JP2007209000A - Method for producing a layer having a predetermined layer thickness characteristic - Google Patents

Abstract

A method of manufacturing a layer that is locally adapted or has a predetermined layer thickness characteristic.
A) At least one layer (7) is formed on a substrate. b) Determine the removal shape for the formed layer. c) At least one ion beam (9) is performed on the layer at least once so that the layer (7) is locally etched at the location of the ion beam depending on the removal characteristics. The result is a layer that is locally adapted or has a predetermined layer thickness characteristic.
[Selection] Figure 4

Description

Detailed Description of the Invention

  The present invention relates to a method for producing a layer having a predetermined or adapted layer thickness profile (Schichtdickenprofil). The invention relates in particular to a method for producing a layer having a predetermined or adapted layer thickness shape for performing frequency compensation in a piezoelektrischen resonant circuit (Schwingkreisen).

  The natural frequency (Eigenfrequenz) of a resonant circuit based on a piezoelectric thin film (piezoelektrischen Duennenfilmen) in the frequency range above 500 MHz is indirectly proportional to the thickness of the piezoelectric layer (Piezoschicht) (indirekt proportional) . The sound-insulating lower structure (Unterbau), the lower electrode, and the upper electrode provide an additional mass load on the resonant circuit. This large amount of load reduces the natural frequency. The thickness variation (Dickenschwankungen) in all these layers determines the range of manufacturing tolerances (Fertigungstoleranzen), within which are the natural frequencies of the resonant circuit samples (Exemplars). In sputter processing by microelectronic technology, 5% layer thickness variation is common, and 1% (1σ) can be achieved with some expense. Such variation occurs statistically for each wafer (Scheibe) and systematically between the wafer center and the edge.

  In the acoustic path (akustischen Pfad) of a resonant circuit based on a piezoelectric thin film, the thickness error (Dickentoleranzen) of the individual layers is basically independent of each other. Therefore, the frequency error (Frequenzfehler) or the frequency deviation (Frequenzstreuungen) due to the thickness error is accumulated based on the error propagation law (Fehlerfortpflanzungsgesetz). In this case, generally, in a resonance circuit based on a piezoelectric thin film, the total frequency deviation (Gesamtfrequenzstreuung) is about 2% (1σ). However, for use in the GHz range, the absolute accuracy of the natural frequency of each individual resonant circuit must be at least 0.5%. In the case of high-precision use (Hochpraezisionsanwendungen), according to the specification, it is only 0.25% tolerance window (Toleranzfenster).

  In order to increase the selectivity of applications, it is necessary to connect a plurality of resonant circuits to each other in a ladder-like, lattice-like or parallel structure. In order to obtain a desired characteristic, it is necessary to detune individual resonant circuits from each other. For cost reasons, it is preferred that all resonant circuits of the device (Bauteils) are made from a piezoelectric layer of constant thickness. Frequency tuning is usually performed using additional layers in the acoustically activated deposit. For each natural frequency that occurs, an additional layer (Zusatzschicht) of different thickness must be produced. This is usually necessary in each case of the vapor deposition or etching process together with the lithography process. In order to limit this expense, only the shape (Topologien) set with only two natural frequencies is usually produced.

  The document US Pat. No. 5,587,620 (US Pat. No. 5,587,620) describes a method for adjusting the frequency by depositing an additional layer specific to the device. However, such a method cannot be carried out on the wafer surface. Therefore, such a method leads to a relatively high manufacturing cost.

  Further, US Pat. No. 5,587,620 proposes frequency adjustment by temperature change. In the document EP 07771070 A2 (EP 07771070 A2), the frequency is adjusted by connecting a passive element (passiver Komponenten) as an auxiliary. Unfortunately, such methods usually have too few frequency effects, leading to other undesirable changes in the characteristics of the resonant circuit.

  Accordingly, an object of the present invention is to provide a method for producing a layer which can reduce or completely avoid the above-mentioned problems and which is locally adapted or has a predetermined layer thickness shape. In particular, it is an object of the present invention to provide a method that can be used to set the natural frequency of a piezoelectric resonant circuit.

  The object is achieved by a method for producing a layer that is locally adapted or has a predetermined layer thickness shape as defined in the independent patent claim 1. Other advantageous embodiments, designs and features of the invention are described in the dependent claims, the text of the description (Beschreibung) and the attached figures.

The present invention provides a method for producing a locally adapted layer having a predetermined layer thickness shape, including the following steps a) to c).
a) At least one layer is formed on the substrate.
b) An abragsprofil is determined for the formed layer.
c) Irradiate at least one ion beam (Ionenstrahl) on the layer at least once, and at the ion beam location, the layer is locally etched based on the removed shape and locally adapted Alternatively, a layer having a predetermined layer thickness shape is manufactured.

  An advantage of the method of the present invention is that it can correct both accidental variability from wafer to wafer and systematic variability between the wafer center and wafer edge. The method of the present invention can cost-effectively correct for variations using a relatively simple device. Furthermore, the method of the invention can be used for the purpose of producing layers having regions of different thickness. Another advantage of the method according to the invention is that it can be used freely for any layer material and layer thickness. Furthermore, the method of the present invention can be used many times if the removal shape is not obtained during the first trial. In this case, the machine processing capacity (Maschienendurchsatz) has greatly benefited from the progress that occurs in the layer deposition process.

  It is preferred that the processing of the layer takes place over the entire wafer. In this case, the method according to the invention is adapted to certain requirements, for example by industrial mass production taking into account the throughput (Durchsatz). The processing time according to the present invention ranges from 1 to 60 minutes.

  According to a preferred embodiment of the present invention, the method of the present invention is used to set the natural frequency of a piezoelectric resonant circuit. In this way, a method that directly affects the natural frequency is obtained. This method can be used before, during, and after manufacturing the resonant circuit. However, this method is preferably used for a nearly complete resonant circuit. Another advantage of the present invention is that frequency adjustments can be made on the wafer surface and the natural frequency of the piezoelectric resonant circuit can be adjusted over a wide adjustment range (Trimmbereich) of up to 20%.

 According to a preferred embodiment of the invention, the ion beam range (Ausdehnung) is greater than 1 mm, preferably greater than 5 mm. Further, the ion beam range is less than 100 mm, preferably less than 50 mm.

  According to a preferred embodiment of the present invention, an argon ion beam is used as the ion beam. Furthermore, it is preferable to use an ion beam having a Gaussian current density distribution. In this case, the half width of the ion beam is interpreted as the range of the ion beam. At this time, it is particularly preferable that the ion beam is irradiated so as to make a trace on the layer (in Spuren), and the interval between the traces is less than the half width of the ion beam.

  Furthermore, it is particularly preferable to use an ion beam having a uniform current density distribution. At this time, it is particularly preferable that the ion beam is irradiated so as to make a trace on the layer, and the trace interval is less than the half width of the ion beam. Therefore, in both cases, for example, ion beam control data such as a moving table (Verschiebetisch) and power supply control (Quellensteuerung) can be removed as desired by the so-called “etching footprint (Aetz-Footpring)” of the ion beam. It is obtained by inversely folding the shape. Furthermore, it is particularly preferred that the local etching of the layer is controlled by the current density of the ion beam and / or the rate at which the ion beam is irradiated onto the layer.

  In another preferred embodiment, a mask, in particular a resist mask, is formed on the layer before step c). This mask exposes only the area of the layer to be etched.

  When the method of the present invention is used to set the natural frequency of the piezoelectric resonant circuit, the natural frequency of the piezoelectric resonant circuit can be electrically measured to determine the removal shape of the formed layer. Particularly preferred.

  The accompanying drawings are described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a piezoelectric resonance circuit manufactured by the method of the present invention. 2 to 4 are diagrams showing an embodiment of the present invention in the example of the piezoelectric resonance circuit shown in FIG. FIG. 5 is a diagram showing a typical removal shape of Mitte-Rand-Fehlers that is approximately rotationsymmetrischen in the thickness of the metal layer. FIG. 6 is a diagram showing the measured removal shape of the ion beam. 7-8 illustrate other embodiments of the method of the present invention.

  FIG. 1 shows a piezoelectric resonant circuit manufactured by the method of the present invention. A carrier layer (Traegerschicht) 2 is provided on the wafer 1. The carrier layer 2 is preferably polysilicon. A cavity (Hohlraum) 4 is provided in the auxiliary layer 3 below the carrier layer 2 and in the region of the layer structure (Schichtstruktur) provided as a resonance circuit. The auxiliary layer 3 includes, for example, an oxide. The dimension of the cavity is generally about 200 μm. On the carrier layer 2, there is provided a layered structure of a resonance circuit including a lower electrode layer 5 provided for the lower electrode, a piezoelectric layer 6, and an upper electrode layer 7 provided for the upper electrode. Yes. The electrode layers 5 and 7 are preferably made of metal, and examples of the piezoelectric layer 6 include AlN, ZnO, and PZT ceramic (PbZrTi). These layer structures are generally about 5 μm thick overall. Other soundproof substructures (eg, acoustic mirrors) can be used in place of the cavities.

  In order to set one of the desired natural frequencies, a top electrode layer 7 having a locally adapted thick shape has been generated. In the present embodiment, the upper electrode layer 7 is formed in an area of the piezoelectric resonance circuit immediately above the piezoelectric layer 6 and is clearly thinner than the remaining area. In this case, the thickness shape of the upper electrode layer 7 shown in FIG. 1 is generated so as to correspond to the method of the present invention.

  2 to 4 show an embodiment of the method of the invention in the example of piezoelectric resonators according to FIG. The structure shown in FIG. 2 corresponding to a piezoelectric resonance circuit without the upper electrode layer 7 is the starting point (Ausgangspunkt). Therefore, the structure shown in FIG. 2 serves as a kind of substrate for the upper electrode layer 7 to be deposited later.

  Next, a relatively thick metal layer such as a tungsten layer is generated by a sputtering method. Instead of the sputtering method, a CVD method or an electrochemical method can also be used. After forming the metal layer, the removal shape for the metal is determined. In this example, the location of the resonant circuit is determined by measuring the natural frequency of the resonant circuit. Furthermore, the needle-like contact part (Nadelkontakt) 8 is guided on the metal layer, and the impedance of the resonance circuit is measured irrespective of the frequency of the electrical excitation (elektrischen Anregung) (FIG. 3). The impedance curve (Impedanzkurve) obtained in this way can identify the natural frequency. Now compare the measured natural frequency with the desired natural frequency for the piezoelectric resonant circuit. As a result, the portion of the layer that must be removed can be determined. These are different portions of the layer thickness due to variations in layer thickness and / or different functions of the resonant circuit when the resonant circuit on the wafer 1 is different, so that ion beam etching is later performed. The specific removal shape used to control occurs on the entire wafer.

  Subsequently, an ion beam is irradiated onto the layer at least once. As a result, the metal layer at the location of the ion beam is locally etched according to the removed shape, resulting in a metal layer 7 having a layer thickness characteristic that is locally adapted to the desired natural frequency of the resonant circuit (FIG. 4). ). A locally controllable removal can be realized by mechanically scanning the wafer with a Gaussian ion beam having a corresponding diameter (Durchmesser) (Abrastern). As the wafer trace is scanned, either the radiated current (Strahlstrom) or the scan speed can be controlled based on the locally required removal. The scan is performed in any series of traces in the x and y directions (or konzentrische ringe or spirals are possible), the trace spacing being clearly less than the half-width of the ion beam.

  The radial diameter is selected according to the most required removal angle. If the radial diameter is small, a steep angle can be obtained, but the amount (Volumenabtrag) that can be removed in units of time is reduced overall. Control data for moving table and power supply control is obtained by inversely folding a desired removal shape by a so-called “etching footprint” of an ion beam.

  Naturally, an ion beam having a uniform current density distribution may be used instead of an ion beam having a Gaussian current density distribution. In this case, the trace interval should be less than the range of the ion beam.

  FIG. 5 shows a typical removal shape of a center-edge error that is approximately rotationally symmetric in the thickness of the metal layer. The removed shape can be calculated by measuring the electrical frequency at about 150 locations on the wafer corresponding to 150 piezoelectric resonance circuits. FIG. 6 shows the measured removal profile of ion beam etching with a Gaussian Ar ion beam (having a half-value diameter of 5 nm to 50 mm) determined by velocity control in the x direction. The trace interval in the y direction is about 10% of the half-value diameter. The remaining error is in the range of 1 nm to 20 nm. The advantages of the method of the present invention are that frequency compensation can be performed on the wafer surface, the frequency accuracy is 0.25%, and the natural frequency of the piezoelectric resonant circuit can be adjusted to a wide range of up to 20% It can be adjusted over a wide range.

  For the method embodiments of the invention described so far, a layer having a layer thickness shape that has been locally adapted to the desired natural frequency of the resonant circuit has been generated. However, the adaptation of the layer thickness shape is not necessarily performed by paying attention to the natural frequency of the resonance circuit. However, the method of the present invention can also produce a large number of resistors and / or capacitors, for example with different impedance values but with the same lateral dimensions (lateralen Abmessungen). Thus, the method of the present invention is utilized to produce a layer thickness profile that is locally adapted to each resistor or capacitor. Furthermore, the method of the invention produces a large number of membranes (Membranen) with different mechanical parameters but the same lateral dimensions. Thus, the method of the present invention is utilized to generate a layer thickness profile of membrane materials adapted to each membrane.

  7-8 illustrate other embodiments of the method of the present invention. A relatively thick layer 11 is produced on the substrate 10. Instead of the sputtering method, a CVD method or an electrochemical method can be used. Depending on the desired application, the substrate 10 may be an insulating layer such as an oxide layer, and the layer 11 may be a conductive layer such as a metal layer. Selecting the material in this way is suitable, for example, for generating resistors having predetermined different resistance values. In contrast, when producing a capacitor having a predetermined different impedance value, a conductive layer (for example, a metal layer) is selected as the substrate 10 and an insulating layer (for example, an oxidation layer) is selected as the layer 11. Material layer).

  After forming the layer 11 and optionally patterning the layer 11, the removal shape for the layer 11 is determined. When a resistor having a predetermined different resistance value is generated, the removal shape is determined by resistance measurement, for example. However, it can also be measured with an interferometer.

  In this example, it is considered that resistors having two different resistance values need to be distributed and generated on the wafer. Accordingly, a resist layer is subsequently formed and developed. As a result, a resist mask 12 is generated. The resist mask 12 has an opening where a resistor 13 having a first resistance value is generated. Next, ion beam etching is performed. In this ion beam etching, the ion beam 9 is used to perform etching corresponding to a predetermined removed shape at the opening position of the resist mask 12. All other remaining regions of layer 11 are now protected by resist mask 12 (FIG. 7).

  When irradiation with the first ion beam is completed, the resist mask 12 is removed, another resist layer is formed, and developed. As a result, another resist mask 14 is generated. The resist mask 14 has an opening where a resistor 15 having a second resistance value is generated. Subsequently, similarly, ion beam etching is performed. This ion beam etching is performed at the opening position of the resist mask 14 based on a predetermined removal shape. All other remaining regions of layer 11 are now protected by resist mask 14 (FIG. 8). Therefore, after removing the resist mask 14, a layer 11 having a layer thickness shape locally adapted to each resistance is generated.

It is a figure which shows the piezoelectric resonance circuit manufactured by the method of this invention. It is a figure which shows embodiment of this invention in the example of the piezoelectric resonance circuit described in FIG. It is a figure which shows embodiment of this invention in the example of the piezoelectric resonance circuit described in FIG. It is a figure which shows embodiment of this invention in the example of the piezoelectric resonance circuit described in FIG. It is a figure which shows the general removal shape of the center part-edge part error which is substantially rotational symmetry in the thickness of a metal layer. It is a figure which shows the measured removal shape of an ion beam. FIG. 6 shows another embodiment of the method of the present invention. FIG. 6 shows another embodiment of the method of the present invention.

Claims (14)

A method of manufacturing a layer that is locally adapted or has a predetermined layer thickness characteristic,
a) forming at least one layer on the substrate;
b) determining an ablation shape for the formed layer;
c) At least one ion beam is irradiated onto the layer at least once so that the speed of the ion beam with respect to the layer can be controlled, and the layer is locally etched at the location of the ion beam based on the removed shape. And producing a layer that is locally adapted or has a predetermined layer thickness shape.   The method according to claim 1, characterized in that the range of the ion beam is greater than 1 mm, preferably greater than 5 mm.   3. A method according to claim 1 or 2, characterized in that the range of the ion beam is less than 100 mm, preferably less than 50 mm.   The method according to claim 1, wherein an argon ion beam is used as the ion beam.   The method according to claim 1, wherein an ion beam having a Gaussian current density distribution is used.   6. The method according to claim 5, wherein the ion beam is irradiated so as to make a trace on the layer, and an interval between the traces is less than a half width of the ion beam.   The method according to claim 1, wherein an ion beam having a uniform current density distribution is used.   The method according to claim 7, wherein the ion beam is irradiated so as to make a trace on the layer, and an interval between the traces is less than a half width of the ion beam.   9. The method according to claim 1, wherein the local etching of the layer is controlled by the current density of the ion beam and / or the speed of the ion beam performed on the layer.   10. A method according to any one of the preceding claims, characterized in that, before step c), a mask, in particular a resist mask, is formed on the layer which exposes only the region to be etched of the layer.   The method according to claim 1, wherein the method is used to set a natural frequency of a piezoelectric resonant circuit.   The method according to claim 11, characterized in that the natural frequency of the piezoelectric resonant circuit is electrically measured to determine the removal shape for the formed layer.   11. A method according to any one of the preceding claims, characterized in that the method is used for setting the impedance of a resistor and / or a capacitor.   11. A method according to any one of the preceding claims, characterized in that the method is used to produce a plurality of membranes having different mechanical parameters.

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