CN1017670B - Integrated circuit isolation process - Google Patents

Abstract

A multiple recess isolation technology avoids stress induced defects while providing a substantially planar surface. A silicon substrate (10) is patterned and etched, creating active moat regions (18) and recesses (20a-b and 21a-b). the recesses are filled with oxide by growing a field oxide (40) in wide recessed regions (21) using a LOCOS process, while depositing a planarization field oxide (44) in narrow recessed regions (20). After etching the structure to obtain a planar surface, standard procedures are used to fabricate the active devices. The process uses a single photolithographic masking step and results in only a very small loss of the width electrically active regions.

Description

Integrated circuit isolation process

Put it briefly, the invention belongs to integrated circuit fields, more particularly, the present invention relates to be applied to have a kind of isolation technology of the very lagre scale integrated circuit (VLSIC) of sub-micron dimension.

In integrated circuit technique, be necessary the active area (or claiming " moat region " (moat regions)) of active device spaced-apart.In the large scale integrated circuit and very lagre scale integrated circuit (VLSIC) that use MOS technology, normally adopt the LOCOS(local oxidation of silicon) method finish active region isolation.For implementing the LOCOS method, use a kind of lip-deep nitride that is certain pattern, covering as the silicon chip zone of moat region a thin oxide blocks.Be exposed among the high-temperature oxidation environment by uncovered area, only make and in the zone that is exposed, could form a relative thicker field oxide (field oxide) silicon chip.

Yet this LOCOS technology not only forms field oxide on the vertical direction of the silicon area that is exposed, and this oxide is the cross growth below the nitride mask edge also.This lateral oxidation thing below the nitride corrodes and is called as " beak ", and its thickness can be grown half that is about oxide thickness; Therefore, the effective coverage has been subjected to waste in this isolation technology.With regard to the LOCOS method of standard, in order to reduce " beak ", the thickness of field oxide must suitably reduce, and if not, remaining " moat region " is just not much of that for the production of active device.But, the performance that reduces to reduce circuit of field oxide thickness, this is to have increased because interconnect electric capacity.In addition, for a given voltage that is added in by field oxide on the conductor, along with reducing of oxide thickness, the leakage current between " moat region " below the field oxide increases sharply, and has caused the isolation variation between the adjacent region.

In standard LOCOS technology, developed the isolation technology of several minimizing oxide erosion amounts.Isolate at a kind of SWAMI(sidewall masking that is referred to as) method in, the transversal erosion of using a kind of silicon erosion agent and sidewall nitride layer (being formed on the silicon nitride layer of the side of the silicon area that falls in) to come the suppressed field oxide.This make to corrode approach zero crucial part and be to have introduced nitride sidewall, this sidewall raised in the process of oxide growth (lifted Up).Although the SWAMI process has reduced the erosion of field oxide, it also has its limitation.A limitation is that oxidation mask (coating is got on after the nitride sidewall layer) has the tendency of fracture at the interface point of ground floor nitride and nitride sidewall layer.The generation of this fracture mainly is to result from undue etching (normal over-etching) on the vertical direction in the sidewall process, this fracture by the localization of field oxide corrode confirm, take place especially easily in the corner of figure.Another limitation of the SWAMI process of this routine is, because the existence of nitride sidewall, this method is for the improve of the sensitivity of the generation of defective in silicon chip.Also have a limitation to be, because nitride that has a relative thin with the moat region adjacent areas, and should not comprise enough channel cutoff impurity in the zone, thereby, dual threshold (double threshold) phenomenon will take place in transistor characteristic.

A kind of improvement to SWAMI is arranged, be called improved pure frame recessed entirely (fully-framed-fully-recessed, MF ³R) partition method has reduced the limitation of SWAMI.When nitride, oxide and the silicon layer that falls in are finished by pattern-forming and etching.After, (undercut and backfill) technology that this process adopts is a kind of " undermining and recharge ", in this technology, nitride layer laterally by wet corrosion method undermining 200-1000 dust.

Fill the undermining cave with a kind of second oxide filler again, be covered with the same nitride sidewall of one deck subsequently more in the above, thereby the connection area between the two-layer nitride is increased.This area that has increased has kept the integrality that nitride connects to nitride in the etching of oxide/nitride/oxide side walls and the field oxide forming process subsequently.This MF ³A main limitation of R process is that the groove etching of silicon (recess-etched) can only reach the degree of depth of about 2000 dusts, and this might cause the isolation between the active area insufficient.

The method that another kind is used for the isolation of device is that oxide is buried (buried oxide) (BOX) method.Growth one deck alleviates (stress relief) oxide skin(coating) of stress in the BOX method, uses chemical vapor deposition (CVD) method deposition to go up silicon nitride then.Then, the nitride/oxide heap is formed figure, and carry out etching with the imprint lithography of standard, as in SWAMI technology, the thicker oxide skin(coating) of deposition last layer after etching is over although the CVD oxide skin(coating) has filled up the silicon area that is etched into depression, should (oxide) layer be uneven, this is because oxide is to be deposited on wide etchback zone, thereby has produced depression in the CVD oxide skin(coating).In order to form an even curface, use the figure of a kind of second photoresist (photoresist), fill out these depressions with photo etching (photoresist) material, use a kind of the 3rd photoresist (photoresist) to be coated on the whole surface, thereby produce a suitable even curface.Use a kind of photoresist (photoresist)/oxide etching agent photoresist (photoresist) and oxide to be corroded (etch-back) repeatedly by identical ratio, thereby after any remaining photoresist is removed, obtain a quite smooth oxide surface.

The BOX process has two subject matters.First problem is that this method needs two masking steps, has increased the complexity of technology.Secondly, this BOX method will adopt a kind of high resist etching process repeatedly that requires.In fact, the thickness of the resist of this spin coating (spun-on) depends on the density of graphics area, and in the higher zone of density, the photoresist layer will be more thinner.Therefore after resist corrodes repeatedly, will not that the surface of some active areas may be subjected to the greatly corrosion of etchant uniformly through etched surface.

From above as seen, need a kind of isolation technology, it can provide even curface haply under the high situation of output, and near the defective that does not have the moat shape to corrode (moat encrochment) or active area, do not produce by stress basically.In addition, we require it that a kind of even curface basically can be provided, and only use a mask to form figure for isolation technology.This improved isolation technology can both provide even curface for the narrow and wide groove between the moat region.

According to the present invention, we provide a kind of isolation technology, shortcoming and difficulty that it has been eliminated basically or has avoided being associated with existing isolation technology.

According to another aspect of the present invention, providing a kind of is used in the method for being isolated moat region by the narrow semiconductor chip that separates with wide groove.Growth first field oxide then, is depositing second field oxide on the substrate in wide groove, in order to the narrow groove of filling and any not filling part of wide groove.

According to another feature of the present invention, also provide a kind of method that in silicon chip, prepares the isolated area of integrated circuit.The predetermined part of substrate is covered by an oxide pad and one deck first silicon nitride layer.Run through the oxide pad and first nitride layer to the substrate etching wide with narrow groove to form the adjacent moat region of groove therewith.Deposition one deck second silicon nitride on substrate.Some wide grooves of etching so that in the bottom of wide groove, run through described second silicon nitride layer and " leave " (clear) slit.Growth forms one deck first field oxide on the substrate region that is exposed by described slit in wide groove, and one deck second field oxide layer deposits to fill the remainder of narrow groove and wide groove.Subsequently, described second field oxide is flattened to a height equal approx with the height of the top of groove, thereby forms the isolated area that is situated between between the moat region.

Present invention is described below with reference to accompanying drawings, at first is the description to accompanying drawing, wherein,

Fig. 1 has showed the cross-sectional view of the first step of the present invention, wherein, one first nitride layer, one deck first oxide pad is arranged below it, this nitride layer has used photoresist (photoresest) to form figure, and the expose portion of its nitride, oxide and silicon has carried out groove etching (recess-etched);

Fig. 2 has showed the cross-sectional view of second stage of the present invention, and wherein, one second thermal oxide layer forms, and photoresist (photoresist) is removed;

Fig. 3 has showed the cross-sectional view in step of the 3rd in the treatment process of the present invention, and this step is after the oxide side walls layer of deposition last layer second nitride layer and a bed thickness;

Fig. 4 has showed the cross-sectional view in step of the 4th in the process of the present invention, wherein oxide side walls has been carried out etching;

Fig. 5 has showed the cross-sectional view in step of the 5th in the process of the present invention, and wherein, remaining side wall layer is removed with a kind of wet corrosion method, subsequently, grows one deck LOCOS field oxide in the slit that silicon exposes;

Fig. 6 has showed the cross-sectional view in step of the 6th in the process of the present invention, and this is after the oxide layer deposition of the smooth mistake of a removal of first and second silicon oxide layers and a bed thickness gets on;

Fig. 7 has showed the cross-sectional view in the 7th step in the process of the present invention, wherein, has carried out smooth plasma etching on smooth field oxide, and oxide pad is removed;

Fig. 8 has showed the cross-sectional view of a CMOS embodiment of the present invention, wherein, has formed oxide of grid in the structure of active area;

Figure 9 shows that corresponding an alternative embodiment of the invention, wherein, between Jie's oxide pad and first silicon nitride layer, disposed one deck polysilicon layer with Fig. 1;

Figure 10 has showed after second thermal oxide layer forms, the structure of Fig. 9.

By reference Fig. 1-8, the application of most preferred embodiment of the present invention can the most clearly obtain understanding, and among the figure, identical number is used for representing corresponding same section among each figure.

Referring to Fig. 1, shown in monocrystalline silicon substrate 10 carried out handling in the groove (tank).For preventing the short channel break-through of active transistor, should use high concentration groove (tank).Use a kind of heat treatment method, wherein silicon dioxide is formed in the lip-deep of silicon chip 10, and first thermal oxide layer, oxide pad 12 are grown on the substrate 10.The thickness of oxide can not wait by from 200 to 500 dusts, preferably 350 dusts.After oxide pad 12 forms, use a kind of low-pressure chemical vapor deposition (LPCVD) method that first silicon nitride layer 14 is deposited on the oxide pad 12.The thickness of first silicon nitride layer 14 is generally 1000 to 2000 dusts, is preferred thickness with about 1800 dusts.

After first silicon nitride layer 14 deposition finishes, use a photoresist (photoresist) figure 16 to determine moat region 18(active area) the position, and with groove area 20a-b and 21a-b exposure, in next step, these groove areas field oxide of will growing.As what be about to point out, groove area 20a-b relative narrower, the then relative broad of groove area 21a-b, this just makes that it is difficult obtaining a smooth oxide surface with existing isolation process.After photoresist 16 had deposited up and formed figure with usual way, first silicon nitride layer 14 and oxide pad 12 were etched according to the figure of photoresist.The etching chemistry medicament that is adopted is CHF preferably ₃-C ₂F ₆Medicament, its corrosion rate is slow, thereby, be convenient to the operator and control well.Certainly, use other etchants also might reach similar effect.

After intact first nitride layer 14 of etching and oxide pad 12, can carry out groove etching (recessed-etched) to form moat region 18 to silicon chip 10, these districts 18 will become the active area of the device that finally obtains.In this most preferred embodiment, it is dark that silicon is etched to 3000 to 7500 dusts, wherein, is preferred depths with 5000 dusts.Fluoro trichloromethane (Freon) 11, argon and nitrogen are selected in silicon erosion agent in this most preferred embodiment for use.Yet, also may select miscellaneous silicon etchant for use, these are known by the personnel that have the knack level in the present technique field.After groove etching (recess etch) finishes, use on record lithography process that photoresist is removed.

Figure 2 shows that the cross-sectional view of semiconductor device, shown in device on the zone of the silicon chip 10 that is exposed by groove etching (recess-etch) and in the side of oxide pad 12, formed thermal oxide layer 22, on silicon chip 10, formed a continuous oxide cover layer.Second thermal oxide layer 22 has several use: the first with the angle 24 of groove area make circle some so that reduce stress on the angle 24.The thickness of second thermal oxide layer 22 is generally 250 to 1000 dusts and does not wait, and its thickness is preferably about 800 dusts.Because second thermal oxide layer 22 is thinner relatively, to the thermal oxide of growing, the loss of boron seldom from P well (P-Well).

It is worthy of note that the growth of second thermal oxide layer 22 on the silicon chip 10 is because the formation meeting consume silicon of silica.The loss meeting of silicon reduces the width of active moat region 18.Yet, in the silicon dioxide growth process quantity of the silicon of institute's loss only be the oxide that grown thickness 45 percent, therefore, if the width of second thermal oxide layer 22 that is grown is 800 dusts, then each side of moat region 18 will only reduce the width of the active area of 360 dusts.

Fig. 3 has showed the cross-sectional view of a semiconductor device, shown in this device adopted chemical vapor deposition (CVD) process deposition to go up second silicon nitride layer 26 and sidewall oxide layer 28.The thickness of described second silicon nitride layer 26 is preferably in the scope of 500 to 1000 dusts, the thickness of general desirable about 800 dusts.The thickness of sidewall oxide layer 28 preferably drops in the scope of 4000 to 8000 dusts, generally is advisable with the thickness of 5000 dusts.Must be pointed out that the thickness of sidewall oxide layer 28 is much thicker than original oxide skin(coating), sidewall oxide layer 28 selected thickness should be enough to fill up narrow groove area 20a and 20b, and unlikely wide groove district 21a and the 21b of filling up.Narrow groove area 20a and 20b place in that side wall oxide 28 is filled out will form dolly dimple 30.In wide groove district 21a and 21b, the relative sidewall of side wall oxide does not lump together, and will stay the dark depression 32 that can not be filled.Distance between the bottom of the bottom of dark depression 32 and corresponding wide groove district 21a or b should approximate the thickness of sidewall oxide layer 28.

Figure 4 shows that and adopt anisotropic oxide/nitride engraving method oppose side wall oxide skin(coating) 28, described second silicon nitride layer 26 and second thermal oxide layer 22 carry out the cross-sectional view of a semiconductor device behind the vertical etching.In wide groove district 21a and 21b, all below dark depression 32, remove for above-mentioned three layers with etchant, take this, by slit 34 and 35 silicon chip 10 is exposed.Although needn't as shown in Figure 4 second thermal oxide layer 22 be removed, and in fact usually with its removal, this is because sidewall etch can not be controlled enough accurately, so that only second silicon nitride layer 26 is removed.This etched anisotropic characteristic makes sidewall oxide layer 28 stay on the sidewall of wide groove district 21a-b, remaining width equal through the thickness of etched layer 28,26 and 22 and 80% to 100%.Can adopt the etching gas identical with being used for first nitride layer 14 and oxide pad 12 is CHF ₃And C ₂F ₆Mixture come oppose side wall to carry out etching.Point out that once more other etchants that have in the present technique field known to the personnel of knack level also might be enough to replace the etchant of being recommended.

For guaranteeing that all nitride 34 are removed from the slit, anisotropic etching process is also removed the part surface of first silicon nitride layer 14.Therefore, described first silicon nitride layer 14 should be enough thick so that can stay the nitride of about 1000 dusts after sidewall etch.It is very important preventing from nitride is removed from the drift angle 36 of the sidewall of groove area 20a-b and 21a-b when etching.In the present invention, also can adopt the identical process that prevents nitride removal that is used among the MFR.

When carrying out sidewall etch, second silicon nitride layer 26 will can not removed from narrow groove area 20a and b, and this etching can not removed the nitride layer 38 around ditch 34 and 35 yet.The selected of the thickness of sidewall oxide layer 28 will make that described narrow groove area 20a and b can be covered fully by sidewall oxide layer 28 after sidewall etch is intact.

Figure 5 shows that the cross section view of semiconductor device, the remaining sidewall oxide layer 28 of this semiconductor device is removed from second silicon nitride layer 26 with the wet corrosion method, has grown a bed thickness and wide thermal field oxide district 40 in the bottom of wide groove district 21a-21b.Etching is with the chemical agent HF solution of handy dilution, and the concentration of HF solution is advisable with 10%.Wet corrosion can not have influence on silicon nitride layer 14 and 26, perhaps by slit 34 and 35 silicon that expose.After the wet corrosion, use the LOCOS(local oxidation of silicon) the technology wide thermal field oxide district 40 of in slit 34 and 35, growing.Thermal field oxide will can not grown on silicon nitride layer 14 and 26, and therefore, wide thermal field oxide district 40 is limited on slit 34 and 35.The thickness in wide thermal field oxide district is so selected: the upper surface in wide thermal field oxide district 40 should with original upper surface of silicon chip 10 haply on same plane, its thickness can be in the scope of 6000 to 15000 dusts, it is thick generally to be about 10000 dusts.

Be also pointed out that in some cases, wide groove district 21a has medium width, therefore, when oppose side wall carries out etching, only has a little slit 34.In this situation, just as shown in FIG. 5, the thickness in wide thermal field oxide district 40 will be littler than resulting thickness in much wide wide groove district 21b.

As seen from Figure 5, growing below the edge of its nitride layer 38 on every side in wide thermal field oxide district 40, has formed " beak " 42.The thickness of sidewall oxide layer 28 should be then selected by comparing with the thickness in the wide thermal field oxide district 40 that grows, thereby make " beak " 42 be unlikely to long top, thereby be unlikely to reduce the active area width of moat region 18 in those places to moat region 18.

Figure 6 shows that a cross section view of nitride layer 14 and 26 having been removed and having deposited the semiconductor device of the smooth field oxide layer 44 of last layer on its surface 1.Can use hot phosphoric acid (160 ℃ H ₃PO ₄) or other suitable chemical solutions nitride layer 14 and 26 is removed from the surface.Smooth field oxide layer 44 is with the chemical vapor deposition (CVD) process deposits, and in this CVD technology, vertically the growth rate of the oxide thickness on the thickness of the oxide on the wall and the horizontal wall is identical.Oxide thickness is generally 10000 dusts, but also can drop in the scope of 8000-15000 dust.The thickness of smooth field oxide layer 44 should select enough greatly so that oxide on the sidewall of groove area 20a-b and 21a-b can be grown together will distinguish 20a-b and 21a-b fills up.

The upper surface of the field oxide layer 44 of smooth mistake may leave some dolly dimples 46, if required, can add last layer photoresist layer (not shown) at the upper surface of the field oxide layer 44 of smooth mistake, further carries out smooth to the surface.

Figure 7 shows that the cross-sectional view of semiconductor, this semiconductor device is removed the field oxide layer 44 of smooth mistake and the following thermal oxide pad 12 of moat region 18 upper surfaces with plasma etching.Reiterate, can use CHF ₃And C ₂F ₆Mixture, or replace with other suitable etchants.For guaranteeing that all oxide pad 12 are removed, can when this EOS, add once very short etching wet or that do.Use well-known technology in this area, present structure just can be made active device 3 at once easily.As an example, the following describes the way of the grid of CMOS, although outer, also can use its different step such as other technologies such as bipolaritys together with the present invention.

Figure 8 shows that the cross section view of semiconductor, formed the CMOS grid thereby this semiconductor has grown gate oxide 48 on moat region 18.The thickness of gate oxide 48 can be 50 to 250 dusts and does not wait, and generally is advisable so that 250 dusts are thick.After gate oxide 48 grew, next processing procedure deposited material (generally being polysilicon) to form transistor gate.In a different embodiment of the present invention, can grow a thickness earlier and preset grid (Pregate Oxide, not shown), and then it was removed in case the Kooi effect before gate oxide 48 is longer from the oxide of 100-500 dust.

At this, be necessary to point out, the upper surface of the field oxide layer 44 of the smooth mistake in groove area 20a-b and 21a-b is comparatively level and smooth, and this is smooth (surface) has guaranteed unlikely out-of-flatness place on the surface of grid material (the steps in surface) cracking that deposition gets in an ensuing step.In addition, even curface has been eliminated the generation of short circuit silk in grid material, and this short circuit silk is to remain later at a height anisotropic etching that is used to limit the grid boundary.

Another key character of the present invention is that the structural defect of the silicon that produces owing to stress on the sidewall of groove area 20a-b or 21a-b has reached minimum quantity.After oxide region layer 44 deposition of smooth mistake finished, unique high-temperature heat treatment of carrying out was grow gate oxide 48 and and then source/drain is injected (not shown) and anneal.If groove area 20a-b or 21a-b fill up fully with thermal oxidation process, can produce many defectives.This is because of the higher cause of employed concentration in groove processing procedure (Tank Processing).The high concentration of n-well (n-well) and P-well (P-Well) will provide enough concentration on the sidewall of groove area 20a-b or 21a-b, and also will prevent to sew with the parasitism of active transistor channel parallel.Equally, as mentioned in conjunction with Fig. 2, the loss of the boron from P-well (P-Well) to second thermal oxide layer 22 of growing will be very little, and this is because the thickness of second thermal oxide layer 22 is very little.Yet, after groove etching (recessetch), improve the threshold voltage in thick district if necessary, can carry out boron channel cutoff injection along the sidewall of groove area 20a-b and 21a-b and in its bottom.

Figure 9 shows that a different embodiment of the present invention, wherein, selectable polysilicon layer 50 is deposited between the oxide pad 12 and first silicon nitride layer 14, so that protect silicon chip 10 when carrying out smooth etching.Use a kind of polysilicon to be had optionally engraving method, that is, a kind of engraving method low to the polysilicon corrosion rate, smooth etching will end on the selectable polysilicon layer 50, can not be etched in the silicon chip 10.

If smooth etching can not enough accurately be controlled, then Fu Jia polysilicon layer may be essential.Be noted that if use polysilicon layer 50, as shown in figure 10, just as with reference to figure 2 time described like that, the growth of second thermal oxide layer 22 is with the side of loss polysilicon layer 50 and the sidewall of groove area 20a-b and 21a-b.Because polysilicon layer 50 do not mix, and that silicon chip 10 mixes comparatively speaking is more, therefore, can the selective oxidation condition so that the etch-rate of polysilicon layer 50 is low than silicon chip 10.This just forms the polysilicon top cover 52 of an extension on the edge at the top of the moat region 18 of silicon, take this to protect it to avoid smooth etching (corrosion).Because the part extension of the polysilicon top cover 52 that the growth of second thermal oxide layer 22 is also extended loss, therefore, the thickness that should select selectable polysilicon layer 50 makes it stay enough polysilicons at (layer 50) edge after second thermal oxide layer 22 grows, in order to avoid make the edge cracking of polysilicon layer 50 at the polysilicon top cover 52 that extends.

Therefore, the present invention has aforesaid and other plurality of advantages, the technical staff who has skilled level in this area is obviously easily seen, the present invention can be improved and be carried out various distortion widely, except proposed in the appended claims and, scope of the present invention will not be subjected to any restriction.

Claims (7)

1, a kind of method of making isolated area on a surface of semiconductor piece comprises:

Described surface etching at described semiconductor piece goes out first and second grooves, each groove has a sidewall and a bottom, the part of described surface outside described first and second grooves is defined as an active area, and the width of described first groove is greater than the width of described second groove;

On described active area and along the sidewall and the bottom of described groove, form an oxidation mask;

Form a masking layer on described oxidation mask, described masking layer is thinner than the part near this recess sidewall near the part at the described first groove center;

The described masking layer of etching, thereby the thin part of removing masking layer in described first groove, and in described first groove, leave the part masking layer near the recess sidewall place, and all leave described masking layer on the whole width of described second groove,

Remove described be positioned at described first bottom portion of groove not by described masking layer near the part at the position that residual fraction covered of recess sidewall, oxidation mask;

Remove the residual fraction of described masking layer;

Described first bottom portion of groove is positioned at the partial oxidation at the position of removing the oxidation barrier layer, to form first oxide layer at this place;

After described oxidation step, deposit one second oxide layer on described active area and in described first and second grooves; With

Second oxide layer on the described active area of etching.

2, the step of the method for claim 1, wherein removing described masking layer residual fraction was carried out before described oxidation step.

3, the method for claim 1, wherein described oxidation barrier layer comprises silicon nitride.

4, the method for claim 1, wherein described masking layer comprises silicon dioxide.

5, the method for claim 1, it also comprises: the impurity that will be used to form the channel cutoff district after the step of the described groove of etching injects the sidewall of described first and second grooves.

6, also second oxide layer on the described groove of etching of the step of second oxide layer on the method for claim 1, wherein described etching active area makes the surface coplane roughly of the surface that remains in second oxide layer in the described groove and described active area.

7, the method for claim 1, it also comprises:

After the step of described second oxide layer of deposit, the shape film is applied in deposit one on described second oxide layer, and, the step of described second oxide layer of etching comprises the described deposited shape film and second oxide layer on described active area of etching and the groove, makes the surface coplane roughly of the surface remain in second oxide layer in the described groove and described active area.

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