A METHOD TO EXTRACT THE BASIC OXIDATION PROCESS PARAMETERS

Alpian Tampubolon, Onno W. Purbo, F. Ihsan Hariadi
IC Process Research Group
Inter University Center on Microelectronics
Institute of Technology Bandung
Bandung 40132
FAX 62-22 214-417
yc1dav@process.paume.itb.ac.id
ihsan@process.paume.itb.ac.id

ABSTRACT
We report on a method to extract the basic oxidation process parameters to be used in SUPREM process simulator. Non linear chi-square fit method is used in the extraction process. We found that oxidation process parameters of our IC Process lab. at Inter University Center on Microelectronics has a deviation on the order of 10-50% as compared to the default SUPREM parameters. Major sources of error during the extraction process in our Lab. are measurement error, control of oxygen flow and control of furnace temperature.

INTRODUCTION

Oxidation process is an important IC processing step. Ability to make an accurate prediction of the oxidation process is important to be able to design a microelectronics process. SUPREM as a standard tool to perform design of microelectronics process is important to be calibrated.

As part of our effort to characterize our microelectronics laboratory, we developed a method to extract SUPREM parameters' of the oxidation process using our microelectronics laboratory.

EXTRACTION METHOD

	The basic oxidation process can be modeled according to Deal-Grove model as follows []:
	
Where Xo is the oxide thickness, Xo1 is the original oxide (t=0) thickness, B is the parabolic growth constant, B/A is the linear growth constant. In SUPREM, the intrinsic growth parameter is devided into two different temperature zones marked by P.BREAK and L.BREAK. The SUPREM model of B and B/A in the intrinsic oxidation process is as follows []:

T<P.BREAK

T>P.BREAK

T<L.BREAK

T>L.BREAK

In this work, we are working on extracting PAR.L.O, PAR.L.E, PAR.H.O, PAR.H.E, LIN.L.O, LIN.L.E, LIN.H.O and LIN.H.E which are an important parameters to model the Bi and (B/A)i.
	To be able to find the parameters of the non-linear oxidation process, we use the following algorithm as shown in Table 1.

	t, Xo | T

	linear regression

	B, (B/A) | T

	non-linear regression

	oxidation process
	parameters

Knowing the combination of t, Xo at certain process temperature T, the extraction of B and B/A is quite straight forward by using a linear regression, such that

which can be treated as a linear system. We use the standard Chi-Square fit algorithm [] to extract B and B/A.
	Knowing B and B/A, the oxidation process parameters is extracted by using a non-linear extraction process. To perform the extraction process, we use heavily the numerical subroutine available in the "Numerical recipes in C" []. These subroutines involved a Levenberg-Marquardt algorithm [] to minimize the Chi-Square value. To minimize the Chi-Square value, we use the standard Jacobian matrix with the calculated first derivative of the functions.

EXPERIMENTAL PROCEDURES
	Prior to perform the experiment, we charaterized the temperature profile of our diffusion furnaces. Based on the profile, the exact flat temperature zone location can be found and used during the experiment.
	We use basically two different crystall orientations, namely, <100> and <111> orientation. All wafers are cleaned using the standard Tokyo Institute of Technology technique []. The cleaning procedure is basically consists of three different objectives, namely, to clean organics entities, to clean anorganics entities and finally to clean the remaining native oxide. TCE and Aceton are used to clean any organics enitities; HNO3 and H2SO4 are used to clean any anorganics enitites; and finally HF is used to clean the native oxide.
	In the real extraction process, we use a carefully controlled oxidation process. For each measured temperature, we extract the data for six different oxidation time. A temperature span of 980-1090oC is used during the extraction process. The oxide thickness is extracted by using non-destructive techniques, namely, using an ellipsometer measuerment [] and a high-frequency CV measurement [].

EVALUATION

	To evaluate the method, first of all, we use a controlled data generated by SUPREM 3. Both t, Xo can be easily generated. The validity of the method can be evaluated by comparing the extracted SUPREM parameters with the actual SUPREM parameters used during the simulation process. Using this method, we can also know the minimum amount of data needed to have a good estimate of SUPREM parameters. Selecting various temperature combination with 41 different temperatures at different intervals, our initial study indicate that to obtain a reasonable time to reach the Chi-Square value less than 10-6 we need at least 10oC interval temperature. The extraction process will reach its convergence faster with large temperature range data.

Parameters	 SUPREM	 Extracted	
<111> Silicon			
PAR.L.O	12.8667	19.6563	
PAR.L.E	1.23	0.9462	
PAR.H.O	12.8667	19.6563	
PAR.H.E	1.23	0.9462	
LIN.L.O	1.038 . 105	0.0061	
LIN.L.E	2.0	0.0856	
LIN.H.O	1.038 . 105	0.0061	
LIN.H.E	2.0	0.0856	
<100> Silicon			
PAR.L.O	12.8667	13.1487	
PAR.L.E	1.23	0.8778	
PAR.H.O	12.8667	13.1487	
PAR.H.E	1.23	0.8778	
LIN.L.O	6.176 . 104	0.0056	
LIN.L.E	2.0	0.0728	
LIN.H.O	6.176 . 104	0.0056	
LIN.H.E	2.0	0.0728	
	The result of our extraction process of our Integrated Circuit Lab. oxidation process shows a 10-50% devation as compared with the SUPREM simulation using the default SUPREM parameters. Table 1 shows the default and the extracted SUPREM parameters. A significant difference is found in our thin oxide process (linear SUPREM parameters) - this indicates our process is not as reliable for thin gate oxide process as yet. Further evaluation of our process is still required to increase its performance.
	Major sources of error during the extraction process in our Lab. are measurement error, control of oxygen flow and control of furnace temperature. A significant modification is still required in the control of oxygen flow in our furnace.

SUMMARY

	We report on a method to extract the basic oxidation process parameters to be used in SUPREM process simulator.
	Non linear chi-square fit method is used in the extraction process. Levenberg-Marquardt algorithm is used for the non-linear extraction procedures. A large span of temperature data should be used to get an accurate SUPREM parameters.
	We found that oxidation process parameters of our IC Process lab. at Inter University Center on Microelectronics has a deviation on the order of 10-50% as compared to the default SUPREM parameters.
	Major sources of error during the extraction process in our Lab. are measurement error, control of oxygen flow and control of furnace temperature.