Charge transfer device
A charge transfer device 1 has an P-type region, an N-type well provided to the surficial portion of the P-type region, and transfer electrodes having P-type conductivity, provided over the N-type substrate while placing an insulating film in between.
1. A method of making a charge transfer device which comprises a P-type region, an N-type well formed in the P-type region, and transfer electrodes provided over the N-type well while placing an insulating film in between, each of the transfer electrodes including a storage electrode and a barrier electrode, the storage electrode being provided as a P-type polysilicon that is formed on the insulating film, comprising:
examining a potential difference between a potential of the N-type well under the storage electrode being provided as an N-type polysilicon and a potential of the N-type well under the storage electrode being provided as a P-type polysilicon on condition that the N-type well has a first impurity concentration and the same potential is applied to the N-type polysilicon and the P-type polysilicon; and
setting an impurity concentration of the N-type well to a second impurity concentration so that a potential of the N-type well having the second impurity concentration under the storage electrode being provided as the P-type polysilicon is substantially equal to the potential of the N-type well having the first concentration under the storage electrode being provided as the N-type polysilicon.
2. The method of making a charge transfer device as claimed in claim 1 , wherein the storage electrode and the barrier electrode included in one transfer electrode are formed from a single polysilicon layer.
3. The method of making a charge transfer device as claimed in claim 1 , wherein the storage electrode and the barrier electrode included in one transfer electrode are joined to each other.
4. The method of making a charge transfer device as claimed in claim 1 , wherein the storage electrode further comprises a conductive material that includes metal formed on the P-type polysilicon.
5. The method of making a charge transfer device as claimed in claim 1 , wherein the barrier electrode is provided as a P-type polysilicon.
6. The method of making a charge transfer device as claimed in claim 1 , wherein the barrier electrode is provided as an N-type polysilicon.
7. The method of making a charge transfer device as claimed in claim 1 , wherein the barrier electrode is provided as a polysilicon and a conductive material that includes metal formed thereon.
8. The method of making a charge transfer device as claimed in claim 1 , further comprising:
an N-type diffusion region formed in an upper portion in the N-type well which is provided under the barrier electrode, N-type diffusion region having
a third impurity concentration lower than the second impurity concentration.