Method of marking sintered body and method for manufacturing magnetic head wafer

1. A method of marking a sintered body, comprising the steps of:

preparing the sintered body by sintering a mixture of a first type of powder particles and a second type of powder particles, the first type of powder particles being made of a first material, the second type of powder particles being made of a second material that has a different etch susceptibility from the first material; and

writing identification information on the surface of the sintered body by forming a first concave region to a depth of at least about 10 nm under the surface of the sintered body and a second concave region under the first concave region, respectively, the first concave region being formed by etching away both the first and second types of powder particles, the second concave region being formed by selectively etching away only the first type of powder particles.

2. The method of claim 1 , wherein the step of writing the identification information includes the step of forming the second concave region to a depth of at least about 50 nm under the bottom of the first concave region.

3. The method of claim 1 , wherein the step of writing the identification information includes the steps of:

performing a selective etching process such that the first type of powder particles are etched at a higher rate than the second type of powder particles; and

performing a non-selective etching process such that the first and second types of powder particles are etched at substantially equal rates after the selective etching process has been performed.

4. The method of claim 3 , wherein the step of writing the identification information includes the step of performing at least one of the selective etching process and the non-selective etching process multiple times.

5. The method of claim 3 , wherein the step of writing the identification information includes the step of performing the non-selective etching process at least as the last etching process thereof.

6. The method of claim 3 , wherein the selective etching process and the non-selective etching process are carried out by the same etching system with etching conditions being changed.

7. The method of claim 1 , wherein the first and second types of powder particles both have a mean particle size of about 0.3 μm to about 5.0 μm.

8. The method of claim 1 , wherein the first concave region has a line width of about 1 μm to about 20 μm.

9. The method of claim 3 , wherein a variation ΔR in reflectance due to the selective etching process is at least about 25% with respect to light having a particular wavelength, the variation ΔR being determined by (R 2 −R 1 )/R 2 , where R 1 is the reflectance of a portion of the surface of the sintered body that has been subjected to the selective etching process and R 2 is the reflectance of another portion of the surface of the sintered body that has not been subjected to the selective etching process.

10. The method of claim 9 , wherein the particular wavelength is included in the wavelength range of light to be radiated toward the sintered body to read the identification information optically.

11. The method of claim 1 , wherein a portion of the surface of the sintered body, which has not been subjected to the selective etching process, has a surface roughness of at most about 5 nm.

12. The method of claim 1 , wherein the depth of the second concave region is about 50 nm to about 5 μm as measured from the bottom of the first concave region.

13. The method of claim 1 , wherein the first and second materials are compounds selected from the group consisting of aluminum oxide, aluminum nitride, silicon oxide, silicon nitride, zirconium oxide, zirconium nitride, silicon carbide, titanium carbide, titanium oxide and iron oxide.

14. A method for manufacturing a wafer for magnetic heads, comprising the steps of:

preparing a sintered body by sintering a mixture of a first type of powder particles and a second type of powder particles, the first type of powder particles being made of a first material, the second type of powder particles being made of a second material that has a different etch susceptibility from the first material; and

writing identification information on the surface of the sintered body by forming a first concave region to a depth of at least about 10 nm under the surface of the sintered body and a second concave region under the first concave region, respectively, the first concave region being formed by etching away both the first and second types of powder particles, the second concave region being formed by selectively etching away only the first type of powder particles.