EP1198841A1

EP1198841A1 - Electric semiconductor element with a contact hole

Info

Publication number: EP1198841A1
Application number: EP00958104A
Authority: EP
Inventors: Alfred Goerlach; Marion Gebhard
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-07-03
Filing date: 2000-07-03
Publication date: 2002-04-24
Also published as: WO2001003195A1; US6787905B1; DE19930797A1; JP2003504852A

Abstract

An electric semiconductor element comprising a monocrystalline semiconductor substrate which is made, for example, out of silicon; an insulating layer (6) which is penetrated by a contact hole (30) on at least one point and arranged on the surface of the semiconductor substrate (1); in addition to a contact element which comes into contact with the semiconductor substrate (1) by means of the contact hole (30) and which is made of a material such as aluminium, whereby the semiconductor material of the substrate can be dissolved in an anisotropic process. The edges of the contact hole (30) are configured as diffusion-preventing structures.

Description

ELECTRICAL SEMICONDUCTOR COMPONENT WITH A CONTACT HOLE

The invention relates to an electrical semiconductor component having a single-crystalline semiconductor substrate, an insulation layer which is broken through at least at one point by a contact hole and is arranged on the surface of the semiconductor substrate, and a contact element which contacts the semiconductor substrate through the contact hole and is made of a material. in which the semiconductor material of the substrate is soluble in an anisotropic dissolution process.

Such semiconductor devices, in which the

Semiconductor substrate silicon and the material of the contact element is aluminum, are common. A problem with the formation of contact between aluminum and silicon in the area of the contact holes of such components is the solid-state reaction of aluminum with silicon that takes place there. For a high conductivity of the contact between the two, the removal of the naturally existing oxide skin between aluminum and silicon in the contact hole is necessary. This is done by means of a temperature treatment in the range from 300 ° C to 500 ° C. At these temperatures, metallurgical areas appear in the areas freed from the oxide Reactions of aluminum with silicon on, due to the solubility of the two substances in the other. Depending on the temperature, the solubility of silicon in aluminum is on the order of a few percent (for example 0.48% at T = 450 ° C). The diffusion of silicon in polycrystalline aluminum is very high due to accelerated diffusion along the grain boundaries. For this reason, not only the immediate contact hole area but also the adjoining aluminum conductor track areas are saturated with silicon in the course of the temperature treatment. Depending on the temperature, a large amount of silicon can be detached from the surface of the semiconductor component and migrate into the aluminum contact structure. In the case of a thirty-minute annealing treatment at 450 ° C., for example, the diffusion length of the silicon atoms is approximately 40 μm. The silicon atoms detached from the crystal are replaced by aluminum atoms that migrate out of the contact structure. These form so-called "spikes", aluminum precipitates with silicon content. The smaller the contact hole and the larger the aluminum volume to be saturated in relation to it, the larger the dimensions of these spikes. They can strongly distort electrical fields in the contact hole area or, if they reach sufficient for a PN transition of the component, leading to its total failure.

To avoid this problem, silicon-doped aluminum is known, for example, from DH Widmann, H. Mader, H. Friedrich, Technology of Highly Integrated Circuits, Berlin, Springer 199S to be used as material for the contact structures of electronic components. The silicon concentration of the doped aluminum is above the solids solubility of the silicon in the aluminum, based on the highest process temperatures reached during the temperature treatment. This concentration can be approximately 1% silicon.

However, this solution cannot be used for contacting in contact holes on high-resistance n-type silicon (donor concentration less than 10 ²⁰ cm ^"3 ). Here, when cooling, epitaxial silicon deposits are formed in the contact hole area. These are aluminum-doped and therefore p-conductive Because of the pn transition formation, the contact resistance deteriorates with increasing degree of coverage in the contact hole. For this reason, aluminum is used as the metallization for contacting high-resistance n-type silicon without the addition of silicon. In order to produce a conductive transition in the contact hole, the appearance of spikes must then occur to be accepted.

Advantages of the invention

The invention is based on the surprising insight that the formation of spikes in a contact hole of a semiconductor component can be significantly restricted by a clever design of the edges of the contact hole. It is not necessary to add additional structures, foreign substances, etc. There are various design options for the edges, which are referred to here as diffusion stop structures. A first such possibility is arcuate segments. For example, a contact hole can be circular as a whole or be constructed from an overlapping of overlapping circles. The effect of the circular segment is based on the fact that, based on crystalline size scales, it is composed of a large number of straight segments, each with different directional indices, and that the dissolution process progresses differently along the individual straight segments until it reaches those surfaces in the crystal interior, that oppose the greatest resistance to the loosening process. The smaller the radius of such a circle, the shorter are the corresponding straight line segments, and the smaller are the spikes, which can each originate from a single straight segment.

A similar effect is achieved if the conventional straight lines of a contact hole are replaced by microstructured sections. These microstructured sections can be, for example, crenellated or sawtooth-like

Show course. Here, too, it applies that the release process regularly starts from a straight segment of the edge and continues until crystal levels that are difficult to remove are reached. The microstructuring ensures that the individual

Fronts, on which the release process takes place, is shortened in comparison to a straight edge, and that accordingly only a smaller volume of the semiconductor material can be dissolved before slow or non-solving levels of the crystal are reached. In general, the spikes that are created in this way are shorter, the finer the microstructure. An edge length of the structural elements of 2 μm or less is preferred.

However, it is also "possible to prevent or at least largely suppress the formation of spikes at the straight edges of the contact holes. The anisotropy of the dissolving process implies that the semiconductor material has at least one class of crystal planes which are difficult or difficult in the dissolving process A class is understood to be a group of crystal planes, the Miller's indices of which are separated by permutation and / or sign reversal. All levels of such a class are equivalent from a crystallographic point of view. Straight-line sections of the edges of a contact hole should preferably be arranged to intersect those crystal planes of the class that run in the semiconductor substrate below the contact hole.

A contact hole can also be designed so that all of its edges meet the above requirement. Such a contact hole can have the shape of an equilateral triangle or an overlay of intersecting equilateral triangles.

The substrate of the semiconductor component is preferably a <111> silicon substrate, since the <111> plane of the silicon is a level that is difficult to attack by loosening it in aluminum.

On such a substrate, the formation of spikes can also be restricted by giving the contact hole edges which are +/- 15 ° against the intersection lines of the <111>, <111> or <111> plane with the Surface are twisted.

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the figures.

characters

Figure 1 shows a cross section of a conventional semiconductor device to illustrate the problem of spike formation;

FIG. 2 shows a surface of a semiconductor substrate with spikes formed on the edge of two contact holes;

Figure 3 shows a semiconductor surface with a contact hole according to the invention in plan view and in section;

FIG. 4 shows a variant of the contact hole from FIG. 3; Figure 5 shows a semiconductor surface with two circular holes according to the invention;

FIG. 6 shows a variant of the contact holes from FIG. 5;

FIG. 7 shows a semiconductor surface with two contact holes with microstructured edges according to the invention;

FIG. 8 shows microstructured edges of a contact hole after a temperature treatment; and

FIG. 9 shows a semiconductor surface with edges which are protected against spike formation by their orientation relative to the difficult-to-solve planes.

Description of the embodiments

To illustrate the problem, FIG. 1 shows a section through an electronic component with a high-resistance semiconductor substrate 1 and two doped regions 2, 3 formed therein, which should be separated from one another with high resistance. An insulation layer 6, which is applied to the surface of the substrate, has two contact windows 7, through which the doped regions 2, 3 are each connected to a contact element 4, 5 made of aluminum of the contact structure. The contact elements 4, 5 should not be connected to one another in a conductive manner his. During a temperature treatment, which is necessary to produce a satisfactory electrical contact between the doped regions and the contact elements, aluminum has diffused into the semiconductor substrate 1 from the contact elements 4, 5. Since the surface of the semiconductor substrate 1 has a <lll> orientation, the aluminum could not penetrate far into the depth of the substrate, but instead has spread further parallel to the surface, and there are spikes 8.9 starting from the different contact holes emerged, which create a - conductive - transition between areas 2,3. The component is therefore unusable.

FIG. 2 shows an enlarged section of a surface of a silicon <111> wafer 20 with two contact holes 21, 22. The insulation layer on the wafer surface is not shown, only the edges of the contact holes 21, 22 formed therein are shown. An inserted directional diagram shows the projections of the directions <111>, <lll> and <111> onto the plane of the figure. The horizontal edges of the contact holes 21, 22 in the figure lie parallel to a <110> -oriented Fiat of the wafer 20. The vertical edges of the contact holes 21, 22 on the left in the figure show almost no spike formation, the original silicon crystal shown hatched extends right up to these edges. At all other edges, spikes 23 extend far beyond the original edges of the contact holes onto the substrate surface. The reason for this is the orientation of the edges relative to the crystal planes, which are the same Class like the surface. The vertical edges run parallel to the intersection lines of a crystal surface of the said class, which is here arbitrarily referred to as the <-lll> plane. This plane intersects the left vertical edges 24, 25 of the two contact holes in such an orientation that it extends below the contact holes within the substrate. If an interface between silicon and aluminum slowly spreads perpendicularly to the <lll> surface of the other substrate during its tempering treatment, a <-lll> -oriented interface immediately arises at the edges 24, 25, which is also only slow can spread inside the substrate. On the right vertical edges 26, 27, on the other hand, there are <100> boundary surfaces which offer only slight resistance to the release process, so that spikes 23 can spread there as well as on the horizontal edges.

Figure 3 shows a contact hole of a semiconductor device according to a first embodiment of the invention, in Figure 3a in plan view and in Figure 3b in a section along the dash-dotted line bb of Figure 3a. The semiconductor substrate is a silicon substrate with a surface. The contact hole 30 is formed in the form of an equilateral triangle in an insulation layer 6 on the surface of the substrate 1. As the direction diagram shows, all three sides run parallel to cutting lines of the surface with crystal planes of class <111>. The crystal planes run through the through the contact hole Semiconductor substrate 1, as shown in FIG. 3b using the example of the <111> plane. The area 3b in FIG. 3B represents a zone in which the silicon of the semiconductor substrate 1 has penetrated into the substrate 1 by an annealing treatment of a contact made of aluminum (not shown in the figure) in the contact hole 30. The interfaces between zone 31 and substrate 1 are all crystal planes of class <111>. The lateral spread of the zone 31 beyond the edges of the contact hole 30 is correspondingly small. This spread is indicated in FIG. 3a by the dashed triangle 32.

It is not critical to the invention that the contact hole 30 is an exact triangle with pointed corners. The corners could also be cut off or rounded, in this case, unlike in the ideal case of a triangle with pointed corners, interfaces between the aluminum-containing zone 31 and the silicon substrate 1 could initially arise which do not belong to class <111> , the final shape that the aluminum-containing zone could reach in such a case would also correspond to triangle 32.

Rectangular contact holes with unequal edge lengths are often desired for contacting semiconductor substrates. FIG. 4 shows, using a plan view of a silicon substrate with the same orientation as in FIG. 3, how such a rectangular contact hole, indicated by line 40, can be approximated in that a large number of equilateral triangles with opposing overlap. An elongated contact hole 41 is thus obtained, the edges of which are partially sawtooth-shaped and in this way meet the requirement everywhere that they should intersect those crystal planes of class <111> that run below the contact hole in the interior of the substrate.

FIG. 5 shows a top view of a circular contact hole 50 on a silicon surface, which is oriented in the same way as in FIGS. 3 and 4. The edge of the contact hole has three regions 51 which at least approximately have the same condition In terms of their orientation, we meet the edges of the contact holes from FIGS. 3 and 4. Accordingly, practically no spike formation occurs in these areas. There are a large number of spikes 53 on the edge regions 52 lying between them, but all of them have only a small lateral extent. The reason for this is that the circular shape of the contact hole 50 in relation to the size scale of the crystal lattice can be regarded as a consequence of many individual straight line segments which have different orientations and therefore withstand the solution attack by aluminum differently, and that it there are a large number of lattice sites, for example at steps or corners of the interface between silicon crystal and aluminum, which, because of their emphasized coordination, can serve as seeds for spike formation or can hinder the spreading of spikes. The process of dissolving silicon in aluminum therefore starts from a large number of closely adjacent points along the edge, and progresses radially outward from there, leaving the crystal areas of the <111> class that are difficult to attack. As soon as two spikes have become so deep that their boundary surfaces touch, the release process essentially comes to a standstill.

It is important that the circular shape of the contact hole 50 is as precise as possible. For comparison, a second, smaller contact hole 54 is shown, which is only approximately circular, and the edge of which is composed of a small number of straight line segments. Each straight line segment forms the starting point for a spike 53, and since the straight line segments are relatively long in comparison to the contact hole 50, relatively larger spikes also arise here.

As shown in FIG. 6 in an illustration analogous to FIG. 5, a rectangular contact hole can also be approximated by superimposing overlapping circular contact holes each having the same diameter r and spacing a _A.

FIG. 7 shows further variants of contact holes, which are also based on the knowledge that to limit the extent of the spikes it makes sense to avoid long straight edge sections. In the case of the contact hole 70, therefore, all the edges have a crenellated course, where small rectangular extensions 71 of the insulation layer 6 engage in the interior of the contact hole. The extensions 71 each have dimensions a parallel to the edge and b perpendicular to it in the order of 2 μm or less. The period of the crenellated pattern can be, for example, 4 μm.

As shown in the example of the contact hole 72, these extensions 71 on an edge 73, the orientation of which fulfills the condition defined for the edges of the triangle from FIG. 3, can be omitted.

The effect of the extensions 71 is illustrated in FIG. 8. The orientation of the semiconductor substrate, more precisely that of its levels of class <111>, in this figure is the same as in FIGS. 2 to 7. FIG. 8 shows the course of an edge 80 of a contact element as a solid line. The edge is richly structured in a large number of sections that are adjacent to each other at right angles. During the annealing of the component, spikes 81 form along the edge 80, which penetrate so far under the insulation layer until they are only surrounded by interfaces of class <111> which are difficult to attack. As the comparison of the two edge profiles of FIG. 8 shows, these spikes are more numerous and smaller, the finer the structure of the edge.

FIG. 9 shows a plan view of a semiconductor substrate with a plurality of rectangular contact holes 90. The orientation of the semiconductor substrate is the same as in the previous figures. The edges of the contact holes are each rotated by ± 15 ° in one of these three directions. This is the largest angle deviation too one of the three directions that is possible on a threefold symmetrical surface such as the <lll> surface of silicon. This orientation ensures that there are a large number of exposed points along each edge from which spike formation can start or which hinder the spreading of the spikes. When the substrate is tempered with aluminum contact elements installed in the contact holes 90, spikes occur in large numbers and densities, the growth of which, however, soon comes to a standstill in the course of the annealing process when the difficult-to-remove interfaces of the spikes begin to touch ,

The invention has been described above in terms of a silicon surface and aluminum as the material of the contact elements. A transfer of the invention to other surfaces - the spikes then possibly extending less parallel to the surface than in the depth of a substrate - and to other combinations of semiconductor material and metal are readily conceivable. The only decisive factor is that the semiconductor material must have an anisotropic solubility behavior towards the metal.

Claims

claims

1. Electrical semiconductor component with a single-crystalline semiconductor substrate (1), one at least at one point of a contact hole

(30, 41, 50, 70) perforated insulation layer (6) arranged on the surface of the semiconductor substrate (1) and a contact structure which contacts the semiconductor substrate (1) through the contact hole (6) and which consists of a material, in which the semiconductor material of the substrate is soluble in an anisotropic dissolving process, characterized in that the edges of the contact hole (30, 41, 50, 70) are designed as diffusion stop structures.

2. Semiconductor component according to claim 1, characterized in that the diffusion stop structures comprise arcuate segments.

3. Semiconductor component according to claim 2, characterized in that the contact hole (50) is circular or designed as a superimposition of overlapping circles.

4. Semiconductor component according to one of the preceding claims, characterized in that the diffusion stop structures microstructured sections of

Include edges (80).

5. Semiconductor component according to claim 4, characterized in that the microstructured Ab- cuts (80) have a crenellated or sawtooth-shaped course.

6. Semiconductor component according to claim 5, characterized in that the battlements or saw teeth

Projections (71) with edge lengths of 2 μm or less are formed.

7. Semiconductor component according to one of the preceding claims, characterized in that the material of the semiconductor substrate has at least one class of crystal planes which are difficult or not attackable in the dissolving process and that the diffusion stop structures comprise rectilinear sections of the edges, which intersect those crystal planes of the class which run in the semiconductor substrate (1) below the contact hole (30, 41).

8. A semiconductor device according to claim 8, characterized in that the contact hole (30, 41)

Shape of an equilateral triangle or an overlay of intersecting equilateral triangles.

9. Semiconductor component according to one of the preceding claims, characterized in that the substrate is a <111> -Si substrate.

10. The semiconductor substrate according to claim 9, characterized in that the contact hole has edges which are rotated with the surface by approximately +/- 15 ° against the cutting lines of the <111>, _< 111> or <111> crystal planes ,