DE102008045216A1 - Method for in-situ end point detection during chemical-mechanical polishing of semiconductor material layers of semiconductor wafer using polishing machine, involves making potential change to occur during polishing - Google Patents

Abstract

The method involves reacting active chemical components of slurry with a polished material and representing the components as ions or compounds that cause a potential change of an ammoniac and/or ammonium sensitive electrode (4). The potential change is measured based on a polishing time. A significant potential change is made to occur during the polishing of silicon nitride structures when the polishing of a total surface of the silicon dioxide/silicon nitride is achieved. The significant potential change is drawn for controlling, end point detection and ending the polishing process. An independent claim is also included for an arrangement for in-situ end point detection during chemical-mechanical polishing of semiconductor material layers with a polishing machine.

Description

The The invention relates to a method for in situ endpoint detection in Chemical-mechanical polishing (CMP) according to the The preamble of claim 1 and an arrangement and measurement according to the Preamble of claim 8.

It It is known that for the planarization of topography surfaces and for the production of structures down to the submicron range Semiconductor wafers as technology, the chemical-mechanical polishing (CMP) is used.

It is known that, for the polishing process, the semiconductor wafer is attached to the polishing head and pressed onto a polishing pad with a defined polishing pad using a controlled pressure. Typically, both the polishing head and the polishing plate rotate during the process and a slurry of active chemical components is placed between the semiconductor wafer and the pad. Such devices for polishing semiconductor wafers are well known and have been described in, for example, US Pat US 41 93 226 . US 48 11 522 and in US 38 41 931 described.

It is also known that the active chemical components of the slurry react with the surface to be polished and have a significant influence on the removal rate, on the selectivity of the removal and the quality of the polished layer. Thus, for the production of electrical interconnect structures by means of damascene technology in the insulator layer, the structure trenches are generated and filled with corresponding deposition processes with barrier layer and then Leitbahnmetall completely to beyond the upper insulator edge out. The CMP process polishes the excess interconnect metal up to the barrier level and, in a second CMP step, polishes the barrier layer down to the insulator level so that interconnect structures embedded in barrier and insulator are present. The point of reaching the polish at the respective boundary layers is crucial for the use and yield of the circuits. As the track metals, mainly Cu and Al are used, and as barrier layers, Ti / TiN or Ta or Ta / TaN or TaSiN are used. The evidence of reaching the boundary layer Cu / barrier and barrier / insulator during polishing was z. In DE 197 26 665 A1 and in DE 199 49 976 C1 detected by a chemical sensor.

For the planarization of topography-containing oxide layers on a structured layer system with embedded SiN, the CMP is used successfully. In this invention, the application of chemical endpoint detection sensors is extended to the detection of SiN in an oxide matrix. An example of a process technology with embedded SiN in oxide is called shallow trench isolation (STI). The STI etches trenches into the SiN and the Si substrate. CVD or SOG fill the trenches with SiO ₂ and the supernatant oxide is then removed with a CMP polishing step. The immediate stopping of the polish on reaching the SiN layer, without significantly removing it, is an outstanding factor of the CMP process, so that the insulating effect of the trench is ensured. The STI process is thus critically dependent on the planarization capability of the oxide and the exact polishing stop on the SiN layer.

On Reason of necessity for this polishing process To provide endpoint detection independent of polishing rate and layer thickness changes are responding lately A number of methods have become known that measure a signal of parameters of friction or by physical evaluation of polished surface generated, which for a Endpoint detection can be used.

In US 50 69 002 describes a method for determining the end point at boundary layers by measuring the change in the motor current when the friction between the wafer surface and the pad changes.

In US 51 96 353 and US 55 97 442 as in EP 0616 362 A2 Temperature measurements for end point determination are described. The measured temperature changes on the pad or also on the polished semiconductor wafer are associated with the change in the layer composition and thus with a possible end point detection.

The direct reflection measurement of the wafer surface with a laser arranged to it is in US 54 61 007 and US 50 81 796 described. Describe Endpunktbestimmung by the substrate and with a transparent window in the pad US 54 99 733 . US 56 05 760 and US 60 45 439 ,

The analysis of the slurry, which leaves the polishing plate after contacting with the surface of the wafer to be peeled off, was carried out by Seitz in IBM Technical Disclosure Bulletin Vol 34, No 4b (1991), 406 described. The indication is carried out in a measuring cell with a photomultiplier, where the absorption of a resulting compound is measured. This process is associated with a complex filtration and so with a time delay of the signal display.

Detection of the oxide / nitride interface was performed by IBM Microelectronic Division (Leping Li and Cong Wie) published in 1999 and an analysis of the resulting NH ₃ carried out by a chemical two-step process. In the first stage, NH _{3 is} catalytically oxidized to NO, which is then excited by means of O ₃ for photoemission. The device consists of a sampler above the polishing pad, from which the gas is then conveyed into cells for the chemical conversion and measurement of the chemiluminescence. The two-step process is complicated and no longer in situ due to the successive reactions.

In situ end point detection during polishing requires the reproducible change of a signal, which correlates with the layer transition SiO ₂ -SiN on the wafer. It is signaled a point in time of polishing, where the layer to be removed (SiO ₂ ) just removed from the substrate and the underlying layer (SiN) is not significantly attacked. The end point of a polish is an event and not a quantitative amount. Thus, it is not decisive the absolute height of the changed signal at the layer transition, but its emergence from the noise floor.

The The object of the invention is now a method and a Specify arrangement, creating an in situ detection of reaching the boundary layer oxide / nitride during the CMP process is possible and at which the signal of the layer transition largely independent of changes in the parameters the CMP process is.

According to the invention the object by a method with the features mentioned in claim 1 solved. Advantageous variants of the method are the subject dependent subclaims.

According to the Process flows after the abrasive suspension (slurry) the contact with the surface of the to be polished Wafer on the pad on one or more ion-sensitive electrodes over and through the appearance of specific ions at the interface Oxide / nitride occurs when exposing the nitride surfaces to a change in potential, depending on used by the polishing time to the end point determination and thus the Control or to finish the polishing can be used.

Farther The object is achieved by an arrangement with the mentioned in claim 8 Characteristics solved. Advantageous embodiments are the subject dependent subclaims.

According to the Arrangement becomes an ion-sensitive electrode with the sensitive Surface held just above the pad and from wets the outgoing slurry, the electrode holder with the Polishing arm is connected, so that the sensitive electrode surface with the start of the polish precisely in the slurry on the Pad can be lowered and the representation of the potential of the Slurry to control the polish and determine the achievement of the Boundary layer can be used.

According to the invention the slurry after passing through the wafer surface to be peeled off so analyzed that the reaction products of the abpolierten layer with the components of the slurry by a potential measurement with the ion-sensitive electrode are displayed.

The measured potentials of the ion-sensitive electrode are proportional the activities of the compounds in the outflowing Slurry. Advantageously, a recording of the potential profile depending on the polishing time, giving you a potential change (Potential drop), which indicates an occurrence of the reaction products in indicate the slurry with the layer to be removed, and thus the layer transition as a function of the polishing time, can recognize.

The formation of the modified surface layers of SiO ₂ and SiN on the wafer occur spontaneously with components of the slurry during polishing and lead to hydrated silicate in oxide layers and the SiN layers ultimately hydrolyze to SiO ₂ and to the formation of ammonia and ammonium ions.
Hydrolysis of Si ₃ N ₄ / sa YZ Hu, RJ Gutman, TP Chow; JES Vol. 145 (11) (1998), 3919 / Si ₃ N ₄ + 6H ₂ O → 3SiO ₂ + 4NH ₃ NH ₃ + H ₂ O ↔ NH ₄ ⁺ + OH ^-

The hydrolysis is pH dependent. In the strongly alkaline range, NH _{3 is} liberated, while NH ₄ ⁺ ions are formed in the neutral to acidic range.

With an ion-sensitive electrode, preferably with a gas-sensitive ammonia electrode (eg corresponding models from HACH and ORION), the NH ₃ formed can be detected by using an alkaline and ammonium-free slurry (pH> 9) if the nitride layer reaches during polishing becomes.

When using a slurry with pH <9, preferably pH 8 to pH 6 and also ammonium-free, the ammonium ions formed from the SiN layer are detected with an ammonium-sensitive solid-state electrode (eg model ELIT 8051 Novodirect). The reaction products NH ₃ and NH ₄ ⁺ allow only the detection of the nitride layer. The SiO ₂ and its hydration forms do not contribute to a falsification of the potential jump, as soon as NH ₃ or NH ₄ ^{+ is present} in the slurry. On reaching the nitride layer, a change of the original signal of the electrode is obtained whose potential level depends on the direct concentration (activity) of the NH ₃ or NH ₄ ⁺ compounds in the slurry.

The proposed ammonium- and ammonia-sensitive electrodes have a measuring range of 10 ^-5 to 10 ^-1 mol / l. Within this range, using the slurry Levasil and added doping levels, an electrode potential slope of 50 mV / decade was measured for the ammonia electrode (HACH) and 55 mV / decade for the ammonium electrode (ELIT). The response times for both electrodes are for a maximum of 10 s for 90% of the equilibrium value. The detectable limit concentration of 10 ^-5 mol NH ₃ or NH ₄ ⁺ are achieved and exceeded in the polish of a 6 '' wafer with 20% open nitride surface and a polishing rate of 300 nm / min in 5 s.

Advantageous is a structure and an arrangement of the electrode over the Polishing plate and selected immediately after the polishing head, so that the slurry almost coincided with the exit from the area of Reaction between wafer pad from the sensitive surface of the Electrode can be recorded. The holder of the electrode is ensured by a device which the sensitive Align the surface parallel to the pad and be 1 mm across the pad is located and the outflowing slurry film completely is wetted. Such a holder can be fixed with the polishing arm be connected or outside (outside the area of the polishing plate).

By the arrangement of several electrodes on the pad after the polishing head may be a flow profile of the outflowing slurry be recognized and leads to an increase in sensitivity of Detection by detection in the maximum of the flow. These Arrangement is also advantageous in a polishing execution with different speed settings, since the flow profile of the rotational speed of the polishing plate dependent is.

Of the Construction and arrangement can easily on any polishing machine be retrofitted. There is no interference with the functionality of Polishing machine and it is the polishing process influenced in any way. The circuit layout on the wafers to be polished does not require one Test fields.

The Invention will be described below with reference to exemplary embodiments explained in more detail. The drawings show:

1 a schematic representation of an arrangement according to the invention

1.1 one too 1 belonging detail

2 a characteristic course of a potential-time curve of the ion-sensitive electrode during the polishing of a SiO ₂ layer with buried Si _x N _y structures.

In 1 is schematically the polishing device with polishing head 1 , the polishing plate 2 with polishing pad and slurry feeder 3 shown. In the direction of rotation of the polishing plate 2 is behind the polishing head 1 the ion-sensitive electrode 4 positioned, wherein the shaft of the electrode 4 stands vertically above the pad surface. According to the invention, the sensitive electrode surface 5 the electrode 4 arranged parallel to the rotating pad, held over this and is thus wetted by the outflowing slurry.

1.1 shows one to the 1 associated detail in which the details of the electrode assembly and its connection are shown enlarged. The distance of the sensitive area 5 the electrode of 1 mm causes, by adhesive forces, the outflowing slurry completely envelops the potential-forming membrane. The electrical potential of the electrode 4 is with a potential measuring unit 6 (Potentiostat) or a corresponding mV meter coupled and the signals can be displayed on a monitor 7 be visualized.

2 Figure 11 shows a typical potential-time behavior of an NH ₃ or NH ₄ ⁺ -sensitive electrode installed on the pad according to the invention for detecting the SiO ₂ / Si _x N _y boundary layer. The particular use of one or the other electrode is determined by the pH of the slurry (see description) Point A is the time of the polishing start, ie the polishing head 1 with the wafer is lowered onto the pad, the rotational speed of polishing head 1 and polishing plates 2 set and a selected polishing pressure abandoned. At the same time the sensor surface of the electrode 5 the ion-selective electrode 4 wetted by the outflowing slurry. The registered potential adjusts to a value which was obtained as a steady-state steady-state value in pure slurry. During the polishing off of the pure oxide layer, no potential change is detected. If the boundary layer SiO ₂ / Si _x N _{y is reached} during polishing, a change in the potential of the electrode voltage resulting from the plateau of the potential in the SiO ₂ polish is produced by the occurrence of NH ₃ or NH ₄ compounds in the outflowing slurry takes off. The negative potential indicates the polishing removal of the Si _x N _y layer. Points A1 ... B1 ... C.

The fall of the potential at B1 indicates the beginning of the exposure of the nitride layer, ie Because of the experimental experience of polishes with the appropriate layout among the selected polishing parameters, the desired end point of the polish will be on this sloping branch of the registered potential curve, in the region of points B1 and B2.

following Examples and variants of polishing with inventive Endpoint determination described.

example 1

A 4 "wafer with 100 nm thermal oxide was coated over the entire surface with 100 nm Si _x N _y by means of a CVD process and then 500 nm oxide were deposited. The subsequent polishing process with a polishing machine MECAPOL E460 on a polishing pad IC1000 / Suba IV and a commercial ILD polishing slurry with SiO ₂ polishing particles and pH 10 (adjusted with KOH), a slurry speed of 120 ml / min and a working pressure of 61 kPa (8.7 psi) and a speed of rotation of polishing head and polishing pad at 50 rpm gave a potential profile of the electrode, analogous to the illustrated 2 , At the point B1, the decrease of the potential due to the occurrence of NH and at the point C, the removal of the SiO ₂ on the Si _x N _{y was} completed.

Example 2

A 4 "wafer with 500 nm thermal oxide was coated with a 100 nm Si _x N _y CVD process, provided with a lithographic mask, and the mask-free areas of Si _x N _{y were} etched to oxide by reactive ion etching (RIE) , After removal of the mask, the area of the nitride structures was 25% of the wafer area and 500 nm of silane oxide were applied over the whole area to this wafer. The polish was carried out as in Example 1, with just such a slurry and the same Polierparametern. The observed potential course is in 2 is shown and recognizes at point B1, the drop in the potential and the associated exposure of the Si _x N _y structures.

Examples 3

A 8 "wafer with 500 nm thermal oxide was coated with 50 nm Si _x N _y , provided with a lithographic mask, and the mask windows etched to oxide with RIE. After removal of the mask, the area of the nitride structures was about 22% of the wafer area and 500 nm of silane oxide was applied over the whole area. The polishing was carried out with the commercial ILD slurry with SiO ₂ particles and the slurry adjusted to pH 10 with KOH, analogously to Examples 1 and 2. Polishing parameters were for the working pressure 61 kPa and the rotation 50 rpm for the polishing head and plate. The recorded potential curve showed, as in the preceding examples, a decrease in the potential value (point B1), which indicated the achievement of the nitride layer.

Example 4

An 8 "500 nm thermal oxide wafer was coated with Si _x N _y , patterned and covered with silane oxide as indicated in Example 3. The polishing was performed here instead of the commercial ILD slurry with a CeO ₂ slurry, which was adjusted to pH 8. Polierarbeitsdruck and rotational speeds were similar to Example 3. The polish shows, as well as Examples 1-3, after the potential plateau (constant electrode potential) a drop due to the influence of the NH compounds formed and thus reaching the Si _x N _y structures.

1

polishing head

2

polishing plate or polishing plate

3

Slurry feed

4

Ammonia- or ammonium-sensitive electrode

5

sensitive electrode area

6

electrode holder

7

Potential measurement unit with feeders

8th

monitor

A

start polishing

B

Start of the drop of the potential value by displaying the SiO ₂ / Si _x N _y boundary layer

C

expiring Curve, now determined by the constant polishing removal of the nitride layer (overpolish)

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 4193226 [0003]
• - US 4811522 [0003]
• US 3841931 [0003]
• DE 19726665 A1 [0004]
• - DE 19949976 C1 [0004]
• - US 5069002 [0007]
• - US 5196353 [0008]
• US 5597442 [0008]
• - EP 0616362 A2 [0008]
• - US 5461007 [0009]
• - US 5081796 [0009]
• US 5499733 [0009]
• US 5605760 [0009]
• - US 6045439 [0009]

Cited non-patent literature

• Seitz in IBM Technical Disclosure Bulletin Vol. 34, No. 4b (1991), 406 [0010]
• YZ Hu, RJ Gutman, TP Chow; JES Vol. 145 (11) (1998), 3919 [0020]

Claims (12)

Method for in situ end point detection in chemical mechanical polishing (CMP) of layers on semiconductor materials with a polishing machine, consisting of polishing plate ( 2 ) with a polishing pad, one with variable working pressure against the polishing plate ( 2 ) held rotating polishing head ( 1 ), which can be equipped with the semiconductor wafer to be polished, a feed ( 3 ) of the abrasive suspension (slurry) on the polishing bath and one or more electrodes of the same type, which mechanically behind the polishing head ( 1 ) in the polishing direction with the sensor surface parallel to the pad and can be adjusted by the mechanical support to a distance of 1 mm above the pad, characterized in that - the abrasive suspension (slurry) after reaction with the wafer surface in the outflowing direction of the ion-sensitive electrode ( 4 ) and contacts the sensor surface of the electrode, - the components of the slurry react with the abpolierten material and show up in the effluent slurry as ions or compounds that change the activity in the slurry and thus a potential change of the electrode ( 4 ), which is measured as a function of the polishing time, a significant potential change in the polishing of Si _x N _y structures buried in SiO ₂ occurs when the polish reaches the SiO ₂ / Si _x N _y interface and thus the significant potential change used for control and end point determination and to end the polishing process. Method according to claim 1, characterized in that a slurry is supplied which does not contain ammonia and contains no ammonium compounds and over the Period of polish and potential measurement in the composition is equal to. Method according to claim 1 or 2, characterized in that as ion-sensitive electrode ( 4 a gas-sensitive ammonia electrode or an ammonia-sensitive solid-state electrode is used, the former being used for the detection of ammonium ions in the application of an alkaline slurry for the detection of the resulting ammonia and the second electrode using neutral and acidic slurries. A method according to claim 3, characterized in that the gas-sensitive ammonia electrode is optimally used in a for the polishing of SiO ₂ / Si _x N _y structures on the wafer with slurries of pH 9 to 11, while the ammonium-sensitive solid-state electrode formed ammonium ions in Slurrymischungen with pH from 0 to 8 proves. A method according to claim 4, characterized in that when using commercial ILD slurries in the pH range of 9 to 11, the end point detection is carried out with the gas-sensitive ammonia electrode and that when using CeO ₂ based slurries, the pH can go from 5 to 8 and that in These pH ranges an optimal potential display of the boundary layer takes place. A method according to claim 4 or 5, characterized in that the abrasive particles in the suspensions of the slurries, both SiO ₂ and CeO ₂ , the detection of the potential jump in forming NH ₃ or NH ₄ ⁺ at the time of reaching the boundary layer SiO ₂ / SiN do not bother. Method according to claim 6, characterized that when using ammonium-sensitive solid-state electrode the adsorption of solid particles on the electrode by lowering the Sensor surface of the electrode on the pad and polish with low speed. is regenerated. Arrangement for in situ end point detection during chemical mechanical polishing (CMP) of layers on semiconductor materials with a polishing machine, consisting of a polishing plate ( 2 ) with a polishing pad, one with variable working pressure against the polishing plate ( 2 ) held rotating polishing head ( 1 ), which can be equipped with the semiconductor wafer to be polished, a feed ( 3 ) of the abrasive suspension (slurry) on the polishing pad and at least one ion-sensitive electrode, which mechanically behind the polishing head ( 1 ) is held in the polishing direction with the sensor surface parallel to the pad and adjusted by the mechanical support to a distance of 1 mm above the pad and means which are provided for the evaluation of the sensor signals and control of the polishing process. Arrangement according to claim 8, characterized that several ion-sensitive electrodes of the same type provided are. Arrangement according to claim 8 or 9, characterized that the ion-sensitive electrodes are arranged sickle-shaped are. Arrangement according to one of claims 8 to 10, characterized in that at least one ion-sensitive electrode a gas-sensitive ammonia electrode or an ammonia-sensitive Solid state electrode is. Arrangement according to one of claims 8 to 11, characterized in that the means for automatically stopping the polishing process is provided on the polishing machine.