Wednesday, September 21, 2016

Manufacturing cost of iPhone 7

IHS published a "bill of materials (BOM) for an iPhone 7 equipped with 32 gigabytes (GB) of NAND flash memory carries $219.80 in bill of materials costs". See more in the article below.

Apple A10 Fusion APL1W24 SoC + Samsung 3 GB LPDDR4 RAM (from
Some of the high cost chips used in the iPhone will go down in price; for example the System-on-Chip (SOC) at a cost of $26.90 (made by TSMC) and the NAND memory chips (made by Hynix) and SDRAM (made by Samsung) at a combined cost of $16.40. The price of the iPhone 7 will not go down.

Insightful, timely, and accurate semiconductor consulting.
Semiconductor information and news at -

The iPhone 7 costs Apple more than you think

LONDON--()--The bill of materials (BOM) for an iPhone 7 equipped with 32 gigabytes (GB) of NAND flash memory carries $219.80 in bill of materials costs, according to a preliminary estimate from IHS Markit (Nasdaq: INFO), a world leader in critical information, analytics and solutions.
“Total BOM costs for the iPhone 7 are more in line with what we have seen in teardowns of recent flagship phones from Apple’s main competitor, Samsung, in that the costs are higher than in previous iPhone teardown analyses,” said Andrew Rassweiler, senior director of cost benchmarking services for IHS Markit. “All other things being equal, Apple still makes more margin from hardware than Samsung, but materials costs are higher than in the past.”After $5 in basic manufacturing costs are added, Apple’s total cost to manufacture the iPhone 7 rises to $224.80. The unsubsidized price for a 32GB iPhone 7 is $649. IHS Markit has not yet performed a teardown analysis on the larger iPhone 7 Plus. This preliminary estimated total is $36.89 higher than the final analysis of the iPhone 6S published by IHS in December 2015.

Apple iPhone 7 32GB (A1778) 
   Cost Summary  
Direct Material Costs $219.80
(Component Costs)
Conversion Costs$5.00
(Assembly / Insertion / Test Costs)
Total Cost$         224.80         
(Direct materials and manufacturing)
Itemized Components Manufacturer Name          Manufacturer Part Number Description Total Cost
Apps Processor        
System-on-Chip TSMC (Apple) APLW24 
Apple A10, Quad-Core 64-Bit ARM Based CPU, Hexa-Core
GPU, 16nm FinFET
 $         26.90
Baseband / RF / PA                $         33.90
Baseband INTEL CORP PMB9943 Baseband Processor, Multi-Mode  
RF Transceiver INTEL CORP PMB5750 RF Transceiver, Multi-Mode (Qty:2)  
RF Front End        
Antenna Switch Module TDK CORP D5313 Antenna Switch Module, w/ Filters  
Antenna Switch Module TDK CORP D5325 Antenna Switch Module, w/ Filters  
Envelope Tracking QORVO INC 81003M Envelope Tracking IC  
  HUIZHOU DESAY   Li-Polymer, 3.8V, 1960mAh $         2.50
BT / GNSS / WLAN       $         8.00
 S39S00201 BT / WLAN Module  
Front End     BT / WLAN & GNSS Front End  
Cameras       $         19.90
Front FaceTime     7MP BSI w/ Fixed Lens  
Rear     12MP BSI, w/ AutoFocus, & Optical Image Stabilization  
Display       $         43.00
Display / Touchscreen Module     4.7" 1334x750 LTPS IPS LCD, w/ In-Cell Touch  
Electromechanicals                $         16.70
Taptic Engine     Taptic Engine  
Other Electro-MechanicalsAntennas, Connectors, Microphones, PCBs, Speakers, etc.
Glue Logic       $         1.30
  LATTICE SEMICONDUCTOR ICE5LP4K-SWG36I          FPGA - iCE40 Ultra, 40nm  
Mechanicals       $         18.20
Enclosure     Enclosure, Main, Bottom - Machined Aluminum  
Other Mechanicals     Hardware, Labels, Insulators, Shielding, vents, etc.  
Memory       $         16.40
Power Management       $         7.20
Others     Other PMICs, Transistors, Diodes, etc.  
User Interface       $         14.00
Audio codec CIRRUS LOGIC CS42L71 Audio Codec  
Audio Amplifier CIRRUS LOGIC 338S00220 Audio Amplifier (Qty:3)  
NFC NXP PN67V NFC Controller  
Others     Interface Ics, discretes, passives, etc.  
Barometer BOSCH SENSORTEC GMBH            Barometric Pressure Sensor  
e-compass ALPS   Electronic Compass  
Other Sensors     
Accelerometer, Gyroscope, Touch ID Fingerprint
sensor, ALS/Proximity sensor, etc.
Box Contents       $         11.80
Lightning Cable     USB to Lightning  
Lightning to 3.5mm Audio Adapter     Audio Adapter, Lightning to 3.5mm Jack  
Headset w/ Lightning Connector              Headset, Stereo, w/ Lightning Connector  

Same shape. No jack.
While the overall shape and physical design of the iPhone 7 is similar to the iPhone 6S that preceded it, the new display has wider color gamut, including DCI-P3 as well as traditional sRGB, which improves the rendering of photos and videos. The device’s haptic engine, which provides the “click” feel for users, has also been improved for longer-duty cycles and better dynamic response. The home button is now static and mimics the MacBook in terms of a solid-state button design.
Apple has also eliminated the 3.5 millimeter headphone jack, allowing a larger battery and haptic motor. “Where there was an audio jack in the previous design, Apple replaced it with a symmetrical grill -- not for speakers, but for the waterproof microphone, leaving more room for the larger battery and Taptic Engine,” Rassweiler said.
Increased base-model storage
Apple has increased the iPhone 7’s storage density. For the first time, the base model starts at 32 gigabytes (GB) – which is only the second time Apple has upgraded the base storage in the iPhone. From a cost perspective, the shift from 16GB/64GB/128GB iPhones to 32GB/128GB/256GB is a big jump. “Despite significant cost erosion in NAND flash over the last year, this increase in the overall memory cost definitely puts pressure on the bill of materials costs -- and therefore margins -- from Apple’s perspective,” Rassweiler said.
Intel returns
The Intel design win, and six years of absence that Intel had from the iPhone, is important to note. Even so, Intel still shares the processor business with Qualcomm. “Whereas Apple strives to have ‘one iPhone model for all carriers and markets,’ there are a number of different hardware permutations supporting various countries and carriers,” Rassweiler said. “Apple will likely look for ways to simplify the design moving forward, which means one supplier – whether Intel or Qualcomm – will likely dominate, as part of supplier and SKU streamlining.”
According to Wayne Lam, principal analyst of smartphone electronics, IHS Markit, “Largely left behind in the 4G LTE market, Intel has finally worked itself back into the iPhone, which is a huge win, but not one that is going to be financially significant in the near term for Intel.”
RF paths
Apple has also eliminated segmented antenna bands, which means the company is pushing all radio-frequency (RF) paths to the very ends of the phone – both on the top and bottom. The aluminum uni-body construction and design forces all RF paths into those two locations. Whereas other smartphones use a glass back and RF components with antennas mounted on the ample back spaces, Apple is restricted to just two physical antennas. “This design limitation may force Apple to go back to an all-glass design again so that they can fit in 4x4MIMO LTE antennas and more features like wireless charging in the next iPhone iteration,” Lam said.
Modem moved
The baseband thin modem has been moved next to the A10 processor. Prior to the iPhone 7, the thin modem was always on the other side of the SIM card receptacle. “This is a subtle change but likely shows us where Apple wants to take this,” Lam said, “eventually putting the thin modem right on the apps processor package or even integrating it into the A-series processor.”
Officially water resistant
iPhone 7 is now officially rated as water resistant. “We also saw evidence of this water proofing design evolution in the earlier iPhone 6S, which included additional gasketing around critical connectors, as well as the use of WiFi antenna at the end of the primary speaker box,”Lam said. “Doing so pushes the antennas near the only other opening, for better reception and transmission.”
Jet-black polished case
Jet black polish is a new option on 128GB and 256GB models. “This is a new feature that produces a whole new look for the iPhone,” Lam said. “It is a lower yielding, time-intensive manufacturing step that adds cost, as well as considerable value, pushing the retail price higher for those requesting this option.”
Antenna speaker design
The antenna speaker design on the iPhone 7 came from the WiFi antenna packed into the speakers of Apple’s MacBook. “Apple likes to reuse these unique designs throughout their product lines,” Lam said. In a first for the iPhone series, the headset speaker now doubles as a stereo speaker.
Upgraded camera
While not as groundbreaking as the two optical paths in the iPhone 7 Plus, the iPhone 7 camera has now been upgraded to optical image stabilization (OIS), for better low light performance.
Improved battery life
The battery has been increased to 1960mAhr capacity from 1715mAh in the previous iPhone 6s. This change is consistent with Apple’s claims of improved battery life.

IHS Markit (
IHS Markit (Nasdaq: INFO) is a world leader in critical information, analytics and expertise to forge solutions for the major industries and markets that drive economies worldwide. The company delivers next-generation information, analytics and solutions to customers in business, finance and government, improving their operational efficiency and providing deep insights that lead to well-informed, confident decisions. IHS Markit has more than 50,000 key business and government customers, including 85 percent of the Fortune Global 500 and the world’s leading financial institutions. Headquartered in London, IHS Markit is committed to sustainable, profitable growth.
IHS Markit is a registered trademark of IHS Markit Ltd. All other company and product names may be trademarks of their respective owners © 2016 IHS Markit Ltd. All rights reserved.


IHS Markit
Lee Graham, +1 303-397-2468

Wednesday, July 27, 2016

Update 3: $30Bill Semiconductor Merger - Analog Devices buying Linear Technology

Semiconductor companies continue to merge in 2016. The latest is Analog Devices buying Linear, to boost its profitability and increase its share in the fragmented market for analog chips, which process signals such as sound, light and temperature and convert them into digital signals. The chips are central to smart phones and devices connected to the internet

Linear products are mainly in 44% industrial, 24% transport, and 18% in high-growth communications. In its transportation business, Linear is the leader in BMS (Battery Management Systems) for electric cars. Specifically, Linear is the brains behind the failsafe mechanisms that keep your electric car from just stopping because the battery died.

A list of previous mergers and acquisitions is at Update:China 2015/2016 Semiconductor Mergers, Acquisitions

A key reason for all these merger and acquisitions is the growing cost of semiconductor fabs (see March 2012 blog - Moore's Law End? (Next semiconductors gen. cost $10 billion)), 

the increased cost of shrinking semiconductor devices (see July 2013 blog -  Latest Transistor Channel (Moore Law Getting Too Expensive)), and 

China push to enter semiconductor market (see China 2015 - 2016 Semiconductor Mergers, Acquisitions)

More about Analog Devices buying Linear the article below

Insightful, timely, and accurate semiconductor consulting.
Semiconductor information and news at -

ADI to Acquire Linear Tech for $14.8 Billion

Dylan McGrath
7/26/2016 05:22 PM EDT 

Wednesday, July 20, 2016

Update2: 2015/2016 Semiconductor Mergers, Acquisitions

ARM has a potential to be a major force in IoT (Internet of Things). See more in the article below.

"ARM's low-power chip designs have revolutionized mobile devices and are now powering smart home devices, smart meters, weather sensors, medical devices, and industrial equipment.
ARM chips also are inside many sensor devices used in the fast-growing internet of things market..."

SoftBank wants to purchase of ARM in order to participate in the large growth of IoT. It is different from the consolidation of the semiconductor industry or the efforts of China the gain stronger foot hold in semiconductor.

Insightful, timely, and accurate semiconductor consulting.
Semiconductor information and news at -

How ARM set itself up for a $32 billion acquisition

ARM's dogged focus on low-power chip designs has paid big dividends.

Agam Shah

The TV you watch perhaps has an ARM processor chip in it. So does the Amazon Echo that helps switch on the lights and air-conditioner through voice commands.
That's just a microcosm of how deep ARM goes in our daily lives. ARM's low-power chip designs have revolutionized mobile devices and are now powering smart home devices, smart meters, weather sensors, medical devices, and industrial equipment.
ARM chips also are inside many sensor devices used in the fast-growing internet of things market. The company set itself up for growth in IoT with its dogged focus on low-power chips since the 1990s, and that vision has paid off with SoftBank announcing plans this week to buy ARM for a stunning US$32 billion.
Some analysts believe SoftBank is overpaying, but the investment could eventually pay off. Some estimate 20 billion to 50 billion connected devices will be online by 2020, and those numbers represent a big growth opportunity for ARM.
"ARM will be an excellent strategic fit within the SoftBank group as we invest to capture the very significant opportunities provided by the internet of things," Masayoshi Son, CEO and chairman of SoftBank, said in a statement.
SoftBank's offer was compelling for shareholders and offers the chip company to grow, Simon Segars, CEO of ARM, said in a video explaining the sale.
ARM designs chips it licenses to manufacturers, which can tweak them to meet the needs of their devices. Apple uses ARM architecture in its iPhone and iPad, and other licensees include Samsung, Microsoft, Nvidia, and AMD. ARM generates revenue through licensing and royalties, unlike rival Intel, which designs and manufactures its own chips.
From its earliest days, ARM's focus on power efficiency over performance hasn't wavered, setting the company up for success in mobile devices, and now IoT, analysts said. An early ARM chip was used in Apple's Newton handheld, which shipped in 1993 but wasn't a commercial success.
"The only other guys that had a shot at [the mobile and IoT markets] were MIPS, which is now a part of Imagination Technologies," said Nathan Brookwood, principal analyst at Insight 64. "But MIPS fell off the horse."
In IoT, a range of devices are powered by external power sources, but a larger number rely on batteries and energy harvesting. ARM processors like Cortex-M0 are targeted at the IoT, but many older microcontrollers are still being used because of their power efficiency features.
ARM started in 1990 as a spin-off from a collaboration between Apple and Acorn Computer Group. Acorn was the brains behind the first ARM RISC chips, which appeared in a personal computer called Archimedes in 1987. 
ARM's early years were mixed, but the company started gaining attention as shipments of devices like BlackBerry started picking up in the late 1990s. Revenues started exploding in 2005, and that year, ARM shipped 1.4 billion chips for mobile devices, crossing the 1 billion threshold for the first time.
The iPhone, which launched in 2007, added to ARM's fortunes, and more than 90 billion ARM-based chips have shipped so far. In 2015 alone, 15 billion ARM chips shipped.
ARM maintained its heritage of developing low-power processors at a time when Intel and AMD cranked up clock speeds and power draw in their PC chips. The iPhone was a big breakthrough, and the mobile explosion caught rivals like Intel off-guard. Intel then took the ARM route and started focusing on power efficiency.
IoT is again changing the shape of the chip industry. Intel in April laid off 12,000 people as it redirected focus from PCs to IoT, data center products, and memory.
Over the decades, ARM microcontrollers were easily available from companies like Marvell and Texas Instruments to build and test devices, and that strategy helped build a large ecosystem, Brookwood said. By comparison, Intel chips weren't as easily available, and that's another reason ARM is built into more devices.
While ARM is growing in the IoT, it has weaknesses. ARM-based chips may not be able to handle demanding tasks in medical devices, digital advertising screens, or gambling machines, where graphics and processing are key. Those devices will better run on x86 chips, said Jim McGregor, principal analyst at Tirias Research.
Mobile and low-power IoT devices are tailor-made for ARM, and they are markets the company should continue chasing, McGregor said. For SoftBank, those markets are low-hanging fruit that will generate instant revenue.
ARM chips could also find their way into storage and networking devices, which are growing more important to the IoT, McGregor said.
The company plans to speed up processor development and double its headcount over the next five years with SoftBank's backing. But questions remain about what ARM will do with the extra resources.
ARM has processor designs and programs in place for a range of chips, from IoT microcontrollers all the way up to beefy servers, for the next couple of years, and most semiconductor companies already have ARM licenses. So there are limited opportunities for the company to expand with its IP licensing business model, Brookwood said.
ARM's price was depressed, and SoftBank may have felt it was a good time to acquire the company, said Richard Fichera, vice president at Forrester Research.
But ARM is still a small company, and its unique business model won't change the way chipmakers like Intel, Nvidia, or AMD do business.
"There's nothing [SoftBank] can do to make ARM five times their size," Fichera said. "I don't think it'll transform the industry in any way."
Though SoftBank may have overpaid, ARM is well positioned to make money with its intellectual property business, and the IoT segment is a big opportunity, Fichera said.
"ARM is well positioned to make money hand-over-fist with their IP business," Fichera said.

Wednesday, June 22, 2016

3D NAND Manufacturing Issues

Currently the 3D manufacturing process is being developed to manufacture NAND flash (see the article below). However, it would be very useful to use for other product technologies such as DRAM, logic and analog. For logic products the process development emphasis would be on increasing the number of metal levels and their connections to vertical transistors. For DRAM products the  emphasis would be on adding memory cells that are located in layers vertically above the silicon substrate surface.

The article below discusses processing issues such as
"the challenges here are focused on variability control of several key processes....Alternating stack deposition must have precise control with good uniformities and low defectivity. “Initially, the uniformities must be good,” Applied’s Ping said. “It’s all going back to stress control because the alternating films are different. For each film there could be a mismatch. Stress could show up.”
“Repeatability at every single step is also critical and it has to be done at high productivity in order to keep costs down,”

"Tiny trenches or channels are etched from the top of the device to the substrate. To illustrate the complexity of this step, Samsung’s 3D NAND device has 2.5 million tiny channels in the same chip. Each of them must be parallel and uniform.”

One area that the article does not mentions is the additional circuitry complication of the 3D NAND products. For example there is a need to sense correctly and repeatedly every one of the larger number of smaller memory cells that are on each 3D NAND. Also the controller of the 3D NAND has to deal with the larger number of memory cells that need to be accessed and controlled. 

Insightful, timely, and accurate semiconductor consulting.
Semiconductor information and news at -

How To Make 3D NAND

Foundries progress with complex combination of high-aspect ratio etch, metal deposition and string stacking.

In 2013, Samsung reached a major milestone in the IC industry by shipping the world’s first 3D NAND device. Now, after some delays and uncertainty, Intel, Micron, SK Hynix and the SanDisk/Toshiba duo are finally ramping up or sampling 3D NAND.
3D NAND is the long-awaited successor to today’s planar or 2D NAND, which is used in memory cards, solid-state storage drives (SSDs), USB flash drives and other products.
There is still huge demand for today’s planar NAND, but this technology is basically reaching its physical scaling limit. Today, NAND flash vendors are shipping planar parts at the mid-1xnm node regime, which represents the end of the scaling road for the technology.
So to extend NAND, OEMs want 3D NAND. 3D NAND is shipping, but the technology isn’t expected to hit the mainstream until 2017, which is one to two years longer than expected.
3D NAND is more difficult to make than previously thought. Unlike 2D NAND, which is a planar structure, 3D NAND resembles a vertical skyscraper. A 3D NAND device consists of multiple levels or layers, which are stacked and then connected using tiny vertical channels.
Today’s leading-edge 3D NAND parts are 32- and 48-layer devices. Scaling 3D NAND to 64 layers and beyond presents some major challenges. And in fact, today’s 3D NAND is expected to hit the ceiling at or near 128 layers.
“This is the limitation,” said Er-Xuan Ping, managing director of memory and materials within the Silicon Systems Group at Applied Materials. “Up to a certain point, a single-string is limited by etching or other process steps.”
So to extend 3D NAND beyond 128 layers, the industry is quietly developing a technology called string stacking. Still in R&D, string stacking involves a process of stacking individual 3D NAND devices on top of each other. For example, if one stacks three 64-layer 3D NAND devices on top of each other, the resulting chip would represent a 192-layer product. The trick is to link the individual 64-layer devices with some type of interconnect scheme.
String stacking is already in the works. For example, Micron Technology, according to multiple sources, recently demonstrated a 64-layer 3D NAND device by stringing two 32-layer chips together.
This is not a simple technology to develop, however. And even with string stacking, 3D NAND would top out at or around 300 layers, according to experts.
All told, 3D NAND is projected to remain viable at least until 2020 and perhaps beyond. “This is a 10-plus year roadmap and we are just at the beginning of it,” said Yang Pan, chief technology officer for the Global Products Group at Lam Research.
In any case, OEMs will need to get a handle on the 3D NAND manufacturing issues in order to have more realistic expectations about their design schedules. To help OEMs, Semiconductor Engineering has taken a look at some of the more challenging process steps for 3D NAND. This includes alternating step deposition, high aspect ratio etch, metal deposition and string stacking.
Why 3D NAND?
In today systems, the memory hierarchy is fairly straightforward. SRAM is integrated into the processor for cache. DRAM is used for main memory. And disk drives and NAND-based SSDs are used for storage.
NAND, a nonvolatile memory technology, is based on the traditional floating gate transistor structure. Thanks to 193nm immersion lithography and multiple patterning, vendors have extended planar NAND down to the 1xnm node regime.
But at 1xnm, there are issues cropping up. “In fact, the floating gate is seeing an undesirable reduction in the capacitive coupling to the control gate,” said Jim Handy, an analyst with Objective Analysis.
So, today’s planar NAND will soon stop scaling, prompting the need for 3D NAND. Basically, 3D NAND resembles a vertical skyscraper or layer cake. The layers, which are horizontal, are the active wordlines. “The bitlines also run horizontally in the metal layers on the top of the chip,” Handy said. “The vertical channels are the NAND ‘strings’ that attach to the bitlines.”
Meanwhile, vendors are at various stages of ramping up the technology. Samsung, the leader in 3D NAND, last year shipped its third-generation 3D NAND device—a 48-layer chip. In addition, Micron and its 3D NAND partner, Intel, have recently begun shipping their first 3D NAND chip—a 32-layer device. Both SK Hynix and the SanDisk/Toshiba duo are separately sampling 48-layer chips.
2016 is expected to be a big year for 3D NAND. At the end of 2015, there was a total of 160,000 wafer starts per month (wspm) in terms of worldwide installed capacity for 3D NAND, according to Lam Research. “We estimate that the industry will ship approximately 350,000 to 400,000 wspm of 3D NAND capable capacity by the end of 2016,” Lam’s Pan said.
Still, 3D NAND represents a fraction of the total installed capacity for NAND (2D and 3D), which is roughly 1.3 million to 1.4 million wspm. “Eventually, we expect a significant majority of the NAND installed base to become 3D capable,” Pan said.
Vendors are ramping up these devices in new or converted 3D NAND fabs. In total, the equipment cost for a 2D NAND fab ranges from $30 million to $45 million for 1,000 wspm, according to Christian Dieseldorff, an analyst with the Industry Research & Statistics group at SEMI.
In comparison, the equipment cost for a 3D NAND fab ranges from $50 million to $65 million for 1,000 wspm, Dieseldorff said. “3D NAND equipment costs are higher because more equipment like CVD and etch tools are needed,” he said.
Some vendors are retrofitting their current fabs into 3D NAND facilities. “We expect 2X to 4X more space is needed when converting from 2D to 3D. In this case, there is a high degree of re-use because most equipment is already there. Again, additional CVD and etch tools are needed,” he said.
Still, a 3D NAND fab is not as expensive as a leading-edge logic fab. A 7nm logic processes, for example, will require a $160 million fab equipment investment for every 1,000 wspm, according to Gartner.
The new litho: alternating stack deposition 
In any case, 3D NAND represents a major departure from today’s planar NAND. In 2D NAND, the fabrication process is dependent on advanced lithography. In 3D NAND, though, vendors are using trailing-edge 40nm to 20nm design rules. Lithography is still used, but it isn’t the most critical step. So for 3D NAND, the challenges shift from lithography to deposition and etch.
In fact, 3D NAND introduces a number of new and difficult process steps to the semiconductor industry. “By moving the bit-string into the third-dimension, this technology eases many of the patterning-scaling challenges,” said David Fried, chief technology officer at Coventor. “But it has introduced several fairly complex and new processes. Uniformity of these processes is critical. So, from my perspective, the challenges here are focused on variability control of several key processes.”
The 3D NAND flow starts with a substrate. Then, vendors undergo the first major challenge in the flow—alternating stack deposition. Using chemical vapor deposition (CVD), alternating stack deposition involves a process of depositing and stacking thin films layer by layer on the substrate.
This process is much like making a layer cake. In simple terms, a layer of material is deposited on the substrate. Then, another layer of material is deposited on top of that. The process is repeated several times until a given device has the desired number of layers.
Each vendor uses a different set of materials to create a stack of layers. For example, to make its 3D NAND devices, Samsung deposits alternating layers of silicon nitride and silicon dioxide on the substrate, according to Objective Analysis. In contrast, Toshiba’s 3D NAND technology consists of alternating layers of conductive polysilicon and insulating silicon dioxide, according to the firm.
Alternating stack deposition must have precise control with good uniformities and low defectivity. “Initially, the uniformities must be good,” Applied’s Ping said. “It’s all going back to stress control because the alternating films are different. For each film there could be a mismatch. Stress could show up.”
The challenges escalate as vendors increase the number of layers in a device. “Repeatability at every single step is also critical and it has to be done at high productivity in order to keep costs down,” Lam’s Pan said.
High aspect ratio etch
Following the alternating stack deposition step, a hard mask is applied on the surface and holes are patterned on the top. Then, here comes the hardest part of the flow—high-aspect ratio etch.
Tiny trenches or channels are etched from the top of the device to the substrate. To illustrate the complexity of this step, Samsung’s 3D NAND device has 2.5 million tiny channels in the same chip. Each of them must be parallel and uniform.
Today’s high-aspect ratio etch tools can handle the requirements for 32- and 48-layer devices. For these chips, the aspect ratios range from 30:1 to 40:1. “This etch is really complex. Uniformity is absolutely critical to the performance of the memory device,” Coventor’s Fried said. “The statistics are also staggering. Once the etch is complete, the amount of processing that takes place inside that hole is also pretty impressive.”
The problem? Current high aspect ratio etch tools are either not ready or struggling to meet the demands for 64-layer devices and beyond. At 64 layers, the aspect ratios are 60:1 to 70:1. “This is too high for current etching capability,” Applied’s Ping said. “The etching and hard mask technologies are not necessarily available for 60:1 or 70:1.”
So going forward, NAND vendors are simultaneously following two paths. First, they will wait for the next-generation high-aspect ratio etch tools and other technologies to arrive. And then, provided the etchers are ready on time, they may scale today’s 3D NAND in the following progressions—32 and 48 layers, to 64 layers, to 96, and then to 128.
In the second path, NAND vendors also will develop next-generation string stacking technology (see below for details).
Charge trap versus floating gate 
Before moving to string stacking, vendors will continue to scale today’s 3D NAND. Besides deposition and etch, today’s 3D NAND undergoes other complex steps, including the formation of the gate.
For this, the industry is moving in two directions. Samsung, SK Hynix and the SanDisk/Toshiba duo are making use of charge trap flash technology. This technology uses a non-conductive layer of silicon nitride. The layer wraps around the control gate of a cell, which, in turn, traps electrical charges to maintain cell integrity.
In contrast, the Intel/Micron duo are not using charge trap. Instead, they have extended the floating gate structure to 3D NAND. “In floating gate, the gate is actually a conductor,” Objective Analysis’ Handy said. “A charge trap layer, which actually looks like a floating gate, is an insulator.”
Floating gate involves some difficult patterning steps. “It’s hard to pattern things on the sides of a vertical hole that you’ve made. You have to go through a lot of process steps,” Handy said.
Charge trap also has some drawbacks. “The advantage with charge trap is that you don’t have to pattern it. Charge trap is easier to make that way,” he said. “Excluding Spansion, which ships over 80% of all bytes in charge trap, nobody else has been able to make charge trap cost effectively.”
Metal deposition
Once the gate is developed, the next step is difficult. The device requires contacts. The device is backfilled with a conductor using a metal deposition step.
“There is a challenge in the metal deposition area,” said Dave Hemker, senior vice president and chief technology officer at Lam Research. “We’re seeing a lot of customers’ backfilling it with tungsten. And that’s a tricky deposition, because you are doing a non-line-of-sight deposition. So you basically have these caves and tunnels in there. You have to go back in there after the fact and put in tungsten metal. If you don’t engineer the process right, you may put in this pre-cursor that wants to plate out metallic tungsten. Given its own way, it could plate out right when it gets into the hole. So you have a lot of ways to create voids.”
String stacking
There are other difficult steps in the flow, but the biggest challenge is clear. Until the industry solves the high aspect ratio etch issues, today’s single-string 3D NAND technology is arguably stuck at 48 and/or 64 layers.
And even when the etchers are ready, today’s single-string 3D NAND hits the wall at 128 layers. “This is because the aspect ratio is limited by the process,” Applied’s Ping said. “So you must figure out a way to bypass the limitations.”
So what’s the answer? String stacking. In this approach, vendors will stack individual 3D NAND devices. Each device might be separated by an insulating layer. “When you do string stacking, you finish one string,” Ping said. “Then, you are repeating the steps. It’s difficult, but you can do it.”
For example, a vendor will develop a 48-layer device. To devise that chip, it will go through the same process flow, such as alternating layer deposition, etch and others.
Then, the vendor will develop a separate 48-layer chip using the same flow. The process is not limited to 48-layer chips. A vendor could also stack multiple 32-layer chips. And if the technology is available, a vendor could stack 64-, 96- and perhaps 128-layer devices.
In theory, though, vendors may opt for string stacking with 32- and 48-layer chips. There is less stress for an individual 32- or 48-layer device, as compared to a 96- or 128-layer chip.
Ultimately, though, 3D NAND with string stacking may run out of steam at or near 300 layers. “It will hit a problem in terms of yield,” Ping said. “When you stack, the yield loss from defects continues building up. That will be the limitation. Plus, everything will be limited by stress. If you put too much film, then the stress presents a limitation.”
Still to be seen, however, is how vendors will connect the individual 3D NAND devices together in string stack. For this, the industry is looking at various interconnect schemes. “There will be four or five different options,” he said. “You can build a shared bit line in the middle. Then, another option is that you build a string, which contacts each string directly.”
To be sure, though, there are still many unknowns and challenges with string stacking. The industry also faces several challenges even without string stacking. In either case, the industry must continue to master and perfect the various process steps with 3D NAND. Otherwise, the technology will remain costly, at least for the vast majority of OEMs.