SUB in the exemplary embodiment illustrated inFIG. 4B.

The exemplary embodiment illustrated inFIG. 4Cforms a combination of the exemplary embodiments illustrated inFIGS. 4A and 4B. As in the exemplary embodiment illustrated inFIG. 4A, the power transistor in the power semiconductor circuit region15is a vertical power DMOS transistor. The layer TL on the rear side of the chip, which layer includes SiC or some other material that has good thermal conductivity but is not electrically conductive, is cut out below the power semiconductor circuit region15, that is to say below the vertical power DMOS transistor, in order to ensure the drain connection V-Drain thereof on the rear side by using the rear side metallization MR+TA. The other features of the exemplary embodiment illustrated inFIG. 4Ccorrespond to the exemplary embodiments ofFIGS. 4A and 4Bthat have already been outlined above.

It should be noted that the above-described exemplary embodiments illustrated in the sectional views ofFIGS. 4A,4B and4C represent a section through the power semiconductor circuit regions12or13and14or15and the intervening temperature-sensitive semiconductor circuit regions22or23and24or25, wherein, in addition to the thermally insulating trenches WIG1and WIG3in each case between the power blocks10A and10B and the intervening temperature-sensitive semiconductor circuit block20, a thermally insulating trench WIG4is also formed between temperature-sensitive semiconductor circuit regions23and25, and22and24.

FIG. 5illustrates, in a schematic cross section through the power semiconductor circuit regions15(14) and13(12) and also an intervening temperature-sensitive semiconductor circuit region23(22), a further measure that improves the thermal insulation still further by using an areal void V in the silicon below the temperature-sensitive semiconductor circuit region23(22). Otherwise, the exemplary embodiment illustrated inFIG. 5largely corresponds to the exemplary embodiment in accordance withFIG. 2A, in which a substrate contact GND is produced by the P-type polysilicon filling P-POLY of the thermally insulating trenches WIG1, WIG2lined with oxide O. The void V could be produced e.g., by using a trench etch prior to the growth of the epitaxial layer N-EPI. If the trenches etched as a result lie very close together, they are not filled during the subsequent epitaxial growth. If heat treatment is effected after the epitaxial growth with hydrogen, then the etched trenches combine to form the void V.

What is characteristic of all the exemplary embodiments of an integrated semiconductor chip according to the invention as described above with reference toFIGS. 1A,1B,1C,2A,2B,3A,3B,4A,4B,4C and5is that at least one thermally insulating trench WIG1, WIG3is provided at least in each interspace in each case between power semiconductor circuit region(s) and temperature-sensitive semiconductor circuit region(s), which at least one thermally insulating trench extends into the depth of the chip right into the substrate SUB and in the longitudinal direction of the chip at least over a lateral side of the at least one power semiconductor circuit region11-15and/or the temperature-sensitive semiconductor circuit region21-23and is either unfilled or filled with a thermally insulating filling material.

The depth t1of the thermally insulating trench or of the thermally insulating trenches WIG1-WIG4is at least approximately one third of the chip thickness.