1. A manufacturing method of a semiconductor device comprising:
forming an oxide semiconductor layer wherein the oxide semiconductor layer comprises an oxide including crystals;
forming a first film over the oxide semiconductor layer;
forming a second film over the first film;
selectively etching the second film under a condition that the first film is less etched than the second film, so that the first film is exposed; and
selectively etching the first film under a condition that the first film is more easily etched than the oxide semiconductor layer, so that the oxide semiconductor layer is exposed.
2. The manufacturing method of a semiconductor device according to claim 1, further comprising a step of forming an insulating film over the oxide semiconductor layer, the first film, and the second film.
3. The manufacturing method of a semiconductor device according to claim 1, wherein a thickness of the first film is equal to or less than a thickness of the oxide semiconductor layer.
4. The manufacturing method of a semiconductor device according to claim 1, wherein the second film has a stacked-layer structure including a film including aluminum as a material.
5. The manufacturing method of a semiconductor device according to claim 1, wherein the first film comprises a tungsten film.
6. The manufacturing method of a semiconductor device according to claim 1, wherein the oxide semiconductor layer comprises indium, gallium, and zinc as main components.
7. The manufacturing method of a semiconductor device according to claim 1, further comprising:
forming a gate electrode layer; and
forming a gate insulating film over the gate electrode layer before forming the oxide semiconductor layer.
8. The manufacturing method of a semiconductor device according to claim 1, further comprising:
forming a gate insulating film over the oxide semiconductor layer before selectively etching the first film; and
forming a gate electrode layer over the gate insulating film to overlap with the oxide semiconductor layer.
9. The manufacturing method of a semiconductor device according to claim 1, wherein the crystals have c-axis alignment.
10. The manufacturing method of a semiconductor device according to claim 1, wherein the first film is conductive.
11. The manufacturing method of a semiconductor device according to claim 1, wherein the second film is conductive.
12. The manufacturing method of a semiconductor device according to claim 1, wherein a thickness of the oxide semiconductor layer is equal to or larger than 3 nm and equal to or smaller than 30 nm.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method of correcting print images in an electrophotographic printer wherein an image formed by a print head on a peripheral surface of a photoconductor drum is transferred and printed on a sheet of paper, characterized in that it comprises the steps of:
furnishing the print head with a standard tacho signal in the form of pulses and thereby printing on a sheet of paper a check mark for each given number of pulses of the standard tacho signal while the photoconductor drum makes one rotation;
by a camera, detecting a periodic deviation in each spacing between successive such check marks;
in response to the deviation in each spacing between the successive check marks, varying the pulse width of pulses of the standard tacho signal for each spacing between the successive check marks, thereby to provide a modified tacho signal; and
effecting printing thereafter based on the modified tacho signal.
2. A method of correcting print images in an electrophotographic printer as set forth in claim 1, characterized in that after the check marks are made constant in spacing subsequent to furnishing of the modified tacho signal, the check marks are no longer printed.
3. A method of correcting print images in an electrophotographic printer as set forth in claim 1, further including the control unit counting a number of pulses of a tacho signal detected between successive check marks and comparing the counted number of pulses of the tacho signal with a number of pulses of the tacho signal between regular dimensional check mark points.
4. A method of correcting print images in an electrophotographic printer as set forth in claim 1, including upon detecting an origin using a sensor, said pulse generator generates pulses at a fixed frequency until the photoconductor drum makes one rotation until the origin is next detected.
5. An apparatus for correcting print images in an electrophotographic printer wherein an image formed by a print head on a peripheral surface of a photoconductor drum is transferred and printed on a sheet of paper, characterized in that it comprises:
a proximity sensor for detecting a rotary position of the photoconductor drum;
a pulse generator responsive to an input signal from the proximity sensor for furnishing the print head with a tacho signal in the form of pulses while the photoconductor drum makes one rotation;
a control unit for controlling the tacho signal furnished from the pulse generator into the print head to cause a check mark to be printed for each given number of pulses of the tacho signal on the sheet of paper while the photoconductor drum makes one rotation; and
a camera for detecting a deviation in each spacing between successive such check marks printed from the photoconductor drum on the sheet of paper,
wherein said control unit is responsive to a detection value detected by the camera to vary the pulse width of pulses of the tacho signal for each spacing between the successive check marks for furnishing a modified tacho signal into the print head.
6. An apparatus for correcting print images in an electrophotographic printer as set forth in claim 5, wherein said control unit is configured such that after the check marks are made constant in spacing subsequent to furnishing of the modified tacho signal, the check marks are no longer printed.
7. An apparatus for correcting print images in an electrophotographic printer as set forth in claim 5, including upon detecting an origin using the proximity sensor, said pulse generator generating pulses at a fixed frequency until the photoconductor drum makes one rotation until the origin is next detected.
8. An apparatus for correcting print images in an electrophotographic printer as set forth in claim 5, further including the control unit counts a number of pulses of a tacho signal detected between successive check marks and compares the counted number of pulses of the tacho signal with a number of pulses of the tacho signal between regular dimensional check mark points.