A method for forming a stair-step structure in a substrate is provided. An organic mask is formed over the substrate. A hardmask with a top layer and sidewall layer is formed over the organic mask. The sidewall layer of the hard mask is removed while leaving the top layer of the hardmask. The organic mask is trimmed. The hardmask is removed. The substrate is etched. The forming the hardmask, removing the sidewall layer, trimming the organic mask, and etching the substrate are repeated a plurality of times.
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1. A method for forming a stair-step structure in a substrate, comprising:
a) forming an organic mask over the substrate;
b) forming a hardmask with a top layer and sidewall layer over the organic mask;
c) removing the sidewall layer of the hard mask while leaving the top layer of the hardmask;
d) trimming the organic mask;
e) removing the hardmask;
f) etching the substrate through the organic mask; and
g) repeating steps ab-f a plurality of times to form the stair-step structure.
14. A method for making a three dimensional memory structure, comprising:
a) providing memory stack comprising a plurality of layers, wherein each layer comprises at least two sublayers;
b) forming an organic mask over the memory stack;
c) forming a hardmask with a top layer and sidewall layer over the organic mask;
d) removing the sidewall layer of the hard mask while leaving the top layer of the hardmask;
e) trimming the organic mask;
f) removing the hardmask;
g) etching the memory stack through the organic mask, so that portions of the memory stack not covered by the organic mask are etched a depth of the thickness of a layer of the plurality of layers; and
h) repeating steps bc-g a plurality of times.
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This application is a continuation-in-part and claims priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/968,210 entitled “Method For Forming Stair-Step Structures,” by Fu et al, filed Dec. 14, 2010, now U.S. Pat. No. 8,329,051, which is hereby incorporated by reference.
The present invention relates to the formation of semiconductor devices. More specifically, the invention relates to the formation of stair-step semiconductor devices.
During semiconductor wafer processing, stair-step features are sometimes required. For example, in 3D flash memory devices, multiple cells are stacked up together in chain format to save space and increase packing density. The stair-step structure allows electrical contact with every gate layer.
To achieve the foregoing and in accordance with the purpose of the present invention, a method for forming a stair-step structure in a substrate is provided. An organic mask is formed over the substrate. A hardmask with a top layer and sidewall layer is formed over the organic mask. The sidewall layer of the hard mask is removed while leaving the top layer of the hardmask. The organic mask is trimmed. The hardmask is removed. The substrate is etched. The forming the hardmask, removing the sidewall layer, trimming the organic mask, removing the hardmask, and etching the substrate are repeated a plurality of times.
In another manifestation of the invention a method for making a three dimensional memory structure is provided. A memory stack is provided comprising a plurality of layers, wherein each layer comprises at least two sublayers. An organic mask is formed over the memory stack. A hardmask is formed with a top layer and sidewall layer over the organic mask. The sidewall layer of the hard mask is removed while leaving the top layer of the hardmask. The organic mask is trimmed. The hardmask is removed. The memory stack is etched, so that portions of the memory stack not covered by the organic mask are etched a depth of the thickness of a layer of the plurality of layers. The forming the hardmask, removing the sidewall layer, trimming the organic mask, removing the hardmask, and etching the substrate are repeated a plurality of times.
In another manifestation of the invention, an apparatus for etching stair-step structures in a substrate is provided. A plasma processing chamber is provided, comprising a chamber wall forming a plasma processing chamber enclosure, a chuck for supporting and chucking a substrate within the plasma processing chamber enclosure, a pressure regulator for regulating the pressure in the plasma processing chamber enclosure, at least one electrode or coil for providing power to the plasma processing chamber enclosure for sustaining a plasma, a gas inlet for providing gas into the plasma processing chamber enclosure, and a gas outlet for exhausting gas from the plasma processing chamber enclosure. A gas source is in fluid connection with the gas inlet and comprises a hardmask deposition gas source, a hardmask sidewall removal gas source, an organic mask trimming gas source, and a substrate etching gas source. A controller is controllably connected to the gas source, the chuck, and the at least one electrode or coil. The controller comprises at least one processor and non-transitory computer readable media. The computer readable media comprises computer readable code for chucking a substrate with an organic mask to the chuck, computer readable code for forming a hardmask over the organic mask, comprising computer readable code for flowing a hardmask deposition gas from the hardmask deposition gas source into the plasma processing chamber, computer readable code for forming a plasma from the hardmask deposition gas, computer readable code for providing a bias voltage, and computer readable code for stopping the hardmask deposition gas, computer readable code for removing a sidewall layer of the hardmask while leaving the top layer of the hardmask, comprising computer readable code for flowing a hardmask sidewall removal gas from the hardmask sidewall removal gas source into the plasma processing chamber, computer readable code for forming a plasma from the hardmask sidewall removal gas, and computer readable code for stopping the hardmask sidewall removal gas, computer readable code for trimming the organic mask, comprising computer readable code for flowing an organic mask trimming gas from the organic mask trimming gas source into the plasma processing chamber, computer readable code for forming a plasma from the organic mask trimming gas, and computer readable code for stopping the organic mask trimming gas, computer readable code for removing the hardmask, comprising computer readable code for flowing a hardmask removal gas from the hardmask removal gas source into the plasma processing chamber, computer readable code for forming a plasma from the hardmask removal gas, and computer readable code for stopping the hardmask removal gas, computer readable code for etching the substrate, comprising computer readable code for flowing a substrate etching gas from the substrate etching gas source into the plasma processing chamber, computer readable code for forming a plasma from the substrate etching gas, and computer readable code for stopping the substrate etching gas, and computer readable code for repeating the forming the hardmask, removing the sidewall layer, trimming the organic mask, and etching the substrate a plurality of times.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
In the formation of stair-step structures a trim and etch scheme is utilized. Basically, one stair will be etched first then a mask is trimmed to pull back the mask without affecting the substrate. Then another stair is etched, where the trim/etch process is cycled a plurality of times. One difficulty with such a scheme is that during the lateral trim of the mask, the height of the mask is also reduced. Such a reduction may be more than the lateral trim of the mask. Such a reduction places a limit on the number of steps that may be etched before requiring the formation of a new mask.
To facilitate understanding,
In an example of an implementation of the invention, a stair-step memory array is etched. In such a memory array, memory stacks are formed over a wafer.
The wafer 208 may be placed in a processing tool to perform subsequent steps.
The TCP power controller 350 sets a set point for TCP power supply 351 configured to supply a radio frequency signal at 13.56 MHz, tuned by a TCP match network 352, to a TCP coil 353 located near the plasma chamber 304. An RF transparent window 354 is provided to separate TCP coil 353 from plasma chamber 304, while allowing energy to pass from TCP coil 353 to plasma chamber 304.
The bias power controller 355 sets a set point for bias power supply 356 configured to supply an RF signal, tuned by bias match network 357, to a chuck electrode 308 located within the plasma chamber 304 creating a direct current (DC) bias above electrode 308 which is adapted to receive a wafer 306, such as a semi-conductor wafer work piece, being processed.
A gas supply mechanism or gas source 310 includes a source or sources of gas or gases 316 attached via a gas manifold 317 to supply the proper chemistry required for the process to the interior of the plasma chamber 304. A gas exhaust mechanism 318 includes a pressure control valve 319 and exhaust pump 320 and removes particles from within the plasma chamber 304 and maintains a particular pressure within plasma chamber 304.
A temperature controller 380 controls the temperature of a cooling recirculation system provided within the chuck electrode 308 by controlling a cooling power supply 384. The plasma processing system also includes electronic control circuitry 370. The plasma processing system may also have an end point detector. An example of such an inductively coupled system is the Kiyo built by Lam Research Corporation of Fremont, Calif., which is used to etch silicon, polysilicon and conductive layers, in addition to dielectric and organic materials. In other embodiments of the invention, a capacitively coupled system may be used.
CPU 422 is also coupled to a variety of input/output devices, such as display 404, keyboard 410, mouse 412, and speakers 430. In general, an input/output device may be any of: video displays, track balls, mice, keyboards, microphones, touch-sensitive displays, transducer card readers, magnetic or paper tape readers, tablets, styluses, voice or handwriting recognizers, biometrics readers, or other computers. CPU 422 optionally may be coupled to another computer or telecommunications network using network interface 440. With such a network interface, it is contemplated that the CPU might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments of the present invention may execute solely upon CPU 422 or may execute over a network such as the Internet in conjunction with a remote CPU that shares a portion of the processing.
In addition, embodiments of the present invention further relate to computer storage products with a computer-readable medium that have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of tangible and non-transient computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as application-specific integrated circuits (ASICs), programmable logic devices (PLDs) and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor.
In this example, a first stair-step etch is performed before the hardmask is applied, forming a stair-step 224, as shown in
The sidewall layer of the hardmask is removed while leaving the top layer of the hardmask (step 112).
The organic mask is trimmed (step 116).
The hardmask is removed (step 117).
A descum process is provided (step 118). The descum process removes the foot from the photoresist.
A stair-step is etched using the organic mask as a mask (step 120).
In another embodiment the hardmask layer is etched away simultaneously instead of in a previous step. In such an embodiment, there is little etch selectivity between the hardmask layer and that the memory stack 204, since it would be desirable to quickly etch away the part of the hard mask over the stair-step.
Preferably, the etch selectively etches the memory stack 204 with respect to the organic mask, so that minimal organic mask is etched away. An example of a recipe for etching the stair-step in a memory stack with a silicon oxide based layer used a C4F6 and O2 based etch gas. Because many different substrates may be etched, many different chemistries may be used for the etch process.
It is determined that additional stair-steps are needed (step 124), so a new hardmask layer is formed over the organic mask (step 108).
It is determined that additional stair-steps are needed (step 124), so a new hardmask layer is formed over the organic mask (step 108).
If no additional stair-steps are needed (step 124), the cyclical process is complete. Additional steps may be provided for further processing. For example, the organic mask 220 may be stripped, as shown in
Because the process allows the organic mask to be trimmed without thinning the organic mask, a large number of stair-steps may be provided. Preferably, the cycle is repeated at least 3 times, so that at least five stair-steps are provided. More preferably, at least 8 stair-steps may be provided with a single organic mask forming process. More preferably, more than twenty stair-steps may be provided using a single organic mask process. The stair-steps may be formed in one or more directions in other embodiments. In one example, a stair-step structure was created with thirty-two steps.
In other embodiments, the substrate may be made of other materials, to be etched. The substrate may be a solid piece of a single material. In a preferred embodiment, the substrate comprises a plurality of layers where each layer comprises at least two sublayers used to form the memory stacks of the substrate. In one example, at least one sublayer is silicon, such as polysilicon. In another example, each layer comprises three sublayers.
While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and various substitute equivalents as fall within the true spirit and scope of the present invention.
Qin, Ce, Fu, Qian, Yu, Hyun-Yong
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