From: Jimmy Chang, Senior Development Engineer

cc: Sia Parsa, Process Engineering Manager

Subject: 2006 Year-End Report

Date: 12 January 2007

In the year of 2006, I concentrated most of my attention on the process support and development in the etch, furnace, and thin film areas, as well as a good number of ETRs assigned to me. This report includes P5000 trench filling process development, preliminary high deposition rate HTO process in both Tystar9 and Tystar17, Tystar16 particle diminution, and the on-going revision of the Tystar furnace recipes. The rest of my works are summarized in the Training and Miscellaneous sections.

P5000 Trench Filling Process Development

P5000 is an industrial tool that consists of TEOS deposition and planization etch chambers. The PECVD TEOS deposition process was developed two years ago. With the etch chamber up and planization process developed, a feasibility study of trench filling was conducted with the cooperation with a BLMA member. The process employed a series of PECVD depositions and RIE sputtering etches to fill the gaps between two side walls of trenches.

The SEM photographs, Figures 1a-d, demonstrate the excellent sidewall conformability from samples of 2 µm deep trenches with various widths from 2 to 0.35 µm. The photographs also show clearly that the TEOS oxide deposited on the entrance of the trench has been etched open to “V” shape, which facilitates the subsequent deposition. The process can fill a trench till the opening reaches 0.25 µm (Figure 1d) when the TEOS oxide on the top surface starts to close the entrance and leave a key hole in the trench.

Figure 1a - Trenches with width from 2 to 0.35 µm

Figure 1b - Trench with 2 µm width

Figure 1c - Trench with 1 µm width

Figure 1d - Trench with 0.35 µm meter width

To prevent the key hole formation, a SACVD process with ozone should be used for submicron, high aspect ration trenches. P5000 has an ozone generator. However it has communication problem with the main control system. Equipment staff is working on the problem.

High Deposition Rate HTO Process in Tystar9 and Tystar17

High Temperature Oxide (HTO) process was developed in Tystar9 for thin oxide deposition a few years ago. The deposition rate was kept below 4 Å/min for better thickness control for thin film (~100 Å) deposition desired by device group. HTO film has superior film quality, uniformity, and sidewall conformability than its counterpart Low Temperature Oxide (LTO). However, the deposition rate needs to be increased several folds for the HTO process to be practical for applications that requires thick deposition, e.g. trench filling.

Some preliminary tests were carried out in both Tystar9 and Tystar17 to increase the deposition rate. Since the maximum operation temperature could not be increased due to equipment limitation, the tests explored the effects of higher process pressure, process gas ratio and total flow.

Table 1 shows the process parameters and results of a 2 X 2 matrix tested on Tystar9. The high process pressure (450 mtorr) and high DCS to N2O ratio can increase the deposition rate by 2 to 3 times. Since Tystar9 can not sustain a stable process pressure over 500 mtorr, the highest deposition rate is not expected to be over 10 Å/min. Another test on Tystar17 with higher process gas flows and pressure showed that the deposition rate can reach 30 Å/min. However, the film refractive index was very low at 1.35 which indicated it is oxygen rich. Further HTO characterization will be conducted in the future with full report on optimized process.

Wafer #	082	120.	063	121	060	025	013	016
	Pump	Load	Pump	Load	Pump	Load	Pump	Load
Dep min.	120	120	120	120	120	120	120	120
Temp	800	800	800	800	800	800	800	800
Press	450	450	450	450	450	450	450	450
DCS	25	25	40	40	20	20	32	32
N2O	75	75	60	60	60	60	48	48
Å /min	8.19	8.05	9.59	9.44	7.79	7.65	9.05	8.93
Non-Unif.	4.58%	5.39%	4.17%	4.24%	4.70%	5.12%	3.96%	4.10%
RI	1.451	1.449	1.459	1.458	1.445	1.444	1.453	1.453

Table 1 - Process Parameters and Test Results of HTO Deposition on Tystar9

Tystar16 Particle Diminution

Last year, the newly upgraded Tystar16 furnace, for non-MOS poly and amorphous silicon deposition, developed a serious particle problem. After weeks of investigation, the sources of the problem were identified and remedy actions were taken as followings.

A temperature profile of the tube through the whole length of the furnace was conducted. The load zone was found to be overheated by 20 to 30ºC, even though the three thermal couples in the furnace stabilized at the deposition temperature (615ºC). This overheat problem would decompose silane gas before it reached the wafers and created particle problem. Equipment engineers checked the heater and found the electric power connection to the load zone heater was defective. The heater was replaced and the furnace temperature profile was checked again to make sure no overheat.
The process pressure of a Tystar LPCVD furnace is maintained by controlling the flow of nitrogen, i.e. N2VAC, directly into the pump. The mass flow controller (MFC) for the N2VAC is normally open type, because nitrogen is non-reactive. This type of MFC, when activated, first opens to its maximum flow then drops to the set value. This action creates a pressure surge at the pump for a couple of seconds. Usually, it is not a problem because the exhaust plumbing system can absorb the pressure surge. But in Tystar16 the plumbing between the pump and the furnace quartz was shortened to minimum, because of the space limitation in the cabinet. The pressure surge blew all the process byproducts in the plumbing system back into the process quartz tube. After consulting with the Tystar engineer to clear the safety concerns, the N2VAC MFC was changed to normally closed type which did not create the pressure surge.
To load and unload the wafers, the process tube needs to be vented to atmosphere pressure. The 5 litters per minute venting nitrogen, flows up to, may stir up the particles settled in the plumbing system connected to the process tube. Because the gate valve is closed, the particles may back stream in to the process tube. To prevent this from happening, equipment engineer installed a shank device that kept the venting nitrogen flow into the pump only.

Support of Tystar Furnace Maintenance and Recipe Update

I have been working closely with the equipment engineer in the area of heater calibrations, problem diagnoses, communicate with the Tystar Company service Engineer, and final testing after the repair.

The Testing of new version of process recipes with features and benefits described in my last year’s report has been mostly completed. After the revision of the online manual, these recipes should be employed in 2007.

Equipment Operation/Process Training

Trained the new baseline engineer on the furnace, etchers, and P5000.
Provided semiconductor process orientation and training to two high school summer interns.
Trained and qualified lab members on Oxford2, a PECVD tool for oxide, nitride, amorphous silicon, and hydrogen plasma annealing. The number of qualified users reaches 30.
Trained new lab assistant (process student).

Miscellaneous

Completed Engineering Test Requests from other universities and research institutes.
Assumed the ownership of Tystar19 and Tystar20.
Trained to changed CMP polishing head (4” &6”). Performed the duty when the equipment engineer in charge was on leave or other assignment.
Graded equipment quizzes, qualified lab members on various tools.
Lead monthly laboratory safety tours. Substitute in the processing session of the orientation as needed.
Revise the following manuals:

Chapter 5.10 Tystar 10 MOS Clean Polycrystalline Silicon LPCVD Furnace

Chapter 5.12 Tystar 12 Non-MOS Clean LTO LPCVD Furnace

Chapter 5.19 Tystar 19 MOS Clean Si-Ge LPCVD Furnaces

Chapter 7.4 Lam4 Poly-Silicon Rainbow Etcher

Chapter 7.5 Lam5 Poly-Silicon TCP Rainbow Etcher