Patent Description:
As is known, on wafers, the various semiconductor components are generally arranged next to and parallel with each other with a uniform pitch, in a substantially matrix arrangement.

Testing these wafers is normally carried out with wafer probers provided with measuring units configured for the sequential testing of the components.

Examples of wafer probers are disclosed in <CIT> and <CIT>.

The manufacturers of semiconductor devices, for a better exploitation of the space in wafers, tend to adopt increasingly complex configurations wherein, for example, the components are arranged rotated one with respect to the other and/or variably spaced.

Therefore, there is a need for a wafer prober with high flexibility that allows the fast and effective measuring of wafers comprising semiconductor components arranged with variable orientations and/or spacing.

The purpose of the present invention is to provide a wafer prober that makes it possible to overcome the above-mentioned problems.

The above-mentioned purpose is achieved by a wafer prober according to claim <NUM>.

For a better understanding of the present invention, a preferred embodiment is described below, by way of nonlimiting example and with reference to the attached drawings, wherein:.

With reference to <FIG>, there is indicated by <NUM> a wafer prober according to the present invention and configured to test a wafer comprising a plurality of semiconductor components. The wafer prober <NUM> comprises a support structure <NUM>, preferably made of granite, comprising a base <NUM> which supports a horizontal lower plane <NUM> and an upper plane <NUM> parallel to the lower plane <NUM> and supported by four columns <NUM>. The wafer prober <NUM> also comprises a plurality of measuring units <NUM> movable within a compartment <NUM> in the shape of a parallelepiped delimited by the lower plane <NUM> and the upper plane <NUM>.

Each of the planes <NUM>, <NUM> carries a respective guide <NUM> fixed thereto and parallel to a horizontal X axis, hereinafter referred to as "X guide". The X guides <NUM> vertically overlap each other.

In the example illustrated, the wafer prober <NUM> comprises four measuring units <NUM>. Each measuring unit <NUM> comprises a carriage sliding along a respective X guide via a linear motor <NUM> and sliding blocks <NUM>. In particular, the wafer prober <NUM> comprises two upper X carriages <NUM>, <NUM> and two lower X carriages <NUM>, <NUM>.

Each of the X carriages carries a movable Y assembly <NUM>. Below, without loss of generality, the first upper movable Y assembly, carried by the X carriage <NUM>, is considered (<FIG>). What is described here applies similarly for the remaining upper movable Y assembly, carried by the X carriage <NUM>, and, in a symmetrical way, for the lower movable Y assemblies, carried by the X carriages <NUM>, <NUM>.

The movable Y assembly <NUM> comprises a Y guide <NUM>, parallel to a horizontal Y axis perpendicular to the X axis, and a Y carriage <NUM> that slides on the Y guide <NUM> via a linear motor <NUM> and sliding blocks <NUM>. Therefore, the movement along the Y axis is similar to that along the X axis.

The Y carriage <NUM> carries a movable terminal assembly <NUM> configured to move a respective measuring head <NUM> in the compartment <NUM> according to three further degrees of freedom (for a total of five degrees of freedom overall): one linear degree of freedom along a vertical Z axis orthogonal to the X and Y axes, and two rotational degrees of freedom, corresponding to a rotation of an angle θ about the Z axis and a rotation of an angle ϕ about a horizontal axis, respectively.

The movable terminal assembly <NUM> (<FIG>) comprises a primary bracket <NUM> comprising a horizontal arm <NUM> extending along the X axis and coupled to the Y carriage <NUM>, and a vertical arm <NUM> extending from one end of the horizontal arm <NUM> along the Z axis downwards. The vertical arm <NUM> carries a rotary motor <NUM> with a vertical axis, on the opposite side of the horizontal arm <NUM>, and a screw-nut system <NUM>, arranged below the horizontal arm <NUM>.

The rotary motor <NUM>, preferably a brushless motor, is responsible for the degree of freedom along the Z axis. In particular, the rotary motor <NUM> drives the screw-nut system <NUM> via a belt transmission (not illustrated).

The screw-nut system <NUM> drives a secondary bracket <NUM> movable along the Z axis and comprising a vertical arm <NUM>, which slides along the Z axis, and a horizontal arm <NUM>.

The horizontal arm <NUM> extends from the lower end of the vertical arm <NUM> and has, at its opposite end, an annular support <NUM> with a vertical axis which supports a movable θ assembly <NUM>.

The movable θ assembly <NUM> comprises a primary motor <NUM> with a vertical axis and a primary support element <NUM>, placed respectively above and below the annular support <NUM>, and a primary gear unit <NUM> vertically interposed therebetween.

The primary motor <NUM>, preferably a stepper motor, is responsible for the first rotational degree of freedom, corresponding to the rotation of angle θ about the Z axis. In particular, the primary motor <NUM> brings into rotation the primary support element <NUM> via the primary gear unit <NUM>, which is a zero-backlash gear unit which allows irreversibility of motion.

The primary support element <NUM> comprises a horizontal plate <NUM>, which is coupled to the primary gear unit <NUM> and has, below, an annular appendage <NUM> with a horizontal axis which supports a movable ϕ assembly <NUM>.

The movable ϕ assembly <NUM> comprises a secondary motor <NUM> with a horizontal axis and a secondary support element <NUM>, placed on axially opposite sides the annular appendage <NUM>, and a secondary gear unit <NUM> axially interposed therebetween.

The secondary motor <NUM>, preferably a stepper motor, is responsible for the second rotational degree of freedom, corresponding to the rotation of angle ϕ about its horizontal axis. In particular, the secondary motor 64brings into rotation the secondary support element <NUM> via the secondary gear unit <NUM>, which is a zero-backlash gear unit which allows irreversibility of motion. Therefore, the movement relating to the movable ϕ assembly <NUM> is similar to that relating to the movable θ assembly <NUM>.

The secondary support element <NUM> comprises an annular structure <NUM> with a horizontal axis coupled to the secondary gear unit <NUM>, and a terminal bracket <NUM> extending cantilevered integrally and axially from the annular structure <NUM> which carries a support structure <NUM>.

The support structure <NUM> may be of a different shape in the various measuring units <NUM> to allow a relatively close arrangement of the measuring heads <NUM> and thus their simultaneous use on the same wafer. The support structure <NUM> is hollow and internally houses a camera <NUM>, with an optical axis A normally vertical, which makes it possible to visualise the device under test. The support structure <NUM> carries a T-shaped support <NUM> which comprises a shank <NUM> extending parallel to the optical axis A and in the opposite direction with respect to the camera <NUM>, and an element <NUM> extending transversely to the shank <NUM>, which carries the measuring head <NUM> described in detail hereinafter.

Preferably, the support structure <NUM> carries a probe <NUM>, interposed between the optical axis A of the camera <NUM> and the shank <NUM> of the support <NUM> and parallel to them, configured to interact with known references so as to perform an initial calibration of the wafer prober <NUM>.

The measuring head <NUM> (<FIG>) comprises a metallic support <NUM> configured to be fixed to the element <NUM> of the support <NUM> of the movable terminal assembly <NUM>, a base printed circuit <NUM> extending parallel to the metallic support <NUM> and fixed thereto, connectors <NUM>, <NUM> coupled to the base printed circuit <NUM> on the side of the metallic support <NUM>, and a probe card <NUM> coupled to the base printed circuit <NUM> on the opposite side with respect to the metallic support <NUM> and configured to contact the wafer under test.

The base printed circuit <NUM> is an elongated board which carries, on its own ends projecting with respect to the metallic support <NUM>, respective connectors <NUM> for power and respective connectors <NUM> for signals. The connectors <NUM>, <NUM> are connected to the control electronics of the wafer prober <NUM> in a conventional way not described in detail.

The probe card <NUM> comprises a main body <NUM> which can be coupled to the metallic support <NUM> via a quick coupling <NUM>, an intermediate printed circuit <NUM> fixed to the main body <NUM> on the side facing the metallic support <NUM>, an intermediate plate <NUM>, and a terminal element <NUM> fixed to a face of the intermediate plate <NUM> opposite the main body <NUM>.

The intermediate printed circuit <NUM> is an elongated board arranged parallel to the base printed circuit <NUM> and connected thereto via a connector <NUM> which internally has elastic needle contacts of a known and non-illustrated type for the transmission of power and signals from the base printed circuit <NUM> to the intermediate printed circuit <NUM>.

The main body <NUM> of the probe card <NUM> has an elongated shape extending parallel to the base printed circuit <NUM> and comprising a lower face <NUM> to which the intermediate printed circuit <NUM> is coupled, and an upper face <NUM>. The lower face <NUM> of the main body <NUM> has, at its ends, lower projections <NUM> connectable to the metallic support <NUM> via the quick coupling <NUM>.

The quick coupling <NUM> comprises a pair of magnets <NUM> housed in the respective lower projections <NUM> and corresponding magnets (not illustrated) housed in the metallic support <NUM>. The quick coupling <NUM> further comprises centring pegs <NUM> carried by the metallic support <NUM> and corresponding seats made in the lower projections <NUM> in the proximity of the magnets <NUM>.

The upper face <NUM> of the main body <NUM> has, centrally, an upper projection <NUM> to which the intermediate plate <NUM> is coupled.

The intermediate plate <NUM> internally houses a terminal printed circuit <NUM> to which power and signals arrive from the intermediate printed circuit <NUM> via a plurality of elastic needle contacts <NUM> housed in the main body <NUM> of the probe card <NUM>.

The end element <NUM> has an upper block <NUM> from which emerges a plurality of needle contacts <NUM> connected with the end printed circuit <NUM> and configured to interact with predetermined points of the wafer.

Since the measuring head <NUM> has a modular structure with interchangeable components, it is possible to use different probe cards <NUM> on the same measuring head <NUM>, and different end elements <NUM> on the same probe card <NUM>.

As specified above, the movable Y assembly <NUM> and each component described successively is replicated four times. In particular, the wafer prober <NUM> comprises two upper measuring heads (including the measuring head <NUM>) and two lower measuring heads (symmetrical with respect to the upper measuring heads), each of which has five degrees of freedom: three linear degrees of freedom, defined by the axes X, Y and Z, and two rotational degrees of freedom, defined by the angles θ and ϕ. The motion associated with each degree of freedom is due to the respective motor <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and has an impact on all the components downstream of it.

As represented schematically in <FIG>, the wafer prober <NUM> comprises a control unit <NUM> which controls, independently of each other, the five motors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of each measuring unit <NUM>.

In use, the wafer to be tested (<FIG>) is arranged on a tray <NUM> movable on a horizontal plane between a wafer loading/unloading position outside the wafer prober <NUM> and a test position inside the compartment <NUM> of the wafer prober <NUM>.

The control unit <NUM> controls, independently of each other, the measuring units <NUM>, whose measuring heads <NUM> contact the wafer and perform measurements.

From an examination of the characteristics of the wafer prober <NUM>, the advantages of the present invention are clear.

In particular, the plurality of the measuring heads <NUM> and their presence on both sides of the wafer makes it possible to simultaneously perform multiple measurements, reducing the overall test time.

Since the control unit <NUM> controls the measuring units <NUM> independently, the measuring heads <NUM> may be combined in an appropriate way depending on the arrangement of the components on the wafer, using probe cards <NUM> equal to or different from each other.

The presence of at least one rotational degree of freedom of the measuring heads <NUM> makes it possible to test wafers with complex configurations of semiconductor components. In particular, the wafer prober <NUM> is provided with at least one rotational degree of freedom, corresponding to the rotation of angle θ about the Z axis. This makes it possible both to read wafers comprising semiconductor components arranged with variable orientations and to manage any angular positioning errors of the wafer on the tray <NUM>, detected e.g. via the cameras <NUM>. In this case, the loading errors may be corrected by appropriately orienting the measuring heads <NUM>.

Optionally, the wafer prober <NUM> may be provided with a second rotational degree of freedom, corresponding to the rotation of angle ϕ about a horizontal axis. In this case, the wafer prober <NUM> may correct non-planarity errors or allow the reading of wafers with non-planar parts.

The wafer prober <NUM> is an extremely versatile machine, since it also offers the possibility of changing the probe card <NUM> and/or the end element <NUM> thereof.

Finally, it is clear that modifications and variations may be made to the wafer prober <NUM> without departing from the scope of protection defined by the claims.

Claim 1:
A wafer prober comprising a support structure (<NUM>) defining a first upper guide (<NUM>) and a first lower guide (<NUM>) parallel to a first horizontal axis and vertically overlapping with each other, a plurality of measuring units (<NUM>) each comprising a first carriage (<NUM>, <NUM>, <NUM>, <NUM>) sliding along one respective first guide (<NUM>), a second guide (<NUM>) carried by the first carriage (<NUM>, <NUM>, <NUM>, <NUM>) and parallel to a second horizontal axis orthogonal to the first axis, a second carriage (<NUM>) sliding along the second guide (<NUM>), a movable terminal assembly (<NUM>) carried by the second carriage (<NUM>), and a measuring head (<NUM>) carried by the movable terminal assembly (<NUM>) and provided with a plurality of needle contacts (<NUM>) configured to interact with respective points of the wafer, said movable terminal assembly (<NUM>) being configured to move the measuring head (<NUM>) according to a linear degree of freedom along a vertical axis and at least one rotational degree of freedom about said vertical axis, the wafer prober (<NUM>) comprising a control unit (<NUM>) which controls the measuring units (<NUM>) independently, wherein the measuring head (<NUM>) comprises a support (<NUM>) fixed to an output member (<NUM>) of the movable terminal assembly (<NUM>) and a probe card (<NUM>) interchangeable and connectable to the support (<NUM>) by means of a quick coupling (<NUM>), wherein the quick coupling (<NUM>) comprises a magnetic connection (<NUM>) and a centring coupling (<NUM>) between the support (<NUM>) and the probe card (<NUM>).