The present invention relates to a flatness measuring equipment, more precisely relates to a flatness measuring equipment capable of highly precisely measuring flatness of a surface of a large-sized planar member, e.g., an abrasive plate of an abrasive machine, which abrades silicon wafers.
In an abrasive machine, a planar member to be abraded, e.g., a silicon wafer, is mounted on an abrasive plate, whose surface must be a highly flat face. Since the flatness of the surface of the abrasive plate directly influences abrading accuracy of the silicon wafer, the surface of the abrasive plate must have high flatness. When the abrasive plate is manufactured, the flatness of the surface is precisely measured to have predetermined flatness.
A conventional method of measuring flatness of an abrasive plate is shown in FIG. 4. A plurality of dial gauges 12 are provided to a bar member 10 with predetermined separations. Steel balls 13 are respectively fixed, on a bottom face of the bar member 10, at both ends of the bar member 10. With this structure, the bar member 10 is supported by the steel balls 13. Projected length (nearly equal to diameter) of the steel balls 13 are designed to be equal to a standard projected length of sensing needles of the dial gauges 12.
The flatness of the surface of the abrasive plate 14 is measured by the steps of: mounting the measuring equipment on a flat standard base, which is made of a ceramic, etc.; resetting the dial gauges 12 zero; mounting the measuring equipment on the abrasive plate 14 to be measured; and measuring the flatness of the abrasive plate 14 by reading measured values of the dial gauges 12. Note that, the flatness can be measured by a laser displacement sensor, a contact displacement sensor, etc. instead of the dial gauges 12.
In the conventional methods, the rigid bar member 10 is spanned over the planar member to be measured, and the bar member 10 is used as a standard level means for measuring the flatness of the planar member. However, the flat standard base for adjusting the dial gauges, etc. usually has about 1 xcexcm of error in level, and the bar member 10 for setting the standard level and the dial gauges, etc. also have errors about 1 xcexcm. Thus, errors about 1-2 xcexcm cannot be avoided in the conventional flatness measuring equipments.
These days, in the field of manufacturing semiconductor devices, a required accuracy of abrading silicon wafers is 0.2 xcexcm. In this case, flatness of silicon wafers cannot be measured by the conventional flatness measuring equipments.
Further, large-sized abrasive machines, which include, for example, 5 m-abrasive plates, are used now. Thus, large-sized flatness measuring equipments are required. In the large-sized flatness measuring equipment, length of the bar member must be longer and longer, so deformation of the bar member, which is caused by its own weight, cannot be ignored. Further, a large-sized flat standard base, which must be highly precisely manufactured, is required. Namely, it is impossible to highly precisely measure flatness of the large-sized planar member by the conventional flatness measuring equipments.
An object of the present invention is to provide a flatness measuring equipment, which is capable of highly precisely measuring flatness of a surface of a large-sized planar member.
Namely, the flatness measuring equipment of the present invention comprises:
an elongated member being provided above and parallel to a surface of a planar member to be measured;
a movable member being provided to the elongated member and capable of moving along the elongated member;
means for measuring distance between the movable member and the surface of the planar member, the measuring means being provided to the movable member so as to measure the distance at positions where the movable member is located;
means for emitting a laser beam, at a fixed level, toward the movable member on the elongated member; and
means for detecting a variation of a level of the movable member with respect of the fixed level of the laser beam.
With this structure, the true distance between the standard level and the surface of the planar member can be known by detecting the variation of the level of the movable member, which is moved along the elongated member. Even if the elongated member is long and deformed by its own weight, said true distance can be known, so that highly rigidity is not required to the elongated member and it can be manufactured easily.
In the equipment, the detecting means may be a light receiving sensor. And, the light receiving sensor may be a plurality of photo sensitive cells or a CCD camera.
In the equipment, the measuring means may be a non-contact distance sensor.