**1. Introduction**

**Corrosion resistance** is a quantitative measure of materials under study in a special corrosion environment. With a continuous development in semiconductor IC industry on silicon wafer fabrication and the rapid shrinkage of silicon wafer feature size as of to 32nm, 25nm and even smaller, the requirement on **corrosion resistance chamber materials** under high density plasma becomes extremely critical and difficult. Therefore, the study, characterization and new development of **corrosion resistance chamber materials** have been a critical task for technologists in semiconductor IC industry. Without the correct selection of **corrosion resistance chamber materials**, it is impossible for semiconductor IC industry to achieve current technology levels. Among steps of semiconductor wafer fabrication, plasma dry etching is the most difficult and comprehensive step which has a very high standard for the selection of **corrosion resistance chamber materials**.

 Different from the traditional corrosion study, materials under high density plasma during dry etching processes should meet a comprehensive requirement. First of all, chamber materials must demonstrate a very **high corrosion/erosion resistance** under high density plasma during etching processes as well as in the defined wet chemicals. Since different etching processes use different reactive gases and chamber conditions, **chamber materials selected** have to vary in order to meet the variations of etch processes and chamber conditions. Secondly, chamber materials should have low particles and defects during etching processes because the particles and defects generated from chamber materials will fall on the silicon wafer, serve as the killer defects, and cause the loss of wafer production yield. Thirdly, chamber materials should avoid metal contamination issues on silicon wafer. The high metal contamination generated from chamber materials such as Na, K, Fe, Ni, Cr, Cu et al will electrically shorten the dies on a silicon wafer and directly impact wafer production yield. In addition to the above requirements for **advance corrosion resistance chamber materials**, chamber etching process stability and transparence, chamber impedance matching and stability, thermal and dielectric properties, capable of surface texturing, microstructure, wet cleaning compatibility, resistance to in-situ waferless plasma

A Systematic Study and Characterization of Advanced Corrosion Resistance Materials


etch byproducts in a plasma etching chamber [21, 22, 35, 36].

Fig. 2


and Their Applications for Plasma Etching Processes in Semiconductor Silicon Wafer Fabrication 3

The relationship among chamber materials used in semiconductor etching equipment, etching, wet cleaning, sputtering, and etch by-products is shown in Fig. 1[21, 22, 35, 36].

Fig. 1. The relationship of chamber materials, etching processes, precision wet cleaning and

For etching process requirement, a metal etch film stack and common issues are shown in

Fig. 2. Aluminum metal film stack and common issues in etching processes [21, 22].

from chamber materials or etch by-products [21, 22, 23, 25, 27].

The killer defects which are generated during metal etching processes fall on metal lines and cause the loss of production yield in wafer fabrication. The killer defects may either come

dry cleaning (WAC), RF coupling/grounding efficiency, adhesion of etch by-products and polymer, bonding strength of surface coatings, fundamental mechanical properties, manufacture ability and reproducibility, and cost of the materials have to be considered as a whole. After reviewing the overall requirements of chamber materials, one can see that it is not an easy task to find a suitable chamber material for semiconductor IC wafer fabrication which can meet all the above requirements. A comprehensive study has to be performed in order to find and to determine **the best chamber materials** among the existing materials in the world for a special etching application. Due to the complexity, the qualification processes of a new advanced corrosion resistance material for plasma etching processes are not only very time-consuming, but also very expensive. The fundamentals and applications of plasma dry etching and the applications on equipment of semiconductor silicon wafer fabrication have been described and studied extensively [1-20].

 Let's take some examples. During metal etch processes (etching aluminum line), Cl2 and BCl3 are the main reactive gases to etch aluminum. Ar, N2, CF4, CHF3, C2H4, or O2 are also used during etching and WAC processes. Therefore, **the selected chamber materials** have to demonstrate **high corrosion (and erosion) resistance** to these gases under the high density plasma. For silicon etch processes, SF6, NF3, HBr and HCl are the main reactive gases used to etch silicon. Other gases may also be used in the etching and WAC processes. **The selected chamber materials** should have a **high corrosion resistance** to both F-based gases and HBr corrosion. In particular, the corrosion of HBr mixed with a very tiny amount of water on the heat effected zone of stainless steel has been an issue for a long time. For dielectric etching processes, CxFx based reactive gases are usually used with a high applied power in order to etch oxide. Chamber materials selected have to show high corrosion and erosion resistance at a relatively high temperature and high power. For special etch processes such as metal hard mask etch, MRAM etch, high K etch and Bevel etch, special process gases and chamber conditions are applied. Therefore, the requirements to **corrosion resistance chamber materials** may be different. Since some plasma etching processes even etch noble metals such as Pt, Ru and Ir, one has to find chamber materials which can survive in these aggressive plasma etching conditions. Therefore, chamber materials which are submitted to sputtering, chemical etching, ion-enhanced etching, as well as ion-enhanced inhibitor etching have to be studied and characterized thoroughly for each special etching applications. There is no any material which can meet all plasma etching applications. In summary, some of the key requiements of chamber materials is listed below [21-39]:



2 Corrosion Resistance

dry cleaning (WAC), RF coupling/grounding efficiency, adhesion of etch by-products and polymer, bonding strength of surface coatings, fundamental mechanical properties, manufacture ability and reproducibility, and cost of the materials have to be considered as a whole. After reviewing the overall requirements of chamber materials, one can see that it is not an easy task to find a suitable chamber material for semiconductor IC wafer fabrication which can meet all the above requirements. A comprehensive study has to be performed in order to find and to determine **the best chamber materials** among the existing materials in the world for a special etching application. Due to the complexity, the qualification processes of a new advanced corrosion resistance material for plasma etching processes are not only very time-consuming, but also very expensive. The fundamentals and applications of plasma dry etching and the applications on equipment of semiconductor silicon wafer

 Let's take some examples. During metal etch processes (etching aluminum line), Cl2 and BCl3 are the main reactive gases to etch aluminum. Ar, N2, CF4, CHF3, C2H4, or O2 are also used during etching and WAC processes. Therefore, **the selected chamber materials** have to demonstrate **high corrosion (and erosion) resistance** to these gases under the high density plasma. For silicon etch processes, SF6, NF3, HBr and HCl are the main reactive gases used to etch silicon. Other gases may also be used in the etching and WAC processes. **The selected chamber materials** should have a **high corrosion resistance** to both F-based gases and HBr corrosion. In particular, the corrosion of HBr mixed with a very tiny amount of water on the heat effected zone of stainless steel has been an issue for a long time. For dielectric etching processes, CxFx based reactive gases are usually used with a high applied power in order to etch oxide. Chamber materials selected have to show high corrosion and erosion resistance at a relatively high temperature and high power. For special etch processes such as metal hard mask etch, MRAM etch, high K etch and Bevel etch, special process gases and chamber conditions are applied. Therefore, the requirements to **corrosion resistance chamber materials** may be different. Since some plasma etching processes even etch noble metals such as Pt, Ru and Ir, one has to find chamber materials which can survive in these aggressive plasma etching conditions. Therefore, chamber materials which are submitted to sputtering, chemical etching, ion-enhanced etching, as well as ion-enhanced inhibitor etching have to be studied and characterized thoroughly for each special etching applications. There is no any material which can meet all plasma etching applications. In

summary, some of the key requiements of chamber materials is listed below [21-39]:





corrosion and to eliminate substrate attack. - Excellent adhesion of etch by-products and polymers. - Excellent corrosion resistance in wet chemistry cleaning.


fabrication have been described and studied extensively [1-20].


The relationship among chamber materials used in semiconductor etching equipment, etching, wet cleaning, sputtering, and etch by-products is shown in Fig. 1[21, 22, 35, 36].

Fig. 1. The relationship of chamber materials, etching processes, precision wet cleaning and etch byproducts in a plasma etching chamber [21, 22, 35, 36].

For etching process requirement, a metal etch film stack and common issues are shown in Fig. 2

Fig. 2. Aluminum metal film stack and common issues in etching processes [21, 22].

The killer defects which are generated during metal etching processes fall on metal lines and cause the loss of production yield in wafer fabrication. The killer defects may either come from chamber materials or etch by-products [21, 22, 23, 25, 27].

A Systematic Study and Characterization of Advanced Corrosion Resistance Materials

indicates that Cl2 has little attack to anodized aluminum [21, 22, 25, 30].

BCl3 + Al2O3 = B2O3 + AlCl3

Fig. 5. Anodized aluminum is fully removed under Cl2/BCl3 plasma after only 1,800 wafers in production (about 60 RF hours). The special attacking pattern depends on the local

The high density plasma reaction rate of BCl3 with anodized aluminum or high purity alumina at different flow is shown in Fig. 6. The high reaction rate occurs on chamber top window due to both high density plasma and gas flow. On the chamber wall, the reaction

plasma density and gas concentration.

and Their Applications for Plasma Etching Processes in Semiconductor Silicon Wafer Fabrication 5

In pattern A, chamber materials can be etched/sputtered by plasma uniformly. The etch rate can be very low or very high. The etch rate depends on the plasma chemistry, process recipe, and materials. For example, high purity Y2O3 has showed very high plasma resistance in both Metal and Silicon etch processes. A uniform corrosion/erosion pattern is observed [21, 22, 25, 30]. For anodized aluminum, a very high corrosion/erosion rate is observed under BCl3-containing plasma during metal etch processes. In fact, an anodized aluminum film with a 75 m in thickness (hot deionized water sealed) can only hold up to 1,800 wafers in some etch process recipes in production. This became a severe problem on the lifetime of anodized aluminum in aluminum etch processes. For Silicon etch processes, the lifetime of anodized aluminum has no issue because there is no obvious attack of reactive gases to anodized aluminum in Silicon etch processes. The only concern is the formation of AlOF on anodized aluminum surface when SF6 and NF3 are used in the etching processes. The formed AlOF can either have chamber particle issue or cause etch process shift due to the surface impedance change on anodized aluminum surface. The wet cleaning to fully remove AlOF film on anodized aluminum surface is very critical to achieve a consistent and reliable etching performance on wafer fabrication. Fig. 5 shows an anodized aluminum metal etch chamber after 1,800 wafer fabrication in production. The anodized aluminum is fully removed under Cl2/BCl3 high density plasma [21, 22, 25, 30]. The major attack of anodized aluminum is due to the chemical reaction between BCl3 and Al2O3 under the high density plasma. The reaction rate of the attack to anodized aluminum highly depends on the gas concentration of BCl3 and the plasma density. Chamber erosion test

Fig. 3. Killer defects generated in aluminum metal etch processes.

The corrosion/erosion patterns of chamber materials showed three different patterns under plasma. Fig. 4 shows the three different patterns [21, 22, 28, 35, 36].

Fig. 4. Corrosion/erosion patterns of chamber materials under plasma etching (pictures are at 10,000x magnification). Model A indicates a uniform corrosion/erosion which can either be higher or low; Model B shows the attack at grains of materials; and Model C shows the attack at grain boundaries of materials.

The corrosion/erosion patterns of chamber materials showed three different patterns under

Fig. 4. Corrosion/erosion patterns of chamber materials under plasma etching (pictures are at 10,000x magnification). Model A indicates a uniform corrosion/erosion which can either be higher or low; Model B shows the attack at grains of materials; and Model C shows the

Fig. 3. Killer defects generated in aluminum metal etch processes.

plasma. Fig. 4 shows the three different patterns [21, 22, 28, 35, 36].

attack at grain boundaries of materials.

In pattern A, chamber materials can be etched/sputtered by plasma uniformly. The etch rate can be very low or very high. The etch rate depends on the plasma chemistry, process recipe, and materials. For example, high purity Y2O3 has showed very high plasma resistance in both Metal and Silicon etch processes. A uniform corrosion/erosion pattern is observed [21, 22, 25, 30]. For anodized aluminum, a very high corrosion/erosion rate is observed under BCl3-containing plasma during metal etch processes. In fact, an anodized aluminum film with a 75 m in thickness (hot deionized water sealed) can only hold up to 1,800 wafers in some etch process recipes in production. This became a severe problem on the lifetime of anodized aluminum in aluminum etch processes. For Silicon etch processes, the lifetime of anodized aluminum has no issue because there is no obvious attack of reactive gases to anodized aluminum in Silicon etch processes. The only concern is the formation of AlOF on anodized aluminum surface when SF6 and NF3 are used in the etching processes. The formed AlOF can either have chamber particle issue or cause etch process shift due to the surface impedance change on anodized aluminum surface. The wet cleaning to fully remove AlOF film on anodized aluminum surface is very critical to achieve a consistent and reliable etching performance on wafer fabrication. Fig. 5 shows an anodized aluminum metal etch chamber after 1,800 wafer fabrication in production. The anodized aluminum is fully removed under Cl2/BCl3 high density plasma [21, 22, 25, 30]. The major attack of anodized aluminum is due to the chemical reaction between BCl3 and Al2O3 under the high density plasma. The reaction rate of the attack to anodized aluminum highly depends on the gas concentration of BCl3 and the plasma density. Chamber erosion test indicates that Cl2 has little attack to anodized aluminum [21, 22, 25, 30].

$$\rm{BCl\_3 + Al\_2O\_3 = B\_2O\_3 + AlCl\_3}$$

Fig. 5. Anodized aluminum is fully removed under Cl2/BCl3 plasma after only 1,800 wafers in production (about 60 RF hours). The special attacking pattern depends on the local plasma density and gas concentration.

The high density plasma reaction rate of BCl3 with anodized aluminum or high purity alumina at different flow is shown in Fig. 6. The high reaction rate occurs on chamber top window due to both high density plasma and gas flow. On the chamber wall, the reaction

A Systematic Study and Characterization of Advanced Corrosion Resistance Materials

Fig. 7. A uniform AlOF film (rainbow color) covers the ceramic surface of a used

**0 20 40 60 80 100 120 Time (min.)**

Fig. 8. The ceramic surface of a used electrostatic chuck contains about 33 atom% fluorine on

TMAH at 20C TMAH at 50C 50C Trendline

hydroxide) is also demonstrated in Fig. 8 [35, 36, 40].

electrostatic chuck after silicon etch processes.

**0**

the surface film with a rainbow color.

**5**

**10**

**15**

**20**

**Fluorine (atom %)**

**25**

**30**

**35**

and Their Applications for Plasma Etching Processes in Semiconductor Silicon Wafer Fabrication 7

plasma. The chemical treatment to remove AlOF using TMAH (tetramethylammonia

rate of BCl3 with Al2O3 is almost a liner relationship, but the reaction rate is much lower than that on the chamber top window. It also indicates that without BCl3 flow, the reaction rate of Cl2 plasma has almost no attack to anodized aluminum or to high purity alumina. In the plasma reaction rate study, the total flow is fixed as of 205 sccm. The Argon gas flow is fixed at 40 sccm. The test starts at 165 sccm Cl2 flow and zero flow of BCl3, then 155 sccm Cl2 flow and 10 sccm BCl3 flow, until the final flow of Cl2 is 85 sccm and BCl3 flow is 80 sccm. The test coupons are either on chamber top window or on the chamber wall. Nine different types of anodized aluminum and high purity alumina are used in the test [21, 22, 25, 30]. The reaction rate is in the unit of mils per RF hour.

Fig. 6. The maximum reaction rate of Al2O3 at different BCl3 gas flow under high density plasma [21, 22, 25, 30].

In pattern B, chamber materials suffered the attack of grains under plasma. CVD SiC grains can be attacked by Cl2-containing plasma and SiC material cannot be used in aluminum etch processes as a chamber material. Grains of high purity ceramic (99.5% or higher alumina) can also be attached by BCl3 in metal etch processes and the glass phases such as SiO2, CaO, and MgO remain. It is obvious that BCl3 can attack anodized aluminum and alumina under high density plasma. For high purity AlN, AlN grains are attacked by fluorine-containing plasma such as SF6 and NF3, the grain boundaries remain.

In pattern C, chamber materials are attacked at grain boundaries only. A typical example is high purity alumina (99.5% or higher in Al2O3), glass phases such as SiO2, MgO, and CaO can react with fluorine-containing gases. In this case, grains of alumina remain. The formation of AlOF may occur on alumina surface. Fig. 7 shows a ceramic ESC surface which is covered by a layer of AlOF after exposure to plasma in silicon etch processes [35, 36].

A 33% atomic% of F is detected on electrostatic chuck ceramic surface (high purity alumina) indicating the formation of AlOF on high purity alumina surface under fluorine-containing

rate of BCl3 with Al2O3 is almost a liner relationship, but the reaction rate is much lower than that on the chamber top window. It also indicates that without BCl3 flow, the reaction rate of Cl2 plasma has almost no attack to anodized aluminum or to high purity alumina. In the plasma reaction rate study, the total flow is fixed as of 205 sccm. The Argon gas flow is fixed at 40 sccm. The test starts at 165 sccm Cl2 flow and zero flow of BCl3, then 155 sccm Cl2 flow and 10 sccm BCl3 flow, until the final flow of Cl2 is 85 sccm and BCl3 flow is 80 sccm. The test coupons are either on chamber top window or on the chamber wall. Nine different types of anodized aluminum and high purity alumina are used in the test [21, 22, 25, 30].

> **MAXIMUM EROSION RATE vs BCL3 FLOW RATE (12mT/7Torr He/80C w&d/45C cath/1600Ws/200Wb/40Ar/165BCL3+CL2/4hr RF-on)**

> > X1,typeIII, sealed(on wafer) X2,typeIII, sealed(on wafer) X3,typeIII, sealed(on wafer) XA,Alcoa, C-276(on wafer) XB,Alcoa, C-276(on wafer) typeIII, sealed(on turbo port wall ) typeIII, sealed(on turbo port wall) Alcoa,C-276(on turbo port wall) Alcoa,C-276(on turbo port wall)

0 10 20 30 40 50 60 70 80 **BCL3 FLOW RATE (sccm)**

Fig. 6. The maximum reaction rate of Al2O3 at different BCl3 gas flow under high density

plasma such as SF6 and NF3, the grain boundaries remain.

In pattern B, chamber materials suffered the attack of grains under plasma. CVD SiC grains can be attacked by Cl2-containing plasma and SiC material cannot be used in aluminum etch processes as a chamber material. Grains of high purity ceramic (99.5% or higher alumina) can also be attached by BCl3 in metal etch processes and the glass phases such as SiO2, CaO, and MgO remain. It is obvious that BCl3 can attack anodized aluminum and alumina under high density plasma. For high purity AlN, AlN grains are attacked by fluorine-containing

In pattern C, chamber materials are attacked at grain boundaries only. A typical example is high purity alumina (99.5% or higher in Al2O3), glass phases such as SiO2, MgO, and CaO can react with fluorine-containing gases. In this case, grains of alumina remain. The formation of AlOF may occur on alumina surface. Fig. 7 shows a ceramic ESC surface which is covered by a layer of AlOF after exposure to plasma in silicon etch processes [35, 36].

A 33% atomic% of F is detected on electrostatic chuck ceramic surface (high purity alumina) indicating the formation of AlOF on high purity alumina surface under fluorine-containing

The reaction rate is in the unit of mils per RF hour.

0

plasma [21, 22, 25, 30].

0.05

0.1

0.15

**MAXIMUM EROSION RATE (mils/hr.)**

0.2

0.25

0.3

0.35

plasma. The chemical treatment to remove AlOF using TMAH (tetramethylammonia hydroxide) is also demonstrated in Fig. 8 [35, 36, 40].

Fig. 7. A uniform AlOF film (rainbow color) covers the ceramic surface of a used electrostatic chuck after silicon etch processes.

Fig. 8. The ceramic surface of a used electrostatic chuck contains about 33 atom% fluorine on the surface film with a rainbow color.

A Systematic Study and Characterization of Advanced Corrosion Resistance Materials

and Their Applications for Plasma Etching Processes in Semiconductor Silicon Wafer Fabrication 9

Fig. 9. Test coupons in etching chamber are mounted on chamber top window (left) and on chamber wall (right) and on the dummy aluminum wafer on an electrostatic chuck surface

Fig. 10 shows the test results of various materials obtained from worldwide suppliers. The letters of A, B, C, D et al represent the suppliers and their materials. Agreements were signed for not allowing to release the names of the worldwide suppliers and their materials. The plasma etching rate is in the unit of mils (1 mil = 25.4 m). It is obvious that either YAG (solid solution of Al2O3 and Y2O3) and solid Y2O3 can reduce the plasma etching rate at the order of 40-50 times in comparison with the previously used chamber materials such as high purity alumina. That is the reason why Y2O3 has been as one of the leading chamber materials in plasma etching tools in the past 10 years for the leading semiconductor etching

Fig. 10. Test results of new and old chamber materials in plasma etching on chamber top window. The etch rate reduction of new chamber materials can reduce the etching rate by 40

(right, white surface).

equipment companies.

to 50 times.

Since the limitation of the space of this chapter, anodized aluminum, boron carbide, and Y2O3 as chamber materials will be demonstrated.
