CN100539153C

CN100539153C - Semiconductor structure and memory cell

Info

Publication number: CN100539153C
Application number: CNB2007100966799A
Authority: CN
Inventors: 廖忠志
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2006-10-02
Filing date: 2007-04-23
Publication date: 2009-09-09
Anticipated expiration: 2027-04-23
Also published as: CN101159268A

Abstract

The invention provides a kind of semiconductor structure and memory cell, comprise semiconductor substrate, plane P MOS element is positioned at the surface of semiconductor substrate, and the NMOS element is positioned at the surface of semiconductor substrate, and wherein this NMOS element is a fin formula field-effect transistor.Embodiments of the invention have than the PMOS of balance and NMOS performance, therefore can improve the performance of memory cell.

Description

Semiconductor structure and memory cell

Technical field

The present invention relates to a kind of semiconductor element, particularly a kind of memory cell, and also relate to a kind of formation method that contains the integrated circuit of static RAM.

Background technology

In the past many decades, semiconductor manufacturing industry continues to dwindle the size of semiconductor element (MOS field-effect transistor), with speed, performance, density and the reduction unit cost that increases integrated circuit.Yet, continue to dwindle the rate travel that the MOS field-effect transistor can reduce charge carrier, the drive current of element is produced into adverse influence.In order to promote the performance of MOS element more, increase the charge carrier rate travel and become following very important problem.At present often the channel region stress application to the MOS element increases the speed that charge carrier moves, and the channel region of NMOS element is applied the tensile stress of one source pole to drain electrode, and the PNMOS element is applied the compression of one source pole to drain electrode.

In general, the channel region of PNMOS element is applied the method for a compression, growth SiGe stress riser in the source electrode of PNMOS element and drain electrode normally, it comprises along the edge of silicon substrate and forms groove, epitaxial growth SiGe stress comes from the groove, and carries out the tempering program.Because the lattice constant of SiGe greater than silicon substrate, therefore after the tempering program, can apply a compression to the channel region between source S iGe stress riser and drain electrode SiGe stress riser.

Yet said method also is not suitable for static RAM (SRAM).Fig. 1 shows six transistorized static RAMs, comprise break-through gridistor PG1, PG2, on draw MOS element (pull-up MOS) PU1, PU2 and drop-down MOS element (pull-down MOS) PD1, PD2.Control the grid 2,4 of break-through gate MOS element PG1, PG2 respectively by character line WL, with the electric current of decision static RAM.By on draw MOS element PU1, PU2 and drop-down MOS element PD1, the formed bolt-lock of PD2 can store a state, and read or write by bit line BL.

Traditionally, forming SiGe stress comes from the PMOS element in the memory chip, draw the drive current of PMOS element on can increasing in the static RAM effectively, but can't increase the drive current of pull-down NMOS element, therefore drop-down MOS element has a less drive current.So PMOS and the unbalanced performance of NMOS interelement can cause and write difficulty.For example, on draw PMOS element PU2 to have a high drive current, electric charge is provided to node 6 from Vcc easily.On the contrary, NMOS element PD2 has a low relatively drive current, then is difficult for making electric charge to be released into Vss from node 6.Therefore, when writing " 0 " to memory cell the time, need long time.In addition, the high drive current of PMOS element can reduce the voltage limit that writes of static RAM, and reduce write voltage limit and may increase wrong writing.Therefore,, must balance write and read, promptly draw the drive current of PMOS element and pull-down NMOS element on the balance in order to form high performance static RAM.

The grid width that general using increases the NMOS element promotes the drive current of NMOS element, however this solution with dwindle the integrated circuit size and contradict.Therefore, be not good method by the grid width that increases the NMOS element.So semiconductor manufacturing industry is needed a kind of method that but can not reduce memory element density that addresses the above problem badly.

Summary of the invention

The object of the present invention is to provide a kind of semiconductor structure and memory cell, in order to form high performance static RAM.

A kind of semiconductor structure provided by the invention comprises semiconductor substrate; Plane P MOS element is positioned on this semiconductor substrate surface, and the NMOS element, is positioned on this semiconductor substrate surface, and wherein this NMOS element is a fin formula field-effect transistor (FinFET).And this NMOS element comprises: NMOS active area, its upper surface are higher than adjacent isolated area upper surface one vertical range, and wherein the ratio of this vertical range and NMOS active area width is greater than 0.5; Gate dielectric is positioned on the surface and sidewall of this NMOS active area, and grid, is positioned on this gate dielectric.

Aforesaid semiconductor structure, wherein the ratio of this vertical range and NMOS active area width is 1.

Aforesaid semiconductor structure, wherein this PMOS element comprises: PMOS active area, its upper surface are higher than adjacent isolated area upper surface one vertical range, and wherein the ratio of this vertical range and PMOS active area width is less than 1; Gate dielectric is positioned on the surface and sidewall of this NMOS active area, and grid, is positioned on this gate dielectric.

Aforesaid semiconductor structure, wherein this PMOS and NMOS element are arranged in a memory cell.

Aforesaid semiconductor structure, wherein this PMOS and NMOS element are separated with a shallow channel isolation area, this shallow channel isolation area includes first and first upper surface and the second portion and second upper surface, adjacent this first of this PMOS element and adjacent this second portion of this NMOS element.

Aforesaid semiconductor structure, wherein all PMOS elements in this memory cell are all plane component, and all NMOS elements in this memory cell are all fin formula field-effect transistor.

Aforesaid semiconductor structure, wherein this PMOS and NMOS element form an inverter of this memory cell.

Aforesaid semiconductor structure, wherein the grid of the grid of this PMOS element and this NMOS element is the continuous conductor bar.

Aforesaid semiconductor structure, wherein this PMOS element is for drawing element on this memory cell, and this NMOS element is to be selected from the group that following elements is formed: drop-down MOS element and break-through gate MOS element.

The present invention provides a kind of memory cell in addition, comprises semiconductor substrate; The PMOS district is arranged in this semiconductor substrate; The n well region is arranged in this PMOS district; First shallow channel isolation area is arranged in this PMOS district, and wherein this first shallow channel isolation area has first upper surface; Nmos area is arranged in this semiconductor substrate; The p well region is arranged in this nmos area; Second shallow channel isolation area is arranged in this nmos area, and wherein this second shallow channel isolation area has second upper surface that is lower than this first upper surface; PMOS district element is positioned on this n well region surface, and nmos area, is positioned on this p well region surface.

The present invention also provides a kind of memory cell, comprises break-through gate MOS (pass-gate MOS) element; Drop-down MOS element, it is electrically connected to this break-through gate MOS element, wherein this break-through gate MOS element and this drop-down MOS element are fin formula field-effect transistor, and on draw the MOS element, it is electrically connected to this break-through gate MOS element and this drop-down MOS element, and wherein being somebody's turn to do and drawing the MOS element is plane MOS element.

Embodiments of the invention have than the PMOS of balance and NMOS performance, therefore can improve the performance of memory cell.

For above-mentioned and other purposes of the present invention, feature and advantage can be become apparent, preferred embodiment cited below particularly, and conjunction with figs. is described in detail below.

Description of drawings

Fig. 1 shows tradition six transistorized static RAMs.

Fig. 2 shows six transistors of the present invention (6T) memory cell.

The part of Fig. 3 A-Fig. 3 B display base plate.

Fig. 4 shows formation n well region, forms and the patterning photoresist.

Fig. 5 shows the formation photoresist.

Fig. 6 shows the top area in etching STI district.

Fig. 7 A shows formation gate dielectric and grid.

Fig. 7 B shows insulation system on formation one silicon, and wherein each active area is isolated mutually with STI district and buried oxide layer.

Fig. 7 C shows the generalized section of another embodiment of the present invention, draws on wherein the active area of MOS element to have a upper surface that is higher than adjacent S TI district upper surface.

Fig. 8 shows the perspective view of break-through MOS element.

Draw the generalized section of MOS element in Fig. 9 demonstration.

Wherein, description of reference numerals is as follows:

WL-character line; BL-bit line;

6-node; 100,300 and 500-p well region;

200,400-n well region; PU1, PU2-on draw the MOS element;

PD1, PD2-drop-down MOS element; PG1, PG2-break-through gate MOS element;

20-substrate; 21-buried oxide layer;

24,26,28,30-shallow channel isolation area; 36-n well region;

38-photoresist; 40-p well region;

42-photoresist; 44-active area (semiconductor bar);

H-vertical range; D-vertical range;

W-width; 46,50-gate dielectric;

48,52-gate electrode; 60-source area;

62-drain region; 66-SiGe stress riser;

68-lightly-doped source/drain region.

Embodiment

Fig. 2 shows four six transistors of the present invention (6T) memory cell, is represented by dotted lines the scope of each memory cell.Wherein p well region 100,300 and 500 is used for forming n type MOS element, and n well region 200,400 can be used to form p type MOS element.For simple expression, the memory cell in displayed map 2 lower left corners only afterwards.

In the present invention, each memory cell comprises six MOS elements.With reference to the shown memory cell in the lower left corner, first inverter comprises and draws MOS element PU1 and drop-down MOS element PD1.Second inverter comprises and draws MOS element PU2 and drop-down MOS element PD2.This memory cell also comprises two break-through gate MOS element PG1, PG2.As drop-down MOS element PD1, PD2 and break-through gate MOS element PG1, when PG2 is the NMOS element, on to draw MOS element PU1, PU2 be the PMOS element.

Fig. 3 to 7 shows the manufacture process profile of memory cell of the present invention, and it is for to the analysing and observe of the A-A ' direction of Fig. 2, so profile is parted on the right side by a left side and do not show MOS element PG2, PU1 and PD1.The part of Fig. 3 A display base plate 20.The substrate 20 preferable silicon that comprise.In one embodiment, substrate 20 comprises SiGe or other semi-conducting materials.Shallow channel isolation area (hereinafter to be referred as STI) 24,26,28,30 is formed in the substrate 20, to isolate each element region.Etching substrates 20 forms groove, and filled dielectric material is to form

STI district

24,26,28,30, dielectric material can be high-density oxide (HDP oxides), tetraethoxy silicate (TEOS oxides), ozone oxidation thing or composite bed, for example composite bed of high dielectric material and oxide.

Fig. 3 B shows another embodiment of the present invention, and wherein substrate 20 comprises insulation system on the

silicon.STI district

24,26,28, the 30 preferable buried oxide layers 21 that extend on the semiconductor 23.

With reference to Fig. 4, form n well region 36.Form and patterning photoresist 38, with masked areas 100,300, but exposed region 200.Inject n type impurity, as phosphorus and/or arsenic, to form n well region 36.Inject n type impurity, with the critical voltage of the PMOS element of adjusting follow-up formation.Then, remove photoresist 38.

With reference to Fig. 5, form photoresist 42 with masked areas 200, exposed region 100 and 300.Inject p type impurity to form p well region 40.Preferable boron and/or the indium of comprising of p type impurity.Inject p type impurity, with the critical voltage of the NMOS element of adjusting follow-up formation.Then, remove photoresist 42.

With reference to Fig. 6, the top area in etching STI

district

24,26,28,30, preferably, etchant is etching STI

district

24,26,28,30 only, and is not etched to substrate 20.Etchant comprises hydrogen fluoride Wet-type etching, chlorine dry-etching, fluorine dry-etching and analog thereof.In a preferred embodiment, behind etching STI

district

24,26,28,30, have a vertical range H to top, STI district from the active area upper surface, distance H is preferable approximately greater than 30nm.The preferable etching one vertical range D of the upper surface in STI

district

24,26,28,30, distance D is preferable approximately greater than 30nm.One of ordinary skill in the art should understand, and described herein distance H, D or other sizes can change according to the manufacture process technology of using.Active area 44, it is the part of substrate 20, and on the upper surface in STI district after the etching 24,26.Active area 44 has a width W.In one embodiment, the height H of active area and width W ratio are preferable approximately greater than 0.5.In another embodiment, as channel width W during less than 40nm, then its ratio is preferable is about 1.It should be noted that through behind etching and the cleaning procedure, it is one circular-arc that the corner of active area 44 is.This circular-arc size corresponding to integrated circuit, in general, the size of integrated circuit is more little, and then the corner of active area 44 is just slick and sly more.After etching, remove photoresist 42.

With reference to Fig. 7 A, form gate dielectric 46,50 and grid 48,52.Gate dielectric 46, the 50 preferable dielectric materials of generally using always that comprise, for example, oxide, nitride, nitrogen oxide, high dielectric constant material (Ta ₂O ₅, Al ₂O ₃, HfO) and above-mentioned combination.The material of

grid

48,52 comprises polysilicon or other electric conducting materials commonly used, for example, and polysilicon metal, silicide metals, nitride metal and above-mentioned combination.Grid layer is stacked on the gate dielectric, and then this stacked structure of patterning just can form gate dielectric 46,50 and

grid

48,52.

Fig. 7 B shows another embodiment of the present invention, forms insulation system on the silicon, and wherein each active area is isolated mutually with STI district and buried oxide layer 21.The formation method of Fig. 7 B structure is with to be formed at semiconductor substrate similar.

Then, masked areas 200, and exposed region 100,300.Form lightly-doped source/drain region, grid gap wall and source/drain electrode to finish NMOS element PG2 and PD1.Fig. 8 is the perspective view of NMOS element PG2 after forming gate dielectric 46 and grid 48, and wherein each feature is shown among Fig. 7 A, and represents with same-sign.

With reference to Fig. 8, active area 44 is higher than the upper surface in STI

district

24,26, to form the semiconductor bar.Dielectric layer 46 and grid 48 are covered in the upper surface and the sidewall of semiconductor bar 44.Then but Doped n-type impurity is to form lightly-doped source/drain region (hereinafter to be referred as LDD) (not shown).LDD district (and after form source/drain region 60,62) but codope nitrogen and/or carbon, to stop the diffusion of impurity.Grid gap wall (not shown) is formed on the sidewall of gate dielectric 46 and grid 48, the axis normal of sidewall and semiconductor bar 44.Inject n type impurity with formation source/

drain region

60,62.

The NMOS element that the present invention finished is a fin formula field-effect transistor (FinFET).Because the sidewall of active area 44 and upper surface can increase width of channel, so the channel width of fin formula field-effect transistor PG2 is greater than plane MOS element, so can increase the drive current of fin formula field-effect transistor PG2.Break-through gate MOS element PG2, break-through gate MOS element PG1 and drop-down MOS element PD1, PD2 also form simultaneously.Because STI

district

28,30 is also etched, so break-through gate MOS element PG1 also is a fin formula field-effect transistor (with reference to Fig. 7 A).In a preferred embodiment, the STI district in all MOS element regions 100,200,300 of etching makes break-through gate MOS element and drop down element be all fin formula field-effect transistor.

Get back to Fig. 7 A, masked areas 100,300, and PMOS element PU1 is formed in the zone 200.The preferable SiGe of the comprising stress riser of PMOS element can increase charge carrier rate travel and drive current so that its channel region is applied a compression.The profile of PMOS element PU1 as shown in Figure 9, this profile is analysing and observe the B-B ' direction of Fig. 2.

The manufacture process of PMOS element PU1 below is described in detail in detail.Utilize and inject p type impurity, for example boron and/or indium form LDD district 68.Form thin illusory clearance wall (not shown), for example thickness about 100

To 200

Between.Deng to or anisotropy etching n well region 36 to form groove.Fill up groove with SiGe, form SiGe stress riser 66.The method of filling up groove comprises selective epitaxial growth (SEG).But doped p type impurity when forming SiGe stress riser 66, and/or forming SiGe stress riser 66 back injection p type impurity, with formation source/drain region.But doping carbon to LDD district 68 and source/drain region to intercept the diffusion of impurity.When forming PMOS element PU1, form PMOS element PU2.

One of ordinary skill in the art are when understanding, and when otherwise forming memory cell of the present invention, the PMOS element may have the passage of a projection, and it exceeds the upper surface in adjacent S TI district.Fig. 7 C shows the PMOS element of another embodiment of the present invention, and the active area of PMOS element PU1 can have a upper surface and sidewall, and the upper surface in the upper surface of active area and adjacent S TI district has a vertical range H '.In this PMOS element, distance H ' with the ratio of width W ' approximately less than 1, preferable less than 0.5.This PMOS element also can be plane MOS element.

In the aforementioned embodiment, before etching

STI district

24,26,28,30, be to form p well region 40 and n well region 36 earlier.Yet in another embodiment, also can first etching

STI district

24,26,28,30 after, form p well region 40 and n well region 36 again.

Though the present invention is an example with the 6T memory cell, one of ordinary skill in the art should understand the memory cell that the present invention can be used for forming various number MOS elements, for example 8T, 10T, 12T etc.

In one embodiment, form the NMOS element of plane formula PMOS element and fin formula field-effect transistor (FinFET).When the drive current of PMOS element is constant, can increase the drive current of NMOS element.And because can increase the drive current of PMOS element easily with the SiGe stress riser, but so electric current of balance PMOS element and NMOS element.In addition, process steps of the present invention can be compatible with existing manufacture process, do not need extra mask.

In one embodiment, the present invention provides a kind of formation method of semiconductor structure in addition, comprises semiconductor substrate is provided, and forms plane p type PMOS element in semiconductor substrate surface, and form n type NMOS element in semiconductor substrate surface, wherein this NMOS element is a fin formula field-effect transistor.This fin formula field-effect transistor can comprise the upper surface (channel width) of different size between drop down element PD and break-through element PG, also can have the identical upper surface size (channel width) of essence on drop down element PD and break-through element PG.

In another embodiment, the present invention also provides a kind of formation method of semiconductor structure, and the semiconductor substrate that contains PMOS district and nmos area is provided, form the n well region in the PMOS district, form the p well region in nmos area, the STI district of etching nmos area, some is higher than the STI district of nmos area in fact to make the p well region.When carrying out etching program, cover the PMOS district, form grid in PMOS district and nmos area, form grid on gate dielectric, patterning grid dielectric layer and grid are stacked in the nmos area to form first grid, and second grid is stacked in the PMOS district, and wherein source/the drain region in PMOS district has at least a part to contain SiGe.

Though the present invention discloses as above with preferred embodiment; right its is not in order to limit the present invention; any those of ordinary skills; without departing from the spirit and scope of the present invention; when can changing and retouching, so protection scope of the present invention is as the criterion when looking the scope that claim defined of enclosing.

Claims

1. semiconductor structure comprises:

Semiconductor substrate;

Plane P MOS element is positioned on this semiconductor substrate surface, and

The NMOS element is positioned on this semiconductor substrate surface, and this NMOS element is a fin formula field-effect transistor, and this NMOS element comprises:

NMOS active area, its upper surface are higher than adjacent isolated area upper surface one vertical range, and wherein the ratio of this vertical range and this NMOS active area width is greater than 0.5;

Gate dielectric is positioned on the surface and sidewall of this NMOS active area, and

Grid is positioned on this gate dielectric.

2. semiconductor structure as claimed in claim 1, wherein the ratio of this vertical range and this NMOS active area width is 1.

3. semiconductor structure as claimed in claim 1, wherein this PMOS element comprises:

PMOS active area, its upper surface are higher than adjacent isolated area upper surface one vertical range, and wherein the ratio of this vertical range and this PMOS active area width is less than 1;

Grid is positioned on this gate dielectric.

4. semiconductor structure as claimed in claim 1, wherein this PMOS and NMOS element are arranged in a memory cell.

5. semiconductor structure as claimed in claim 4, wherein this PMOS and NMOS element are separated with a shallow channel isolation area, this shallow channel isolation area includes first and first upper surface and the second portion and second upper surface, adjacent this first of this PMOS element and adjacent this second portion of this NMOS element.

6. semiconductor structure as claimed in claim 4, wherein all PMOS elements in this memory cell are all plane component, and all NMOS elements in this memory cell are all fin formula field-effect transistor.

7. semiconductor structure as claimed in claim 4, wherein this PMOS and NMOS element form an inverter of this memory cell.

8. semiconductor structure as claimed in claim 7, wherein the grid of the grid of this PMOS element and this NMOS element is the continuous conductor bar.

9. semiconductor structure as claimed in claim 4, wherein this PMOS element is for drawing element on this memory cell, and this NMOS element is to be selected from the group that following elements is formed: drop-down MOS element and break-through gate MOS element.