DE10249855B4 - Material for supplying current to semiconductor devices and method for producing such - Google Patents

Abstract

Semiconductor with a material for supplying electricity, in which
the material has a coefficient of material thermal expansion (α _V ) and a material elastic modulus (E _V ) and can be fastened to at least a part of the semiconductor (Si) in such an electrically contacting manner that the current is conducted through the material as a conductor into the semiconductor .
the material of the semiconductor (Si) has a semiconductor thermal _expansion coefficient (α _HL ) and a semiconductor elastic modulus (E _HL ), and
the material consists of a composite material (1a, 2a) of at least one conductive material (1a) and at least one other material (2a) which is poor or non-conductive relative thereto,
characterized in that
the conductive material (1a) and the other material (2a) extend two-dimensionally and
the conductive material (1a) with a dimension (z) extends in the direction of the surface of the semiconductor (Si).

Description

semiconductor with a material for supplying Electricity and method of making such The invention relates on a semiconductor, in particular semiconductor device, with a material for feeding of electricity with the preamble features of the claim 1 or to a method for producing such.

Such semiconductors and the associated production methods are known for example from DE 195 09 202 A1 , of the DE 689 23 717 T2 or US 6 028 364 A known.

At the Use of semiconductors must often, especially in power electronics, strong currents on silicon chips to be brought. For this purpose, the silicon chips are contacted with highly conductive metals. Good conductive However, metals have thermal expansion coefficients that are approx. ten times as high as the coefficient of expansion of silicon. This results in problems with temperature stresses at the contact surface between the supply line and the chip. For example, the deliverable current densities are typical Modules for controlling three-phase motors are limited by this problem.

Similar problems exist in the production of flat semiconductors, when a highly conductive carrier wafer is required, on which a very thin and fracture-prone under the processing of silicon wafer with a metallic compound, for. B. with eutectic gold bonding is applied. However, the well-conductive carrier wafer can not be a plate of metal, since it in any case thermally expands by a factor of ten stronger than the silicon wafer, so they would destroy the latter. To solve the problem is for example from the DE 101 40 826 A1 a method for multi-step processing of a thin and breakable under the processing steps semiconductor wafer product known. In this case, it is described that the rear side of the actual wafer product is subjected to a high-temperature treatment, while a front-side carrier substrate is mounted on its active front side. Then, a metal-base bonding capping layer is applied to the back side and / or a backside substrate of conductive material. Another backside substrate is then heat bonded to the back surface of the wafer product by forming the intervening metal base bonding material. This creates a central conductive metal-based bonding layer.

at the application of such a metal-based bonding cover layer on a Carrier substrate or carrier wafer there is the problem that in subsequent processing steps, which still have to be done with such a stack of layers and at temperatures up to 400 ° C It is important to have no problems due to differences thermal expansion coefficients between the semiconductor product and the carrier wafer consist.

For the supply line from power to chip is most common used the wire bonding. Bonding wires with a curved Shaping between the point of contact with the chip and a contact point on the other wire side can compensate for different thermal expansion coefficients. Such bonding wires often become very big Number parallel to the contact surfaces of circuit breakers guided. However, circuit breakers and diodes are currently in preparation, those with bonding wires deliverable Current densities will not be enough.

Purely physically is to feeding higher current densities also more total volume of conductive material required. The simplest device would be a very good electric conductive, possibly also structured plate with the same thermal expansion coefficient like that of mono crystalline silicon. This goal can indeed with highly doped silicon has been achieved, but so far nevertheless not enforced, because in the production of carrier wafers Hitherto highly doped silicon wafers have been used, preferably Arsenic-doped wafers with conductivities down to about 3 mΩ · cm. The Disadvantages why this procedure in the current generation of IGBTs and power diodes is not yet used, the relatively high cost of monocrystalline Silicon as well as the effort for the eutectic gold bonding. Furthermore is the conductivity still about a factor of 100 lower than for highly conductive metals, so that the use is limited to high-barrier components.

The The object of the invention is a semiconductor, in particular a semiconductor device having an arrangement for supplying Electricity available to provide, on the one hand, a significantly higher electrical conductivity as highly doped silicon and on the other hand mechanical stresses by different thermal expansion coefficients of the materials compensated.

These The object is achieved by a semiconductor having the features of the claim 1 or a method for producing such a semiconductor the features of claim 12 solved.

Around a power supply to a semiconductor in operation with the lowest possible temperature voltages between the semiconductor material and a current supplying To allow material It is suggested that the material be made of a composite material of at least one conductive material and at least one relative to bad conductive, preferably insulating material. Especially insulating material usually has smaller thermal expansion coefficients and / or a smaller modulus of elasticity as those of the semiconductor material. The conductive material and the other material extend substantially two-dimensionally, wherein the conductive material is dimensioned in one direction the surface of the semiconductor.

advantageous Embodiments are the subject of dependent claims.

It is also a structure advantageous in which alternating layers alternate from the different materials used, where the conductive material and the particular insulating material extend substantially layered or plate-shaped. Possible are but also alternative embodiments, z. B. metals with interspersed insulator elements.

semiconductor can while chips, in particular silicon chips or wafers, in particular Be silicon wafer. In addition to pure support materials can also directly complex components with such materials for supplying Electricity to be equipped.

advantageously, The composite material is constructed so that the material property of the composite as such comparable to the material property of the semiconductor is when temperature fluctuations in the surrounding area or occur in the materials themselves. The temperature fluctuations arise especially when supplying current with a large current density.

embodiments become closer with the drawing explained. It shows:

1 an embodiment of a composite material with a layered structure of conductive and insulating material layers.

In the in the 1 illustrated embodiment, the material consists of a sheet-like arrangement of a very highly conductive material 1a and a relatively poorly conductive or insulating material 2a , A current flow is thus possible in two spatial directions z, x. The material is arranged on the surface of the semiconductor Si in such a way that the plane zx spanned by the individual layers runs with one of its extension directions z perpendicular to the plane xy, which is spanned by the surface of the semiconductor Si.

In the contact area to the attached material 1a . 2a the material of the semiconductor Si is characterized by a coefficient of thermal expansion or thermal expansion coefficient α _HL and a modulus of elasticity E _HL . In the case of temperature fluctuations, the volume or the size of the contact surface of the semiconductor Si changes according to these coefficients.

Since the patch on the semiconductor Si material in the form of a composite material of at least two different materials 1a . 2a different coefficients should be taken into account in this regard. The ladder 1a have a conductor-thermal expansion coefficient α _L and a modulus of elasticity E _L and behave according to temperature differences. That's the ladder 1a surrounding poor conductive or insulating material 2a has a thermal expansion coefficient α _I and a modulus of elasticity E _I.

In the case of temperature fluctuations, the material behaves in accordance with the various materials, and according to a simple consideration, an averaging of the respective coefficients can be established. Realistically, the volume ratios and the relative distribution to each other of the materials used 1a . 2a of the material.

In the following, however, a balanced relationship should be assumed simplifying, so that the product of expansion coefficient α x elastic modulus E almost always occurs in the calculation of thermal stresses of the material. The corresponding coefficients α _V , E _{V of} the composite material can thus, according to a simple consideration, be regarded as the mean value of the products of expansion coefficient α _L , α _I and the corresponding elastic modulus E _L or E _I. In order to reduce the critical loads in the event of temperature fluctuations, the composite material becomes the plurality of conductors 1 in the poorly conductive or insulating material 2 such that the coefficients α _V and E _{V are} adapted to the coefficients α _HL and E _HL . In this case, the mean value of the respective products of expansion coefficient α _V x elastic modulus E _V should be approximated to the coefficient of elasticity α _HL x elastic modulus E _HL , so that the temperature stresses between the composite material on the one hand and the semiconductor Si on the other hand are minimized. This can also be done Current with a very high current density over the composite material or the conductors 1 in which the semiconductor Si are supplied:

These mathematical condition can be understood as follows: There are analytical solutions of temperature stresses in homogeneous plates. These are won, by extending Hooke's law linearly with thermal expansion, and a temperature gradient instead of a homogeneous mechanical load normal to the disk plane. In these solutions comes the local temperature of the plate always multiplied by the expansion coefficient and elastic modulus in front. Now you swap the temperature with the product of expansion coefficient sometimes elastic modulus (in the sense of a pure renaming of variables) so changes purely mathematical nothing from which it is concluded that the problem a homogeneous plate with inhomogeneous temperature distribution the Problem of an inhomogeneous plate with homogeneous temperature equivalent is.

From The geometrical idea would have to deal with such problems necessarily the thermal expansion coefficient of the two brought into contact Materials are matched, what with an excellent conductor material and monocrystalline silicon can never succeed. The exact theory provides but in the case of the rod or the circular plate, the result that it depends on the product of coefficient of expansion times elastic modulus arrives.

By the arrangement of the ladder 1a in the direction z perpendicular to the surface xy of the semiconductor Si, an electric current applied on the side of the material opposite to the semiconductor Si flows in the spatial direction z directly to the surface of the semiconductor Si. This requires the highest possible electrical conductivity of the material. In the usual way, the material on the side of the semiconductor Si is such that the material is attached to the semiconductor Si with conventional metallized contact surfaces.

The preferred material for supplying current with a high current density to a semiconductor Si thus consists of a layer material of alternating layers of a highly conductive, solderable metal and a relatively poorly conductive material or preferably insulating material. In this case, the mean value of the products from thermal expansion coefficients α _L , α _I , modulus of elasticity E _L , E _I and volume fraction of the two materials forming the coating material should be approximated to the product of coefficient of expansion α _HL and elastic modulus E _{HL of} the semiconductor.

The preferred material for making the conductors 1a is copper, which can be used very easily in the form of films. As insulation for the production of the insulating material 2a both ceramics such as quartz but also magnesium-aluminum silicate can be used, since these have a smaller coefficient of expansion than silicon, which is usually present as a material of the semiconductor Si in the contact region to the material. Usable as insulating materials but other materials, for example, up to z. B. 350 ° C temperature-resistant plastics. Although they have a high thermal expansion coefficient α _I , but a very small modulus of elasticity E _I.

The Materials which are composed in this way lead to the semiconductor Si to be supplied Current in two spatial directions x, z.

The materials of a variety of such conductors 1a and the less conductive materials or insulating materials 2a are preferably produced in the form of blocks. In a subsequent manufacturing step, these blocks are then decomposed such. B. sawn that the individual to be arranged on a semiconductor Si material pieces are constructed so that the conductors lead in the direction of the surface of the semiconductor Si.

Of course, a variety of variants can be used. So have the ladder 1a not necessarily perpendicular to the surface of the semiconductor Si. Also, a use of more than two different materials for the production of the material can be used, for example, a very good conductive material, a relatively less conductive material and an insulating material.

ever according to requirements, in particular the current density zuzuführender streams can adapt to the circumstances the coefficients between on the one hand the composite material and on the other hand a request is made to the semiconductor material which set within a tolerance measure Δ becomes. The deviations of the products from thermal expansion coefficient and Modulus of elasticity the composite material on the one hand and the semiconductor material on the other should be in accordance with the requirements within each to be determined Tolerance measure Δ lie.

The composite material described is thus preferably a temperature voltage compensated, anisotropic conductor material for the power electronics.

Claims (11)

Semiconductor comprising a material for supplying current, in which the material has a material thermal expansion coefficient (α _V ) and a material elastic modulus (E _V ) and can be fastened to at least a part of the semiconductor (Si) in such an electrically contacting manner that the current is guided through the material as a conductor into the semiconductor, the material of the semiconductor (Si) has a coefficient of semiconductor thermal _expansion (α _HL ) and a semiconductor elastic modulus (E _HL ), and the material is made of a composite material ( 1a . 2a ) of at least one conductive material ( 1a ) and at least one relatively poor or non-conductive other material ( 2a ), characterized in that the conductive material ( 1a ) and the other material ( 2a ) extend two-dimensionally and the conductive material ( 1a ) having a dimension (z) extending toward the surface of the semiconductor (Si). Semiconductor according to claim 1, consisting of alternating layers of the different materials ( 1a . 2a ). Semiconductor according to Claim 1 or 2, in which the conductive material ( 1a ) and the other material ( 2a ) extend in a layered manner. Semiconductor according to Claim 1 or 2, in which the conductive material ( 1a ) and the other material ( 2a ) extend in a plate shape. A semiconductor according to any preceding claim, wherein the material material as a whole within a tolerance measure (Δ) for heat changes has similar material properties (α _v , E _v ) as the material properties (α _HL , E _HL ) of the semiconductor (Si). Semiconductor according to claim 5, wherein at least the material thermal expansion coefficient (α _V ) is similar within the tolerance dimension, in particular equal to the coefficient of semiconductor thermal expansion (α _HL ). Semiconductor according to claim 5 or 6, wherein at least the material elastic modulus (E _V ) is similar within the tolerance dimension, in particular equal to the semiconductor elastic modulus (E _HL ). Semiconductor according to one of Claims 5 to 7, in which the mean value of the material thermal coefficients (α _v ) over the various materials used ( 1a . 2a ) within the tolerance level and / or the mean value of the modulus of elasticity (E _L , E _I ) of the various materials used ( 1a . 2a ) are within the tolerance level. A semiconductor according to claim 8, wherein

with α _HL , α _H , α _L , α _I as the thermal coefficient of the semiconductor (Si), of the composite material ( 1a . 2a ), the conductive material ( 1a ) or the other material ( 2a ) and with E _HL , E _V , E _L , E _I as modulus of elasticity. Semiconductor according to Claim 8, in which, in the formation of the mean values, the extent of the contact surfaces between material ( 1a ; 2a ) and semiconductors (Si) and / or the volume of the material are taken into account. Method for producing a semiconductor according to one of the preceding claims, comprising the following steps: layer-by-layer stacking of the conductive material ( 1a ) and the less conductive or insulating material ( 2a ) and / or incorporation of rods or fibers of the conductive material into the poorly conductive or insulating material ( 2a ) and - cutting a block made in this way and attaching it to the semiconductor (Si) so that the conductive material ( 1a ) is in any case in the direction (z) of the surface (xy) of the semiconductor.