CONTACT STRUCTURE AND FORMING METHOD
A method for forming a contact structure includes forming a stack of alternating active layers and insulating layers. The stack includes first and second sub stacks each with active layers separated by insulating layers. The active layers of each sub stack include an upper boundary active layer. A sub stack insulating layer is formed between the first and second sub stacks with an etching time different from the etching times of the insulating layers for a given etching process. The upper boundary active layers are accessed, after which the remainder of the active layers are accessed to create a stairstep structure of landing areas on the active layers. Interlayer conductors are formed to extend to the landing areas, the interlayer conductors separated from one another by insulating material.
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The present invention relates to high density devices. In particular, embodiments of the present invention provide methods for forming contact structure in which conductors connected to multiple active layers in a three-dimensional high density semiconductor device, such as memory device.
Three dimensional (3D) semiconductor devices are characterized by multiple layers forming a stack of alternating active layers and insulating layers. In a memory device, each of the layers can include a planar array of memory cells. For certain three-dimensionally stacked memory devices, active layers can comprise active strips of materials configured as bit lines or word lines for memory cells stacked in spaced-apart ridge-like structures. The active layers can be made from a doped (p-type or n-type) or undoped semiconductor material. In such 3D memory, memory cells can be disposed at the cross-points of the stacked bit lines or word lines and the crossing word lines or bit lines, forming a 3D memory array.
One way of connecting interlayer conductors to the active layers in the stack can be referred to as a multiple lithographic-etch process, disclosed in commonly owned U.S. Pat. No. 8,383,512, entitled Method for Making Multilayer Connection Structure, the disclosure of which is incorporated by reference. Another way of doing so, which can be referred to as a trim-etch process, is disclosed in commonly owned U.S. patent application Ser. No. 13/735,922, filed 7 Jan. 2013, entitled Method for Forming Interlayer Conductors to a Stack of Conductor Layers, the disclosure of which is incorporated by reference.
SUMMARYAn example of a method for forming a stairstep contact structure is carried out as follows. A stack of alternating active layers and insulating layers is formed by the following. A first sub stack is formed. The first stack includes N active layers separated by insulating layers, the N active layers including an upper boundary active layer. A second sub stack is formed over the first sub stack. The second sub stack includes M active layers separated by insulating layers, the M active layers including an upper boundary active layer. A first sub stack insulating layer is formed between the first and second sub stacks. The first sub stack insulating layer has an etching time different from the etching times of the insulating layers of the second sub stack for a given etching process. The upper boundary active layers are accessed. After accessing the upper boundary active layers, the remainder of the active layers of the first and second sub stacks are accessed create a stairstep structure of landing areas on the active layers of the first and second sub stacks. Interlayer conductors are formed to extend to the landing areas, the interlayer conductors separated from one another by insulating material.
An example of a method for forming a contact structure is carried out as follows. A stack of alternating active layers and insulating layers is formed. The stack includes sub stacks having upper boundary active layers, the sub stacks having insulating layer and active layer pairs below the upper boundary active layer. The insulating layer and active layer pairs constitute first layer pairs with uniform first sub stack etch times for a given etch process. The stack also includes second layer pairs, the second layer pairs including sub stack insulating layers between the sub stacks. The second layer pairs have second etch times for the given etch process different from the first sub stack etch times. A plurality of openings are etched in the stack, the openings stopping on the boundary layer active layers. Selected openings are etched to form vias that expose active layers inside each of the sub stacks. Interlayer conductors are formed (1) in the vias to extend to the active layers, and (2) in the openings that were not etched during the etching to deepen step to extend to upper boundary active layers.
An example of a stairstep contact structure includes a stack of alternating active layers and insulating layers having non-simple periods so that for the same etch process, at least one of (1) the active layers have different etch times, or (2) the insulating layers have different etch times. A stairstep structure of landing areas is on the active layers. Interlayer conductors extend to the stairstep structure of landing areas. The interlayer conductors are separated from one another by insulating material.
Other aspects and advantages of the technology are described with reference to the drawing in the detailed description and claims which follow.
A detailed description of various embodiments is described with reference to the figures. The following description will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments and methods, but that the invention may be practiced using other features, elements, methods and embodiments. Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows. Unless otherwise stated, in this application, specified relationships, such as parallel to, aligned with, having uniform characteristics, or in the same plane as, mean that the specified relationships are within limitations of manufacturing processes and within manufacturing variations. When components are described as being coupled, connected, being in contact or contacting one another, they need not be physically directly touching one another unless specifically described as such. Like elements in various embodiments are commonly referred to with like reference numerals.
Each stack of active strips is terminated at one end by semiconductor pads and the other end by a source line. Therefore, active strips 102, 103, 104, 105 terminate on the proximal end by semiconductor pads 102B, 103B, 104B, and 105B and a source line terminal 119 on the distal end of the strips passing through gate select line 127. Active strips 112, 113, 114, 115 terminate on the distal end by semiconductor pads 112B, 113B, 114B, and 115B and a source line terminal (for example, source line 128) passing through gate select line 126 near the proximal end of the strips.
In the embodiment of
Depending upon the implementation, layer 152 of memory material can comprise multilayer dielectric charge storage structures. For example, a multilayer dielectric charge storage structure includes a tunneling layer comprising a silicon oxide, a charge trapping layer comprising a silicon nitride, and a blocking layer comprising a silicon oxide. In some examples, the tunneling layer in the dielectric charge storage layer can comprise a first layer of silicon oxide less than about 2 nanometers thick, a layer of silicon nitride less than about 3 nanometers thick and a second layer of silicon oxide less than about 3 nanometers thick. In other implementations, layer 152 of memory material can comprise only a charge trapping layer without the tunneling layer or the blocking layer.
In the alternative, an anti-fuse material such as a silicon dioxide, silicon oxynitride or other silicon oxides, for example, having a thickness on the order of 1 to 5 nanometers, can be utilized. Other anti-fuse materials may be used, such as silicon nitride. For anti-fuse embodiments, active strips 102, 103, 104, 105 can be a semiconductor material with a first conductivity type (e.g. p-type). Conductors (for example, word lines or source select lines) 125-N can be a semiconductor material with a second conductivity type (e.g. n-type). For example, the active strips 102, 103, 104, 105 can be made using p-type polysilicon while the conductors 125-N can be made using relatively heavily doped n+-type polysilicon. For anti-fuse embodiments, the width of the active strips should be enough to provide room for a depletion region to support the diode operation. As a result, memory cells comprising a rectifier formed by the p-n junction with a programmable anti-fuse layer in between the anode and cathode are formed in the 3D array of cross-points between the polysilicon strips and conductor lines.
In other embodiments, different programmable resistance memory materials can be used as the memory material, including metal oxides like tungsten oxide on tungsten or doped metal oxide, and others. Some of such materials can form devices that can be programmed and erased at multiple voltages or currents, and can be implemented for operations for storing multiple bits per cell.
As can be seen in
One way of connecting interlayer conductors to the active layers in the stack can be referred to as a multiple lithographic-etch process, disclosed in commonly owned U.S. Pat. No. 8,383,512, entitled Method for Making Multilayer Connection Structure, the disclosure of which is incorporated by reference. Another way of doing so, which can be referred to as a trim-etch process, is disclosed in commonly owned U.S. patent application Ser. No. 13/735,922, filed 7 Jan. 2013, entitled Method for Forming Interlayer Conductors to a Stack of Conductor Layers, the disclosure of which is incorporated by reference.
Stack 200 is made of active layers 202 having common etching characteristics and insulating layers 204 having common etching characteristics. In this example, active layers 202 are made of the same conductive material and have the same nominal thickness. Likewise, insulating layers 204 are made of the same insulating material with the same nominal thickness. Therefore each pair of insulating layer and active layer will have a uniform etch time for a given etch process. This arrangement of the pairs of insulating and active layers can be referred to as stacked layers with a simple period.
As described herein, structures are provided that have non-simple periods, in which the active and/or insulating layers have different etch times, typically because the active and/or insulating layers are made of different materials with different etching characteristics, or different thicknesses, or a combination of different materials and different thicknesses for the active and/or insulating layers.
With that as a background, an example of a contact structure 250 in which the stack of active and insulating layers do not have a simple period is shown in
Sub stack insulating layer 256 and the underlying, adjacent active layer 202.1 constitute a second layer pair 262 having a second etch time for the given etch process. Sub stack insulating layer 260 and the underlying, adjacent active layer 202.1 constitute a third layer pair 264, also having the second etch time for the given etch process. Sub stack insulating layer 258 and the underlying, adjacent active layer 202.1 constitute a fourth layer pair 266 having a fourth etch time different from any of the first through third etch times. Etch times for the different layer pairs 254, 262, 264, 266 can be made the same or different using a wide range of different materials having different etch rates together with the same or different thickness of the insulating and active layers.
Contact structure 250 also includes an upper insulating layer 268 overlying active layer 202.1 of stack 252.1 and a lower insulating layer 270 underlying active layer 202.4 of sub stack 252.4; both can made of silicon dioxide. A set of interlayer conductors 272 extend through upper insulating layer 268 to make contact with each active layer 202 of each sub stack 252 in a stairstep fashion. Each interlayer conductor 272 is surrounded by sidewall insulation 274, which can be made of silicon nitride.
A controller implemented, in this example, using bias arrangement state machine 969 controls the application of bias arrangement supply voltage generated or provided through the voltage supply or supplies in block 968, such as read, erase, program, erase verify and program verify voltages. The controller can be implemented using special-purpose logic circuitry as known in the art. In alternative embodiments, the controller comprises a general-purpose processor, which may be implemented on the same integrated circuit, which executes a computer program to control the operations of the device. In yet other embodiments, a combination of special-purpose logic circuitry and a general-purpose processor may be utilized for implementation of the controller.
In various embodiments, a 3D array of devices, for example, memory devices, is provided. The 3D array of devices includes a plurality of patterned layers of semiconductor material. Each patterned layer includes parallel strips of semiconductor material with one of their ends connected to a first side of a semiconductor pad. The semiconductor pads connected to the plurality of patterned layers are disposed in a stack. Each of the semiconductor pads includes a landing area for an interlayer conductor connected to an overlying interconnect conductor aligned along the parallel strips of semiconductor material. The interlayer conductors are arranged in rows in a top view and disposed in a via structure surrounded by an insulating material. Each of the rows is aligned along an X direction, parallel to the first side. In various embodiments, the interlayer conductors can be partially offset in a Y direction, perpendicular to the X direction. In various embodiments, the landing areas can be formed in various types of stair step arrangements, such as illustrated in
While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.
Claims
1. A method for forming a stairstep contact structure comprising:
- forming a stack of alternating active layers and insulating layers, comprising:
- forming a first sub stack comprising N active layers separated by insulating layers, the N active layers comprising an upper boundary active layer;
- forming a second sub stack over the first sub stack, the second sub stack comprising M active layers separated by insulating layers, the M active layers comprising an upper boundary active layer; and
- forming a first sub stack insulating layer between the first and second sub stacks, the first sub stack insulating layer having an etching time different from the etching times of the insulating layers of the second sub stack for a given etching process;
- accessing the upper boundary active layers;
- following the upper boundary active layers accessing step, accessing the remainder of the active layers of the first and second sub stacks create a stairstep structure of landing areas on the active layers of the first and second sub stacks; and
- forming interlayer conductors extending to the landing areas, the interlayer conductors separated from one another by insulating material.
2. The method according to claim 1, wherein the stack forming step comprises:
- forming a stack including first, second, third and fourth sub stacks;
- forming a second sub stack insulating layer between the second and third sub stacks; and
- forming a third sub stack insulating layer between the third and fourth sub stacks.
3. The method according to claim 2, wherein each of the first, second, third and fourth sub stacks comprises the same number of active layers.
4. The method according to claim 3, wherein:
- the insulating layers of the first, second, third and fourth sub stacks have substantially equal thicknesses and are made of a first insulating material;
- the first, second and third sub stack insulating layers are made of a second, third and fourth insulating materials; and
- at least two of the first, second, third and fourth insulating materials are of different insulating materials having different etching characteristics.
5. The method according to claim 3, wherein:
- the insulating layers of each of the first, second, third and fourth sub stacks have substantially equal etching times for a given etch process; and
- each of the first, second and third sub stack insulating layers having an etching time different from the etching times of the insulating layers of the first, second, third and fourth sub stacks for the given etch process.
6. The method according to claim 5, where the etching times for the first and third sub stack insulating layers are substantially equal for the given etch process.
7. The method according to claim 1, wherein:
- the upper boundary active layers accessing step comprises: in one or more etching steps, exposing a section of the upper boundary active layers of selected ones of the sub stacks; and
- the remainder of the active layers accessing step comprising: etching the exposed sections of the upper boundary active layers to expose active layers below the upper boundary active layers of the selected ones of the sub stacks; covering the exposed active layers, including upper boundary active layers, with a material; and etching vias through the material to expose active layers of the selected ones of the sub stacks.
8. The method according to claim 7, wherein:
- the one or more etching steps exposing sections of the upper boundary active layers creates a stairstep structure of said sections; and
- the exposed sections etching step is carried out to create a stairstep structure of interlayer conductor contact areas on said active layers.
9. A method for forming a contact structure, comprising
- forming a stack of alternating active layers and insulating layers, the stack including sub stacks having upper boundary active layers, the sub stacks having insulating layer and active layer pairs below the upper boundary active layer, said insulating layer and active layer pairs constituting first layer pairs, the first layer pairs have uniform first sub stack etch times for a given etch process, the stack also including second layer pairs, the second layer pairs including sub stack insulating layers between the sub stacks, the second layer pairs have second etch times for the given etch process different from the first sub stack etch times;
- in one or more etching steps, etching a plurality of openings in the stack, the openings stopping on the boundary layer active layers;
- etching to deepen selected openings to form vias that expose active layers inside each of the sub stacks; and
- forming interlayer conductors: in the vias, said interlayer conductors extending to the active layers; and in the openings that were not etched during the etching to deepen step, said interlayer conductors extending to upper boundary active layers.
10. The method according to claim 9, wherein the stack forming step comprises forming a stack including first, second and third sub stacks.
11. The method according to claim 10, wherein each of the first, second and third sub stacks comprises the same number of first layer pairs.
12. The method according to claim 10, wherein:
- the insulating layers of the first, second and third sub stacks are made of a first insulating material;
- the sub stack insulating layer between the first and second sub stacks is made of a second insulating material; and
- the sub stack insulating layer between the second and third sub stacks is made of a third insulating material, at least two of the first, second and third insulating materials being different insulating materials having different etching characteristics.
13. The method according to claim 9, wherein each sub stack comprises at least three first layer pairs.
14. The method according to claim 9, further comprising:
- forming sidewall insulation in the vias; and
- forming sidewall insulation in the openings that were not etched during the etching to deepen step.
15. The method according to claim 14, wherein the steps of forming interlayer conductors in the vias and in the opening that was not etched during the etching to deepen step are carried out substantially simultaneously.
16. A stairstep contact structure comprising:
- a stack of alternating active layers and insulating layers having non-simple periods;
- a stairstep structure of landing areas on the active layers; and
- interlayer conductors extending to the landing areas, the interlayer conductors separated from one another by insulating material.
17. The stairstep contact structure according to claim 16, wherein the stack of alternating active layers and insulating layers comprises:
- a first sub stack comprising N active layers separated by insulating layers, the N active layers comprising an upper boundary active layer;
- a second sub stack over the first sub stack, the second sub stack comprising M active layers separated by insulating layers, the M active layers comprising an upper boundary active layer; and
- a first sub stack insulating layer between the first and second sub stacks, the first sub stack insulating layer having an etching time different from the etching times of the insulating layers of the second sub stack for a given etching process.
18. The stairstep contact structure according to claim 17, wherein the stack comprises:
- third and fourth sub stacks;
- a second sub stack insulating layer between the second and third sub stacks;
- a third sub stack insulating layer between the third and fourth sub stacks; and wherein:
- the insulating layers of the first, second, third and fourth sub stacks have substantially equal thicknesses and are made of a first insulating material;
- the first, second and third sub stack insulating layers are made of a second, third and fourth insulating materials; and
- at least two of the first, second, third and fourth insulating materials are of different insulating materials having different etching characteristics.
19. The stairstep contact structure according to claim 18, wherein:
- the insulating layers of each of the first, second, third and fourth sub stacks have substantially equal etching times for a given etch process; and
- each of the first, second and third sub stack insulating layers having an etching time different from the etching times of the insulating layers of the first, second, third and fourth sub stacks for the given etch process.
20. The stairstep contact structure according to claim 19, where the etching times for the first and third sub stack insulating layers are substantially equal for the given etch process.
21. The stairstep contact structure according to claim 16, wherein for the same etch process at least one of (1) the active layers have different etch times, or (2) the insulating layers have different etch times.
Type: Application
Filed: Sep 26, 2013
Publication Date: Mar 26, 2015
Applicant: Macronix International Co., Ltd. (Hsinchu)
Inventor: Shih-Hung Chen (Jhudong Township)
Application Number: 14/038,526
International Classification: H01L 21/768 (20060101); H01L 23/528 (20060101);