EP1101389B1 - Method for producing an integrated circuit comprising a cavity in a material layer and integrated circuit produced using said method - Google Patents

Abstract

A recess is produced in a material layer by creating at least a first and a second structure in various steps. The layers define each other laterally and extend to the bottom of the recess. The first structure and the second structure are so narrow that they can be made by creating conformally produced layers that have an independent thickness and are smaller than the depth of the recess. The conformally produced layers are formed in an appropriate deposition process. A covering structure can be produced on top of the first and second structure. An opening can be made in the covering structure, through which the first structure and the second structure can be removed in an etching step.

Description

The invention relates to a method for producing an integrated circuit arrangement comprising a cavity in a material layer, as well as an integrated circuit arrangement produced by the method.

There are a variety of integrated circuit arrangements for which it is advantageous to have a recess with dimensions of at least a few microns.

For example, such a circuit arrangement comprises a CMOS microphone, in which a depression forms a cavity, the so-called backside volume, above which a membrane is arranged which is set in vibration by sound waves. With the help of a capacitor, the vibrations are converted into electrical signals. The more volume the well has, the easier it is for the membrane to vibrate, and the lower the sound levels can be detected. For microphones, it is therefore desirable to provide the deepest possible depression with a large horizontal cross section.

In PR Scheeper et al, "A Review of Silicon Microphones", Sensors and Actuators A 44 1994, pages 1 to 11 , a first microphone is described in which a recess serving as backside volume is generated in a first silicon substrate. In a second silicon substrate, a perforated cover layer and above a membrane are produced. The first silicon substrate is bonded to the second silicon substrate. A capacitance is formed by the lid layer and the first silicon substrate. Since the recess and the cover layer are produced in separate substrates, the process cost is very high. The bonding of the substrates requires high temperatures, which can affect process safety.

These disadvantages are avoided in a second microphone described in the above-mentioned article. The cover layer and the recess are produced in a single substrate. For this purpose, the recess is filled with a sacrificial layer. Over the sacrificial layer, a perforated cover layer and above a membrane is produced. Through an opening at the edge of the membrane, the sacrificial layer is then removed by etching.

If a circular area whose diameter corresponds at least to the depth of the depression fits into a horizontal cross-section of a depression, the thickness of a conformally deposited layer must be at least the depth of the depression in order to fill the depression through the layer. For microphones, the corresponding recesses usually have the dimensions described.

Generally, however, deposition of a layer thicker than a few microns will cause the layer to flake off or crack in the layer. In addition, the circuit in question can be bent due to layer stresses. Not least, the deposition of a thick layer requires a lot of time and money. Wells that are filled at any one time therefore have dimensions in the prior art below a few microns.

Since the second microphone is filled with the recess during the manufacturing process by deposition of the sacrificial layer, it is flat in contrast to the recess of the first microphone. The backside volume of the second microphone is correspondingly smaller than that of the first microphone.

Other integrated circuit arrangements for which it is advantageous to have a recess with dimensions of at least have a few microns include, for example, micromechanical components, such as rotation rate sensors or acceleration sensors having arranged in cavities movable structures for which the greatest possible freedom of movement is sought. In the German patent application DE 195 09 868 A1 a production process for such micromechanical components is described. This publication discloses an integrated circuit arrangement according to the preamble of claim 4. On a substrate, a lower sacrificial layer and above a structural layer are produced and patterned, whereby a structure surrounded by a depression is produced. The recess is filled by deposition of an upper sacrificial layer over which a cover layer is applied. Using etch holes in the cap layer, the sacrificial layers are removed and the recess forms part of a cavity in which the structure can move.

In the case of the acceleration sensor or the rotation rate sensor, vibrations or rotations are detected with the aid of the structure, which can be set into lateral oscillations. The cover layer serves to protect the circuit arrangement. The sensitivity of the acceleration sensor or yaw rate sensor is greater the thicker the structure, i. the deeper the depression is.

The production of depressions for the formation of trench capacitors or trench isolations is in US 5,665,622 respectively. US 5,358,891 described. Out US 4,753,901 , according to which the preamble of claim 1 has been delimited, it is known to produce a recess for a trench isolation in two stages, wherein initially first trenches are made in a material and filled with an insulating material. Subsequently, the material remaining between the first trenches is removed to form second trenches and likewise filled with an insulating material. The first and second trenches together form the recess. The invention is based on the problem of specifying a production method in which a filled, at least a few microns deep recess can be produced in a material layer having a horizontal cross section in which at least one circular surface with a diameter of a few microns fits. Furthermore, an integrated circuit arrangement produced by the production method should be specified.

The problem is solved by a method according to claim 1 and by a circuit arrangement according to claim 4. Embodiments of the invention will become apparent from the other claims.

In a method according to the invention, at least one first structure and at least one second structure are produced in a region of the material layer provided for the depression, which adjoin one another laterally and form a filling of the depression, and in which each of its parts has respective opposing flank parts whose spacing is smaller than about half of a depth of the recess. The recess is not initially produced as in the prior art and then filled in one step, which is why the deposition of a thick layer with all its disadvantages is avoided. The method according to the invention makes it possible to produce filled deep depressions with large horizontal cross sections.

Such a method is advantageous for any technical field in which pits are filled by default with substantially conformal layers. One such area is, for example, semiconductor process technology.

The described dimensions of the first structure and the second structure enable the formation of these structures by method steps that are independent of the depth of the recess.

To produce the first structure, at least one narrow depression is initially produced in a region of the material layer provided for the depression by removing a portion of the material layer. The narrow recess has a smaller horizontal cross section than the recess to be formed and forms part of the recess to be created. Next, edge-forming layer-like parts of the first structure are produced, which are laterally thickened until the parts collide and thereby form the first structure. An interface between the abutting parts is thus located inside the first structure. The first structure will either be in the narrow recess or generated outside the narrow pit. The second structure is created by first producing flanking layered portions of the second structure that are laterally thickened until the pieces collide to form the second structure. By creating the first structure and the second structure reaching to the bottom of the well, the filled well is formed.

The first structure and the second structure are created in respective narrow recesses which are filled by depositing a substantially conformal filling layer. Among other things, the filling layer is initially formed on the flanks of the narrow depression, where it forms the flank-forming layer-like parts of the structures. In the further course of the deposition, these parts thicken laterally towards the center of the narrow depression until opposite of the parts collide and the narrow depression is filled. Due to the small spacing of the flank parts from one another, the minimum thickness of the filling layer is determined by this distance and not by the depth of the narrow depression. It is only half of this distance. The filling layer may therefore have a substantially smaller thickness than a thickness of a layer which would be required to fill the entire recess in one step.

For example, the first structure is meandering and winds through the depression. In this case, the second structure is also meandering, for example. Alternatively, there are a plurality of strip-shaped second structures arranged in the turns of the first structure. For the second structures correspondingly many narrow recesses are generated. It can also be provided a plurality of first structures, which are for example cylindrical or strip-shaped. The forms described are examples of an unlimited number of shapes that satisfy the above condition for the Filler parts meet and are also within the scope of the invention.

It is within the scope of the invention to provide further structures that fill the well along with the first structures and the second structures.

The first structure may be created in the narrow cavity by filling the narrow cavity by substantially conformally depositing a first fill layer. Subsequently, a further narrow depression is produced by removing the parts of the material layer arranged between flanks of the first structure. The second structure is created by filling the further narrow depression by substantially compliant deposition of a second fill layer.

So that these parts of the material layer arranged between the flanks of the first structure can be removed, it is expedient to remove parts of the first filling layer lying over the parts of the material layer. The narrow depression can be produced by etching the material layer selectively to the first filling layer. The above-mentioned parts of the first filling layer can be removed by masked etching. Alternatively, the first filling layer is chemically mechanically polished until the material layer is exposed. In this case, a mask covers outside of the recessed portion of the material layer in the formation of the narrow recess.

The filling of the depression serves as a sacrificial layer and is removed in a later process step.

Over the filled well, a lid structure is created which lies completely outside the well and into which an opening is made. Using the opening, the first structure and the second structure are removed by etching, whereby the recess forms a cavity. In the prior art, it has hitherto only been possible to produce such cavity-forming depressions with large dimensions by two-sided machining of a substrate, which requires a considerably greater process outlay.

To reduce the process cost, it is advantageous if the first structure and the second structure consist of the same material. The removal can then take place in an etching step. If the etching step is isotropic, then it is advantageous if the first structure and the second structure are selectively etchable to the material layer.

From the material layer, a movable structure can be generated. For this purpose, a lower sacrificial layer is applied and patterned on a semiconductor substrate. On the lower sacrificial layer, the material layer is applied. The creation of the filled recess creates the structure from the material layer which is laterally surrounded by the depression. The first structure and the second structure form part of an upper sacrificial layer adjacent to the lower sacrificial layer. For this purpose, the narrow depression is produced so that it extends to the lower sacrificial layer and cuts through the material layer. On the top sacrificial layer covering the structure, the lid structure with the opening is applied. Using the opening of the lid structure, the sacrificial upper layer and the sacrificial lower layer are removed, whereby the recess forms a first part of the cavity, which has at least further parts arranged below and above the structure.

So that the structure is not completely freely movable in the cavity, supports or suspensions may be provided which connect the structure to the substrate or to the lid structure. To create a support is in the lower sacrificial layer creates an opening that reaches down to the substrate. When depositing the material layer, the opening is filled. The filled opening forms the support connecting the layer of material to the substrate. To create a suspension, an opening is created in the upper sacrificial layer, which extends to the structure. When depositing the lid structure, the opening is filled. The filled opening forms the suspension that connects the structure to the lid structure.

Due to fault tolerances in the process steps, the structures forming the filling of the recess will generally not be the same thickness. Therefore, in a circuit arrangement produced by the method according to the invention, a bottom of the recess may have mutually adjacent regions over which one of the structures has been produced in each case during the method and which lie at different depths. Due to the dimensions of the structures, each of the parts of these regions each have opposite edges whose spacing from one another is less than a few μm. Because a depth difference between the regions is due to the fault tolerances, it is much smaller than the depths of the regions, i. as the depths of the depression. If no lower sacrificial layer is provided, the shape of the bottom is retained even if the structures were removed in the manufacturing process.

If the first structures and the second structures are strip-shaped, first of the regions of the bottom of the depression can be strip-shaped, extend essentially parallel to one another and traverse the depression. Second of the regions of the bottom of the depression are arranged between the first regions. The bottom has in each first area a cuboid flat projection which is substantially longer than it is wide.

An upper surface of the filler layer for the second structure, when not planarized, has a slight indentation along a centerline of the associated narrow groove. If the lid structure is deposited on the filling layer, then a lower surface of the lid structure facing the depression has a corresponding projection which fills the indentation. The projection tapers downwards and is much smaller than the depth of the recess.

If the narrow recesses are in the form of strip-shaped trenches running parallel to one another, grooves form in an upper surface of this filling layer during the deposition of the filling layer for the second structures along center lines of the trenches. The lid structure deposited over it fills the grooves and thus has protrusions in the form of burrs.

It is within the scope of the invention, when the recess has a depth which is greater than about 5 microns. It is within the scope of the invention if the recess has horizontal dimensions which are more than about 10 microns.

It is within the scope of the invention if the circuit arrangement comprises a rotation rate sensor or an acceleration sensor, in which the movable structure can be displaced into lateral oscillations.

It is within the scope of the invention if the circuit arrangement comprises a microphone in which the recess serves as a backside volume, and in which the lid structure is a perforated electrode. As another electrode, e.g. a membrane disposed above the lid structure.

It is within the scope of the invention if the circuit arrangement is a thermal sensor. A temperature measuring point is arranged above the recess, so that a heat flow between the temperature measuring point and the substrate is as small as possible.

It is within the scope of the invention if the circuit arrangement is a high-frequency coil. The high frequency coil is disposed over the recess filled with insulating material so that a capacitance between the high frequency coil and the semiconductor substrate is as small as possible.

It is within the scope of the invention if the circuit arrangement is a pump or a valve for gases or liquids. The depression acts as a flow channel.

The first structure and the second structure may include oxide.

Figur 1

zeigt einen Querschnitt durch ein erstes Substrat, nachdem eine untere Opferschicht, eine Schicht, eine Stütze, eine erste Maske und erste Gräben erzeugt wurden.

Figur 2

zeigt den Querschnitt aus Figur 1, nachdem als Teile einer oberen Opferschicht erste Strukturen und eine zweite Maske erzeugt wurden und Teile der ersten Maske entfernt wurden.

Figur 3

zeigt den Querschnitt aus Figur 2, nachdem Teile der Schicht entfernt wurden und als Teile der oberen Opferschicht zweite Strukturen erzeugt wurden.

Figur 4

zeigt den Querschnitt aus Figur 3, nachdem eine Dekkelschicht und eine hohlraumbildende Vertiefung durch Entfernen der oberen Opferschicht und der unteren Opferschicht erzeugt wurden.

In the following, embodiments of the invention, which are illustrated in the figures, explained in more detail.

FIG. 1

shows a cross-section through a first substrate after a sacrificial lower layer, a layer, a support, a first mask and first trenches have been created.

FIG. 2

shows the cross section FIG. 1 after first structures and a second mask have been produced as parts of an upper sacrificial layer and parts of the first mask have been removed.

FIG. 3

shows the cross section FIG. 2 after parts of the layer have been removed and second structures have been created as parts of the top sacrificial layer.

FIG. 4

shows the cross section FIG. 3 after a cover layer and a cavity forming recess are formed by removing the sacrificial upper layer and the sacrificial lower layer.

In a first embodiment, a first substrate 1 made of silicon is provided as the starting material.

In order to produce a lower sacrificial layer U is deposited to a thickness of about 1 micron on the first substrate 1 in a TEOS process SiO ₂ and patterned (see FIG. 1 ). In this case, a recess is produced in a part of the lower sacrificial layer U, which reaches down to the first substrate 1.

About the lower sacrificial layer U is to produce a material layer S polysilicon deposited in a thickness of about 5 .mu.m (see FIG. 1 ). The recess is filled, in which a support T is formed. To produce a first mask 2, SiO _{2 is} deposited in a thickness of about 200 nm and patterned by a photolithographic process.

With the aid of the first mask 2, in a region of the material layer S, in which a depression V is to be produced, parallel first approximate 1 μm-wide first trenches G1 are produced. The first trenches G1 are at a distance of approx. 1μm from each other (see FIG. 1 ). The first trenches G1 extend to the first (lower) sacrificial layer U and are approximately 5 μm deep.

Subsequently, in a TEOS method, an approximately 600 nm thick first filling layer F1 made of SiO _{2 is} deposited. Parts of the first filling layer F1, which fill the first trenches G1 form first structures S1 (see FIG. 2 ). The thickness of the first structures S1 corresponds approximately to the depth of the first trenches G1.

With the aid of a second mask 3 made of photoresist which covers parts of the first filling layer F1 and the first structures S1 outside the recess to be produced, parts of the first filling layer F1 and the first mask 2 arranged in the region of the recess V to be produced are provided with z. B. hydrofluoric acid removed (see FIG. 2 ). Subsequently, the second mask 3 is removed.

By a highly selective wet etch with e.g. Choline is generated between the first structures S1 second trenches G2 by selectively removing exposed parts of the material layer S from the first filling layer F1.

In a TEOS process, an approximately 1 μm thick second filling layer F ₂ of SiO _{2 is} deposited. Parts of the second filling layer F2 filling the second trenches G2 form second structures S2. The first filling layer F1 and the second filling layer F2 together form an upper sacrificial layer. The first trenches G1 and the second trenches G2 together form the recess V. A bottom of the recess V has adjoining first regions B1 and second regions B2 in which each of their parts has respective opposite edges, the distance of which is smaller than a few microns is. In each case one of the first structures S1 is arranged above the first regions B1. Above the second regions B2, the second structures S2 are respectively arranged. A bottom of the first trenches G1 coincides with the first regions B1. A bottom of the second trenches G2 coincides with the second regions B2. Through the depression V, a semiconductor structure is formed from the material layer S, which is laterally surrounded by the depression V. The semiconductor structure is about 50μm wide and about 50μm long. By the support T, it is connected to the first substrate 1. An upper surface of the second filling layer F2 has along center lines of second trenches G2 extending grooves (see FIG. 3 ). The recess V has a horizontal cross section in which a circular surface with a diameter of about 7μm fits.

To produce a cover structure D, polysilicon is deposited in a thickness of approximately 1 μm. The lid structure D has in the region of the depression V projections a in the form of burrs extending in the grooves (see FIG. 4 ).

The downwardly tapering projections a are substantially smaller than the depth of the recess V and are disposed over the second portions B2 of the bottom of the recess V. The progressions of the protrusions a substantially coincide with the progressions of center lines of the second regions B2.

An opening O is produced in the cover structure D, through which the upper sacrificial layer and the lower sacrificial layer U are removed in an etching step. As etchant, for example, a buffered hydrofluoric acid is suitable. The depression V forms a part of a cavity, which is bounded by the lid structure D upwards. The semiconductor structure can be vibrated by vibrations. The lateral freedom of movement is about 7μm.

The circuit arrangement is suitable, for example, as a rotation rate sensor or as an acceleration sensor. For this purpose, further components are arranged in the first substrate 1.

There are many variations of the embodiment conceivable, which are also within the scope of the invention. Thus, dimensions of the structures, layers and semiconductor structures can be adapted to the respective requirements. Recesses made by the described method can also be used for other circuit arrangements. Such circuit arrangements are for example microphones, thermal sensors, pumps and valves for gases or liquids and integrated radio frequency coils.

Claims (5)

1. Method for producing an integrated circuit arrangement comprising a cavity in a material layer (S),

   - in which, starting from the material layer (S), a portion of the material layer (S) is removed in a region provided for a recess (V) until the bottom of the recess (V) is exposed in this region, as a result of which at least one narrow recess (G1) is produced which has a smaller horizontal cross section than the recess (V) to be produced and forms part of the recess (V) to be produced,

   - in which the at least one narrow recess (G1) is replaced by a first structure (S1), provided for part of the filling in the recess (V), by depositing a first filling layer (F1) essentially conformally, the first structure (S1) formed in the narrow recess (G1) having opposite side parts whose distance from one another is less than half the depth of the recess (V), and the thickness of the filling layer (F1) being less than half the depth of the recess (V),

   - in which the remaining portion of the material layer (S) is removed in the region provided for the recess (V), as a result of which at least one further narrow recess (G2) is produced,

   - in which the at least one further narrow recess (G2) is replaced by a second structure (S2), provided for a further part of the filling in the recess (V) and laterally adjacent to the first structure (S1), by depositing a second filling layer (F2) essentially conformally, the second structure (S2) formed in the further narrow recess (G2) having opposite side parts whose distance from one another is less than half the depth of the recess (V), and the thickness of the filling layer (F2) being less than half the depth of the recess (V),

   characterized in that

   - the first structure (S1) and the second structure (S2) are produced as parts of a top sacrificial layer,

   - a cover structure (D) is applied on the top sacrificial layer,

   - at least one opening (O) is produced in the cover structure (D) and is used to remove the top sacrificial layer with an etchant, as a result of which the recess (V) forms the cavity.
2. Method according to Claim 1,

   - in which a plurality of first structures (S1) and second structures (S2) are produced.
3. Method according to Claim 1 or 2,

   - in which a bottom sacrificial layer (U) is applied on a semiconductor substrate (1) and is patterned,

   - in which the material layer (S) is applied on the bottom sacrificial layer (U),

   - in which the narrow recesses (G1, G2) are produced such that they extend as far as the bottom sacrificial layer (U) and cut through the material layer (S),

   - in which the opening (O) in the cover structure (D) is used to remove the top sacrificial layer and the bottom sacrificial layer (U) using the etchant, as a result of which the recess (V) forms part of the cavity, which has at least one further part arranged below the material layer (S).
4. Integrated circuit arrangement,

   - in which a material layer (S) contains a recess (V) which is at least a few µm deep and has a horizontal cross section in which at least one circular plane having a diameter of a few µm fits,

   - in which a cover structure (V) is arranged above and outside the recess (V), which forms at least part of a cavity, characterized in that

   - a bottom of the recess (V) has mutually adjacent regions (B1, B2) each having opposite edges whose distance from one another is shorter than a few µm,

   - a bottom face of the cover structure (D) which faces the recess (V) has at least one projection (a) which tapers toward the bottom, is much smaller than the depth of the recess (V) and is arranged above one of the regions (B2) on the bottom of the recess (V), and whose path essentially coincides with the path of a center line of that region (B2).
5. Circuit arrangement according to Claim 4,

   - which encompasses one of the following components;

   1. Rotation rate sensor or acceleration sensor in which a semiconductor structure which can be made to oscillate laterally is surrounded at the sides by the recess, which forms part of a cavity,

   2. Microphone in which the recess serves as a rear volume and the cover structure is a perforated electrode.

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