U.S. patent application number 15/465642 was filed with the patent office on 2018-09-27 for method to remove sidewall damage after mtj etching.
The applicant listed for this patent is Headway Technologies, Inc.. Invention is credited to Jesmin Haq, Zhongjian Teng, Tom Zhong.
Application Number | 20180277751 15/465642 |
Document ID | / |
Family ID | 61691587 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180277751 |
Kind Code |
A1 |
Teng; Zhongjian ; et
al. |
September 27, 2018 |
Method to Remove Sidewall Damage After MTJ Etching
Abstract
A method for etching a magnetic tunneling junction (MTJ)
structure is described. A stack of MTJ layers on a bottom electrode
on a wafer is provided. A hard mask layer is provided on the MTJ
stack. The hard mask layer is patterned to form a hard mask. The
MTJ stack is patterned to form a MTJ device wherein sidewall damage
is formed on sidewalls of the MTJ device. The sidewall damage is
removed by applying a CMP slurry which physically attacks and
removes the sidewall damage on the MTJ device.
Inventors: |
Teng; Zhongjian; (Santa
Clara, CA) ; Zhong; Tom; (Saratoga, CA) ; Haq;
Jesmin; (Milpitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Headway Technologies, Inc. |
Milpitas |
CA |
US |
|
|
Family ID: |
61691587 |
Appl. No.: |
15/465642 |
Filed: |
March 22, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/3909 20130101;
H01L 21/02096 20130101; H01L 43/12 20130101; H01L 43/08 20130101;
H01L 43/02 20130101; H01L 21/02071 20130101 |
International
Class: |
H01L 43/12 20060101
H01L043/12 |
Claims
1. A method for etching a magnetic tunneling junction (MTJ)
structure comprising: providing a stack of MTJ layers on a bottom
electrode on a wafer; patterning said MTJ stack to form a MTJ
device wherein sidewall damage is formed on sidewalls of said MTJ
device; and thereafter removing said sidewall damage by applying a
physical treatment comprising applying a slurry which physically
attacks and removes said sidewall damage on said MTJ device.
2. The method according to claim 1 further comprising: providing a
hard mask layer on said MTJ stack; patterning said hard mask layer
to form a hard mask; and using said hard mask in said patterning of
said MTJ stack.
3. The method according to claim 1 wherein said MTJ stack is
patterned using a physical etching process wherein said sidewall
damage is formed by said physical etching process.
4. The method according to claim 3 wherein said sidewall damage is
formed after said physical etching process when said MTJ device is
exposed to atmosphere.
5. The method according to claim 1 wherein said physical treatment
comprises: holding said wafer in a chemical mechanical polishing
(CMP) tool; and applying said slurry to said wafer while rotating
said CMP tool wherein said slurry physically attacks and removes
said sidewall damage.
6. The method according to claim 1 wherein said physical treatment
removes said sidewall damage layer to a depth of between about 5
and 150 Angstroms.
7. The method according to claim 1 wherein said slurry has a pH of
between about 5 and 10 and a particle size of between about 1 and
1000 Angstroms, and preferably between about 30 and 100
Angstroms.
8. The method according to claim 5 wherein said holding said wafer
in said CMP tool is without pressure and without vacuum.
9. The method according to claim 1 wherein said applying a slurry
to said wafer comprises one or both of: applying a first slurry
having a pH of between about 5 and 10 and a particle size of
between about 1 and 1000 Angstroms, and preferably between about 30
and 100 Angstroms in a CMP process without pressure and without
vacuum; and immersing said wafer in a second slurry in a tank
having megasonic or ultrasonic generators wherein said second
slurry has a pH between 0 and 14 and a particle size of up to
100,000 Angstroms.
10. A method for etching a magnetic tunneling junction (MTJ)
structure comprising: providing a stack of MTJ layers on a bottom
electrode on a wafer; providing a hard mask layer on said MTJ
stack; patterning said hard mask layer to form a hard mask;
patterning said MTJ stack to form a MTJ device wherein sidewall
damage is formed on sidewalls of said MTJ device; and thereafter
removing said sidewall damage by applying a slurry which physically
attacks and removes said sidewall damage on said MTJ device.
11. The method according to claim 10 wherein said MTJ stack is
patterned using a physical etching process.
12. The method according to claim 11 wherein said sidewall damage
is formed by said physical etching process.
13. The method according to claim 11 wherein said sidewall damage
is formed after said physical etching process when said MTJ device
is exposed to atmosphere.
14. The method according to claim 10 wherein said applying said
slurry comprises: holding said wafer in a chemical mechanical
polishing (CMP) tool; and applying said slurry to said wafer while
rotating said CMP tool.
15. The method according to claim 10 wherein said applying said
slurry removes said sidewall damage layer to a depth of between
about 5 and 150 Angstroms.
16. The method according to claim 14 wherein said applying said
slurry to said wafer comprises one or both of: applying a first
slurry having a pH of between about 5 and 10 and a particle size of
between about 1 and 1000 Angstroms, and preferably between about 30
and 100 Angstroms in a CMP process without pressure and without
vacuum; and immersing said wafer in a second slurry in a tank
having megasonic or ultrasonic generators wherein said second
slurry has a pH between 0 and 14 and a particle size of up to
100,000 Angstroms.
17. The method according to claim 14 wherein said holding said
wafer in said CMP tool is without pressure and without vacuum.
18. A method for etching a magnetic tunneling junction (MTJ)
structure comprising: providing a stack of MTJ layers on a bottom
electrode on a wafer; providing a hard mask layer on said MTJ
stack; patterning said hard mask layer to form a hard mask;
patterning said MTJ stack to form a MTJ device wherein sidewall
damage is formed on sidewalls of said MTJ device; and thereafter
removing said sidewall damage by applying a slurry which physically
attacks and removes said sidewall damage on said MTJ device using
one or both of a CMP process and a megasonic or ultrasonic
process.
19. The method according to claim 10 wherein said applying said
slurry comprises: holding said wafer in a polishing tool; and
applying said slurry to said wafer while rotating said polishing
tool.
20. The method according to claim 18 wherein said CMP process
comprises applying a first slurry having a pH of between about 5
and 10 and a particle size of between about 1 and 1000 Angstroms,
and preferably between about 30 and 100 Angstroms; and said
megasonic or ultrasonic process comprises immersing said wafer in a
second slurry in a tank having megasonic or ultrasonic generators
wherein said second slurry has a pH between 0 and 14 and a particle
size of up to 100,000 Angstroms.
Description
TECHNICAL FIELD
[0001] This application relates to the general field of magnetic
tunneling junctions (MTJ) and, more particularly, to etching
methods for forming MTJ structures.
BACKGROUND
[0002] For spin torque applications, the dry etching process of the
magnetic tunnel junction (MTJ) is the critical step determining MTJ
performance. The key issue is the sidewall damage caused by the MTJ
etching process. A typical MTJ etched by a RIE (reactive ion
etching) process is found to have sidewall damage, possibly caused
by oxygen or other chemicals during the etching process and/or by
exposure to oxygen after the etching process. The sidewall damage
will lead to a size dependence of magnetic resistance ratio (DRR)
which will reduce the read margin for the MRAM (magneto-resistive
random-access memory) chip functionality. This damage will be
getting worse as MRAM technology decreases in size to 65 nm
technology and beyond.
[0003] This sidewall damaged layer around the MTJ is believed to be
a chemically unstable layer. The thermal treatment of the
semiconductor back end of line (BEOL) process will enhance the
sidewall damage due to atom diffusion and will result in quickly
degraded MTJ performance.
[0004] Several patents teach methods to remove sidewall damage.
These include US Patent Applications 2017/0025603 (Hara),
2016/0020386 (Kim et al), and 2006/0132983 (Osugi et al). Other
patents teach uses of chemical mechanical polishing (CMP),
including U.S. Pat. No. 8,105,948 (Zhong et al) and U.S. Pat. No.
8,822,994 (Zhang et al). All of these references are different from
the present disclosure.
SUMMARY
[0005] It is an object of the present disclosure to provide an
improved method of forming MTJ structures.
[0006] Yet another object of the present disclosure is to provide a
method of removing sidewall damage after etching in the fabrication
of MTJ devices.
[0007] A further object is to provide a method of removing sidewall
damage by molecular action after etching in the fabrication of MTJ
devices.
[0008] Yet another object is to provide a method of removing
sidewall damage by molecular action of a chemical mechanical
polishing (CMP) slurry after etching in the fabrication of MTJ
devices.
[0009] In accordance with the objectives of the present disclosure,
a method for etching a magnetic tunneling junction (MTJ) structure
is achieved. A stack of MTJ layers is provided on a bottom
electrode on a wafer. A hard mask layer is provided on the MTJ
stack. The hard mask layer is patterned to form a hard mask. The
MTJ stack is patterned to form a MTJ device wherein sidewall damage
is formed on sidewalls of the MTJ device. The sidewall damage is
removed by applying a physical treatment to the sidewall of the MTJ
device.
[0010] Also in accordance with the objectives of the present
disclosure, a method for etching a magnetic tunneling junction
(MTJ) structure is achieved. A stack of MTJ layers is provided on a
bottom electrode on a wafer. A hard mask layer is provided on the
MTJ stack. The hard mask layer is patterned to form a hard mask.
The MTJ stack is patterned to form a MTJ device wherein sidewall
damage is formed on sidewalls of the MTJ device. The sidewall
damage is removed by applying a slurry which physically attacks and
removes the sidewall damage on the MTJ device.
[0011] Also in accordance with the objectives of the present
disclosure, a method for etching a magnetic tunneling junction
(MTJ) structure is achieved. A stack of MTJ layers on a bottom
electrode on a wafer. A hard mask layer is provided on the MTJ
stack. The hard mask layer is patterned to form a hard mask. The
MTJ stack is patterned to form a MTJ device wherein sidewall damage
is formed on sidewalls of the MTJ device. The sidewall damage is
removed by applying a slurry which physically attacks and removes
the sidewall damage on the MTJ device using one or both of a CMP
process and a megasonic or ultrasonic process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the accompanying drawings forming a material part of this
description, there is shown:
[0013] FIGS. 1 through 6 illustrate in cross-sectional
representation steps in a preferred embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0014] The basic idea of the present disclosure is to use molecular
movement to attack the sidewall damage layer caused by MTJ etching.
The molecular movement is created by a CMP polisher with particular
slurries.
[0015] Referring now to FIGS. 1 through 6, the novel disclosure
will be described in detail. The process begins with a traditional
MTJ etching process. Referring now more particularly to FIG. 1,
there is shown a bottom electrode 12 formed on the substrate 10 and
insulation layer 14. Now, layers 16 are deposited on the bottom
electrode to form a magnetic tunnel junction. Layers 16 include one
or more pinned layers, tunnel barrier layers, and free layers, as
is conventional in the art. Finally a hard mask layer 18 is
deposited on the MTJ layers 16.
[0016] A photoresist mask 25 is formed over the hard mask layer. As
shown in FIG. 2, the hard mask layer is patterned using the
photoresist mask 25 to form a hard mask 18. The MTJ etching
preferably is performed with a RIE process, which includes hard
mask etching, as shown in FIG. 2, followed by RIE etching of the
MTJ layers 16, as shown in FIG. 3.
[0017] After the MTJ etching process, the wafer will be unloaded
from the etcher tool and exposed to the atmosphere. The MTJ
sidewall can be damaged 22 either during the etching process or by
exposure to the atmosphere causing sidewall oxidation, illustrated
in FIG. 3. The damaged layer 22 will lead to lower MR ratio and
worse magnetic properties (lower coercivity (Hc), lower energy
barrier (Eb), higher critical writing current (Ic), higher critical
writing voltage (Vc)) and also will induce non-uniformity of
electric and magnetic performance. This kind of sidewall damage
will worsen especially as the MTJ size decreases.
[0018] Referring now to FIG. 4, we introduce a new scheme for
protecting the MTJ by removing the sidewall damaged layer 22. The
sidewall damage caused by the MTJ etching process and by exposing
the MTJ sidewall to the atmosphere can be removed by applying a
physical treatment, which uses a chemical mechanical polishing
(CMP) slurry 27 to attack the sidewall materials. The wafer is held
in the head of a CMP tool (not shown). The head and platen rotate
29 during the CMP process. The slurry particles contact and attack
the sidewall materials 22. The physical treatment process will
remove the sidewall damaged layer 22 to a depth of between about 5
to 150 A SiOx equivalent, and preferably 50 A SiOx equivalent.
[0019] For achieving a good treatment performance, the polishing
slurry pH value should be between about 5 to 10 and the slurry
particle size should be between about 1 A to 1000 A, and preferably
30 A.about.100 A. The wafer seating in the CMP tool should be
without pressure and without vacuum during the polishing time.
Normally, CMP is under pressure or vacuum, but for our purposes of
removing sidewall damage, no pressure or vacuum should be
applied.
[0020] Other physical treatments including megasonic or ultrasonic
methods with slurries can also remove sidewall damage. Megasonic or
ultrasonic methods work by generating controlled acoustic
cavitation in the cleaning fluid. Acoustic cavitation is produced
by the pressure variations in sound waves moving through a liquid.
We use a CMP slurry having a pH value of between 0 and 14 and
particle size of up to 10 .mu.m (100,000 Angstroms) as the fluid.
The slurry particles will attack the sidewall with the megasonic or
ultrasonic enhancement. Those methods can be applied after the CMP
process described above or in place of the CMP process. In those
methods, as shown in FIG. 5, slurry 42 will be put into a tank 40
which includes Megasonic or Ultrasonic generators 46. The wafer 10
will be immersed into the tank for processing. The wafer will be
held in a polishing head, not shown, and rotated during processing.
The slurry particles 47 contact and attack the sidewall materials
22.
[0021] FIG. 6 illustrates the wafer after physical treatment by the
CMP process described with respect to FIG. 4, optionally followed
by or replaced by the megasonic or ultrasonic process described
with respect to FIG. 5. The sidewall damaged layer 22 has been
removed from the MTJ stack 16.
[0022] The size dependence of DRR % is always observed if the MTJ
etching process is performed without the sidewall damage removal of
the present disclosure. The DRR % will drop as the MTJ size
decreases. To maintain the DRR % for small MTJ size will be the
main issue for STT-MRAM products. Using the process of the present
disclosure, the DRR % could be maintained without MTJ size
dependence due to the removal of the sidewall damaged layer.
Advantageously, spin torque efficiency could be enhanced and lower
Vc and Ic could be achieved as well.
[0023] The physical sidewall damage removal of the present
disclosure could be used for MTJ devices with in-plane/out-of plane
or/partial out-of-plane anisotropy for embedded memory applications
in, e.g., embedded high-density PMA Spin-Torque-Transfer (STT)
MRAM.
[0024] Although the preferred embodiment of the present disclosure
has been illustrated, and that form has been described in detail,
it will be readily understood by those skilled in the art that
various modifications may be made therein without departing from
the spirit of the disclosure or from the scope of the appended
claims.
* * * * *