WO1999016843A1

WO1999016843A1 - Polishing agent, method for chemical and mechanical planishing and use of said polishing agent to planish a semiconductor substrate

Info

Publication number: WO1999016843A1
Application number: PCT/DE1998/002868
Authority: WO
Inventors: Catharina Pusch; Jocelyne Boiton; Peter Golz; Alexandre Pierron-Darbonne; Franz Hagl
Original assignee: Infineon Technologies Ag
Priority date: 1997-09-26
Filing date: 1998-09-28
Publication date: 1999-04-08
Also published as: EP1019456A1

Abstract

The invention relates to a polishing agent which is comprised of a solution containing a chemically active constituent in addition to polishing grains suspended therein. The inventive polishing agent is characterised in that the pH value of the solution is at least 0.1 lower than the pKs value of the chemically active constituent. The invention also relates to a method for chemical and mechanical planishing, whereby a polishing agent comprised of a solution is introduced between a substrate to be planished and an abrasive disk moving in relation to the substrate, and said solution contains a chemically active component in addition to polishing grains suspended therein. The inventive method is characterised in that the pH value of the solution is reduced by at least 0.1 in comparison with the pKs value of the chemically active component. The invention also relates to the use of a polishing agent to planish a semiconductor substrate. The polishing agent is comprised of a solution containing a chemically active constituent in addition to polishing grains suspended therein. The polishing agent is characterised in that the pH value of the solution is at least 0.1 lower than the pKs value of the chemically active component.

Description

description

Polishing agent, method for chemical-mechanical planarization and use of the polishing agent for planarizing a semiconductor substrate

The invention relates to a polishing agent with a solution, a chemically active component being contained in the solution and polishing grains being suspended. The invention further relates to a method for chemical-mechanical planarization, in which a polishing agent with a solution is fed between a substrate to be planarized and a grinding wheel moving relative to the substrate, wherein a chemically active component is contained in the solution and polishing grains are suspended. The invention also relates to the use of a polishing agent for planarizing a semiconductor substrate.

The known polishing agents and methods for chemical mechanical polishing are used in a variety of ways in practice. In the known methods for the chemical-mechanical planarization of a semiconductor substrate, a polishing agent is used which, in addition to the polishing grains, also contains active chemical additives. These active chemical additives are matched to the material to be removed. The active chemical additives have the effect that the material to be planarized is removed more than an underlying stop layer made of another material. The quotient from the removal rate of the layer to be planarized (.ffiP / time) is one Multiple the removal rate of the stop layer

(JES / time). The EP / RS ratio denotes selectivity.

When removing thicker layers, especially layers thicker than 100 nm, several adverse effects occur. The polishing agent or an active chemical component contained in it lose their effectiveness, i.e. a so-called depletion of the slurry occurs. This reduces the removal rate for the material to be planarized and the selectivity. In addition, the removal rate is often different at different points on the substrate to be planarized. There may also be an increase in profiles embossed in previous process steps. In this way, the uniformity of the planarization process deteriorates. The irregularities that occur can impair the functionality, particularly in the case of substrates which form complex integrated electronic circuits.

The object of the invention is to avoid the disadvantages of the prior art. In particular, a polishing agent and a method for chemical mechanical planarization are to be created, by means of which it is possible to planarize even thick semiconductor substrates with the highest possible removal rate. Furthermore, the selectivity should be as large as possible compared to a stop layer. According to the invention this object is achieved in that the pH of the solution is smaller by at least 0.1 than the _pK a of the chemically active component.

Thus, the invention provides for making a polishing agent so that the pH of the solution is less than the _pK a of the chemically active component contains. The invention thus includes a targeted lowering of the pH. The term “chemically active component” is to be understood here to mean any substance which is able to interact with a material to be planarized in such a way that its chemical bonds are weakened or destroyed.

A particularly advantageous embodiment of the inventive SSEM polishing agent is characterized in that the pH value of the solution to 0.4 to 1.2 is less than the _pK a of the chemically active component.

It is surprising that such a lowering of the pH can lead to an increase in selectivity by five to ten times.

The invention works regardless of how big the pK _s - is value of the chemically active component. The pH of the solution only has to be lower than this.

A particularly useful polishing agent is characterized in that the pH of the solution is a maximum of 6.7. Particularly high selectivities of the polishing agent according to the invention can be achieved in that the pH of the solution is in the range from 5.0 to 6.7.

It has surprisingly been found that precisely in this pH range there is both a high selectivity in the removal of semiconductor layers - in particular oxide layers - on stop layers, especially on nitride layers, and a high speed of the removal process.

A high removal rate while largely avoiding microscratches can expediently be achieved in that the polishing grains consist of corundum.

It is particularly expedient that the concentration of the polishing grains in the solution is 0.03% by weight to 30% by weight.

It is even more advantageous that the concentration of the polishing grains in the solution is 0.3% by weight to 10% by weight. With this concentration range, sedimentation of the polishing grains is avoided and a high removal rate is achieved.

In order to combine a high removal rate of the material to be planarized with a simultaneous avoidance of microscratches, it is advantageous that the diameter of the polishing grains is 0.001 μm to 100 μm, with diameters of 0.01 μm to 0.5 μm being particularly suitable. To avoid micro-scratches, it is particularly expedient that the diameters of 95% of the polishing grains differ from one another by less than 20%.

The invention further provides to perform the generic method for chemical mechanical planarization so that the pH value of the solution is lowered by at least 0.1 compared to the _pK of the chemically active component.

The invention therefore provides for the method to be carried out in such a way that the pH of the solution is lowered in a targeted manner. This lowering of the pH takes place, for example, by adding an acid to the polishing agent.

It is particularly convenient that the pH value of the solution compared to the _pK of the chemically active component is lowered by 0.4 to 1.2.

To avoid micro-scratches and to achieve a sufficiently high removal rate with high selectivity and good uniformity, it is advisable to fill in at least 100 ml of the polishing agent every minute.

A high removal rate can be achieved with a low consumption of the polishing agent by filling in 150 ml to 200 ml of the polishing agent every minute. An advantageous embodiment of the method according to the invention is characterized in that the grinding wheel is moved at a speed of rotation of at least 10 rpm. It is even more advantageous that the speed of rotation is 40 rpm to 60 rpm, with 50 rpm having proven to be favorable.

It is also expedient that the substrate to be planarized is moved at a speed of rotation of at least 10 rpm. It is even more expedient that the speed of rotation is 40 rpm to 60 rpm, with 50 rpm being preferred here as well.

In order to achieve a sufficient removal rate, the method is expediently carried out in such a way that the grinding wheel and the substrate to be planarized are pressed against one another with a force, the force producing a pressure between the grinding wheel and the material to be planarized.

High material removal rates without the occurrence of microscratches can be generated in that the pressure between the grinding wheel and the material to be planarized is in the range from 7 x 10 ² kg / m ² to 10.5 x 10 ³ kg / m ² .

In order to achieve abrasion proportional to the polishing time even with polishing times of several minutes, it is also advantageous to carry out the method in such a way that the pressure between the grinding wheel and the material to be planarized is changed during the procedure. This leads to a stable removal rate and thus to a more effective and faster process. The change in pressure does not require that the polishing process be interrupted. Rather, the polishing process can be carried out as a continuous process with variable pressure.

In an expedient embodiment of the invention, the method is carried out in such a way that the polishing process is interrupted.

The invention further provides for the use of the polishing agents found for planarizing a semiconductor substrate.

This use is particularly advantageous because a high removal rate of the semiconductor substrate to be planarized can be achieved in this way. The terms “semiconductor substrate” and “semiconductor layer” are to be understood broadly in the present invention. They also contain connections of semiconducting materials - like their oxides - which are insulators from their electrical properties.

A particularly useful use is distinguished by the fact that the pH of the solution is selected as a function of a stop layer located below the substrate to be planarized. In this embodiment of the use according to the invention, the pH can be adapted to the stop layer in such a way that removal of the stop layer is largely avoided.

Such an adaptation of the polishing agent to the stop layer can expediently take place in that the pH value of the solution is reduced as the content of nitrogen or a nitrogen compound in the stop layer decreases.

Further advantages and special features of the invention result from the following illustration of preferred exemplary embodiments.

Example 1:

A 600 nm to 700 nm thick layer of tetraethyl orthosilicate (TEOS) is used to fill a 500 nm to 600 nm deep isolation trench formed in a shallow trench isolation process on a 110 nm to 170 nm thick stop layer made of silicon nitride (Si ₃ N ₄ ) applied. This stop layer is applied on a silicon layer. These structures are on a wafer that contains a variety of electrical circuits.

a.) A polishing agent containing potassium hydroxide is made from its components

A and B mixed in a ratio of 1: 5 and then used in the process of chemical mechanical polishing. Components A and B of this polishing agent are the two-component polishing agent Corundum 05 from Rodel, with component Corundum A having the batch number XSHD3562A and component B, for example, the batch number XSHD3562B. The mixture of the components Corundum A and Corundum B contains, in addition to the polishing grains, a surface-active substance and a buffer system. The buffer system is designed so that a constant pH between 6.8 and 7.0 is established. The mixing process takes place immediately before the polishing process in order to avoid flocculation of components. Here, 3.8 kg of Co-all around A are mixed with 19 kg of Corundum B.

The selectivity of the removal process of the TEOS layer compared to the silicon nitride layer is less than 4.

Thus, the silicon nitride layer is etched away by the planarization process, so that the underlying silicon layer is attacked. This leads to the destruction of a CMOS circuit constructed with this insulation structure.

In order to avoid etching away the silicon nitride layer, it is therefore necessary to use a multi-stage planarization process. The multi-stage planarization process essentially comprises the following steps - regardless of the polishing agent used: applying a photoresist, plasma etching and a subsequent chemical-mechanical polishing step.

These steps each comprise several sub-steps. For example, the photoresist is first applied selectively at selected points in two partial steps and then on the entire surface by means of a spinning process.

Plasma etching requires placing the wafer to be processed in an etching chamber.

A conventional polishing step is then carried out after the plasma etching.

b.)

A polish containing potassium hydroxide solution is mixed from its components A and B in a ratio of 1: 5 and then used in the process of chemical mechanical polishing. Components A and B of this polishing agent are the two-component polishing agent Corundum 05 from Rodel, with component Corundum A having the batch number XSHD3562A and component B, for example, the batch number XSHD3562B. The mixture of the components Corundum A and Corundum B contains, in addition to the polishing grains, a surface-active substance and a Buffer system. The buffer system is designed so that a constant pH between 6.8 and 7.0 is established.

Again, 3.8 kg of Corundum A are mixed with 19 kg of Corundum B. By adding about 40 to 60 ml of 15% HN0 ₃ , the pH is lowered from 6.8 to 6.2. The polishing agent with a lowered pH is then used in the planarization process.

According to the invention, the pH of the polishing agent is thus reduced by about 0.5 to 1.1 units, which can be done by adding any acid. This small drop in pH alone increases the selectivity of the removal process of the TEOS layer on structured semiconductor wafers compared to the silicon nitride layer to more than 20.

This high selectivity means that the silicon nitride stop layer remains intact. Its thickness after the planarization process only decreases by 30 nm to 40 nm to 80 nm to 130 nm.

According to the invention, therefore, only a single planarization step is required. The multi-stage removal process shown in a.) Is thus replaced by a one-stage process. This shortens the manufacturing time from 16

MBit DRAMs by two days. At the same time, the manufacturing effort is reduced. In addition, the reduction in rejects increases the yield of the process. Example 2;

A 250 nm thick layer of silicon oxide (Si0 ₂ ) is applied to a stop layer made of silicon nitride (Si ₃ N ₄ ) in order to fill isolation trenches. For this purpose, a silicon layer is applied to the non-oxidizable silicon nitride layer in a LOCOS process. The silicon layer is then oxidized to a silicon oxide layer, so that an insulation structure is formed.

a.)

A polishing agent containing potassium hydroxide from its components A and B is also mixed in a ratio of 1: 5 and then used in the process of chemical mechanical polishing. Components A and B of this polishing agent are the two-component Corundum 05 polishing agent from Rodel, with component Corundum A being the batch number XSHD3562A and component B being the batch number

XSHD3562B has. The mixture of the components Co-rundum A and Corundum B contains, in addition to the polishing grains, a surface-active substance and a buffer system. The buffer system is designed so that a constant pH between 6.8 and 7.0 is set. The mixing process takes place immediately before the polishing process in order to avoid flocculation of components. Here, 3.8 kg of Co-all around A are mixed with 19 kg of Corundum B. The selectivity of the removal process of the silicon oxide layer compared to the silicon nitride layer is approximately 4.

Thus, as in Example 1 a.), The silicon nitride layer is etched away by the planarization process, so that the silicon layer below the silicon nitride layer is attacked. This leads to the destruction of a CMOS circuit constructed with this insulation structure.

b.)

A polish containing potassium hydroxide solution is mixed from its components A and B in a ratio of 1: 5 and then used in the process of chemical mechanical polishing. Components A and B of this polishing agent are the two-component Corundum 05 polishing agent from Rodel, whereby the Corundum A component has the batch number XSHD3562A and the component B has the batch number XSHD3562B. The mixture of the components Corundum A and Corundum B contains, in addition to the polishing grains, a surface-active substance and a buffer system. The buffer system is designed so that a constant pH between 6.8 and 7.0 is established.

Again 3.8 kg of Corundum A are mixed with 19 kg of Corundum B. By adding about 40 to 60 ml of 15% HN0 ₃ , the pH is lowered from 6.8 to 6.2. Then the post Liermittel with lowered pH used in the planarization process.

This small drop in pH alone increases the selectivity of the removal process of the oxide layer compared to the silicon nitride layer to more than 20.

In the examples shown, the pH to be set depends on the composition of a semiconductor wafer as follows:

• If a nitride-containing TEOS is applied during the TEOS deposition in a low-pressure CVD process, the pH value has to be lowered the less the more silicon or oxonitride is contained in the TEOS in order to achieve a high removal rate of several 100 nm TEOS per minute.

• The less silicon nitride (Si ₃ N ₄ ) is present on the surface as a stop layer on the surface, the further the pH value of the solution must be reduced in order to achieve a selectivity of 20 or more.

The polishing agent according to the invention and the method according to the invention are particularly suitable for etching a silicon oxide-containing layer, which is applied as a stop layer on a nitride layer, with high selectivity. However, the method according to the invention is also generally suitable for planarizing insulation structures. Such insulation structures can be formed, for example, in a LOCOS process by thermal oxidation of an insulation layer. It is equally possible to form the isolation structures using a shallow trench isolation process. With the help of an etching mask, trenches are etched in the substrate, which are filled with insulating material.

Since there has hitherto been a risk in the production of highly integrated CMOS circuits in accordance with the LOCOS process that a wide transition region is formed between field oxide and gate oxide, the shallow trench isolation process is used in practice. Until now, this was associated with the disadvantage that a coating step, an exposure step, a development step, a further coating step, an etching step and a chemical-mechanical polishing were necessary after the application of the insulation layer. The invention makes it possible to dispense with these steps.

On top of that, the invention increases - particularly due to the increased selectivity of the planarization process - the stability of insulation structures produced in a LOCOS process.

Claims

Claims:

1. polishes with a solution in the solution being a chemically active component included and polishing grains are diert suspensions, characterized in that the pH value of the solution by at least 0.1 less than the _pK a of the chemically active component.

2. The polishing agent according to claim 1, characterized in that the pH value of the solution to 0.4 to 1.2 is less than the _pK a of the chemically active component.

3. Polishing agent according to one of claims 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the pH of the solution is a maximum of 6.7.

4. Polishing agent according to claim 3, d a d u r c h g e k e n n z e i c h n e t that the pH of the solution is in the range of 5.0 to 6.7.

5. Polishing agent according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the polishing grains consist of corundum.

6. Polishing agent according to one of claims 1 to 5, characterized in that the concentration of the polishing grains in the solution 0.03 wt.

% to 30% by weight.

7. Polishing agent according to one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that the diameter of the polishing grains is 0.01 microns to 0.5 microns.

8. Polishing agent according to one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that the diameters of 95% of the polishing grains differ from one another by less than 20%.

9. A method for chemical mechanical planarization, in which a polishing agent is supplied with a solution between a substrate to be planarized and a grinding wheel moving relative to the substrate, wherein a chemically active component is contained in the solution and polishing grains are suspended, characterized in that the pH of the solution is reduced by at least 0.1 compared to the pK _{s of} the chemically active component.

10. The method according to claim 9, characterized in that the pH of the solution is reduced by 0.4 to 1.2 compared to the pK _s - value of the chemically active component.

11. The method according to any one of claims 9 or 10, so that at least 100 ml of the polishing agent are poured in per minute.

12. The method of claim 11, d a d u r c h g e k e n n z e i c h n e t that 150 ml to 200 ml of the polishing agent are filled per minute.

13. The method according to any one of claims 9 to 12, so that the grinding wheel is moved at a speed of rotation of at least 10 rpm.

14. The method according to claim 13, d a d u r c h g e k e n n z e i c h n e t that the grinding wheel is moved at a speed of rotation of 40 rpm to 60 rpm.

15. The method according to any one of claims 9 to 14, so that the substrate to be planarized is moved at a speed of rotation of at least 10 rev / min.

16. The method according to claim 15, characterized in that the substrate to be planarized is moved at a rotational speed of 40 rpm to 60 rpm.

17. The method according to any one of claims 9 to 16, so that the grinding wheel and the substrate to be planarized are pressed against one another with a force, the force generating a pressure between the grinding wheel and the material to be planarized.

18. The method according to claim 17, characterized in that the pressure between the grinding wheel and the material to be planarized is in the range of 7 x 10 ² kg / m ² to 10.5 x 10 ³ kg / m.

19. The method according to any one of claims S to 18, so that the pressure between the grinding wheel and the material to be planarized is changed during the process.

20. The method according to any one of claims 9 to 19, so that a solution is poured in, the pH of which is selected as a function of a stop layer located below the substrate to be planarized.

21. The method according to claim 20, characterized in that the pH of the solution is lowered as the content of nitrogen or a nitrogen compound in the stop layer decreases.

22. Use of a polishing agent according to one of claims 1 to 8 for planarizing a semiconductor material.

23. Use according to claim 22, so that the pH of the solution is selected as a function of a stop layer located below the substrate to be planarized.

24. Use according to claim 23, d a d u r c h g e k e n n z e i c h n e t that the pH of the solution is lowered with decreasing content of nitrogen or a nitrogen compound in the stop layer equally.