WO2008006340A1 - Method for heat- and impact-resistant connection of a semiconductor by means of pressure sintering - Google Patents

Abstract

Method for producing a pressure sintering connection for a semiconductor chip (22) on a connecting partner from the following group: substrate, further semiconductor or circuit carrier, and for pressure sintering prepared semiconductor chips (22), where: before a semiconductor wafter (14) is split into individual semiconductor chips (22), a metal powder suspension (10) is applied in highly viscous form to at least the areas of the individual semiconductor chips (22) which are later to be connected by sintering; the suspension layer is dried by out-gassing the volatile constituents and by producing a porous layer; the porous layer is pre-compressed by applying pressure and heat so that it is resistant to the sawing of a wafer silicon saw; the semiconductor chips (22) are separated using sintering material layers of suitable size which are on them; the semiconductor chips are oriented on the connection substrate; and the final sintering is produced to form a permanent connection by diffusing/introducing sintering material atoms into the respective connecting partners.

Description

 Danfoss Silicon Power GmbH D 5148

Process for the heat and impact-resistant connection of a semiconductor by pressure sintering

The invention relates to a method for heat and impact resistant connection of a semiconductor by pressure sintering according to the preamble of the main claim.

State of the art

The increasingly high operating temperatures to which semiconductors are subjected, in particular the operating temperatures which power semiconductors such as diodes, IGBTs or MOSFETs with a very high power loss, but also semiconductors and semiconductor sensors operating in very hot environments (eg an engine compartment of a motor vehicle) are calling for improved connection techniques.

One possibility of the connection, in particular of the power semiconductor itself, is the low-temperature connection technique (NTV), as used e.g. in DE 34 14 065 C2 or EP 0 242 626 Bl.

In the first-mentioned DE 3414065 C2 an NTV method is presented which has the following method steps:

Applying a metal powder suspension to the contact surface of the device to be connected or the substrate,

Applying the component to the substrate, wherein the metal powder suspension is between the component and the substrate, drying the layer, - pressure sintering of the composite of the component and the substrate. Disadvantage of this method is that the drying process is carried out after the application of the device. Since a rapid outgassing over large surfaces is poorly possible here (only the thin boundary surface for drying remains after the component has been placed on the surface of the metal powder suspension), the process is characterized by very long process times.

In addition, there is the process risk of insufficient volatilization of the solvent from the middle of the tie layer, which may result in pores and / or poor thermal and mechanical bonding.

In EP 0242626 Bl a method is presented which has the following method steps:

Applying a metal powder suspension to the contact surface of the device or substrate to be connected,

Drying the layer,

Applying the component to the substrate, wherein the metal powder suspension is located between the component and the substrate, and pressure sintering of the composite of the component and the substrate

The main disadvantages of DE 3414065 C2 are reduced here, but also in this case it is a purely serial process which precludes economic production. In addition, the metal powder layer is very easy to remove after drying, so that there is a considerable risk of damage to the metal powder layer in the further processing of the component or substrate

(Transport, equipping, vacuum gripping, abrasion resistance), which can lead to the later failure of the entire assembly.

One way to prevent these disadvantages is shown in EP 1 599 078 A2. This process is characterized by the following process steps:

Applying a metal powder suspension a carrier film, drying the layer, Pressurizing at least one component onto the dried layer, whereby the adhesion of the metal powder layer to the component is stronger than to the carrier film,

Applying the device to the substrate, wherein the metal powder suspension is between the device and the substrate, and

Pressure sintering of the composite of component and substrate.

This method allows partially parallel processing and thus lower process times than in the above-mentioned patents. However, here as well, there is a considerable process risk when handling the metal powder layer on the carrier film and the components, since this is also very sensitive mechanically (adhesion to the film, delamination / cracking during bending and transport of the film).

Further, the US 5,169,804 may be mentioned, the hitherto practiced sintering a

Layer at high temperature for up to 20 minutes before the layer is separated from an adhesive film.

Another disadvantage is the additional cost of the film and the additional process steps ("stamping" the metal powder layer of the carrier film), and the metal powder residues on the carrier film, which can not be used.

Another disadvantage of this method is particularly noticeable in very sensitive devices, e.g. very thin semiconductor (<100μm). Here there is a risk of further damage (crack propagation of the microcracks resulting from the separation of the wafer) of the semiconductors during a pressure applied only at points by the tool of the "pick and place" machine when the metal powder layer is transferred from the carrier film to the component.

The method of a second carrier foil for the semiconductors, which is only removed after pressure sintering, presented in EP 1 599 078 A2, involves a considerable risk for local, uncontrolled contamination of the surface of the component (in particular semiconductor). This contamination can be increased in further process steps - A -

a significant deterioration of subsequent process steps lead (pressure contact technology, wire bonding, potting, wrapping, stack assembly of semiconductors).

The object of the invention has been found to eliminate the disadvantages of the individual methods represented in the prior art, in particular in the subsequent processing of a semiconductor wafer.

This is achieved by the features of the main claim. The dependent claims give advantageous embodiments again. In particular, a method is provided, which provides a coating of a semiconductor wafer with a metal powder layer, while avoiding unintentional damage / detachment of the metal powder layer in further process steps. In particular, the separation of the wafer is now done by a "sawing step" (cut-off grinding) and only then follows a "pick and place" process. The process represented in the patent can thus be characterized by the following process steps:

Applying a metal powder suspension to the wafer back, drying the layer,

Applying pressure and temperature to the wafer, - separating the semiconductors,

Positioning of the semiconductor on the substrate or circuit carrier, and pressure sintering of the composite of semiconductor and substrate.

The application of the metal powder suspension, consisting essentially of a metal powder and a solvent, to the wafer back can be applied by various methods, such as screen / stencil printing, spraying or spin coating known in the semiconductor field. In this case, only small parts (on the edge of the wafer) are unnecessarily coated with metal powder suspension, since the remainder of the wafer rear side simultaneously represents the connection of the individual semiconductors to be contacted. Therefore, a cost advantage over the method with the full-surface covered carrier film arises.

The drying of the now bare surface of the metal powder suspension is effected by heating and flashing off, preferably between 100 ° C and 150 ⁰ C. Subsequently, the wafer with the dried metal powder suspension is pre-compressed to a pressure of only 5 MPa - 10 MPa and a temperature of 120 ° C - 180 ° C. A sintering of the metal powder layer does not take place yet. Due to the precompression, however, the metal powder layer previously applied as a suspension adheres so well to the wafer that the metal powder layer does not dissolve again in the following process steps, even as described in the following, "sawable", but still fully sinterable during pressure sintering.

Only after pre-compacting can the wafers be separated according to the usual methods known in semiconductor manufacturing by laminating the wafer with the back side onto a sawing foil, and separating the individual chips by a cut-off.

The use of UV-curable sawing foils can be particularly advantageous with thin waveguides. The coated grinding ("sawing") of the coated wafer is not possible in the previously existing methods since the metal powder layer would be detached from the wafer when the semiconductors were separated, and only the special method of precompression described here permits such a treatment.

After separation, the metal powder layer is additionally protected by the sawing foil until it is processed. The placement of the components can also be carried out inexpensively without additional devices on standard "pick and place" machines, since the semiconductor brings with it the metal powder view on the rear side required for the printing sintering process, so it is not an additional process of "stamping" one Connection layer required.

After the semiconductor components are placed on the substrate, which may be preheated at a better cycle time, the actual pressure sintering process takes place above 220 ° C. and with more than 30 MPa within a few seconds.

In this way, it is possible to integrate the low-temperature connection technique without major changes to the actual standard connection process (soldering or gluing) by replacing the soldering oven or the curing oven with a heatable press. Further advantages and features of the invention will become apparent from the following description of the drawings. Showing:

1 shows the wafer during pre-compression with the back up,

2 shows the wafer after sawing with the sawing foil still connecting the separated semiconductors, the coated rear side being laminated,

Fig. 3, the lifting of the sawing film.

The compaction shown in FIG. 1 takes place at a temperature which is the same or slightly higher (30-70 ° C.) than the drying temperature.

The electronic assembly to be formed, for example, a power module with a solid electrically and thermally well-conducting sintered compound of a semiconductor device on a connection partner, e.g. A substrate, further semiconductor or circuit carrier, is achieved by the sintering compound is carried out by pressure sintering as usual, but a sintered layer is previously generated as dried, at least on the wafer back side before the separation of the semiconductor devices and pre-compressed metal powder suspension 10, through the Pre-compaction step for sawing when singulating is mechanically immobilized. The wafer 14 is preferably provided with a metallization 12 below the metal powder.

Before the actual sintering of the dried suspension layer, the chip is usually singulated from a wafer for the connection process by sawing in the respective dimensions of the relevant semiconductor chip. However, applications are also conceivable ("wafer-on-wafer") in which, for example, sensors are used as stacked components in special products.

Furthermore, a tradable intermediate product has been created by the method according to the invention, which is characterized by the precompressed layer. Therefore, the use of such an intermediate product for a Drucksin- wrestle can be addressed. The pre-compression leads on a microscopic level to a rounding of the grain boundaries, so it can be considered as the start phase of a sintering process, which leads to the diffusion of the metal atoms, so that grain boundaries are largely eliminated.

FIG. 2 shows the wafer after sawing with the sawing foil 24 still connecting the singulated semiconductors 22, the sawing frame 20 being shown at the edge, and FIG. 3 schematically showing the lifting off of the sawing foil 24.

The semiconductor prepared by the pre-compression according to the invention for a subsequent pressure sintering process is characterized in that prior to singulating a semiconductor wafer into individual building blocks, at least the areas of the individual sintered-to-be-connected individual semiconductor building blocks, a metal powder suspension was applied pasty, and the The suspension layer was dried with degassing of the volatile constituents and with the formation of a porous layer, after which the porous layer was precompacted with application of pressure and temperature for a wafer saw, and if this is not already done by the buyers of the intermediate product, the Semiconductor devices are separated with appropriately sized sintered material layers on top of them, the semiconductors are aligned on the connection pad, and finally the final sintering to form a solid connection by diffusion / introduction of sintered material To create atoms in the respective connection partners.

The precompacting step leads, under pressure and at temperatures below the sintering temperature, to a compressed, dried, firmly adhering layer, in particular on the rear side of the semiconductor.

However, it may also be the application of a metal powder suspension and pre-compression with pressure and at temperature below the sintering temperature to a compressed, dried layer on the front and back of a semiconductor for mounting contact terminals and / or heat sinks on the second side.

This allows the use of a semiconductor module with two dried metal powder suspensions applied to the wafer front and rear sides before the singulation of the semiconductor components, which are mechanically mechanically immobilized in a precompacting step for sawing on singulation, for sintering on a circuit board. carrier or substrate while sintering another heat sink or contact terminal.

The suspension for sintering advantageously consists of a noble metal-alcohol mixture with vegetable oil or terpene or balsam or resinous

Components. Tests with silver (CAS No. 7440-22-4 in concentration 50% -90%, EC No. 231-131-3) with butan-1-ol (CAS No. 71-36-3) and 10 -17.5% terpineol (CAS # 800-41-7) was successful.

The suspension is gray and insoluble in water, has a low flash point, so that when drying a sudden increase in temperature is to be avoided.

Claims

Danfoss Silicon Power GmbH D 5148Patentansprüche 1. A method for producing a pressure sintered connection of a semiconductor device (22) on a connection partner from the group: substrate, further semiconductor or circuit carrier, characterized in that before the singulation of a semiconductor wafer (14) into individual semiconductor components (22), a metal powder suspension (10) is pastyly applied to at least the regions of the individual semiconductor components (22) which are to be sintered to be sintered later, the suspension layer is dried with outgassing of the volatiles and to form a porous layer, the porous layer under application of pressure and temperature for a Wafer-silicon saw is pre-compacted the semiconductor components (22) are separated with suitably sized sintered material layers on them, the semiconductor devices are aligned on the connection pad, and the final sintering is produced by forming a solid bond by indiffusion / introduction of sintered material atoms into the respective bonding partners. 2. The method according to any one of the preceding claims, characterized in that the pre-compression with pressure and at temperature below the sintering temperature leads to a compressed, dried layer. 3. The method according to any one of the preceding claims, characterized in that the application of a metal powder suspension (10) and pre-compression with pressure and at temperature below the sintering temperature to a compressed, dried layer on the front and back of a semiconductor for mounting contact terminals and / or Heat sinks on the second side takes place. 4. Semiconductor unit (22) prepared for pressure sintering with a dried, saw-resistant layer for the sintered connection, which is applied to at least the area of the wafer backs to be joined later before singulation, characterized by a pressure-compressed layer for the sintered connection.