EP1581967A1

EP1581967A1 - Creation of hermetically sealed, dielectrically isolating trenches

Info

Publication number: EP1581967A1
Application number: EP03782133A
Authority: EP
Inventors: Karlheinz Freywald
Original assignee: X Fab Semiconductor Foundries GmbH
Current assignee: X Fab Semiconductor Foundries GmbH
Priority date: 2002-12-05
Filing date: 2003-12-05
Publication date: 2005-10-05
Also published as: WO2004051739A1; AU2003289820A1; US20060199298A1

Abstract

The invention relates to a method, which enables the production of an assembly comprising hermetically sealed, filled isolation trenches (1, 2), as required in the production of modern MEMS containing sensor components in hermetically sealed, cavities (8). Production is achieved by a slight enlargement (2, 3) of the isolation trench at specific points and by the use of a low-pressure deposition method for the trench isolation material. Sealing points laterally seal the hollow channels (5) that remain in trenches of a normal width in the longitudinal direction of the trench. The deposition method ensures the deposition of an approximately isotropic material and eliminates the risk of dangerously high gas residues in the cavities (8).

Description

Generation of hermetically sealed, dielectric isolating trenches

The invention relates to a method and an arrangement for the production of dielectrically isolated structures by means of filled, hermetically sealed isolation trenches for the production of mechanical-electrical sensor structures which require a hermetically sealed cavity for their function, in which the movable sensor elements are located. The usual separating trenches for the dielectric isolation of various electronic circuit parts from one another do not automatically meet the conditions for the production of microelectromechanical systems (MEMS), in which the formation of the cavities for the mechanically movable sensor elements is also necessary across trench-isolated circuits or circuit parts.

Backfilled trench structures are used, for example, for the dielectric insulation of high-voltage elements, see DE-A 198 28 669 or for dielectric and low-capacitance insulation for integrated RF elements and for producing isolated areas for electromechanical structures, see DE-C 100 29 012. Backfilled trench structures preferably used for SOI wafers as well as for single-crystalline semiconductor wafers for dielectric all-round insulation of source / drain regions in CMOS circuit, cf. DE-A 197 06 789.

The electrical, mechanical and thermal requirements for such trench structures and their backfilling vary depending on the technology and the subsequent technological steps required (e.g. integration into a CMOS technology). Various materials and methods are therefore also used to backfill such electrically insulating trench structures. The materials used are preferably silicon dioxide, silicon nitride, polysilicon or organic substances such as polyamides. In general, a void-free or low-void filling is important to avoid gas inclusions. The process conditions required for this, however, can rarely be reconciled with those of a highly integrated circuit technology and are very complex in the case of adaptation.

In most cases, trench shapes are chosen that either have vertical walls or narrow downwards in a V-shape in order to facilitate void-free filling, cf. JP-A 2002 100 672, "Formed method of isolation trench". The advanced development in this area includes mechanical electrical structures in the complex semiconductor production process (eg with CMOS technology) and thus requires the realization of hermetically sealed cavities (cavities) for the functionality of these mechanically movable structures, cf. DE-A 100 17 976. When filling the trench, channel-shaped cavities in the interior of the trench easily occur due to a faster growing together of the filler material on the top of the trench, which starts from the upper trench edges. The cavities can tunnel through the boundary of the hermetically tightly required sensor cavity and thus lead to the rejection of the component via damage to the actual sensor element.

For special requirements for the trench geometry, where vertical side walls or V-shaped cross-sections cannot be realized and undercut edges are permitted, new solutions must be sought.

The object of the invention is to eliminate the deficiencies described when backfilling isolation trenches with ordinary cross sections, which are related to the laterally continuous cavity channels that arise during backfilling, with the aim of ensuring hermetic tightness of the voids for the mechanical-electrical sensor structures in connection with the hermetically sealed disk bonding. In addition, a method that is as simple and cost-effective as possible is to be specified, which ensures hermetically sealed sealing of possible cavity channels that expand in the lateral direction and arise when the insulation trenches are filled. Wafers processed in this way are said to be able to be further processed in a conventional CMOS process.

The object is achieved according to the invention in that the trench is widened by a small amount (sealing points or points) in at least one defined point in the trench course in each case in a short area (section) and a sealing method (low-pressure separation) for the deposition of the filling material for sealing is used, which works approximately with vacuum (claim 1 or 5). The result is a trench geometry with at least two narrow sections and a wider intermediate section connecting these two (claim 13).

The sealing points or points can be repeated several times depending on the requirement. The principle of the sealing is based on a three-dimensional filling in the area of the respective sealing point. The locations of the widened trench remain free (open) longer during layer deposition to backfill the trench than the immediately adjacent trench areas with normal width.

If the normal trench closes upwards during filling and residual parasitic voids have already remained, there is normally no longer any chance of using further material to fill up these remaining voids. According to the invention, however, the widened trench area, which is still open at this point in time, will now also be used for lateral separation in the lateral direction of the trench course. This lateral separation causes backfilling into the remaining cavities from the front (three-dimensional backfilling) and clogs the cavity in the normal-wide channel area from the long side, before the somewhat wider channel point slowly grows upwards, where a slightly larger remaining cavity naturally arises , but this is not a problem because there is a hermetic seal on both sides and upwards.

This hermetic seal ensures that any subsequent gas exchange and thus the harmful property of the gas passage in the case of laterally extending cavities in filled trenches can be prevented.

The approximately vacuum working (claim 10) layer deposition process brings a largely isotropic backfilling into the enlarged trench sections and ensures that an (almost good) vacuum is present in the parasitic remaining cavities.

Since there is now (almost) no more gas in the hermetically sealed remaining cavities, high-temperature processes can then also be used without fear of such residual cavities bursting.

No particular requirements are placed on the trench shape and steepness of the side walls with this method.

The importance of the solution according to the invention is particularly important when remaining cavities cannot be avoided without additional expenditure during the filling. The invention is explained and supplemented on the basis of exemplary embodiments, it being pointed out that the following illustration is a description of preferred examples of the invention.

Figure 1 is a schematic representation of a slight channel widening 2 inserted in the trench (channel) in supervision.

Figure 2,

Figure 2a,

FIG. 2b illustrate a schematic illustration and two sections A-A and B-B with a slight widening inserted in the course of the trench, the trench regions of normal width b1 already being closed at the top. Layer deposition only takes place in the slightly widened channel area 2.

Figure 3,

Figure 3c show the trench filling 9 in the trench widening b2

(Channel widening) and the closing of parasitic ones

Cavities.

Figure 4,

Figure 4d,

Figure 4e,

FIG. 4f show the result of the trench filling 9 with hermetic sealing of the parasitically remaining cavities in the trench area using different trench cross sections (FIGS. 4d, e, f) at different points of the entire trench 1, 2,1 according to FIG. 4.

FIG. 1 shows the trench widening 2 as a channel widening b2, which adjoins the trench region 1 (channel) with normal width b1 on both sides (front ends). The transition area 3 between the two trench regions should be conical. A layer deposition on the two side walls 4 is shown schematically in FIGS. 2 and the sections of FIGS. 2b, 2a. The deposition (see black arrows, FIG. 2b) likewise takes place on the side walls 4 in the region of the slight trench widening 2, FIG. 2b, after the trench in area 1 has already been closed upwards and a small cavity / channel 5 emerged, Figure 2a. The trenches (the channel) are located within the silicon environment 10.

The trench backfill 9 is a filler that is deposited. It ensures that the normally wide trench sections 1 in FIG. 1 (to the left and right of the conical widenings of the trench width b1 to the slightly wider trench width b2 of section 2) are closed. When filling in the area of the normally wide trenches, the upper trench areas close earlier than in the trench section 2 widened to b2. In the upper trench area there is then filler material, leaving the cavity (cavity channel 5) in the longitudinal direction of the trench, here the sections 1 of FIG 1 or FIG. 2. With a low-pressure material separation in the widened trench region (the longitudinal section 2), the cavity channels are hermetically sealed in the longitudinal direction. This material separation is a low-pressure material separation, in which a pressure close to vacuum is used. A layer deposition process is used, which achieves largely isotropic backfilling in the enlarged trench section. Cavities remaining parasitic there will hardly have any pressure, but will have an almost good vacuum due to the low-pressure deposition process.

The sealing takes place on the basis of a backfilling (three-dimensional backfilling) of the trench in its entire longitudinal direction, which includes the narrower sections 1, the conically widening sections 3 and the slightly enlarged trench section 2 which has the width b2. Several of these individual sections can be lined up, in FIG. 1 only a widening 2 with adjacent conical sections 3 and narrower channel sections 1 is shown.

The at least one point 2, in the case of a plurality of sections 2, the several slightly wider trench sections, remain open for longer than the sections 1 with normal width b1 when the layer is cut off for backfilling. A lateral separation in the lateral direction of the trench course can now also be carried out from the widened trench region 2, which is still open at the time the narrower sections 1 are closed (open at the top). This lateral separation causes a filling in the remaining cavities from the end face as a three-dimensional filling and also clogs the (parasitic) cavity in the normal-wide channel area 1 from the long side. Only later does the wider channel section 2 slowly grow upwards, forming a somewhat larger one Cavity, which is indicated in Figure 2b (the inner, open area) and which is explained in more detail in the following figures. This section does not interfere because a hermetic seal has been made on both sides and upwards.

Subsequent gas exchange is avoided. Hardly any gas remains under pressure in the remaining cavities, so that subsequent temperature processes can be used as desired without fear of bursting of closed channels due to the build-up of excess pressure in the cavities 5 or the larger cavities 8 to be described according to FIG. 4f ,

In contrast to known methods which seek to avoid cavities (voids or blowholes), the method explained with reference to FIG. 2, which is deepened in the following figures, can live with such cavities, tolerate them and nevertheless cause difficulties from the cavities in the further process Avoid processing. The trenches, or "trenches" for short, are filled using a separation process and are hermetically sealed. They are used for dielectric insulation on the pane.

FIGS. 3 and 3c show a schematic illustration of a slight trench widening 2, FIG. 3, inserted in the trench course 1, the trench regions 1 having a normal width b1 already being closed at the top. In this phase, only the side walls 4 are coated in the trench widening 2, and the inventive parasitic remaining cavities are also filled at the location of the lateral filling 6, FIG. 3c.

The dimensioning of the deposition process and the trench arrangement take place in such a way that any remaining lateral cavities are completely sealed off before the trench section closes with the slight widening at the top, so that further backfilling can no longer take place.

The layer deposition in FIGS. 3, 3c only takes place in the widened channel section 2, or its area, with particular attention to the lateral filling of the remaining remaining cavities.

Figures 4 and the sections of Figures 4d, 4e, 4f schematically show the result after the trench filling. FIGS. 4d to 4f are three cross-sectional images along the planes EE, FF and GG according to FIG. 4. Figure 4d section D shows the smaller remaining cavity 5 in the normal

Trench area 1. Figure 4e section E shows the hermetically sealed closure 7 in the area of the conical intermediate or transition area 3. Figure 4f section F shows the somewhat larger remaining cavity 8 in the

Area of slight trench widening 2, also covered by

Filling material 9.

FIG. 4 shows, in supervision, the trench area to be filled in sections 1, 2 and again 1. The corresponding information from FIG. 1 can easily be transferred here.

The slight widening of the trench width b2 (or b2-b1) and the conical transition area 3 with walls that run obliquely to the central plane are evident. There are two transition areas 3 per a slightly widened trench section 2 in the course of the overall trench 1, 2, 1. This is also called a channel. In the sectional views, the section D-D is provided in the area of the narrower trench section 1. A small remaining cavity 5 can be seen, which is already closed at the top by filling material 9. A section plane E-E which is shifted further down in FIG. 4 shows a hermetically sealed closure at the sealing point 7, which is also called the "sealing point".

A closed cavity or inner channel 5 can no longer be seen. The hermetically sealed closure 7 takes place at the location of the side filling 6. The hermetically sealed closure 7 lies in the region of the conical section 3.

Closer to the narrow trench section 1 is the lateral backfilling 6, closer to the widened section 2, or in the widened section 2 there is a slightly enlarged, remaining cavity 8, which is also closed at the top by filler material 9, but was closed later in the course of the method than that upper closure 9 of Figure 4d.

With 10, as in all other examples, the silicon environment of the pane is shown.

The widened trench locations 2 as “sealing locations” of the channel in the vicinity of connecting surfaces of two semiconductor wafers, when these two wafers are bonded, are placed more densely than along the other parts of the isolation trenches (not shown graphically).

The use of the method naturally results in the trench structures also evident with the aforementioned method description as a device on or with a disk which has separating trenches which are hermetically sealed and are used for dielectric insulation. The filling was carried out using a deposition process as described.

Reference numeral Overview

Figure 1 to be filled trench area slight trench spreading conical transition area

Figures 2,2a, 2b

1: Trench area to be filled

2: slight widening of the ditch (ditch, slightly widened)

4: Side walls of the slight trench widening

5: Small remaining cavity in the area of the normal trench area

9: Material with which the trench is filled

10: silicon environment

- »Arrows between walls 4: direction of layer deposition

Figures 3.3c

1: Trench area to be filled

2: slight widening of the trench

3: conical transition area

4: Side walls of the slight trench widening

5: Small remaining cavity in the area of the trench area 1 of normal width.

6: Place of backfilling from the side

9: Material with which the trench is filled

10: silicon environment

- »Arrows between walls 4: direction of layer deposition Figures 4,4d, e, f

1: Trench area to be filled

2: slight widening of the trench

3: conical transition area

5: Small remaining cavity in the area of the normal trench area

6: Place of backfilling from the side

7: Place of the hermetic seal in the area of the conical transition zone

8: Slightly larger remaining cavity in the area of the minor

grave widening

9: Material with which the trench is filled

10. Silicon environment

* * * * *

Claims

Expectations:

1. Method for hermetically sealing dielectric isolating trenches by filling using a deposition process, the trenches (1, 2) being widened slightly at certain points (2) and a low-pressure deposition process being used so that the Filling in the area of the normally wide trenches by closing the upper trench areas with a filling material (9) forming cavity channels (5) in the longitudinal direction of the trench by low-pressure material separation from the widened trench area (2, 3) in the longitudinal direction of the trench.

2. The method according to claim 1, wherein the widened trench locations (2, 3) in the vicinity of the connection surfaces of the two semiconductor wafers are bonded more densely when bonding the two wafers than along the other parts of the isolation trenches.

3. The method according to claim 1, wherein the widened trench locations (2,3) are installed at regular intervals.

4. Arrangement, manufactured or producible according to one of the aforementioned methods.

5. A method for hermetically sealing dielectric isolating trenches (trenches 1, 2) by filling using a deposition method, (i) the trenches (1, 2) being slightly widened at least at a certain point (2,3); (ii) a low-pressure deposition process is used in order to form a cavity (5) in the longitudinal direction of the separating trench by means of low-pressure material separation when filling in the region of the normally wide separating trenches (1) by closing upper trench regions with filler material (9) to hermetically seal the widened trench area (2, 3) in the longitudinal direction of the trench.

6. The method according to claim 5, wherein the widened trench locations (2) in the vicinity of connection surfaces of two semiconductor wafers are bonded more densely when bonding the wafers than along the other sections of the isolation trenches.

7. The method according to claim 5, wherein a plurality of widened trench locations (2) in. be attached at regular intervals to form sealing points along a channel (1, 2,1).

8. The method according to claim 5, wherein the slightly widened separating trenches (1, 2) at the at least one specific location are widened by no more than the width of the trench (1) at the non-expanded location.

9. The method according to claim 8 or 5, wherein the widening (2,3) via conical sections (3).

10. The method of claim 5, wherein the low pressure process operates approximately with vacuum.

11. The method according to claim 5, wherein the widening (2,3) takes place on at least a short piece, relative to the total length of the channel.

12. The method according to claim 5, wherein the dimensioning of the deposition process and the trench arrangement take place in such a way that any remaining lateral cavities (5) are completely sealed before the trench section closes with the slight widening (b2) at the top, and thus another Backfilling can no longer take place.

3. Device with a disk provided with separating trenches, which has hermetically sealed, dielectrically insulating separating trenches (trenches 1, 2) by filling by means of a separating process,

(i) the separating trenches (1, 2) being slightly widened at at least one specific point (2, 3);

(ii) by means of a low-pressure separation process which, when filling in the area of the normally wide trenches (1) by closing the upper trench areas with filling material, forming cavity channels (5) in the longitudinal direction of the trench by low-pressure material separation from the widened trench area (2, 3) are hermetically sealed in the longitudinal direction of the trench (7).