1. A method for forming a semiconductor structure, comprising:
providing a substrate;
forming a positive photoresist layer over the substrate;
forming a negative photoresist layer on the positive photoresist layer;
performing an exposure process to form a first exposure region in the positive photoresist layer and a second exposure region in the negative photoresist layer,
wherein the second exposure region having a second width is located on the first exposure region having a first width, and the first exposure region and the second exposure region have a same central axis according to the exposure process, and wherein the first width is less than the second width;
performing a negative-tone development process to remove portions of the negative photoresist layer outside of the second exposure region to form one or more first openings to expose the positive photoresist layer;
etching the positive photoresist layer along the one or more first openings to form one or more second openings through both the negative photoresist layer and the positive photoresist layer;
removing the second exposure region of the negative photoresist layer; and
performing a positive-tone development process to remove portions of the positive photoresist layer in the first exposure region to form a double patterned positive photoresist layer.
2. The method according to claim 1, wherein the exposure process provides an exposure energy having a first intensity threshold and a second intensity threshold, the first intensity threshold being greater than the second intensity threshold.
3. The method according to claim 2, wherein: the first exposure region is formed in response to the exposure energy greater than or equal to the first intensity threshold, the second exposure region is formed in response to the exposure energy greater than or equal to the second intensity threshold, and the second exposure region is wider than the first exposure region.
4. The method according to claim 2, wherein the positive photoresist layer comprises a photo acid generator and a resin, the photo acid generator generating a photo acid when the exposure energy is greater than or equal to the first intensity threshold, and the photo acid reacting with the resin in the positive photoresist layer to form the first exposure region.
5. The method according to claim 1, wherein the negative photoresist layer includes a radiation-induced cross-linking negative resist, a radiation-induced polymerization negative resist, or a radiation-induced polarity change negative resist.
6. The method according to claim 1, wherein the second width of the second exposure region is about 1.5 times to about 4.5 times of the first width of the first exposure region.
7. The method according to claim 1, wherein the negative-tone development process uses a developer comprising an organic solution or an aqueous alkali solution, and the second exposure region of the negative photoresist layer is insoluble in the developer and the portions of the negative photoresist layer outside of the second exposure region are soluble in the developer.
8. The method according to claim 1, wherein the positive-tone development process uses a developer comprising an aqueous alkali solution, and the first exposure region of the positive photoresist layer is soluble in the developer and portions of the positive photoresist layer outside of the first exposure region are insoluble in the developer.
9. The method according to claim 1, wherein etching the positive photoresist layer along the one or more first openings comprises a reactive ion etching process, the reactive ion etching process using oxygen as an etching gas.
10. The method according to claim 1, wherein removing the remaining negative photoresist layer and etching the positive photoresist layer along the one or more first openings are performed in a same process.
11. The method according to claim 1, further comprising: performing a post exposure baking process to the substrate after the exposure process.
12. The method according to claim 1, wherein each of the positive photoresist layer and the negative photoresist layer is formed by a spin-on process comprising: forming the positive photoresist layer over the substrate; performing a first post application baking process to bake the positive photoresist layer; forming the negative photoresist layer on the positive photoresist layer; and performing a second post application baking process to bake the negative photoresist layer.
13. A semiconductor structure, comprising:
a substrate; and
a double patterned positive photoresist layer disposed over the substrate, wherein the double patterned positive photoresist layer is formed by:
forming a positive photoresist layer over the substrate;
forming a negative photoresist layer on the positive photoresist layer;
performing an exposure process to form a first exposure region in the positive photoresist layer and a second exposure region in the negative photoresist layer, wherein the second exposure region having a second width is located on the first exposure region having a first width, and the first exposure region and the second exposure region have a same central axis according to the exposure process, and wherein the first width is less than the second width;
performing a negative-tone development process to remove portions of the negative photoresist layer outside of the second exposure region to form one or more first openings to expose the positive photoresist layer;
etching the positive photoresist layer along the one or more first openings to form one or more second openings through both the negative photoresist layer and the positive photoresist layer;
removing the second exposure region of the negative photoresist layer; and
performing a positive-tone development process to remove portions of the positive photoresist layer in the first exposure region to form the double patterned positive photoresist layer.
14. The structure according to claim 13, wherein the exposure process provides an exposure energy having a first intensity threshold and a second intensity threshold, the first intensity threshold being greater than the second intensity threshold.
15. The structure according to claim 14, wherein:
the first exposure region is formed in response to the exposure energy greater than or equal to the first intensity threshold, the second exposure region is formed in response to the exposure energy greater than or equal to the second intensity threshold.
16. The structure according to claim 13, wherein an anti-reflection coating layer is disposed between the substrate and the positive photoresist layer.
17. The structure according to claim 16, wherein the anti-reflection coating layer is an organic anti-reflection coating layer or an inorganic anti-reflection coating layer.
18. The structure according to claim 16, wherein the anti-reflection coating layer has a thickness within a range from about 100 \u212b to about 1500 \u212b.
19. The structure according to claim 13, wherein the negative photoresist layer has a thickness in a range from about 500 \u212b to about 3000 \u212b, and the positive photoresist layer has a thickness in a range from about 500 \u212b to about 3000 \u212b.
20. The structure according to claim 13, further comprising a target layer disposed between the substrate and the positive photoresist layer.
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 distributed router, comprising:
a plurality of line connection units;
a main processor disposed to construct and manage a routing table, to receive changes of routing information from adjacent routers, update the routing table, and to broadcast changes of routing information received through internal InterProcessor Communication paths within the distributed router;
a switching unit coupled to switch transmission of packets between the line connection units and the main processor;
a plurality of forwarding tables positioned in different corresponding ones of the plurality of line connection units, to copy, store and manage parts of the routing table; and
a plurality of forwarding processors positioned in different corresponding ones of the plurality of line connection units, to receive the changes of routing information broadcast by the main processor through the internal InterProcessor Communication paths of the distributed router, to update different corresponding ones of the forwarding tables, to ascertain a source address of a packet received, to ascertain an output direction of a packet having a source address of an external router by looking-up forwarding information in corresponding ones of the forwarding tables for the packet received from the external router, and transmitting the packet to the output direction ascertained, to determine whether an output direction of a packet having a source address of the switching unit is toward an external router or toward the switching unit by looking-up the forwarding information in the corresponding forwarding table for the packet, to transmit the packet to the external router when the determined output direction of the packet is toward the external router, and to discard the packet when the determined output direction of transmission of the packet is toward the switching unit.
2. The distributed router of claim 1, wherein the main processor comprises:
a plurality of inputoutput interfaces handling packets transmitted and received to and from the switching unit;
a switch interface buffering packets transmitted and received via the inputoutput interfaces, and interfacing with the switching unit; and
a routing table lookup and management unit receiving packets from the inputoutput interfaces through the switch interface, and transmitting packets received to the inputoutput interfaces in conformance with routing information stored in the routing table, and receiving the changes of routing information from external routers, updating the routing information with the changes of routing information, and transmitting updated routing information to the forwarding processors through the internal InterProcessor Communication paths of the distributed router.
3. The distributed router of claim 1, wherein each of the forwarding processors comprises:
an Internet Protocol packet receiving unit for extracting an IP header field from each incoming packet;
an IP header analyzing unit extracting an IP address required for lookup control from each IP header received from the Internet Protocol packet receiving unit;
a lookup table storing address indices for the forwarding tables where information on each packet is stored;
a lookup control unit latching the address of the forwarding table intended for reference from the lookup table using the IP address extracted by the IP header analyzing unit, reading forwarding information from the forwarding table, when a packet is received from the switching unit and an output direction of the packet is toward an external router, making a determination to transmit the packet to the external router, when a packet is received from the switching unit and the output direction of the packet is toward the switching unit, making an determination to discard the packet, and when a packet is received from an external router, transmitting the packet to an output address associated with the packet;
an IP header changing unit changing information of the IP header of each packet based on the forwarding information obtained by the lookup control unit; and
an IP packet transmitting unit transmitting the stored packets according to the changes in information for the header of each packet to the external router.
4. A distributed router, comprising:
a plurality of line connection units;
a plurality of main processors positioned in corresponding different ones of the plurality of line connection units, to construct and manage a routing table, receive changes in routing information from adjacent routers, update the routing table, and broadcast changes of routing information through IPC paths of the distributed router;
a switching unit switching packets received from the line connection units to corresponding ones of the line connection units to which these packets are transmitted;
a plurality of forwarding tables positioned in corresponding different ones of the plurality of line connection units, to copy, store and manage parts of the routing table; and
a plurality of forwarding processors positioned in corresponding different ones of the plurality of line connection units, to ascertain an output direction of a packet received from an external router by making a lookup in a corresponding one of the forwarding tables and transmit the packet received to the output direction ascertained, to determine whether an output direction of a packet received from the switching unit is toward an external router or the switching unit by making a search of forwarding information stored in the corresponding one of the forwarding tables for the packet, transmit the packet to the external router when the output direction is toward the external router, and discard the packet when the output direction is toward the switching unit, and update the forward table in response to reception of changes in routing information broadcast by the main processor through the internal IPC paths of the distributed router.
5. A ping-pong preventing method using a distributed router, comprising:
a step 1 in the distributed router having a switch unit connecting a main processor and a plurality of line connection units, of the main processor updating a routing table, and transmitting changes of routing information to respective line connection units through internal paths of the distributed router, when the main processor receives changes of routing information from an adjacent router;
a step 2 of a forwarding processor positioned in each of the line connection units updating a forwarding table in response to reception of the changes of routing information broadcast from the main processor through the internal paths of the distributed router; and
a step 3 of the forwarding processor receiving a packet from one of an external router and the switching unit, ascertaining input and output directions of the packet, transmitting the packet received from an external router to the switching unit, discarding the packet received from the switching unit when the output direction of the packet is toward the switching unit, and transmitting the packet received from the switching unit when the output direction of the packet is not toward the switching unit.
6. The method of claim 5, wherein step 1 of updating the routing table, comprises:
a step 1-1 with the main processor updating the routing table when the main processor receives the changes of routing information;
a step 1-2 with the main processor adjusting changes in a routing path to fit the forwarding table of each of the line connection units; and
a step 1-3 with the main processor transmitting the changes of the routing information to the respective line connection units through the internal paths of the distributed router.
7. The method of claim 5, wherein step 3 of the forwarding processor ascertaining input and output ports, comprises:
a step 3-1 with the forwarding processor ascertaining the output direction of the packet received from an external router by searching the forwarding table and transmitting the packet according to the output port ascertained;
a step 3-2 with the forwarding processor ascertaining the output direction of the packet received from the switching unit by searching the forwarding table, and transmitting the packet when the output direction is toward an external router; and
a step 3-3 with the forwarding processor ascertaining the output direction of the packet received from the switching unit by searching the forwarding table, and discarding the packet when the output direction is toward the switching unit.
8. The method of claim 5, wherein the forwarding processor receiving a packet from one of an external router and the switching unit, and ascertaining input and output directions of the packet in step 3 comprises:
a step of the forwarding processor extracting an IP header from an incoming IP packet;
a step of the forwarding processor extracting an IP address for lookup control from the IP header; and
a step of the forwarding processor ascertaining the output direction by using the IP address to make a search of forwarding table using the IP address.
9. A router with a distributed architecture, comprised of:
a main processor constructing and managing a routing table, receiving changes of routing information from adjacent routers, updating the routing table, and broadcasting changes of routing information received through internal paths within the distributed router;
a plurality of line connection units;
a switching unit directing transmission of packets between said main processor and said line connection units; each of said line connection units comprising:
a forwarding table storing a copy of parts of said routing table, and
a forwarding processor making a discontinuance of transmission of any packet received by a corresponding one of said line connection units from said switching unit and designated by a destination address to be subsequently forwarded to said switching unit, determining source addresses of received packets, transmitting any packet having a source address of said switching unit to a destination address associated with the packet if the destination address does not correspond to said switching unit, and transmitting any packet having a source address of an external router to a destination address associated with the packet.
10. The router of claim 9, with said forwarding processor comprised of:
when the packet has a source address of said switching unit and said destination address of the packet indicates that an output direction of the packet is toward an external router, transmitting the packet to the external router,
when the packet has a source address of said switching unit and said destination address of the packet indicates that an output direction of the packet is toward said switching unit, making said discontinuance, and
when the packet has a source address of an external router, transmitting the packet to a destination address associated with the packet.